WE-G-217BCD-01: BEST IN PHYSICS (IMAGING) - High-Quality CT Imaging in the Presence of Surgical Instrumentation Using Spectral System Models and Knowledge of Implanted Devices.

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. This work was supported in part by NIH 2R01-CA-112163.