ARDMS SPI Ultrasound Bioeffects and Safety 5 — Questions and Answers
Question 1: Which clinical scenario represents the LOWEST bioeffect risk from diagnostic ultrasound?
- Pulsed Doppler of the fetal heart at 10 weeks gestation
- Color Doppler evaluation of a renal transplant in an adult (Correct answer)
- Transcranial Doppler of fetal middle cerebral artery
- Continuous wave Doppler across the fetal aorta
Correct answer: Color Doppler evaluation of a renal transplant in an adult
Adult renal transplant evaluation has no embryonic sensitivity concern and involves tissue with normal repair capacity, making it the lowest-risk scenario listed.
Question 2: Microstreaming as a non-thermal ultrasound bioeffect is best described as:
- Large-scale fluid motion driven by overall radiation pressure through a vessel
- Localized, high-velocity fluid currents generated near an oscillating bubble interface (Correct answer)
- Shear wave propagation perpendicular to the sound beam
- Steady heating of tissue adjacent to a gas-filled reflector
Correct answer: Localized, high-velocity fluid currents generated near an oscillating bubble interface
Microstreaming is the high-shear localized fluid motion that occurs immediately around a cavitating or oscillating bubble, capable of disrupting cell membranes.
Question 3: According to the AIUM, which statement about ultrasound use for 'entertainment' or 'keepsake' imaging is most appropriate?
- It is acceptable if performed by a certified sonographer
- It should be discouraged because it exposes the fetus without medical benefit (Correct answer)
- It is safe provided TI remains below 1.0 throughout the session
- It has been explicitly approved by the FDA for non-diagnostic use
Correct answer: It should be discouraged because it exposes the fetus without medical benefit
The AIUM and FDA discourage keepsake imaging because exposing the developing fetus without a medical indication violates the ALARA principle and provides no clinical benefit.
Question 4: The peak rarefactional pressure of an ultrasound pulse is most relevant to which type of bioeffect?
- Thermal heating of soft tissue
- Mechanical cavitation (Correct answer)
- Radiation force on calcified structures
- Acoustic impedance mismatch artifacts
Correct answer: Mechanical cavitation
Peak rarefactional (negative) pressure determines whether dissolved gas can expand explosively to form cavitation bubbles, making it the key parameter for mechanical bioeffects.
Question 5: A research study reports a 'free-field' ISPTA value versus a 'derated' ISPTA.3 value. Which statement is correct?
- Free-field values are always lower because water attenuates sound more than tissue
- Derated values are lower because they account for tissue attenuation between the transducer and target (Correct answer)
- The two values are identical for all clinical probes
- Derated values apply only to cardiac applications
Correct answer: Derated values are lower because they account for tissue attenuation between the transducer and target
Derated (ISPTA.3) values are calculated by applying 0.3 dB/cm/MHz attenuation to free-field water measurements, producing a lower, more clinically realistic intensity estimate.
Question 6: Which structure absorbs the most ultrasound energy per unit length and therefore poses the greatest risk of localized heating?
- Amniotic fluid
- Fatty tissue
- Cortical bone (Correct answer)
- Blood within cardiac chambers
Correct answer: Cortical bone
Cortical bone has a very high attenuation coefficient (absorption >> soft tissue), causing disproportionate energy absorption and localized heating at the bone surface.
Question 7: What is the primary reason pulsed Doppler is considered higher risk than B-mode for thermal bioeffects?
- Pulsed Doppler uses a lower frequency, increasing tissue penetration and heating
- Pulsed Doppler has a higher duty factor and keeps the beam stationary at the sample volume (Correct answer)
- Pulsed Doppler reverses polarity of the transducer crystals, generating extra heat
- B-mode uses continuous wave transmission that produces more total energy
Correct answer: Pulsed Doppler has a higher duty factor and keeps the beam stationary at the sample volume
Pulsed Doppler's high duty factor combined with a fixed, stationary sample volume concentrates time-averaged acoustic energy in a small region, substantially increasing local heating risk.
ARDMS SPI Ultrasound Bioeffects and Safety 5
Which clinical scenario represents the LOWEST bioeffect risk from diagnostic ultrasound?