서강대학교

초록/요약

Combining positron emission tomography (PET) and magnetic resonance imaging (MRI) in research on small animals has shown the advantage of simultaneous imaging of structural and functional information. The multiplexing circuit called high-resolution event positioning circuit (EPC) was developed to reduce a large number of readout channel in this study. High-resolution PET dedicated small animal imaging has been developed by extending an EPC module to the system level. The developed small animal PET was inserted into 9.4T MRI to achieve a simultaneous small animal imaging. This dissertation reports on the principle of EPC, performance of small animal PET and PET-MRI and imaging capability of simultaneous small animal imaging. A PET detector block was composed of 2 × 3 detector modules, each of which consisted of an 8 × 8 array of 1.52 × 1.52 × 6 mm3 LYSO, a 4 × 4 array MPPC and 0.7 mm thickness of light guide. The PET insert consisted of 18 detector blocks comprising 65 mm transverse FOV and 41 mm axial FOV. The output signals from the PET detectors were transmitted to readout electronics using 4 m long flexible flat cables to minimize mutual interference between PET and MRI by separately locating PET detector and electronics. The PET gantry having only detector blocks was placed in an MRI bore and RF coil was fitted inside the PET insert. The PET performance including energy resolution, time resolution, spatial resolution and sensitivity was measured in 9.4T preclinical MRI. Interference between PET and MRI was assessed by measuring SNR and uniformity of MR images and flood map of PET in high magnetic field. The simultaneous whole-body images of mice injected with 10-20 MBq [18F]FDG or 18F were obtained to demonstrate the imaging performance of preclinical PET-MRI system. Energy and time resolutions measured for 511 keV gamma rays were 13.2 ± 0.3% and 3.8 ns, respectively. The spatial resolution at the center of transaxial FOV was 1.5 mm and a peak sensitivity at the center of axial FOV was 2.1%. No considerable degradation of MRI performance was observed and SNR and homogeneity of MR image were only slightly degraded 5% and 3% by the inserted PET, respectively. The acquired simultaneous images of phantom and animals demonstrated high-quality tracer uptake patterns and high-resolution anatomy. Experimental results indicated that high-quality simultaneous images of mice could be obtained using the developed PET-MRI system. MRI insertable small animal PET developed in this study offers light-weight design to integrate MR system and cost effective using readout circuit having a high multiplexing ratio.