Abstract
MRI-based oxygen extraction fraction imaging has a great potential benefit in the selection of clinical strategies for ischemic stroke patients. This study aimed to evaluate the performance of a challenge-free oxygen extraction fraction (OEF) mapping in a cohort of acute and subacute ischemic stroke patients. Consecutive ischemic stroke patients (a total of 30 with 5 in the acute stage, 19 in the early subacute stage, and 6 in the late subacute stage) were recruited. All subjects underwent MRI including multi-echo gradient echo (mGRE), diffusion weighted imaging (DWI), and 3D-arterial spin labeling (ASL). OEF maps were generated from mGRE phase + magnitude data, which were processed using quantitative susceptibility mapping (QSM) + quantitative blood oxygen level-dependent (qBOLD) imaging with cluster analysis of time evolution. Cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) maps were reconstructed from 3D-ASL and DWI, respectively. Further, cerebral metabolic rate of oxygen (CMRO2) was calculated as the product of CBF and OEF. OEF, CMRO2, CBF, and ADC values in the ischemic cores (absolute values) and their contrasts to the contralateral regions (relative values) were evaluated. One-way analysis of variance (ANOVA) was used to compare OEF, CMRO2, CBF, and ADC values and their relative values among different stroke stages. The OEF value of infarct core showed a trend of decrease from acute, to early subacute, and to late subacute stages of ischemic stroke. Significant differences among the three stroke stages were only observed in the absolute OEF (F = 6.046, p = 0.005) and relative OEF (F = 5.699, p = 0.009) values of the ischemic core, but not in other measurements (absolute and relative CMRO2, CBF, ADC values, all values of p > 0.05). In conclusion, the challenge-free QSM + qBOLD-generated OEF mapping can be performed on stroke patients. It can provide more information on tissue viability that was not available with CBF and ADC and, thus, may help to better manage ischemic stroke patients.
Highlights
MRI-based oxygen extraction fraction imaging has a great potential benefit in the selection of clinical strategies for ischemic stroke patients
A total of 30 consecutive patients with ischemic stroke from January 2014 to January 2015 were recruited according to the following inclusion criteria: (1) the time interval between stroke onset and MRI examination was quantifiable and ranged between 6 h and 15 days; (2) ischemic lesion caused by the stenosis or occlusion of the middle cerebral artery; (3) MRI scan protocol included 3D multi-echo gradient echo (mGRE) and 3D-arterial spin labeling (ASL), in addition to conventional T1 weighted (T1w), T2 weighted (T2w), T2w FLAIR, and diffusion weighted imaging (DWI) sequences; (4) patients did not receive therapy of intravenous thrombolysis or mechanical thrombectomy before the MRI scan; and (5) patients did not show hemorrhage transformation in subsequent MRI scans
Our preliminary results demonstrate that challenge-free oxygen extraction fraction (OEF) mapping can be performed in a clinical setting
Summary
MRI-based oxygen extraction fraction imaging has a great potential benefit in the selection of clinical strategies for ischemic stroke patients. OEF maps were generated from mGRE phase + magnitude data, which were processed using quantitative susceptibility mapping (QSM) + quantitative blood oxygen level-dependent (qBOLD) imaging with cluster analysis of time evolution. The challenge-free QSM + qBOLD-generated OEF mapping can be performed on stroke patients It can provide more information on tissue viability that was not available with CBF and ADC and, may help to better manage ischemic stroke patients. OEF mapping can be achieved by combining QSM processing of phase and quantitative blood oxygen level-dependent (qBOLD) modeling of magnitude (Ogawa et al, 1990; Yablonskiy and Haacke, 1994b) of mGRE data without any vascular challenge administration (Cho et al, 2018, 2020), making it ready for routine use in imaging acute ischemic patients. When 3D OEF is multiplied by cerebral blood flow (CBF) from 3D arterial spin labeling (ASL) images, CMRO2 can be generated from MRI examinations
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