The aim of this study was to develop a prototype magnetic resonance (MR)-compatible positron emission tomography (PET) that can be inserted into a MR imager and that allows simultaneous PET and MR imaging of the human brain. This paper reports the initial results of the authors’ prototype brain PET system operating within a 3-T magnetic resonance imaging (MRI) system using newly developed Geiger-mode avalanche photodiode (GAPD)-based PET detectors, long flexible flat cables, position decoder circuit with high multiplexing ratio, and digital signal processing with field programmable gate array-based analog to digital converter boards.
A brain PET with 72 detector modules arranged in a ring was constructed and mounted in a 3-T MRI. Each PET module was composed of cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled to a tileable GAPD. The GAPD output charge signals were transferred to preamplifiers using 3 m long flat cables. The LYSO and GAPD were located inside the MR bore and all electronics were positioned outside the MR bore. The PET detector performance was investigated both outside and inside the MRI, and MR image quality was evaluated with and without the PET system.
The performance of the PET detector when operated inside the MRI during MR image acquisition showed no significant change in energy resolution and count rates, except for a slight degradation in timing resolution with an increase from 4.2 to 4.6 ns. Simultaneous PET/MR images of a hot-rod and Hoffman brain phantom were acquired in a 3-T MRI. Rods down to a diameter of 3.5 mm were resolved in the hot-rod PET image. The activity distribution patterns between the white and gray matter in the Hoffman brain phantom were well imaged. The hot-rod and Hoffman brain phantoms on the simultaneously acquired MR images obtained with standard sequences were observed without any noticeable artifacts, although MR image quality requires some improvement.
These results demonstrate that the simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.
The authors appreciate Jung Yeol Yeom, Ealgoo Kim, and Peter Olcott from Stanford University, USA for their critical review of this paper. The research was supported by the Converging Research Center Program (Grant No. 2012K001495) through the Ministry of Education, Science and Technology, and by the Industrial Strategic Technology Development Program (Grant No. 10030029) and the CITRC (Convergence Information Technology Research Center) support program (Grant No. NIPA-2013-H0401-13-1007) supervised by the NIPA (National IT Industry Promotion Agency) funded by the Ministry of Knowledge Economy, Republic of Korea.
II. MATERIALS AND METHODS
II.A. BrainPETsystem design
II.B. PETdetector module
II.C. Analog signal processing
II.D. Digital signal processing
II.E. MRIsystem and PET/MRI integration
II.F. PET performance evaluations
II.G.1. Effect of the MRI on the PETsystem
II.G.2. Effect of the PETsystem on the MRimage
II.H. Simultaneous PET-MR phantom imaging
III.A. Basic performance of the MR-compatible brainPETsystem
III.C. Simultaneous PET-MR phantom imaging
- Positron emission tomography
- Magnetic resonance imaging
- Medical magnetic resonance imaging
- Medical image noise
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