Physics can be Phun!

SPI Physics Review Part 1: Sound Fundamentals, Variables, Wave Types, and Core Relationships**

Sound vs Ultrasound

Sound wave: series of compressions and rarefactions.
Mechanical wave: requires a medium; cannot travel through a vacuum.
Longitudinal wave: particle motion parallel to propagation; ultrasound in tissue is longitudinal.
Transverse wave: particle motion perpendicular to propagation.
Ultrasound: mechanical, longitudinal wave; ≥ 20,000 Hz (20 kHz, 0.02 MHz).
Infrasound: < 20 Hz.
Audible sound: 20 Hz–20,000 Hz.

Acoustic Variables

Acoustic variables are the rhythmical cycling of: pressure, temperature, density, distance/particle motion.
Pressure units: Pa, can be expressed in atm or mmHg.
Temperature units: °C, °F, Kelvin.
Density: mass per volume.

Continuous vs Pulsed Waves

Continuous wave (CW): uninterrupted stream; cannot create an image.
Pulsed wave (PW): bursts of sound then listening; used to construct an image.
Same for CW and PW (cycle properties): propagation speed, period, wavelength, frequency.

Wave Parameters and Definitions

Hertz (Hz): cycles per second.
Cycle: one compression + one rarefaction.
Frequency (f): cycles per second; reciprocal of period.
Period (T): time for one cycle; T = 1/f.
- 1 MHz → 1 μs, 10 MHz → 0.1 μs.
Wavelength (λ): distance of one cycle.
Propagation speed (c): determined by density and stiffness of the medium.
Key equation: c = f × λ.
- If c increases (in a given medium), λ increases if f is constant.

Propagation Speed Facts

Average soft tissue: 1540 m/s (1.54 mm/μs; ~1 mile/sec).
Fat: 1450 m/s.
Muscle: 1580 m/s.
Bone: ~4080 m/s.
Air: ~330 m/s.

“What changes what” (High-yield SPI rules)

Source only; cannot be changed by the sonographer (without changing transducer):
- Frequency, period.
Source; can be changed by the sonographer:
- Amplitude, power, intensity (via output).
Medium only:
- Propagation speed.
Medium + source:
- Wavelength.

SPI Must-Know Equations & Constants

Core Wave Equations

c = f × λ
T = 1/f
f = 1/T

Pulsed Parameters

PD = period × (# cycles per pulse)
SPL = (# cycles per pulse) × wavelength
PRF = 1/PRP
PRP = 1/PRF
DF = PD/PRP

Intensity

Power ∝ amplitude²
Intensity = power/area
SPPA × DF = SPTA
SPTA ÷ (SP/SA factor) = SATA

Impedance

Z = density × propagation speed

Depth / Timing

Depth = (speed × time of flight) / 2
13 μs rule: 13 μs round trip = 1 cm depth

Nyquist / Aliasing

Nyquist limit = PRF/2

Propagation Speeds (answers)

Soft tissue: 1540 m/s
Fat: 1450 m/s
Muscle: 1580 m/s
Bone: 4080 m/s
Air: 330 m/s

Decibel Intensity Ratios (answers)

−3 dB = 1/2
−6 dB = 1/4
−10 dB = 1/10
−20 dB = 1/100

SPI Physics Review Part 2: Pulsed Parameters, Intensity, Attenuation/Impedance, Artifacts, & Doppler Essentials**

Pulsed Ultrasound Parameters

Pulse: collection of cycles with a beginning and end.
Pulse Duration (PD): time from start to end of a pulse; does not include listening time.
- PD = period × number of cycles.
- Cannot be changed by sonographer unless changing transducer.
Spatial Pulse Length (SPL): physical length of the pulse in space.
- SPL = number of cycles × wavelength.
- SPL is directly proportional to wavelength.
Pulse Repetition Period (PRP): start of one pulse to start of next (transmit + listen).
Pulse Repetition Frequency (PRF): pulses per second.
- PRF = 1/PRP.
Depth relationship:
- Depth increases → PRP increases → PRF decreases.
- Depth decreases → PRP decreases → PRF increases.
Duty Factor (DF): fraction of time transmitting.
- DF = PD / PRP.
- CW: DF = 1 (100%).
- PW: DF is < 1.

Intensity Fundamentals (definitions + ranking)

Power: total energy in the wave; units Watts; Power ∝ amplitude².
Intensity: power per area; units W/cm²; Intensity = Power/Area; also related to amplitude².
Spatial peak: center of beam.
Spatial average: averaged across beam.
Temporal peak: max intensity during transmit instant.
Temporal average: averaged over transmit + listen time.
Pulse average: averaged over transmit time only.

Intensity types (SPI recognition):

SPTP: largest intensity (peak in space and time).
SPTA: lowest intensity (includes listening time).
SPPA: between SPTP and SPTA; only meaningful for pulsed.

Intensity Conversion “Answers”

Convert Pulse Average → Temporal Average: multiply by Duty Factor
- SPPA × DF = SPTA.
Convert Spatial Peak → Spatial Average: divide by SP/SA factor
- SPTA ÷ (SP/SA factor) = SATA.
Beam Uniformity Coefficient (BUC): ratio describing distribution in space; ≥ 1.

Attenuation, Decibels, and Impedance

Attenuation: weakening of sound with depth; in negative dB.
Attenuation coefficient: dB/cm (the key coefficient with units).
Major cause in soft tissue: absorption (~80%).
Positive dB: increase; Negative dB: decrease.
- −3 dB = 1/2 intensity, −6 dB = 1/4, −10 dB = 1/10, −20 dB = 1/100.
Impedance (Z): Z = density × propagation speed; units Rayls.
- Greater impedance mismatch → greater reflection.

Range Equation and Timing Rules

Depth = (speed × time of flight) / 2.
13 microsecond rule: 13 μs round trip corresponds to 1 cm depth; each additional 13 μs adds 1 cm.

Artifacts (cause = violated assumptions; “answers”)

Artifacts occur when system assumptions are violated:

Sound travels in a straight line.
Reflectors lie on beam axis.
Echo strength matches reflector strength.
Imaging plane is thin.
Sound returns directly.
Speed is 1540 m/s.
Attenuation is uniform.

Key artifacts and what they look like:

Reverberation: equally spaced echoes diminishing with depth.
Comet-tail / ring-down: bright line below a reflector; a reverberation subtype.
Mirror image: duplication across strong reflector.
Multipath: incorrect depth due to different travel paths.
Side lobes / grating lobes: misplaced echoes from off-axis beams.
Shadowing: dark area distal to strong attenuator/reflector (bone, calcification, air).
- Refraction (edge) shadowing at curved interfaces.
Enhancement: increased brightness distal to weak attenuator (fluid).
Range ambiguity: high PRF; echoes assigned too shallow; fix by decreasing PRF/increasing depth.
Propagation speed error: faster tissue → structure appears too shallow; slower tissue → too deep.
Slice thickness artifact: false echoes in anechoic structure due to finite beam thickness.
Speckle: granular noise from interference.

Doppler Essentials (SPI answers)

Doppler shift depends on angle: measured velocity = true velocity × cos θ.
Best imaging angle: 90°.
Best Doppler angle: 0°; Doppler hates 90°.
At 90°: cosine = 0 → no Doppler shift.
Aliasing occurs in pulsed wave Doppler when Doppler shift exceeds Nyquist limit.
- Nyquist limit = PRF/2.
Reduce aliasing: increase PRF (shallower depth), use lower frequency, or use CW Doppler.
CW Doppler: no aliasing; measures high velocities; has range ambiguity.

To convert between metric units with a factor of 1000, move the decimal point three places to the right for larger to smaller units, and three places to the left for smaller to larger units. Step 1: Understand the conversion factor The primary conversion factor in the metric system for common units like liter (L) and milliliter (mL) is 1000 (103). This factor applies generally between base units and their kilo- (103) and milli- (10-3) forms. A "million" corresponds to a factor of 1, 000, 000 ( 10º), used for prefixes like mega- or micro-. Step 2: Determine the direction of movement The direction of decimal movement depends on whether the rec lease loessee smaller than the starting unit: • Larger unit to smaller unit (e.g., L to mL): You multiply by 1 moving the decimal point to the right. • Smaller unit to larger unit (e.g., mL to L): You divide by the moving the decimal point to the left. Step 3: Count the number of places to move The number of places to move the decimal is the number of zeros in the conversion factor (or the absolute value of the exponent of 10): • For 1000: Move the decimal 3 places. • For a million: Move the decimal 6 places. Step 4: Apply to Liters and Milliliters • Liters (L) to Milliliters (mL) (larger to smaller): Move the decimal 3 places to the right. For example, 1.5 L = 1500 mL. • Milliliters (mL) to Liters (L) (smaller to larger): Move the decimal 3 places to the left. For example, 500 mL = 0.5 L. Answer: To convert between metric units with a factor of 1000, move the decimal point three places to the right for larger to smaller units, and three places to the left for smaller to larger units. For factors of a million, move the decimal six places.

Physics I Lecture

11:30am | Physics I: Math

00:00 / 04:07

How to Solve Unit Conversions in Ultrasound Physics. Today, we are going to focus on the math logic behind unit conversions in ultrasound physics. This is not about memorizing numbers. This is about learning a process you can use every time. That said, once you understand the process, there are a few common answers you can recognize on exams. Any unit conversion problem always starts the same way. Step One: Find the Decimal. Every number has a decimal, even if you cannot see it. If the number is eighty, the decimal is to the right of the zero. If the number is zero point zero zero five, the decimal is between the zero and the first nonzero digit. Before you move a decimal, you must know where it is. That is step one. Step Two: Decide What the Question Is Asking. You must determine whether you are converting from a bigger unit to a smaller unit, or from a smaller unit to a bigger unit. If you go from a big unit to a small unit, the number gets larger, and the decimal moves to the right. If you go from a small unit to a big unit, the number gets smaller, and the decimal moves to the left. This logic never changes. Step Three: Understand Metric Prefixes Metric prefixes tell you the size of the unit. Kilo means one thousand. There are one thousand meters in one kilometer. Milli means one thousandth. There are one thousand millimeters in one meter. Micro means one millionth. One microsecond is one-millionth of a second, which means there are one million microseconds in one second. You do not guess. You count zeros. Applying This to Ultrasound Physics. The speed of sound in soft tissue is one thousand five hundred forty meters per second. That same speed can also be written as: 1.54 kilometers per second, 1,540,000 millimeters per second, or 1.54 millimeters per microsecond. The question does not always ask for meters per second. Sometimes the question asks for kilometers per second. Sometimes it asks for millimeters per microsecond. When that happens, you must convert both distance and time. Step Four: Convert the Numerator. Distance. First, convert meters to kilometers. Meters are smaller than kilometers. You are going from a small unit to a bigger unit. So the decimal moves to the left three places. One thousand five hundred forty meters becomes 1.54 kilometers. Now convert meters to millimeters. Meters are bigger than millimeters. You are going from a big unit to a smaller unit. So the decimal moves to the right three places. One thousand five hundred forty meters becomes 1,540,000 millimeters. Step Five: Convert the Denominator. Time. This step is critical. Speed is a fraction: distance divided by time. One second contains one million microseconds. Many students stop too early. You are not finished after converting distance. Both the top unit and the bottom unit must be converted. Putting It All Together. When you divide millimeters by microseconds and cancel the zeros, the final value becomes: 1.54 millimeters per microsecond That is where the number comes from. Strategic Exam Tip: Pattern Recognition. Once you understand the conversion process, you may also recognize correct answers without doing every step. For example, the speed of sound in soft tissue often appears as: 1540 m/s. 1.54 km/s. 1.54 mm/µs. 1,540,000 mm/s. If one of these appears as an answer choice and the units match the question, it is very likely correct. This does not replace understanding. It simply saves time on exams when you are confident. Final Reminder. You are not just converting a number. You are converting units. If you slow down, find the decimal, decide whether you are going from big to small or small to big, convert both the numerator and the denominator, and recognize common ultrasound values, you will get ultrasound physics conversion questions right every time.

Physics I Questions

Ultrasound Physics: Math & Unit Conversion Questions Timing: 1 question every 5 minutes Question 1 (0–5 minutes) What is the first step you should take before moving a decimal in any unit-conversion problem? Question 2 (5–10 minutes) You are converting from meters to millimeters. Are you going from a bigger unit to a smaller unit, or from a smaller unit to a bigger unit? Which direction does the decimal move? Question 3 (10–15 minutes) Convert 0.002 meters to millimeters. Question 4 (15–20 minutes) Convert 2,500 millimeters to meters. Question 5 (20–25 minutes) How many microseconds are in one second? Question 6 (25–30 minutes) The speed of sound in soft tissue is 1540 m/s. Convert this value to kilometers per second. Question 7 (30–35 minutes) Convert 1540 m/s to millimeters per second. Question 8 (35–40 minutes) Why must you convert both the numerator and the denominator when changing the units of speed? Question 9 (40–45 minutes) Convert 1540 m/s to millimeters per microsecond. Question 10 (45–50 minutes) Which of the following answer choices would immediately look reasonable for the speed of sound in soft tissue? A. 0.00154 mm/µs B. 1.54 mm/µs C. 154,000 mm/µs D. 15.4 mm/µs Explain why. Answer Key 1. Find the decimal 2. Bigger to smaller; decimal moves right 3. 2 mm 4. 2.5 m 5. 1,000,000 microseconds 6. 1.54 km/s 7. 1,540,000 mm/s 8. Speed is distance divided by time; both units must match the question 9. 1.54 mm/µs 10. B — 1.54 mm/µs, because it matches known ultrasound values

Physics I Answers

ANSWERS Explained11:30am | Physics I: Math

00:00 / 02:48

ANSWERS Explained 1. Where do you start every unit conversion problem? The answer is: You start by finding the decimal. This is because every number has a decimal, even if you cannot see it, and you must know where it is before you can move it. 2. How do you know which way the decimal should move? The answer is: You determine whether you are converting from a bigger unit to a smaller unit, or from a smaller unit to a bigger unit. This is because converting from big to small makes the number larger and moves the decimal to the right, while converting from small to big makes the number smaller and moves the decimal to the left. 3. What happens when you convert meters to millimeters? The answer is: The decimal moves to the right. This is because meters are larger than millimeters, and milli means one thousandth. 4. What happens when you convert millimeters to meters? The answer is: The decimal moves to the left. This is because millimeters are smaller than meters, so you are converting from a smaller unit to a larger unit. 5. How many microseconds are in one second? The answer is: One million microseconds. This is because micro means one millionth, and one second contains one million microseconds. 6. What is the speed of sound in soft tissue? The answer is: One thousand five hundred forty meters per second. This is because 1540 meters per second is the accepted average propagation speed. used in diagnostic ultrasound. 7. What is the speed of sound in soft tissue in kilometers per second? The answer is: 1.54 kilometers per second. This is because converting meters to kilometers. moves the decimal three places to the left. 8. What is the speed of sound in soft tissue in millimeters per second? The answer is: 1,540,000 millimeters per second. This is because converting meters to millimeters. moves the decimal three places to the right. 9. What is the speed of sound in soft tissue in millimeters per microsecond? The answer is: 1.54 millimeters per microsecond. This is because both distance and time must be converted, and one second equals one million microseconds. 10. Which values represent the same speed of sound in soft tissue? The answer is: 1540 meters per second, 1.54 kilometers per second, 1,540,000 millimeters per second, and 1.54 millimeters per microsecond. This is because all of these values describe the same speed using different units. Final Teaching Point. Unit conversion is not memorization. It is a process. Find the decimal. Determine direction. Convert distance and time. That is how you get these questions right.

Physics II Lecture

2:30pm | Physics II

00:00 / 01:52

Ultrasound Physics: Defining Sound. Now that we understand unit conversions, we can move on to the foundation of ultrasound physics. We need to define sound. Sound is a mechanical wave. That means sound requires a medium to travel. Sound cannot travel through a vacuum. It must move through matter. That matter can be a solid, a liquid, or a gas. Sound is created by vibration. When something vibrates, it causes surrounding particles to move. Those particles bump into neighboring particles. This creates a wave of energy that moves through the medium. The particles themselves do not travel across the medium. They oscillate back and forth around their resting position. Energy moves forward. Particles do not. In ultrasound, sound travels as a longitudinal wave. This means particle motion is parallel to the direction the wave is traveling. This is different from light, which is a transverse wave. As sound travels, it creates two important regions. The first is compression. Compression is an area where particles are pushed closer together. The second is rarefaction. Rarefaction is an area where particles are pulled farther apart. Compression and rarefaction alternate as the wave moves forward. This pattern is what defines a sound wave. Sound energy moves through tissue, but tissue does not move with the sound. This is critical for understanding ultrasound imaging. Key Exam Concept. Sound is: Mechanical. Longitudinal. A transfer of energy. Dependent on a medium. Sound is not electromagnetic. Sound cannot travel through a vacuum. Final Summary. Sound is a mechanical, longitudinal wave created by vibration. It travels through a medium by compressions and rarefactions. Energy moves forward. Particles oscillate in place. This definition is the foundation of all ultrasound physics.

Physics IIA. Questions

Ultrasound Physics: Defining Sound — Practice Questions Timing: 1 question every 5 minutes Question 1 (0–5 minutes) What does it mean when we say that sound is a mechanical wave? Question 2 (5–10 minutes) Which of the following is required for sound to travel? A. Light B. A vacuum C. A medium D. Electricity Question 3 (10–15 minutes) Why can sound not travel through a vacuum? Question 4 (15–20 minutes) In ultrasound, sound waves are classified as what type of wave? A. Transverse B. Electromagnetic C. Longitudinal D. Standing Question 5 (20–25 minutes) In a longitudinal sound wave, particle motion is best described as: A. Perpendicular to wave direction B. Circular around the source C. Parallel to wave direction D. Random Question 6 (25–30 minutes) Which two regions make up a sound wave as it travels through a medium? Question 7 (30–35 minutes) What happens to particles during compression? A. They move farther apart B. They are pushed closer together C. They stop moving D. They change direction permanently Question 8 (35–40 minutes) True or False: Particles move forward through tissue as the sound wave travels. Explain your answer. Question 9 (40–45 minutes) Which statement best describes how sound energy travels through tissue? A. Particles travel with the wave B. Energy moves forward while particles oscillate in place C. Sound converts to light energy D. Tissue flows in the direction of propagation Question 10 (45–50 minutes) Which of the following statements is true about sound? A. Sound is electromagnetic B. Sound can travel in a vacuum C. Sound transfers energy, not matter D. Sound changes tissue position permanently Answer Key 1. Sound requires a medium to propagate 2. C — A medium 3. No particles are present to transmit energy 4. C — Longitudinal 5. C — Parallel to wave direction 6. Compression and rarefaction 7. B — They are pushed closer together 8. False — particles oscillate in place 9. B — Energy moves forward while particles oscillate 10. C — Sound transfers energy, not matter

Physics IIA. Answers

ANSWERS Explained2:30pm | Physics IIA

00:00 / 02:23

ANSWERS Explained 1. What is sound? The answer is: Sound is a mechanical wave. This is because sound requires a medium to travel and cannot propagate through a vacuum. 2. What does it mean that sound is mechanical? The answer is: It means sound requires matter to transmit energy. This is because sound travels by causing particles in a medium to vibrate and transfer energy to neighboring particles. 3. Can sound travel through a vacuum? The answer is: No, sound cannot travel through a vacuum. This is because there are no particles in a vacuum to transmit sound energy. 4. What type of wave is sound in ultrasound? The answer is: Sound is a longitudinal wave. This is because particle motion occurs parallel to the direction the sound wave travels. 5. How do particles move as sound travels? The answer is: Particles oscillate back and forth in place. This is because sound transfers energy, not matter, so particles do not move forward with the wave. 6. What are compressions in a sound wave? The answer is: Compressions are regions where particles are pushed closer together. This is because the vibration of the source creates areas of increased pressure in the medium. 7. What are rarefactions in a sound wave? The answer is: Rarefactions are regions where particles are farther apart. This is because particle density decreases between areas of compression. 8. What creates a sound wave? The answer is: Sound is created by vibration. This is because vibrating objects disturb nearby particles and initiate wave propagation. 9. Does tissue move forward when sound travels through it? The answer is: No, tissue does not move forward with the sound wave. This is because particles oscillate around a resting position while energy moves through the medium. 10. Why is understanding the definition of sound important in ultrasound physics? The answer is: Because all ultrasound imaging is based on sound behavior in tissue. This is because sound’s mechanical, longitudinal nature determines how it reflects, refracts, attenuates, and produces diagnostic images. Final Teaching Point. Sound is mechanical. Sound is longitudinal. Sound transfers energy, not matter. Sound requires a medium. These principles form the foundation of all ultrasound physics.

Physics IIB. Questions

Ultrasound Physics: Sound Classification Questions (Infrasound • Audible Sound • Ultrasound) Timing: 1 question every 5 minutes Question 1 (0–5 minutes) What is the definition of frequency, and what unit is it measured in? Question 2 (5–10 minutes) What is the lowest frequency the average human ear can hear? Question 3 (10–15 minutes) Sound with a frequency of 10 Hz is classified as what type of sound? A. Audible sound B. Ultrasound C. Infrasound D. Electromagnetic energy Question 4 (15–20 minutes) What is the upper limit of human hearing in hertz? Question 5 (20–25 minutes) A sound wave with a frequency of 5,000 Hz falls into which category? A. Infrasound B. Audible sound C. Ultrasound D. Mechanical noise Question 6 (25–30 minutes) At what frequency does sound officially become ultrasound? Question 7 (30–35 minutes) Diagnostic medical ultrasound typically operates in which frequency range? A. 20–20,000 Hz B. Below 20 Hz C. Above 20 kHz, in the megahertz range D. In the gigahertz range Question 8 (35–40 minutes) Why is ultrasound not audible to humans? Question 9 (40–45 minutes) Which type of sound is most commonly associated with natural events such as earthquakes and severe storms? A. Audible sound B. Ultrasound C. Infrasound D. Radiofrequency Question 10 (45–50 minutes) True or False: Ultrasound follows different physical laws than audible sound. Explain your answer. Answer Key 1. Number of cycles per second; hertz 2. 20 Hz 3. C — Infrasound 4. 20,000 Hz (20 kHz) 5. B — Audible sound 6. Above 20,000 Hz (20 kHz) 7. C — Above 20 kHz, in the megahertz range 8. Frequency is above human hearing range 9. C — Infrasound 10. False — ultrasound follows the same sound physics

Physics IIB. Answers

ANSWERS Explained2:30pm | Physics IIB

00:00 / 02:21

Ultrasound Physics: Sound Classification 1. How is sound classified? The answer is: Sound is classified by frequency. This is because frequency describes how many vibrations occur per second and determines how sound is perceived and used. 2. What is frequency measured in? The answer is: Frequency is measured in hertz. This is because one hertz represents one cycle per second. 3. What is infrasound? The answer is: Infrasound is sound with a frequency below 20 hertz. This is because the human ear cannot detect frequencies below approximately 20 hertz. 4. What is audible sound? The answer is: Audible sound is sound with a frequency between 20 hertz and 20,000 hertz. This is because this is the range the average human ear can hear. 5. What is ultrasound? The answer is: Ultrasound is sound with a frequency greater than 20,000 hertz. This is because frequencies above 20 kilohertz are beyond human hearing. 6. What frequency range is used in diagnostic medical ultrasound? The answer is: Diagnostic ultrasound uses frequencies in the megahertz range. This is because higher frequencies provide better image resolution. 7. Why is ultrasound not audible to humans? The answer is: Because its frequency is above the human hearing range. This is because the human ear cannot detect vibrations greater than 20,000 hertz. 8. Does ultrasound follow different physical laws than audible sound? The answer is: No, ultrasound follows the same physical laws as all sound. This is because ultrasound is still mechanical, longitudinal sound and behaves according to the same principles. 9. Why is high frequency sound used in ultrasound imaging? The answer is: Because higher frequency sound produces better spatial resolution. This is because increasing frequency decreases wavelength. 10. What happens to penetration as frequency increases? The answer is: Penetration decreases. This is because higher frequency sound attenuates more rapidly in tissue. Final Teaching Point Sound is classified by frequency. Infrasound is below human hearing. Audible sound is what we can hear. Ultrasound is above human hearing. Diagnostic ultrasound uses very high frequencies to create medical images.

Physics III Lecture

11:30am | Physics III: Acoustic Variables

00:00 / 02:48

Ultrasound Physics Lecture: Acoustic Variables. Now that we understand what sound is, we can describe how sound behaves in a medium using acoustic variables. Acoustic variables are the physical quantities that oscillate as a sound wave travels through matter. They describe what is actually changing in the medium itself. In ultrasound physics, there are three acoustic variables: pressure, density, and particle motion. These variables change continuously as sound propagates through tissue. Pressure. Pressure is an acoustic variable. It refers to changes in pressure within the medium as the sound wave passes through. Pressure increases during compression and decreases during rarefaction. Pressure is measured in pascals. The unit matters because pressure describes force per unit area. In ultrasound, echoes are created by changes in pressure at tissue boundaries. Density. Density is an acoustic variable. It describes how closely packed the particles are in a given volume of the medium. Density increases during compression and decreases during rarefaction. Density is measured in kilograms per cubic meter. The unit matters because density affects how sound propagates and how much sound is reflected or transmitted at an interface. Particle Motion. Particle motion is an acoustic variable. It describes how particles move in response to sound energy. Particles oscillate back and forth around their equilibrium position. They do not travel forward with the sound wave. Particle motion is measured as: displacement in meters, or velocity in meters per second. The units matter because particle motion determines how energy is transferred through the medium. Why Acoustic Variables Are Important. Acoustic variables describe what the sound wave physically does to tissue. They explain: how compressions and rarefactions form how energy moves without matter moving how echoes are generated Without understanding acoustic variables, ultrasound physics becomes memorization instead of logic. Acoustic Variables vs Wave Parameters Acoustic variables describe the medium. Wave parameters describe the sound wave. Acoustic variables oscillate in the tissue. Wave parameters describe: how often the wave vibrates how long it is how strong it appears This distinction is critical for exam success. Final Teaching Emphasis. Acoustic variables are: Pressure. The units are pascals. Density. The units are kilograms per cubic meter. Particle motion. The units are meters or meters per second. These are the quantities that actually change in tissue as ultrasound propagates. Understanding acoustic variables explains how sound interacts with matter

Physics III Questions

Ultrasound Physics: Acoustic Variables Lecture Questions (10) What are acoustic variables? What do acoustic variables describe as sound travels through a medium? How many acoustic variables are there in ultrasound physics? What are the three acoustic variables? What happens to pressure during compression and rarefaction? What unit is used to measure pressure in ultrasound physics? How does density change as a sound wave passes through tissue? What unit is used to measure density? What is particle motion, and how do particles move as sound travels? How is particle motion measured, and why are its units important? Acoustic Variables — Lecture Answer Key 1. Physical quantities that oscillate in a medium as sound travels 2. What is physically changing in the medium 3. Three 4. Pressure, density, and particle motion 5. Pressure increases during compression and decreases during rarefaction 6. Pascals 7. Density increases during compression and decreases during rarefaction 8. Kilograms per cubic meter 9. Oscillation of particles around their resting position; particles move back and forth, not forward 10. Displacement in meters or velocity in meters per second

Physics III Answers

11:30am | Physics III - Acoustic Variables

00:00 / 02:46

Ultrasound Physics: Acoustic Variables Lecture Questions with Answers and Explanations 1. What are acoustic variables? The answer is: Acoustic variables are the physical quantities that oscillate in a medium as sound travels through it. This is because sound energy causes changes in the medium itself, not just motion of the wave. 2. What do acoustic variables describe as sound travels through a medium? The answer is: They describe what is physically changing in the medium. This is because acoustic variables represent pressure, density, and particle motion within the tissue. 3. How many acoustic variables are there in ultrasound physics? The answer is: There are three acoustic variables. This is because pressure, density, and particle motion are the only quantities that oscillate in the medium. 4. What are the three acoustic variables? The answer is: Pressure, density, and particle motion. This is because these are the physical properties of the medium that change as the sound wave passes. 5. What happens to pressure during compression and rarefaction? The answer is: Pressure increases during compression and decreases during rarefaction. This is because particles are pushed closer together during compression and spread farther apart during rarefaction. 6. What unit is used to measure pressure in ultrasound physics? The answer is: Pressure is measured in pascals. This is because pressure is defined as force per unit area in the metric system. 7. How does density change as a sound wave passes through tissue? The answer is: Density increases during compression and decreases during rarefaction. This is because particle spacing changes as sound energy moves through the medium. 8. What unit is used to measure density? The answer is: Density is measured in kilograms per cubic meter. This is because density describes mass per unit volume. 9. What is particle motion, and how do particles move as sound travels? The answer is: Particle motion is the oscillation of particles around their resting position. This is because sound transfers energy, not matter, so particles do not move forward with the wave. 10. How is particle motion measured, and why are its units important? The answer is: Particle motion is measured as displacement in meters or velocity in meters per second. This is because these units describe how far and how fast particles move in response to sound energy. Final Teaching Emphasis Acoustic variables describe the medium, not the wave. Pressure, density, and particle motion are the quantities that oscillate as sound propagates. Understanding these variables explains how sound interacts with tissue and forms the foundation of ultrasound physics.

Physics IV Lecture

2:30pm | Physics IV

00:00 / 01:52

Ultrasound Physics Lecture: Amplitude, Power, and Intensity Now that we understand acoustic variables, we can describe how strong a sound wave is. In ultrasound physics, sound strength is described using amplitude, power, and intensity. These terms are related, but they are not the same thing. Amplitude describes the strength of the sound wave at a single point. It refers to the amount of pressure variation in the medium. As sound travels, pressure rises and falls. The greater the pressure change, the greater the amplitude. Amplitude is measured in units of pressure, such as pascals. In ultrasound imaging, amplitude determines the strength of returning echoes. Stronger echoes appear brighter on the image. Weaker echoes appear darker. Power describes the total amount of sound energy produced by the transducer. It is the rate at which energy is transmitted. Power is measured in watts. Power is determined by the ultrasound system operator. When power is increased, more energy is sent into the body. Power affects patient exposure and must be controlled for safety. Intensity describes how concentrated the sound energy is. It is defined as power divided by area. Intensity tells us how much energy is delivered to a specific location in tissue. Intensity is measured in watts per square centimeter. Amplitude, power, and intensity are related. If power increases and beam area stays the same, intensity increases. If beam area increases and power stays the same, intensity decreases. In ultrasound, intensity is especially important because it describes the biological effect of sound on tissue. Safety guidelines are based on intensity, not amplitude alone and not power alone. Key Teaching Emphasis Amplitude describes pressure change. Power describes energy output. Intensity describes energy concentration. Understanding the difference between these terms is essential for ultrasound physics and patient safety.

Physics IV. Questions

Ultrasound Physics: Amplitude, Power, and Intensity Lecture Questions Question 1 What does amplitude describe in ultrasound physics? Question 2 Amplitude represents which physical change in the medium? A. Density variation B. Pressure variation C. Particle velocity D. Frequency change Question 3 What unit is used to measure amplitude? Question 4 What does power describe in ultrasound? Question 5 Power is measured in which unit? A. Joules B. Hertz C. Watts D. Pascals Question 6 How is intensity defined in ultrasound physics? Question 7 Intensity is measured in which unit? A. Watts B. Watts per square centimeter C. Pascals D. Kilograms per cubic meter Question 8 Which term describes how concentrated sound energy is at a specific location? Question 9 Why is intensity more important than power alone when discussing biological effects? Question 10 If power increases and beam area remains the same, what happens to intensity? A. It decreases B. It stays the same C. It increases D. It becomes zero Answer Key 1. The strength or height of the sound wave 2. B 3. Pascals 4. The rate at which sound energy is transmitted 5. C 6. Power divided by area 7. B 8. Intensity 9. Because intensity describes how much energy is delivered to a specific area of tissue 10. C

Physics IV. Answers

ANSWERS Explained2:30pm | Physics IV

00:00 / 02:08

ANSWERS Explained Question 1 What does amplitude describe in ultrasound physics? The answer is: The strength or height of the sound wave. This is because amplitude reflects the size of the pressure changes in the medium as the sound wave passes. Question 2 Amplitude represents which physical change in the medium? The answer is: Pressure variation. This is because sound waves create alternating increases and decreases in pressure during compression and rarefaction. Question 3 What unit is used to measure amplitude? The answer is: Pascals. This is because amplitude is a pressure change, and pressure is measured in pascals. Question 4 What does power describe in ultrasound? The answer is: The rate at which sound energy is transmitted. This is because power describes how much energy the transducer delivers per unit time. Question 5 Power is measured in which unit? The answer is: Watts. This is because watts measure energy per second, which defines power. Question 6 How is intensity defined in ultrasound physics? The answer is: Power divided by area. This is because intensity describes how concentrated the sound energy is over a given area. Question 7 Intensity is measured in which unit? The answer is: Watts per square centimeter. This is because intensity includes both power and the area over which that power is distributed. Question 8 Which term describes how concentrated sound energy is at a specific location? The answer is: Intensity. This is because intensity tells us how much energy reaches a particular region of tissue. Question 9 Why is intensity more important than power alone when discussing biological effects? The answer is: Because intensity describes local energy delivery. This is because biological effects depend on how much energy is concentrated in tissue, not just total output. Question 10 If power increases and beam area remains the same, what happens to intensity? The answer is: Intensity increases. This is because more power delivered over the same area results in greater energy concentration.

Physics V Lecture

11:30am | Physics V

00:00 / 04:07

Ultrasound Physics Lecture: Wavelength, Frequency, and Period Now that we understand sound strength, we can describe sound using wave parameters. Wave parameters describe the sound wave itself, not the medium. The three primary wave parameters are wavelength, frequency, and period. Wavelength describes the physical length of one complete cycle of a sound wave. It is the distance from one compression to the next compression, or from one rarefaction to the next rarefaction. Wavelength is measured in units of distance, such as meters or millimeters. In ultrasound, wavelength depends on the speed of sound in the medium and the frequency. Wavelength equals propagation speed divided by frequency. When frequency increases, wavelength decreases. When frequency decreases, wavelength increases. Frequency describes how often the sound wave vibrates. It is the number of cycles that occur in one second. Frequency is measured in hertz. Higher frequency means more cycles per second. Lower frequency means fewer cycles per second. Frequency is determined by the sound source, which is the transducer. Once the sound enters the body, frequency does not change. Period describes the time required for one cycle to occur. It is the inverse of frequency. Period is measured in seconds. As frequency increases, period decreases. As frequency decreases, period increases. Wavelength, frequency, and period are directly related. Changing one affects the others. Understanding these relationships is essential for understanding image resolution and penetration. Key Teaching Emphasis Wavelength describes distance. Frequency describes cycles per second. Period describes time per cycle. These are wave parameters, not acoustic variables.

Physics V Questions

Ultrasound Physics: Wavelength, Frequency, and Period Lecture Questions Question 1 What do wavelength, frequency, and period describe? Question 2 What is wavelength? Question 3 Wavelength is measured in which type of unit? A. Time B. Distance C. Pressure D. Energy Question 4 What two factors determine wavelength in tissue? Question 5 What is frequency? Question 6 Frequency is measured in which unit? A. Seconds B. Meters C. Hertz D. Watts Question 7 What is period? Question 8 Period is measured in which unit? A. Hertz B. Meters C. Seconds D. Pascals Question 9 How are frequency and period related? Question 10 What happens to wavelength when frequency increases? Answer Key 1. Wave parameters that describe the sound wave 2. The physical length of one complete cycle 3. B 4. Propagation speed and frequency 5. The number of cycles per second 6. C 7. The time required to complete one cycle 8. C 9. They are inversely related 10. Wavelength decreases

Physics V Answers

ANSWERS Explained11:30am | Physics V

00:00 / 01:53

ANSWERS Explained Question 1 What do wavelength, frequency, and period describe? The answer is: They describe the sound wave itself. This is because wavelength, frequency, and period are wave parameters, not properties of the medium. Question 2 What is wavelength? The answer is: The physical length of one complete cycle of a sound wave. This is because wavelength measures the distance from one compression to the next compression, or one rarefaction to the next. Question 3 Wavelength is measured in which type of unit? The answer is: Distance. This is because wavelength describes a physical length, so it is measured in units such as meters or millimeters. Question 4 What two factors determine wavelength in tissue? The answer is: Propagation speed and frequency. This is because wavelength equals propagation speed divided by frequency. Question 5 What is frequency? The answer is: The number of cycles that occur in one second. This is because frequency describes how often the sound wave vibrates over time. Question 6 Frequency is measured in which unit? The answer is: Hertz. This is because one hertz represents one cycle per second. Question 7 What is period? The answer is: The time required to complete one cycle. This is because period measures how long a single vibration lasts. Question 8 Period is measured in which unit? The answer is: Seconds. This is because period describes time per cycle. Question 9 How are frequency and period related? The answer is: They are inversely related. This is because as frequency increases, the time for each cycle decreases, and vice versa. Question 10 What happens to wavelength when frequency increases? The answer is: Wavelength decreases. This is because wavelength and frequency are inversely related when propagation speed is constant.

Physics VI Lecture

2:30pm | Physics VI

00:00 / 01:34

Ultrasound Physics Lecture: Pulsed and Continuous Waves Now that we understand wavelength, frequency, and period, we can describe how sound is transmitted. Sound can be transmitted as either continuous waves or pulsed waves. Continuous wave sound is produced when the transducer is transmitting sound all the time. There is no pause between sound cycles. Sound energy is sent continuously into the medium. Because transmission never stops, continuous wave ultrasound cannot determine depth. Pulsed wave sound is produced when the transducer transmits sound in short bursts, followed by listening periods. The transducer alternates between transmitting and receiving. This allows ultrasound systems to determine the depth of returning echoes. In pulsed ultrasound, sound is sent as a pulse. Each pulse contains multiple cycles. The time between pulses is called the pulse repetition period. The number of pulses sent per second is called the pulse repetition frequency. Pulsed ultrasound is used for diagnostic imaging because it provides range resolution. Range resolution allows the system to know where echoes come from in the body. Continuous wave ultrasound is primarily used in Doppler. It is useful for measuring very high velocities because it does not suffer from aliasing. Key Teaching Emphasis Continuous wave transmits sound continuously. Pulsed wave transmits sound in bursts. Only pulsed wave ultrasound provides depth information. Both types are important, but they serve different purposes.

Physics VI. Questions

Ultrasound Physics: Pulsed and Continuous Waves Lecture Questions Question 1 What is a continuous wave? Question 2 What is a pulsed wave? Question 3 Which type of ultrasound transmits sound continuously with no pauses? A. Pulsed wave B. Continuous wave C. Harmonic wave D. Standing wave Question 4 Why can continuous wave ultrasound not determine depth? Question 5 Which type of ultrasound alternates between transmitting and receiving? A. Continuous wave B. Standing wave C. Pulsed wave D. Mechanical wave Question 6 Why is pulsed wave ultrasound used for diagnostic imaging? Question 7 What is pulse repetition period? Question 8 What is pulse repetition frequency? Question 9 Which type of ultrasound is primarily used for Doppler measurements? Question 10 Which type of ultrasound allows range or depth resolution? A. Continuous wave B. Pulsed wave C. Infrasound D. Audible sound Answer Key 1. Sound that is transmitted continuously with no interruptions 2. Sound transmitted in short bursts followed by listening periods 3. B 4. Because transmission never stops, so echo return time cannot be measured 5. C 6. Because it allows depth determination of returning echoes 7. The time from the start of one pulse to the start of the next pulse 8. The number of pulses transmitted per second 9. Continuous wave 10. B

Physics VI. Answers

ANSWERS Explained2:30pm | Physics VI

00:00 / 02:00

ANSWERS Explained Question 1 What is a continuous wave? The answer is: Sound that is transmitted continuously with no interruptions. This is because the transducer is always transmitting and never stops to listen. Question 2 What is a pulsed wave? The answer is: Sound transmitted in short bursts followed by listening periods. This is because the transducer alternates between sending sound and receiving echoes. Question 3 Which type of ultrasound transmits sound continuously with no pauses? The answer is: Continuous wave. This is because continuous wave systems do not include listening periods. Question 4 Why can continuous wave ultrasound not determine depth? The answer is: Because transmission never stops. This is because the system cannot measure the time it takes for echoes to return. Question 5 Which type of ultrasound alternates between transmitting and receiving? The answer is: Pulsed wave. This is because pulsed systems send sound, then pause to listen for echoes. Question 6 Why is pulsed wave ultrasound used for diagnostic imaging? The answer is: Because it allows depth determination. This is because echo return time can be measured during listening periods. Question 7 What is pulse repetition period? The answer is: The time from the start of one pulse to the start of the next pulse. This is because pulses are separated by quiet listening intervals. Question 8 What is pulse repetition frequency? The answer is: The number of pulses transmitted per second. This is because PRF describes how often pulses are sent over time. Question 9 Which type of ultrasound is primarily used for Doppler measurements? The answer is: Continuous wave. This is because continuous wave can measure very high velocities without aliasing. Question 10 Which type of ultrasound allows range or depth resolution? The answer is: Pulsed wave. This is because depth is calculated from echo return time.

Physics VII Lecture

Intensities Physics VII

00:00 / 04:01

Intensities. In ultrasound physics, intensity describes how sound energy is distributed in space and time. To understand intensity, we must first define the terms used to describe it. Spatial refers to space or distance. It describes where in the ultrasound beam the intensity is measured. Temporal refers to time. It describes when the intensity is measured. Peak means the maximum value. Average means the mean value. By combining these terms, we can describe specific types of ultrasound intensities. Spatial Peak refers to the intensity located at the center of the ultrasound beam, where the intensity is highest. Spatial Average refers to the mean intensity throughout the entire beam. Temporal Peak is the maximum intensity at any instant in time, measured only when the pulse is on. With continuous wave ultrasound, the temporal peak and the temporal average are the same because the sound is always on. Temporal Average is the intensity averaged over all time, including both transmitting time and receiving time. With continuous wave ultrasound, the temporal average and the temporal peak are the same because there is no off time. Pulse Average is the intensity averaged over the duration of a single pulse, meaning only the transmitting time. Pulse average ignores listening time. Intensity Types Spatial Peak Temporal Peak, also called S P T P, is the largest intensity recorded at any location in space and at any instant in time. Spatial Average Temporal Peak, also called S A T P, is the average intensity across the beam measured at the peak moment in time. Spatial Peak Temporal Average, also called S P T A, is affected by both listening time and pulsing time. This is the lowest intensity measured at the spatial peak. Spatial Average Temporal Average, also called S A T A, represents the average intensity across space and across time. Spatial Peak Pulse Average, also called S P P A, has a value between S P T P and S P T A. S P P A always exceeds S P T A. S P P A is only relevant for pulsed ultrasound and is meaningless for continuous wave ultrasound. Spatial Average Pulse Average, also called S A P A, represents the pulse average across the beam and ignores receiving time. I m is the maximum intensity observed in an ultrasonic wave when averaged over the largest half-layer. All intensities are measured in watts per square centimeter. Beam Uniformity Coefficient The Beam Uniformity Coefficient, or B U C, is a unitless ratio. It is the ratio of spatial peak intensity divided by spatial average intensity. The beam uniformity coefficient is equal to or greater than one. It describes how ultrasound energy is distributed across the beam. It is used to convert spatial peak intensities to spatial average intensities, and vice versa. Duty Factor The duty factor is a unitless number between zero and one. It represents the percentage of time the sound pulse is on. For continuous wave ultrasound, the duty factor is one, or one hundred percent, because the sound is always on. The duty factor is used to convert pulse average intensities to temporal average intensities. Three Step Process to Intensity Conversions Converting Pulse Average to Temporal Average Intensities You will be given the spatial peak pulse average intensity and the duty factor. Multiply the spatial peak pulse average times the duty factor to find the spatial peak temporal average. Spatial peak pulse average times duty factor equals spatial peak temporal average. Converting Spatial Peak to Spatial Average Intensities You will be given the spatial peak to spatial average factor. Divide the spatial peak temporal average by the spatial peak to spatial average factor to find the spatial average temporal average. Spatial peak temporal average divided by the spatial peak to spatial average factor equals spatial average temporal average. This structured approach ensures accurate intensity conversions in ultrasound physics.

Physics VII Questions

Ultrasound Physics: Intensities Lecture Questions Question 1 What do the terms spatial and temporal describe when referring to intensity? Question 2 What is meant by spatial peak intensity? Question 3 What is meant by spatial average intensity? Question 4 What is temporal peak intensity? Question 5 Why are temporal peak and temporal average the same in continuous wave ultrasound? Question 6 What is pulse average intensity? Question 7 What does S P T P stand for? A. Spatial Peak Temporal Peak B. Spatial Pulse Temporal Peak C. Spatial Peak Temporal Pulse D. Spatial Power Temporal Peak Question 8 Which intensity is affected by both listening time and pulsing time and is the lowest intensity? Question 9 What is the Beam Uniformity Coefficient, or B U C? Question 10 What unit is used to measure all ultrasound intensities? Answer Key 1. Spatial describes location in space, and temporal describes time 2. The intensity located at the center of the beam 3. The mean intensity throughout the entire beam 4. The maximum intensity at any instant when the pulse is on 5. Because the sound is always on and there is no off time 6. The intensity averaged over the duration of a single pulse 7. A 8. Spatial Peak Temporal Average 9. A unitless ratio of spatial peak intensity divided by spatial average intensity 10. Watts per square centimeter

Physics VII Answers

ANSWERS ExplainedPhysics VII - Intensity

00:00 / 02:24

ANSWERS Explained What do the terms spatial and temporal describe when referring to intensity? The answer is: Spatial describes location in space, and temporal describes time. This is because intensity can vary depending on where it is measured in the beam and when it is measured during transmission. Question 2 What is meant by spatial peak intensity? The answer is: The intensity located at the center of the beam. This is because the center of the ultrasound beam contains the highest concentration of sound energy. Question 3 What is meant by spatial average intensity? The answer is: The mean intensity throughout the entire beam. This is because spatial average accounts for all intensities across the beam, not just the center. Question 4 What is temporal peak intensity? The answer is: The maximum intensity at any instant when the pulse is on. This is because temporal peak measures intensity at a single moment during sound transmission. Question 5 Why are temporal peak and temporal average the same in continuous wave ultrasound? The answer is: Because the sound is always on. This is because continuous wave ultrasound has no off time, so the maximum intensity and the average over time are identical. Question 6 What is pulse average intensity? The answer is: The intensity averaged over the duration of a single pulse. This is because pulse average includes only transmitting time and ignores listening time. Question 7 What does S P T P stand for? The answer is: Spatial Peak Temporal Peak. This is because it represents the highest intensity measured at the beam center at the peak moment in time. Question 8 Which intensity is affected by both listening time and pulsing time and is the lowest intensity? The answer is: Spatial Peak Temporal Average. This is because temporal averaging includes both on time and off time, which lowers the measured intensity. Question 9 What is the Beam Uniformity Coefficient, or B U C? The answer is: A unitless ratio of spatial peak intensity divided by spatial average intensity. This is because it describes how evenly sound energy is distributed across the ultrasound beam. Question 10 What unit is used to measure all ultrasound intensities? The answer is: Watts per square centimeter. This is because intensity is defined as power per unit area.

Physics VIII Lecture

AttenuationPhysics VIII

00:00 / 03:11

VIII. Interaction of Sound and Media When sound travels through tissue, it does not remain unchanged. Sound interacts with the medium it travels through, and these interactions affect sound strength. To describe these changes, ultrasound physics uses logarithms, decibels, and attenuation. Logarithms A logarithm is a method of ranking numbers. The logarithm of a number represents the number of times ten is multiplied by itself to create that number. For example: Ten times ten times ten equals one thousand. The logarithm of one thousand is three. As a number gets larger, its logarithm also gets larger. Decibels Decibels are units used to describe amplitude and attenuation. Decibels are not absolute measurements. A decibel describes the relationship between two values. When comparing two intensities, powers, or amplitudes, decibels describe how much stronger or weaker one is compared to the other. Decibel notation is based on a logarithmic scale. Positive Decibels Positive decibels represent an increase or strengthening of intensity. A change of: Three decibels means intensity doubles. Six decibels means intensity increases four times. Nine decibels means intensity increases eight times. Ten decibels means intensity increases ten times. Twenty decibels means intensity increases one hundred times. Negative Decibels Negative decibels represent a decrease or weakening of intensity. A change of: Negative three decibels means intensity is cut in half. Negative six decibels means intensity is one fourth. Negative nine decibels means intensity is one eighth. Negative ten decibels means intensity is one tenth. Negative twenty decibels means intensity is one one hundredth. Attenuation Attenuation is the weakening of a sound wave as it travels through a medium. Attenuation is measured in negative decibels. When a wave undergoes attenuation, its intensity is reduced. Because attenuation represents a loss of intensity, decibels used to describe attenuation must be negative. Path Length Path length refers to the distance or depth a sound beam travels through tissue. Path length is measured in centimeters. As path length increases, attenuation increases. Attenuation Coefficient The attenuation coefficient describes how much attenuation occurs per centimeter of travel. The unit of the attenuation coefficient is decibels per centimeter. Most ultrasound coefficients are unitless, but the attenuation coefficient is not. For soft tissue, the attenuation coefficient can be approximated. The attenuation coefficient is approximately the frequency in megahertz divided by two. Example If the frequency is six megahertz, Six divided by two equals three. This means the attenuation coefficient is three decibels per centimeter. So the ultrasound beam loses about three decibels of intensity for every centimeter it travels through soft tissue. Key Teaching Emphasis Logarithms rank numbers. Decibels compare two values. Attenuation describes loss of intensity. Attenuation increases with frequency and with distance traveled.

Physics VIII. Questions

Ultrasound Physics: Interaction of Sound and Media Lecture Questions Question 1 What is a logarithm? Question 2 What does the logarithm of a number represent? Question 3 As a number increases, what happens to its logarithm? A. It decreases B. It stays the same C. It increases D. It becomes negative Question 4 What are decibels used to describe in ultrasound physics? Question 5 Why is a decibel considered a relationship rather than an absolute measurement? Question 6 What do positive decibels represent? Question 7 What does negative three decibels indicate? A. Double the intensity B. Half the intensity C. One fourth the intensity D. No change in intensity Question 8 What is attenuation? Question 9 What unit is used for the attenuation coefficient? Question 10 How is the attenuation coefficient for soft tissue approximated? Answer Key 1. A method of ranking numbers 2. The number of times ten is multiplied by itself to create the original number 3. C 4. Amplitude and attenuation 5. Because it compares two values rather than measuring a single value 6. An increase or strengthening of intensity 7. B 8. The weakening of a sound wave as it travels through a medium 9. Decibels per centimeter 10. Frequency in megahertz divided by two

Physics VIII. Answers

AttenuationPhysics VII

00:00 / 02:01

Question 1 What is a logarithm? The answer is: A method of ranking numbers. This is because a logarithm expresses the size of a number based on powers of ten rather than its absolute value. Question 2 What does the logarithm of a number represent? The answer is: The number of times ten is multiplied by itself to create the original number. This is because logarithms are based on powers of ten. Question 3 As a number increases, what happens to its logarithm? The answer is: It increases. This is because larger numbers require more powers of ten to be created. Question 4 What are decibels used to describe in ultrasound physics? The answer is: Amplitude and attenuation. This is because decibels describe changes in sound strength and sound loss. Question 5 Why is a decibel considered a relationship rather than an absolute measurement? The answer is: Because it compares two values. This is because a decibel expresses how much one value differs from another, not a standalone quantity. Question 6 What do positive decibels represent? The answer is: An increase or strengthening of intensity. This is because positive decibels indicate a gain in sound energy. Question 7 What does negative three decibels indicate? The answer is: Half the intensity. This is because a decrease of three decibels corresponds to a fifty percent reduction in intensity. Question 8 What is attenuation? The answer is: The weakening of a sound wave as it travels through a medium. This is because sound loses energy as it interacts with tissue. Question 9 What unit is used for the attenuation coefficient? The answer is: Decibels per centimeter. This is because the attenuation coefficient describes sound loss per unit distance. Question 10 How is the attenuation coefficient for soft tissue approximated? The answer is: Frequency in megahertz divided by two. This is because soft tissue attenuation increases roughly linearly with frequency.

Physics IX. Lecture

Transducers Physics IX

00:00 / 06:36

IX. Transducers and Transducer Materials Ultrasound imaging begins with the transducer. A transducer is any device that converts one form of energy into another. In ultrasound, the transducer converts electrical energy into sound energy, and returning sound energy back into electrical signals. Piezoelectric Effect The piezoelectric effect is the ability of certain crystals to produce a voltage when they are mechanically deformed. The same crystals can also deform when an electrical voltage is applied. This two-way behavior allows ultrasound transmission and reception. Active Element The active element is the piezoelectric crystal itself. The most commonly used material in ultrasound transducers is lead zirconate titanate, also called P Z T. P Z T is a man-made piezoelectric crystal used in all diagnostic ultrasound transducers. The speed of sound in P Z T is approximately four to six millimeters per microsecond. This is about three to four times faster than the speed of sound in soft tissue. For pulsed ultrasound, the thickness of the crystal and the speed of sound in the crystal determine the frequency of the sound produced. For continuous wave ultrasound, the frequency is determined by the electrical signal from the ultrasound system, not by crystal thickness or crystal speed. In continuous wave ultrasound, the frequency of the acoustic signal equals the frequency of the electrical signal driving the crystal. Crystal Thickness Crystal thickness affects frequency. Thicker crystals produce lower frequencies. Thinner crystals produce higher frequencies. This is because different thicknesses create pulses with different cycle lengths. Crystal Speed Crystal speed also affects frequency. Faster crystals produce higher frequencies. Slower crystals produce lower frequencies. Both thickness and crystal speed contribute to the frequency of the acoustic wave. Curie Temperature The Curie temperature is the temperature above which a piezoelectric crystal loses its polarization and its piezoelectric properties. For P Z T, this temperature is approximately six hundred to seven hundred degrees Fahrenheit, or three hundred to four hundred degrees Celsius. When a crystal is heated above the Curie temperature, it becomes depolarized. A depolarized crystal can no longer transmit or receive ultrasound. Damping Element The damping element is an epoxy resin combined with tungsten and attached to the back of the P Z T crystal. The damping element reduces crystal ringing. This shortens the pulse, reduces pulse duration, and improves image resolution. Damping increases bandwidth. The wider the bandwidth, the shorter the pulse. The shorter the pulse, the better the image resolution. A wider bandwidth results in a lower Q factor. Damping decreases pulse duration and spatial pulse length. Wire The wire provides electrical contact between the ultrasound system and the crystal during both transmission and reception. Case or Insulator The case, or insulator, is a plastic or metal housing that surrounds and protects the transducer’s internal components. It shields the patient from electric shock and prevents damage to internal components. Matching Layer The matching layer is positioned between the crystal and the skin. Its purpose is to reduce impedance mismatch and improve sound transmission into the body. The decreasing order of acoustic impedance is: Active element, then matching layer, then gel, then skin. Bandwidth Bandwidth is the difference between the highest and lowest frequencies within a pulse. It represents a range of frequencies. Bandwidth is measured in hertz. The narrower the bandwidth, the more exact the frequency emitted by the transducer. Imaging transducers have wide bandwidths, which produce shorter pulses. Therapeutic transducers have narrow bandwidths, which produce longer pulses. Bandwidth equals highest frequency minus lowest frequency. Q Factor The Q factor, or quality factor, is a unitless number representing a transducer’s ability to emit a single, pure frequency. Imaging transducers have low Q factors and wide bandwidths. Therapeutic transducers have high Q factors and narrow bandwidths. Q factor equals resonant frequency divided by bandwidth. Resonant Frequency The resonant frequency is the transducer’s designated operating frequency. It is typically the highest frequency within the bandwidth. Transducer Shapes and Arrays Transducers can have different shapes and array designs. Rectangular transducers include linear switched and linear sequential arrays. Sector or wedge-shaped transducers include linear phased arrays, mechanical transducers, and annular phased arrays. Blunted sector transducers include convex and curvilinear arrays. Trapezoidal transducers include vector arrays. Array Definitions Linear means arranged in a straight line. Annular means arranged in a ring or circular shape. An array is a collection of active elements within a single transducer housing. Switched arrays use no beam steering and rely on conventional focusing. Phased arrays use electronic focusing and steering. Mechanical Transducers Mechanical transducers physically move or rotate one or more crystals to steer the ultrasound beam. They can focus at only one fixed depth. Steering and Focusing Mechanical steering is achieved with motors or moving mirrors. Electronic steering occurs when timing differences are applied to crystal elements to steer the beam electronically. Conventional focusing uses an acoustic lens, curved crystal, or mirrors. Conventional focus is fixed and cannot be changed by the operator. Electronic focusing uses electrical delays applied to crystal elements. This allows dynamic focusing and multiple focal zones. Curvature and Slope Curvature refers to the bending of the crystal or lens. Greater curvature produces a shallower focal point. Less curvature produces a deeper focal point. Slope refers to the angle of electronic delay used for beam steering. A greater slope produces a greater steering angle. Additional Systems Some systems include: Electronic curvature, electronic slope, beam focusing, beam steering, water path scanners, and small parts scanners. Small parts scanners are designed for high-resolution imaging of superficial structures such as the thyroid, breast, and scrotum.

Click transducer image for a better image.

Physics IX. Questions

Ultrasound Physics: Transducers and Transducer Materials Lecture Questions Question 1 What is a transducer? Question 2 What is the piezoelectric effect? Question 3 What is the active element in an ultrasound transducer? Question 4 What material is most commonly used as the piezoelectric crystal in ultrasound transducers? A. Quartz B. Ceramic glass C. Lead zirconate titanate D. Aluminum oxide Question 5 How does crystal thickness affect frequency? Question 6 For pulsed ultrasound, what two crystal properties determine the frequency of sound produced? Question 7 What is the Curie temperature? Question 8 What is the purpose of the damping element in a transducer? Question 9 What is the function of the matching layer? Question 10 What does bandwidth describe? Answer Key 1. A device that converts one form of energy into another 2. The ability of a crystal to generate voltage when mechanically deformed and deform when voltage is applied 3. The piezoelectric crystal itself 4. C 5. Thicker crystals produce lower frequencies and thinner crystals produce higher frequencies 6. Crystal thickness and crystal speed 7. The temperature above which a crystal loses its piezoelectric properties 8. To reduce ringing, shorten pulse duration, and improve image resolution 9. To reduce impedance mismatch and improve sound transmission 10. The range of frequencies within a pulse

Physics IX. Answers

TransducersPhysics IX. Transducers

00:00 / 02:48

ANSWERS Explained Question 1 What is a transducer? The answer is: A device that converts one form of energy into another. This is because an ultrasound transducer converts electrical energy into sound energy during transmission and converts returning sound energy back into electrical signals during reception. Question 2 What is the piezoelectric effect? The answer is: The ability of a crystal to generate voltage when mechanically deformed and to deform when voltage is applied. This is because piezoelectric crystals respond to both mechanical stress and electrical stimulation, allowing them to transmit and receive ultrasound. Question 3 What is the active element in an ultrasound transducer? The answer is: The piezoelectric crystal itself. This is because the crystal is the component that actually produces and receives the sound waves. Question 4 What material is most commonly used as the piezoelectric crystal in ultrasound transducers? The answer is: Lead zirconate titanate. This is because P Z T is a man-made crystal with strong piezoelectric properties suitable for diagnostic ultrasound. Question 5 How does crystal thickness affect frequency? The answer is: Thicker crystals produce lower frequencies, and thinner crystals produce higher frequencies. This is because crystal thickness determines the time it takes for sound waves to reflect within the crystal and form a pulse. Question 6 For pulsed ultrasound, what two crystal properties determine the frequency of sound produced? The answer is: Crystal thickness and crystal speed. This is because frequency depends on how fast sound travels in the crystal and how thick the crystal is. Question 7 What is the Curie temperature? The answer is: The temperature above which a crystal loses its piezoelectric properties. This is because heating above the Curie temperature causes the crystal to lose polarization and stop functioning as a transducer. Question 8 What is the purpose of the damping element in a transducer? The answer is: To reduce ringing, shorten pulse duration, and improve image resolution. This is because damping absorbs excess vibrations in the crystal, producing shorter pulses and wider bandwidth. Question 9 What is the function of the matching layer? The answer is: To reduce impedance mismatch and improve sound transmission into the body. This is because the matching layer helps sound energy pass efficiently from the crystal into the patient’s tissue. Question 10 What does bandwidth describe? The answer is: The range of frequencies within a pulse. This is because bandwidth represents the difference between the highest and lowest frequencies emitted by the transducer.

Physics X. Lecture

Sound BeamsPhysics X

00:00 / 05:06

X. Sound Beams. As ultrasound travels through tissue, it forms a sound beam. The shape and behavior of this beam determine image resolution and image quality. Focus and Focal Point. The focus, also called the focal point, is the most narrow point of the sound beam. At this location, the beam diameter is the smallest. This is where optimum transverse resolution is obtained. When a beam is focused, it narrows near the end of the near zone and at the beginning of the far zone. Focal Length. Focal length is the distance from the transducer to the focus. Focal length is determined by: the diameter of the P Z T crystal, and the emitted frequency. Crystal diameter is not the same as crystal thickness. Changes in pulse repetition period do not affect the depth of focus. Only crystal diameter and frequency do. Crystal Diameter. Crystal diameter affects beam focus. A larger crystal diameter results in: a longer focal length, and a deeper beam focus. A smaller crystal diameter results in: a shorter focal length, and a shallower beam focus. Emitted Frequency. Emitted frequency also affects focal length. A higher emitted frequency results in: a longer focal length, and a deeper beam focus. A lower emitted frequency results in: a shallower beam focus. Near Zone. The near zone is the portion of the sound beam between the transducer and the focus. In an unfocused disc transducer operating in continuous mode, at the end of the near zone, the beam diameter equals one half of the transducer diameter. At two near zone lengths, the beam diameter equals the full transducer diameter. Far Zone. The far zone is the portion of the sound beam beyond the near zone. In the far zone, the beam diameter increases as the distance from the transducer increases. Focal Zone. The focal zone is the narrow region that surrounds the focus. This region provides the best image resolution. Diffraction. Diffraction is the spreading of a sound wave as it propagates away from a small sound source. Diffraction causes the beam to widen as it travels. Huygens’ Principle. Huygens’ principle explains why imaging transducers do not diffract excessively. Each particle of the P Z T crystal acts as a source of its own wave. These many waves interfere constructively and destructively, forming a sound beam shaped like an hourglass. Divergence. Divergence describes how much the sound beam spreads in the far zone. Small diameter crystals produce more divergent beams, similar to a pen light. Large diameter crystals produce less divergent beams, similar to a search light. Lateral Resolution. Lateral resolution describes the ability to distinguish objects that lie side by side. Most imaging systems have better axial resolution than lateral resolution. Therefore, lateral resolution usually has a higher numerical value. Higher frequency sound produces narrower beams, which improves lateral resolution. To improve lateral resolution, the beam diameter must be reduced. Spatial Resolution. Spatial resolution is the system’s overall ability to accurately display small structures in their correct anatomic location. Temporal Resolution. Temporal resolution is the ability of the system to accurately display moving structures over time. Temporal resolution is not affected by pulse duration. Temporal resolution improves as the number of images per second increases. Increasing: sector angle, line density, or frequency will decrease temporal resolution. The lowest temporal resolution occurs in color flow imaging. The best temporal resolution occurs in M-mode. The worst temporal resolution occurs in B-mode imaging. Frame Rate. Frame rate is the number of images created per second. Frame rate is measured in: frames per second, or hertz. Typical frame rates range from ten to sixty images per second. Lower pulse repetition period means more pulses per second, which increases frame rate. Frame rate is determined by the ultrasound system and is not directly controlled by the sonographer. More frames per second result in: better accuracy for moving structures, less time available to build each frame, and decreased line density. Line Density. Line density is the number of acoustic lines per degree of sector angle. Higher line density produces greater anatomic detail. Line density equals pulses per image divided by sector angle. Imaging Depth and P R F Relationship. Imaging depth is the total distance sound travels per pulse. Pulse repetition frequency equals: pulses per scan line times image lines per frame times frame rate. Sound travels at one hundred fifty-four thousand centimeters per second in soft tissue. Because sound must travel out and back, the maximum travel distance per second is seventy-seven thousand centimeters. If the total required travel distance exceeds seventy-seven thousand centimeters, imaging is not possible. Understanding these beam relationships is essential for controlling resolution, depth, and frame rate in diagnostic ultrasound.

Physics X. Questions

Ultrasound Physics: Sound Beams. Lecture Questions. Question 1 What is the focus or focal point of a sound beam? Question 2 Where is optimum transverse resolution obtained? Question 3 What is focal length? Question 4 Which two factors determine focal length? A. Pulse repetition period and frequency B. Crystal thickness and damping C. Crystal diameter and emitted frequency D. Bandwidth and duty factor Question 5 How does crystal diameter affect beam focus? Question 6 What is the near zone? Question 7 What happens to beam diameter in the far zone? Question 8 What is diffraction? Question 9 Which type of crystal produces a more divergent beam? A. Large diameter crystal B. High frequency crystal C. Small diameter crystal D. Curved crystal Question 10 What does temporal resolution describe? Answer Key. 1. The narrowest point of the sound beam 2. At the focus 3. The distance from the transducer to the focus 4. C 5. Larger diameter produces a longer focal length and deeper focus; smaller diameter produces a shallower focus 6. The region of the beam between the transducer and the focus 7. The beam diameter increases with distance 8. The spreading of a sound wave as it propagates 9. C 10. The ability to accurately display moving structures over time

Physics X. Answers

Sound BeamsPhysics X

00:00 / 02:08

Question 1. What is the focus or focal point of a sound beam? The answer is: The narrowest point of the sound beam. This is because focusing causes the beam diameter to decrease to its smallest size at that location. Question 2. Where is optimum transverse resolution obtained? The answer is: At the focus. This is because transverse, or lateral, resolution is best where the beam is narrowest. Question 3. What is focal length? The answer is: The distance from the transducer to the focus. This is because focal length describes how far the beam travels before it reaches its narrowest point. Question 4. Which two factors determine focal length? The answer is: Crystal diameter and emitted frequency. This is because beam focusing depends on the size of the crystal and the wavelength of the sound produced. Question 5. How does crystal diameter affect beam focus? The answer is: A larger crystal diameter produces a longer focal length and deeper focus, while a smaller diameter produces a shallower focus. This is because larger apertures focus sound farther from the transducer. Question 6. What is the near zone? The answer is: The region of the sound beam between the transducer and the focus. This is because the beam converges and narrows throughout the near zone. Question 7. What happens to beam diameter in the far zone? The answer is: The beam diameter increases with distance. This is because sound waves diverge after passing the focal region. Question 8. What is diffraction? The answer is: The spreading of a sound wave as it propagates. This is because waves naturally spread as they move away from a small source. Question 9. Which type of crystal produces a more divergent beam? The answer is: A small diameter crystal. This is because smaller apertures allow sound to spread more rapidly, similar to a pen light. Question 10. What does temporal resolution describe? The answer is: The ability to accurately display moving structures over time. This is because temporal resolution depends on how many images are produced each second.

Physics XI. Lecture

Artifacts Physics XI

00:00 / 05:17

XI. Artifacts and Resolution Errors. An artifact is any displayed image feature that does not correspond to the true anatomy. Artifacts occur because ultrasound systems make assumptions about how sound travels. When those assumptions are violated, artifacts appear. Axial Resolution Artifact. Axial resolution describes the ability to distinguish objects that lie along the direction of the beam. When two reflectors are too close together axially, they appear as one reflector. Axial resolution is measured in millimeters. It is also known as: longitudinal resolution range resolution depth resolution Typical axial resolution ranges from zero point three to one millimeter. Smaller numerical values indicate better resolution. Lateral Resolution Artifact. Lateral resolution describes the ability to distinguish objects that lie side by side. When objects are too close laterally, they appear as one reflector. Lateral resolution is measured in millimeters. It is also known as: lateral resolution transverse resolution angular resolution Typical lateral resolution ranges from two to ten millimeters. Lateral resolution is approximately equal to beam diameter. It improves with focusing and higher frequency. Smaller numerical values produce better images. Acoustic Speckle. Acoustic speckle is a form of image noise. It is caused by constructive and destructive interference from many small scatterers within tissue. Speckle appears as a grainy or textured pattern that does not represent actual anatomic structures. Speckle can be reduced using: spatial compounding persistence Slice Thickness Artifact. Slice thickness artifact occurs because the ultrasound beam has finite thickness. Structures above or below the imaging plane may be included in the image. This can cause false internal echoes, especially within anechoic structures such as cysts. Slice thickness artifact can be reduced by: thinner elevational beam width improved focusing in the elevational plane Refraction. Refraction is the bending of the sound beam as it passes between tissues with different propagation speeds. Refraction causes lateral displacement of structures. It can result in: duplication distortion incorrect positioning of anatomy Refraction is most common when the beam strikes a boundary at an oblique angle. Reverberation. Reverberation occurs when sound reflects back and forth between two strong reflectors. It appears as multiple, equally spaced echoes that decrease in intensity with depth. Common locations include: between the transducer and pleura diaphragm bladder wall Comet Tail and Ring-Down Artifact. Comet tail and ring-down artifacts are types of reverberation. They appear as a bright linear echo extending distally from a reflector. They are caused by: gas bubbles metallic objects cholesterol crystals surgical clips Mirror Image Artifact. Mirror image artifact occurs when sound reflects off a strong interface such as the diaphragm or pleura. The structure is duplicated on the opposite side of the reflector. The true structure and the mirror image appear equidistant from the reflecting surface. Multipath Artifact. Multipath occurs when sound travels along multiple paths to and from a reflector. Echoes return at different times, causing incorrect depth placement. The structure may appear deeper or displaced from its true location. Side Lobes. Side lobes are weak off-axis sound beams generated by a transducer. They can produce false echoes adjacent to strong reflectors. Side lobes are reduced by: apodization subdicing Grating Lobes. Grating lobes are extra beams produced by array transducers due to regular spacing of elements. They can cause echoes to appear in incorrect locations. Grating lobes are reduced by: subdicing apodization Shadowing. Shadowing appears as a dark region distal to a structure that strongly attenuates or reflects sound. It commonly occurs with: bone calcifications air Shadowing results from: absorption reflection refraction Enhancement. Enhancement is increased brightness distal to a weakly attenuating structure. It commonly occurs with: cysts bladder gallbladder Enhancement occurs because sound loses less energy passing through fluid than through surrounding tissue. Range Artifact (Range Ambiguity). Range artifact occurs when a new pulse is transmitted before all echoes from the previous pulse have returned. Echoes are displayed too close to the transducer. Range ambiguity is associated with high pulse repetition frequency. It can be corrected by: decreasing pulse repetition frequency increasing imaging depth Propagation Speed Error. Propagation speed error occurs when sound travels at a speed other than one thousand five hundred forty meters per second. This results in incorrect depth placement. If sound travels faster, structures appear too shallow. If sound travels slower, structures appear too deep. System and Operator Controls. Functions primarily controlled by the sonographer include: amplification compensation reject Functions primarily set by the system include: compression demodulation

Physics XI. Questions

Ultrasound Physics: Artifacts and Resolution Errors. Lecture Questions. Question 1. What is an artifact in ultrasound imaging? Question 2. What causes an axial resolution artifact? Question 3. Axial resolution is measured in which type of unit? A. Hertz B. Decibels C. Millimeters D. Seconds Question 4. What causes a lateral resolution artifact? Question 5. Lateral resolution is approximately equal to which beam characteristic? Question 6. What is acoustic speckle? Question 7. Slice thickness artifact most commonly produces what appearance within a cyst? Question 8. Which artifact results from bending of the sound beam at tissue boundaries? A. Reverberation B. Refraction C. Shadowing D. Multipath Question 9. What causes reverberation artifact? Question 10. If sound travels slower than one thousand five hundred forty meters per second, how will the structure appear on the image? Answer Key. 1. An image feature that does not correspond to true anatomy 2. Reflectors that are too closely spaced along the beam direction 3. C 4. Reflectors that are too closely spaced side by side 5. Beam diameter 6. Image noise caused by interference from many small scatterers 7. False internal echoes 8. B 9. Multiple reflections between strong reflectors 10. Too deep

Physics XI. Answers

ArtifactsPhysics XI.

00:00 / 02:25

ANSWERS Explained Question 1. What is an artifact in ultrasound imaging? The answer is: An image feature that does not correspond to true anatomy. This is because artifacts occur when the ultrasound system’s assumptions about sound propagation are violated. Question 2. What causes an axial resolution artifact? The answer is: Reflectors that are too closely spaced along the beam direction. This is because axial resolution depends on pulse length, and closely spaced reflectors cannot be separated if the pulse is too long. Question 3. Axial resolution is measured in which type of unit? The answer is: Millimeters. This is because axial resolution describes distance along the beam. Question 4. What causes a lateral resolution artifact? The answer is: Reflectors that are too closely spaced side by side. This is because lateral resolution depends on beam width, and objects within the same beam width cannot be separated. Question 5. Lateral resolution is approximately equal to which beam characteristic? The answer is: Beam diameter. This is because beam width determines how well side-by-side objects can be distinguished. Question 6. What is acoustic speckle? The answer is: Image noise caused by interference from many small scatterers. This is because scattered wavelets interfere constructively and destructively, producing a grainy appearance. Question 7. Slice thickness artifact most commonly produces what appearance within a cyst? The answer is: False internal echoes. This is because echoes from structures outside the imaging plane are included in the image. Question 8. Which artifact results from bending of the sound beam at tissue boundaries? The answer is: Refraction. This is because sound changes direction when it crosses tissues with different propagation speeds. Question 9. What causes reverberation artifact? The answer is: Multiple reflections between strong reflectors. This is because sound bounces back and forth before returning to the transducer, creating repeated echoes. Question 10. If sound travels slower than one thousand five hundred forty meters per second, how will the structure appear on the image? The answer is: Too deep. This is because slower sound takes longer to return, causing the system to place the structure deeper than its true location.

Physics XII. Lecture

DopplerPhysics XII

00:00 / 04:51

XII. Doppler Principles. The Doppler principle explains how motion affects sound frequency. In ultrasound, Doppler is used to evaluate blood flow. Doppler Effect. The Doppler effect is a change in frequency that occurs when the sound source and the receiver are moving relative to each other. If they are moving closer together, the frequency increases. If they are moving farther apart, the frequency decreases. Doppler Shift. The Doppler shift is the difference between the transmitted frequency and the received frequency. Doppler shift is measured in hertz. In clinical imaging, red blood cells are the primary reflectors that produce Doppler shifts. Red blood cells are constantly moving and make up nearly forty-five percent of blood volume. Increasing transducer frequency results in an increased Doppler shift and increases the likelihood of aliasing. Decreasing transducer frequency results in a smaller Doppler shift and decreases the likelihood of aliasing. Positive Doppler Shift. A positive Doppler shift occurs when red blood cells move toward the transducer. The reflected frequency is higher than the transmitted frequency. Negative Doppler Shift. A negative Doppler shift occurs when red blood cells move away from the transducer. The reflected frequency is lower than the transmitted frequency. Maximum Doppler Shift. Maximum Doppler shift occurs when blood cells move directly toward or directly away from the transducer. An angle of one hundred eighty degrees exists when motion is directly away. Absence of Doppler Shift. Doppler shift depends on the angle between blood flow and the sound beam. When blood flow is perpendicular to the beam at ninety degrees, the cosine of ninety degrees is zero. When cosine equals zero, no Doppler shift is detected. Speed and Velocity. Speed describes how fast an object moves without regard to direction. Velocity describes both speed and direction of motion. Doppler ultrasound measures velocity, not just speed. Cosine Relationship. Doppler measurements depend on the cosine of the Doppler angle. Cosine of zero degrees equals one. Cosine of ninety degrees equals zero. Doppler loves zero degrees and hates ninety degrees. Measured velocity equals true velocity times cosine of the Doppler angle. Key Doppler Equation Terms. Reflector speed refers to the velocity of blood. Incident frequency is the transmitted frequency. Theta represents the Doppler angle. Propagation speed is the speed of sound in tissue, approximately one thousand five hundred forty meters per second. The factor of two accounts for sound traveling to the reflector and back. Continuous Wave Doppler. Continuous wave Doppler transmits and receives sound continuously. Aliasing does not occur with continuous wave Doppler. Continuous wave Doppler can measure very high velocities. However, it has range ambiguity. Doppler shifts arise along the entire beam, so depth cannot be precisely determined. Pulsed Wave Doppler. Pulsed wave Doppler uses a single crystal that alternates between transmitting and receiving. It provides range resolution. The sample volume, or gate, identifies the exact location where Doppler shifts are measured. Aliasing. Aliasing is an incorrect display of Doppler information. High velocities in one direction appear as flow in the opposite direction. Aliasing occurs when the Doppler shift exceeds the Nyquist limit. Continuous wave Doppler cannot alias. Aliasing is less likely when pulse repetition frequency is high. Aliasing occurs when the Doppler frequency exceeds half the pulse repetition frequency. Nyquist Limit. The Nyquist limit equals pulse repetition frequency divided by two. It represents the highest Doppler shift that can be displayed without aliasing. Reducing Aliasing. Aliasing can be reduced by: increasing pulse repetition frequency imaging at a shallower depth using a lower frequency transducer using continuous wave Doppler Spectral Doppler Analysis. Spectral analysis breaks down complex Doppler signals into individual frequency components. Early methods included: zero crossing detection time interval histograms These methods are now obsolete. The Fast Fourier Transform, or F F T, is the current method used for pulsed and continuous wave Doppler analysis. Color Flow Doppler. Color flow Doppler displays Doppler information over a two-dimensional image. It is a pulsed technique and is subject to aliasing. Color flow Doppler reduces temporal resolution. Color maps indicate: direction of flow velocity variance Velocity mode shows direction. Variance mode identifies turbulence. Flow Patterns. Laminar flow is smooth and orderly. Turbulent flow is chaotic and irregular.

Where:

Δf = Doppler frequency shift
f₀ = Transmitted ultrasound frequency
V = Velocity of blood flow (component parallel to the beam)
θ = Angle of insonation
c = Speed of sound in tissue (~1540 m/s)

Angle Dependence (HIGH-YIELD FOR EXAMS)

Doppler shift is maximal at 0°
Doppler shift is zero at 90°
Angle correction errors increase significantly above 60°
Only the velocity component parallel to the ultrasound beam is measured

Spectral Doppler Interpretation (Exam Language)

Higher velocities → higher Doppler frequency shifts
Lower velocities → lower Doppler frequency shifts
Spectral Doppler displays:
- Velocity on the vertical axis
- Time on the horizontal axis
Audible Doppler:
- Higher frequency shifts are perceived as higher pitch
- Lower frequency shifts are perceived as lower pitch

(Important distinction: pitch is audio perception, frequency shift is the physical parameter.)

Physics XII. Questions

Ultrasound Physics: Doppler Principles. Lecture Questions. Question 1. What is the Doppler effect? Question 2. What is the Doppler shift? Question 3. In clinical Doppler imaging, which structures primarily produce Doppler shifts? A. Vessel walls B. Plasma C. Red blood cells D. Valves Question 4. What happens to the Doppler shift when red blood cells move toward the transducer? Question 5. What happens to the Doppler shift when blood cells move away from the transducer? Question 6. At what Doppler angle does the Doppler shift become zero? A. Zero degrees B. Thirty degrees C. Sixty degrees D. Ninety degrees Question 7. Why does continuous wave Doppler not experience aliasing? Question 8. What is aliasing in Doppler ultrasound? Question 9. What is the Nyquist limit? Question 10. Which actions can reduce the likelihood of aliasing? Answer Key. 1. A change in frequency caused by relative motion between the sound source and receiver 2. The difference between transmitted and received frequency 3. C 4. The Doppler shift increases and becomes positive 5. The Doppler shift decreases and becomes negative 6. D 7. Because it continuously transmits and receives and is not limited by PRF 8. An incorrect display where high velocities appear reversed 9. Half the pulse repetition frequency 10. Increasing PRF, decreasing imaging depth, using a lower frequency transducer, or using continuous wave Doppler

Physics XII. Answers

DopplerPhysics XII

00:00 / 02:37

XII. Doppler Principles. Question 1. What is the Doppler effect? The answer is: A change in frequency caused by relative motion between the sound source and the receiver. This is because motion alters the spacing of sound wave cycles reaching the receiver. Question 2. What is the Doppler shift? The answer is: The difference between the transmitted frequency and the received frequency. This is because moving reflectors change the frequency of the sound that returns to the transducer. Question 3. In clinical Doppler imaging, which structures primarily produce Doppler shifts? The answer is: Red blood cells. This is because red blood cells are constantly moving and act as the primary reflectors in blood flow. Question 4. What happens to the Doppler shift when red blood cells move toward the transducer? The answer is: The Doppler shift increases and is positive. This is because the reflected frequency is higher than the transmitted frequency when the source and receiver move closer together. Question 5. What happens to the Doppler shift when blood cells move away from the transducer? The answer is: The Doppler shift decreases and is negative. This is because the reflected frequency is lower than the transmitted frequency when the source and receiver move farther apart. Question 6. At what Doppler angle does the Doppler shift become zero? The answer is: Ninety degrees. This is because the cosine of ninety degrees is zero, resulting in no measured Doppler shift. Question 7. Why does continuous wave Doppler not experience aliasing? The answer is: Because it continuously transmits and receives and is not limited by pulse repetition frequency. This is because aliasing only occurs in systems that sample intermittently. Question 8. What is aliasing in Doppler ultrasound? The answer is: An incorrect display where high velocities appear to reverse direction. This is because the Doppler shift exceeds the Nyquist limit and is misrepresented. Question 9. What is the Nyquist limit? The answer is: Half the pulse repetition frequency. This is because the Nyquist limit represents the maximum Doppler frequency that can be accurately displayed without aliasing. Question 10. Which actions can reduce the likelihood of aliasing? The answer is: Increasing pulse repetition frequency, decreasing imaging depth, using a lower frequency transducer, or using continuous wave Doppler. This is because all of these actions reduce the likelihood that the Doppler shift will exceed the Nyquist limit.

Physics XIII. Lecture

System Physics XIII

00:00 / 05:17

XIII. Ultrasound System Instrumentation. Ultrasound imaging requires multiple system components working together in a precise sequence. Each component has a specific role in producing, receiving, processing, and displaying ultrasound data. Master Synchronizer. The master synchronizer coordinates all components of the ultrasound system. It ensures that transmission, reception, processing, and display occur in the correct order. Pulser. The pulser controls the electrical signals sent to the transducer. The pulser determines: pulse repetition frequency pulse repetition period pulse amplitude firing pattern for phased array systems frequency for continuous wave systems Phased array systems use more complex pulsers than mechanical transducer systems. The electrical signal produced by the pulser may reach approximately one hundred volts. Greater electrical voltage produces pulses with greater intensity. Pulser Modes. Continuous Wave Mode. A constant electrical signal, in the form of a sine wave, stimulates the P Z T crystal. Electrical frequency equals ultrasound frequency. Pulsed Wave Mode, Single Crystal. A short-duration electrical spike strikes the P Z T crystal. The crystal vibrates at its resonant frequency. One electrical spike produces one ultrasound pulse. Pulsed Wave Mode, Array Systems. Multiple short-duration electrical spikes stimulate the many crystals within the array. These spikes create the ultrasound beam pattern. Receiver. The receiver accepts small electrical voltages produced by the transducer in response to returning echoes. These signals are processed and prepared for display. Functions of the Receiver. The receiver performs five functions in alphabetical order: Amplification Compensation Compression Demodulation Threshold, also called reject or suppression Display. The display presents the processed data visually. The display may include: a monitor a spectral plot numeric data The display has the lowest dynamic range of all system components. Refraction. Refraction is the change in direction of a sound wave as it crosses a boundary at an oblique angle. Refraction occurs during transmission, not reflection. Refraction depends only on: the angle of incidence the propagation speeds of the two media Refraction does not depend on frequency. An everyday example is a straw appearing bent in water. Snell’s Law. Snell’s law defines the relationship between the angle of incidence and the angle of transmission. When sound enters a medium with a higher propagation speed, the transmitted angle increases. Range Equation. The range equation relates: propagation speed time of flight reflector depth Time of flight is the time between pulse transmission and echo reception. Depth equals: velocity of sound times time of flight divided by two. You divide by two because sound travels to the reflector and back to the transducer. Thirteen Microsecond Rule. In soft tissue, every thirteen microseconds of go-return time corresponds to one centimeter of depth. Greater time of flight means greater depth. Echo Ranging. Echo ranging estimates distance based on go-return time. The longer the time of flight, the deeper the reflector. Angles and Incidence. An acute angle is less than ninety degrees. An obtuse angle is greater than ninety degrees. A right angle is exactly ninety degrees. Incident angle is the angle at which the sound beam strikes a boundary. Normal incidence occurs at ninety degrees. Oblique incidence occurs at any angle other than ninety degrees. When reflection occurs with oblique incidence, the angle of reflection equals the angle of incidence. Intensity Relationships. Incident intensity is the intensity just before the boundary. Reflected intensity is the portion that returns toward the transducer. Transmitted intensity is the portion that continues forward. Incident intensity minus transmitted intensity equals reflected intensity. Incident intensity minus reflected intensity equals transmitted intensity. Intensity Coefficients. The Intensity Reflection Coefficient, or I R C, is the fraction of sound intensity reflected. It is unitless. Reflected intensity divided by incident intensity equals the intensity reflection coefficient. The Intensity Transmission Coefficient, or I T C, is the fraction transmitted forward. Transmitted intensity divided by incident intensity equals the intensity transmission coefficient. The I R C and I T C always add up to one, or one hundred percent. Absorption. Absorption is the conversion of sound energy into heat. It is the primary source of attenuation in soft tissue, accounting for approximately eighty percent. Bone is a strong absorber and attenuates more than soft tissue. Reflection and Scattering. Reflection is the return of sound after striking a boundary. Specular reflection occurs at smooth surfaces and produces organized echoes. A boundary is smooth when surface irregularities are larger than the wavelength. Scattering occurs at rough surfaces and produces chaotic echoes. A boundary is rough when irregularities are smaller than the wavelength. Air and lung tissue are strong scatterers. Rayleigh Scattering. Rayleigh scattering is organized scattering in all directions from small structures such as red blood cells. Blood attenuates similarly to soft tissue. Half Value Layer Thickness. The half value layer thickness is the depth at which beam intensity is reduced by one half. Half value layer thickness equals three divided by the attenuation coefficient. It is also called: penetration depth half boundary layer Acoustic Impedance. Acoustic impedance compares the density and propagation speed of two media. It is measured in rayls and symbolized by the letter Z. Impedance equals density times propagation speed. Greater differences in impedance produce stronger reflections. No difference in impedance produces no reflection. Calculating Total Attenuation. To determine attenuation at a specific depth: First, find the attenuation coefficient. Next, multiply the attenuation coefficient by the path length. This gives total attenuation in decibels. Attenuation values are negative because intensity decreases. Use the intensity ratio associated with that decibel value. Multiply the initial intensity by the intensity ratio. This yields the remaining intensity at the specified depth.

Physics XIII. Questions

Ultrasound Physics: Ultrasound System Instrumentation. Lecture Questions. Question 1. What is the primary function of the master synchronizer? Question 2. What does the pulser control in an ultrasound system? Question 3. Which of the following is determined by the pulser? A. Dynamic range B. Pulse repetition frequency C. Acoustic impedance D. Display brightness Question 4. What is the difference between continuous wave and pulsed wave excitation of the crystal? Question 5. What is the role of the receiver in an ultrasound system? Question 6. Which five functions are performed by the receiver, and in what order do they occur? Question 7. Which system component has the lowest dynamic range? A. Pulser B. Receiver C. Display D. Transducer Question 8. What is time of flight? Question 9. Why is the range equation divided by two? Question 10. What does the thirteen microsecond rule describe? Answer Key. 1.Coordinates all components of the ultrasound system 2.The electrical signals sent to the transducer 3.B 4. Continuous wave uses a constant electrical signal, while pulsed wave uses short electrical spikes 5. To accept and process returning electrical signals from echoes 6. Amplification, compensation, compression, demodulation, threshold 7. C 8. The time between pulse transmission and echo return 9. Because sound travels to the reflector and back 10. The relationship between go-return time and reflector depth in soft tissue

Physics XIII. Answers

SystemPhysics XIII

00:00 / 02:35

ANSWERS Explained Question 1. What is the primary function of the master synchronizer? The answer is: To coordinate all components of the ultrasound system. This is because transmission, reception, processing, and display must occur in a precise sequence for accurate imaging. Question 2. What does the pulser control in an ultrasound system? The answer is: The electrical signals sent to the transducer. This is because the pulser initiates sound production by stimulating the piezoelectric crystal. Question 3. Which of the following is determined by the pulser? The answer is: Pulse repetition frequency. This is because the pulser controls the timing of electrical signals that determine how often pulses are transmitted. Question 4. What is the difference between continuous wave and pulsed wave excitation of the crystal? The answer is: Continuous wave uses a constant electrical signal, while pulsed wave uses short electrical spikes. This is because continuous wave systems transmit continuously, whereas pulsed systems transmit discrete pulses. Question 5. What is the role of the receiver in an ultrasound system? The answer is: To accept and process returning electrical signals from echoes. This is because the transducer converts returning sound into small voltages that must be amplified and processed for display. Question 6. Which five functions are performed by the receiver, and in what order do they occur? The answer is: Amplification, compensation, compression, demodulation, and threshold. This is because receiver operations follow a fixed sequence to prepare echo signals for display. Question 7. Which system component has the lowest dynamic range? The answer is: The display. This is because the display can show fewer shades of gray compared to the wide range of signal intensities processed by the system. Question 8. What is time of flight? The answer is: The time between pulse transmission and echo return. This is because the system uses this time to calculate reflector depth. Question 9. Why is the range equation divided by two? The answer is: Because sound travels to the reflector and back to the transducer. This is because time of flight includes both forward and return travel. Question 10. What does the thirteen microsecond rule describe? The answer is: The relationship between go-return time and reflector depth in soft tissue. This is because sound travels approximately one centimeter in thirteen microseconds in soft tissue.

Physics XIV. Lecture

QAPhysics XIV

00:00 / 03:44

XIV. Quality Assurance. Quality assurance, often called Q A, is the routine evaluation of ultrasound systems to ensure accurate performance and patient safety. Quality assurance programs help detect equipment problems before they affect clinical imaging. Quality Assurance Phantoms. Quality assurance testing uses phantoms, which are objects designed to simulate tissue or motion. A I U M Test Object. The A I U M test object contains pins or wires used to test: distance measurement accuracy axial resolution lateral resolution The A I U M test object does not evaluate grayscale performance. Tissue Equivalent Phantom. A tissue equivalent phantom simulates soft tissue. It has similar: speed of sound attenuation The speed of sound in the phantom is approximately one thousand five hundred forty meters per second. This phantom evaluates: grayscale resolution contrast resolution Doppler Phantom. A Doppler phantom simulates blood flow motion. It is used to test: spectral Doppler color Doppler power Doppler It helps verify Doppler accuracy and velocity measurements. Beam Profile and Slice Thickness Phantom. A beam profile, or slice thickness phantom, evaluates: beam thickness slice sensitivity Thicker slices increase the likelihood of partial volume artifacts. Vibrating String Phantom. A vibrating string phantom is used to test: Doppler frequency shifts velocity calibration It provides a known motion for accurate Doppler assessment. Performance Measurements. Quality assurance testing evaluates specific system performance parameters. Minimum sensitivity is the weakest echo signal that can still be seen on the display. Normal sensitivity is the system setting where all structures and pins are displayed accurately. Registration accuracy is the system’s ability to place echoes in the correct position both horizontally and vertically. Range accuracy, also called vertical depth calibration, verifies correct depth placement along the beam axis. Horizontal calibration verifies measurement accuracy perpendicular to the beam. Dead Zone. The dead zone is the region closest to the transducer where imaging cannot occur. This is caused by ringing of the crystal after pulse transmission. Resolution Assessment. Longitudinal resolution is the ability to distinguish reflectors front to back. Lateral resolution is the ability to distinguish reflectors side by side. Compensation and Uniformity. Compensation operation, also called uniformity, verifies that: time gain compensation overall gain are balanced correctly across the image. Mock Cysts and Tumors. Mock cysts and tumors are used to evaluate: grayscale performance contrast resolution They help assess image realism. Display and Grayscale Dynamic Range. This test evaluates the system’s ability to display multiple shades of gray. It reflects the quality of grayscale imaging. Instrumentation Devices Used in Quality Assurance. A hydrophone measures acoustic pressure within a sound beam. Acousto-optic systems convert sound energy into light to visualize beam shape. The Schlieren principle uses light deflection to study ultrasound beam patterns. A radiation force balance measures the total output power of an ultrasound transducer. A calorimeter measures acoustic power by detecting heat produced. A thermocouple measures temperature rise within tissue-mimicking material. Crystals are piezoelectric elements that convert electrical energy into sound and sound back into electrical energy. Key Point. Quality assurance ensures: consistency accuracy equipment reliability patient safety

Physics XIV. Questions

XV. Quality Assurance. Ultrasound Physics: Quality Assurance. Lecture Questions. Question 1. What is quality assurance in diagnostic ultrasound? Question 2. What is the primary purpose of quality assurance testing? Question 3. Which phantom is used to test axial and lateral resolution but not grayscale? A. Tissue equivalent phantom B. Doppler phantom C. A I U M test object D. Vibrating string phantom Question 4. What does a tissue equivalent phantom simulate? Question 5. Which phantom is used to test Doppler accuracy and blood flow simulation? Question 6. What is minimum sensitivity? Question 7. What does registration accuracy evaluate? Question 8. What is the dead zone? Question 9. Which device measures total output power of an ultrasound transducer? A. Hydrophone B. Thermocouple C. Radiation force balance D. Calorimeter Question 10. Why is quality assurance important in ultrasound imaging? Answer Key. 1.Routine evaluation of ultrasound systems to ensure accurate performance and patient safety 2. To detect equipment problems and ensure accurate imaging 3. C 4. Soft tissue with similar speed and attenuation 5. Doppler phantom 6. The weakest echo signal visible on the display 7. The system’s ability to place echoes in the correct position 8. The region closest to the transducer where imaging cannot occur 9. C 10. To ensure consistency, accuracy, and patient safety

Physics XIV. Answers

QPhysics XIV

00:00 / 02:17

Question 1. What is quality assurance in diagnostic ultrasound? The answer is: Routine evaluation of ultrasound systems to ensure accurate performance and patient safety. This is because regular testing verifies that equipment functions correctly and safely. Question 2. What is the primary purpose of quality assurance testing? The answer is: To detect equipment problems and ensure accurate imaging. This is because early detection prevents image errors and protects patients. Question 3. Which phantom is used to test axial and lateral resolution but not grayscale? The answer is: The A I U M test object. This is because it contains pins or wires for distance and resolution testing, not grayscale evaluation. Question 4. What does a tissue equivalent phantom simulate? The answer is: Soft tissue with similar speed and attenuation. This is because it mimics real tissue properties for grayscale and contrast testing. Question 5. Which phantom is used to test Doppler accuracy and blood flow simulation? The answer is: The Doppler phantom. This is because it simulates moving blood to evaluate Doppler performance. Question 6. What is minimum sensitivity? The answer is: The weakest echo signal visible on the display. This is because it reflects the system’s ability to detect low-level echoes. Question 7. What does registration accuracy evaluate? The answer is: The system’s ability to place echoes in the correct position. This is because accurate spatial placement is essential for correct anatomy display. Question 8. What is the dead zone? The answer is: The region closest to the transducer where imaging cannot occur. This is because crystal ringing prevents detection of returning echoes in this region. Question 9. Which device measures total output power of an ultrasound transducer? The answer is: The radiation force balance. This is because it measures acoustic power by detecting force exerted by the sound beam. Question 10. Why is quality assurance important in ultrasound imaging? The answer is: To ensure consistency, accuracy, and patient safety. This is because reliable system performance is essential for correct diagnosis and safe operation.

Physics XV. Lecture

Bioeffects Physics XV

00:00 / 03:21

XVI. Bioeffects and Safety. Ultrasound bioeffects describe how sound energy may interact with biological tissue. Safety principles ensure that diagnostic ultrasound is used responsibly and effectively. Dosimetry. Dosimetry is the study of ultrasound exposure and its potential biological effects. It evaluates how much acoustic energy is delivered to tissue and what effects may result. Approaches to Studying Bioeffects. There are two primary approaches to studying ultrasound bioeffects. Mechanistic Approach. The mechanistic approach is based on understanding physical mechanisms such as heating and cavitation. It predicts biological effects by analyzing cause-and-effect relationships. Empirical Approach. The empirical approach is based on observation and data from laboratory and epidemiological studies. It determines exposure-response relationships by studying actual outcomes. Thermal Effects. Thermal effects occur when sound energy is absorbed by tissue and converted into heat. Tissue heating depends on: beam intensity exposure time absorption rate Fetal tissues and bone interfaces are the most susceptible to heating. Thermal Index. The thermal index, or T I, indicates the likelihood of tissue heating. It does not measure temperature directly, but provides a relative estimate of potential heating. Cavitation. Cavitation is the formation and behavior of gas bubbles in tissue exposed to ultrasound. Stable Cavitation. In stable cavitation, bubbles oscillate but do not collapse. This motion may enhance microstreaming in surrounding tissue. Transient Cavitation. In transient cavitation, bubbles expand and collapse violently. This produces localized shock waves. Transient cavitation poses the greatest risk of bioeffect damage. Mechanical Index. The mechanical index, or M I, indicates the likelihood of cavitation. Higher mechanical index values suggest increased cavitation risk. Physical Vibration. Physical vibration refers to micro-vibrations in tissue caused by radiation force. These vibrations are typically minimal at diagnostic levels. Thermal and Cavitation Mechanisms. The thermal mechanism describes bioeffects caused by tissue heating. The cavitation mechanism describes bioeffects caused by bubble activity. ALARA Principle. Always follow A L A R A. As Low As Reasonably Achievable. This principle means using the lowest ultrasound exposure necessary to obtain diagnostic information. Epidemiology. Epidemiology is the statistical study of populations to evaluate ultrasound safety. There are no confirmed long-term adverse effects of diagnostic ultrasound in humans when used appropriately. In Utero Exposure. Diagnostic ultrasound is considered safe during pregnancy when standard limits and guidelines are followed. In Vivo Studies. In vivo studies are performed within living organisms. They provide clinically relevant data. In Vitro Studies. In vitro studies are performed in laboratory environments such as test tubes or tissue models. Results from in vitro studies may not accurately predict in vivo effects. Quality use of ultrasound depends on understanding bioeffects, monitoring safety indices, and applying ALARA principles at all times.

Physics XV. Questions

Ultrasound Physics: Bioeffects and Safety. Lecture Questions. Question 1. What is dosimetry in diagnostic ultrasound? Question 2. What is the mechanistic approach to studying ultrasound bioeffects? Question 3. What is the empirical approach to studying ultrasound bioeffects? Question 4. What causes thermal effects in tissue during ultrasound imaging? Question 5. Which tissues are most susceptible to thermal effects? A. Muscle and fat B. Skin and blood C. Fetal tissue and bone interfaces D. Tendons and ligaments Question 6. What does the Thermal Index indicate? Question 7. What is cavitation? Question 8. Which type of cavitation poses the greatest risk of bioeffect damage? A. Stable cavitation B. Transient cavitation C. Acoustic streaming D. Physical vibration Question 9. What does the Mechanical Index indicate? Question 10. What does the ALARA principle mean? Answer Key. 1.The study of ultrasound exposure and its potential biological effects 2. An approach based on understanding physical mechanisms such as heating and cavitation 3. An approach based on observation and data from laboratory and population studies 4. Absorption of sound energy and its conversion into heat 5. C 6. The likelihood of tissue heating 7. The formation and behavior of gas bubbles in tissue exposed to ultrasound 8. B 9. The likelihood of cavitation 10. As Low As Reasonably Achievable

Physics XV. Answers

BioeffectsPhysics XV

00:00 / 02:21

ANSWERS Explained Question 1. What is dosimetry in diagnostic ultrasound? The answer is: The study of ultrasound exposure and its potential biological effects. This is because dosimetry evaluates how much acoustic energy is delivered to tissue and what biological effects may occur. Question 2. What is the mechanistic approach to studying ultrasound bioeffects? The answer is: An approach based on understanding physical mechanisms such as heating and cavitation. This is because it predicts biological effects by analyzing cause-and-effect relationships. Question 3. What is the empirical approach to studying ultrasound bioeffects? The answer is: An approach based on observation and data from laboratory and population studies. This is because it relies on measured outcomes rather than theoretical models. Question 4. What causes thermal effects in tissue during ultrasound imaging? The answer is: Absorption of sound energy and its conversion into heat. This is because tissues absorb ultrasound energy, raising temperature. Question 5. Which tissues are most susceptible to thermal effects? The answer is: Fetal tissue and bone interfaces. This is because bone absorbs ultrasound energy efficiently and fetal tissues are more sensitive to heating. Question 6. What does the Thermal Index indicate? The answer is: The likelihood of tissue heating. This is because the Thermal Index provides a relative estimate of potential temperature rise. Question 7. What is cavitation? The answer is: The formation and behavior of gas bubbles in tissue exposed to ultrasound. This is because pressure changes in the sound wave affect microscopic gas bubbles. Question 8. Which type of cavitation poses the greatest risk of bioeffect damage? The answer is: Transient cavitation. This is because violent bubble collapse can generate localized shock waves. Question 9. What does the Mechanical Index indicate? The answer is: The likelihood of cavitation. This is because the Mechanical Index reflects the potential for pressure-related bubble activity. Question 10. What does the ALARA principle mean? The answer is: As Low As Reasonably Achievable. This is because ultrasound exposure should be minimized while still obtaining diagnostic information.