Faculty of Physics, Astronomy
and Applied Computer Science

Author: Faranak Tayefi Ardebili

Supervisor: prof. Paweł Moskal
Auxilliary supervisor: dr Szymon Niedźwiecki

Defence year: 2024

This study aim is to evaluate the performance characteristics of the Modular Jagiellonian Positron Emission Tomograph (Modular J-PET) in accordance with the recognized standards established by the National Electrical Manufacturers Association (NEMA) for Positron Emission Tomography (PET) scanners. The Modular J-PET represents the lat-est prototype within the Jagiellonian-PET group, distinguished by its utilization of plastic scintillator strips optimized for the precise detection of back-to-back gamma quanta arising from electron-positron annihilations. The Modular J-PET comprises 24 individual mod-ules arranged in a symmetrical 24-sided polygon circumscribing a circular configuration with a diameter of 73.9 cm. Each module is constructed from 13 scintillator strips, aligned adjacently, each measuring 50 cm in length and possessing a cross-sectional dimension of 6 mm × 24 mm. Dual-ended scintillation light readout is accomplished through analog Silicon Photomultipliers (SiPMs).Data collected during the experimentation phase were subjected to analysis employing software known as the J-PET Framework. The average system sensitivity of the ModularJ-PET was determined to be 0.768?0.003 cps/kBq in the center with the peak sensitivity of 2.1 cps/kBq. The system sensitivity has improved by sixfold compared to the first generation of the J-PET prototype with 192 strips.Radial spatial resolution for TOF image reconstruction methods was found to be 4.92?0.56 mm,7.38?0.49 mm, and 6.94?0.38 mm at positions 1 cm, 10 cm, and 20 cm from the detector center, respectively. Tangential spatial resolution for TOF image reconstruction methods was determined as 7.38?0.51 mm,7.37?0.10 mm, and 14.67?0.31 mm at the same positions, while axial spatial resolution was calculated as 30.73?0.52 mm,30.73?0.64 mm, and 31.96?0.29 mm. It is worth noting that the tangential and radial spatial resolution values of the Modular J-PET detector align closely with those of commercialPET devices. Future enhancements are anticipated in axial spatial resolution through anextended axial field of view scanner and the application of wavelength shifting (WLS)techniques. The determination of the scattered fraction based on single-scatter randoms background (SSRB) algorithms yielded a value of 41.68?0.19 [%], which is consistent with that observed in commercial PET devices. To validate the experimental findings,GATE simulations were conducted.The simulations included spatial resolution assessments using a sodium source, as wellas evaluations of sensitivity and scatter fraction involving a phantom conforming to NEMA standards. The simulations indicated that the Modular J-PET achieves a system sensitivity of 1.324?0.032 cps/kBq at the center of the detector?s field of view and 1.313?0.001 cps/kBq at a 10 cm offset from the tomograph center. The peak sensitivity at the center of the detector?s filed of view to be 2.9 cps/kBq across various multiplicity cuts. Fur-thermore, the scatter fraction, computed utilizing SSRB algorithms, was established at(40.25?2.3)%. Radial spatial resolution for TOF image reconstruction methods was found to be 4.80?0.59 mm,7.26?0.55 mm, and 6.67?0.42 mm at positions 1 cm, 10 cm, and 20 cm from the detector center, respectively. Tangential spatial resolution for TOF image reconstruction methods was determined as 7.27?0.47 mm ,7.27?0.59 mm, and 15.1?0.4 mm at the same positions, while axial spatial resolution was calculated as 29.97?0.49 mm,30.53?0.74 mm, and 31.78?0.11 mm.The Modular J-PET, characterized by its single-layer configuration with 50 cm scintillator strips, exhibits the potential for extension to an extended axial field-of-view through multi-layer arrangements. Consequently, the presented Modular J-PET prototype holds promise for the cost-effective development of a total-body J-PET system constructed from plastic scintillators.

Author: Shivani Shivani

Supervisor: prof. Paweł Moskal

Defence year: 2023

The thesis focuses on the design and fabrication of a specialized detector system called J-PEM (Jagiellonian Positron Emission Mammography) optimized for breast imaging. This system utilizes plastic scintillators, wavelength shifters, and photodetectors to improve spatial resolution and detection of annihilation photons. The prototype system consists of a single module comprising two layers of plastic scintillators and one layer of wavelength shifters. Silicon Photomultipliers are used for signal readout. The use of plastic scintillators and wavelength shifters enables the achievement of a spatial resolution of approximately 5 mm, as validated by simulation studies and experimental analyses. Despite being a single-head module, the J-PEM system demonstrates spatial resolution comparable to established imaging modalities, making it a cost-effective tool for breast cancer detection. Comparisons between different configurations suggest that employing wavelength shifters without optical separation yields superior resolution. The J-PEM system incorporates DOI (depth of interaction) sensitivity, which indicates the potential for further enhancements through narrower wavelength shifters in future advancements. Overall, the research findings highlight the effectiveness, efficiency, and potential of the J-PEM system for improving breast cancer detection with enhanced spatial resolution.

Author: Gabriela Łapkiewicz

Supervisor: dr Szymon Niedźwiecki

Defence year: 2024

Positronium imaging is a tool that could raise the specificity of medical imaging. A part of the development of the positronium imaging technique is establishing the method for the assessment of detector imaging precision and comparison of the results obtained between various scanners. This thesis presents the methods and results of positronium imaging of 4 materials per- formed with modular J-PET and Biograph Vision Quadra PET/CT scanners and compares them with Positronium Annihilation Lifetime Spectroscopy studies of the same samples. The compared materials were disks of quartz glass and 3 metals of high purity: aluminum, nickel and copper. The metal samples spectra are expected to be characterised by short- living components that correspond to positrons directly annihilating in the metal lattice. The mean lifetime of positron in such samples are dependent on the lattice parameters but may be influenced by the lattice defects. The quartz glass is an amorphous substance that is characterised by the ortho-positronium mean lifetime in range representative for biological tissues. A hypothesis was formulated that that it is possible to obtain the positronium mean lifetime spectra with three detection systems presented in this thesis and analysis of the spectra will yield similar results: the quartz glass will stand out by longer component of ortho-positronium lifetime in comparison with metal samples. To test the stated hypothesis, the author had performed measurements on PALS system and modular J-PET scanner, preselected the data using dedicated software and analysed the spectra with PALS Avalanche software. Author had also performed analysis of the spectra obtained with Biograph Vision Quadra. This work have shown that the applied method of measurement and analysis is applica- ble for each of the presented setup. The percentage difference between mean lifetime values obtained with PALS and Biograph Vision Quadra scanner does not exceed 7%. The per- centage difference between mean lifetime values obtained with PALS and modular J-PET scanner does not exceed 30%. The stated hypothesis was proven that in all measurement setups it is possible to differentiate between quartz glass and metal, based on the mean lifetime of ortho-positronium and positron mean lifetime components.