KS48: A NEW TECHNIQUE FOR REGISTRATION OF 2D X-RAY FLUOROSCOPY TO 3D CT DATA FOR THE ANALYSIS OF KNEE KINEMATICS

Abstract

To better understand the functional effects of pathologies, a system to capture accurate real-time 3D imaging of functional activities, without the limitations of RSA, is desirable. To address this problem, a new registration algorithm was developed to automatically determine the 3D kinematics of the knee using commonly available imaging modalities.

To evaluate this new registration algorithm, three cadaveric knees were implanted with 1mm tantalum beads to act as gold standard fiducial markers. The knees were flexed between 0 and 90° and fluoroscopy data was captured at a rate of 25 frames/sec and a resolution of 0.5 mm/pixel (Axiom Artis MP). “Pin-cushion” distortion and beam spreading were accounted for. CT data was captured using a Toshiba Aquillon 16 using bone and soft tissue algorithms. For every frame of the fluoroscopy data, the 3D femur and tibia data was individually registered to the fluoroscopy images using the new algorithm. This position data was then used to generate a kinematic 3D model. Similar fluoroscopy-to-CT registration techniques have been proposed for stationary image-guided surgery applications. The majority of these techniques use fluoroscopy images projected onto at least two different planes (with some systems using as many as 18 planes). Other techniques have been proposed that use a single-plane but require stochastic optimization procedures that perform in the order of 500 iterations to find the optimal 3-D registration. The reported average target registration errors (TREs) of these systems range from 0.5–1.2 mm. The newly developed registration technique requires only a single-plane fluoroscopy image and uses a novel gradient-descent optimization strategy that converges to the optimal 3-D position within 20–30 iterations. Preliminary results demonstrate that the performance of the new registration algorithm is able to align the bones of the knee with an average TRE of 0.57 mm. Up to 7 degrees of concurrent axial rotation was observed during flexion of the knees to 90°. The new registration algorithm developed for the project is capable of automatically determining the 3D kinematics of a knee joint using only single-plane fluoroscopy data. The new algorithm requires approximately one-tenth the number of iterations to find the optimal registration position when compared with existing single-plane techniques. Once it is established in vivo that this image registration technique has the accuracy of RSA, this method will permit real-time kinematic studies without tantalum beads. This will enable prospective longitudinal and controlled studies of reconstruction surgery, and conservative management of joint pathologies.