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Prototype time-of-flight PET ring integrated with a 3T MRI system for simultaneous whole-body PET/MR imaging
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2013
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EngineeringPet-mriAdvanced ImagingBiomedical EngineeringTreatment VerificationMagnetic Resonance ImagingX-ray ImagingPositron Emission TomographySipm DevicesDance ImagesIntegrated SystemInstrumentationNuclear MedicineRadiologyHealth SciencesMedical ImagingMri SystemAxial FovNeuroimagingMri-guided Radiation TherapyBiomedical ImagingFunctional X-ray ImagingImaging
148 Objectives A prototype time-of-flight PET system based on silicon photomultipliers (SiPM) has been developed for simultaneous whole body PET/MR imaging. In this study, performances of PET and MR components were evaluated in the integrated system. Methods The PET system comprises of 5 rings of 112 detector blocks (each a 4 x 9 array of LYSO crystals, 3.95 x 5.3 x 25 mm^3) coupled to 1 x 3 arrays of SiPM devices. The transaxial FOV is 60 cm and axial FOV is 25 cm. The PET detector gantry is centered inside the MR gradient set of a GE MR 750w 3T scanner on the outer diameter of the RF body coil. All the PET and MR measurements were performed with the two sub-systems integrated. To monitor the interaction between PET and the MR, standard MR sequences were employed. NEMA standard measurements were used to evaluate PET performance with MR idle and during synched PET/MR acquisition. MR IQ was assessed using a silicon oil-filled spherical phantom scanned during active PET acquisition. Results Using a Ge-68 pin source the measured PET energy resolution was 10.5 % FWHM at 511 keV for both RF ON and RF OFF. The per crystal timing resolution was 390 ps with RF OFF and 399 ps with RF ON. Transaxial spatial resolution of 3.9 mm FWHM was measured at 1 cm from isocenter using an F-18 capillary tube point source. The PET NEMA sensitivity measured with an F-18 line source was 23.8 cps/kBq with source at center and 23.5 cps/kBq at 10 cm radial offset including recovery of Compton scatter events that had energy deposited in adjacent blocks. The PET NEMA IQ phantom images with and without RF ON were visually comparable. Likewise, the powered PET detectors did not cause negative image artifacts on MR images and the B1 field homogeneity was maintained. Conclusions Initial PET and MR performance with and without MR pulse sequences running are promising and demonstrate feasibility for simultaneous imaging using the prototype hybrid PET/MR system.