31P-MRS and simultaneous quantification of dynamic human quadriceps exercise in a whole body MR scanner.

An ergometer for dynamic quadriceps exercise in a magnetic resonance (MR) scanner is physiologically validated, and its technical aspects are presented. The reproducibility of heart rate (HR), O2 consumption (VO2), and power (P) during two graded exercises on the MR ergometer was good (n = 8). Graded exercises on the MR ergometer and on a cycle ergometer (n = 17) were similar with respect to the regression lines between 1) HR and VO2 and 2) HR and P; also peak P did not differ significantly (280 +/- 37 and 298 +/- 41 W, respectively). Peak HR (171 +/- 14 and 184 +/- 15 beats/min, respectively), peak VO2 (3.00 +/- 0.51 and 3.54 +/- 0.44 l/min, respectively), and the slope of the regression line between P and VO2 were lower for MR exercise (P < 0.01). During quadriceps exercise in an MR scanner (n = 12), peak P was 64-143 W for the right leg, with corresponding inorganic phosphate-to-phosphocreatine ratios of 0.85-7.2. It is concluded that continuous noninvasive assessment of energy metabolism with 31P-MR spectroscopy and quantification of power output can be performed simultaneously during dynamic quadriceps exercise, without major reduction of the spectral resolution or the signal-to-noise ratio, and that exercise on this MR ergometer currently is the best possible approximation of cycling exercise for MR purposes.