MO‐G‐18C‐07: Improving T2 Determination and Quantification of Lipid Methylene Protons in Proton Magnetic Resonance Spectroscopy at 3 T

Abstract

Purpose:To improve proton magnetic resonance spectroscopy (MRS) transverse relaxation (T2) determination and quantification of lipid methylene chain (1.3 ppm) protons by rewinding their J‐coupling evolution.Methods:MRS experiments were performed on four lipid phantoms, namely, almond, corn, sunflower and oleic acid, using a 3 T Philips MRI scanner with a transmit/receive birdcage head coil. Two PRESS (Point RESolved Spectroscopy) pulse sequences were used. The first PRESS sequence employed standard bandwidth (BW) (∼550 Hz) RF (radiofrequency) refocussing pulses, while the second used refocussing pulses of narrow BW (∼50 Hz) designed to rewind J‐coupling evolution of the methylene protons in the voxel of interest. Signal was acquired with each sequence from a 5×5×5 mm3 voxel, with a repetition time (TR) of 3000 ms, and with echo times (TE) of 100 to 200 ms in steps of 20 ms. 2048 sample points were measured with a 2000 Hz sampling bandwidth. Additionally, 30 mm outer volume suppression slabs were used to suppress signal outside the voxel of interest. The frequency of the RF pulses was set to that of the methylene resonance. Methylene peak areas were calculated and fitted in MATLAB to a monexponentially decaying function of the form M0exp(‐TE/T2), where M0 is the extrapolated area when TE = 0 ms and yields a measure of concentration.Results:The determined values of M0 and T2 increased for all fatty acids when using the PRESS sequence with narrow BW refocussing pulses. M0 and T2 values increased by an average amount (over all the phantoms) of 31% and 14%, respectively.Conclusion:This investigation has demonstrated that J‐coupling interactions of lipid methylene protons causes non‐negligible signal losses which, if not accounted for, Result in underestimations of their levels and T2 values when performing MRS measurements.Funded by the Natural Sciences and Engineering Research Council of Canada and the Canadian Breast Cancer Foundation – Prairies.NWT