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BEST IN PHYSICS (IMAGING) - High-Quality CT Imaging in the Presence of Surgical Instrumentation Using Spectral System Models and Knowledge of Implanted Devices

W Zbijewski

W Zbijewski*, J Stayman, Y Otake, J Carrino, A Khanna, J Siewerdsen, Johns Hopkins University, Baltimore, MD

WE-G-217BCD-1 Wednesday 4:30:00 PM - 6:00:00 PM Room: 217BCD

Purpose: Imaging in the presence of implants (instrumentation and prostheses) presents a notoriously difficult challenge to CT because of photon starvation and beam hardening. To alleviate these limitations, a statistical reconstruction approach that includes knowledge of implant shape and composition was previously reported. This work extends the approach to modeling of photon transport, including polychromatic x-ray beams and scatter, and evaluates the method in simulated and real data.

Methods: Previous work on Known-Component Reconstruction (KCR) is first extended to include a polyenergetic beam (KCR-POLY). The method simultaneously estimates the unknown background volume and the position of implants with known attenuation and shape. Simulations included an anthropomorphic knee with a Co-Cr-Mo implant and system model for an extremities CT system (110 kVp+0.2 mm Cu). Experimental validation was performed on an imaging bench in which a Titanium spine fixation rod (65 mm long, 5.5 mm diameter) was imaged within a 20.5 cm diameter water cylinder (120 kVp+0.2 mm Cu) in geometry simulating an interventional C-arm.

Results: The polyenergetic system model was essential to high image quality in KCR reconstructions of large, highly attenuating implants such as knee prostheses and spine instrumentation, where standard penalized-likelihood and monoenergetic variants of KCR fail. The first application of KCR-POLY in real data demonstrates the potential of the algorithm in practice, reducing or eliminating artifacts and restoring image uniformity.

Conclusions: The KCR-POLY algorithm yielded major reduction in metal artifacts, owing both to a priori component knowledge (the implant) and account of the polyenergetic beam, object attenuation, and x-ray scatter. Ongoing research focuses on improvements to the registration algorithm, scatter, and experimental studies with complex, deformable implants. The work supports application of CT to a range of applications conventionally prohibited by metal implants - e.g. surgical guidance or diagnostic imaging of joints with prostheses.

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