FIG 1. Representative case of a 55-year-old man. MR angiogram shows left ICA artery occlusion, but MR image is normal. Xe-CT image with acetazolamide shows poor response in the left hemisphere.FIG 2. The same patient presented with hemisensory disturbance 2 years later. MR angiogram shows a new occlusion of the right ICA, and MR image shows a small infarction in the left thalamus (arrow). Xe-CT scan with acetazolamide shows poor response on both sides