Feasibility of omega‐3 fatty acid fraction mapping using chemical shift encoding‐based imaging at 3 T

Abstract

PurposeThe aim of this work is to develop an ω‐3 fatty acid fraction mapping method at 3 T based on a chemical shift encoding model, to assess its performance in a phantom and in vitro study, and to further demonstrate its feasibility in vivo.MethodsA signal model was heuristically derived based on spectral appearance and theoretical considerations of the corresponding molecular structures to differentiate between ω‐3 and non‐ω‐3 fatty acid substituents in triacylglycerols in addition to the number of double bonds (ndb), the number of methylene‐interrupted double bonds (nmidb), and the mean fatty acid chain length (CL). First, the signal model was validated using single‐voxel spectroscopy and a time‐interleaved multi‐echo gradient‐echo (TIMGRE) sequence in gas chromatography–mass spectrometry (GC–MS)‐calibrated oil phantoms. Second, the TIMGRE‐based method was validated in vitro in 21 adipose tissue samples with corresponding GC–MS measurements. Third, an in vivo feasibility study was performed for the TIMGRE‐based method in the gluteal region of two healthy volunteers. Phantom and in vitro data was analyzed using a Bland–Altman analysis.ResultsCompared with GC–MS, MRS showed in the phantom study significant correlations in estimating the ω‐3 fraction (p < 0.001), ndb (p < 0.001), nmidb (p < 0.001), and CL (p = 0.001); MRI showed in the phantom study significant correlations (all p < 0.001) for the ω‐3 fraction, ndb, and nmidb, but no correlation for CL. Also in the in vitro study, significant correlations (all p < 0.001) between MRI and GC–MS were observed for the ω‐3 fraction, ndb, and nmidb, but not for CL. An exemplary ROI measurement in vivo in the gluteal subcutaneous adipose tissue yielded (mean ± standard deviation) 0.8% ± 1.9% ω‐3 fraction.ConclusionThe present study demonstrated strong correlations between gradient‐echo imaging‐based ω‐3 fatty acid fraction mapping and GC–MS in the phantom and in vitro study. Furthermore, feasibility was demonstrated for characterizing adipose tissue in vivo.