Development and Initial Results of a Brain PET Insert for Simultaneous 7-Tesla PET/MRI Using an FPGA-Only Signal Digitization Method.

Jun Yeon Won,Jeong-Whan Son,Yina Chung,Haewook Park,Jun-Young Chung,Kyeong Yun Kim,Yeunchul Ryu,Junghyun Song,Seungeun Lee,Jae Sung Lee,Guen Bae Ko,Seongho Seo

doi:10.1109/tmi.2021.3062066

Abstract

In study, we developed a positron emission tomography (PET) insert for simultaneous brain imaging within 7-Tesla (7T) magnetic resonance (MR) imaging scanners. The PET insert has 18 sectors, and each sector is assembled with two-layer depth-of-interaction (DOI)-capable high-resolution block detectors. The PET scanner features a 16.7-cm-long axial field-of-view (FOV) to provide entire human brain images without bed movement. The PET scanner early digitizes a large number of block detector signals at a front-end data acquisition (DAQ) board using a novel field-programmable gate array (FPGA)-only signal digitization method. All the digitized PET data from the front-end DAQ boards are transferred using gigabit transceivers via non-magnetic high-definition multimedia interface (HDMI) cables. A back-end DAQ system provides a common clock and synchronization signal for FPGAs over the HDMI cables. An active cooling system using copper heat pipes is applied for thermal regulation. All the 2.17-mm-pitch crystals with two-layer DOI information were clearly identified in the block detectors, exhibiting a system-level energy resolution of 12.6%. The PET scanner yielded clear hot-rod and Hoffman brain phantom images and demonstrated 3D PET imaging capability without bed movement. We also performed a pilot simultaneous PET/MR imaging study of a brain phantom. The PET scanner achieved a spatial resolution of 2.5 mm at the center FOV (NU 4) and a sensitivity of 18.9 kcps/MBq (NU 2) and 6.19% (NU 4) in accordance with the National Electrical Manufacturers Association (NEMA) standards.

Highlights

POSITRON emission tomography (PET) allows for quantitative measurement of the spatiotemporal distribution of radiotracers
We evaluated the performance of the brain PET insert using both National Electrical Manufacturers Association (NEMA) NU 2-2018 and NU 4-2008 standards because no NEMA standards dedicated for the brain PET scanner is currently available
We developed the 7T MRI-compatible brain PET insert based on the field-programmable gate array (FPGA)-only data acquisition (DAQ) system and evaluated the PET performance in terms of spatial resolution and sensitivity using the NEMA NU 2 and NU 4 standards

Summary

Introduction

POSITRON emission tomography (PET) allows for quantitative measurement of the spatiotemporal distribution of radiotracers. The simultaneous operation of PET and magnetic resonance imaging (PET/MRI) scanners enables better spatiotemporal correlation between the functional and anatomical data from both imaging modalities [11, 12]. PET/MRI yields less radiation exposure and features a superior soft-tissue contrast than PET/computed tomography (CT), resulting in better diagnostic performance in various applications despite the fact that attenuation correction in PET/MRI is more complex than the PET/CT [12,13,14]. The optical fiber made it possible to transfer scintillation photons to the photomultiplier tubes (PMTs) placed away from the scintillation crystals, thereby preventing the influence of the strong static magnetic field on the PET system [15, 16]. The transfer of scintillation lights through the optical fibers resulted in the degradation of energy and timing performances caused by the significant light loss during the light transfer

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Discussion

Conclusion