Second-Generation, Tri-Modality Pre-Clinical Imaging System

A second-generation, tri-modality instrument, comprising PET, SPECT, and CT subsystems, for pre-clinical imaging is described. Significant improvements have been made in each of the modalities as well as the integrated computer system. The SPECT system uses up to four CZT detectors with multiple pinhole apertures for each head, thereby increasing count sensitivity. Geometric corrections for pinhole size and alignment combine with spiral acquisition to give high-resolution, whole body images. Energy resolution of less than 5% at 140 keV gives full separation of gamma-ray peaks for dual-isotope imaging and scatter rejection. Dual-isotope images (I-123 and Tc-99m) from the new CZT SPECT system have been acquired in a mouse tumor model. The CT imager is positioned on the same plane as the SPECT system, providing precise co-registration. Unique shutters protect the SPECT and PET sensors from overexposure during CT data collection. The custom-designed X-ray tube has been configured to allow variable magnification and focal spot, thereby giving resolution down to less than 15 microns. CT acquisition can be completed in less than one minute, and the display software has been enhanced to display clinically-relevant Hounsfield units. Improved production methods yield superior light output for the BGO crystals used in the PET ring, resulting in better signal-to-noise ratios and consequently lower detection limits. Additionally, new software tools allow a significantly improved work flow and analysis capability.