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Optimization of the Design of a Moving Blocker for Cone-Beam CT Scatter Correction: Experimental Evaluation

X Chen

X Chen1*, L Ouyang1 , H Yan2 , X Jia1 , Y Zhang1 , J Wang1 , (1) UT Southwestern Medical Center, Dallas, TX, (2) Cyber Medical Corporation, Xi'an, China


WE-AB-207A-9 (Wednesday, August 3, 2016) 7:30 AM - 9:30 AM Room: 207A

Purpose: A moving blocker based strategy has shown promising results for scatter correction in cone-beam computed tomography (CBCT). Different geometry designs and moving speeds of the blocker affect its performance in image reconstruction accuracy. The goal of this work is to optimize the geometric design and moving speed of the moving blocker system through experimental evaluations.

Methods: An Elekta Synergy XVI system and an anthropomorphic pelvis phantom CIRS 801-P were used for our experiment. A blocker consisting of lead strips was inserted between the x-ray source and the phantom moving back and forth along rotation axis to measure the scatter signal. Accoriding to our Monte Carlo simulation results, three blockers were used, which have the same lead strip width 3.2mm and different gap between neighboring lead strips, 3.2, 6.4 and 9.6mm. For each blocker, three moving speeds were evaluated, 10, 20 and 30 pixels per projection (on the detector plane). Scatter signal in the unblocked region was estimated by cubic B-spline based interpolation from the blocked region. CBCT image was reconstructed by a total variation (TV) based algebraic iterative reconstruction (ART) algorithm from the partially blocked projection data. Reconstruction accuracy in each condition is quantified as CT number error of region of interest (ROI) by comparing to a CBCT reconstructed image from analytically simulated unblocked and scatter free projection data.

Results: Highest reconstruction accuracy is achieved when the blocker width is 3.2 mm, the gap between neighboring lead strips is 9.6 mm and the moving speed is 20 pixels per projection. RMSE of the CT number of ROIs can be reduced from 436 to 27.

Conclusions: Image reconstruction accuracy is greatly affected by the geometry design of the blocker. The moving speed does not have a very strong effect on reconstruction result if it is over 20 pixels per projection.

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