An echocardiogram uses 4.4 MHz ultrasound to measure blood flow in the aorta. Th

Question

An echocardiogram uses 4.4 MHz ultrasound to measure blood flow in the aorta. The blood is moving away from the probe at 1.5 m/s . What is the frequency shift of the reflected ultrasound? Use values given in figure if necessary. Enter a positive value if the received frequency is higher than the emitted frequency, and a negative value if the received frequency is lower than the emitted frequency.

The speed of sound Medium Air (0PC) Air (20°C) Helium (0°C) Ethyl alcohol Water Speed (m/s) 331 343 970 1170 1480 ultrasound 1540 1200 5100 6000 12.000 Human tissue Lead Aluminum Granite Diamond

Explanation / Answer

f = 2vf / c

= 2 *-1.5m/s * 4.4MHz / 1540m/s

= - 8571 Hz

With precision,
f' = 4.4Mz * (1540 - 1.5) / (1540 + 1.5)

= 4.391 MHz
and f = f' - f

= (4.391 - 4.4)MHz = - 9000 Hz

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