MRA in the evaluation of EC-IC bypass patency.

Abstract

Our goal was to determine the value and limitations of three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) for evaluating the patency of extracranial (EC)-intracranial (IC) bypasses. The 3D TOF MRA was performed in 35 patients to evaluate their EC-IC bypasses (50 sites) at 1.5 T. Subtraction (rephased-dephased) MRA was performed to visualize slowly flowing blood in all patients. Angiographic images were obtained using maximum intensity projection from subtraction images and from rephased images. The patency of bypasses was confirmed at 22 sites and was suggestive at 17 other sites using MRA alone. The diagnostic value of subtraction MRA proved to be superior to that of rephased MRA, and the findings of subtraction MRA correlated relatively well with those of conventional angiography. Edited reprojection MR angiograms were helpful in visualizing collateral vessels without overlapping of vessels. Although there have been some problems with MRA so far, it is a useful imaging modality for following up patients who have undergone EC-IC bypass operations, in conjunction with clinical examination, transcranial Doppler sonography, and cerebral blood flow studies using single photon emission CT or PET.