FIG 4. A and B, MR angiograms (32/8/2; flip angle = 17°) obtained 2 (A) and 9 (B) days after acute SAH. At day 2, all vessels are normal (rating = 0); at day 9, significant vasospasm of the right ACA is identified (A1 segment, rating = 2) (arrowheads, B). The diagnosis is easy when a previous MR angiogram is available for comparison.

C, IA-DSA (right carotid arteriogram) obtained 10 days after SAH and 18 hours after MR angiography (B). The narrowing of the right A1 segment (arrowheads; rating = 2) was thought to be hypoplasia by one of the reviewers, but MR angiography performed before the spasm proved this interpretation to be incorrect.