Objective: Versatile emission computed tomography (VECTor) for small-animal imaging enables fully simultaneous SPECT/PET image acquisition based on clustered multi-pinhole collimation. The present study experimentally evaluated the detailed performance characteristics of the clustered multi-pinhole system for simultaneous (99m)Tc and (18)F imaging from the user perspective.
Methods: Spatial resolution, sensitivity, count rate linearity were determined for the VECTor system (MILabs). Two hot-rod micro-resolution phantoms with 6 sectors were created to test the resolution of (99m)Tc and (18)F. Sensitivity and count rate linearity were measured by scanning (99m)Tc and (18)F point sources positioned at the center of the field of view. Furthermore, we quantified the influence of (18)F on (99m)Tc SPECT images. The ratios of SPECT counts on the (99m)Tc-only and simultaneous (18)F-(99m)Tc at various time points were evaluated as a function of the (18)F-to-(99m)Tc activity concentration ratio.
Results: The 0.5-mm hot-rods can be visually distinguished in the (99m)Tc image, and 0.8-mm rods for (18)F remained clearly visible. The point-source sensitivity was 2800 cps/MBq for (99m)Tc and 2899 cps/MBq for (18)F, respectively. Count rates up to 120,000 cps for one bed position were linear for the activity. Spill-over from (18)F into (99m)Tc SPECT images was negligible when the activity concentration of the administered (18)F solution exceeded that of the (99m)Tc solution by up to a factor of 2.
Conclusions: We evaluated the performance characteristics of the VECTor that lead to determination of the optimal administered doses of (99m)Tc and (18)F tracers. We found that the VECTor achieved high resolution and high sensitivity as well as good (99m)Tc and (18)F linearity. Simultaneous SPECT/PET imaging with (99m)Tc and (18)F tracers, and stand-alone (99m)Tc and (18)F imaging using clustered-pinhole collimators is feasible and practical for a wide range of research applications using small animals.