Comparison of iodine-123-epidepride and iodine-123-IBZM for dopamine D2 receptor imaging.

Abstract

Although 123I-IBZM is widely used as a D2 receptor imaging agent, image quality is compromised by a relatively low target-to-nontarget ratio. Animal studies suggest that 123I-epidepride (Kd 0.024 nM) may be superior to 123I-IBZM, but this agent has not been systematically studied in humans. We directly compared 123I-epidepride and 123I-IBZM in five normal volunteers (age range 30-58 yr, mean 43 yr). Brain SPECT imaging was performed 2 hr after the 123I-IBZM injection (average dose 153 MBq). Iodine-123-epidepride scans were performed 1 hr (n = 3), 2 hr (n = 5) and 3 hr (n = 3) postinjection (average dose 149 MBq). Both radiopharmaceuticals were well tolerated. Iodine-123-epidepride provided excellent visualization of the striatum. Percent specific striatum uptake at 2 hr (71.7 +/- 4.9%) was much greater than with 123I-IBZM (32.6 +/- 5.3%, p < 0.01). Iodine-123-epidepride is a new D2 receptor agent that exhibits excellent neuroimaging properties and has a much higher affinity for striatal uptake than 123I-IBZM.