In vivo comparison of MRI-based and MRS-based quantification of adipose tissue fatty acid composition against gas chromatography

Abstract

Purpose: To compare MR-based fatty acid composition (FAC) quantification methods against the gold standard technique, gas chromatography (GC), with comparison of a free and a constrained signal model. The FAC was measured in the healthy and edematous legs of lymphedema patients.

Methods: In vivo MRS and MRI data were acquired from 19 patients at 3 T. Biopsies were collected from subcutaneous adipose tissue of both thighs during liposuction. The saturated, monounsaturated, and polyunsaturated fatty acid fractions (f_SFA , f_MUFA and f_PUFA , respectively) were estimated with the MR-based methods using two signal models: free and constrained (number of methylene-interrupted double bonds expressed in number of double bonds, based on GC data). Linear regression, Bland-Altman plots, and correlation coefficients were used to evaluate the MR methods against the GC of the biopsies. Paired t-test was used to compare the FAC difference between edematous and healthy legs.

Results: The estimated parameters correlated well with the GC data (r_SFA , r_MUFA , and r_PUFA = 0.82, 0.81 and 0.89, respectively) using the free model MRI-based approach. In comparison, the MRS-based method resulted in weaker correlations and larger biases compared with MRI. In both cases, correct estimation of f_MUFA and f_PUFA fractions were not possible using the constrained model. The difference in FAC of healthy and edematous legs were estimated to 0.008 (P = .01), -0.009 (P = .005), and 0.002 (P = .03) for f_SFA , f_MUFA , and f_PUFA .

Conclusion: In this study, MRI-based FAC quantification was highly correlated, although slightly biased, compared with GC, whereas the MRS-based approach resulted in weaker correlations. Small but significant differences could be found between the healthy and edematous legs of lymphedema patients using GC analysis.

Keywords: MR spectroscopy; adipose tissue; chemical shift-encoded imaging; fatty acid composition quantification; gas chromatography; lymphedema.