The activation and expansion of brown adipose tissue (BAT) has emerged as a promising strategy to counter obesity and the metabolic syndrome by increasing energy expenditure. The subsequent testing and validation of novel agents that augment BAT necessitates accurate pre-clinical measurements in rodents regarding the capacity for BAT-derived thermogenesis. We present a novel method to measure BAT thermogenesis using infrared imaging following β3-adrenoreceptor stimulation in mice. We show that the increased body surface temperature observed using this method is due solely to uncoupling protein-1 (UCP1)-mediated thermogenesis and that this technique is able to discern differences in BAT activity in mice acclimated to 23 °C or thermoneutrality (30 °C). These findings represent the first standardized method utilizing infrared imaging to specifically detect UCP1 activity in vivo.

Three-dimensional (3D) mode imaging is the current standard for PET/CT systems. Dynamic imaging for quantification of myocardial blood flow with short-lived tracers, such as 82 Rb-chloride, requires accuracy to be maintained over a wide range of isotope activities and scanner counting rates. We proposed new performance standard measurements to characterize the dynamic range of PET systems for accurate quantitative imaging. Methods: 82 Rb or 13 Nammonia (1,100-3,000 MBq) was injected into the heart wall insert of an anthropomorphic torso phantom. A decaying isotope scan was obtained over 5 half-lives on 9 different 3D PET/CT systems and 1 3D/2-dimensional PET-only system. Dynamic images (28 · 15 s) were reconstructed using iterative algorithms with all corrections enabled. Dynamic range was defined as the maximum activity in the myocardial wall with less than 10% bias, from which corresponding dead-time, counting rates, and/or injected activity limits were established for each scanner. Scatter correction residual bias was estimated as the maximum cavity blood-to-myocardium activity ratio. Image quality was assessed via the coefficient of variation measuring nonuniformity of the left ventricular myocardium activity distribution. Results: Maximum recommended injected activity/body weight, peak dead-time correction factor, counting rates, and residual scatter bias for accurate cardiac myocardial blood flow imaging were 3-14 MBq/kg, 1.5-4.0, 22-64 Mcps singles and 4-14 Mcps prompt coincidence counting rates, and 2%-10% on the investigated scanners. Nonuniformity of the myocardial activity distribution varied from 3% to 16%. Conclusion: Accurate dynamic imaging is possible on the 10 3D PET systems if the maximum injected MBq/kg values are respected to limit peak dead-time losses during the bolus first-pass transit. PETi maging in 3-dimensional (3D) mode has become the standard for new whole-body scanners. The increased sensitivity allows for reduction of injected activity to the patient while maintaining excellent image quality; however, random and scattered photon counts are increased, requiring systems with high counting rate capability and accurate corrections for these physical effects. Current PET instrumentation and National Electrical Manufacturers Association (NEMA) performance evaluation methods (1) have been developed primarily to optimize whole-body oncology imaging with 18 F-FDG. However, dynamic PET imaging for myocardial blood flow (MBF) quantification with short-lived tracers, such as 82 Rb, 15 O-water, or 13 N-ammonia, requires high counting rates and correction accuracy to be maintained over a wide range of measured activities (2). An ideal PET system should allow for conventional relative myocardial perfusion imaging (MPI) of tracer retention without compromising accuracy of first-pass dynamic data (3). Routine MBF imaging is clinically feasible with the 76-s half-life generator-produced tracer 82 Rb, resulting in accurate (4,5) and reproducible measurements (3,6-8), as validated against 13 N-ammonia...

Counter WB, Wang IQ, Farncombe TH, Labiris NR. Airway and pulmonary vascular measurements using contrast-enhanced micro-CT in rodents. Am J Physiol Lung Cell Mol Physiol 304: L831-L843, 2013. First published April 5, 2013 doi:10.1152/ajplung.00281.2012.-Preclinical imaging allows pulmonary researchers to study lung disease and pulmonary drug delivery noninvasively and longitudinally in small animals. However, anatomically localizing a pathology or drug deposition to a particular lung region is not easily done. Thus, a detailed knowledge of the anatomical structure of small animal lungs is necessary for understanding disease progression and in addition would facilitate the analysis of the imaging data, mapping drug deposition and relating function to structure. In this study, contrast-enhanced micro-computed tomography (CT) of the lung produced high-resolution images that allowed for the characterization of the rodent airway and pulmonary vasculature. Contrast-enhanced micro-CT was used to visualize the airways and pulmonary vasculature in Sprague-Dawley rats (200 -225 g) and BALB/c mice (20 -25 g) postmortem. Segmented volumes from these images were processed to yield automated measurements of the airways and pulmonary vasculature. The diameters, lengths, and branching angles of the airway, arterial, and venous trees were measured and analyzed as a function of generation number and vessel diameter to establish rules that could be applied at all levels of tree hierarchy. In the rat, airway, arterial, and venous tress were measured down to the 20th, 16th, and 14th generation, respectively. In the mouse, airway, arterial, and venous trees were measured down to the 16th, 8th, and 7th generation, respectively. This structural information, catalogued in a rodent database, will increase our understanding of lung structure and will aid in future studies of the relationship between structure and function in animal models of disease. computed tomography; contrast agents; pulmonary circulation; airway nomenclature THE LUNG IS A COMPLEX ORGAN that works dynamically and must react to changes in posture, environment, and disease (20). Its major function is gas exchange, bringing oxygen into the body while removing carbon dioxide. To accomplish this task, a well-coordinated interaction between the lung and pulmonary circulation is essential. The rodent lung is comprised of two branching networks: the airways and pulmonary vasculature. With the advent of small animal imaging systems, researchers are able to visualize these networks in situ and noninvasively study the progression of lung disease and assess drug efficacy in animal models of disease. Much of this research involves combining the anatomical data obtained using computed tomography (CT) with the functional data obtained using single photon emission computed tomography (SPECT) or positron emission tomography (PET). A detailed knowledge of the structure of the lung would facilitate the mapping of functional data relative to lung anatomy and thus further our understandi...

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