Abstract 2636: Magnetic Resonance Oxygen Metabolic Index Distinguishes infarct from peri-infarct tissue better than ADC and PWI In hyperacute ischemic Stroke Patients
Background: Diffusion (DWI) and perfusion weighted imaging (PWI) have been extensively studied to delineate irreversibly-injured tissue (that will progress to infarct) from reversibly-injured tissue (that will remain viable). An MR-based method, oxygen metabolism index (MROMI), may provide relevant metabolic information critical for determining tissue viability. We compared the ability of hyperacute MROMI, mean transit time (MTT), and apparent diffusion coefficient (ADC) to distinguish brain tissue that infarcted one month later from an initially hypoperfused region that survived, and contralateral mirror brain regions.
Methods: Ischemic stroke patients were imaged at <4.5hr and at 1 month after stroke onset. Dynamic susceptibility contrast method measured cerebral blood flow (CBF) and MTT. An asymmetric spin echo sequence measured oxygen extraction fraction (OEF). MROMI=CBF x OEF. Co-registration and segmentation aligned images and separated gray from white matter, respectively. Hypoperfusion was defined as tissue with MTT > 4sec + the contralateral median MTT. Three ROIs were defined: (1) ROIInfarct (final infarct as manually outlined on the 1month FLAIR); (2) ROIPeri (acutely hypoperfused, but not included in the final infarct); and (3) ROIMirror (the contralateral mirror region of the ROIInfarct. Each patient’s ROIs were normalized (n) to the contralateral hemisphere as follows: nMTT= MTT-contralateral median MTT, nADC= ADC/contralateral median ADC, and nMROMI=MROMI/contralateral median MROMI. nMROMI was calculated in gray and white matter separately. The 3 ROI’s were compared for nMROMI, nMTT and nADC using the Kruskal-Wallis test with Dunn’s post-tests.
Results: 25 patients were imaged at 2.9 ± 0.7 hrs and 1 month after stroke onset. Mean values for nMTT, nADC, and nMR-OMI were obtained for the 3 ROI’s (ROIInfarct ROIPeri and ROIMirror) for each patient. Significant differences were found between ROIInfarct and ROIMirror (P<0.001) for all three parameters (nMTT, nADC and nMROMI). However, only nMROMI demonstrated a significant difference between ROIInfarct and ROIMirror (P<0.05) (Figure). Both nMTT and nADC values in ROIInfarct varied greatly across patients and no significant differences between ROIInfarct and ROIPeri were found.
Conclusions: Identifying tissue that would die from hypoperfused but survived tissue is challenging during acute ischemia. Our results have demonstrated that hyperacute MROMI show significant differences between these two regions, while MTT and ADC did not, likely due to high inter-individual variability using the latter parameters.
- © 2012 by American Heart Association, Inc.