Performance characteristics of a novel clustered multi-pinhole technology for simultaneous high-resolution SPECT/PET

Objectives The present study experimentally evaluated the detailed performance characteristics of the clustered multi-pinhole system for simultaneous ^99mTc and ¹⁸F 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 ^99mTc and ¹⁸F. Sensitivity and count rate linearity were measured by scanning ^99mTc and ¹⁸F point sources positioned at the center of the field of view. Furthermore, we quantified the influence of ¹⁸F on ^99mTc SPECT images. The ratios of SPECT counts on the ^99mTc-only and simultaneous ¹⁸F-^99mTc at various time points were evaluated as a function of the ¹⁸F-to-^99mTc activity concentration ratio.

Results The 0.5-mm hot-rods can be visually distinguished in the ^99mTc image, and 0.8-mm rods for ¹⁸F remained clearly visible. The point source sensitivity was 2,800 cps/MBq for ^99mTc and 2,899 cps/MBq for ¹⁸F, respectively. Count rates up to 120,000 cps for one bed position were linear for the activity concentration. Spill-over from ¹⁸F into ^99mTc SPECT images was negligible when the activity concentration of the administered ¹⁸F solution exceeded that of the ^99mTc 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 ^99mTc and ¹⁸F tracers. We found that the VECTor achieved high resolution and high sensitivity as well as good ^99mTc and ¹⁸F linearity. Simultaneous SPECT/PET imaging with ^99mTc and ¹⁸F tracers, and stand-alone ^99mTc and ¹⁸F imaging using clustered pinhole collimators, is feasible and practical for a wide range of research applications using small animals.