Time-dependent Changes of the Infarct Volume in a Rat Stroke Model: A Comparison of the Use of MRI and TTC- staining as Monitoring Tools

Objectives : Serial changes of focal ischemic lesions as seen on magnetic resonance (MR) images and triphenyltetrazolium chloride (TTC)-stained samples of transient middle cerebral artery occlusion in a rat model were evaluated to investigate the natural course of the lesions and the feasibility of the use of each method as a monitoring tool. Methods : Transient middle cerebral artery occlusion (MCAO) was induced in fifteen adult female Sprague Dawley rats using the method of intraluminal vascular occlusion. Two hours after MCAO was induced, reperfusion was performed. Serial MR images were obtained and the volume of the brain infarct was estimated. For macroscopic and microscopic evaluation of the ischemic lesions, the ten animals were sacrificed at different times after MCAO. The rat brains were then removed and six coronal sections were made. Each section was incubated at $37^{\circ}C$ in 2% TTC solution for 15 minutes. Results : Postischemic injury evaluations that were made periodically for eight weeks revealed that the lesion volume as determined from T2 maps had reached a peak on the second day after ischemic injury and the volume decreased afterwards for one week; by the fourth week, the lesion volume again increased to stabilize initial lesion development. There were considerable discrepancies between the infarct area of the samples determined by TTC staining and the in vivo infarct area estimated from the MR images, especially for late stages. Conclusion : T2 map MR images, with a careful consideration of the natural course of infarction development, can provide an adequate and noninvasive means to evaluate the degree of ischemic injury under diverse experimental circumstances.