Simultaneous calibration phantom commission and geometry calibration in cone beam CT

Abstract

Geometry calibration is a vital step for describing the geometry of a cone beam computed tomography (CBCT) system and is a prerequisite for CBCT reconstruction. In current methods, calibration phantom commission and geometry calibration are divided into two independent tasks. Small errors in ball-bearing (BB) positioning in the phantom-making step will severely degrade the quality of phantom calibration. To solve this problem, we propose an integrated method to simultaneously realize geometry phantom commission and geometry calibration. Instead of assuming the accuracy of the geometry phantom, the integrated method considers BB centers in the phantom as an optimized parameter in the workflow. Specifically, an evaluation phantom and the corresponding evaluation contrast index are used to evaluate geometry artifacts for optimizing the BB coordinates in the geometry phantom. After utilizing particle swarm optimization, the CBCT geometry and BB coordinates in the geometry phantom are calibrated accurately and are then directly used for the next geometry calibration task in other CBCT systems. To evaluate the proposed method, both qualitative and quantitative studies were performed on simulated and realistic CBCT data. The spatial resolution of reconstructed images using dental CBCT can reach up to 15 line pair cm. The proposed method is also superior to the Wiesent method in experiments. This paper shows that the proposed method is attractive for simultaneous and accurate geometry phantom commission and geometry calibration.

A line fiducial method for geometric calibration of cone-beam CT systems with diverse scan trajectories

“…The proposed calibration method assumes that for each fixed wire, i , line parameters X i , D i describing the 3D pose of the wire be known a priori with negligible error. This is analogous to traditional BB-based calibration which supposes a known 3D model for the BB locations (although extensions may be possible, similar to (Xu et al 2017)). With sophisticated manufacturing resources, it may be possible to precisely fabricate the wire phantom so that desired X i , D i are achieved with high accuracy.…”

C1 Posterior Arch Flare Point: A Useful Landmark for Fluoroscopically Guided C1–2 Puncture

“…26,27 This contrasts with CT images, which are calibrated to a phantom. 28,29 Thus, measurements between modalities can vary due to geometric distortion. Although normative distances on this study were acquired by CT myelography rather than fluoroscopy, the flare point technique itself does not depend on transposition of distances from one technique to another.…”

1-point RANSAC for circular motion estimation in computed tomography (CT)

“…An alternative approach to improving the result of tomographic reconstruction is the so-called online calibration. Methods of online calibration allow to evaluate and correct geometric errors after or directly during the tomographic experiment [16,17,18,19,20]. It can be seen that there is a gradual transition from methods with an a priori known position and shape of the calibration object (for example, [18], 2014) to methods with the simultaneous reconstruction and and geometric error correction ( [17], 2017).…”

“…Methods of online calibration allow to evaluate and correct geometric errors after or directly during the tomographic experiment [16,17,18,19,20]. It can be seen that there is a gradual transition from methods with an a priori known position and shape of the calibration object (for example, [18], 2014) to methods with the simultaneous reconstruction and and geometric error correction ( [17], 2017). An important step in tomographic reconstruction methods with a simultaneous refinement of the motion parameters is the estimation of the relative camera motion using tomographic projections.…”