ARDMS SPI EXAM 2025 COMPLETE
ULTRASOUND PHYSICS REVIEW STUDY
GUIDE || UPDATED VERSION
Section 1: Basic Principles & Waves (Q1-15)
1. Q: What type of wave is a sound wave?
A: Mechanical, longitudinal pressure wave.
2. Q: What are the acoustic variables that define a sound wave?
A: Pressure, density, temperature, and particle motion.
3. Q: What is the medium requirement for ultrasound travel?
A: A material with mass and elasticity (e.g., tissue, fluid). It cannot travel in a vacuum.
4. Q: What is the typical frequency range for diagnostic ultrasound?
A: 2 MHz to 15 MHz.
5. Q: If frequency increases, what happens to wavelength?
A: Wavelength decreases (inverse relationship).
6. Q: What is the propagation speed of sound in soft tissue (the assumed average)?
A: 1,540 m/s or 1.54 mm/µs.
7. Q: Which tissue has the highest propagation speed?
A: Bone (>3,000 m/s). Lung tissue has the lowest.
8. Q: The determinants of propagation speed are:
A: The density (stiffness) and elasticity (compressibility) of the medium. Stiffness
increases speed; density alone decreases it.
9. Q: What is the formula relating propagation speed (c), frequency (f), and wavelength
(λ)?
A: c = f × λ
10. Q: What are the seven parameters used to describe a sound wave?
A: Period, frequency, amplitude, power, intensity, wavelength, propagation speed.
, 11. Q: Period and frequency have a _____ relationship.
A: Reciprocal (inverse). Period = 1 / Frequency.
12. Q: If amplitude is doubled, what happens to power?
A: Power increases by a factor of four (Power ∝ Amplitude²).
13. Q: What is the unit for intensity?
A: Watts per centimeter squared (W/cm²).
14. Q: Which intensity is most relevant for bioeffects and thermal safety?
A: Spatial Peak-Temporal Average (SPTA).
15. Q: What is the range equation? What does it determine?
A: SPL = # of cycles × λ. It determines spatial pulse length, which affects axial resolution.
Section 2: Attenuation & Interaction with Matter (Q16-30)
16. Q: What is attenuation?
A: The decrease in sound wave intensity as it travels through a medium.
17. Q: What are the three processes that cause attenuation?
A: Absorption, reflection, and scattering.
18. Q: What is the unit for the attenuation coefficient?
A: dB/cm.
19. Q: The attenuation coefficient in soft tissue is approximately _____.
A: 0.5 dB/cm per MHz.
20. Q: A 5 MHz sound beam will attenuate _____ a 2.5 MHz beam in the same tissue.
A: Twice as much as (attenuation increases with frequency).
21. Q: What type of reflection occurs when the reflector is much larger than the
wavelength?
A: Specular reflection (e.g., diaphragm, organ capsules).
22. Q: What type of reflection occurs with small, irregular boundaries (e.g., parenchyma)?
A: Scattering (Rayleigh scattering when particle << λ).
23. Q: What acoustic event creates the texture in a parenchymal image?
A: Backscatter (scattered sound reflected back to the transducer).
, 24. Q: Refraction is a change in direction of sound transmission due to a change in _____.
A: Propagation speed.
25. Q: Refraction can cause what type of artifact?
A: Lateral displacement or duplication artifact.
26. Q: The intensity reflection coefficient (IRC) depends on what?
A: The difference in acoustic impedance (Z) of the two media. Greater difference = more
reflection.
27. Q: What is the formula for acoustic impedance (Z)?
A: Z = density × propagation speed.
28. Q: What is the impedance mismatch at a tissue-air interface?
A: Very large, resulting in near-total reflection (~99.9%).
29. Q: Why is gel used in ultrasound?
A: To eliminate the air gap between transducer and skin, minimizing impedance
mismatch and reflection.
30. Q: What interaction produces the Doppler shift?
A: Scattering from moving red blood cells.
Section 3: Transducers & Beam Formation (Q31-50)
31. Q: What is the piezoelectric effect?
A: The conversion of pressure (sound) into electricity (receive) and electricity into
pressure (transmit).
32. Q: What is the typical piezoelectric material in modern transducers?
A: Lead zirconate titanate (PZT) ceramic.
33. Q: What is the operating frequency of a transducer determined by?
A: The thickness and propagation speed of the PZT crystal. Thinner crystal = higher
frequency.
34. Q: What is the matching layer's purpose?
A: To minimize the impedance mismatch between the PZT and the skin, increasing sound
transmission.
ULTRASOUND PHYSICS REVIEW STUDY
GUIDE || UPDATED VERSION
Section 1: Basic Principles & Waves (Q1-15)
1. Q: What type of wave is a sound wave?
A: Mechanical, longitudinal pressure wave.
2. Q: What are the acoustic variables that define a sound wave?
A: Pressure, density, temperature, and particle motion.
3. Q: What is the medium requirement for ultrasound travel?
A: A material with mass and elasticity (e.g., tissue, fluid). It cannot travel in a vacuum.
4. Q: What is the typical frequency range for diagnostic ultrasound?
A: 2 MHz to 15 MHz.
5. Q: If frequency increases, what happens to wavelength?
A: Wavelength decreases (inverse relationship).
6. Q: What is the propagation speed of sound in soft tissue (the assumed average)?
A: 1,540 m/s or 1.54 mm/µs.
7. Q: Which tissue has the highest propagation speed?
A: Bone (>3,000 m/s). Lung tissue has the lowest.
8. Q: The determinants of propagation speed are:
A: The density (stiffness) and elasticity (compressibility) of the medium. Stiffness
increases speed; density alone decreases it.
9. Q: What is the formula relating propagation speed (c), frequency (f), and wavelength
(λ)?
A: c = f × λ
10. Q: What are the seven parameters used to describe a sound wave?
A: Period, frequency, amplitude, power, intensity, wavelength, propagation speed.
, 11. Q: Period and frequency have a _____ relationship.
A: Reciprocal (inverse). Period = 1 / Frequency.
12. Q: If amplitude is doubled, what happens to power?
A: Power increases by a factor of four (Power ∝ Amplitude²).
13. Q: What is the unit for intensity?
A: Watts per centimeter squared (W/cm²).
14. Q: Which intensity is most relevant for bioeffects and thermal safety?
A: Spatial Peak-Temporal Average (SPTA).
15. Q: What is the range equation? What does it determine?
A: SPL = # of cycles × λ. It determines spatial pulse length, which affects axial resolution.
Section 2: Attenuation & Interaction with Matter (Q16-30)
16. Q: What is attenuation?
A: The decrease in sound wave intensity as it travels through a medium.
17. Q: What are the three processes that cause attenuation?
A: Absorption, reflection, and scattering.
18. Q: What is the unit for the attenuation coefficient?
A: dB/cm.
19. Q: The attenuation coefficient in soft tissue is approximately _____.
A: 0.5 dB/cm per MHz.
20. Q: A 5 MHz sound beam will attenuate _____ a 2.5 MHz beam in the same tissue.
A: Twice as much as (attenuation increases with frequency).
21. Q: What type of reflection occurs when the reflector is much larger than the
wavelength?
A: Specular reflection (e.g., diaphragm, organ capsules).
22. Q: What type of reflection occurs with small, irregular boundaries (e.g., parenchyma)?
A: Scattering (Rayleigh scattering when particle << λ).
23. Q: What acoustic event creates the texture in a parenchymal image?
A: Backscatter (scattered sound reflected back to the transducer).
, 24. Q: Refraction is a change in direction of sound transmission due to a change in _____.
A: Propagation speed.
25. Q: Refraction can cause what type of artifact?
A: Lateral displacement or duplication artifact.
26. Q: The intensity reflection coefficient (IRC) depends on what?
A: The difference in acoustic impedance (Z) of the two media. Greater difference = more
reflection.
27. Q: What is the formula for acoustic impedance (Z)?
A: Z = density × propagation speed.
28. Q: What is the impedance mismatch at a tissue-air interface?
A: Very large, resulting in near-total reflection (~99.9%).
29. Q: Why is gel used in ultrasound?
A: To eliminate the air gap between transducer and skin, minimizing impedance
mismatch and reflection.
30. Q: What interaction produces the Doppler shift?
A: Scattering from moving red blood cells.
Section 3: Transducers & Beam Formation (Q31-50)
31. Q: What is the piezoelectric effect?
A: The conversion of pressure (sound) into electricity (receive) and electricity into
pressure (transmit).
32. Q: What is the typical piezoelectric material in modern transducers?
A: Lead zirconate titanate (PZT) ceramic.
33. Q: What is the operating frequency of a transducer determined by?
A: The thickness and propagation speed of the PZT crystal. Thinner crystal = higher
frequency.
34. Q: What is the matching layer's purpose?
A: To minimize the impedance mismatch between the PZT and the skin, increasing sound
transmission.
