brain mri t2 flairmri t2 flair hyperintensityt2 hyperintensity symptomst2 prolongation mrit2 flair hyperintensityt2 hyperintense lesionsubcortical t2 hyperintensitiesabnormal t2 hyperintensityperiventricular t2 hyperintensityt2 flair hyperintense lesionsscattered t2 hyperintensitiespunctate t2 hyperintensities