Whole-body biodistribution, radiation absorbed dose and brain SPECT imaging with iodine-123-β-CIT in healthy human subjects

SPECT imaging with ¹²³I-labeled methyl 3β-(4-iodophenyl)tropane-2β- carboxylate ([¹²³I]β-CIT) in nonhuman primates has shown brain striatal activity, which primarily reflects binding to the dopamine transporter. The biodistribution and calculated radiation-absorbed doses of [¹²³I]β-CIT administered to eight healthy subjects were measured with attention to the accurate determination of organ time-activity data. Methods: Whole-body transmission images were obtained with a scanning line source for attenuation correction of the emission images. Following administration of 92.5 ± 22.2 MBq (2.5 ± 0.6 mCi) of [¹²³I]β-CIT, subjects were imaged with a whole- body imager every 30 min for 3 hr, every 60 min for the next 3 hr and at 12, 24 and 48 hr postinjection. Regional body conjugate counts were converted to microcuries of activity, with a calibration factor determined in a separate experiment using a distributed source of ¹²³I. Results: The peak brain uptake represented 14% of the injected dose, with 2% of the activity approximately overlying the striatal region. Highest radiation-absorbed doses were to the lung (0.1 mGy/MBq, 0.38 rads/mCi), liver (0.087 mGy/MBq, 0.32 rads/mCi) and lower large intestine (0.053 mGy/mBq, 0.20 rads/mCi). Conclusions: Iodine-123-β-CIT is a promising SPECT agent for imaging of the dopamine transporter in humans with favorable dosimetry and high brain uptake.