Determining Stroke Onset Time Using Quantitative MRI: High Accuracy, Sensitivity and Specificity Obtained from Magnetic Resonance Relaxation Times

Many ischaemic stroke patients are ineligible for thrombolytic therapy due to unknown onset time. Quantitative MRI (qMRI) is a potential surrogate for stroke timing. Rats were subjected to permanent middle cerebral artery occlusion and qMRI parameters including hemispheric differences in apparent diffusion coefficient, T(2)-weighted signal intensities, T(1) and T(2) relaxation times (qT(1), qT(2)) and f(1), f(2) and V(overlap) were measured at hourly intervals at 4.7 or 9.4 T. Accuracy and sensitivity for identifying strokes scanned within and beyond 3 h of onset was determined. Accuracy for V(overlap), f(2) and qT(2) (>90%) was significantly higher than other parameters. At a specificity of 1, sensitivity was highest for V(overlap) (0.90) and f(2) (0.80), indicating promise of these qMRI indices in the clinical assessment of stroke onset time.