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Electrodynamics Of Continuous Media

Dynamic PET (dPET) studies have been used until now primarily within research purposes. Although it is generally accepted that the information provided by dPET is superior to that of conventional static PET acquisitions acquired usually 60 min post injection of the radiotracer, the duration of dynamic protocols, the limited axial field of view (FOV) of current generation clinical PET systems covering a relatively small axial extent of the human body for a dynamic measurement, and the complexity of data evaluation have hampered its implementation into clinical routine. However, the development of new-generation PET/CT scanners with an extended FOV as well as of more sophisticated evaluation software packages that offer better segmentation algorithms, automatic retrieval of the arterial input function, and automatic calculation of parametric imaging, in combination with dedicated shorter dynamic protocols, will facilitate the wider use of dPET. This is expected to aid in oncological diagnostics and therapy assessment. The aim of this review is to present some general considerations about dPET analysis in oncology by means of kinetic modeling, based on compartmental and noncompartmental approaches, and parametric imaging. Moreover, the current clinical applications and future perspectives of the modality are outlined.

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Kinetic modeling and parametric imaging with dynamic PET for oncological applications: general considerations, current clinical applications, and future perspectives

Total-body PET opens a new diagnostic paradigm with prospects for personalized disease treatment, yet the high cost of the current crystal-based PET technology limits dissemination of total-body PET in hospitals and even in research clinics. The J-PET tomography system is based on axially arranged low-cost plastic scintillator strips. It constitutes a realistic cost-effective solution of a total-body PET for broad clinical applications. High sensitivity of total-body J-PET and triggerless data acquisition enable multiphoton imaging, opening possibilities for multitracer and positronium imaging, thus promising quantitative enhancement of specificity in cancer and inflammatory disease assessment.

Prospects and Clinical Perspectives of Total-Body PET Imaging Using Plastic Scintillators.

PET instruments are now available with a long axial field-of-view (LAFOV) to enable imaging the total-body, or at least head and torso, simultaneously and without bed translation. This has two major benefits, a dramatic increase in system sensitivity and the ability to measure kinetics with wider axial coverage so as to include multiple organs. This article presents a review of the technology leading up to the introduction of these new instruments, and explains the benefits of an LAFOV PET-CT instrument. To date there are two platforms developed for total-body PET (TB-PET), an outcome of the EXPLORER Consortium of the University of California at Davis (UC Davis) and the University of Pennsylvania (Penn). The uEXPLORER at UC Davis has an AFOV of 194 cm and was developed by United Imaging Healthcare. The PennPET EXPLORER was developed at Penn and is based on the digital detector from Philips Healthcare. This multiring system is scalable and has been tested with 3 rings but is now being expanded to 6 rings for 140 cm. Initial human studies with both EXPLORER systems have demonstrated the successful implementation and benefits of LAFOV scanners for both clinical and research applications. Examples of such studies are described in this article.

Total Body PET: Why, How, What for?

Actions of radiations on living cells

PURPOSE There is a growing interest in extending the axial fields-of-view (AFOV) of PET scanners. One major limitation for the widespread clinical adoption of such systems is the multifold increase in the associated material costs. In this study, we propose a cost-effective solution to extend the PET AFOV using a sparse detector rings configuration. The corresponding physical performance was validated using Monte Carlo simulations. METHODS Monte Carlo model of the Siemens BiographTM mCT PET/CT, with a 21.8 cm AFOV and a set of compact rings of LSO crystals was developed as a gold standard. The mCT configuration was then modified by interleaving the LSO crystals in the axial direction within each detector block with 4 mm physical gaps (equivalent to the LSO crystal axial dimension) thus extending the AFOV to 43.6 cm (Ex-mCT). The physical performances of the two MC models were assessed and then compared using NEMA NU 2-2007 standards. RESULTS Ex-mCT showed <0.2 mm difference in transaxial spatial resolution, and, 0.8 mm and 0.3 mm deterioration in axial spatial resolution, compared to the mCT, at 1 and 10 cm off-center of the transaxial field-of-view respectively. The system sensitivities for the mCT and Ex-mCT models were 9.4 ± 0.2 and 10.75 ± 0.2 cps/kBq respectively. The higher sensitivity of Ex-mCT was due to four additional detector rings required to double the mCT AFOV. PET images of the NEMA Image Quality (IQ) phantom showed no artifacts due to detector rings sparsity, and all spheres were visible in both configurations. Ex-mCT achieved percent contrast recoveries within 5.6% of those of the mCT for all spheres and a maximum of 36% higher background variability at the center of the AFOV. The Ex-mCT, however, showed a more uniform noise distribution over an axial range of almost twice the length of the mCT AFOV. CONCLUSIONS Using the proposed sparse detector-ring configuration, the AFOV of current generation PET systems can be doubled while maintaining the original number and volume of detector crystal elements, and without jeopardizing the system's overall physical performance. Despite an increase in the noise level, the Ex-mCT exhibited an improved noise uniformity.

Physical performance of a long axial field‐of‐view PET scanner prototype with sparse rings configuration: A Monte Carlo simulation study

Virus irradiation has been performed for many decades for basic research studies, sterilization, and vaccine development The COVID-19 outbreak is currently causing an enormous effort worldwide for finding a vaccine against coronavirus High doses of γ-rays can be used for the development of vaccines that exploit inactivated virus This technique has been gradually replaced by more practical methods, in particular the use of chemicals, but irradiation remains a simple and effective method used in some cases The technique employed for inactivating a virus has an impact on its ability to induce an adaptive immune response able to confer effective protection We propose here that accelerated heavy ions can be used to inactivate SARS-CoV-2 viruses with small damage to the spike proteins of the envelope and can then provide an intact virion for vaccine development © Copyright © 2020 Durante, Schulze, Incerti, Francis, Zein and Guzman

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Virus Irradiation and COVID-19 Disease

We report on the NEMA-NU2-2012 performance of a hypothetical Monte Carlo (MC) model, Ex-PET, of the Siemens Biograph Vision positron emission tomography (PET)/CT (Bio-Vis) with sparse detector module rings and extended axial field of view (AFOV). MC simulations were performed with the detector module rings interleaved with 32-mm gaps, equivalent to the axial dimension of each detector module, yielding an AFOV of 48.0 cm (Bio-Vis has 25.6-cm AFOV). 3D-PET acquisition combined with a limited continuous-bed-motion (limited-CBM) was used to compensate for the loss in sensitivity within the gaps’ regions. MC simulations of the Bio-Vis were performed for comparison purposes. All MC simulations were performed using GATE MC toolkit. Ex-PET exhibited 0.49, 0.16, and 0.16 mm deterioration in axial resolution at 1, 10, and 20 cm off-center of the transaxial field of view, respectively, compared to Bio-Vis. Only 1% reduction in system sensitivity and 6% reduction in peak NECR was observed with Ex-PET compared to Bio-Vis. 3D-OSEM image reconstruction, combined with CBM, allowed compensating for the lack of counts within the gaps’ regions. NEMA Image Quality test showed < 6% reduction in contrast recovery with Ex-PET versus Bio-Vis, yet the background variability was increased by up to 8%. The feasibility of PET imaging with an easily adoptable sparse detector configuration was demonstrated. This can lay the pathway for future development of cost-effective PET systems with long and conventional AFOV’s.

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Monte Carlo Simulation of the Siemens Biograph Vision PET With Extended Axial Field of View Using Sparse Detector Module Rings Configuration

The purpose of this work is to extend the Geant4-DNA Monte Carlo toolkit to include electron interactions with the four DNA bases using a set of cross sections recently implemented in Geant-DNA CPA100 models and available for liquid water. Electron interaction cross sections for elastic scattering, ionisation, and electronic excitation were calculated in the four DNA bases adenine, thymine, guanine and cytosine. The electron energy range is extended to include relativistic electrons. Elastic scattering cross sections were calculated using the independent atom model with amplitude derived from ELSEPA code. Relativistic Binary Encounter Bethe Vriens model was used to calculate ionisation cross sections. The electronic excitation cross sections calculations were based on the water cross sections following the same strategy used in CPA100 code. These were implemented within the Geant4-DNA option6 physics constructor to extend its capability of tracking electrons in DNA material in addition to liquid water. Since DNA nucleobases have different molecular structure than water it is important to perform more accurate simulations especially because DNA is considered the most radiosensitive structure in cells. Differential and integrated cross sections calculations were in good agreement with data from the literature for all DNA bases. Stopping power, range and inelastic mean free path calculations in the four DNA bases using this new extension of Geant4-DNA option6 are in good agreement with calculations done by other studies, especially for high energy electrons. Some deviations are shown at the low electron energy range, which could be attributed to the different interaction models. Comparison with water simulations shows obvious difference which emphasizes the need to include DNA bases cross sections in track structure codes for better estimation of radiation effects on biological material.

Electron transport in DNA bases: An extension of the Geant4-DNA Monte Carlo toolkit

Positron Emission Tomography (PET) cameras encompass a set of compact crystal detector rings. In this proof of principle study, we introduce a sparse ring configuration involving half the original number of rings uniformly spaced across the same axial Field-of-view (FOV) and assess its effect on image quality and quantitation in PET imaging. The Siemens PET/MR (mMR) system matrix was adopted in our proposed configuration. mMR consists of 64 detector rings made of 4×4×20 mm3 LSO crystals, and extending over 25.6cm axial Field-of-view (FOV). To emulate our sparse rings configuration, counts in sinograms associated with at least one even ring number were zeroed (Sparse-Sinograms). To account for the loss in spatial information, the zeroed sinograms were estimated by linear interpolation in sinogram space (Inter-Sinogram). The PET images for the compact, the sparse and the interpolated sparse sinogram data were reconstructed using the OSEM algorithm (21 subsets, 5 iterations) provided by the Software for Tomographic Image Reconstruction using the original mMR system matrix to maintain the same number of slices in all images. We validated our approach for one brain FDG PET/MR dataset in terms of image quality, target-to-background ratio (TBR) and contrast-to-noise ratio (CNR) scores for different number of OSEM iterations. Sparse rings configuration yielded comparable image quality to that of the clinical dataset. TBR and CNR showed increased error with the number of OSEM iterations (8.3% and 23.6% respectively at 5 iterations), decreasing to 1.7% and 5.4% respectively in the Inter-Sinogram images. PET imaging with half the number of original detector rings uniformly spaced over the same axial FOV, yielded comparable image quality, yet reduced TBR and CNR, which may be recovered via linear inter-sinogram interpolation. Uniformly spacing a given set of PET detector rings to double their axial FOV is possible without significant losses in image quality and quantitation.

Sara A. Zein

Papers

Physical performance of a long axial field‐of‐view PET scanner prototype with sparse rings configuration: A Monte Carlo simulation study

Virus Irradiation and COVID-19 Disease

Monte Carlo Simulation of the Siemens Biograph Vision PET With Extended Axial Field of View Using Sparse Detector Module Rings Configuration

Electron transport in DNA bases: An extension of the Geant4-DNA Monte Carlo toolkit

Evaluation of Image Quality and Quantitation in a Clinical PET Scanner with a Uniformly Sparse Detector Rings Configuration