Focal brain ischemia in rat: acute changes in brain tissueT1 reflect acute increase in brain tissue water content

Abstract

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.

Relaxation time constants and apparent diffusion coefficients of rat retina at 7 Tesla

“…This minor discrepancy could be due to different imaging parameters. By comparison, rat brain T 1 is 1.6-1.8 s at 7 T (Guilfoyle et al, 2003;Barbier et al, 2005). B. T 2 .…”

“…Error bars are standard deviations (N 5 5 for T 1 , T 2 , and ADC, N 5 4 for T 2 *). Guilfoyle et al, 2003. d Barbier et al, 2005. e Unpublished data. f de Graaf et al, 2006. g The three values indicate inner, middle and outer strip from cat retina.…”

Blood-flow magnetic resonance imaging of the retina

“…λ is the water tissue-blood partition coefficient and was taken to be 0.9 (Herscovitch and Raichle, 1985). Brain T 1 of 1.8 s at 7 T was used (Barbier et al, 2005). α, the arterial spin-labeling efficiency, was measured to be 0.8 (Shen et al, 2005).…”

Effect of osmotherapy with hypertonic saline on regional cerebral edema following experimental stroke: a study utilizing magnetic resonance imaging

“…Recently, MRI has been utilized as an effective tool to study temporal profiles and pre-clinical therapeutics in experimental brain injury [19] including ischemic stroke [20][21][22]. The advantage of MRI is the allowance of repeated measurements of brain water content in anesthetized animals; however, little is known about the impact of repeated exposure to anesthetics on injury volume.…”

“…Magnetic resonance imaging (MRI) has been utilized to study temporal profiles and pre-clinical therapeutics of cerebral edema associated with experimental brain injury in a variety of animal models [19][20][21][22]. While MRI is a powerful tool to characterize and quantify repeated measurements of cerebral water content in anesthetized experimental animal models, few studies have correlated T 1 and T 2 -weighted MRI imaging with regional brain water content with conventional methods such as wet-to-dry weight ratios (WDR) or microgravimetry for tissue water determination [23].…”