Vinod Kaimal PhD, Presenter: Employee, Materialise NV

Sebastian De Boodt, Abstract Co-Author: Employee, Materialise NV

Michel Janssens MSc,PhD, Abstract Co-Author: Employee, Materialise NV

Tom Cluckers MSc,PhD, Abstract Co-Author: Employee, Materialise NV

Koen Engelborghs MSc,PhD, Abstract Co-Author: Employee, Materialise NV

Lara Vigneron MSc,PhD, Abstract Co-Author: Employee, Materialise NV

The use of external radio-opaque marker could provide tremendous benefit in assessment of surgical outcomes, particularly in orthopedic applications, where a pre-op CT is acquired but post-op follow up is done by X-ray imaging.

Quantitative evaluation of a post-op X-ray in relation to a 3D pre-op scan could result in better assessment of the outcome of surgery and  provide information that could be used to optimize similar procedures in the future. Accurate 3D positioning of the virtual models of a patient’s anatomy with respect to a postoperative X-ray is the first step in a quantitative comparison. Existing positioning technologies are based on the recognition of tantalum markers implanted in the patient’s bone. This approach, however, is too expensive and invasive for use in daily clinical practice. In this study, the use of custom external  radio-opaque markers for positioning of virtual models, was investigated. The goal of this study was to quantify the effect of using these markers on the accuracy of X-ray registration.

Preliminary results indicate that external markers significantly improved the accuracy of the position measurements. Using multiple markers further increased the accuracy.

Radio-opaque markers, for external fixation on a patient, were engineered for this study. The markers had known 3D geometry, which was easily detectable by the image processing software. Experiments were performed in a setup that allowed for accurate 3D positioning of a phantom and the markers in relation to the X-ray detector. After fixing markers, an optical 3D scan of the setup was taken to accurately determine the phantom’s position in relation to the X-ray detector. Next, an X-ray image of the phantom together with the markers was acquired.A novel algorithm was developed to determine, from the X-ray, the position of the phantom (x,y & z coordinates) using two different approaches: (i) based solely on 3D geometry of the phantom, (ii) using geometry information of both phantom and markers. The accuracy of the registration was defined as the difference between the object’s x,y and z coordinates determined by the algorithm and the location obtained from the 3D optical scan.

Kaimal, V, De Boodt, S, Janssens, M, Cluckers, T, Engelborghs, K, Vigneron, L, The Benefit of Using External Markers on the Accuracy of X-ray Registration on 3D Models, for Postoperative Evaluation.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12033241.html