Quantification of Fatty Acid Composition Using MRI: Comparison of Accuracy at 1.5, 3 and 7 T

Abstract: The increasing prevalence of obesity and obesity related diseases in this modern world has resulted in a lot of research in the area of water-fat separation with magnetic resonance imaging (MRI). Since the introduction of the two-point Dixon technique, this area of research has expanded and relationships have been discovered between fat content and fatty acid (FA) composition, and diseases such as diabetes and non-alcoholic fatty liver disease. In this work, an image-based method to quantify fat content and FA composition using MRI has been investigated at three different field strengths (1.5, 3 and 7 T). The aim was to explore the potential advantages associated with increased spectral resolution gained at higher field strengths, such as more accurate estimations of FA composition. The method is based on a concept of describing the FA composition in terms of chain length (cl), number of double bonds (ndb) and number of methylene interrupted double bonds (nmidb), originally published for use in magnetic resonance spectroscopy (MRS). Both phantom and in vivo experiments were performed. In both studies, MRS measurements were carried out for validation of the method. In addition, values of the FA composition obtained from the Swedish National Food Administration were also used as reference in the phantom study. The in vivo experiment was carried out on subcutaneous adipose tissue in the calf of a volunteer. Comparing the estimated parameters at all field strength with values obtained from MRS or the values from the Swedish National Food Administration, the accuracy of the estimations seem to increase at higher field strengths. The main drawback of the study was that the acquired images of the phantom at 7 T were not evaluable due to large field inhomogeneity. When comparing the estimations of the FA composition in vivo to the values obtained using MRS, the estimation at 1.5 T was the least accurate and the estimations at 7 T somewhat more accurate than the ones obtained at 3 T. Even though the results indicate better accuracy, additional research is needed to investigate the benefits in using higher field strengths.