A NEW IN-VIVO METHOD FOR QUANTITATIVE-ANALYSIS OF STROKE LESIONS USING DIFFUSION-WEIGHTED MAGNETIC-RESONANCE MICROSCOPY

Using three-dimensional diffusion-weighted MR microscopy and a rat mod el of focal cerebral ischemia, we evaluated the statistical characteri stics of two parameters: absolute stroke volumes and change in stroke volumes over 6 h of middle cerebral artery (MCA) occlusion. In all rat s, the absolute stroke volumes increased linearly over the 6-h MCA occ lusion time period. On average, stroke volume growth rate was 2.1 +/- 0.5%/h. Sample size power analysis of our data demonstrated that to de monstrate a 10% reduction of the 6-h volumes, sample size per group wo uld require 29 animals (these calculations are based on alpha = 0.05, beta = 0.20 using normal approximation). A similar 30% reduction of st roke volume at 6 h poststroke (from approximate to 200 to 140 mm(3)) w ould, in our ''slope model,'' translate into a reduction of stroke gro wth rate from the normal +11.25 mm(3)/h (150 to 200 mm(3) over 4 h) to 7 mm(3)/h (150 to 178 mm(3) over 4 h); power analysis in this case de monstrated that sample size is reduced to 15 animals per group (these calculations are based on alpha = 0.05, beta = 0.20 using normal appro ximation). We conclude that from a statistical standpoint our study de monstrates that stroke growth rate might be a more suitable parameter for evaluating the effect of treatment in both clinical and experiment al stroke trials. (C) 1996 Academic Press, Inc.