Dynamic tracking of acute ischemic tissue fates using improved unsupervised ISODATA analysis of high-resolution quantitative perfusion and diffusion data

High-resolution (200 x 200 x 1 500 pm 3) imaging Was performed to derive quantitative cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) maps in stroke rats (permanent occlusion) every 30 minutes up to 3 hours after occlusion onset. followed by histology at 24 hours. An improved automated iterative-self-organizing-data-analysis-algorithm (ISODATA) was developed to dynamically track ischemic tissue fate on a pixel-by-pixel basis during the acute phase. ISODATA-resolved clusters were overlaid on the CBF-ADC scatterplots and image spaces. Tissue volume ADC, and CBF of each ISODATA cluster were derived. In contrast to the single-cluster normal left hemisphere (ADC = 0.74 +/- 0.02 x 10(-3) mm(2)/s, CBF = 1.36 +/- 0.22 mL g(-1) min(-1). mean +/- SD, It = 8), the right ischemic hemisphere exhibited three ISODATA clusters. namely: "normal" (normal ADC and CBF), "ischemic core" (low CBF and ADC), and at-risk "perfusion-diffusion mismatch" (low CBF but normal ADC). At 180 minutes. the mismatch disappeared in five rats (Group 1, 180-minute "core" lesion volume = 255 +/- 62 mm(3) and 24- hour infarct volume = 253 +/- 55 mm(3), P > 0.05), while a substantial mismatch persisted in three rats (Group II, 180-minute CBF-abnormal Volume = 198 +/- 7 mm(3) and 24-hour infarct Volume 148 18 mm(3), P < 0.05). The CBF (0.3 +/- 0.09 mL g(-1) min(-1)) of the "persistent mismatch" (Group II, 0.3 +/- 0.09 mL g(-1) min(-1)) was above the CBF viability threshold (0.2 to 0.3 mL g(-1) min(-1)) throughout and its ADC (0.70 +/- 0.03 x 10(-3) mm(2)/S) did not decrease as ischemia progressed. In contrast, the CBF (0.08 +/- 0.03 mL g(-1)min(-1)) of the analogous brain region in Group I was below the CBF viability threshold, and its ADC gradually decreased from 0.63 +/- 0.05 to 0.43 +/- 0.03 x 10(-3) m(2)/S (ADC viability threshold 0.53 +/- 0.02 x 10(-3) mm(2)/S). The modified ISODATA analysis of the ADC and CBF tissue characteristics during the acute phase could provide a useful and unbiased means to characterize and predict tissue fates in ischemic brain injury and to monitor therapeutic intervention.