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Simultaneous PET/MRI Imaging During Mouse Cerebral Hypoxia-ischemia
Published on: September 20, 2015
Functional, perfusion and diffusion MRI of acute focal ischemic brain injury
Qiang Shen1, Hongxia Ren, Haiying Cheng
1Department of Neurology, Yerkes Primate Research Center, Emory University, Atlanta, Georgia, USA.
Abstract:
Combined functional, perfusion and diffusion magnetic resonance imaging (MRI) with a temporal resolution of 30 mins was performed on permanent and transient focal ischemic brain injury in rats during the acute phase. The apparent diffusion coefficient (ADC), baseline cerebral blood flow (CBF), and functional MRI (fMRI) blood-oxygen-level-dependent (BOLD), CBF, and CMRO(2) responses associated with CO(2) challenge and forepaw stimulation were measured. An automated cluster analysis of ADC and CBF data was used to track the spatial and temporal progression of different tissue types (e.g., normal, 'at risk,' and ischemic core) on a pixel-by-pixel basis. With permanent ischemia (n=11), forepaw stimulation fMRI response in the primary somatosensory cortices was lost, although vascular coupling (CO(2) response) was intact in some animals. Control experiments in which the right common carotid artery was ligated without causing a stroke (n=8) showed that the delayed transit time had negligible effect on the fMRI responses in the primary somatosensory cortices. With temporary (15-mins, n=8) ischemia, transient CBF and/or ADC declines were observed after reperfusion. However, no T(2) or TTC lesions were observed at 24 h except in two animals, which showed very small subcortical lesions. Vascular coupling and forepaw fMRI response also remained intact. Finally, comparison of the relative and absolute fMRI signal changes suggest caution when interpreting percent changes in disease states in which the baseline signals are physiologically altered; quantitative CBF fMRI are more appropriate measures. This approach provides valuable information regarding ischemic tissue viability, vascular coupling, and functional integrity associated with ischemic injury and could have potential clinical applications.
Insights
This study used advanced MRI techniques to assess brain injury in rats. It found that quantitative measures are better than percentage changes for evaluating stroke, especially in disease states.
Area of Science:
- Neuroscience
- Radiology
- Biomedical Engineering
Background:
- Focal ischemic brain injury impacts brain tissue viability and function.
- Assessing acute ischemic injury requires sensitive imaging techniques to evaluate tissue status and functional integrity.
- Magnetic Resonance Imaging (MRI) offers multimodal capabilities for brain imaging.
Purpose of the Study:
- To evaluate the utility of combined functional, perfusion, and diffusion MRI in characterizing acute focal ischemic brain injury in rats.
- To assess tissue viability, vascular coupling, and functional integrity following permanent and transient ischemia.
- To compare the effectiveness of quantitative MRI measures versus percentage changes in disease states.
Main Methods:
- Combined functional MRI (fMRI), perfusion MRI, and diffusion MRI were performed on rats with permanent and transient focal ischemic brain injury.
- Apparent diffusion coefficient (ADC), cerebral blood flow (CBF), and fMRI responses (BOLD, CBF, CMRO2) to CO2 challenge and forepaw stimulation were measured.
- Automated cluster analysis tracked the spatial and temporal progression of ischemic tissues.
Main Results:
- Permanent ischemia abolished fMRI responses to forepaw stimulation in the somatosensory cortex, though vascular coupling remained intact in some cases.
- Transient ischemia showed temporary declines in CBF and/or ADC after reperfusion, with minimal lesions observed.
- Quantitative CBF fMRI measures were deemed more appropriate than percent changes for disease states with altered baseline signals.
Conclusions:
- Combined MRI provides valuable insights into ischemic tissue viability, vascular coupling, and functional integrity.
- The findings suggest caution when interpreting percentage changes in fMRI in disease states.
- This multimodal MRI approach holds potential for clinical applications in stroke assessment.
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