Feasibility and reproducibility of measurement of whole muscle blood flow, oxygen extraction, and VO2 with dynamic exercise using MRI.

PURPOSE Develop an MRI method to estimate skeletal muscle oxygen consumption (VO2 ) with dynamic exercise using simultaneous measurement of venous blood flow (VBF) and venous oxygen saturation (SvO2 ). METHODS Real-time imaging of femoral VBF using a complex-difference method was interleaved with imaging of venous hemoglobin oxygen saturation (SvO2 ) using magnetic susceptometry to estimate muscle VO2 (Fick principle). Nine healthy subjects performed repeated 5-watt knee-extension (quadriceps) exercise within the bore of a 1.5 Tesla MRI scanner, for test/re-test comparison. VBF, SvO2 , and derived VO2 were estimated at baseline and immediately (<1 s) postexercise and every 2.4 s for 4 min. RESULTS Quadriceps muscle mass was 2.43 ± 0.31 kg. Mean baseline values were VBF = 0.13 ± 0.06 L/min/kg, SvO2 = 69.4 ± 10.1%, and VO2 = 6.8 ± 4.1 mL/min/kg. VBF, SvO2 , and VO2 values from peak exercise had good agreement between trials (VBF = 0.9 ± 0.1 versus 1.0 ± 0.1 L/min/kg, R(2) = 0.83, CV = 7.6%; SvO2 = 43.2 ± 13.5 versus 40.9 ± 13.1%, R(2) = 0.88, CV = 15.6%; VO2 = 95.7 ± 18.0 versus 108.9 ± 17.3 mL/min/kg, R(2) = 0.88, CV = 12.3%), as did the VO2 recovery time constant (26.1 ± 3.5 versus 26.0 ± 4.0 s, R(2) = 0.85, CV = 6.0%). CV = coefficient of variation. CONCLUSION Rapid imaging of VBF and SvO2 for the estimation of whole muscle VO2 is compatible with dynamic exercise for the estimation of peak values and recovery dynamics following exercise with good reproducibility.