Feasibility of 2D antiscatter grid concept for flat panel detectors: preliminary investigation of primary transmission properties.

Suppressing the effects of scattered radiation in flat panel detector, FPD, based CBCT still remains to be a challenge. To address the scatter problem, we have been investigating the feasibility of a two dimensional antiscatter grid (2D ASG) concept for FPDs. Although a 2D ASG can potentially provide high scatter rejection capability, primary transmission characteristics of a 2D ASG and its implications in image quality plays a more critical role in implementation of the 2D ASG concept. Thus, in this work, a computational model was developed to investigate the primary transmission properties of the 2D ASG for various grid and FPD pixel geometries, and the improvement in signal to noise ratio,SNR, was calculated analytically to demonstrate the impact of 2D ASG's transmission characteristics on image quality. Computational model showed that average primary transmission fraction (Tp) strongly depends on the septal thickness of 2D ASG, and 2D ASG can provide higher Tp than existing radiographic ASGs at a septal thickness of 0.1 mm. Due to the higher Tp, 2D ASG was also predicted to provide SNR improvements in projections in low to moderate scatter environments typically observed in CBCT imaging. On the other hand, the model also indicated that the shadow or footprint of the 2D ASG leads to spatially nonuniform variations in primary signal in FPD pixels. Reduction of septal thickness and optimization of 2D ASG's pitch may play an essential role in reducing such variations in primary image signal, and avoiding potential image artifacts associated with 2D ASG's footprint.