Benchmarking transverse spin relaxation based oxygenation measurements in the brain during hypercapnia and hypoxia

Purpose To simultaneously assess reproducibility of three MRI transverse relaxation parameters (R 2 ′ ,R 2 * , and R 2 ) for brain tissue oxygenation mapping and to assess changes in these parameters with inhalation of gases that increase and decrease oxygenation, to identify the most sensitive parameter for imaging brain oxygenation. Materials and Methods Forty‐eight healthy subjects (25 male, ages 35 ± 8 years) were scanned at 3.0 Tesla, each with one of four gases (mildly and strongly hypercapnic and hypoxic) administered in a challenge paradigm, using a gas delivery setup designed for patient use. Cerebral blood flow mapping with arterial spin labeling, and simultaneousR 2 ′ ,R 2 * , and R 2 mapping with gradient‐echo sampling of free induction decay and echo (GESFIDE) were performed. Reproducibility in air and gas‐induced changes were evaluated using nonparametric analysis with correction for multiple comparisons. Results Our gas delivery setup achieved stable gas challenges as shown by physiological monitoring. Test–retest variability ofR 2 ′ ,R 2 * , and R 2 were found to be 0.24 s −1 (8.6% of mean), 0.24 s −1 (1.3% of mean), and 0.15 s −1 (1.0% of mean), respectively. Strong hypoxia produced the most conclusive oxygenation‐driven relaxation change, inducing increases inR 2 ′(25 ± 13%, P  = 0.03),R 2 *(5 ± 2%, P  = 0.02), and R 2 (2 ± 2%, NS). Conclusion We benchmarked the intra‐scan test–retest variability in GESFIDE‐based transverse relaxation rate mapping. Using a reliable framework for gas challenge paradigms, we recommend strong hypoxia for validating oxygenation mapping methods, and the use of tissueR 2 ′change, instead ofR 2 *or R 2 , as a metric for studying brain tissue oxygenation using transverse relaxation methods. Level of Evidence: 1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:704–714