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Oxygen metabolism MRI - A comparison with perfusion imaging in a rat model of MCA branch occlusion and reperfusion
Philip V Little1,2, Sandra E Kraft3, Arvin Chireh1,2
1Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Abstract:
The penumbra is sustained by an increased extraction of oxygen (OEF) from blood to brain tissue. Metabolic imaging may improve penumbra specificity when examining stroke patients with wake-up stroke and a long time between admission and symptom onset. We used MRI to examine OEF, and compared the volume of regions with elevated OEF to the volume of regions with perfusion deficit in a M2 occlusion model (M2CAO) with preserved collateral blood flow. OEF was calculated from BOLD MRI examining tissue R2', with ASL perfusion imaging employed to determine cerebral blood flows (CBF) and volumes. Diffusion imaging was used to identify the ischemic core (IC). Examinations were performed during and after transient M2CAO in rats. The IC-OEF mismatch was significantly smaller than the IC-CBF mismatch during M2CAO. The penumbra OEF was significantly increased during M2CAO, and decreased significantly after reperfusion. The IC-OEF mismatch may provide increased penumbra specificity compared to IC-CBF mismatch regimens. Results strongly indicate the potential of metabolic MRI for thrombectomy patient selection in cases with a long time from symptom onset to admission. Results demonstrate the effectiveness of reperfusion in alleviating metabolic disturbances in ischemic regions, emphasizing fast treatment to achieve significant neurological recovery in stroke patients.
Insights
Metabolic MRI using oxygen-extraction fraction (OEF) shows promise for identifying stroke penumbra, especially in wake-up stroke cases. This approach may improve patient selection for thrombectomy when treatment is delayed.
Area of Science:
- Neuroscience
- Radiology
- Biomedical Engineering
Background:
- The ischemic penumbra, a region of brain tissue at risk during stroke, is sustained by increased oxygen extraction fraction (OEF).
- Accurate identification of the penumbra is crucial for effective stroke treatment, particularly in wake-up stroke patients or those with delayed presentation.
- Metabolic imaging offers a potential method to improve penumbra specificity.
Purpose of the Study:
- To investigate the utility of MRI-based oxygen extraction fraction (OEF) for characterizing the ischemic penumbra in a rat stroke model.
- To compare the mismatch between the ischemic core and elevated OEF regions versus the ischemic core and perfusion deficit regions.
- To assess the potential of metabolic MRI for selecting patients for thrombectomy, especially in cases with delayed treatment.
Main Methods:
- Utilized MRI to measure OEF from BOLD MRI (R2') and cerebral blood flow (CBF) from ASL perfusion imaging in a transient middle cerebral artery occlusion (M2CAO) rat model.
- Employed diffusion imaging to define the ischemic core (IC).
- Compared the volume of regions with elevated OEF to regions with perfusion deficit during and after M2CAO.
Main Results:
- The ischemic core-OEF mismatch was smaller than the ischemic core-CBF mismatch during M2CAO.
- Penumbra OEF was significantly elevated during M2CAO and decreased upon reperfusion.
- The IC-OEF mismatch demonstrated higher penumbra specificity compared to IC-CBF mismatch.
Conclusions:
- Metabolic MRI, specifically OEF measurement, shows potential for enhanced penumbra specificity in stroke imaging.
- This technique may aid in selecting thrombectomy candidates, particularly in scenarios with a long delay between symptom onset and hospital admission.
- Reperfusion effectively mitigates metabolic disturbances, highlighting the importance of timely stroke treatment for neurological recovery.
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