In the past few years, a number of two-dimensional (2-D) to three-dimensional (3-D) (2-D-3-D) registration algorithms have been introduced. However, these methods have been developed and evaluated for specific applications, and have not been directly compared. Understanding and evaluating their performance is therefore an open and important issue. To address this challenge we introduce a standardized evaluation methodology, which can be used for all types of 2-D-3-D registration methods and for different applications and anatomies. Our evaluation methodology uses the calibrated geometry of a 3-D rotational X-ray (3DRX) imaging system (Philips Medical Systems, Best, The Netherlands) in combination with image-based 3-D-3-D registration for attaining a highly accurate gold standard for 2-D X-ray to 3-D MR/CT/3DRX registration. Furthermore, we propose standardized starting positions and failure criteria to allow future researchers to directly compare their methods. As an illustration, the proposed methodology has been used to evaluate the performance of two 2-D-3-D registration techniques, viz. a gradient-based and an intensity-based method, for images of the spine. The data and gold standard transformations are available on the internet (http://www.isi.uu.nl/Research/Databases/).

Performing minimally invasive vascular interventions requires proper training, as a guide wire needs to be manipulated, by the tail, under fluoroscopic guidance. To provide a training environment, the motion of the guide wire inside the human vasculature can be simulated by computer. Such a simulation needs to be based on an algorithm that is both realistic and fast. To meet these two demands, an analytical solution to the problem of guide wire motion has been derived, using a new parametrisation of guide wire shape. The algorithm is highly generic, is entirely based on elementary physics and has good convergence properties (accuracy of 22 micron after two iterations). In an experimental validation of the algorithm in a planar model, the RMS of the spatial discrepancy between the real and simulated catheter positions was about 10% of the lumen size. Comparison of the simulated guide wire motion with 3D rotational angiography data of a real guide wire advanced in a plastic phantom of the cerebral vasculature showed that the new algorithm produced realistic results.

Using three-dimensional rotational X-ray angiography (3DRA), three-dimensional (3-D) information of the vasculature can be obtained prior to endovascular interventions. However, during interventions, the radiologist has to rely on fluoroscopy images to manipulate the guide wire. In order to take full advantage of the 3-D information from 3DRA data during endovascular interventions, a method is presented that yields an integrated display of the position of the guide wire and vasculature in 3-D. The method relies on an automated method that tracks the guide wire simultaneously in biplane fluoroscopy images. Based on the calibrated geometry of the C-arm, the 3-D guide-wire position is determined and visualized in the 3-D coordinate system of the vasculature. The method is evaluated in an intracranial anthropomorphic vascular phantom. The influence of the angle between projections, distortion correction of the projection images, and accuracy of geometry knowledge on the accuracy of 3-D guide-wire reconstruction from biplane images is determined. If the calibrated geometry information is used and the images are corrected for distortion, a mean distance to the reference standard of 0.42 mm and a tip distance of 0.65 mm is found, which means that accurate guide-wire reconstruction from biplane images can be performed.

Abstract. In the past few years a number of 2D-3D registration algorithms have been introduced. However, these methods have not been directly compared or only work for specific applications. Understanding and evaluating their performance is therefore an open and important issue. To address this challenge we introduce a standard evaluation method, which can be used for all types of methods and different applications. Our method uses the geometry of the 3D Rotational Xray (3DRX) imaging system in combination with 3D-3D registration for attaining a highly accurate ground truth for 2D multiple X-ray to 3D MR/CT/3DRX registration. The data and ground truth transformations will be made available on the Internet. Furthermore, we propose starting positions and failure criteria to allow future researchers to directly compare their methods. As an illustration, the proposed method has been used to evaluate the performance of two 2D-3D registration techniques, viz. a gradient-based and an intensity-based method, in spinal applications.

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