Influence of (99m)Tc-pertechnetate thyroid imaging on radioactive iodine uptake

To observe the influence of (99m)Tc-pertechnetate on radioactive iodine uptake (RAIU) in patients with Graves' disease (GD) hyperthyroidism after thyroid scintigraphy.

Totally 40 patients in whom thyrotoxicosis was diagnosed at Peking Union Medical College Hospital from 2013 March to May were recruited, and RAIU were performed in all patients. Gamma-count rates at 1 h,25 h,49 h,73 h and 169 h were examined respectively after intravenous injection of 185 MBq (5mCi)of (99m)Tc-pertechnetate. The counts of (99m)Tc and (131)I as well as effective half-life of (99m)Tc (Teff (99m)Tc) were calculated respectively according to the half-life formula. The ratio of (99m)Tc to background counts (1200) was calculated as a reference value to evaluate biokinetics of (99m)Tc.The relationship between the effective half-life of (99m)Tc(Teff (99m)Tc) and the level of free triiodothyronine (FT3), free thyroxine (FT4), and effective half-life of (131)I (Teff (131)I)were also evaluated.

After intravenous injection of (99m)Tc-pertechnetate, (99m)Tc counts at 1h, 25h, 49h, 73h and 169h was (440.16±247.35)×10(4), (11.37±10.67)×10(4), (0.13±0.36)×10(4), (-0.1±0.19)×10(4), respectively, and the ratio of (99m)Tc to background at 1h, 25 h, and 49 h was 3668, 94.75, and 1.08, respectively. The Teff (99m)Tc was (4.41±0.49)h. Inverse correlations were noted between the effective half-life of Teff (131)I and level of FT3 (r=-0.503, P=0.003) and FT4 (r=-0.516, P=0.002), while no significant correlation was found between the Teff (99m)Tc and FT3, FT4 as well as the Teff (131)I.

Teff (99m)Tc is 4.41h, (99m)Tc-pertechnetate thyroid imaging does not influence RAIU three days after injection of (99m)Tc-pertechnetate. Teff (99m)Tc shows no correlation with the thyroid hormone level and RAIU of Graves's hyperthyroidism.