ARDMS SPI Ultrasound Bioeffects and Safety 4 — Questions and Answers
Question 1: The FDA regulatory limit for spatial-peak temporal-average intensity (ISPTA.3) for fetal/obstetric ultrasound is:
- 72 mW/cm² (Correct answer)
- 430 mW/cm²
- 720 mW/cm²
- 1000 mW/cm²
Correct answer: 72 mW/cm²
The FDA limits ISPTA.3 to 72 mW/cm² for fetal and neonatal cephalic applications to protect the developing fetus.
Question 2: When scanning directly over fetal bone in the third trimester, which Thermal Index should be displayed?
- TIS (Soft Tissue Thermal Index)
- TIC (Cranial Bone Thermal Index)
- TIB (Bone Thermal Index) (Correct answer)
- TI (generic Thermal Index)
Correct answer: TIB (Bone Thermal Index)
TIB (Bone Thermal Index) is used when the beam is focused at or near fetal bone, which absorbs more ultrasound energy and can heat adjacent tissue significantly.
Question 3: Which operator action would most effectively reduce thermal bioeffect risk without eliminating diagnostic utility?
- Switching from 2D grayscale to pulsed Doppler to shorten total scan time
- Reducing output power and using gain controls to compensate image brightness (Correct answer)
- Increasing frequency to improve resolution at the cost of penetration
- Turning off harmonic imaging to increase fundamental signal strength
Correct answer: Reducing output power and using gain controls to compensate image brightness
Reducing output power lowers acoustic energy deposition, while compensating with receive gain maintains image quality without additional thermal risk.
Question 4: Non-thermal mechanical bioeffects of ultrasound include all of the following EXCEPT:
- Acoustic cavitation
- Acoustic streaming
- Microstreaming near oscillating bubbles
- Protein denaturation from elevated tissue temperature (Correct answer)
Correct answer: Protein denaturation from elevated tissue temperature
Protein denaturation is a thermal effect caused by temperature rise, not a non-thermal mechanical effect; cavitation, streaming, and microstreaming are all mechanical in nature.
Question 5: The Output Display Standard (ODS) requires that real-time MI and TI values be displayed on the monitor when they exceed:
- MI > 0.4 or TI > 0.4
- MI > 0.5 or TI > 0.5 (Correct answer)
- MI > 1.0 or TI > 1.0
- MI > 2.0 or TI > 2.0
Correct answer: MI > 0.5 or TI > 0.5
The ODS mandates display of MI and TI when either exceeds 0.5, alerting operators that exposure is approaching levels warranting attention.
Question 6: A sonographer performing an extended neonatal brain exam should be MOST concerned about which type of Thermal Index?
- TIS — because soft tissue heating dominates in neonates
- TIB — because fetal bone is the target near the fontanelle
- TIC — because the cranial bone is in the near field of the beam (Correct answer)
- TI is irrelevant for neonatal imaging
Correct answer: TIC — because the cranial bone is in the near field of the beam
TIC (Cranial Bone Thermal Index) applies when the beam passes through the skull in the near field, as the bone absorbs energy and heats the adjacent brain tissue.
Question 7: Which statement correctly describes the relationship between ultrasound frequency and cavitation threshold?
- Higher frequency lowers the cavitation threshold, making it easier to induce
- Lower frequency lowers the cavitation threshold, making cavitation more likely (Correct answer)
- Frequency has no effect on cavitation threshold
- Cavitation only occurs at frequencies above 10 MHz
Correct answer: Lower frequency lowers the cavitation threshold, making cavitation more likely
Lower frequencies produce longer rarefaction half-cycles that allow bubbles more time to grow, thereby lowering the pressure threshold required to initiate cavitation.
ARDMS SPI Ultrasound Bioeffects and Safety 4
The FDA regulatory limit for spatial-peak temporal-average intensity (ISPTA.3) for fetal/obstetric ultrasound is: