Combined clinical PET/CT and microPET small animal imaging

Recent advances in multi-detector CT design have enabled isotropic sub-millimeter spatial resolution. Although dedicated small animal CT scanners have been developed, the latest generation of high-performance clinical CT scanners may have sufficient spatial resolution for the purposes of small animal imaging. We have investigated the use of a clinical 16-slice PET/CT scanner in combination with the microPETreg scanner for rodent imaging. A method for co-registering PET/CT and microPET images was developed to improve the anatomical localization of PET uptake and perform attenuation and scatter correction. CT and PET visible fiducial markers containing a ⁶⁸Ge point source are attached to a flat platform used in both the microPETreg and PET/CT imaging sessions to perform landmark based co-registration of the CT and microPETreg images. An automated registration method based on mutual information was also evaluated. The co-registered CT images were segmented into bone, soft tissue, and lungs and the respective attenuation coefficients at 511 keV were used to generate a transmission image for attenuation and scatter correction. Using this approach, high resolution co-registered CT and microPETreg images were obtained without the need for a dedicated small animal CT scanner or traditional PET transmission scanning. This improves the intreptation of microPET images and the correction for attenuation and scatter may be important when scanning larger species or multiple animals simultaneously