Can we use 1H MRS shimming values to obtain 31P spectra?

Abstract

The perfect shimming of 31P magnetic resonance spectroscopy (MRS) is not easy in vivo. The purpose of this study was to examine the feasibility of using 1H MRS shimming values to obtain 31P spectra in a same sequence. Both phantom and volunteer studies were carried out in this study. Phantom was a sphere filled with physiological metabolites of brain. In vivo study was performed on 4 healthy volunteers. The studies were performed on a 3-T GE scanner. A same localizer and a same cursor were used for both 1H and 31P scans. A spin echo MRS sequence was utilized for both 1H scans with a standard head coil and 31P scans with a GE service coil. 1H scan was performed using first and automatic shimming and water linewidth (FWHM) of 3 Hz for phantom and 5 Hz for the volunteer were obtained. Shimming values of 1H scan in x, y, z directions were copied to 31P scan. A routine procedure of 31P scan without value coping was also performed. Spectra were analyzed using SAGE/IDL program. Signal to noise ratio (SNR) was defined as the ratio of the signal height / maximum noise height. Good 1H spectra and 31P spectra were obtained for both phantom and volunteer studies. The 31P spectra with 1H MRS shimming values were similar with the 31P spectra obtained with routine procedure. Lower SNRs of 31P spectra were obtained in phantom with 1H MRS shimming values, compared with routine procedure scan. Average SNR for Pi of 31P spectra was 7.45:1 in the volunteer study with routine procedure, and 7.275:1 with 1H MRS shimming values. 1H MRS shimming values can be used to obtain useful 31P spectra in a same sequence.