SIMULTANEOUS 99mTc AND 123I DUAL-ISOTOPE BRAIN STRIATAL PHANTOM SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY: VALIDATION OF 99mTc-TRODAT-1 AND 123I-IBZM SIMULTANEOUS DOPAMINE SYSTEM BRAIN IMAGING

[2[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo[3,2,1]-oct-2-yl]-methyl](2-mercaptoethyl)amino]ethyl]amino]ethanethiolato(3-)-N2,N2',S2,S2]oxo-[1R-exo-exo)])-[Tc-99m]-technetium (Tc-99m-TRODAT-1) and I-123-iodobenzamide (I-123-IBZM) are radiotracers for brain dopamine pre- and postsynaptic neuron imaging. The purpose of this study was to evaluate imaging parameters and crossed energy interference using simultaneous single photon emission computed tomography (SPECT) Tc-99m and I-123 data acquisition. A five-compartment brain striatal phantom was filled with Tc-99m and/or I-123 radioactive solutions with different striatal-to-background ratios, ranging from 3:1 to 9:1. SPECT data were acquired with energy window settings of 15% for the centered window at 140 keV for Tc-99m and a 10% asymmetric window at 159 keV for I-123. The experiments were carried out using either individual (Tc-99m or I-123 only) or both radionuclides. The striatal-to-background ratios and energy crossed interference between Tc-99m and I-123 were calculated. The phantom SPECT images demonstrated that the energy crossed interferences from I-123 to Tc-99m, and vice versa, were 22 +/- 12.4% and 0.4 +/- 1.0%, respectively. A net interference of 7.1 +/- 4.0% for the counts in the 15% centered 99mTc window can be expected from I-123 and a net interference of 1.6 +/- 3.3% for the counts in the 10%, asymmetric I-123 window was derived from I-123 to Tc-99m. The correlation of striatal-to-background ratios between single isotope and simultaneous dual-isotope was excellent (R-2=0.99). The imaging parameters used in this simultaneous dual-isotope SPECT imaging could be used in future clinical practice for imaging patients with movement disorders by using Tc-99m-TRODAT-1 and I-123-IBZM. The striatal-to-background ratios were not affected by the crossed interference between Tc-99m and I-123.