Hi
@fa21212 -
Excellent question, as usual! What's going on here is that in general, the accuracy of Doppler imaging will be affected by the angle formed between the measuring beam and the velocity that is being measured. I'm attaching an image from a Next Step passage that deals with this topic in the context of police cars catching speeders.
In this setup, the measured speed (Vm) will equal the true speed (Vt) times cos(beta): Vm = Vt cos(beta). The accuracy of the measurement will be maximized when the angle β is small, making cos(beta) close to 1. That will also correspond to the maximum measured values. In other words, as beta increases, the measured velocity will become both
smaller and
less accurate.
This question is asking you to apply this same reasoning to the accuracy of ultrasound beams. Equation 2 is a way to calculate the velocity of the blood if you know theta, which is a different problem than what the question asks you to reason about. Here's a
neat and short article that discusses some of these issues. That said, I definitely understand how this confusion could arise, and as usual, I will bring it to the FL team's attention for review.