Quantitative analysis of grid geometry effects on spatial harmonic imaging–based single-grid phase-contrast X-ray imaging

Single-grid phase-contrast X-ray imaging (SG-PCXI) enables simultaneous reconstruction of absorption, phase-contrast, and dark-field images from a single exposure using spatial harmonic imaging (SHI). Although the geometry of X-ray absorbing grids is known to influence imaging performance, its quantitative impact on SHI-based SG-PCXI has not been systematically characterized. This study investigates how the duty cycle (DC) and strip height of a grid affect fringe modulation, harmonic separation, and the resulting phase and dark-field sensitivity. Monte Carlo simulations were performed using the GATE 9.0 platform under controlled conditions (1 μm focal spot size and 10 μm detector pixel size). Increasing the DC from 0.16 to 0.66 improved grid visibility (GV) from 0.25 to 0.91 and the harmonic peak ratio (HPR) from 0.11 to 0.73. Increasing the strip height from 1.5 to 24.1 μm similarly raised GV from 0.09 to 0.91 and the HPR from 0.04 to 0.73. These changes resulted in a substantial increase in the edge signal-to-noise ratio (ESNR), from 5.4 to 32.6, with clearer edge definition in differential phase-contrast images and increased contrast in dark-field images. This work elucidates fundamental relationships between grid geometry, fringe modulation, and SHI performance, providing a quantitative basis for understanding design trade-offs in laboratory-scale SG-PCXI.