Lineshapes in phase-encoded spectroscopic imaging experiments

Two procedures for recording spectroscopic images with pure absorption mode lineshapes using phase-encoding pulsed field gradients are discussed and compared experimentally. Using a small phantom sample, both methods are shown to give significant improvements compared to the conventional absolute value display. It is found that the method based on the use of a symmetric data set is preferable to that based on a reversed precession experiment. To demonstrate its applicability to in vivo³¹P NMR, a surface coil placed over the scalp of a rabbit was used to record a one-dimensional phase-encoded spectrum. While the absolute value display of this data set contains overlap between the low-field ATP and the phosphocreatine resonances, these signals are completely resolved in the phase-sensitive spectrum.