Changes of relaxation times (T1, T2) and apparent diffusion coefficient after permanent middle cerebral artery occlusion in the rat: temporal evolution, regional extent, and comparison with histology

Abstract

The quantitative NMR parameters T₁, T₂, p, and apparent diffusion coefficient (ADC) were determined during the 7 h after middle cerebral artery occlusion in rats. In the normal caudate-putamen (CP), 869 ± 145 ms and 72 ± 2ms for T₁ and for T₂, respectively, were found; the corresponding values for cortex were 928 ± 117 ms and 73 ± 2 ms. The ADC showed significant dependence on gradient direction: diffusion along x resulted in 534 ± 53 μm²/s (CP) and 554 ± 62 μm²/s (cortex), and along y in 697 ± 58 μm²/s (CP) and 675 ± 53 μm²/s (cortex). In the ischemic territory, a continuous increase over time of both relaxation times was observed in the CP, leading to an increase of 29 ± 20% (T₁) and 51 ± 41% (T₂ above control level. ADC dropped to 63 ± 15% of control in the CP and to 74 ± 4% of control in the temporal cortex. No significant change was noted in proton density during the observation period. Strongest ADC reduction was in the center of the ischemic territory (≤ 60% of control) surrounded by a region of lesser reduction (≤ 80% of control). During the early part of the study, the area of reduced ADC was larger than that of elevated relaxation times. Toward the end of the experiment, the area of increased relaxation times approached that of decreased ADC at ≤ 80% of control. Good agreement of histological presentation of infarct with the total area of decreased ADC (≤ 80%) was demonstrated.