Table 1.

Basis of fat quantification, advantages, disadvantages, and typical applications for T₁-weighted MRI, T₂-weighted MRI, frequency-selective MRI, spectroscopy, and water-fat MRI techniques in fat quantification.

Technique	Basis of Water and Fat Signal Differentiation	Basis of Tissue Signal Contrast	Dimensionality and Typical Pulse Sequence Implementation	Advantages	Disadvantages	Typical Quantitative Endpoints
T1-Weighted MRI	T1 longitudinal relaxation	Fat is brighter than water (lean tissue)	2D multi-slice 3D volumetric Spin echo and gradient echo based	• Available on all scanners • Strong water-fat tissue signal contrast • Easy to implement • Rapid breath-hold capable scans • Can be coupled with preparation schemes such as inversion recovery • High spatial resolution	• T1 contrast varies with B0 field strength, protocols require TR, TE, flip angle optimization to maximize tissue signal contrast • Partial volume effects • Tissue contrast can be sensitive to RF pulse inhomogeneities and hardware imperfections	Volume of adipose tissue depots e.g. SCAT, VAT, intermuscular adipose tissue, bone marrow Detect presence of fat
T2-Weighted MRI	T2 transverse relaxation	Fat is brighter than water (lean tissue)	2D multi-slice 3D volumetric Spin echo based	• Available on all scanners • Good water-fat tissue signal contrast • Easy to implement • Can be coupled with preparation schemes such as T2-prep • High spatial resolution	• T2 contrast varies with B0 field strength • Partial volume effects • Relatively long scan times • Tissue contrast can be sensitive to RF pulse inhomogeneities and hardware imperfections	Typically not used for adipose tissue depot volumes Detect presence of edema Detect presence of fat Ectopic fat-signal fraction
Frequency-Selective MRI	chemical shift assumes fixed resonance frequency difference between water protons and methylene fat protons	Fat or water is selective excited or suppressed CHEmically Selective Saturation (CHESS) Fat Saturation (FAT-SAT)	2D multi-slice 3D volumetric Spin echo and gradient echo based	• Available on all scanners • Strong water-fat tissue signal contrast via magnetization preparation • Easy to implement • Rapid breath-hold capable scans • Coupled with T1- and T2-weighted sequences to increase tissue contrast • High spatial resolution	• Performance varies with B0 field strength • Artifacts can arise from susceptibility to B0 field inhomogeneity	Volume of adipose tissue depots e.g. SCAT, VAT, intermuscular adipose tissue, bone marrow Detect presence of fat Ectopic fat-signal fraction
Single-voxel Spectroscopy (MRS) Chemical Shift Imaging (CSI)	chemical shift does not assume fixed or known resonance frequency differences between water and fat protons	Water and fat signals are uniquely identified by their chemical shift locations along the frequency spectrum	1D spectrum 2D multi-slice 3D volumetric spectra STEAM PRESS	• Available option on most scanners • High spectral resolution • Robust water-fat signal identification accurate representation of proton moieties • Characterization of mono-, di- and poly- unsaturated triglycerides • Accurate and sensitive measure of fat-signal fraction, especially at low fat content	• Limited coverage in single-voxel MRS approaches • Moderate spatial resolution in CSI • Voxel boundaries less well defined in CSI • Data analysis may require dedicated software • Moderate scan times	Ectopic fat-signal fraction e.g. liver, pancreas, heart Muscle fat-signal fraction and concentration e.g. IMCL, EMCL
Chemical-Shift-Encoded Water-Fat MRI	chemical shift assumes fixed resonance frequency difference between water and fat protons	Water and fat signals are acquired simultaneously and subsequently separated based on chemical-shift-encoding and fat spectrum modeling	2D multi-slice 3D volumetric Spin echo variants typically used for fat suppression Gradient echo variants typically used for fat quantification IDEAL mDIXON DIXON	• Available option on some scanners • Very strong water-fat tissue signal contrast • Robust water-fat tissue identification and separation • Can be an accurate estimate of proton-density fat fraction • Rapid breath-hold capable scans • High spatial resolution • Can also estimate T2* and characterize triglyceride composition (e.g. chain length, number of double bonds, etc.)	• Data reconstruction requires specific algorithms that can be computationally intensive • Requires protocol optimization for different B0 field strengths • Water-fat signal swap artifacts can arise from incorrect B0 field map estimation • Not available on all scanners and from all manufacturers	Volume of adipose tissue depots e.g. SCAT, VAT, intermuscular adipose tissue bone marrow Ectopic fat-signal fraction Relaxometry and noise-corrected proton-density fat fraction