Prototype integrated system of DOI- PET and the RF-coil specialized for simultaneous PET-MRI measurements

We are developing a PET system integrated with a birdcage RF coil for PET-MRI. The integrated system is intended to realize a highly sensitive PET system for simultaneous measurements. In the proposed PET-MRI system, PET detectors which consist of scintillator crystal blocks, photo sensors and front-end circuits with four-layer DOl encoding capability are placed close to the objective. Therefore, the proposed system can achieve high sensitivity without degradation of spatial resolution at the edge of the FOV due to parallax error. The photo sensors and front-end circuits should be shielded to minimize noises from the MRI and noise influence on the MRI imaging. Elements of the RF coil are inserted between the crystal blocks inside of the shielding material so as not to interfere with the RF-pulse. At the last MIC conference, we demonstrated the possibility of realizing the proposed PET-MRI system with a prototype PET detector and a commercial RF-coil. The prototype PET detector consisted of a LGSO crystal block and a 4 × 4 MPPC array. The crystals were arranged in a 4 × 4 × 4 layer with four-layer DOl capability. The detector and electrical circuit were packaged in an aluminum shielding box. Since they were located inside the MRI magnetic field, most circuit elements were made of nonmagnetic materials. As a next step, we constructed a new RF-coil system which can be mounted on PET detectors between each coil element. We carried out experiments with the prototype RF-coil and the fourlayer DOl detector. The prototype RF-coil has eight RF-coil elements and the PET detector can be mounted on gaps between them. Only one detector was mounted in the gap positioned at one side of the prototype RF-coil. We evaluated the performances from the 2D flood histogram, energy resolution and MRI images. We observed