This paper presents a simple method and new material which allow transferring results of surgical planning — such as the implant fixture axis — to the surgical site. This method is based on drilling a linear guide in a resin splint corresponding to the fixture axis. A simple mechanical setup links the Computed Tomography (CT) data set with the drilling machine. Since the optimal fixture axis is determined with a software interface, it can be transferred as a linear guide to the resin splint with the drilling machine. Technical validation demonstrates that the accuracy of the method is 0.2 mm in translation and 1 degree in rotation. These results provide a high level of accuracy and clinical validation has begun with several patients. The results for the patients are very satisfactory.

Research on "Computer Assisted Medical Interventions" (CAMI) was initiated in Grenoble in 1984, as an attempt to take up the challenge of "Minimally Invasive Interventions", thanks to the introduction of Information and Communication Techniques in the Operating Room. In a first section, we will describe our initial vision. The corresponding achievements will then be presented. A final section will show that the challenge now is to "invert this movement": instead of moving the computer in the Operating Room, we should embed the surgeon (or at least his or her expertise) into the Information Technology based tools he or she uses.

The invention relates to a method for determining the position of an X-ray machine or fluoroscope (16) relative to a reference mark (Rref) when carrying out a radiograph of an object (10 ). The position of the apparatus (16) relative to a reference mark (Rref) is determined from the determination of the position, relative to the apparatus (16), a test pattern (25) mechanically connected to the object using the image of the pattern on the radiograph and the determination of the position of the pattern relative to the reference mark (Rref). The present invention also relates to a determination device for carrying out the method.

Image intensifiers suffer from distortions due to magnetic fields. In order to use this X-ray projections images for computer-assisted medical interventions, image intensifiers need to be calibrated. Opaque markers are often used for the correction of the image distortion and the estimation of the acquisition geometry parameters. Information under the markers is then lost. In this work, we consider the calibration of image intensifiers in the framework of 3D reconstruction from several 2D X-ray projections. In this context, new schemes of marker distributions are proposed for 2D X-ray sensor calibration. They are based on efficient sampling conditions of the parallel-beam X-ray transform when the detector and source trajectory is restricted to a circle around the measured object. Efficient sampling are essentially subset of standard sampling in this situation. The idea is simply to exploit the data redundancy of standard sampling and to replace some holes of efficient schemes by markers. Optimal location of markers in the sparse efficient sampling geometry can thus be found. In this case, the markers can stay on the sensor during the measurement with--theoretically--no loss of information (when the signal-to-noise ratio is large). Even if the theory is based on the parallel-beam X-ray transform, numerical experiments on both simulated and real data are shown in the case of weakly divergent beam geometry. We show that the 3D reconstruction from simulated data with interlaced markers is essentially the same as those obtained from data with no marker. We show that efficient Fourier interpolation formulas based on optimal sparse sampling schemes can be used to recover the information hidden by the markers.

In this study, an image-guided system for oral implant placement was assessed. A specially designed mechanical tool has been elaborated to transfer the preoperative implant axis planned on 3-dimensional imagery into a surgical template by a numerically controlled drilling machine. The main drawback of image-guiding systems is the use of preoperative computed tomography, which is expensive and delivers high radiation doses. Therefore, in this study the image-guiding system was coupled with a cone-beam tomograph that significantly decreased both cost and radiation doses. Three edentulous models were used. To determine the accuracy of the system, the ability of a 1.8-mm diameter drill to enter a 2.0-mm diameter, 10-mm-long titanium tube inserted on the model with no contact was verified. Because the drill entered the tubes with no contact and went beyond the end of the tube, the transfer error was less than 0.2 mm for translation and less than 1.1 degrees for rotation. The method presented here is low cost and high precision compared to other technological solutions such as tracking. Further assessment in the surgical field should lead to daily use of this system for flapless surgery, to prepare a prosthesis prior to surgery for immediate loading, to reduce risk of injuring critical anatomical structures and to eliminate manual placement error.

OBJECTIVE:Conformal radiation therapy requires accurate patient set-up for each fraction delivery. Electronic portal imaging devices allow the acquisition of portal images just before and even during dose delivery. However, the quantitative interpretation of these images in determining and correcting the patient's position remains uncertain, and automated methods are therefore being developed. Such methods must be usable for the different radiation therapy techniques. They must be robust and as automated as possible for use in clinical routines. This work was undertaken to establish the feasibility of 2D/2D registration for portal/portal and portal/simulator images in radiotherapy.MATERIALS AND METHODS:This paper describes an automated method based on the combination of calibration algorithms and pixel-based registration algorithms. We present experiments with the different imaging techniques, some of which use a phantom with and without a gold standard. Preliminary results obtained using patient data are also presented and discussed.RESULTS:The results obtained with a phantom demonstrated that this automated method for 2D/2D registration is fast, accurate, and robust, even in the case of blurred images for small treatment fields.CONCLUSIONS:Mutual information is a feasible method for 2D/2D portal/portal and portal/simulator image registration in radiotherapy.

Whilst computers are more and move used in the medical and surgical domains, medical education is still very conservative. However, new information technology could bring a lot to this area. In particular, simulators are of paramount interest: they would allow one both to experiment with surgical or imaging techniques for a wide range of pathologies without the need for patients and to quantitatively evaluate the trainees' performances. Ultrasound imaging is a typical area where virtual reality may change educational uses. This paper describes an ultrasound imaging simulator dedicated to the training of physicians for the detection of deep venous thromboses of the lower limbs. Like this one, a lot of other pathologies of soft tissue are diagnosed using ultrasound imaging. Because this examination is difficult and operator-dependent, developing a simulator is very useful to give common databases of pathological samples on which physicians can both experiment with image acquisition and evaluate their understanding of clinical cases. Real-time simulation is mandatory. An ultrasound imaging simulator has been developed and is being tested. This paper presents the hardware and software components of the simulator and describes the status of this project. Copyright (C) 2000 John Wiley & Sons, Ltd.

The use of medical imaging techniques to make a very precise surgical guide for implant placement is described. This template is the combination of a currently used template and a very simple mechanical system designed to transfer a preoperatively defined implant position onto the surgical site. With the planning software, the practitioner determines the implant position according both to the ideal position dictated by the final restorative prosthesis and the available volume of bone. The surgical template then communicates the actual implant position to the surgical site. The template can be used not only in critical anatomical situations but also in placing the implant in an ideal position on bone because it eliminates possible manual placement errors and matches planning to prosthetic requirements.

Conformal radiation therapy requires the accurate set-up of the patient for each fraction delivery. Electronic portal imaging devices (EPID) enable the acquisition of portal images just before and even during dose delivery. An issue still lies in the quantitative exploitation of such images to determine and correct the position of the patient. Such methods should be robust and as much automatic as possible to be used in clinical routine. In this paper we describe a method based on a combination of calibration algorithms with registration algorithms avoiding segmentation of anatomical structures. Experiments on phantoms that have been conducted to evaluate this approach are presented and results are discussed.

Although accurate predictions of the behavior and function of the anterior cruciate ligament would aid in diagnosis and operative treatment, no agreement exists on the best way to model the ligament with a reliable description of its mechanical and geometric features. We propose a new model of the anterior cruciate ligament based on multiple viscoelastic curvilinear fibers. This model was used for quasi-static simulations of the passive motion of eight porcine knees, after registration of the passive trajectories and digitization of the surface of the ligament in flexion. Simulations of anterior cruciate ligament deformations during passive motion predicted a fiber strain of less than 20%, low insertion forces, and isometric anterior fibers. The model explains actions of the ligament fibers, as reported in the literature, better than classic models based on linear fibers and consistent with the mechanical properties of the anterior cruciate ligament.

Passive and semi-active aids ince 1985, a team of computer scien-surgeons has been involved in a project at Grenoble Hospital called computer assisted medical interventions (CAMI). The aim of the project is to help surgeons and physicians use multimodal data in a rational and quantitative way in order to plan and to perform medical interventions. Recent advances in medical imaging systems such as CT and MRI have stimulated research on the interpretation of medical images. Nevertheless, very few systems allow for an efficient therapeutic use of the wealth of information these images contain , which is CAMI's twofold objective: =Define an operative strategy that takes advantage of the localizing capabilities of imaging, and make this strategy available in an operative reference system. This goal requires models and processing of basic data, in conjunction with a priori knowledge , in order to define an optimal strategy. =Perform the previously defined operative strategy, with the aid of a suitable guidance system, under appropriate imaging supervision. Without help, executing a strategy can sometimes be very difficult. First, reproducing a defined strategy directly raises problems, for one has to mentally match geometrical information observed in different reference systems (mainly intra-operative scenes or images with pre-operative images). Then, complex interventions may be necessary on organs difficult to reach or for which a human operator will only have poor or no visibility. In addition, surgical tools, such as probes, most often have to be very precisely positioned, and submillimetric accuracy may be required for microsurgery. Finally, some interventions may be dangerous for the medical staff (e.g., contamination or irradiation). In all these instances, optical or mechanical guidance systems are required. The ultimate success of this research hinges on complex robotics systems and their various sensors. The aforementioned objectives aim at improving the quality of the interventions by making it easier, more accurate, closer to a a pre-operative simulation where accurate objectives can be defined, and sometimes faster. Also, it may be possible to devise new interventions and to validate protocols of therapeutic research. Obviously , this is long term research, with many potential clinical applications. Yet, a general methodology can be applied to various clinical situations [ 11, as presented below. In order to understand the methodology and applications of CAMI, it is necessary to be aware of current technology. Many issues in the CAMI project are concerned with geometrical localization problems. Hardware issues mainly refer …

Misalignment of the extensor apparatus is an essential factor in impairment of the patellar-femoral joint. This may be partly or entirely responsible for patellar dislocation or lateral patellar-femoral arthrosis. One surgical method to correct the pathology is medial transposition of the patellar ligament on the tibial tuberosity (anteriorly or posteriorly, distally or ventrally). These interventions correct misalignment of the extensor apparatus relative to statistical norms. We propose a mathematical method based on the use of computed tomography (CT) images to determine the ideal tibial insertion for the patellar tendon. This method is based on biomechanical modeling and the use of equipressure criteria. It is the first step in allowing the use of mathematics to model correctly tibial insertion of the patellar ligament, an entirely new development. This is important because it will allow surgeons greater accuracy in distal correction of extensor apparatus misalignments.

In the field of Augmented Reality in Surgery, building a hybrid patient's model, i.e. merging all the data and systems available for a given application, is a difficult but crucial technical problem. The purpose is to merge all the data that consitute the patient model with the reality of the surgery, i.e. the surgical tools and feedback devices. In this paper, we first develop this concept, we show that this construction comes to a problem of registration between various sensor data, and we detail a general framework of registration The state of the art in this domain is presented. Finally, we show results that we have obtained using a method which is based on the use of anatomical reference surfaces. We show that in many clinical cases, registration is only possible through the use of internal patient structures.

A method is presented for modeling and calibration of sensors, to reach an accuracy similar in magnitude to the resolution of the sensors. The authors focus on camera and range image calibration. They show the limitations of existing methods, and present an approach and camera calibration using mathematical B-Spline functions. This method is abbreviated as NPBS (N-Planes B-Spline). It is an extension of the two-planes method, but relies on pure mathematical modeling based on spline approximation theory. The mathematical modeling is combined with a calibration device that enables accurate data acquisition to calibrate a camera and a light plane independently. Experimental results are presented showing accuracy on the determination of a scattered plane.<>