Paramagnetic susceptibility versus QSM for estimating OEF: A comparative study in cerebral small vessel disease

The oxygen extraction fraction (OEF) is a key parameter of cerebral metabolism and a potential biomarker for cerebral small vessel disease (SVD). Quantitative susceptibility mapping (QSM) allows non-invasive OEF mapping but is confounded by the opposing magnetic susceptibilities of deoxyhemoglobin and oxyhemoglobin. We evaluated a novel method that separates the paramagnetic susceptibility component for OEF estimation and compared it with conventional QSM in SVD patients and healthy controls (HC).

27 SVD patients and 23 HC underwent multi-echo GRE MRI for QSM reconstruction. The paramagnetic susceptibility was separated using APART-QSM. The straight sinus (SS) and superior sagittal sinus (SSS) were segmented for regional OEF calculation using both conventional QSM and paramagnetic susceptibility. Statistical comparisons were performed using Welch's t-test.

Paramagnetic susceptibility was significantly higher than total QSM (p < 0.05), while OEF derived from paramagnetic susceptibility was significantly lower (p < 0.05). OEF values derived from paramagnetic susceptibility (HC: 22.5 ± 4.8% in SS, 19.3 ± 4.6% in SSS; SVD: 23.4 ± 5.1% in SS, 19.0 ± 4.5% in SSS) were significantly lower (p < 0.05) than those obtained via conventional QSM (HC: 29.0 ± 3.5% in SS, 26.8 ± 3.3% in SSS; SVD: 29.8 ± 3.8% in SS, 26.5 ± 3.2% in SSS). No significant OEF differences were found between HC and SVD cohorts in the analyzed venous regions.

This study demonstrates the feasibility of separating the paramagnetic susceptibility component via APART-QSM for quantitative OEF estimation. While the derived OEF values were lower than those from conventional QSM, the method theoretically offers improved specificity by disentangling deoxygenation-driven susceptibility from diamagnetic confounds, highlighting its potential as a refined biomarker for cerebral oxygen metabolism subject to further optimization.