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  4. A KV-MV Cone Beam CT Metal Artifact Reduction Technique Using a Multi-Layer MV Imager and Poly-Energetic Correction

A KV-MV Cone Beam CT Metal Artifact Reduction Technique Using a Multi-Layer MV Imager and Poly-Energetic Correction

M Jacobson1*, M Lehmann2, P Huber2, M Myronakis1, M Shi4, D Ferguson1, I Lozano1, P Baturin3, T Harris1, R Fueglistaller2, C Williams1, D Morf2, R Berbeco1 (1) Brigham and Women's Hospital, Dana-Farber Cancer Institute, and Harvard Medical School, Boston, MA (2) Varian Medical Systems, Baden-Dattwil, Switzerland (3) Varian Medical Systems, Palo Alto, CA (4) University of Massachusetts, Lowell, Lowell MA

Presentations

(Monday, 7/15/2019) 7:30 AM - 9:30 AM

Room: 221AB

Purpose: Cone beam CT scans at typical kV energies produce metal implant artifacts that may obscure anatomy of interest in IGRT. As a remedy, we propose an artifact-reducing scan technique that incorporates low dose, full field of view projections acquired with a high DQE, multi-layer MV-imager. The supplementary MV data serves two functions: (1) to provide additional data for the final reconstruction (2) to provide an initial low-artifact reconstruction in which metal implants are easily segmented, giving a prior 3D geometric model of the implants.

Methods: The prior geometric model facilitates an adaptation of Joseph & Spital’s beam hardening technique (1978, J. Comp. Assist. Tomogr., 2:100-108), and is used to remove poly-energetic effects from the projections. Photon-starved kV projections corresponding to long path lengths through metal are also pre-detected using the prior model and inpainted with MV measurements. The corrected MV and kV data are FDK reconstructed and consolidated into a single image via weighted averaging. Performance tests were based on simulated acquisitions of phantoms with titanium implants: a thorax phantom with pedicle screws and a pelvis phantom with a hip replacement. The simulations captured x-ray source spectrum, noise, and detector efficiency characteristics observed in actual scans with the MV-imager prototype, as integrated into the Varian TrueBeam. The simulated dose of the kV and MV scans were each 12.5 mGy, the CTDI of the TrueBeam’s clinical Spotlight mode protocol. The proposed method was compared to images generated from TrueBeam’s simpler water-equivalent beam hardening correction algorithm.

Results: The proposed technique demonstrated artifact suppression superior to the TrueBeam’s usual image reconstruction chain, while nearly preserving soft tissue contrast typical of kV-only set-up CBCT scans.

Conclusion: Supplementing kV-imager projections with measurements from a high efficiency, multi-layer MV-imager promises to improve image guidance in patients with metal implants at modest additional dose.

Funding Support, Disclosures, and Conflict of Interest: NIH/NCI R01CA188446

Keywords

Cone-beam CT, Reconstruction, Image-guided Therapy

Taxonomy

IM- Cone Beam CT: Development (New Technology and Techniques)

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