Striatal and extrastriatal imaging of dopamine D2 receptors in the living human brain with [123I]epidepride single-photon emission tomography.

The iodine-123 labelled ligand benzamide epidepride was evaluated as a probe for in vivo imaging of striatal and extrastriatal dopamine D2 receptor sites in the human brain. Four healthy males were imaged with a high-resolution single-photon emission tomography scanner. Striatal radioactivity peaked at 3 h after injection. The specific binding in the striatum was 0.91+/-0.03 at 3 h and this ratio steadily increased with time. Extrastriatal radioactivity was highest in the thalamus, in the midbrain and in the temporal cortex, and peaked at 45-60 min after injection of tracer. A smaller amount of radioactivity was found in the parietal, frontal and occipital cortices. Two radioactive metabolites were observed, of which one was more lipophilic than the parent compound. The radiation burden to the patient was 0.035 mSv/MBq (effective dose equivalent). The preliminary results showed that [123I]epidepride can be used for imaging striatal and extrastriatal dopamine D2 receptor sites in the living human brain.