Phase-contrast MRA in the evaluation of EC-IC bypass patency

We have assessed three-dimensional (3-D) phase-contrast (PC) MR angiography (MRA) in the evaluation of extracranial (EC)-intracranial (IC) bypasses. This technique was performed in 22 patients (26 examinations) to evaluate the patency of their EC-IC bypasses (a total of 37 operated sites). Three sets of phase images for antero-posterior, right-left, and supero-inferior flow velocity components were also obtained in eight patients to produce directional flow images. Directional 2-D PC flow imaging was also performed in three other patients. The patency of bypasses was confirmed in 57% and suggested in 24% of operated sites using 3-D PC MRA alone. The diagnostic value of PC MRA proved superior to that of time-of-flight MRA, because the former emphasizes the signal intensity of vessels without interference from stationary tissues and is less affected by progressive saturation of inflowing spins. 2-D or 3-D directional flow images aided in understanding the flow dynamics in 69%. In patients who had been examined pre-operatively changes in intracranial flow of dynamics could be estimated on post-operative PC MRA. Although PC MRA has several limitations, it proved to be a useful imaging modality for following up patients who had undergone EC-IC bypass operations.