Longitudinal relaxation in fat‐water mixtures and its dependence on fat content at 3 T

Longitudinal (T1) relaxation of triglyceride molecules and water is of interest for fat‐water separation and fat quantification. A better understanding of T1 relaxation could benefit modeling for applications in fat quantification and relaxation mapping. This work investigated T1 relaxation of spectral resonances of triglyceride molecules and water in liquid fat‐water mixtures and its dependence on the fat fraction. Dairy cream and a safflower oil emulsion were used. These were diluted with distilled water to produce a variety of fat mass fractions (4.4% to 35% in dairy cream and 6.3% to 52.3% in safflower oil emulsion). T1 was measured at room temperature at 3 T using an inversion recovery STimulated Echo Acquisition Mode (STEAM) MR spectroscopy method with a series of inversion times. T1 variations as a function of fat fraction were investigated for various resonances. A two‐component model was developed to describe the relaxation in a fat‐water mixture as a function of the fat fraction. The T1 of water and of all fat resonances studied in this work decreased as the fat fraction increased. The relative variation in T1 was different for each fat resonance. The T1 of the methylene resonance showed the least variation as a function of the fat fraction. The proposed two‐component model closely fits the observed T1 variations. In conclusion, this work clarifies how the T1 of major and minor fat resonances and of the water resonance varies as a function of the fat fraction in fat‐water mixtures. Knowledge of these variations could serve modeling, analysis of MRI measurements in fat‐water mixtures, and phantom preparation. A detailed understanding of fat T1 relaxation in fat‐water mixture is valuable for applications in fat quantification and relaxation mapping. The T1 of major and minor fat resonances of fat molecules was shown to decrease as a function of the fat fraction. Water T1 also decreased with fat fraction.