What is the Doppler shift at 0 degrees?

A Doppler shift is 10,000 Hz at an angle of flow of 60 degrees.

What is the Doppler shift at 0 degrees?
A . 20,000 Hz
B . 10,000 Hz
C . 5,000 Hz
D . 2,500 Hz

Answer: A

Explanation:

depends on the angle between the ultrasound beam and the direction of blood flow. The Doppler equation includes a cosine function of the angle of insonation (θ). At 60 degrees, the cosine is 0.5, and at 0 degrees (parallel to the flow), the cosine is 1. Thus, if the Doppler shift is 10,000 Hz at 60 degrees, it would double to 20,000 Hz at 0 degrees because the cosine of 0 degrees is 1 (cos(0°) = 1) and the cosine of 60 degrees is 0.5 (cos(60°) = 0.5). The formula is: Doppler shift at 0 degrees = Doppler shift at 60 degrees / cos(60 degrees) = 10,000 Hz / 0.5 = 20,000 Hz.

Reference: ARDMS Sonography Principles and Instrumentation (SPI) Review, Doppler Shift and Angle of Insonation section.