Room: Exhibit Hall | Forum 5
Purpose: We have been investigating two-dimensional antiscatter grids (2D grid) to reduce x-ray scatter in CBCT, and consequently improve the reconstructed image quality. In this work, we present 2D grid prototypes with high grid ratios, and benchmark their performance with respect to a high grid ratio one-dimensional antiscatter grid in CBCT images.
Methods: Two 2D grid prototypes, with grid ratios of 12 (R12) and 16 (R16), were fabricated from tungsten using an additive manufacturing techniques. Both prototypes have a grid pitch of 2mm and septal thickness of 100Âµm, with septa focused to the x-ray focal point in Varian TrueBeam CBCT half-fan geometry. Prototypes were mounted directly on the flat panel detector, and images were reconstructed using the FDK algorithm. To study the effect of object size on CT number accuracy, CBCT, head and body electron density phantoms were employed, and contrast-to-noise ratio (CNR) improvements were evaluated for each grid configuration under identical conditions.
Results: In comparisons of head and body phantoms with identical contrast inserts, HU values were underestimated from a range of 12-37% with 1D grid, whereas HU underestimation was reduced to a range of 2-16% with both 2D grid prototypes. In the Head and Body phantoms, 2D grid prototypes provided 50-181% and 47-103% improvement in CNR, respectively, when compared to 1D grid. While 2D grid (R16) provided better HU accuracy, 2D grid (R12) provided slightly higher CNR improvement.
Conclusion: Our study indicates that 2D antiscatter grids can provide significantly improved CT number accuracy, and CNR when compared to contemporary, high grid ratio 1D grids. Thus, we believe 2D grids may play a critical role in improving quality of CBCT images. Hence, we strongly believe that 2D antiscatter grids may lead to improved utilization of CBCT in a range of clinical applications, such as CBCT guided radiation therapy.
Funding Support, Disclosures, and Conflict of Interest: This project is supported in part by NIH/NCI R21CA198462. Tesla K40 GPU was provided by NVIDIA Corporation. CBCT electron density phantom was provided by Gammex Inc.