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, T2-weighted signal intensities, T1 and T2 relax- ation times (qT1, qT2) and f1, f2 and Voverlap 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 Voverlap, f2 and qT2 (>90%) was significantly higher than other param- eters. At a specificity of 1, sensitivity was highest for Voverlap (0.90) and f2 (0.80), indicating promise of these qMRI indices in the clinical assessment of stroke onset time.