Which method could help to increase the PRF or Nyquist limit?

The Nyquist limit is the highest frequency that can be accurately sampled in ultrasound and is influenced by the pulse repetition frequency (PRF) used during the imaging process. The relationship is critical because the Nyquist limit is half of the PRF. Therefore, when the baseline is decreased, it effectively allows for a higher PRF without the risk of aliasing, which is when higher velocity blood flow appears incorrectly on the image.

By decreasing the baseline, you essentially shift the frequency range being sampled, thereby allowing you to capture faster moving structures while maintaining clear imaging. This results in an increased Nyquist limit, allowing better assessment of higher velocity blood flow.

Increasing depth typically lowers the pulse repetition frequency because the system cannot pulse rapidly enough to accurately sample deeper structures. Using a higher frequency transducer affects resolution and penetration depth but does not directly impact the effective sampling of the PRF. Altering the angle of insonation can change the flow velocity measurements but does not directly increase the PRF or the Nyquist limit itself. Thus, decreasing the baseline is the most effective method among the options to increase the PRF or Nyquist limit.