Introduction: Brain edema is an adverse complication of ischemic stroke, and is associated with substantial morbidity and mortality. We investigated whether relaxometry parameters of MRI are a reliable measure of brain edema in an animal model.
Hypothesis: We hypothesize that quantitative relaxometry parameters of MRI in a rat model of stroke tightly correlate with brain edema.
Methods: We permanently occluded the middle cerebral artery of 18 rats using the filament occlusion method. Fifteen surviving animals were imaged at 48 hours with a Bruker 4.7 T MRI scanner with Diffusion-weighted imaging (DWI), T1 and T2 maps, and proton-density weighted (PDW) imaging. Hemispheric and lesional volumes were generated on DWI. For quantitative T1, quantitative T2 and PDW images, signal intensity values relative to the contralateral hemisphere were determined. The percent water content in the rat brain was measured using the wet-dry method. Additional volumetric measurements of swelling were calculated based on hemisphere volumes determined on MRI. Correlation testing and logistic regression was performed to assess the relationship between imaging measures and swelling.
Results: The mean lesion volume was 352 mm3. Brain water content and swelling volume were closely associated (r=0.80, p<0.001). PDW, T1 and T2 ratios highly correlated with brain water content (r=0.91, p<0.0001, r=0.94, p<0.0001 and r=0.97, p<0.0001, respectively). Ratios for PDW, T1 and T2 were also associated with swelling volume (r=0.67, p<0.0063, r=0.73, p<0.0022, and r=0.74, p<0.0017).
Conclusion: Signal intensity ratios derived from PDW as well as quantitative T1 and T2 MRI can be leveraged to quantify brain water content and brain edema. These measures are useful markers for edema quantification that can be applied to any condition that leads to brain edema in both animal models and human patients.