Triglyceride Saturation in Patients at Risk of NASH and NAFLD: A Cross-Sectional Study

Mark Bydder,Rohit Loomba,Jessica Lam,Roxana Chavarria,Claude Sirlin,Gavin Hamilton,Nick Pinto,Tanya Chavez,Walter Henderson,Alex D Pham,Jeff Schwimmer

doi:10.3390/biophysica2010002

Mark Bydder, Rohit Loomba + Show 9 more

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https://doi.org/10.3390/biophysica2010002

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Abstract

Chemical shift magnetic resonance imaging (MRI) is commonly used to estimate the amount of fat in tissues, namely the proton density fat fraction (PDFF). In addition to PDFF, the type of fat can be inferred and characterized in terms of the number of double bonds (NDB), number of methylene-interrupted double bonds (NMIDB) and the chain length (CL) of the fatty acid chains. The saturation index is potentially a marker for metabolic disorders. This study assesses the feasibility of estimating these parameters independently or in a constrained manner. Correlations with spectroscopy were measured in 109 subjects’ subcutaneous and visceral fat depots (p = 2 × 10−28), and with the NAFLD Activity Score (NAS) from histological evaluation of biopsies. The findings indicate that imaging estimates are comparable to spectroscopy (p = 0.0002), but there is no significant association of NDB with NAS (p = 0.1).

Highlights

Chemical shift encoded magnetic resonance imaging (CSE-MRI) techniques for separating water and fat exploit differences in the precession frequencies of water and fat protons [1,2]
Several magnetic resonance spectroscopy (MRS) studies have used the dependance of the fat spectrum on triglyceride type to estimate triglyceride composition (TC) in terms of one of two interchangeable characterizations; either saturated, monounsaturated and diunsaturated fat fractions [8,10], or the number of -CH =CHdouble bonds per molecule (NDB), the number of double bonds separated by a single -CH2 (NMIDB; number of methylene-interrupted double bonds), and fatty-acid chain length (CL) [9,11,12]
If the fat spectrum used for proton density fat fraction (PDFF) estimation is not fixed but is allowed to vary in a fashion dependent on the type of fat, CSE-MRI can estimate TC [13,14]

Summary

Introduction

Chemical shift encoded magnetic resonance imaging (CSE-MRI) techniques for separating water and fat exploit differences in the precession frequencies of water and fat protons [1,2]. Standard CSE-MRI techniques estimating PDFF are not able to assess TC because they assume a predetermined triglyceride spectrum [1,2]. Several magnetic resonance spectroscopy (MRS) studies have used the dependance of the fat spectrum on triglyceride type to estimate TC in terms of one of two interchangeable characterizations; either saturated, monounsaturated and diunsaturated fat fractions [8,10], or the number of -CH =CHdouble bonds per molecule (NDB), the number of double bonds separated by a single -CH2 (NMIDB; number of methylene-interrupted double bonds), and fatty-acid chain length (CL) [9,11,12]. If the fat spectrum used for PDFF estimation is not fixed but is allowed to vary in a fashion dependent on the type of fat, CSE-MRI can estimate TC [13,14]

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