Aspects of spinal bone marrow fat to water quantification with magnetic resonance spectroscopy at 3 T

Abstract

Aspects of spinal bone marrow fat to water ratio (FWR) quantification with magnetic resonance spectroscopy (MRS) at 3 T were examined in this work. A Point RESolved Spectroscopy (PRESS) sequence with TE = 40 ms and TE = 70 ms was employed to obtain spectra from L3 and T7 vertebrae of twenty healthy volunteers within the age range of 21–50 years (8 female, 12 male); measurements from the C4 vertebra were obtained from 19 of the volunteers. The spectra were used to determine FWR and fat and water T2 values. Spectra were fitted to yield areas for the fat peak (≈1.3 ppm), the water peak (≈4.7 ppm) and the olefinic resonance (≈5.3 ppm). Ignoring the olefinic contribution to the water signal results in about 10% lower FWRs using short-TE PRESS and overestimates water T2 by about 8% in the L3 vertebrae. Neglecting to correct for T2 relaxation resulted in an average overestimation of FWR by a factor 3.11 ± 1.30 (when comparing T2 corrected FWR to that obtained with PRESS TE = 40 ms) in L3 vertebrae. Paired t-tests were employed to investigate statistical significance of differences between different pairs of vertebrae in each volunteer. On average, it was found that FWRs in the T7 and C4 vertebrae were approximately 75% and 57%, respectively, of the corresponding value for the L3 vertebra in each volunteer (p-values < 0.01). Fat T2 values were on average, in each volunteer, lower in C4 vertebrae compared to those of L3 and T7 (17% and 23% lower, respectively) and C4 water T2 values were ≈6% lower than the T7 values. To our knowledge, this is the first MRS study to examine the variation of FWR and T2 values across different vertebral sections.