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A Magnetic Resonance Imaging Protocol for Stroke Onset Time Estimation in Permanent Cerebral Ischemia
Published on: September 16, 2017
A Magnetic Resonance Imaging Protocol for Stroke Onset Time Estimation in Permanent Cerebral Ischemia
Bryony L McGarry1, Kimmo T Jokivarsi2, Michael J Knight1
1School of Experimental Psychology and Clinical Research and Imaging Center Bristol, University of Bristol.
Abstract:
MRI provides a sensitive and specific imaging tool to detect acute ischemic stroke by means of a reduced diffusion coefficient of brain water. In a rat model of ischemic stroke, differences in quantitative T1 and T2 MRI relaxation times (qT1 and qT2) between the ischemic lesion (delineated by low diffusion) and the contralateral non-ischemic hemisphere increase with time from stroke onset. The time dependency of MRI relaxation time differences is heuristically described by a linear function and thus provides a simple estimate of stroke onset time. Additionally, the volumes of abnormal qT1 and qT2 within the ischemic lesion increase linearly with time providing a complementary method for stroke timing. A (semi)automated computer routine based on the quantified diffusion coefficient is presented to delineate acute ischemic stroke tissue in rat ischemia. This routine also determines hemispheric differences in qT1 and qT2 relaxation times and the location and volume of abnormal qT1 and qT2 voxels within the lesion. Uncertainties associated with onset time estimates of qT1 and qT2 MRI data vary from ± 25 min to ± 47 min for the first 5 hours of stroke. The most accurate onset time estimates can be obtained by quantifying the volume of overlapping abnormal qT1 and qT2 lesion volumes, termed 'Voverlap' (± 25 min) or by quantifying hemispheric differences in qT2 relaxation times only (± 28 min). Overall, qT2 derived parameters outperform those from qT1. The current MRI protocol is tested in the hyperacute phase of a permanent focal ischemia model, which may not be applicable to transient focal brain ischemia.
Insights
Quantitative MRI relaxation times (qT1 and qT2) can estimate acute ischemic stroke onset in rats. Measuring T2 relaxation time differences or overlapping lesion volumes provides the most accurate stroke timing, outperforming T1 measures.
Area of Science:
- Neuroimaging
- Stroke Research
- Biomedical Engineering
Background:
- Magnetic Resonance Imaging (MRI) is crucial for detecting acute ischemic stroke.
- Quantitative T1 and T2 MRI relaxation times (qT1, qT2) change over time in ischemic lesions.
- Estimating stroke onset time is critical for effective treatment.
Purpose of the Study:
- To evaluate quantitative T1 and T2 MRI relaxation times for estimating stroke onset time in a rat model.
- To develop and validate a method for delineating ischemic stroke tissue and quantifying relaxation time changes.
- To compare the accuracy of different MRI parameters for stroke timing.
Main Methods:
- Utilized a rat model of permanent focal cerebral ischemia.
- Employed a semi-automated computer routine to delineate ischemic lesions based on diffusion coefficients.
- Quantified hemispheric differences in qT1 and qT2 relaxation times and lesion volumes.
- Assessed the time dependency of relaxation time differences and lesion volumes.
Main Results:
- Differences in qT1 and qT2 between ischemic and non-ischemic hemispheres increased linearly with time post-stroke.
- Lesion volumes with abnormal qT1 and qT2 also increased linearly with time.
- The most accurate onset time estimates were achieved using overlapping abnormal qT1/qT2 lesion volumes (Voverlap, ±25 min) or qT2 differences only (±28 min).
- qT2-derived parameters demonstrated superior performance compared to qT1.
Conclusions:
- Quantitative MRI relaxation times, particularly qT2, offer a reliable method for estimating acute ischemic stroke onset in rats.
- The developed automated routine effectively delineates lesions and quantifies timing parameters.
- This MRI protocol shows promise for hyperacute stroke assessment but requires validation for transient ischemia.
