We propose to create and explore a radio-frequency (RF)-penetrable positron emission tomography (PET) system technology that can be inserted into a magnetic resonance imaging (MRI) system for acquiring simultaneous PET/MRI data. Integrated PET/MRI has risen to the cutting edge of medical imaging technology, showing promise to be a powerful tool in disease characterization as it enables the simultaneous measurement of molecular, functional, and anatomical information in soft tissues of the body. Because of this promise, companies such as Siemens, GE, and Philips have developed and are now offering combined PET/MR systems. However, one of the challenges affecting the long-term impact of this technology is the current cost ($5-6M) due to the huge investment required by a company to develop an integrated product, and the need for the user to purchase both PET and MRI sub-systems. Our lab is addressing these issues by creating the world's first RF-penetrable PET ring, which can in principle be inserted into any existing MR system, while still allowing use of the built-in MR RF transmit coil. This would avoid the expensive integration of the two modalities, which, up to now, in order to achieve whole-body PET/MR, has required substantial modifications to the MR system, including re-engineering the body transmit coil sub-system to reside inside the PET ring. Thus, the proposed technology would substantially lower the cost barrier for an existing MR site to upgrade to PET/MR capability since they would just need to purchase the RF-transmissive PET insert, and it also would reduce the industry investment to achieve integrated PET/MRI. Hypothesis: Using the novel electro-optical signal transmission scheme proposed, we can create a PET insert that is penetrable to a RF field and thus can achieve simultaneous ToF-PET/MR using the built in body transmit coil of an MR system. The basic idea to enable the PET ring insert to be RF-penetrable (i.e. for the RF field to leak inside of the PET ring) is to have it electrically floating with respect to the MR system, and to have small gaps between PET detector modules where the field lines can leak in. This floating PET ring is made possible via the concept of ?electro-optical? signal transmission, which draws from the field of telecommunications; in our formulation, the fast scintillation detector signals are coupled to tiny lasers, converted to near infrared light, and transmitted down long telecommunications-grade optical fibers, thus enabling electrical isolation from the MR system. In addition, since the electro-optical approach uses optical fibers, it substantially reduces the electrical footprint within the MR system compared to a PET system design that uses long electrical cables, while achieving excellent spatial, energy, and temporal resolutions required for PET. In this project, we will develop a full proof-of-principle of this RF-penetrable concept via a brain-size PET insert, and test its RF transmissivity in a 3T MRI system. In order to achieve these goals, we explore many innovative concepts.

Public Health Relevance

Integrated PET/MRI shows great promise to be a powerful, tool for multi-parameter disease characterization, however, currently available systems have a very high ($5-6M) price tag, which, in the long term will limit the availability and impact that this new multi-modal imaging modality has on medicine. If successful, the proposed RF-transmissive PET ring insert technology can be inserted into any existing MR system, without requiring modifications to the main MR system electromagnetic hardware, and, in particular, the built-in body coil may be used as the RF transmitter, and only the PET system is purchased. Such an insertable and removable ?PET coil? technology would greatly reduce the cost barrier required to achieve integrated, simultaneous PET/MR, thus increasing its availability to hospitals and overall impact on medicine.

National Institute of Health (NIH)
National Institute of Biomedical Imaging and Bioengineering (NIBIB)
Research Project (R01)
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Biomedical Imaging Technology Study Section (BMIT)
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Zubal, Ihor George
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Stanford University
Schools of Medicine
United States
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Lee, Brian J; Watkins, Ronald D; Chang, Chen-Ming et al. (2018) Low eddy current RF shielding enclosure designs for 3T MR applications. Magn Reson Med 79:1745-1752
Lee, Brian J; Grant, Alexander M; Chang, Chen-Ming et al. (2018) MR Performance in the Presence of a Radio Frequency-Penetrable Positron Emission Tomography (PET) Insert for Simultaneous PET/MRI. IEEE Trans Med Imaging 37:2060-2069
Cates, Joshua W; Bieniosek, Matthew F; Levin, Craig S (2017) Highly multiplexed signal readout for a time-of-flight positron emission tomography detector based on silicon photomultipliers. J Med Imaging (Bellingham) 4:011012
Chang, Chen-Ming; Cates, Joshua W; Levin, Craig S (2017) Time-over-threshold for pulse shape discrimination in a time-of-flight phoswich PET detector. Phys Med Biol 62:258-271
Grant, Alexander M; Lee, Brian J; Chang, Chen-Ming et al. (2017) Simultaneous PET/MR imaging with a radio frequency-penetrable PET insert. Med Phys 44:112-120