ANATOMIC EVALUATION OF THE CIRCLE OF WILLIS - MR-ANGIOGRAPHY VERSUS INTRAARTERIAL DIGITAL SUBTRACTION ANGIOGRAPHY

PURPOSE: To evaluate the reliability of source images and maximum inte nsity projection images of MR angiography in showing the arterial segm ents of the circle of Willis. METHODS: In 62 patients, 526 arterial se gments of the circle of Willis were determined to be present, partiall y present, or absent by blinded observers evaluating MR angiographic s ource images and maximum intensity projection images. Vessel diameter was measured on source images. These results were then compared with t he results from intraarterial digital subtraction angiography. RESULTS : MR angiographic maximum intensity projection images had a sensitivit y of 87% and a specificity of 88% and MR angiographic source images ha d a sensitivity of 89% and a specificity of 63% in depicting the prese nce of a vessel segment. The positive predictive value of an arterial segment with a diameter of at least 1 mm was 99%. CONCLUSION: MR angio graphy is a sensitive technique for detecting the anatomy of the circl e of Willis. Maximum intensity projection images are more specific tha n source images. An arterial segment with a diameter of at least 1 mm on the source image is almost always present and patent.