In vivo characterization of the liver fat ¹H MR spectrum

A theoretical triglyceride model was developed for in vivo human liver fat ¹H MRS characterization, using the number of double bonds (-CH=CH-), number of methylene-interrupted double bonds (-CH=CH-CH ₂-CH=CH-) and average fatty acid chain length. Five 3 T, single-voxel, stimulated echo acquisition mode spectra (STEAM) were acquired consecutively at progressively longer TEs in a fat-water emulsion phantom and in 121 human subjects with known or suspected nonalcoholic fatty liver disease. T ₂-corrected peak areas were calculated. Phantom data were used to validate the model. Human data were used in the model to determine the complete liver fat spectrum. In the fat-water emulsion phantom, the spectrum predicted by the model (based on known fatty acid chain distribution) agreed closely with spectroscopic measurement. In human subjects, areas of CH ₂ peaks at 2.1 and 1.3ppm were linearly correlated (slope, 0.172; r=0.991), as were the 0.9ppm CH ₃ and 1.3ppm CH ₂ peaks (slope, 0.125; r=0.989). The 2.75ppm CH ₂ peak represented 0.6% of the total fat signal in high-liver-fat subjects. These values predict that 8.6% of the total fat signal overlies the water peak. The triglyceride model can characterize human liver fat spectra. This allows more accurate determination of liver fat fraction from MRI and MRS.