Voxel-based mapping of irreversible ischaemic damage with PET in acute stroke

Objective mapping of irreversible tissue damage in the acute stage of ischa emic stroke would be useful for prognosis and in assessing the efficacy of therapeutic manoeuvres in impeding extension of infarction, From our databa se of 30 patients studied with O-15-PET within 5-18 h after onset of first- ever middle cerebral artery territory stroke, we extracted a subgroup of 19 survivors (age 74.6 +/- 8,5 years) in whom late CT coregistered with PET w as available to determine final infarct topography, By means of a voxel-bas ed analysis of the PET data, we determined putative thresholds for irrevers ible tissue damage as the lower limit of the 95% confidence interval calcul ated from all voxels within the ultimately noninfarcted brain parenchyma ip silateral to the insult, The following values were found: 8.43 ml/100 ml/mi n, 0.87 ml/100 ml/min, 1.64 ml/100 mi, 0.27 and 2,21/min, for cerebral bloo d flow (CBF), oxygen consumption (CMRO2), blood volume (CBV), oxygen extrac tion fraction and the ratio CBF:CBV, respectively, Voxels below these thres holds occurred significantly more frequently in the final infarct region th an in the noninfarcted parenchyma for CBF and CMRO2 (P = 0.016 and P = 0,00 45, respectively, Wilcoxon test), but not for the other PET variables, Furt hermore, with both CBF and CMRO2, the percentage of irreversible tissue dam age voxels in the affected hemisphere relative to the opposite hemisphere w as significantly positively correlated to both the volume of final infarct and the neurological outcome at 2 months tall P < 0,005, Spearman ranked te st), These findings validate our voxel-based CBF and CMRO2 thresholds for p robabilistic mapping of irreversible tissue damage within the 5-18 h interv al after stroke onset; however, whether they would be applicable to earlier intervals remains to be determined, Transfer of our procedure for determin ation of irreversible tissue damage thresholds to other imaging modalities such as single proton emission computed tomography and diffusion-weighted M RT should be straightforward.