Stroke Onset Time Determination Using MRI Relaxation Times without Non-Ischaemic Reference in A Rat Stroke Model.

BACKGROUND: Objective timing of stroke in emergency departments is expected to improve patient stratification. Magnetic resonance imaging (MRI) relaxations times, T-2 and Tip, in abnormal diffusion delineated ischaemic tissue were used as proxies of stroke time in a rat model. METHODS: Both 'non-ischaemic reference'-dependent and-independent estimators were generated. Apparent diffusion coefficient (ADC), T-2 and Tip, were sequentially quantified for up to 6 hours of stroke in rats (n = 8) at 4.7T. The ischaemic lesion was identified as a contiguous collection of voxels with low ADC. T-2 and Tip in the ischaemic lesion and in the contralateral non-ischaemic brain tissue were determined. Differences in mean MRI relaxation times between ischaemic and non-ischaemic volumes were used to create reference-dependent estimator. For the reference-independent procedure, only the parameters associated with log-logistic fits to the T-2 and Tip distributions within the ADC-delineated lesions were used for the onset time estimation. RESULT: The reference-independent estimators from T-2 and Tip data provided stroke onset time with precisions of +32 and +27 minutes, respectively. The reference-dependent estimators yielded respective precisions of +47 and +54 minutes. CONCLUSIONS: A 'non-ischaemic anatomical reference'-independent estimator for stroke onset time from relaxometric MRI data is shown to yield greater timing precision than previously obtained through reference-dependent procedures.