Differentiating supraclavicular from gluteal adipose tissue based on simultaneous PDFF and T(2)* mapping using a 20‐echo gradient‐echo acquisition

BACKGROUND: Adipose tissue (AT) can be classified into white and brown/beige subtypes. Chemical shift encoding‐based water–fat MRI‐techniques allowing simultaneous mapping of proton density fat fraction (PDFF) and T(2)* result in a lower PDFF and a shorter T(2)* in brown compared with white AT. However, AT T(2)* values vary widely in the literature and are primarily based on 6‐echo data. Increasing the number of echoes in a multiecho gradient‐echo acquisition is expected to increase the precision of AT T(2)* mapping. PURPOSE: 1) To mitigate issues of current T(2)*‐measurement techniques through experimental design, and 2) to investigate gluteal and supraclavicular AT T(2)* and PDFF and their relationship using a 20‐echo gradient‐echo acquisition. STUDY TYPE: Prospective. SUBJECTS: Twenty‐one healthy subjects. FIELD STRENGTH/SEQUENCE ASSESSMENT: First, a ground truth signal evolution was simulated from a single‐T(2)* water–fat model. Second, a time‐interleaved 20‐echo gradient‐echo sequence with monopolar gradients of neck and abdomen/pelvis at 3 T was performed in vivo to determine supraclavicular and gluteal PDFF and T(2)*. Complex‐based water–fat separation was performed for the first 6 echoes and the full 20 echoes. AT depots were segmented. STATISTICAL TESTS: Mann‐Whitney test, Wilcoxon signed‐rank test and simple linear regression analysis. RESULTS: Both PDFF and T(2)* differed significantly between supraclavicular and gluteal AT with 6 and 20 echoes (PDFF: P < 0.0001 each, T(2)*: P = 0.03 / P < 0.0001 for 6/20 echoes). 6‐echo T(2)* demonstrated higher standard deviations and broader ranges than 20‐echo T(2)*. Regression analyses revealed a strong relationship between PDFF and T(2)* values per AT compartment (R(2) = 0.63 supraclavicular, R(2) = 0.86 gluteal, P < 0.0001 each). DATA CONCLUSION: The present findings suggest that an increase in the number of sampled echoes beyond 6 does not affect AT PDFF quantification, whereas AT T(2)* is considerably affected. Thus, a 20‐echo gradient‐echo acquisition enables a multiparametric analysis of both AT PDFF and T(2)* and may therefore improve MR‐based differentiation between white and brown fat. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:424–434.