Optimized detector angle for improving signal-to-noise ratio of pinhole x-ray fluorescence computed tomography

In this work, we studied how the detector angle affects the signal-to-noise ratio (S/N) of X-ray fluorescence CT (XFCT), which is a major factor in reducing background noise and improving the detection sensitivity. We simulated a benchtop multi-pinhole XFCT system including a fan-beam x-ray source, a phantom (2.5 cm in diameter) consisting of one insert with gold nanoparticles (GNPs) , 2-sided multi-pinhole (3 pinholes) collimator aimed to acquire multiple projections simultaneously and 2-sided two-dimensional (2D) detector based on Geant4. The signal and noise were defined as the emitted Kα1=68.8keV X-ray fluorescence and Compton scatter fluorescence, respectively. The result was evaluated in three approaches at four different detector angles 60° (forward-scatter), 90° (side-scatter), 120° and 150° (back-scatter). In the simulation, the tube voltage was set to 90,100,110 and 120keV with fixed GNPs concentration (2%) and insert diameter (6mm).Then, the GNPs concentration was increased from 0.25%, 0.5%, 1% to 2% with fixed tube voltage (120keV) and insert diameter (6mm). Next, the insert diameter was set to 4, 6, 8, and 10mm with fixed tube voltage (120keV) and GNPs concentration (1%). The optimized detection angle was acquired by comparing the correlation between S/N and detector angles in terms of tube voltage, GNPs concentration and insert diameter. The experimental results demonstrated that, for most circumstances, the highest S/N could be obtained when detector angle was set to 120°.