Development of a tweezers-type coincidence imaging detector

Objective: When employing F-18-fluorodeoxyglucose (FDG)-guided surgery to detect positron accumulation in isolated small organs, sampling these organs from opposite directions is a useful way of determining a tumor's position, similar to sampling a small organ with tweezers. The coincidence method is suitable for this purpose because only the positrons between two detectors can be detected. For this purpose, we developed a tweezers-type coincidence imaging detector. Methods: The detector employs two depth-of-interaction (DOI) detectors positioned at the tip of the tweezers and images the positron distribution between them using the coincidence method. The DOI detector consists of a 4 × 3 Gd₂SiO₅:Ce (GSO) array optically coupled to a one-dimensionally arranged quad-photomultiplier tube. These GSOs were arranged to form a DOI detector using the Anger principle. The useful field of view is 20 mm × 15 mm. With these configurations, we could resolve 4 × 3 GSO arrays on a position histogram. Results: Because the imaging detectors were positioned at the tip of the tweezers, one could easily sample the target part manually from opposed sides. A real-time image in coincidence between these two DOI detectors could be obtained. The point spread functions were approximately 3-mm full width at half-maximum (FWHM) parallel to the tweezers and 4-mm FWHM perpendicular to them. The sensitivity was ∼1% when the two imaging detectors were 10 mm apart. Conclusions: With these results, we conclude that the developed tweezers-type imaging detector has a potential to be a new instrument in nuclear medicine