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Error analysis of the x-ray projection geometry of camera-augmented mobile C-arm

The Camera-Augmented Mobile C-arm (CamC) augments X-ray by optical camera images and is used as an advanced visualization and guidance tool in trauma and orthopedic surgery. However, in its current form the calibration is suboptimal. We investigated and compared calibration and distortion correction between: (i) the existing CamC calibration framework (ii) Zhang's calibration for video images, and (iii) the traditional C-arm fluoroscopy calibration technique. Accuracy of the distortion correction for each of the three methods is compared by analyzing the error based on a synthetic model and the linearity and cross-ratio properties. Also, the accuracy of calibrated X-ray projection geometry is evaluated by performing C-arm pose estimation using a planar pattern with known geometry. The RMS errors based on a synthetic model and pose estimation shows that the traditional C-arm method (μ=0.39 pixels) outperforms both Zhang (μ=0.68 pixels) and original CamC (μ=1.07 pixels) methods. The relative pose estimation comparison shows that the translation error of the traditional method (μ=0.25mm) outperforms Zhang (μ=0.41mm) and CamC (μ=1.13mm) method. In conclusion, we demonstrated that the traditional X-ray calibration procedure outperforms the existing CamC solution and Zhang's method for the calibration of C-arm X-ray projection geometry.