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Optimization of the WLS design for positron emission mammography and Total-Body J-PET systems

Georgadze Anzori, Shivani Shivani, Ardebili Keyvan Tayefi, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

114--123

EN

Total-body positron emission tomography (PET) instruments are medical imaging devices that detect and visualize metabolic activity in the entire body. The PET scanner has a ring-shaped detector that surrounds the patient and detects the gamma rays emitted by the tracer as it decays. Usually these detectors are made up of scintillation crystals coupled to photodetectors that convert the light produced by the scintillation crystal into electrical signals. Jagiellonian Positron Emission Mammograph (J-PEM) is the first J-PET prototype module based on a novel idea with a plastic scintillator and wavelength shifter (WLS). At the same time, it is a prototype module for the Total-Body J-PET system. J-PEM can be an effective system for the detection and diagnosis of breast cancer in its early stage by improving sensitivity. This can be achieved using the superior timing properties of plastic scintillators combined with the WLS sheets readout. In this paper we present an application of the Geant4 program for simulating optical photon transport in the J-PEM module. We aim to study light transport within scintillator bars and WLS sheets to optimize gamma-ray hit position resolution. We simulated a pencil beam of 511 keV photons impinging the scintillator bar at different locations. For each condition we calculated the value of the pulse height centroid and the spread of the photon distribution. Some free parameters of the simulation, like reflectivity and the effective attenuation length in the sheet, were determined from a comparison to experimental data. Finally, we estimated the influence of the application of WLS layer in the Total-Body J-PET on the scatter fraction. To optimize the performance of the J-PEM module we compared geometry WLS strips 50 and 83. It was found that spatial resolution was 2.7 mm and 3.5 mm FWHM for 50 and 83 WLS strips, respectively. Despite the better granularity, the 83-strip WLS geometry exhibited poorer resolution due to fewer photons being transmitted to the strip, resulting in large fluctuations of signal.

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Optimization of positronium imaging performance of a simulated modular J-PET scanner using GATE software

Parzych Szymon

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

80--86

EN

Recently, a novel PET imaging method - positronium imaging - has been proposed to take advantage of previously unused information about the positronium states. The first ex-vivo and in-vivo images of positronium characteristics were acquired with the J-PET tomograph. Complementary to the standard annihilation photon’s detection, positronium imaging also requires the registration of the prompt photon, which follows β+ decay. To that end, the introduction of an additional energy threshold for prompt γ registration and optimization of the energy window for annihilation γ are required. This simulation-based work undertook the mentioned task in the case of the modular J-PET scanner. Based on the 44Sc radioisotope, the energy window for annihilation photons was established to 0.2 MeV - 0.37 MeV, while the threshold for prompt gamma was fixed at 0.37 MeV, closely following the end of the energy window for annihilation photons.

3

J-PET application as a Compton camera for proton beam range verification: A preliminary study

Kozani Majid, Rucinski Antoni, Moskal Pawel

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

23--30

EN

Hybrid in-beam PET/Compton camera imaging currently shows a promising approach to use of the quasi-real-time range verification technique in proton therapy. This work aims to assess the capability of utilizing a configuration of the Jagiellonian-positron emission tomography (J-PET) scanner made of plastic scintillator strips, so as to serve as a Compton camera for proton beam range verification. This work reports the production yield results obtained from the GATE/Geant4 simulations, focusing on an energy spectrum (4.2-4.6) MeV of prompt gamma (PG) produced from a clinical proton beam impinging on a water phantom. To investigate the feasibility of J-PET as a Compton camera, a geometrical optimisation was performed. This optimisation was conducted by a point spread function (PSF) study of an isotropic 4.44 MeV gamma source. Realistic statistics of 4.44 MeV PGs obtained from the prior step were employed, simulating interactions with the detector. A sufficient number of detected photons was obtained for the source position reconstruction after performing a geometry optimisation for the proposed J-PET detector. Furthermore, it was demonstrated that more precise calculation of the total deposited energy of coincident events plays a key role in improving the image quality of source distribution determination. A reasonable spatial resolution of 6.5 mm FWHM along the actual proton beam direction was achieved for the first imaging tests. This preliminary study has shown notable potential in using the J-PET application for in-beam PET/Compton camera imaging at quasi-real-time proton range monitoring in future clinical use.

4

Exploration of simultaneous dual-isotope imaging with multiphoton modular J-PET scanner

Beyene Ermias Y., Das Manish, Durak-Kozica Martyna, Korcyl Grzegorz, Mryka Wiktor, Niedźwiecki Szymon, Parzych Szymon, Tayefi Keyvan, Walczak Rafał, Wawrowicz Kamil, Stępien Ewa, Moskal Pawel

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

101--108

EN

The modular J-PET scanner, comprising 24 compact and versatile modules, each consisting of 13 plastic strips with four SiPM detectors at the ends, represents a powerful tool for clinical applications in nuclear medical imaging. This study presents preliminary results from the exploration of simultaneous dual-isotope imaging using the modular J-PET system. Our approach involved two isotopes: 68Ge, characterized by a ringlike shape, and 22Na, exhibiting a point-like shape. The imaging was based on double-coincidence and triple-coincidence events. In the double coincidence case, both isotopes contributed comparably, whereas in the triple coincidence case 22Na dominated due to the prompt gamma being emitted with 100% of positron emissions, unlike 68Ga, where the prompt gamma was emitted in only 1.3% of cases after positron emission. In this work we present direct 2γ images determined for two-signal events and images for three-signal events, with two signals from annihilation photons and one from a prompt gamma. These results showcase the preliminary findings from simultaneous dual-isotope imaging of 68Ga and 22Na isotopes using the modular J-PET scanner, which will be presented and discussed.

5

Evaluation of Modular J-PET sensitivity

Tayefi Ardebili Faranak, Niedźwiecki Szymon, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

132--138

EN

The Modular J-PET represents the latest advancement in the Jagiellonian-PET series, utilizing extended plastic scintillator strips. This prototype's modular design enables cost-effective imaging of multi-photon annihilation and positronium, allowing for easy assembly, portability, and versatility. Additionally, its lightweight construction facilitates static bed examinations with a mobile detection system that can be positioned conveniently alongside the patient, negating the requirement for spacious clinical settings. Comprising 24 modules arranged in regular 24-sided polygons circumscribing a 73.9 cm diameter circle, each module integrates 13 scintillator strips, measuring 50 cm in length and 6 mm × 24 mm in cross-section. Scintillation light is captured at both ends through analog Silicon Photomultipliers (SiPMs). This research presents Sensitivity of the Modular J-PET tomograph, adhering to the NEMA_NU 2-2018 standards. Sensitivity measurement was performed with 68Ge line source inside the 5 sleeves aluminium phantom placed at center of the detector`s field-of-view (FOV) and 10 cm offset from the center of detector. Analyzing the gathered data involved employing the specialized J-PET Framework software, developed within the C++ architecture. To validate the experimental findings, comparisons were made with GATE simulations, wherein the source and phantom were emulated in the same configuration as employed in the actual experiment. The system sensitivity of the Modular J-PET was assessed to be 1.03 ± 0.02 cps/kBq in the center of the detector`s FOV with the peak sensitivity of 2.1 cps/kBq. However, the simulations indicate that at the center of the detector's FOV, the Modular J-PET achieves a system sensitivity of 1.32 ± 0.03 cps/kBq, with a peak sensitivity of 2.9 cps/kBq.

6

Estimating the efficiency and purity for detecting annihilation and prompt photons for positronium imaging with J-PET using toy Monte Carlo simulation

Das Manish, Mryka Wiktor, Beyene Ermias Y., Parzych Szymon, Sharma Sushil, Stępień Ewa, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

87--95

EN

The positronium imaging technique represents a potential enhancement of the PET imaging method. Its core principle involves employing a β+ radiation source that emits additional gamma (γ) quanta referred to as prompt gamma. Our aim is to evaluate the capability to differentiate between annihilation and prompt gamma emissions, a vital aspect of positronium imaging. For this purpose, the selected isotopes should enable high efficiency and purity in detecting both prompt gamma and annihilation gamma. The assessment of the efficiency in identifying prompt and annihilation photons for various isotopes, which are potentially superior candidates for β++ γ emitters, is conducted through toy Monte-Carlo simulation utilizing the cross-section formula for photon-electron scattering. In this article, we have performed calculations for efficiency and purity values across different isotopes under ideal conditions and examined how these values evolve as we incorporate the fractional energy resolution into the analysis. Ultimately, the primary goal is to determine the energy threshold that optimizes both efficiency and purity, striking a balance between accurately identifying and recording events of interest while minimizing contamination from undesired events.

7

Convolutional neural networks in the classification of multiphoton coincidences in a J-PET scanner

Konieczka Paweł, Raczyński Lech, Wiślicki Wojciech

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

43--47

EN

This work describes an investigation into the utilization of convolutional neural networks for the classification of three-photon coincidences, focusing specifically on the para- -positronium decay associated with a photon from nuclear deexcitation. The data were simulated using the Monte Carlo method, with scandium-44 as the source of β+ decays. A preprocessing method that allowed for initial cleaning of the training data was described. Subsequently, the parameters of the method for transforming tabular data into images were optimized. Finally, the created images were used to train a binary classifier using a convolutional network model. The developed data preprocessing step and transformation method into image format enabled the achievement of a precision rate of 52% at a sensitivity level of 95%, which was a 10 percentage point improvement compared to the logistic regression model.

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A cross-staged gantry for total-body PET and CT imaging

Kaplanoğlu Muhammed Tevfik, Moskal Paweł

Bio-Algorithms and Med-Systems

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2023

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Vol. 19, no. 1

109--113

EN

Total-body Positron Emission Tomography (PET) scanning is a promising new method for rapidly acquiring comprehensive wide-volume metabolic data with a lower radiation dosage compared to discrete whole-body PET imaging. PET scanners are generally used with Computed Tomography (CT) scanners to precisely understand tumor location and composition with the help of anatomical images. However, PET/CT sequential imaging methods for simultaneous total-body imaging are impractical for claustrophobic patients due to the enclosed gantry design and require large examination rooms because of the need for an exceptionally long patient table. To address this challenge, the Jagiellonian-PET Tomography (J-PET) Total-body scanner employs an innovative approach: utilizing both PET and CT devices on the same patient table but from different axes. The motion system of the J-PET Total Body scanner requires custom linear stages to move both PET and CT gantries. In this study, a novel cross-staged linear guiding solution is proposed by combining scanners on intersecting separable stages. The proposed sliding system is a combination of different machine elements and will be produced for the J-PET Total-body PET/CT Scanner. Concept designs are shown, and the proposed system is described. The application of the system for the J-PET total-body PET/CT scanner is discussed. The proposed solution is still in the development phase. The system holds the potential to achieve combining CT and PET scanners from different axes and enables motion artifact-free imaging for total-body imaging.

9

Multi-photon time-of-flight MLEM application for the positronium imaging in J-PET

Shopa Roman Y., Dulski Kamil

Bio-Algorithms and Med-Systems

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2022

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Vol. 18, no. 1

135--143

EN

We develop a positronium imaging method for the Jagiellonian PET (J-PET) scanners based on the timeof-flight maximum likelihood expectation maximisation (TOF MLEM). The system matrix elements are calculated on-the-fly for the coincidences comprising two annihilation and one de-excitation photons that originate from the ortho-positronium (o-Ps) decay. Using the Geant4 library, a Monte Carlo simulation was conducted for four cylindrical 22Na sources of β+ decay with diverse o-Ps mean lifetimes, placed symmetrically inside the two JPET prototypes. The estimated time differences between the annihilation and the positron emission were aggregated into histograms (one per voxel), updated by the weights of the activities reconstructed by TOF MLEM. The simulations were restricted to include only the o-Ps decays into back-to-back photons, allowing a linear fitting model to be employed for the estimation of the mean lifetime from each histogram built in the log scale. To suppress the noise, the exclusion of voxels with activity below 2% - 10% of the peak was studied. The estimated o-Ps mean lifetimes were consistent with the simulation and distributed quasi-uniformly at high MLEM iterations. The proposed positronium imaging technique can be further upgraded to include various correction factors, as well as be modified according to realistic o-Ps decay models.

10

Positronium as a biomarker of hypoxia

Moskal Paweł, Stępień Ewa Ł.

Bio-Algorithms and Med-Systems

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2021

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Vol. 17, no. 4

311--319

EN

In this review article, we present arguments demonstrating that the advent of high sensitivity total-body PET systems and the invention of the method of positronium imaging, open realistic perspectives for the application of positronium as a biomarker for in-vivo assessment of the degree of hypoxia. Hypoxia is a state or condition, in which the availability of oxygen is not sufficient to support physiological processes in tissue and organs. Positronium is a metastable atom formed from electron and positron which is copiously produced in the intramolecular spaces in the living organisms undergoing positron emission tomography (PET). Properties of positronium, such as e.g., lifetime, depend on the size of intramolecular spaces and the concentration in them of oxygen molecules. Therefore, information on the partial pressure of oxygen (pO2) in the tissue may be derived from the positronium lifetime measurement. The partial pressure of oxygen differs between healthy and cancer tissues in the range from 10 to 50 mmHg. Such differences of pO2 result in the change of ortho-positronium lifetime e.g., in water by about 2–7 ps. Thus, the application of positronium as a biomarker of hypoxia requires the determination of the mean positronium lifetime with the resolution in the order of 2 ps. We argue that such resolution is in principle achievable for organ-wise positronium imaging with the total-body PET systems.

11

Novel biomarker and drug delivery systems for theranostics - extracellular vesicles

Stępień Ewa Ł., Rząca Carina, Moskal Paweł

Bio-Algorithms and Med-Systems

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2021

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Vol. 17, no. 4

301--309

EN

Extracellular vesicles (EVs) are nano- and micro-sized double-layered membrane entities derived from most cell types and released into biological fluids. Biological properties (cell-uptake, biocompatibility), and chemical (composition, structure) or physical (size, density) characteristics make EVs a good candidate for drug delivery systems (DDS). Recent advances in the field of EVs (e.g., scaling-up production, purification) and developments of new imaging methods (total-body positron emission tomography [PET]) revealed benefits of radiolabeled EVs in diagnostic and interventional medicine as a potential DDs in theranostics.

12

History of positron emission tomography (PET) in Poland

Cegła Paulina, Piotrowski Tomasz

Bio-Algorithms and Med-Systems

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2021

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Vol. 17, no. 4

259--264

EN

In this short chronological review, we showed the development of positron emission tomography (PET) starting from research on first isotopes through the concepts and prototype of PET machine to the current clinical practice and technological and clinical research. Particular emphasis was placed on a clear description of the milestones of PET development in Poland.

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Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector

Kamińska D., Gajos A., Czerwiński E., Bednarski T., Białas P., Gorgol M., Jasińska B., Kapłon Ł., Korcyl G., Kowalski P., Kozik T., Krzemień W., Kubicz E., Niedźwiecki S., Pałka M., Raczyński L., Rudy Z., Rundel O., Sharma N. G., Silarski M., Słomski A., Strzelecki A., Wieczorek A., Wiślicki W., Zieliński M., Zgardzińska B., Moskal P.

Nukleonika

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2015

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Vol. 60, No. 4, part 1

729--732

EN

In this paper, we present prospects for using the Jagiellonian positron emission tomograph (J-PET) detector to search for discrete symmetries violations in a purely leptonic system of the positronium atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium decays into three photons. No zero expectation values for chosen correlations between ortho-positronium spin and momentum vectors of photons would imply the existence of physics phenomena beyond the standard model. Previous measurements resulted in violation amplitude parameters for CP and CPT symmetries consistent with zero, with an uncertainty of about 10−3. The J-PET detector allows to determine those values with better precision, thanks to the unique time and angular resolution combined with a high geometrical acceptance. Achieving the aforementioned is possible because of the application of polymer scintillators instead of crystals as detectors of annihilation quanta.