IODINE-223-IBF SPECT EVALUATION OF EXTRAPYRAMIDAL DISEASES

Iodine-123-IBF is a dopaminergic antagonist suitable for SPECT imaging of D2 receptors. Initial animal studies demonstrated that its affinit y for D2 receptors is approximately four times that of the commonly us ed SPECT D2 ligand [I-123]IBZM. I, this study we investigated whether this higher affinity would lead to an improved accuracy in differentia ting between various extrapyramidal diseases. Methods: SPECT imaging w as performed in 17 patients with idiopathic Parkinson's syndrome (IFS) ; 4 patients with progressive supranuclear palsy (PSP), 2 patients wit h multiple system atrophy (MSA) and 7 age-matched control subjects. SP ECT imaging was performed 5, 60, 120 and 180 min following intravenous bolus injection of 150-250 MBq of [I-123]IBF. The ratio of ligand upt ake in the basal ganglia and frontal cortex was determined as a measur e of receptor status. Results: In PSP and MSA patients, the basal gang lia-to-frontal cortex ratio reached a plateau at 2 hr; in the control subjects and the IFS patients the ratio was steadily increasing. At 3 hr the basal ganglia-to-frontal cortex ratio was 2.66 +/- 0.29 (contro l subjects), 3.01 +/- 0.41 (IFS), 2.09 +/- 0.22 (PSP) and 2.10 (MSA). In the IFS patients with predominantly one-sided symptoms, the striatu m contralateral to symptoms showed a tendency towards relatively incre ased ligand uptake. Despite the higher affinity of IBF for the D2 rece ptor compared to IBZM, the separation of individual PSP and MSA patien ts from the control subjects was not as clear cut as reported for IBZM due to a relatively high variation in the control subjects. We hypoth esize that the latter is due to imaging in nonequilibrium conditions. Conclusion: The data suggest that IBF-SPECT can help in discriminating extrapyramidal disease. The accuracy might be improved by an administ ration protocol that allows imaging in ''true equilibrium'' conditions , such as a bolus injection followed by a constant infusion.