Feasibility study for a PET detector integrated with an RF coil for PET-MRI

Various PET-MRI systems are being developed by a number of research groups. Since almost all the PET detectors used in these PET-MRI systems have no depth-of-interaction (DOI) capability. the parallax error restricts their performances in studies for rodents and the human brain. The DOI detector can reduce the parallax error and lead to improved performance, especially for the spatial resolution of the PET system portion. We have proposed a four-layer DOI encoding method and are developing a new PET system integrated with an RF-coil of the MRI using the four-layer DOI detectors. In the proposed system, PET detectors which consist of a scintillator block, photo sensors and front-end circuits are placed close to the objective. The photo sensors and front-end circuits should be shielded to minimize noises from the MRI and influence on MRI imaging. Elements of the RF coil are inserted between gaps of the scintillation crystal block. The RF-coil element is positioned inside the shielding material. We constructed a prototype four-layer DOI-PET detector and carried out experiments for performance evaluation in an actual MRI system. Additionally, we investigated influences on the PET detector and the MRI system from each other. As a result, sufficient detector performance regarding crystal identification and energy resolution was achieved in simultaneous measurements. The MRI images were also obtained as usual even though the DOI-PET detector was positioned close to the RF coil elements.