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Answer #7
The correct answer is C: 1.25 m/s To answer this question you need to know the Doppler equation and how to use it. It is shown in the figure.
We are given the operating frequency is 3 MHz, and Doppler shift of 5 KHz. We also assume the angle is 0 degrees if the ultrasound beam is lined up well with the blood flow. The cosine of 0 degrees is 1. Now you must also know that the velocity of ultrasound in soft tissue is 1540m/s. We can estimate this as 1500m/s for this question. To correct the units note that 3MHz is the same as 3000KHz
Plugging these numbers in we have: 5 KHz = 2* 3000KHz * velocity *1 /1500m/s
so velocity = (5*1500)/(2*3000) = 1.25 m/s. This is top normal for blood flow within the LVOT.
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