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Relationship between diffusion-weighted MR images, cerebral blood flow, and energy state in experimental brain
K Kohno1, M Hoehn-Berlage, G Mies
1Max-Planck-Institute for Neurological Research, Department of Experimental Neurology, Cologne, Germany.
Abstract:
The regional evolution of brain infarction was studied in Wistar rats submitted to remotely controlled thread occlusion of the middle cerebral artery. Occlusion was performed in the magnet of an NMR tomography system to allow continuous recording of diffusion-weighted images. After 30 min (n = 6) or 2 h (n = 9), cerebral blood flow was measured by [14C] iodoantipyrine autoradiography while the regional distribution of ATP, glucose, lactate, and pH was imaged using pictorial bioluminescence and fluoroscopic methods. In diffusion-weighted images, the hemispheric lesion area (HLA) at the level of caudate-putamen amounted to 54.2 +/- 10.9% after 30 min and to 67.0 +/- 5.9% after 2 h vascular occlusion. These areas corresponded to the regions exhibiting tissue acidosis (60.8 +/- 9.3% and 70.4 +/- 4.5%), but were clearly larger than those in which ATP was depleted (22.3 +/- 20.8% and 49.6 +/- 12.9% after 30 min and 2 h, respectively). The threshold of blood flow for the increase of signal intensity in diffusion-weighted images increased between 30 min and 2 h occlusion from 34 to 41 ml/100 g per minute, the threshold of acidosis from 40 to 47 ml/100 g per minute, and the threshold for ATP depletion from 13 to 19 ml/100 g per minute. Our study demonstrates that diffusion-weighted imaging detects both the core and the penumbra of the evolving infarction but is not able to differentiate between the two parts. It further shows that the ischemic lesion grows during the initial 2 h of vascular occlusion, and that the size of the infarct core increases more rapidly than that of the penumbra.
Insights
Diffusion-weighted imaging detects evolving brain infarction, including the core and penumbra, but cannot differentiate them. The ischemic lesion area grows within 2 hours, with the infarct core expanding faster than the penumbra.
Area of Science:
- Neuroscience
- Medical Imaging
- Biochemistry
Background:
- Middle cerebral artery occlusion is a common model for studying ischemic stroke.
- Diffusion-weighted imaging (DWI) is a sensitive MRI technique for detecting acute ischemic stroke.
- Understanding the spatiotemporal evolution of ischemic lesions is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the regional evolution of brain infarction using diffusion-weighted imaging (DWI) in a rat model.
- To correlate DWI findings with regional cerebral blood flow, ATP, glucose, lactate, and pH levels.
- To assess the ability of DWI to differentiate between the infarct core and penumbra.
Main Methods:
- Wistar rats underwent remotely controlled middle cerebral artery occlusion within an NMR tomography system for continuous DWI.
- Cerebral blood flow was measured using [14C] iodoantipyrine autoradiography.
- Regional ATP, glucose, lactate, and pH were imaged using bioluminescence and fluoroscopic methods.
Main Results:
- Hemispheric lesion area (HLA) in DWI increased from 54.2% at 30 min to 67.0% at 2 h of occlusion.
- DWI lesion areas corresponded to regions of tissue acidosis but were larger than areas of ATP depletion.
- The threshold of blood flow for DWI signal increase, acidosis, and ATP depletion all rose between 30 min and 2 h occlusion.
Conclusions:
- Diffusion-weighted imaging detects both the core and penumbra of evolving ischemic infarction but cannot distinguish between them.
- The ischemic lesion area significantly grows within the first 2 hours of vascular occlusion.
- The infarct core expands more rapidly than the ischemic penumbra during the early stages of stroke.