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CHAPTER 1: PHYSICS OF TWO-DIMENSIONAL AND DOPPLER IMAGING

1. Which of the following is not an acoustic variable?

a. Pressure

b. Density

c. Distance

d. Intensity

d. The three acoustic variables are pressure, density, and distance. Intensity is a parameter used to describe a sound wave. It is the concentration of power in a beam.

2. Which of the following sound wave frequencies is ultrasonic?

a. 10 Hz

b. 10 MHz

c. 10 kHz

d. 10,000 Hz

b. US is a wave with a frequency greater than 20 kHz, or 20,000 Hz. Clinical US imaging typically occurs between 2 and 15 MHz.

3. An increase in the strength of the US pulse will increase:

a. Frequency

b. Intensity

c. Pulse duration

d. Pulse repetition frequency

b. Intensity is related to the strength of the sound beam and is equal to the power (watts) divided by the beam area. Frequency is the number of cycles that occur in 1 second. Pulse duration is the time from the beginning to the end of a US pulse (usually made up of three to five cycles). Pulse repetition frequency is the time from the beginning of one US pulse to the beginning of the next pulse.

4. If imaging depth decreases, pulse repetition frequency:

a. Decreases

b. Does not change

c. Increases

d. Varies

c. Pulse repetition frequency is the number of pulses that occur in 1 second. When a US system images shallower depths, the receive time decreases, thus increasing the pulse repetition frequency.

5. An example of a Rayleigh scatterer is the:

a. Red blood cell

b. Kidney

c. Mitral valve

d. Pericardium

a. Rayleigh scattering is a special type of scattering that occurs when the reflector is much smaller than the wavelength. Scattering increases with higher frequencies. In clinical US, the best example of Rayleigh scattering is the interaction between US and red blood cells.

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