Focal brain ischemia in rat: acute changes in brain tissue T1 reflect acute increase in brain tissue water content

Several recent studies have reported changes of brain tissue T(1) in ischemic models during the first minutes after occlusion of the middle cerebral artery (MCA). In order to assess whether these tissue T(1) changes are related to an increase in tissue water content, we performed T(1) (7 T) and tissue water content measurements in a rat model (n = 10, Sprague-Dawley) of focal cerebral ischemia (intraluminal occlusion model). The tissue water content was determined using a gravimetric technique. The animals were divided into two groups: an ischemic group, with an effective MCA occlusion (n = 6) and a control group, with animals having undergone sham surgery but no MCA occlusion (n = 4). In the ipsilateral cortex, the tissue water content was 81.1 +/- 0.7% at 2 h 15 min following ischemic insult (contralateral value: 79.3 +/- 0.5%). Concomitantly, the tissue T(1) in the ipsilateral cortex was 2062 +/- 60 ms at ischemia onset + 1 h (contralateral 1811 +/- 28 ms) and 2100 +/- 38 ms at ischemia onset + 2 h (contralateral 1807 +/- 18 ms). The tissue T(1) and tissue water content values measured in the contralateral area do not differ from the values obtained in the control group. A significant T(1) increase is observed at ischemia onset + 1 h (+ 14%) and ischemia onset (+ 2 h) + 16%, together with a significant increase in tissue water content (+ 2.3%). This suggests that there is an increase in tissue water content concomitant with cell swelling during the first hours of ischemia.