Section 13 Biologic Hazards of Ultrasonography

1. At the point of interest in the ultrasonic field, the instantaneous intensity is directly proportional to the square of the ________.
A. Acoustic pressure
B. Acoustic velocity
C. Frequency
D. Mass density

2. Which of the following describes intensity measurements using the unit of the decibel?
A. Based on a logarithmic scale
B. Measure of relative intensity
C. A factor of two reduction in intensity corresponds to a 3-dB change
D. Point of interest may be greater or less than the reference value
E. All of the above

3. In 1992, the American Institute of Ultrasound in Medicine (AIUM) and the National Electrical Manufacturers Association (NEMA) adopted the voluntary standard for the display of acoustic output information called the output display standard (ODS). What two acoustic output parameters, shown in real time on the monitor, were defined as indicators of the potential for biologic effect?
A. Derated power and scan time
B. Acoustic intensity averaged over the focal area and duty factor
C. Mechanical index and thermal index
D. Intensity index and thermal index

4. In ultrasound, the acoustic output parameter thermal index (TI) indicates ________ for the current scanning parameters.
A. Maximum temperature rise in tissue
B. Minutes of exposure time before heating is too great
C. Likelihood of inducing cavitation
D. Acoustic power in milliwatts

5. As the ultrasound beam propagates through tissue, the intensity decreases as sonic energy is absorbed and converted into heat. What factor(s) affect(s) the rate of temperature rise in tissue?
A. Temporal average intensity
B. Frequency
C. Duration of exposure
D. Pulse repetition frequency
E. All of the above
F. B, D

6. As the ultrasound beam propagates through tissue, the intensity decreases as sonic energy is absorbed and converted into heat. The increased temperature has the potential to cause irreversible tissue damage. The biologic response is a ________ phenomenon.
A. Nonthreshold linear
B. Nonthreshold quadratic
C. Threshold (temperature only)
D. Threshold (temperature and time)

7. Which of the following real-time scanner settings can affect the acoustic output index?
A. Time-gain compensation
B. Frame rate
C. Transmit power
D. Frequency
E. Gray-scale mapping
F. All of the above
G. A, C, D
H. B, C, D

8. The output display standard of mechanical index (MI) increases in magnitude as the ________ is decreased.
A. Acoustic pressure
B. Acoustic velocity
C. Frequency
D. Peak intensity

9. According to the AIUM statement on “Mammalian In Vivo Ultrasonic Biological Effects,” no independently confirmed significant biologic effects have occurred with spatial peak, temporal average intensities below ________ for mammalian tissues exposed in vivo. Assume focused ultrasound.
A. 1 1 W/cm²
B. 1 100 W/cm²
C. 1 1 mW/cm²
D. 1 100 mW/cm² 

10. As the ultrasound wave propagates through tissue, regions of compression and rarefaction are created. Thus localized regions are subjected to increases and decreases in pressure in an alternating fashion, and these cause gas bubbles to exhibit dynamic behavior. This phenomenon is known as ________.
A. Radiation force
B. Cavitation
C. Ionization
D. Fourier force

11. Multiple models have been developed for the thermal index (TI). These different models are necessary because temperature profiles in tissue are highly dependent on the presence of a strong absorber such as ________.
A. Air
B. Bone
C. Fluid
D. All of the above

12. A number of epidemiologic studies of in utero ultrasound exposure have been conducted over the past 20 years. What is the conclusion of the NCRP regarding a causal relationship between diagnostic ultrasound and any adverse effect?
A. Low birth weight is an adverse effect caused by in utero ultrasound exposure
B. Dyslexia is an adverse effect caused by in utero ultrasound exposure
C. Delayed speech development is an adverse effect caused by in utero ultrasound exposure
D. Insufficient justification to warrant the conclusion that there is a causal relationship between diagnostic ultrasound and any adverse effect

13. What is the conclusion of the National Institutes of Health (NIH) regarding the appropriate use of ultrasound in obstetrics?
A. Routine screening is recommended
B. Ultrasound examination in pregnancy should be performed for a specific medical indication
C. Ultrasound examination performed solely to satisfy the family’s desire to obtain a picture of the fetus should be encouraged to enhance bonding between mother and child
D. None of the above

14. According to recommendations by the NCRP, a risk-benefit decision should be considered when the mechanical index (MI) exceeds a value of ________ and the thermal index (TI) exceeds a value of ________.
A. 1 1.0, 1.0
B. 0.5, 0.5
C. 0.5, 1.0
D. 1 1.0, 0.5
E. None of the above; the NCRP makes no recommendations with respect to MIs and Tis

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