Positron-Emission Tomography and Computed Tomography Measurement of Brown Fat Thermal Activation: Key Tools for Developing Novel Pharmacotherapeutics for Obesity and Diabetes

Unlike white adipose tissue, brown adipose tissue is a heat-generating fat that burns energy and may have beneficial effects on obesity. This chapter reviews computed tomography and fluorodeoxyglucose positron-emission tomography studies of adipose tissue type, volume, and activation. We present imaging data on a group of insulin-resistant subjects (HOMA = 5.2, SD = 2.5) and overweight healthy volunteers with fluorodeoxyglucose positron-emission tomography and x-ray computed tomography (FDG-PET/CT) of the thorax (C6–T8) to assess the glucose metabolic rate of brown and white fat. Subjects were exposed to a 90-min period of either cold (67–68 °F) or warm (72–73 °F) temperature on separate days. Metabolic rate was quantified using aortic uptake PET values and the PMOD software. A higher cold than warm glucose metabolic rate (GMR) was observed to the greatest extent in the −120 to −80 and −80 to −40 Hounsfield bands of thoracic levels consistent with earlier reports of brown fat metabolic rate sensitivity to thermal exposure. Additionally, FDG-PET may prove sensitive enough to detect metabolic effects of therapeutic interventions on functional brown fat volume and activity.