Mechanism of perfusion MRI

Contrast is administered as a rapid bolus into a peripheral vein and arrives at the cerebral capillaries about 20 seconds after injection, the exact time depending both on the patient's cardiac output and cerebral blood flow (CBF). A rapid MR sequence (T2*-weighted gradient-echo echo-planar sequence) is repeated every few seconds as the bolus of contrast passes through the cerebral vasculature, allowing the first-pass effects of the contrast on the parenchyma to be observed.

 Perfusion imaging, however, is performed with T2*-weighted imaging.