Quantifying T<sub>2</sub> relaxation time changes within lesions defined by apparent diffusion coefficient in grey and white matter in acute stroke patients.
Damion R., Knight MJ., McGarry BL., Bosnell R., Jezzard P., Harston GWJ., Carone D., Kennedy J., El-Tawil S., Elliot J., Muir KW., Clatworthy P., Kauppinen RA.
Apparent diffusion coefficient (ADC) of cerebral water, as measured by diffusion MRI, rapidly decreases in ischaemia highlighting a lesion in acute stroke patients. The MRI T2 relaxation time changes in ischaemic brain such that T2 in ADC lesions may be informative of the extent of tissue damage, potentially aiding in stratification for treatment. We have developed a novel user-unbiased method of determining the changes in T2 in ADC lesions as a function of clinical symptom duration based on voxel-wise referencing to a contralateral brain volume. The spherical reference method calculates the most probable pre-ischaemic T2 on a voxel-wise basis, making use of features of the contralateral hemisphere presumed to be largely unaffected. We studied whether T2 changes in the two main cerebral tissue types, i.e. in grey matter (GM) and white matter (WM), would differ in stroke. Thirty-eight acute stroke patients were accrued within 9 hours of symptom onset and scanned at 3T for 3D T1-weighted, multi b-value diffusion and multi-echo spin echo MRI for tissue type segmentation, quantitative ADC and absolute T2 images, respectively. T2 changes measured by the spherical reference method were 1.94 ± 0.61, 1.50 ± 0.52 and 1.40 ± 0.54 ms/hour in the whole, GM and WM lesions, respectively. Thus, T2 time courses were comparable between GM and WM independent of brain tissue type involved. We demonstrate that T2 changes in ADC-delineated lesions can be quantified in the clinical setting in a user unbiased manner and that T2 change correlated with symptom onset time, opening the possibility of using the approach as a tool to assess severity of tissue damage in the clinical setting.