**4.4 Thallium-201**

242 12 Chapters on Nuclear Medicine

Fig. 12. Iodine negative and F-18 FDG PET positive case. A 65-year-old female underwent I-123 DxWBS (A) and F-18 FDG PET/CT (B,C) for elevated serum thyroglobulin level (3 to 17 ng/ml) after left modified radical lymph node dissection two years ago. I-123 DxWBS (A) does not show abnormal uptake. On F-18 FDG PET/CT (B), focal uptakes were shown in the left lateral neck (arrow). On axial view of fusion image (C), two hypermetabolic lesions were

cells (Moretti et al., 2005; Piwnica-Worms et al., 1994; Saggiorato et al., 2009). MIBI irreversibly passes into the mitochondria using the electrical gradient generated by a high negative inner transmembrane mitochondrial potential of malignant cells (Chernoff et al., 1993; Moretti et al., 2005; Piwnica-Worms et al., 1994). Also, there is a report that TSH simulates both F-18 FDG PET and Tc-99m MIBI uptake in poorly differentiated papillary thyroid cancer in vitro experiment (Kim et al., 2009). Even though Tc-99m MIBI is inferior to I-131 scintigraphy in detecting I-131 avid lesions (Al Saleh et al., 2007), it can be applied for patients with elevated serum human thyroglobulin levels but negative I-131 whole body scan (Wu et al., 2003). However, there are several reports that F-18 FDG PET is more sensitive than Tc-99m MIBI SPECT in detecting metastatic cervical lymph node in differentiated thyroid cancer patients with elevated serum thyroglobulin level but negative

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).

seen in the left cervical level II. Biopsy revealed recurred papillary carcinoma.

I-131 whole body scan (Iwata et al., 2004; Wu et al., 2003) (Figure 13).

**4.3 Tc-99m tetrofosmin**

Thallium-201 (Tl-201) is a monovalemt cationic radioisotope listed in same group with gallium in the periodic table. The membrane permeability for Tl-201 is almost equal to that for potassium (Elgazzar et al., 1993). It is suggested that intracellular accumulation of thallous ions is due to the transmembrane electropotential gradient (Mullins & Moore, 1960). The primary role of Tl-201 in nuclear medicine is for imaging of myocardial perfusion and viability (Pauwels et al., 1998). Also, Tl-201 chloride has affinity for various malignant tumors, although it is not specific for malignant tumor (Senga et al., 1982). Uptake of Tl-201 in tumor seems to be determined by blood flow, grade of malignancy, viability of tumor cells and tumor necrosis (Pauwels et al., 1998). There are several reports regarding Tl-201 and thyroid cancer. Shiga et al. compared FDG PET with I-131 and Tl-201 scintigraphy and reported that FDG uptake was concordant with I-131 in 38% and with Tl-201 uptake in 94% (Shiga et al., 2001). Senga et al. reported that when tumor showed a positive scan with Tl-

Post-Therapeutic I-131 Whole Body Scan in Patients with Differentiated Thyroid Cancer 245

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201 chloride but negative results using Ga-67 citrate, it was differentiated thyroid carcinoma or poorly differentiated adenoma (Senga et al., 1982). Carril et al. analyzed Tl-201 and I-131 in ablated thyroid cancer patients. They reported that the sensitivity and specificity were 94% and 96% for Tl-201 and 29% and 100% for I-131 (Carril et al., 1997). Nakada et al. reported that Tl-201 uptake correlated well with the proliferating cell nuclear antigen index, which represents proliferative activity (Nakada et al., 1999).
