What happens when fresh blood moves into an imaging slice in GE MRA?

When fresh blood moves into an imaging slice during Gradient Echo Magnetic Resonance Angiography (GE MRA), it creates high signal intensity due to its exposure to the radiofrequency (RF) pulse. Fresh blood, as it enters the imaging slice, has not been previously exposed to RF pulses and thereby retains more of its magnetization. This results in a strong signal when the RF pulse is applied, creating a contrast that enhances the visibility of blood vessels in the image. This phenomenon harnesses the concept of magnetization recovery, where blood that has a higher signal compared to surrounding tissues contributes significantly to the overall signal observed in the MRA image.

In contrast, the other options relate to different aspects of blood flow and imaging processes that do not align with the physics of how fresh blood interacts with RF pulses during the imaging process. For example, fresh blood contributing no signal would mean it is not visualized at all, which is contrary to the fundamental principles of MRA that aim to enhance blood signal. Moreover, the idea that fresh blood would experience immediate saturation doesn't reflect the selective nature of RF pulse application, nor does it explain the increased signal from freshly introduced blood. Finally, stating that it would alter the image to low resolution misrepresents the goal