**4.3 Tc-99m tetrofosmin**

Tetrofosmin is a lipophilic phosphine useful for myocardial perfusion imaging. Significant uptake of Tc-99m tetrofosmin in the thyroid, breast and lung tumors is reported. Tc-99m tetrofosmin is useful in detection of thyroid metastatic disease, particularly when the tumor is not iodine avid. In addition, it does not require withdrawal of thyroid hormone suppression therapy (Sharma et al., 2007). Nishiyama et al. reported that detectability of thyroid cancer metastases using Tc-99m tetrofosmin was 79.4% and that Tc-99m tetrofosmin is more sensitive than I-131 for detection of differentiated thyroid cancer metastasis, particulary for regional lymph node (Nishiyama et al., 2000). Unal et al. reported different results that the sensitivities of Tl-201, Tc-99m tetrofosmin and I-131 in diagnosing distant metastases were comparable (0.85, 0.85, and 0.75, respectively) (Unal et al., 1998).

Fig. 13. I-131, Tc-99m MIBI and F-18 FDG images. A 62-year-old woman with metastatic papillary thyroid cancer to the left proximal humerus, clavicle and sternum underwent I-131 therapy with 7.4 GBq (200 mCi). Her serum thyroglobulin level was 260 ng/mL. I-131 RxWBS (A) shows focal hot uptakes in the left clavicle and huemrus. On Tc-99m MIBI WBS, irregular hot uptakes are detected in the sternal area and faint uptake in the left clavicle (B). F-18 FDG PET/CT (C-E) shows multiple hypermetabolic lesions in the sternum, both hilar lymph nodes and lungs.
