Dynamic changes of ADC, perfusion, and NMR relaxation parameters in transient focal ischemia of rat brain

Abstract

The potential of multiparametric MRI parameters for differentiating between reversibly and irreversibly damaged brain tissue was investigated in an experimental model of focal brain ischemia in the rat. The middle cerebral artery (MCA) was occluded by intraluminal suture insertion for 60 or 90 min, followed by 4.5 h of reperfusion. The apparent diffusion coefficient (ADC) of brain water, T 1 and T 2 relaxation times, and CBF i , an MRderived index of cerebral perfusion, were repeatedly measured and correlated with the outcome from the ischemic impact. A novel user-independent approach for segmentation of ADC maps into classes of increasing injury was introduced to define regions of interest (ROIs) in which these parameters were evaluated. MCA occlusion led to a graded decline of ADC, which corresponded with both the severity of flow reduction and an increase in T 1 and T 2 relaxation times. Removal of the suture led to a triphasic restitution of blood flow consisting of a fast initial rise, a secondary decline, and final normalization. Postischemic reperfusion led to a rise of ADC irrespective of the duration of ischemia. However, the quality of recovery declined with increasing severity of the ischemic impact. Throughout the observation time, T 1 and T 2 showed a continuous increase, the intensity of which correlated with the severity of ADC decline during ischemia. Particularly with longer ischemia time, elevated T 2 in combination with reduced ADC yielded a lower probability of recovery during recirculation, while intraischemic perfusion information contributed less to the prediction of outcome. In conclusion, the combination of MR parameters at the end of ischemia correlated with the probability of tissue recovery but did not permit reliable differentiation between reversibly and irreversibly damaged tissue. Magn Reson Med 47:97-104, 2002.

Temporal profile of T2-Weighted MRI Distinguishes between Pannecrosis and Selective Neuronal Death after Transient Focal Cerebral Ischemia in the Rat

“…Absolute T 1 and T 2 Times in the Lesions T 1 and T 2 relaxation times derived from quantitative parameter maps on the unaffected, contralateral side corresponded to previously published values for normal tissue during the whole observation period (Table 1) (Hoehn-Berlage et al, 1995;van Dorsten et al, 2002). Both groups showed higher absolute T 1 and T 2 times within the lesioned area on parameter maps 1 day after MCAO (Figure 1).…”

Detection of the Ischemic Penumbra Using pH-Weighted MRI

“…The same anesthesia procedure was repeated at the 24 h follow-up MRI. T 2 -hyperintensity was used to quantify infarction, which has been shown to be a reliable approach (Neumann-Haefelin et al, 2000;Palmer et al, 2001;van Dorsten et al, 2002).…”

Characterizing Tissue Fate After Transient Cerebral Ischemia of Varying Duration Using Quantitative Diffusion and Perfusion Imaging

“…8 In contrast, van Dorsten et al did not observe a clear relationship between blood flow dynamics and tissue recovery after 60 and 90 minutes of ischemia. 9 In this study, we used quantitative perfusion and diffusion imaging to investigate the effects of reperfusion after temporary focal cerebral ischemia of varying duration in rats. The main goals were (1) to delineate the temporal evolution of the core and mismatch volume after different reperfusion times, and (2) to characterize the ADC and CBF pixel-by-pixel dynamics in core and mismatch pixels that were subsequently salvaged by reperfusion at distinct time points and those that subsequently became infarcted.…”