Physics process level discrimination of detections for GATE: Assessment of contamination in SPECT and spurious activity in PET

Abstract

The GEANT4 application for tomographic emission (GATE) is one of the most detailed Monte Carlo simulation tools for SPECT and PET. It allows for realistic phantoms, complex decay schemes, and a large variety of detector geometries. However, only a fraction of the information in each particle history is available for postprocessing. In order to extend the analysis capabilities of GATE, a flexible framework was developed. This framework allows all detected events to be subdivided according to their type: In PET, true coincidences from others, and in SPECT, geometrically collimated photons from others. The framework of the authors can be applied to any isotope, phantom, and detector geometry available in GATE. It is designed to enhance the usability of GATE for the study of contamination and for the investigation of the properties of current and future prototype detectors. The authors apply the framework to a case study of Bexxar, first assuming labeling with 124I, then with 131I. It is shown that with 124I PET, results with an optimized window improve upon those with the standard window but achieve less than half of the ideal improvement. Nevertheless, 124I PET shows improved resolution compared to 131I SPECT with triple-energy-window scatter correction.

Virtual grating approach for Monte Carlo simulations of edge illumination-based x-ray phase contrast imaging

“…In other words, one MC simulation can serve as a basis for a virtually unlimited number of grating parameter variations. To achieve this high degree of flexibility, the concept of virtual volumes is introduced in GATE, relying on the ProcessGATE library [46]. The virtual volumes replace the explicit gratings in GATE, as shown in Fig.…”

Simulated grating-based x-ray phase contrast images of CFRP-like objects

“…Tracking of the optical path length was done using the processGate library [17] and the refraction process was implemented in the GATE source code, hereby extending the existing physics library [18].…”

Fast simulation of yttrium‐90 bremsstrahlung photons with GATE

“…During the initial simulations, the properties of the emitted photons, i.e., their type ͑bremsstrahlung or gamma͒, their energy, and their emission position, are stored. 15 Furthermore, the relative emission incidence of gamma and bremsstrahlung photons is also computed. Positron emission is not incorporated in the radioactive decay of 90 Y implemented in GEANT4.…”

“…The dimensions of the phantom ensure that all bremsstrahlung photons are created. The GATE code was modified 15 to record the position, energy, and origin of all bremsstrahlung and gamma photons emitted from the 90 Y decay. This information was then processed, and the PDFs required by the fast bremsstrahlung photon generator were created.…”