Brown fat activity determined by infrared thermography and thermogenesis measurement using whole body calorimetry (BRIGHT Study)

To assess BAT activity in humans at a population level, infrared thermography (IRT) represents a safe, readily repeatable and affordable alternative to 18F-FDG-PET. Building upon a previously proposed method by our laboratory, we further refined the image computational algorithm to quantify BAT activation in the cervical-supraclavicular (C-SCV) region of healthy young men under thermo-neutral and cold exposure conditions. Additionally, we validated the whole-body calorimeter (WBC) in reliably measuring cold-induced thermogenesis. The temperature gradient between C-SCV-deltoid regions, and the corresponding difference in heat power output, increased upon cold air exposure relative to thermo-neutral conditions (by 74.88 %, p<0.0001; and by 71.34 %, p<0.0001 respectively). Resting and cumulative energy expenditure (EE) rose significantly (by 13.14 % and 9.12 % respectively, p=0.0001) while positive correlations between IRT measures and EE were found with cold air exposure (percentage change in heat power gradient between ROI and deltoid, cold air: r(2)=0.29, p=0.026, Pearson's correlation). IRT and WBC can be used to study BAT activation. The refined algorithm allows for more automation and objectivity in IRT data analysis, especially under cold air exposures.

EPR oxygen mapping (EPROM) of engineered cartilage grown in a hollow-fiber bioreactor

A novel electron paramagnetic resonance (EPR)-based oxygen mapping procedure (EPROM) is applied to cartilage grown in a single-, hollow-fiber bioreactor (HFBR) system. Chondrocytes harvested from the sterna of 17-day-old chick embryos were inoculated into an HFBR and produced hyaline cartilage over a period of 4 weeks. Tissue oxygen maps were generated according to the EPROM technique (Velan et al., Magn Reson Med 2000;43:804-809) by making use of the line-broadening effects of oxygen on the signal generated from nitroxide spin probes. In addition, the effect on oxygen consumption of the addition of cyanide to the tissue was investigated. Cyanide is a potent inhibitor of oxidative phosphorylation, and accordingly, given the constant provision of oxygen to the tissue, it would be expected to increase oxygen levels within the HFBR. The EPROM measurements showed a significant increase in oxygen concentration in the cartilage after the addition of cyanide. In contrast to other methods for studying oxygen in cartilage, EPROM can provide direct, noninvasive visualization of local concentrations in three dimensions.

Electron paramagnetic resonance oxygen mapping (EPROM): direct visualization of oxygen concentration in tissue

Tissue oxygen content is a central parameter in physiology but is difficult to measure. We report a novel procedure for spatial mapping of oxygen by electron paramagnetic resonance (EPR) utilizing a spectral-spatial imaging data set, in which an EPR spectrum is obtained from each image volume element. From this data set, spatial maps corresponding to local spin density and maximum EPR spectral line amplitude are generated. A map of local EPR spectral linewidth is then computed. Because linewidth directly correlates with oxygen concentration, the linewidth image provides a map of oxygenation. This method avoids a difficulty inherent in other oxygen content mapping techniques using EPR, that is, the unwanted influence of local spin probe density on the image. We provide simulation results and data from phantom studies demonstrating the validity of this method. We then apply the method to map oxygen content in rat tail tissue and vasculature. This method provides a new, widely applicable, approach to direct visualization of oxygen concentration in living tissue. Magn Reson Med 43:804-809, 2000.