Brain Water Accumulation and Potential Protein Estimation Through T1 and Magnetization Transfer at 7 Tesla in Acute Ischemic Infarct in the Rat Model
Five Wistar rats subjected to acute stroke (in the right hemisphere) via intralumenal suture occlusion of the middle cerebral artery, and their five controlled nonoccluded left hemispheres were studied. In this study techniques for drying were compared. Wet/dry weights of rat brain tissue were used to compare heating at 90°C for 24 and 48 hours. It was determined that 48 hours of heating would allow adequate drying of the tissue. The speed vacuum was used to dry tissue that had been maintained at a frozen state. These wet/dry weights were obtained and the percent water content showed no statistical difference than the results from the heating method (P>O.241). In order to study cerebral ischemic infarction MRI was used to detect both water accumulation and protein mobilization, which are results of stroke in the brain. It was the goal of this experiment to use Tl, the relaxation time, and magnetization transfer at a magnetic field strength of 7 Tesla to begin to discriminate between water accumulation and protein mobilization in tissue undergoing infarction. In MRI studies to 4 hours postocclusion, serial data acquisition allowed the measurement of cerebral blood flow (CBF), apparent diffusion coefficient of water (ADCw), Tl, Tl sat (TI under saturation of the proton pool) and various other parameters. Using these parameters, images were constructed. The ratio of Tl/Tl sat in the region of infarction showed that water accumulation was the major contributor to contrast, but there also existed a small contribution due to changes at the water macromolecular interface, possibly due to proteolysis or the mobilization of protein. Following data acquisition, the animals were euthanized. Wet and dry weights were measured and the percent water content calculations revealed the increase in brain water in the right infarcted hemispheres.