NMR SPECTRAL QUANTITATION BY PRINCIPAL-COMPONENT ANALYSIS .2. DETERMINATION OF FREQUENCY AND PHASE-SHIFTS

This paper extends the use of principal-component analysis in spectral quantification to the estimation of frequency and phase shifts in a s ingle resonant peak across a series of spectra. The estimated paramete rs can be used to correct the spectra accordingly, resulting in more a ccurate peak-area estimation. Further, the removal of the variations i n phase and frequency caused by instrumental and experimental fluctuat ions makes it possible to determine more accurately the remaining vari ations, which bear biological significance. The procedure is demonstra ted on simulated data, a 3D chemical-shift-imaging dataset acquired fr om a cylinder of inorganic phosphate (P-i), and a set of 736 P-31 NMR in vivo spectra taken from a kinetic study of rat muscle energetics. I n all cases, the procedure rapidly and automatically identifies the fr equency and phase shifts present in the individual spectra. In the kin etic study, the procedure is used twice, first to adjust the phase and frequency of a reference peak (phosphocreatine) and then to determine the individual frequencies of the P-i peak in each of the spectra whi ch further can be used for estimation of pH changes during the experim ent. (C) 1996 Academic Press, Inc.