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

Abstract

Modern cone-beam CT systems, especially C-arms, are capable of diverse source-detector orbits. However, geometric calibration of these systems using conventional configurations of spherical fiducials (BBs) may be challenged for novel source-detector orbits and system geometries. In part, this is because the BB configurations are designed with careful forethought regarding the intended orbit so that BB marker projections do not overlap in projection views. Examples include helical arrangements of BBs (Rougee et al 1993 Proc. SPIE 1897 161-9) such that markers do not overlap in projections acquired from a circular orbit and circular arrangements of BBs (Cho et al 2005 Med. Phys. 32 968-83). As a more general alternative, this work proposes a calibration method based on an array of line-shaped, radio-opaque wire segments. With this method, geometric parameter estimation is accomplished by relating the 3D line equations representing the wires to the 2D line equations of their projections. The use of line fiducials simplifies many challenges with fiducial recognition and extraction in an orbit-independent manner. For example, their projections can overlap only mildly, for any gantry pose, as long as the wires are mutually non-coplanar in 3D. The method was tested in application to circular and non-circular trajectories in simulation and in real orbits executed using a mobile C-arm prototype for cone-beam CT. Results indicated high calibration accuracy, as measured by forward and backprojection/triangulation error metrics. Triangulation errors on the order of microns and backprojected ray deviations uniformly less than 0.2 mm were observed in both real and simulated orbits. Mean forward projection errors less than 0.1 mm were observed in a comprehensive sweep of different C-arm gantry angulations. Finally, successful integration of the method into a CT imaging chain was demonstrated in head phantom scans.

A novel calibration method incorporating nonlinear optimization and ball‐bearing markers for cone‐beam CT with a parameterized trajectory

“…That means that the proposed method makes an effective improvement on the calibration accuracy and robustness against noise compared to the competing method. In particular, it is shown that the parameter η , which has a more significant impact on the image reconstruction, is one of the most improved() in terms of RE and RD , guaranteeing an optimal choice for the geometric parameters when noise is involved. In addition to the accuracy improvement, the proposed method can obtain the tilt angle ϕ which the competing method assumes to be zero.…”

“…These methods are computationally intensive and do not always give high‐resolution results. To calibrate some systems with irregular configurations, a number of methods are available based on complex phantoms . The main advantage of these methods is that they can obtain the full projection matrix using one projection.…”

“…To achieve this, the markers that compose a dedicated phantom need to satisfy some special conditions. Some of these methods require that the spatial position of these markers are known, and others need that the markers are arranged in a special pattern such as two circles or straight lines . The basic assumption for these methods is that the phantom should be fabricated precisely.…”

Marker trajectory assessment in optical cone beam computed tomography scanner geometry

“…An example of this is the IsoCal phantom and imaging protocol used to characterize the kilovoltage and megavoltage imaging systems on Varian medical linear accelerators [2]. X-ray cone beam CT scanner geometry calibration has been addressed by many researchers [3][4][5]. Often the calibrations involve analysis of small spheres or wires at optimum locations in a custom calibration cylinder.…”

Online Calibration of a Linear Micro Tomosynthesis Scanner

“…As a brief review of the literature, there is a wealth of calibration methods for cone-beam computed tomography (CT) and tomosynthesis imaging in diverse applications [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. They can broadly be separated into offline phantom-based calibration methods and online phantom-less methods [ 39 ].…”