Improvement of Depth Position in 2-D/3-D Registration of Knee Implants Using Single-Plane Fluoroscopy

Abstract

Two-dimensional (2-D)/three-dimensional (3-D) registration techniques using single-plane fluoroscopy are highly important for analyzing 3-D kinematics in applications such as total knee arthroplasty (TKA) implants. The accuracy of single-plane fluoroscopy-based techniques in the determination of translation perpendicular to the image plane (depth position), however, is relatively poor because a change in the depth position causes only small changes in the 2-D silhouette. Accuracies achieved in depth position using conventional 2-D/3-D registration techniques are insufficient for clinical applications. Therefore, we propose a technique for improving the accuracy of depth position determination in order to develop a system for analyzing knee kinematics over the full six degrees of freedom (6 DOF) using single-plane fluoroscopy. In preliminary experiments, the behaviors of errors for each free variable were quantified as evaluation curves by examining changes in cost function with variations in the free variable. The evaluation curve for depth position was more jagged, and the curve peak less pointy, compared to the evaluation curves of the other five variables, and the curve was found to behave differently. Depth position is therefore optimized independently of the other variables, using an approximate evaluation curve of depth position prepared after initial registration. Accuracy of the proposed technique was evaluated by computer simulation and in vitro tests, with validation of absolute position and orientation performed for each knee component. In computer simulation tests, root-mean-square error (RMSE) in depth position was improved from 2.6 mm (conventional) to 0.9 mm (proposed), whereas for in vitro tests, RMSE improved from 3.2 mm to 1.4 mm. Accuracy of the estimation of the remaining two translational and three rotational variables was found to be almost the same as that obtained by conventional techniques. Results of in vivo tests are also described in which the possibility of full 6 DOF kinematic analysis of TKA implants is shown.

A method for measuring three-dimensional mandibular kinematicsin vivousing single-plane fluoroscopy

“…19 The current study was the first experimental validation of a 3D fluoroscopy method dedicated to the in vivo measurement of mandibular motion under real-life conditions. This was in contrast to previous validation studies of 3D fluoroscopy on other joints, which either used ''clean'' images of the bone outside the body 27 or only assessed the accuracy of the measurement at static conditions. 28 The current study reported the means and standard deviations of the measurement errors.…”

A statistical framework for the registration of 3D knee implant components to single-plane X-ray images

“…Zuffi et al [8] and Yamazaki et al [7] use an Iterative Closest Point (ICP) algorithm to align the object's occluding contour with its observed X-ray silhouette. Since these methods are not robust against the presence of edge points generated by other objects (i.e.…”

“…1(b) and 1(c)). Consequently, traditional 2D/3D registration algorithms [6,7,8] might converge towards a local optimum representing a pose symmetrical to the true one.…”

“…However, in contrast to [6,7,8], the method does not enforce these aligned sets to be on the object's occluding contour. Consequently, a distance measure between 2D edge information and the 3D object is minimized, which expresses a necessary, but insufficient, condition for 2D/3D registration.…”

“…When a (nearly) planar-symmetrical object is considered, SinPosDet, akin [6,7,8], might converge towards a local optimum representing a pose symmetrical to the true one. Therefore, this algorithm is extended to the Symmetrical Pose Determination algorithm (SymPosDet) which simultaneously estimates two symmetrical object poses, both minimizing the distance between their related occluding contours and the corresponding 2D X-ray silhouette points.…”