Quantification of human and rodent brown adipose tissue function using 99mTc-methoxyisobutylisonitrile SPECT/CT and 18F-FDG PET/CT.

UNLABELLED: For brown adipose tissue (BAT) to be effective at consuming calories, its blood flow must increase enough to provide sufficient fuel to sustain energy expenditure and also transfer the heat created to avoid thermal injury. Here we used a combination of human and rodent models to assess changes in BAT blood flow and glucose utilization. METHODS: (99m)Tc-methoxyisobutylisonitrile (MIBI) SPECT (n = 7) and SPECT/CT (n = 74) scans done in adult humans for parathyroid imaging were reviewed for uptake in regions consistent with human BAT. Site-directed biopsies of subcutaneous and deep neck fat were obtained for electron microscopy and gene expression profiling. In mice, tissue perfusion was measured with (99m)Tc-MIBI (n = 16) and glucose uptake with (18)F-FDG (n = 16). Animals were kept fasting overnight, anesthetized with pentobarbital, and given intraperitoneally either the ß3-adrenergic receptor agonist CL-316,243, 1 mg/kg (n = 8), or saline (n = 8) followed by radiotracer injection 5 min later. After 120 min, the mice were imaged using SPECT/CT or PET/CT. Vital signs were recorded over 30 min during the imaging. BAT, white adipose tissue (WAT), muscle, liver, and heart were resected, and tissue uptake of both (99m)Tc-MIBI and (18)F-FDG was quantified by percentage injected dose per gram of tissue and normalized to total body weight. RESULTS: In 5.4% of patients (4/74), (99m)Tc-MIBI SPECT/CT showed increased retention in cervical and supraclavicular fat that displayed multilocular lipid droplets, dense capillary investment, and a high concentration of ovoid mitochondria. Expression levels of the tissue-specific uncoupling protein-1 were 180 times higher in BAT than in subcutaneous WAT (P < 0.001). In mice, BAT tissue perfusion increased by 61% (P < 0.01), with no significant changes in blood flow to WAT, muscle, heart, or liver. CL-316,243 increased glucose uptake in BAT even more, by 440% (P < 0.01). CONCLUSION: Pharmacologic activation of BAT requires increased blood flow to deliver glucose and oxygen for thermogenesis. However, the glucose consumption far exceeds the vascular response. These findings demonstrate that activated BAT increases glucose uptake beyond what might occur by increased blood flow alone and suggest that activated BAT likely uses glucose for nonthermogenic purposes.

Efficacy of radiofrequency ablation in the treatment of small functional adrenal neoplasms.

PURPOSE: To evaluate the use of radiofrequency (RF) ablation as a primary treatment for symptomatic primary functional adrenal neoplasms and determine the efficacy of treatment with use of clinical and biochemical follow-up. MATERIALS AND METHODS: After obtaining institutional review board approval, the authors retrospectively evaluated images and medical records from 13 consecutive patients with symptomatic functional adrenal neoplasms (<3.2 cm in diameter) who underwent RF ablation during a 7-year period. There were six men and seven women with a mean age of 54.1 years (range, 42-71 years). Cross-sectional images, findings from clinical examination, and adrenal biochemical markers were available for all patients. Ten of the 13 patients (77%) had an aldosteronoma and one patient each had a cortisol-secreting tumor, testosterone-secreting tumor, and pheochromocytoma. RF ablation was performed by two radiologists using an internally cooled electrode and a pulsed technique according to manufacturer's specifications. Clinical and laboratory follow-up was performed for all patients. Three patients underwent imaging follow-up for other reasons. RESULTS: All patients demonstrated resolution of abnormal biochemical markers after ablation (mean biochemical follow-up, 21.2 months). In addition, all patients experienced resolution of clinical symptoms or syndromes, including hypertension and hypokalemia (in patients with aldosteronoma), Cushing syndrome (in the patient with cortisol-secreting tumor), virilizing symptoms (in the patient with testosterone-secreting tumor), and hypertension (in the patient with pheochromocytoma). For the patients with aldosteronoma, improvements in hypertension management were noted. The mean blood pressure before ablation was 149/90 mm Hg with a mean (±standard deviation) of 3.1 ± 0.6 blood pressure medications, and this decreased to 122/77 mm Hg at a mean of 2.8 months after ablation with 1.3 ± 0.9 medications (P < .001) and 124/75 mm Hg at a mean of 41.4 months. There were two minor complications: one small pneumothorax and one limited hemothorax, neither of which required overnight admission. There were two episodes of transient self-remitting procedural hypertension-one in a patient with aldosteronoma and one in the patient with a cortisol-secreting tumor; however, none of these patients required further therapy during overnight observation. CONCLUSION: RF ablation may be an effective, minimally invasive method for treating small functional primary adrenal tumors.