Dual SPECT of dopamine system using [^99mTc]TRODAT-1 and [¹²³I]IBZM in normal and 6-OHDA-lesioned formosan rock monkeys

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by a severe loss of the dopaminergic neurons in the substantia nigra pars compacta. In this study, we evaluated pre- and post-synaptic binding sites of the dopamine system in three normal and one parkinsonian monkeys using simultaneous [^99mTc]TRODAT-1 and [¹²³I]IBZM imaging. The parkinsonian monkey was induced by injecting 6-hydroxydopamine (6-OHDA) bilaterally into the medial forebrain bundle under MRI guidance. [^99mTc]TRODAT-1 (targeting dopamine transporters) and [¹²³I]IBZM (targeting D₂/D₃ receptors) were administered almost simultaneously and the SPECT images were acquired over 4 h using a dual-headed gamma camera equipped with ultra-high resolution fan-beam collimators. Data were obtained using energy window of 15% centered on 140 keV for ^99mTc in conjunction with 10% asymmetric energy window in a lower bound at 159 keV for ¹²³I. Single SPECT studies of [^99mTc]TRODAT-1 and [¹²³I]IBZM were also performed. We found a comparable image quality and uptake ratios between single- and dual-isotope studies. There are higher TRODAT-1 uptakes in the control monkeys than the 6-OHDA-lesioned monkey. The uptake of [¹²³I] IBZM showed no significant difference between controls and 6-OHDA-lesioned monkey. Our results suggest that dual isotope imaging using [^99mTc]TRODAT-1 and [¹²³I]IBZM may be a useful means in evaluating the changes of both pre- and post-synaptic dopamine system in a primate model of parkinsonism.