On neglecting chemical exchange when correcting in vivo P-31 MRS data for partial saturation: Commentary on: "Pitfalls in the measurement of metabolite concentrations using the one-pulse experiment in in vivo NMR

This article replies to Spencer et al, (J, Magn, Resan, 149, 251-257, 2001) concerning the degree to which chemical exchange affects partial saturatio n corrections using saturation factors. Considering the important case of i n vivo P-31 NMR, we employ differential analysis to demonstrate a broad ran ge of experimental conditions over which chemical exchange minimally affect s saturation factors, and near-optimum signal-to-noise ratio is preserved, The analysis contradicts Spencer et at's broad claim that chemical exchange results in a strong dependence of saturation factors upon M-0's and T-1 an d exchange parameters, For Spencer et al.'s example of a dynamic P-31 NMR e xperiment in which phosphocreatine varies 20-fold, we show that our strateg y of measuring saturation factors at the start and end of the study reduces errors in saturation corrections to 2% for the high-energy phosphates, (C) 2001 Academic Press.