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 radiopharmaceuticals, 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 = 0.044). Conclusion: 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.