Contrast-Enhanced Ultrasound: A Novel Noninvasive, Nonionizing Method for the Detection of Brown Adipose Tissue in Humans.

BACKGROUND: Brown adipose tissue (BAT) consumes glucose when it is activated by cold exposure, allowing its detection in humans by (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) with computed tomography (CT). The investigators recently described a novel noninvasive and nonionizing imaging method to assess BAT in mice using contrast-enhanced ultrasound (CEUS). Here, they report the application of this method in healthy humans.

METHODS: Thirteen healthy volunteers were recruited. CEUS was performed before and after cold exposure in all subjects using a continuous intravenous infusion of perflutren gas-filled lipid microbubbles and triggered imaging of the supraclavicular space. The first five subjects received microbubbles at a lower infusion rate than the subsequent eight subjects and were analyzed as a separate group. Blood flow was estimated as the product of the plateau (A) and the slope (β) of microbubble replenishment curves. All underwent (18)F-FDG PET/CT after cold exposure.

RESULTS: An increase in the acoustic signal was noted in the supraclavicular adipose tissue area with increasing triggering intervals in all subjects, demonstrating the presence of blood flow. The area imaged by CEUS colocalized with BAT, as detected by ¹⁸F-FDG PET/CT. In a cohort of eight subjects with an optimized CEUS protocol, CEUS-derived BAT blood flow increased with cold exposure compared with basal BAT blood flow in warm conditions (median Aβ = 3.3 AU/s [interquartile range, 0.5-5.7 AU/s] vs 1.25 AU/s [interquartile range, 0.5-2.6 AU/s]; P = .02). Of these eight subjects, five had greater than twofold increases in blood flow after cold exposure; these responders had higher BAT activity measured by (18)F-FDG PET/CT (median maximal standardized uptake value, 2.25 [interquartile range, 1.53-4.57] vs 0.51 [interquartile range, 0.47-0.73]; P = .02).

CONCLUSIONS: The present study demonstrates the feasibility of using CEUS as a noninvasive, nonionizing imaging modality in estimating BAT blood flow in young, healthy humans. CEUS may be a useful and scalable tool in the assessment of BAT and BAT-targeted therapies.