CT acquisition using PET detectors and electronics

The emergence of positron emission tomography/computerized tomography (PET/CT) multimodality imaging has provided the ability to sequentially obtain anatomic and functional information using adjacent PET and CT scanners without having to move the patient from the bed. To avoid the need for successive PET and CT scans, we have investigated the possibility of acquiring both the anatomic and functional images using the same detection system, based on PET detectors and electronics operated in photon-counting mode. The detector consisted of a high-luminosity LSO scintillator individually coupled to an avalanche photodiode (APD) to enable low-energy X-ray detection at a high-count rate. A simulator was set up to collect tomographic data using a monochromatic 60 keV source (²⁴¹Am) to irradiate a phantom made of tissue-equivalent materials. The observed spatial resolution with this nonoptimized setup was better than 2 mm, demonstrating the capability to provide fairly accurate anatomical localization in CT counting mode. The three main constituents of biological tissues (bones, water, and air) could be clearly identified in the images with a dose significantly lower than with conventional CT operated in current mode. These preliminary results demonstrate the feasibility of dual-modality PET/CT imaging based on PET detectors and electronics, and suggest that substantial dose reduction would be possible by acquiring the CT image in photon-counting mode.