A combined positron emission tomography (PET)-electron paramagnetic resonance imaging (EPRI) system: initial evaluation of a prototype scanner

Abstract

The advent of hybrid scanners, combining complementary modalities, has revolutionized the application of advanced imaging technology to clinical practice and biomedical research. In this project, we investigated the melding of two complementary, functional imaging methods: positron emission tomography (PET) and electron paramagnetic resonance imaging (EPRI). PET radiotracers can provide important information about cellular parameters, such as glucose metabolism. While EPR probes can provide assessment of tissue microenvironment, measuring oxygenation and pH, for example. Therefore, a combined PET/EPRI scanner promises to provide new insights not attainable with current imagers by simultaneous acquisition of multiple components of tissue microenvironments. To explore the simultaneous acquisition of PET and EPR images, a prototype system was created by combining two existing scanners. Specifically, a silicon photomultiplier (SiPM)-based PET scanner ring designed as a portable scanner was combined with an EPRI scanner designed for the imaging of small animals. The ability of the system to obtain simultaneous images was assessed with a small phantom consisting of four cylinders containing both a PET tracer and EPR spin probe. The resulting images demonstrated the ability to obtain contemporaneous PET and EPR images without cross-modality interference. Given the promising results from this initial investigation, the next step in this project is the construction of the next generation pre-clinical PET/EPRI scanner for multi-parametric assessment of physiologically-important parameters of tissue microenvironments.

Development of a PET/EPRI combined imaging system for assessing tumor hypoxia

“…We have integrated a PET system with an EPRI system and produced successful imaging results for animals. Recently, a combined PET/PERI system was reported by Tseytlin et al [32], showing successful imaging of a multi-modality phantom containing trityl and FDG solution, but no animal imaging results. This system is different from ours reported here in terms of the PET detector technology and the integration of the PET and EPRI systems.…”

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

“…The reported PET/EPRI scanner potentially enables the detection of components of tumor microenvironments. Relatively low spatial resolution and d sensitivity which are common limitations of the reported preclinical scanner po can be overcome using EPR-compatible PET systems with higher resolution and d sensitivity than the reported scanner [287]. Kim and co-workers reported MRI-guided PET/EPRI scanner to probe oxyg centration in hypoxic regions of mice bearing squamous cell carcinoma [288].…”

“…Raylman and co-workers reported a combined PET/EPRI prototype scanner for simultaneous acquisition of EPR and PET images of hypoxic samples that are created by removing endogenous oxygen by adding glucose and glucose oxidase [ 287 ]. The PET/EPRI scanner was used to detect oxygen-sensing EPR spin probe [per-deuterated ‘Finland’ trimethyl (trityl) radical (dFT)] and PET radiotracer 6 in samples ( Figure 17 ).…”

“…The reported PET/EPRI scanner potentially enables the detection of cellular components of tumor microenvironments. Relatively low spatial resolution and detection sensitivity which are common limitations of the reported preclinical scanner potentially can be overcome using EPR-compatible PET systems with higher resolution and detection sensitivity than the reported scanner [ 287 ].…”

“…Adapted with permission of IOP Publishing, Ltd., from A combined positron emission tomography (PET)-electron paramagnetic resonance imaging (EPRI) system: initial evaluation of a prototype scanner, Tseytlin, M.; Stolin, A. V.; Guggilapu, P.; Bobko, A. A.; Khramtsov, V. V.; Tseytlin, O.; Raylman, R. R. 63 , 2018 ; permission conveyed through Copyright Clearance Center, Inc. [ 287 ].…”