Performance Tests and Preliminary Results of the 3TMR-BrainPET Scanner Installed at the Forschungszentrum Julich

Recently a prototype of a new bimodal scanner was installed in our laboratory. This scanner combines magnetic resonance imaging (MRI) and positron emission tomography (PET) for brain studies. As the PET detector is located within the bore of the MRI scanner, simultaneous measurements are possible. The MR-component consists of a commercial 3T MRI scanner MAGNETOM Trio, whereas the PET detector has been newly developed. The readout electronics of the PET is based on Avalanche photodiodes (APDs) which are not affected by the magnetic field. The inner diameter of the PET ring, which consists of 32 cassettes, is 36 cm so that a MRI head coil can be inserted into this ring. First tests were done to analyze the countrate behavior, the scatter fraction and the image resolution. To assess the image quality of simultaneous MR-PET studies a brain-shaped phantom containing F-18-solution was scanned. The prompt-minus-delayed countrate showed a peak of 680000 cps at 50 kBq/cc. The scatter fraction was 27%. The image resolution in the centre was between 2.1 and 2.5 mm in x,y,z directions. The MR-PET studies of the brain-shaped phantom showed no visible artifacts of the MR image and the PET images showed much better delineation of the cortex compared to equivalent images recorded with the PET-only scanner Siemens HR+. The tests done until now yielded promising results so that a first qualitative human brain study could be performed.