ARDMS SPI Ultrasound Bioeffects and Safety 2 — Questions and Answers
Question 1: Which index displayed on modern ultrasound systems specifically relates to the risk of acoustic cavitation?
- Thermal Index (TI)
- Mechanical Index (MI) (Correct answer)
- Dynamic Range Index
- Pulsatility Index
Correct answer: Mechanical Index (MI)
The Mechanical Index (MI) quantifies the likelihood of cavitation by comparing peak negative pressure to the square root of frequency.
Question 2: Stable cavitation differs from inertial cavitation in that stable cavitation involves:
- Violent bubble collapse that produces free radicals
- Bubbles oscillating in a sustained, non-destructive manner (Correct answer)
- Immediate tissue destruction at the focal zone
- Complete vaporization of the liquid medium
Correct answer: Bubbles oscillating in a sustained, non-destructive manner
Stable (non-inertial) cavitation describes gas bubbles that oscillate repetitively without collapsing, whereas inertial cavitation involves violent implosion.
Question 3: The ALARA principle in diagnostic ultrasound means the operator should:
- Maximize output power to shorten scan time
- Use the lowest output that still yields diagnostic information (Correct answer)
- Avoid all pulsed Doppler modes in obstetrics
- Keep MI below 0.1 at all times
Correct answer: Use the lowest output that still yields diagnostic information
ALARA (As Low As Reasonably Achievable) requires minimizing acoustic exposure while still obtaining the necessary diagnostic image quality.
Question 4: Which ultrasound mode typically produces the highest time-averaged acoustic intensity and greatest potential for thermal bioeffects?
- B-mode imaging
- M-mode
- Pulsed-wave Doppler (Correct answer)
- Harmonic imaging
Correct answer: Pulsed-wave Doppler
Pulsed-wave Doppler has a high duty factor and focuses the beam on a small sample volume, resulting in the highest time-averaged intensity and greatest heating potential.
Question 5: A Thermal Index value of 2.0 indicates that the ultrasound system is capable of raising tissue temperature by approximately:
- 0.2°C
- 0.5°C
- 2.0°C (Correct answer)
- 20°C
Correct answer: 2.0°C
The TI is defined as the ratio of acoustic power to the power needed to raise tissue temperature by 1°C, so TI = 2.0 suggests a potential 2°C rise.
Question 6: During a first-trimester obstetric exam, which combination of indices represents the greatest concern for bioeffects?
- Low MI, low TI
- High MI, low TI
- Low MI, high TI
- High MI, high TI (Correct answer)
Correct answer: High MI, high TI
Both a high MI (cavitation risk) and high TI (thermal risk) together represent maximal bioeffect potential and should be minimized during embryonic development.
Question 7: Which biological tissue is considered MOST sensitive to the thermal effects of diagnostic ultrasound?
- Liver parenchyma
- Skeletal muscle
- Developing embryonic/fetal tissue (Correct answer)
- Adult bone cortex
Correct answer: Developing embryonic/fetal tissue
Developing embryonic and fetal tissues are most sensitive to thermal bioeffects because rapidly dividing cells have lower heat tolerance and reduced repair capacity.
ARDMS SPI Ultrasound Bioeffects and Safety 2
Which index displayed on modern ultrasound systems specifically relates to the risk of acoustic cavitation?