In an MRA sequence, how is signal removed from vessels?

In an MRA (Magnetic Resonance Angiography) sequence, the removal of signal from stationary tissues surrounding vessels is crucial for enhancing the visibility of blood vessels. Spatial presaturation involves specifically applying an RF (radiofrequency) pulse to saturate the signal from stationary tissues, effectively nullifying their contribution to the image. This technique allows the blood vessels to stand out, as the flow-related signals from moving blood are less affected by the saturation that has been induced in the background tissues.

Spatial presaturation is particularly beneficial in MRA because it helps to suppress signals from unwanted structures, such as fat or muscle, allowing for clearer imaging of the vasculature. This suppression aids in improving image contrast and diagnostic interpretation.

While gradient moment nulling also plays a role in removing stationary signals, especially in time-of-flight MRA techniques where it helps to reduce flow-related artifacts, the primary answer regarding signal removal from vessels specifically aligns with the technique of spatial presaturation. Thus, the correct answer highlights the importance of selectively suppressing certain signals to enhance the quality of an angiographic examination.