MR flow imaging in vascular malformations using gradient recalled acquisition.

Twenty patients with known or suspected intracranial vascular lesions were evaluated with gradient recalled MR (GRASS) imaging, and the results were compared with those obtained by standard spin-echo MR, CT, and angiography. GRASS imaging with a short TR (40 msec) and a partial flip angle (60 degrees or 70 degrees) demonstrated flow-related enhancement within vascular structures in nearly all cases. The only exception to the enhancement of flowing blood was when slow flow was encountered within venous structures oriented parallel to the imaging plane, in which case flow signal void occurred. GRASS imaging was particularly useful for differentiating flowing blood from calcium or air, or for delineating vascular structures adjacent to the inner table of the skull. The major limitation of the technique is the presence of hemosiderin, which causes marked signal dropout due to the exquisite sensitivity of GRASS to magnetic susceptibility effects.