C-arm orbits for metal artifact avoidance (MAA) in cone-beam CT

Area of Science:

• Medical Imaging
• Radiological Physics
• Surgical Navigation

Background:

• Metal artifacts in cone-beam CT (CBCT) hinder visualization of surgical instruments and anatomy.
• These artifacts are particularly problematic in image-guided surgery, obscuring critical regions of interest.
• Existing methods often struggle with the complexity and variability of metal implants.

Purpose of the Study:

• To develop and evaluate a novel method for reducing metal artifacts in CBCT image-guided surgery.
• To prospectively define C-arm source-detector orbits that mitigate metal-induced biases in projection data.
• To ensure compatibility with existing reconstruction and post-processing techniques.

Main Methods:

• The Metal Artifact Avoidance (MAA) method involves: (i) localizing metal objects using low-dose scout views and segmentation, (ii) predicting metal-induced X-ray spectral shifts, and (iii) identifying optimal circular or non-circular C-arm orbits.
• The method was tested using digital simulations, phantom experiments, and cadaveric spine surgery models.
• It is compatible with filtered backprojection (FBP), model-based image reconstruction (MBIR), and metal artifact reduction (MAR) post-processing.

Main Results:

• MAA accurately predicted orbits that reduced metal artifact magnitude in CBCT reconstructions.
• Metal instrumentation was localized with a 0.71 median Dice coefficient from scout views.
• Tilted circular orbits reduced RMSE by 46%-70% and blooming artifacts by 20-45%.
• Non-circular orbits achieved an additional ~46% RMSE reduction compared to circular orbits.

Conclusions:

• The MAA method provides a practical approach to predict C-arm orbits that minimize spectral bias caused by metal instrumentation.
• Optimized orbits, including complex non-circular paths, substantially reduce metal artifacts in raw CBCT data.
• The improved projection data enhance subsequent MAR post-processing and MBIR for further artifact reduction.