# Intrinsic Tolerance in C-Arm Imaging: How Extrinsic Re-optimization Preserves 3D Reconstruction Accuracy

arXiv: https://arxiv.org/abs/2603.14031 · HTML: https://mlsanity.com/paper/2603.14031/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- Builds on 2 of its 24 references that are in the map.
- First posted on arXiv 14 Mar 2026.

## Builds on (most cited first, 2 of 2)

- [X-ray-transform Invariant Anatomical Landmark Detection for Pelvic Trauma Surgery](https://mlsanity.com/paper/1803.08608/) (2018)
- [Pedicle Screw Pairing and Registration for Screw Pose Estimation from Dual C-arm Images Using CAD Models](https://mlsanity.com/paper/2511.05702/) (2025)

## Built on by (most cited first, 1 of 1)

- [Projection-Domain Sensitivity Analysis of Vertebral DRRs Under Intrinsic Calibration Perturbation](https://mlsanity.com/paper/2607.10551/) (2026)

## Abstract (arXiv)

Purpose: C-arm fluoroscopy's 3D reconstruction relies on accurate intrinsic calibration, which is often challenging in clinical practice. This study ensures high-precision reconstruction accuracy by re-optimizing the extrinsic parameters to compensate for intrinsic calibration errors. noindentMethods: We conducted both simulation and real-world experiments using five commercial C-arm systems. Intrinsic parameters were perturbed in controlled increments. Focal length was increased by 100 to 700 pixels (≈20 mm to 140 mm) and principal point by 20 to 200 pixels. For each perturbation, we (1) reconstructed 3D points from known phantom geometries, (2) re-estimated extrinsic poses using standard optimization, and (3) measured reconstruction and reprojection errors relative to ground truth. noindentResults: Even with focal length errors up to 500 pixels (≈100 mm, assuming a nominal focal length of ~1000 mm), mean 3D reconstruction error remained under 0.2 mm. Larger focal length deviations (700 pixels) elevated error to only ≈0.3 mm. Principal point shifts up to 200 pixels introduced negligible reconstruction error once extrinsic parameters were re-optimized, with reprojection error increases below 0.5 pixels. noindentConclusion: Moderate errors in intrinsic calibration can be effectively mitigated by extrinsic re-optimization, preserving submillimeter 3D reconstruction accuracy. This intrinsic tolerance suggests a practical pathway to relax calibration precision requirements, thereby simplifying C-arm system setup and reducing clinical workflow burden without compromising performance.