Fig 1. MTT maps in a 66-year-old woman.

A, MTT map before acetazolamide infusion shows prolonged MTT in the left hemisphere represented as areas displayed (yellow and green arrow). The ROI placed in the left hemisphere (arrowhead) does not include the areas of maximal MTT elevation.

B, MTT map obtained 15 minutes after infusion of acetazolamide, with use of the same section location and display parameters as those in A. Despite appropriate response on the right, no shortening in MTT is apparent in the left hemisphere. Instead, additional prolongation in MTT can be seen in areas in the left middle cerebral artery territory and the frontal lobe (arrow). By using ROI analysis, we measured a paradoxical prolongation in mean cortical MTT value of 93.7% on the left and interpreted it as evidence of hemodynamic impairment due to reduced perfusion pressure.