Modeling of a PET system in GATE and CASToR, and evaluating the magnetic field effect on image reconstruction

• Main Author: Ξενάκης, Χαράλαμπος
• Other Authors: Xenakis, Charalampos
• Language: English
• Published: 2022
• Subjects: PET-MR; Monte Carlo; Τομογραφία εκπομπής ποζιτρονίων; Μαγνητική τομογραφία

Integrated PET/MR (Positron Emission Tomography/Magnetic Resonance) systems are present in the clinical field of medical diagnosis for the last decade, being considered a new and innovative modality. The pairing of the high detailed soft tissue anatomic information of the MRI (Magnetic Resonance Imaging) and the high sensitivity functional imaging of a PET scanner establishes a very promising future on the diagnostic field. The purpose of this study is to examine whether or not the co-existence of these two systems, has any unwanted consequences in the final reconstructed image dataset of the scan, due to the presence of positrons inside the magnetic field of the MRI, as well as due to the interference of the PET hardware in the gradients of the magnetic field. To achieve that, Monte Carlo simulations using the GATE software were performed, using a cylindrical PET system along with three cylindrical phantoms and radioactive sources of 68Ga and 18F inside various magnetic fields, and measuring the FWHM, to compare the spatial resolution of each separate case. The results came to be promising for the integrated system, as spatial resolution was lower (improved) in every case where a magnetic field was present, both in the two different sources and geometries (cylindrical and point source). Lastly, some concerns are mentioned, regarding some possible obstacles in the implementation of this modality, especially due to the hardware of the two systems, and the intervention of the PET scanner inside the MR. These problems could be solved by performing attenuation correction with the crystals of the PET into consideration, as well as incorporating more appropriate materials and electronics, to avoid unwanted temperatures on them or possible interactions with the magnetic field.