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A Feasibility Study On Reducing Metal Artifact in CT Using Collimation at the X-Ray Source

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R Schurr

R Schurr*, A Morrow , Baylor Scott & White Health, Temple, TX


SU-H3-GePD-I-1 (Sunday, July 30, 2017) 4:00 PM - 4:30 PM Room: Imaging ePoster Lounge

Purpose: To evaluate the feasibility of using lead collimation at the x-ray source during CT to reduce metal artifacts by blocking photons that would be otherwise scattered by a high density material.

Methods: A cylindrically symmetric phantom was fabricated using 2.2 cm diameter cerrobend cylinder and the CIRS Head and Torso Freepoint phantom. CBCT scans were taken using a Varian Clinac equipped with on-board imaging both with and without a hand-made cerrobend block which projected to the size of the metallic portion of the phantom at the detector plane. The block was 3.5 mm wide and 1 cm thick, and was placed in front of the full fan bowtie filter. Orthogonal kV images were used to position the CIRS phantom equipped with the cerrobend insert at isocenter. These images were evaluated using the tools provided in Eclipse. Simulations were performed to emulate the experimental setup using EGSnrc. An isotropic, monoenergetic 40 keV photon source was used with a 10:1 antiscatter grid. Due to the cylindrical symmetry, a single projection was simulated and the sinogram calculated mathematically. Image reconstruction for the simulation was performed using MATLAB.

Results: CBCT acquisitions taken with the cerrobend block attached to the bowtie filter had greater amounts of metal artifact, likely due to uncertainties in both the manufacturing process and block placement. There was not a noticeable difference in the amount of metal artifact present in the simulated CT images. However, the Monte Carlo simulations showed dose deposited in the phantom decreased by approximately 22% for the specific geometry evaluated.

Conclusion: Neither experimentation with CBCT nor simulations in EGSnrc demonstrated reduced metal artifact. Placement of collimation close to the CT x-ray source may have the ability to reduce the imaging dose delivered to the patient without adversely affecting image quality in axial scans.

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