MRI/histological correspondence during the build-up phase of edema. A representative rat examined at 1 dpi is shown. (A) A large hypersignal area was seen on the T2WI (dotted line) with high ADC values (dotted line, ADC = 1377 μm2/s as opposed to 1039 μm2/s in the symmetric contralateral area), indicating increased water content. A slight midline shift resulted from the cerebral edema (dotted arrows on T2WI). (B) The corresponding histological sections (low magnification, with white boxes indicating higher magnification positions) showed an increase in AQP4 immunoreactivity in the MRI-defined edematous area, with staining located around the capillaries (arrows) and larger vessels (arrowhead) at the BBB level. AQP4 staining in the symmetric contralateral area is fainter around the capillaries (arrows). (C) Double labeling of GFAP (Alexa 488, green) and AQP4 (CY3, red), examined using confocal microscopy confirmed the perivascular location of AQP4 on astrocyte endfeet surrounding capillaries (arrows) without any AQP4 on the astrocyte body.