Abstract
BackgroundBrown adipose tissue (BAT) is a thermogenic tissue which can generate heat in response to mild cold exposure. As it constitutes a promising target in the fight against obesity, we need reliable techniques to quantify its activity in response to therapeutic interventions. The current standard for the quantification of BAT activity is [18F]FDG PET/CT. Various sequences in magnetic resonance imaging (MRI), including those measuring its relative fat content (fat fraction), have been proposed and evaluated in small proof-of-principle studies, showing diverging results. Here, we systematically compare the predictive value of adipose tissue fat fraction measured by MRI to the results of [18F]FDG PET/CT.MethodsWe analyzed the diagnostic reliability of MRI measured fat fraction (FF) for the estimation of human BAT activity in two cohorts of healthy volunteers participating in two prospective clinical trials (NCT03189511, NCT03269747). In both cohorts, BAT activity was stimulated by mild cold exposure. In cohort 1, we performed [18F]FDG PET/MRI; in cohort 2, we used [18F]FDG PET/CT followed by MRI. Fat fraction was determined by 2-point Dixon and 6-point Dixon measurement, respectively. Fat fraction values were compared to SUVmean in the corresponding tissue depot by simple linear regression.ResultsIn total, 33 male participants with a mean age of 23.9 years and a mean BMI of 22.8 kg/m2 were recruited. In 32 participants, active BAT was visible. On an intra-individual level, FF was significantly lower in high-SUV areas compared to low-SUV areas (cohort 1: p < 0.0001 and cohort 2: p = 0.0002). The FF of the supraclavicular adipose tissue depot was inversely related to its metabolic activity (SUVmean) in both cohorts (cohort 1: R2 = 0.18, p = 0.09 and cohort 2: R2 = 0.42, p = 0.009).ConclusionMRI FF explains only about 40% of the variation in BAT glucose uptake. Thus, it can currently not be used to substitute [18F] FDG PET-based imaging for quantification of BAT activity.Trial registrationClinicalTrials.gov. NCT03189511, registered on June 17, 2017, actual study start date was on May 31, 2017, retrospectively registered. NCT03269747, registered on September 01, 2017.
Highlights
Brown adipose tissue (BAT) is a thermogenic tissue which contributes to energy homeostasis in human adults
Within depot variance of fat fraction in comparison to local metabolic activity The metabolic activity as assessed by [18F]FDG uptake varies considerably within the supraclavicular adipose tissue depot leading to areas which are PETpositive and others which are PET-negative
In the present study, we evaluated whether measurement of the fat fraction (FF) within the supraclavicular fat depot in vivo can reliably predict the metabolic activity of brown adipose tissue (BAT) as assessed by [18F]FDG PET/CT
Summary
Brown adipose tissue (BAT) is a thermogenic tissue which contributes to energy homeostasis in human adults. Brown adipocytes are found in the cervical, supraclavicular, axillary, and retroperitoneal region with the cervical and supraclavicular regions being the most predominant [6] In these adipose tissue depots, thermogenic adipocytes can emerge from white adipocytes in response to cold stimulation. This lineage of brown adipocytes is different from the classical BAT found in human newborns. Brown adipose tissue (BAT) is a thermogenic tissue which can generate heat in response to mild cold exposure As it constitutes a promising target in the fight against obesity, we need reliable techniques to quantify its activity in response to therapeutic interventions. We systematically compare the predictive value of adipose tissue fat fraction measured by MRI to the results of [18F]FDG PET/CT
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