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 (MRIFick), 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, P < 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, P < 0.01; mean bias: -2.7%) and SBO (ICC: 0.90, 95% CI: 0.80-0.95, P < 0.01; mean bias: -0.3%), V̇o2 calculated from MRIFick demonstrated excellent agreement with pulmonary V̇o2 (ICC: 0.98, 95% CI: 0.97-0.99, P < 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.NEW & NOTEWORTHY 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.