ARDMS (American Registry for Diagnostic Medical Sonography) Practice Test

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What will the aliasing frequency be if a renal artery duplex exam is performed at a depth of 6 cm, the length of the sample volume is 0.50 mm, and the pulse repetition frequency (PRF) is 8 kHz with the Doppler frequency at 3.5 MHz?

3.5 MHz
8 kHz
7 MHz
4 kHz

The correct answer is: 3.5 MHz

In this scenario, the aliasing frequency can be calculated using the formula: Aliasing frequency = | (PRF / 2) - Doppler frequency | Given: Depth = 6 cm Sample volume length = 0.50 mm PRF = 8 kHz Doppler frequency = 3.5 MHz Convert the sample volume length to cm: 0.50 mm = 0.05 cm Calculate the Nyquist limit: Nyquist limit = (Depth × 2) ÷ 2 = 6 cm × 2 = 12 cm = 0.12 m Calculate the PRF in meters: PRF in m = 8 kHz = 8,000 Hz Calculate aliasing frequency: Aliasing frequency = | (8,000 / 2) - 3,500,000 | = | 4,000 - 3,500,000 | = 3,496,000 Hz = 3.496 MHz The correct answer is A. 3.5 MHz, as the aliasing frequency will be 3.496 MHz when performing a renal artery duplex exam with the given parameters.