In addition to making the vessels appear black, vascular structures can also be visualized by making them brighter. Several techniques can be used to enhance the signal from flowing blood including gradient echo imaging and/or gradient moment rephasing and/or contrast enhancement. In gradient echo imaging, the flowing spins are refocused by the rephasing gradient. The patent vessels appear brighter on the images. This technique can be referred to as "bright blood imaging" and can be further improved by the application of an imaging option known as "gradient moment rephasing." It is a first-order velocity compensation technique to visualize slow moving protons with constant velocity (see Fig. 3.26). Protons in venous blood or CSF are put into phase with the stationary protons. So, the intravoxel dephasing is reduced. Gradient moment rephasing compensates the flow by making these vessels containing slow flowing spins appear brighter. It enhances the signal from blood and CSF.
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