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

Abstract

Brown adipose tissue (BAT) is retained into adulthood in some patients. It has been imaged using several radiopharmaceuticals, including 18 F-FDG. Using SPECT/CT, we assessed whether and how frequently uptake of 99m Tc-methoxyisobutylisonitrile ( 99m Tc-MIBI) was present in expected locations of BAT. Methods: A total of 205 SPECT/CT scans using 99m Tc-MIBI for parathyroid imaging were reviewed for the presence of 99m Tc-MIBI uptake in expected locations of BAT. Results: We detected 99m Tc-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 99m Tc-MIBI uptake in BAT were younger than the patients with no 99m Tc-MIBI uptake (P 5 0.044). Conclusion: Uptake of 99m Tc-MIBI in BAT is relatively common in this adult patient population and should not be confused with 99m Tc-MIBI-avid-tumors. SPECT/CT can be useful for defining such tracer uptake as a normal physiologic variant. Brown adipose tissue (BAT) is metabolically active in some adults and can cause inaccurate diagnoses on several types of nuclear scans because of substantial tracer uptake, which can be confused with or mask disease. Previously, BAT has been visualized by PET using 18 F-FDG (1,2), and by single-photon imaging using 123 I-metaiodobenzylguanidine (3,4) or 99m Tc-tetrofosmin (5) in humans. 99m Tcmethoxyisobutylisonitrile ( 99m Tc-MIBI) is widely used for many imaging applications, most notably for both cardiac and parathyroid imaging. To our knowledge, there have been 2 case reports (6,7) describing the possible uptake of 99m Tc-MIBI into brown fat in humans. Studies in rodents show clearly an increased uptake of 99m Tc-MIBI into BAT relative to background blood levels (8). Thorough examination of a 99m Tc-MIBI scan of the heart or parathyroid glands includes assessment of the visualized body to exclude incidental incremental tumor involvement, which may be 99m Tc-MIBI-avid. This is particularly important in instances when 99m Tc-MIBI is used for tumor imaging. We suspected that 99m Tc-MIBI might accumulate in BAT and evaluated this possibility, reviewing consecutive SPECT/ CT scans. MATERIALS AND METHODS Patient PopulationWe retrospectively reviewed scintigrams of consecutive patients who were evaluated for parathyroid adenomas from May 2004 to July 2005, using dual-phase (early and late) planar imaging and SPECT/CT. We identified 205 patients (153 female, 52 male; mean age, 59.7 6 13.1 y, range, 23-94 y). Our retrospective study was approved by the Institutional Review Board, and informed consent was waived. Imaging Protocol and AnalysisAll patients were injected intravenously with 925-1,110 MBq of 99m Tc-MIBI. Planar ImagingAt 15 min and 2 h after injection, 10-min anterior, 35°right anterior oblique, and 35°left anterior oblique planar images were acquired in a 128 · 128 matrix, with a 20% window centered around the 140-keV photopeak, using a low-energy, high-resolution parallel collimator. SPECT/CTNeither oral nor intravenous contrast material was used. Hyb...

Imaging of Brown Adipose Tissue: State of the Art

“…Sestamibi is a perfusion agent that accumulates in cells with high cellular and mitochondrial membrane potentials, and the overall prevalence of detectable human BAT with use of 99m Tc-sestamibi is approximately 6%-7%, which is similar to that observed in studies that used 18 F-FDG PET (77). Although increased validated for cell surface markers in other systems (73).…”

Is minimally invasive parathyroidectomy without QPTH monitoring justified?

“…On the one hand, the sensitivity of MIBI (with/without US) is lower in the presence of thyroid nodules; on the other hand, false-positive uptake of MIBI may occur in thyroid nodules, lymph nodes, and brown adipose tissue [4,19,20]. As shown recently [4], the combined interpretation of MIBI and US are false positive in 12% and false negative in 1% in patients with SGD in an endemic goiter area.…”

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“…Recently, indirect measurements in patients with cancer suggest that brown fat may be retained in small amounts in these individuals (34) . Its location is, however, primarily in the neck region (35,36) and whether it has any functional importance in energy balance remains to be established.…”