The effect of subchronic treatment with l‐dopa/carbidopa or l‐selegiline on striatal dopamine transporters (DAT) was examined in patients with idiopathic Parkinson's disease with SPECT (single photon emission computed tomography) using [123I]β‐CIT (2β‐carbomethoxy‐3β‐[4‐iodophenyl]tropane) as the radiotracer. Patients who were not currently being treated with these medications were given either 750 mg l‐dopa/carbidopa per day (n = 8) or 10 mg l‐selegiline per day (n = 8). [123I]β‐CIT imaging was performed three times in each patient: at baseline before treatment, while on medication and after 4–6 weeks of drug treatment, and following withdrawal from medication (approximately 1 week for l‐dopa/carbidopa and 9 weeks for l‐selegiline). Comparison of scans 2 and 3 provided a measure of drug occupancy of the [123I]β‐CIT binding site; comparison of scans 1 and 2 provided a measure of both up‐ or downregulation of DAT levels and drug occupancy following subchronic drug treatment. DAT levels were assessed from an image acquired approximately 22 hours after radiotracer injection as a ratio of regional brain activities: (striatum − occipital)/occipital. Striatal DAT levels were not significantly different when any two of the three scans were compared for both drug treatments. These results suggest that typical clinical doses of l‐dopa/carbidopa and l‐selegiline do not induce significant occupancy of the [123I]β‐CIT binding site and that 4–6 weeks of treatment causes no significant modulation of DAT levels. These results support the validity of measuring DAT levels with [123I]β‐CIT without the need to withdraw patients from medication treatment.

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The proposed camera-based method for measuring thyroid uptake is accurate and reproducible. It can be performed readily in conjunction with the routine scan procedure. Adoption of this technique reduces equipment requirements in the nuclear medicine department.

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