Differences between 99mTc-sestamibi and 99mTc-tetrofosmin uptake in thyroid and salivary glands: comparison with 99mTc-pertechnetate in 86 subjects

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Abstract
99mTc-tetrofosmin seems to show a prolonged thyroid retention when compared with 99mTc-sestamibi; this may explain its poorer performance in the dual-phase parathyroid scintigraphy. In order to verify objectively whether and to what extent 99mTc-sestamibi and 99mTc-tetrofosmin uptake and retention differ in the thyroid gland, we performed a head-to-head comparison between the tracers in 86 euthyroid subjects enrolled in five centres. Data were compared with those of 99mTc-pertechnetate obtained from the same subjects. For comparison purposes, quantitative data from the salivary glands were also obtained. 99mTc-sestamibi showed a higher early thyroid uptake (2.26±0.52 vs. 2.01±0.49, respectively; P<0.002) and a lower retention (1.4±0.37 vs. 1.65±0.58, respectively; P<0.002) when compared with 99mTc-tetrofosmin. This finding provides an objective basis for the poorer results of 99mTc-tetrofosmin in dual-phase parathyroid scintigraphy. Delayed 99mTc-tetrofosmin salivary gland uptake was unexpectedly high and approached the 99mTc-pertechnetate value (2.29±0.56 vs. 2.46±0.75, respectively; P=not significant). This finding should be kept in mind in order to avoid interpretation pitfalls in thyroid and parathyroid imaging with 99mTc-tetrofosmin, as well as in other oncological imaging of the neck region. This study definitely establishes that 99mTc-tetrofosmin and 99mTc-sestamibi are not twin but rather sibling tracers.