T1 measurement of 31P metabolites at rest and during steady-state dynamic exercise using a clinical nuclear magnetic resonance scanner

This article illustrates some problems and possible solutions to determine the apparent spin-lattice relaxation time (T-1) of the muscular P-31 metabolites at rest and during dynamic steady-state exercise using a clinical 1.5 T NMR scanner and a surface coil. T-1 was first estimated on a phosphates solution (phantom) using four different acquisition protocols, all based on the multiple-point progressive saturation method, and by fitting each data set with two different mathematical models. Subsequently, two of the four protocols and both models were used to estimate T-1 both at rest and during exercise on the calf muscles of 10 healthy volunteers. Experimental results obtained on the phantom showed that T-1 is greatly affected by the longest nominal explored repetition time (P < 0.001) and by the mathematical model (P < 0.001), ranging from 0.65 +/- 0.10 to 8.4 +/- 0.8 s. The two acquisition protocols applied on volunteers yielded significantly different T-1 (P < 0.001), which were also rather different from the literature values for the same metabolites. Nevertheless, independently of the acquisition protocol and/or the fitting procedure, T-1 of all muscular phosphagens did not change statistically from rest to steady-state aerobic exercise.