The Effect of Nuclear Overhauser Enhancement in Liver and Heart 31P NMR Spectra Localized by 2D Chemical Shift Technique

ABSTRACT

PURPOSE: To investigate the signal enhancement ratio by NOE effect on in vivo 31P MRS in human heart muscle and liver. we also evaluated the enhancement ratios of different phosphorus metabolites, which are important in 31P MRS for each organ. MATERIALS AND METHODS: Ten normal subjects (M: F = 8: 2, age range = 24-32 yrs) were included for in vivo 31P MRS measurements on a 1.5 T whole-body MRI/MRS system using 1H-31P dual tuned surface coil. Two-dimensional Chemical Shift Imaging (2D CSI) pulse sequence for 31P MRS was employed in all 31P MRS measurements. First, 31P MRS performed without NOE effect and then the same 2D CSI data acquisitions were repeated with NOE effect. After postprocessing the MRS raw data in the time domain, the signal enhancements in percent were estimated from the major metabolites. RESULTS: The calculated NOE enhancement for liver 31P MRS were: alpha-ATP (7%), beta- ATP (9%), gamma-ATP (17%), Pi (1%), PDE (19%), and PME (31%). Because there is no creatine kinase activity in liver, PCr signal is absent. For cardiac 31P MRS, whole body coil gave better scout images and thus better localization than surface coil. In 31P cardiac multi-voxel spectra, DPG signal increased from left to right according to the amount of blood included. The calculated enhancement for cardiac 31P MRS were: alpha -ATP (12%), beta-ATP (19%), gamma-ATP (30%), PCr (34%), Pi (20%), PDE (51%), and DPG (72%). CONCLUSION: Our results revealed that the NOE effect was more pronounced in heart muscle than in liver with different coupling to 1H spin system and thus different heteronuclear cross-relaxation.