Quantitative ¹H MRI and MRS of fatty acid composition

Abstract

Adipose tissue as well as other depots of fat (triglycerides) are increasingly being recognized as active contributors to the human function and metabolism. In addition to the fat concentration, also the fatty acid chemical composition (FAC) of the triglyceride molecules may play an important part in diseases such as obesity, insulin resistance, hepatic steatosis, osteoporosis, and cancer. MR spectroscopy and chemical-shift-encoded imaging (CSE-MRI) are established methods for non-invasive quantification of fat concentration in tissue. More recently, similar techniques have been developed for assessment also of the FAC in terms of the number of double bonds, the fraction of saturated, monounsaturated, and polyunsaturated fatty acids, or semi-quantitative unsaturation indices. The number of papers focusing on especially CSE-MRI-based techniques has steadily increased during the past few years, introducing a range of acquisition protocols and reconstruction algorithms. However, a number of potential sources of bias have also been identified. Furthermore, the measures used to characterize the FAC using both MRI and MRS differ, making comparisons between different techniques difficult. The aim of this paper is to review MRS-and MRI-based methods for in vivo quantification of the FAC. We describe the chemical composition of triglycerides and discuss various potential FAC measures. Furthermore, we review acquisition and reconstruction methodology and finally, some existing and potential applications are summarized. We conclude that both MRI and MRS provide feasible non-invasive alternatives to the gold standard gas chromatography for in vivo measurements of the FAC. Although both are associated with gas chromatography, future studies are warranted.

High-fructose feeding suppresses cold-stimulated brown adipose tissue glucose uptake in young men independently of changes in thermogenesis and the gut microbiome

“…Correction for T1 and T2 decay was performed for each resonance. For T1, data from the literature was used (Hamilton et al, 2011; Peterson et al, 2021). For T2, correction was based on the multi-echo data for the liver and on the literature for BAT and scWAT (Hamilton et al, 2011; Peterson et al, 2021).…”

Magnetic Resonance Spectroscopy of Hepatic Fat from Fundamental to Clinical Applications

“…It has been suggested that the degree of saturation of liver lipids may be associated with liver fat accumulation on hepatocellular damage and disease progression [ 99 , 101 ]. Each peak of lipid spectra reflects the different chemical positions within the triglyceride molecule, including unsaturated, saturated, monounsaturated, and polyunsaturated fatty acids [ 102 ]. The fatty acid composition quantification obtained from MRS has also shown good agreement with other MRI-based methods [ 103 , 104 ].…”

The role of hepatic lipid composition in obesity‐related metabolic disease

“…91 The theoretical basis for 1 H-MRS is underpinned by the 'chemical shift' effect whereby, when placed in a strong magnetic field, hydrogen protons within water molecules and hydrocarbon fatty acid chains resonate at different frequencies based on their surrounding chemical milieu (Figure 2A). 90 By irradiating these molecules with a radio frequency field, protons are excited and subsequently emit a signal at specific frequencies. Consequently, in a typical liver MR spectrum, water forms a large spectral peak, whilst six smaller lipid peaks are formed owing to different functional groups within a fatty acid chain (Figure 2B).…”