Effect of triglyceride glycerol CH signal on olefinic resonance quantification with proton magnetic resonance spectroscopy at 3 T

Abstract

The in-vivo Magnetic Resonance Spectroscopy (MRS) techniques STimulated Echo Acquisition Mode (STEAM) and Point RESolved Spectroscopy (PRESS) are used to assess fat unsaturation levels in human adipose tissue by measuring the olefinic proton resonance at ≈5.4 ppm. At clinical field strengths, the resonance is overlapped by that of the triglyceride glycerol CH proton at ≈5.2 ppm. In the presented work, olefinic resonance contamination by that of the glycerol CH proton for STEAM and PRESS as a function of echo time (TE) is assessed at 3 T. MRS spectra were acquired from the triglyceride tricaprylin (contains glycerol but no olefinic protons), and from free oleic acid (contains olefinic but no glycerol protons) using STEAM (TE of 20 to 300 ms, mixing time of 20 ms) and PRESS (TE of 40 to 300 ms), with TE increments of 10 ms. Estimated olefinic signal contamination by the glycerol CH resonance was evaluated for short-TE (STEAM with TE of 20 ms and PRESS with TE of 40 ms) for human adipose tissue based on a literature composition and using the spectra acquired for tricaprylin and oleic acid. Contaminations of ≈20% for STEAM with a TE = 20 ms and ≈13% for PRESS with a TE = 40 ms were obtained. Glycerol CH contributions to the olefinic resonance was also estimated for eight oils in a similar manner. High-resolution in-vitro 16.5 T Nuclear Magnetic Resonance (NMR) spectra of the oils suggest that in the absence of significant T2 relaxation and J-coupling effects, 9 to 17% (depending on unsaturated fatty acid content) of the olefinic signal is attributable to the glycerol CH proton. The signal yield responses of the glycerol CH and the olefinic protons as a function of TE indicate that a TE of 90 ms for STEAM and a TE of 200 ms for PRESS are suitable for quantification of the olefinic resonance with minimal impact from the glycerol CH resonance. Signal area yields relative to those obtained with short-TE were 30% and 29% for the olefinic resonance and 4% and 5% for the glycerol resonance for STEAM with a TE of 90 ms and PRESS with a TE of 200 ms, respectively. The efficacy of the timings was verified in vivo on tibial bone marrow.