Reduction of Brown Fat 2-Deoxy-2-[F-18]fluoro-d-glucose Uptake by Controlling Environmental Temperature Prior to Positron Emission Tomography Scan

Potential false positive Tc-99m sestamibi parathyroid study due to uptake in brown adipose tissue

We report on a 55-year-old woman with suspected primary hyperparathyroidism who underwent dual phase Tc-99m sestamibi parathyroid imaging. Symmetric, patchy activity in the neck and shoulders was localized to low attenuation areas on integrated SPECT/CT and attributed to uptake in brown adipose tissue (BAT). Focal uptake in the anterior thorax on SPECT images, which potentially may have been misinterpreted as ectopic parathyroid tissue, was demonstrated on SPECT/CT as uptake in BAT. Recognition of this pattern on parathyroid SPECT/CT scintigraphy may avoid false positive reports. Our case provides further evidence that in addition to F-18 FDG, I-123 MIBG, and Tc-99m tetrofosmin, Tc-99m sestamibi may also accumulate in BAT.

PET and PET/CT in pediatric oncology

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and FDG-PET/computed tomography (CT) are becoming increasingly important imaging tools in the noninvasive evaluation and monitoring of children with known or suspected malignant diseases. In this review, we discuss the preparation of children undergoing PET studies and review radiation dosimetry and its implications for family and caregivers. We review the normal distribution of 18F-fluorodeoxyglucose (FDG) in children, common variations of the normal distribution, and various artifacts that may arise. We show that most tumors in children accumulate and retain FDG, allowing high-quality images of their distribution and pathophysiology. We explore the use of FDG-PET in the study of children with the more common malignancies, such as brain neoplasms and lymphomas, and the less-common tumors, including neuroblastomas, bone and soft-tissue sarcomas, Wilms' tumors, and hepatoblastomas. For comparison, other PET tracers are included because they have been applied in pediatric oncology. Multiple multicenter trials are underway that use FDG-PET in the management of children with neoplastic disease; these studies should give us greater insight into the impact FDG-PET can make in their care. PET is emerging as an important diagnostic imaging tool in the evaluation of pediatric cancers. The recent advent of dual-modality PET-computed tomography (PET/CT) imaging systems has added unprecedented diagnostic capability by revealing the precise anatomical localization of metabolic information and metabolic characterization of normal and abnormal structures. The use of CT transmission scanning for attenuation correction has shortened the total acquisition time, which is an especially desirable attribute in pediatric imaging. Moreover, expansion of the regional distribution of the most common PET radiotracer, FDG, and the introduction of mobile PET units have greatly increased access to this powerful diagnostic imaging technology. Here, we review the clinical applications of PET and PET/CT in pediatric oncology. General considerations in patient preparation and radiation dosimetry will be discussed.

Atypical Brown Fat Distribution in Young Males Demonstrated on PET/CT

The development of PET/CT has led to the recognition that metabolically active fat, referred to as "brown fat," can accumulate FDG and represents a possible source of false-positive scans in oncology patients. Numerous reports have described the typical appearance of brown fat, which most commonly presents as neck and paravertebral uptake in young female patients. Other described sites of uptake include the mediastinum and retroperitoneum. We present examples of 2 cases of atypical diffuse brown fat uptake seen in the subcutaneous fat of the thighs, abdomen, and pelvis. Both of these patients were young men and did not show uptake in the typical supraclavicular and neck fat. Although rare in our experience, knowledge of this condition may prevent misinterpretation of this finding as an infiltrative condition of the skin, such as lymphoma.

Unexpected evidence for active brown adipose tissue in adult humans

The contention that brown adipose tissue is absent in adult man has meant that processes attributed to active brown adipose tissue in experimental animals (mainly rodents), i.e., classical nonshivering thermogenesis, adaptive adrenergic thermogenesis, diet-induced thermogenesis, and antiobesity, should be either absent or attributed to alternative (unknown) mechanisms in man. However, serendipidously, as a consequence of the use of fluorodeoxyglucose positron emission tomography (FDG PET) to trace tumor metastasis, observations that may change that notion have recently been made. These tomography scans have visualized symmetrical areas of increased tracer uptake in the upper parts of the human body; these areas of uptake correspond to brown adipose tissue. We examine here the published observations from a viewpoint of human physiology. The human depots are somewhat differently located from those in rodents, the main depots being found in the supraclavicular and the neck regions with some additional paravertebral, mediastinal, para-aortic, and suprarenal localizations (but no interscapular). Brown adipose tissue activity in man is acutely cold induced and is stimulated via the sympathetic nervous system. The prevalence of active brown adipose tissue in normal adult man can be only indirectly estimated, but it would seem that the prevalence of active brown adipose tissue in the population may be at least in the range of some tens of percent. We conclude that a substantial fraction of adult humans possess active brown adipose tissue that thus has the potential to be of metabolic significance for normal human physiology as well as to become pharmaceutically activated in efforts to combat obesity.

Deiodinases: implications of the local control of thyroid hormone action

The deiodinases activate or inactivate thyroid hormone, and their importance in thyroid hormone homeostasis has become increasingly clear with the availability of deiodinase-deficient animals. At the same time, heightened interest in the field has been generated following the discovery that the type 2 deiodinase can be an important component in both the Hedgehog signaling pathway and the G protein-coupled bile acid receptor 1-mediated (GPBAR1-mediated) signaling cascade. The discovery of these new roles for the deiodinases indicates that tissue-specific deiodination plays a much broader role than once thought, extending into the realms of developmental biology and metabolism.