Validation of magnetic resonance imaging-derived venous oxygen saturation and oxygen consumption measurements during exercise

Accurate measurement of venous oxygen saturation ([Formula: see text]) is fundamental for quantifying oxygen consumption (V̇o₂) and its Fick determinants. This study evaluated the validity of a novel magnetic resonance imaging (MRI) approach using susceptometry-based oximetry (SBO) to noninvasively measure [Formula: see text] during exercise. First, [Formula: see text] was measured from an antecubital vein in 14 adults (26 ± 5 yr; 8 males) via portable blood analyzer (iSTAT) at rest and during two 5-min bouts of rhythmic handgrip exercise at 30% of maximum voluntary contraction, with temporally matched SBO measures of [Formula: see text] during an identical in-scanner exercise protocol. Separately, 21 adults (27 ± 6 yr; 8 males) completed incremental step ergometry exercise with simultaneous pulmonary V̇o₂ measurement (indirect calorimetry) and MRI-derived V̇o₂ from the Fick determinants (MRI_Fick), including inferior vena cava [Formula: see text] (SBO) and cardiac output (cardiac MRI). Agreement between methods was assessed by interclass correlation coefficients (ICCs), linear regression, and Bland-Altman plots. There was good to excellent agreement between iSTAT and SBO [Formula: see text] for arm exercise (ICC: 0.86, 95% CI: 0.71-0.93, <i>P</i> < 0.01; mean bias: +5.2%). Test-retest reliability demonstrated excellent agreement for [Formula: see text] measures between trials using iSTAT (ICC: 0.97; 95% CI: 0.93-0.96, <i>P</i> < 0.01; mean bias: -2.7%) and SBO (ICC: 0.90, 95% CI: 0.80-0.95, <i>P</i> < 0.01; mean bias: -0.3%), V̇o₂ calculated from MRI_Fick demonstrated excellent agreement with pulmonary V̇o₂ (ICC: 0.98, 95% CI: 0.97-0.99, <i>P</i> < 0.01; mean bias: +0.10 L/min). MRI-SBO-derived [Formula: see text] measurements demonstrated excellent reliability and strong agreement with both venous measures and respiratory gas analysis, validating this technique across a wide range of [Formula: see text] values during exercise.<b>NEW & NOTEWORTHY</b> Noninvasive MRI susceptometry-based [Formula: see text] measurements demonstrated excellent repeatability and validity against established direct blood sampling during localized handgrip exercise. The technique's accuracy for determining V̇o₂ during step ergometer exercise was validated through strong agreement between combined cardiac MRI and susceptometry-based Fick calculations and reference pulmonary measures, establishing this method as a reliable tool for noninvasive assessment of oxygen uptake and its Fick determinants across varying exercise intensities.