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

Abstract

Longitudinal (T 1 ) relaxation of triglyceride molecules and water is of interest for fatwater separation and fat quantification. A better understanding of T 1 relaxation could benefit modeling for applications in fat quantification and relaxation mapping. This work investigated T 1 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). T 1 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. T 1 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 T 1 of water and of all fat resonances studied in this work decreased as the fat fraction increased. The relative variation in T 1 was different for each fat resonance. The T 1 of the methylene resonance showed the least variation as a function of the fat fraction. The proposed two-component model closely fits the observed T 1 variations. In conclusion, this work clarifies how the T 1 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 fatwater mixtures, and phantom preparation.