Magnetic Resonance Imaging (MRI) Practice Test

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

1. Temporal manipulation

2. Spatial presaturation

3. Phase encoding

4. Frequency selection

The correct answer is: Spatial presaturation

In Magnetic Resonance Angiography (MRA), the signal from blood vessels is typically removed using spatial presaturation techniques. This method involves applying specific radiofrequency pulses in targeted areas before the actual imaging sequence. By doing this, the magnetization of the flowing blood is effectively nullified in the regions where the presaturation pulses are applied. This allows for better visualization of the stationary tissues and minimizes background signals from blood, enhancing the contrast and prominence of the vessels of interest. Spatial presaturation is particularly effective because it selectively targets the regions with flowing blood, ensuring that the dynamic signal from vessels is suppressed without affecting the surrounding stationary structures. This results in clearer images of anatomical details that might otherwise be obscured by the strong signals from the blood vessels if they were left unaltered.