A Feasibility Study of a Prototype PET Insert Device to Convert a General-Purpose Animal PET Scanner to Higher Resolution

We developed a prototype system to evaluate the feasibility of using a PET insert device to achieve higher resolution from a general-purpose animal PET scanner. Methods: The system consists of a high-resolution PET detector, a computer-controlled rotation stage, and a custom mounting plate. The detector consists of a cerium-doped lutetium oxyorthosilicate array (12 × 12 crystals, 0.8 × 1.66 × 3.75 mm3 each) directly coupled to a position-sensitive photomultiplier tube (PS-PMT). The detector signals were fed into the scanner electronics to establish coincidences between the 2 systems. The detector was mounted to a rotation stage that is attached to the scanner via the custom mounting plate after removing the transmission source holder. The rotation stage was concentric with the center of the scanner. The angular offset of the insert detector was calibrated via optimizing point-source images. In all imaging experiments, coincidence data were collected from 9 angles to provide 180° sampling. A 22Na point source was imaged at different offsets from the center to characterize the in-plane resolution of the insert system. A 68Ge point source was stepped across the axial field of view to measure the sensitivity of the system. A 23.2-g mouse was injected with 38.5 MBq of 18F-fluoride and imaged at 3 h after injection for 2 h. Results: The transverse image resolution of the PET insert device ranges from 1.1- to 1.4-mm full width at half maximum (FWHM) without correction for the point-source dimension. This corresponds to approximately 33% improvement over the resolution of the original scanner (1.7- to 1.8-mm FWHM) in 2 of the 3 directions. The sensitivity of the device is 0.064% at the center of the field, 46-fold lower than the sensitivity of an existing animal PET scanner. The mouse bone scan had improved image resolution using the PET insert device over that of the existing animal PET scanner alone. Conclusion: We have demonstrated the feasibility of using a high-resolution insert device in an existing PET scanner to provide high-resolution PET. A PET insert device with more detector modules will improve sensitivity and may become an alternative to special-purpose PET systems for high-resolution PET.