A Geant4-based Monte Carlo study of a benchtop multi-pinhole X-ray fluorescence computed tomography imaging

Luzhen Deng,1,2 Biao Wei,1 Peng He,1,3 Yi Zhang,4 Peng Feng1,3 1Key Laboratory of Optoelectronics Technology and System, Chongqing University, Ministry of Education, Chongqing 400044, China; 2Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; 3Engineering Research Center of Industrial Computed Tomography Nondestructive Testing, Chongqing University, Ministry of Education, Chongqing 400044, China; 4College of Computer Science, Sichuan University, Chengdu 610065, China Background: X-ray fluorescence (XRF) computed tomography (XFCT) has shown promise for molecular imaging of metal nanoparticles such as gold nanoparticles (GNPs) and benchtop XFCT is under active development due to its easy access, low-cost instrumentation and operation. Purpose: To validate the performance of a Geant4-based Monte Carlo (MC) model of a benchtop multi-pinhole XFCT system for quantitative imaging of GNPs. Methods: The MC mode consisted of a fan-beam x-ray source (125 kVp), which was used to stimulate the emission of XRF from the GNPs, a phantom (3 cm in diameter) which included six or nine inserts (3 mm in diameter), each of which contained the same (1 wt. %) or various (0.08–1 wt. %) concentrations of GNPs, a multi-pinhole collimator which could acquire multiple projections simultaneously and a one-sided or two-sided two-dimensional (2D) detector. Various pinhole diameters (3.7, 2, 1, 0.5 and 0.25 mm) and various particle numbers (20, 40, 80 and 100 billion) were simulated and the results for single pinhole and multi-pinhole (9 pinholes) imaging were compared. Results: The image resolution for a 1 mm multi-pinhole was between 0.88 and 1.38 mm. The detection limit for multi-pinhole operation was about 0.09 wt. %, while that for the single pinhole was about 0.13 wt. %. For a fixed number of pinholes, noise increased with decreasing number of photons. Conclusion: The MC mode could acquire 2D slice images of the object without rotation and demonstrated that a multi-pinhole XFCT imaging system could be a potential bioimaging modality for nanomedical applications. Keywords: Geant4, Monte Carlo simulation, multi-pinhole, X-ray fluorescence computed tomography, gold nanoparticles, bioimaging modalit