ARDMS SPI Ultrasound Bioeffects and Safety 3 — Questions and Answers
Question 1: The term 'derated' intensity (e.g., ISPTA.3) in ultrasound safety refers to intensity that has been adjusted for:
- Electronic noise subtraction
- Assumed tissue attenuation of 0.3 dB/cm/MHz (Correct answer)
- Transducer efficiency losses
- Patient body habitus correction
Correct answer: Assumed tissue attenuation of 0.3 dB/cm/MHz
Derated values apply a standardized attenuation of 0.3 dB/cm/MHz to account for tissue absorption when reporting intensities in safety standards.
Question 2: Which statement about ultrasound bioeffects in diagnostic imaging is most accurate based on current evidence?
- Confirmed hazardous bioeffects have been documented at diagnostic exposure levels
- No confirmed hazardous bioeffects exist at diagnostic levels, but prudent use is advised (Correct answer)
- Thermal bioeffects are impossible below 1 MHz
- Cavitation is impossible with modern digital systems
Correct answer: No confirmed hazardous bioeffects exist at diagnostic levels, but prudent use is advised
No independently confirmed hazardous bioeffects have been established at diagnostic exposure levels, yet prudent minimization of exposure (ALARA) remains the standard of care.
Question 3: Acoustic streaming in ultrasound refers to:
- The Doppler shift caused by moving blood cells
- Steady unidirectional fluid flow induced by acoustic radiation force (Correct answer)
- The propagation of shear waves through soft tissue
- Reflection of sound waves at fluid-tissue interfaces
Correct answer: Steady unidirectional fluid flow induced by acoustic radiation force
Acoustic streaming is a mechanical bioeffect where sustained radiation pressure drives fluid in a net directional flow, independent of the Doppler effect.
Question 4: Which transducer characteristic most directly influences the potential for heating at the transducer face?
- Transducer efficiency (electroacoustic conversion) (Correct answer)
- Crystal diameter only
- Center frequency alone
- Focal depth setting
Correct answer: Transducer efficiency (electroacoustic conversion)
Poor electroacoustic conversion efficiency means more electrical energy is dissipated as heat at the transducer face rather than converted to acoustic energy.
Question 5: In the context of obstetric ultrasound, TIS (Soft Tissue Thermal Index) is preferred over TIB (Bone Thermal Index) during which trimester?
- First trimester, before ossification is significant (Correct answer)
- Second trimester, after limb bones are fully ossified
- Third trimester only
- TIS and TIB are interchangeable throughout pregnancy
Correct answer: First trimester, before ossification is significant
TIS is used in the first trimester when fetal ossification is minimal; TIB becomes more relevant later when bone absorbs more ultrasound energy and heats significantly.
Question 6: Epidemiological studies of diagnostic ultrasound in pregnancy have consistently shown:
- Increased incidence of childhood leukemia
- Decreased birth weight in exposed fetuses
- No confirmed adverse outcomes at diagnostic exposure levels (Correct answer)
- Elevated rates of fetal cardiac arrhythmia
Correct answer: No confirmed adverse outcomes at diagnostic exposure levels
Large epidemiological studies have not identified adverse pregnancy outcomes attributable to diagnostic ultrasound exposure at clinical levels.
Question 7: Which factor does NOT increase the risk of thermally induced bioeffects during an ultrasound exam?
- Increasing output power
- Prolonged dwell time over a single region
- Using harmonic imaging instead of fundamental frequency (Correct answer)
- Scanning over a region with elevated patient temperature (fever)
Correct answer: Using harmonic imaging instead of fundamental frequency
Harmonic imaging uses lower overall acoustic power and is generally considered safer thermally; in contrast, higher power, longer dwell time, and pre-existing fever all increase thermal risk.
ARDMS SPI Ultrasound Bioeffects and Safety 3
The term 'derated' intensity (e.g., ISPTA.3) in ultrasound safety refers to intensity that has been adjusted for: