Blood Flow Imaging Technique

This second class of imaging sequence gains its contrast from the presence of moving spins, and in particular from water molecules in blood that have been magnetically labeled. When the perturbed water molecules pass through capillaries in the slice of interest, they diffuse into the brain tissue, where they exchange with extravascular tissue water molecules and cause an altering of the image signal intensity from that which would be seen had the arterial spins not been tagged. Though this effect is quite subtle, in a carefully designed experiment the signal change can be detected, and an rCBF map calculated. Such spin "tagging" sequences can theoretically yield a quantitative measure of rCBF, but are more often used to generate qualitative relative rCBF maps.

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