Sci—Sat AM: Brachy — 12: Resolving the olefinic lipid resonance from water in proton magnetic resonance spectra of vertebral bone marrow at 3 T

Abstract

Proton magnetic resonance spectroscopy (MRS) of vertebral lipids has been shown to be relevant in the study of cancer. The olefinic resonance (≈ 5.4 ppm) yields a measure of lipid unsaturation. However, its measurement with standard short echo time (TE) MRS sequences is difficult due to the large overlapping water signal. The purpose of this work is to optimize the TE of a PRESS (Point RESolved Spectroscopy) sequence to measure the olefinic resonance from spinal bone marrow with minimal losses due to J-coupling and minimal contamination from water at 3 T, a field strength becoming more common in the clinic. Experiments were conducted on nine oils and on L4 vertebral bone marrow in vivo at 3 T. The methyléne (or methyl + méthyléne), and olefinic resonances were measured with PRESS using multiple TEs. The effects of J-coupling evolution of the olefinic protons appeared to be minimal when TE = 200 ms. The TE = 200 ms olefinic/methylene peak area ratios calculated for each oil correlated well with ratios deduced from oil compositions in the literature (R = 0.92). The TE = 200 ms PRESS spectra obtained from vertebra of four volunteers showed negligible contribution from water to the olefinic resonance, thereby enabling the olefinic peak area to be quantified more accurately. The results of this work demonstrate that a PRESS sequence with TE = 200 ms is suitable for measuring relative levels of lipid unsaturation and for resolving the olefinic resonance from contaminating water signal in spinal bone marrow.

Quantitative 1H MRI and MRS of fatty acid composition

“…The olefinic signal (peak J) needed for estimation of the UI may be difficult to resolve when the water signal is strong or when short causes substantial line broadening. As a remedy, water suppression, 39 or acquisition with sufficiently long TE (TE = 200 ms) to remove the water signal 40,41 has been suggested. Drawbacks of these techniques are that the quality of water suppression can vary and result in poor quality of the olefinic peak, 7 and the use of a long‐TE PRESS technique requires calibration against known fatty acid compositions for absolute estimation of unsaturation 27 .…”