Projection-Domain Sensitivity Analysis of Vertebral DRRs Under Intrinsic Calibration Perturbation

2026-07-11

AI Summary

The impact of geometric calibration errors on projection consistency in digitally reconstructed radiographs (DRRs) of vertebrae and on 2D–3D registration performance remains unclear. This study establishes a synthetic simulation framework that systematically quantifies, for the first time in the projection domain, how intrinsic parameter perturbations—applied under fixed anatomy and imaging poses—affect DRR geometry, contour morphology, and registration accuracy. Leveraging CT-derived vertebral models, controllable cone-beam geometry, and multi-metric evaluation—including fiducial displacement, contour distance, overlap metrics, and image similarity—the work reveals distinct sensitivities between anteroposterior and lateral views to calibration errors. Even minor intrinsic parameter deviations significantly distort DRR projections, particularly in lateral views, and substantially degrade rotational accuracy in 2D–3D registration, thereby establishing a new paradigm for assessing calibration robustness.

Abstract

Accurate geometric calibration is essential for fluoroscopy-guided spinal imaging, digitally reconstructed radiograph (DRR) generation, and 2D--3D vertebral registration. Although calibration quality is typically evaluated using reconstruction-based metrics such as reprojection error, its influence on projection-domain consistency remains poorly understood. This study presents a synthetic framework for evaluating how intrinsic calibration perturbations affect vertebral fluoroscopic projections and downstream registration performance. CT-derived vertebral models and controlled cone-beam imaging geometry were used to generate DRRs with both ground-truth and perturbed intrinsic calibration parameters while maintaining identical anatomy and acquisition pose. Projection-domain changes were quantified using anatomical landmark displacement, contour distance, silhouette overlap, image similarity, and landmark-based 2D--3D registration accuracy in anterior--posterior (AP) and lateral (LAT) views. Results show that even small intrinsic calibration perturbations produce measurable changes in vertebral projection geometry, contour morphology, landmark localization, and DRR appearance. Sensitivity is strongly view dependent, with LAT projections exhibiting substantially greater deformation and anatomical displacement than AP projections. These projection inconsistencies also degrade downstream 2D--3D registration, particularly rotational alignment accuracy. The findings demonstrate that projection-domain consistency complements conventional reconstruction-based calibration metrics and provides a practical framework for assessing calibration robustness. This approach may improve the reliability of DRR generation and fluoroscopy-guided vertebral registration in image-guided spinal applications.

Problem

• intrinsic calibration
• projection-domain consistency
• vertebral DRR
• 2D--3D registration
• fluoroscopy-guided imaging

Innovation

• projection-domain analysis
• intrinsic calibration perturbation
• digitally reconstructed radiograph (DRR)
• 2D–3D vertebral registration
• fluoroscopy-guided imaging