Spin echo entrapped perfusion image (SEEPAGE). A nonsubtraction method for direct imaging of perfusion

Arterial spin-labeled perfusion imaging is increasingly being applied to the study of the brain and other organs. To date, perfusion information has invariably been obtained by subtraction of images with and without spin-labeling of inflowing water. Due to the relatively small amount of blood which enters tissue over a typical inflow period (1-1.5 sec), subtraction errors due to image instability or, in certain circumstances, magnetization transfer effects, can lead to very significant amounts of artifactual image intensity. These problems are avoided in the nonsubtraction method described here. Initially, spins in the imaging slice are selectively saturated, leaving other spins unaffected. A subsequent spin-echo train traps these magnetizations irrespective of flow. Finally, an imaging module generates intensity only from those spins which have entered the imaging slice during the inflow period. A slight modification of the sequence facilitates validation by detecting any contaminating signal in a control image.