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Image guidance and visualization play an important role in modern surgery to help surgeons perform their surgical procedures. Here, the focus is on neurosurgery applications, in particular brain tumor surgery where a craniotomy (opening of the skull) is performed to access directly the brain region to be treated. In this type of surgery, once the skull is opened the brain can change its shape, and this deformation is known as brain shift. Moreover, the boundaries of many types of tumors are difficult to identify by the naked eye from healthy tissue. The main goal of this work was to study and develop image guidance and visualization methods for tumor surgery in order to overcome the problems faced in this type of surgery. Due to brain shift the magnetic resonance dataset acquired before the operation (preoperatively) no longer corresponds to the anatomy of the patient during the operation (intraoperatively). For this reason, in this work methods were studied and developed to compensate for this deformation. To guide the deformation methods, information of the superficial vessel centerlines of the brain was used. A method for accurate (approximately 1 mm) reconstruction of the vessel centerlines using a multiview camera system was developed. It uses geometrical constraints, relaxation labeling, thin plate spline filtering and finally mean shift to find the correct correspondences between the camera images. A complete non-rigid deformation pipeline was initially proposed and evaluated with an animal model. From these experiments it was observed that although the traditional non-rigid registration methods (in our case coherent point drift) were able to produce satisfactory vessel correspondences between preoperative and intraoperative vessels, in some specific areas the results were suboptimal. For this reason a new method was proposed that combined the coherent point drift and thin plate spline semilandmarks. This combination resulted in an accurate (below 1 mm) non-r

We aim at reconstructing superficial vessels of the brain. Ultimately, they will serve to guide the deformationmethods to compensate for the brain shift. A pipeline for three-dimensional (3-D) vessel reconstructionusing three mono-complementary metal-oxide semiconductor cameras has been developed. Vessel centerlinesare manually selected in the images. Using the properties of the Hessian matrix, the centerline points areassigned direction information. For correspondence matching, a combination of methods was used. The processstarts with epipolar and spatial coherence constraints (geometrical constraints), followed by relaxation labelingand an iterative filtering where the 3-D points are compared to surfaces obtained using the thin-plate spline withdecreasing relaxation parameter. Finally, the points are shifted to their local centroid position. Evaluation invirtual, phantom, and experimental images, including intraoperative data from patient experiments, showsthat, with appropriate camera positions, the error estimates (root-mean square error and mean error) are∼1 mm., ARIOR

In this study we present a non-rigid point set registration for 3D curves (composed by 3D set of points). Themethod was evaluated in the task of registration of 3D superficial vessels of the brain where it was used to matchvessel centerline points. It consists of a combination of the Coherent Point Drift (CPD) and the Thin-PlateSpline (TPS) semilandmarks. The CPD is used to perform the initial matching of centerline 3D points, whilethe semilandmark method iteratively relaxes/slides the points. For the evaluation, a Magnetic Resonance Angiography (MRA) dataset was used. Deformations were appliedto the extracted vessels centerlines to simulate brain bulging and sinking, using a TPS deformation where afew control points were manipulated to obtain the desired transformation (T1). Once the correspondences areknown, the corresponding points are used to define a new TPS deformation(T2). The errors are measured in thedeformed space, by transforming the original points using T1 and T2 and measuring the distance between them.To simulate cases where the deformed vessel data is incomplete, parts of the reference vessels were cut and thendeformed. Furthermore, anisotropic normally distributed noise was added. The results show that the error estimates (root mean square error and mean error) are below 1 mm, even inthe presence of noise and incomplete data., ARIOR

Purpose The aim of this work was to introduce a Computer Aided Design (CAD)tool that enables the design of large skull defects (> 100cm2) implants. Functional and aesthetically correct custom implants are extremely important for patients with large cranial defects. For these cases pre-operative fabrication of implants is recommended to avoid problems of donor site morbidity, sufficiencyof donor material and quality. Finally, crafting the correct shape is a non-trivial task increasingly complicated by defect size. Methods We present a Computer Aided Design (CAD) tool to design such implants for the neurocranium. A combination of Geometric Morphometrics (GM) and Radial Basis Functions (RBF), namely Thin Plate Splines (TPS), allows semiautomatic implant generation. The method uses symmetry and the best fitting shape to estimate missing data directly within the radiologic volume data. In addition, this approach delivers correct implant fitting via a boundary fitting approach. Results This method generates a smooth implant surface, free of sharp edges that follows the main contours of the boundary, enabling accurate implant placementin the defect site intraoperatively. The present approach is evaluated and compared to existing methods. A mean error of 89.29% (72.64% - 100%)missing landmarks with an error less or equal to 1 mm was obtained. Conclusion In conclusion, the results show that our Computer Aided Design (CAD)tool can generate patient specific implants with high accuracy., Funding agencies: EU [MRTN-CT-2005-019564], EVAN

Depth perception of semi-transparent virtual objects and the visu-alization of their spatial layout are crucial in many applications, in particular medical applications. Depth cues for opaque objects have been extensively studied, but this is not the case for stereo-scopic semi-transparent objects, in particular in the case when one 3D object is enclosed within a larger exterior object. In this work we explored different stereoscopic rendering methodsto analyze their impact on depth perception accuracy of an enclosed3D object. Two experiments were performed: the first tested the hypotheses that depth perception is dependent on the color blending of objects (opacity - alpha) for each rendering method and that one of two rendering methods used is superior. The second experiment was performed to corroborate the results of the first experiment and to test an extra hypothesis: is depth perception improved if an auxiliary object that provides a relationship between the enclosed objectand the exterior is used? The first rendering method used is simple alpha blending with Blinn-Phong shading model, where a segmented brain (exterior object) and a synthetic tumor (enclosed object) were blended. The second rendering method also uses Blinn-Phong, but the shading was modified to preserve silhouettes and to provide an illustrative rendering. Comparing both rendering methods, the brighter regionsof the first rendering method will become more transparent in the second rendering method, thus preserving silhouette areas. The results show that depth perception accuracy of an enclosed object rendered with a stereoscopic system is dependent on opacity for some rendering methods (simple alpha blending), but this effect is less pronounced than the dependence on object position in relation to the exterior object. The illustrative rendering method is less dependent on opacity. The different rendering methods also perform slightly differently; an illustrative rendering method was superior an

A new single-monitor-mirror stereoscopic display is presented. The stereoscopic display system is composed of one monitor and one acrylic first-surface mirror. The mirror reflects one image for one of the eyes. The geometrical transformations to compute correctly the stereo pair are derived and presented. System considerations such as mirror placement and implications are also discussed. In contrast to other similar solutions that use fixed configurations, we try to optimize the display area by controlling the mirror placement. Consequently, one of the images needs to be skewed. Advantages of the system include absence of ghosting and flickering. We also developed the rendering engine for direct volume rendering (DVR) of volumetric datasets mostly for medical imaging visualization and using OpenGL for polygonal datasets and stereoscopic digital photography. The skewing process in this case is integrated into the ray-casting of DVR. Using geometrical transformations, we can compute precisely the directions of the rays, producing accurate stereo pairs. A similar operation is also performed using OpenGL., arior

The correct visualization of anatomical structures is a critical component of neurosurgical navigation systems, to guide the surgeon to the areas of interest as well as to avoid brain damage. A major challenge for neuronavigation systems is the brain shift, or deformation of the exposed brain in comparison to preoperative Magnetic Resonance (MR) image sets. In this work paper, a non-rigid deformation pipeline is proposed for brain shift compensation of preoperative imaging datasets using superficial blood vessels as landmarks. The input was preoperative and intraoperative 3D image sets of superficial vessel centerlines. The intraoperative vessels (obtained using 3 Near-Infrared cameras) were registered and aligned with preoperative Magnetic Resonance Angiography vessel centerlines using manual interaction for the rigid transformation and, for the non-rigid transformation, the non-rigid point set registration method Coherent Point Drift. The rigid registration transforms the intraoperative points from the camera coordinate system to the preoperative MR coordinate system, and the non-rigid registration deals with local transformations in the MR coordinate system. Finally, the generation of a new deformed volume is achieved with the Thin-Plate Spline (TPS) method using as control points the matches in the MR coordinate system found in the previous step. The method was tested in a rabbit brain exposed via craniotomy, where deformations were produced by a balloon inserted into the brain. There was a good correlation between the real state of the brain and the deformed volume obtained using the pipeline. Maximum displacements were approximately 4.0 mm for the exposed brain alone, and 6.7 mm after balloon inflation.

Surgeons are used to treat bone defects with autograft material due tothe good chance that it will be successfully incorporated by defect sitetissues. However, problems of donor site morbidity, sufficient donormaterial, bone tissue quality and crafting the correct shape fromavailable donor material increase dramatically with the size of thedefect. Large skull defects ([100 cm2) are not uncommon sequelae of trauma, cancer, stroke, and re-constructive surgery. An aesthetically correct and precisely tailored reconstruction of the defect by means of prefabricated implants remains challenging because the majority of current implant design techniques are heavily dependent on subjective procedures. Dealing with prefabricated implants allows the reduction of surgery intervention time, and therefore reduces the risks for the patient and the costs of surgery. We transfer existing anthropological methods to neurosurgical planning in order to reduce the dependence on subjective skills and to improve the custom implant form. The purpose of this study is to compare two different approaches allowing the generation of implant surfaces.

This paper presents a solution to minimize a problem that normally arises from the huge amount of images that a radiologist usually has to interpret. A multi-agent system that implements a multi-display for medical imaging based on computer clustering of normal personal computers is therefore described, as well as the multi-agent architecture that caters for the system evolution. An evaluation study was performed and its results are presented.

This paper describes a solution for the calculation of the correct stereo pairs of a Mirror-Based Augmented Reality System (MBARS).To achieve augmentation half-silvered mirrors are applied due to their dual reflection characteristic that allow simultaneous seeing-through of real objects and the viewing of reflected virtual ones. This way it is possible to merge virtual content reflected by the mirror with real objects that the user can see through it. The virtual con-tent can be either generated by a monitor or a projector. In this paper we will only refer to the monitor-based systems. These systems are view dependent, meaning that depending upon the viewer’s position the reflected im-ages have to be recomputed. This is why a Head-Tracking System is needed to supply the current viewer’s posi-tion. Also we need to consider the main system components and there location, to correctly compute the stereo pairs. Furthermore we present how the result of the mathematical calculations can be used in combination with com-mands of the OpenGL API to achieve the desired transformations and to allow interactivity.

The support and enhancement of cultural heritage scenarios through the application of virtual and augmented reality technology has been a subject of intensive research and study in the last years. Some results have been already deployed and used in end-user environments such us museums or archaeology sites. In this paper we present our own solution – a virtual showcase – designed based on an augmented reality system. This system integrates half-silvered mirrors that are used to merge the real scene, visible through the mirror, together with the computer generated images projected on it. Using a head tracking system, the correct images can be computed according to the observer’s point of view. Our showcase configuration consists of 8 different points of visualization, all oriented to the centre of the real scene, thus maximizing the number of users as well allowing the integration of high interactive mechanisms suitable for game-oriented applications. An augmented game is here presented as a use case to serve cultural heritage purposes.