QUANTIFICATION OF PHOSPHORUS METABOLITES FROM CHEMICAL-SHIFT IMAGING SPECTRA WITH CORRECTIONS FOR POINT-SPREAD EFFECTS AND B-1 INHOMOGENEITY

A method is described for quantifying phosphorus metabolites in tissue using spectra localized with surface coils and chemical shift imaging (CSI) and assuming that metabolites are uniformly distributed within a well-defined volume, An analytical expression is developed that yiel ds a single numerical correction factor that takes into account the ex citation and receiver profiles of the coil, T-1 saturation, and point spread effects associated with Fourier transformation of CSI data, An external phosphorus standard is used to calibrate instrument gain and the B-1 profile of the coil. For spherical samples, point spread effec ts can modulate the signal intensities of three-dimensional CSI spectr a from -32% to +54%, depending on the voxel size. Measurements of phan toms of known concentrations showed systematic variations of +/- 10% a nd random errors of +/- 5%. We have used this method to measure the co ncentration of phosphocreatine in the thigh muscle of normal volunteer s.