What is meant by high velocity signal loss in SE MRA?

High velocity signal loss in Spin Echo Magnetic Resonance Angiography (SE MRA) refers to the phenomenon where rapidly flowing blood does not produce a detectable signal during the imaging sequence. This occurs because when blood moves at high velocities, it may traverse the imaging slice during the time when radiofrequency pulses are being applied.

In this context, blood that is moving quickly can effectively leave the slice of interest before the imaging sequence is able to capture its signal. The timing of the radiofrequency pulses and the movement of the blood are such that the high-velocity flow does not register in the acquired images. Therefore, those areas of high flow may appear as voids or areas of signal loss, leading to significant gaps or artifacts in the angiographic representation.

In contrast, the other options describe scenarios that do not align with the concept of high velocity signal loss. For instance, if blood were to remain fully within the slice during the pulse timing, it would signal correctly. Similarly, if only stationary blood were detected, that would imply that the imaging parameters are enabling the capture of slower flows effectively, and if blood flow were consistent throughout the imaging process, there would be no high velocity signal loss. Thus, the correct answer directly captures the essence of why