Dynamic Cardiac SPECT for diagnostic and theranostics applications: latest results

To cost-effectively satisfy the high spatial resolution, high sensitivity, and SNR needs for cardiac SPECT imaging that has not been met with the conventional gamma camera, we are developing Dynamic Cardiac SPECT (DC-SPECT) for diagnostic and theranostics applications featuring: static body-contouring geometry with large detector coverage (~225 deg), large number of views using 80 detector modules each with a dedicated loft-hole collimator, and laser-processed CsI:Tl with converging pixels to avoid depth of interaction (DOI) blurring. The DC-SPECT design is based on using 10 mm thick CsI:Tl scintillators that can provide high stopping power for gamma-ray energies beyond the 140 keV. Given the DOI blurring issue inherent with pinhole collimators, the CsI:Tl pixels in our detectors have converging pixel volumes with a focal length equal to the detector-pinhole distance. Geometry optimization show that at 15 mm fixed resolution, DC-SPECT's sensitivity is 15x larger than that of a gamma camera. At 0.01% sensitivity, 4.1 mm resolution can be achieved which is close to whole-body PET. Also, at 10 mm resolution, sensitivity of ~0.07
^%
can be achieved. Note that the resolution values are without employing resolution recovery techniques. We have laser-processed multiple CsI:Tl crystals using a programmable femtosecond high power laser. Flood map of laser processed 17.4x17.4x6 mm3 detector coupled to Hamamatsu MPPC array shows that all pixel-like volumes can be resolved even with the unfavorable geometry imposed by the converging pixels. Another laser processed CsI:Tl crystal (50x50x10 mm3) coupled to SensL SiPM show that while most pixels are resolved, the 20% QE of the SiPM at 550nm (peak wavelength of CsI:Tl) compared with 35% of the MPPC array results in deteriorated flood map quality and lower energy resolution (~250/0 at 122 keV). We are now optimizing the laser process and readout electronics to improve flood map quality before implementing detector and collimator integration for phantom studies.