Concept of a novel small animal PET system based on liquid TriMethyl Bismuth

This study focuses on the development of a concept for small animal PET systems based on energetic-photon readout using a heavy organometallic liquid. TriMethyl Bismuth (TMBi) is a transparent liquid with 82 % by weight of Bismuth. It effectively converts 511 keV photons by the photo-electric effect allowing to build detectors with high spatial resolution. For charge transport evaluation in TMBi we built a single-wire ionization chamber manufactured from electropolished ultra-high-vacuum compatible components. Ion yield measurements were performed under the presence of a Cs-137 source. Based on these findings we simulated a PET scanner in a ring shaped geometry using a dodecagonal design of detectors each divided into 5 layers to allow for depth-of-interaction measurements. The central point source sensitivity was determined as 10 %. Spatial resolution was sub-millimeter (0.7 mm FWHM) in the center of the FOV, and below 1 mm for a mouse-sized object. The excellent performance of the proposed PET system manifests in a high peak count rate of 232 kcps at 10 MBq activity for a mouse-sized object with an optimal operation range of the system between 5 and 20 MBq (count rates beyond 200 kcps). This study demonstrates that a small animal PET scanner based on liquid TMBi is an interesting concept for future research where the liquid TMBi would offer a variable scanner geometry avoiding gaps between detector volumes.