Visualization of Brown Adipose Tissue with 99mTc-Methoxyisobutylisonitrile on SPECT/CT

Brown adipose tissue (BAT) is retained into adulthood in some patients. It has been imaged using several radiopharmaceuti-cals, including 18F-FDG. Using SPECT/CT, we assessed whether and how frequently uptake of 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) was present in expected locations of BAT. Methods: A total of 205 SPECT/CT scans using 99mTc-MIBI for parathyroid imaging were reviewed for the presence of 99mTc-MIBI uptake in expected locations of BAT.Results:We detected 99mTc-MIBI uptake in BAT in 13 of 205 patients (6.3%). When BAT was visualized, it was detected on both early and delayed scans. The patients with 99mTc-MIBI uptake in BAT were younger than the patients with no 99mTc-MIBI uptake (P 5 0.044). Con-clusion: Uptake of 99mTc-MIBI in BAT is relatively common in this adult patient population and should not be confused with 99mTc-MIBI-avid–tumors. SPECT/CT can be useful for defining such tracer uptake as a normal physiologic variant. Key Words: brown adipose tissue; hybrid imaging; 99mTc-methoxyisobutylisonitrile; SPECT/C