Sexual Dimorphisms in Adult Human Brown Adipose Tissue.

OBJECTIVE: This study aimed to quantify and compare the amount, activity, and anatomical distribution of cold-activated brown adipose tissue (BAT) in healthy, young, lean women and men. METHODS: BAT volume and 18 F-fluorodeoxyglucose uptake were measured by positron emission tomography and computerized tomography in 12 women and 12 men (BMI 18.5-25 kg/m2 , aged 18-35 years) after 5 hours of exposure to their coldest temperature before overt shivering. RESULTS: Women had a lower detectable BAT volume than men (P = 0.03), but there was no difference after normalizing to body size. The mean BAT glucose uptake and relative distribution of BAT did not differ by sex. 18 F-fluorodeoxyglucose uptake consistent with BAT was observed in superficial dorsocervical adipose tissue of 6 of 12 women but only 1 of 12 men (P = 0.02). This potential BAT depot would pose fewer biopsy risks than other depots. CONCLUSIONS: Despite differences in adiposity and total BAT volume, we found that healthy, lean, young women and men do not differ in the relative amount, glucose uptake, and distribution of BAT. Dorsocervical 18 F-fluorodeoxyglucose uptake was more prevalent in women and may be a remnant of interscapular BAT seen in human newborns. Future studies are needed to discern how BAT contributes to whole-body thermal physiology and body weight regulation in women and men.

Cerebral oximetry performance testing with a 3D-printed vascular array phantom.

Cerebral oximetry based on near-infrared spectroscopy represents a unique noninvasive tool for real-time surgical monitoring, yet studies have shown a significant discrepancy in accuracy among commercial systems. Towards the establishment of a standardized method for performance testing, we have studied a solid phantom approach - based on a 3D-printed cerebrovascular module (CVM) incorporating an array of 148 cylindrical channels - that has several advantages over liquid phantoms. Development and characterization of a CVM prototype are described, including high-resolution imaging and spectrophotometry measurements. The CVM was filled with whole bovine blood tuned over an oxygen saturation range of 30-90% and molded-silicone layers simulating extracerebral tissues were used to evaluate penetration depth. Saturation measurement accuracy was assessed in two commercially-available clinical cerebral oximeters. For one oximeter, both neonatal and pediatric sensors showed a high degree of precision, whereas accuracy was strongly dependent on saturation level and extracerebral geometry. The second oximeter showed worse precision, yet greater robustness to variations in extracerebral layers. These results indicate that 3D-printed channel array phantoms represent a promising new approach for standardized testing of clinical oximeters.