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Figure 6. Diffusion-perfusion mismatch after left middle cerebral artery stroke. The patient was imaged 3.8 hours after a witnessed sudden onset of a right hemiparesis. Transverse DW images (DWI; b = 1,000 sec/mm2; effective gradient, 14 mT/m; 6,000/108; matrix, 256 x 128; field of view, 400 x 200 mm; section thickness, 6 mm with 1-mm gap) demonstrate hyperintensity in the subcortical region, including in the lenticular nucleus and corona radiata (arrowheads, right-hand image in top row). Transverse cerebral blood volume (CBV) images (spin-echo echo-planar technique; 0.2 mmol/kg gadopentetate dimeglumine [Magnevist; Berlex Laboratories, Wayne, NJ]; 51 images per section; 1,500/75; matrix, 256 x 128; field of view, 400 x 200 mm; section thickness, 6 mm with 1-mm gap) demonstrate decreased dynamic cerebral blood volume in the region of hyperintensity on the DW images. However, there are areas of abnormal cerebral blood volume (arrows) that appear relatively normal on the DW study. Follow-up study performed 10 hours after the onset of symptoms demonstrates an increase in the size of the DW imaging abnormality (arrowheads, right-hand image in fifth row) as it extends into the region of brain that was previously normal on DW images but abnormal on cerebral blood volume images.