A three-dimensional (3-D) method for tracking the coronary arteries through a temporal sequence of biplane X-ray angiography images is presented. A 3-D centerline model of the coronary vasculature is reconstructed from a biplane image pair at one time frame, and its motion is tracked using a coarse-to-fine hierarchy of motion models. Three-dimensional constraints on the length of the arteries and on the spatial regularity of the motion field are used to overcome limitations of classical two-dimensional vessel tracking methods, such as tracking vessels through projective occlusions. This algorithm was clinically validated in five patients by tracking the motion of the left coronary tree over one cardiac cycle. The root mean square reprojection errors were found to be submillimeter in 93% (54/58) of the image pairs. The performance of the tracking algorithm was quantified in three dimensions using a deforming vascular phantom. RMS 3-D distance errors were computed between centerline models tracked in the X-ray images and gold-standard centerline models of the phantom generated from a gated 3-D magnetic resonance image acquisition. The mean error was 0.69 (+/- 0.06) mm over eight temporal phases and four different biplane orientations.

Minimally invasive surgery (MIS) is an increasingly important approach in many specialties, where robots are poised to play an important role in displacing the limits set to such techniques through increased precision and dexterity. However, the potential of robotically assisted minimally invasive surgery (RMIS) is still far from being fully exploited because of the newness of the approach. One of the best immediate solutions to remedy this discrepancy is through a more efficient preparation of the intervention. This paper presents a two-step strategy to optimize the most critical settings of an RMIS intervention, namely, the port placement (incision sites for minimally invasive access) and the pose of the robot (initial configuration of stationary joints). The first step relies on a patient-dependent modeling of the intervention by the surgeon that is transformed into an optimization problem where criteria such as visibility and dexterity serve as a cost function. The second one, referred to as the pose planning problem, aims at guaranteeing a collision-free operation of the robot throughout the intervention, by properly assigning stationary extra flexibility at the beginning of the intervention, under the constraint of ensuring the fixed positions of the minimally invasive port access.

Positioning a surgical robot in a typically cluttered operating room for optimal operation is a challenging task. Surgical tele-operated manipulators are designed to have a flexible structure to adapt to the operating environment, and thus have a high number of degrees of freedom to position. They are also usually subject to additional spatial constraints such as having a fixed point during the intervention, which is typically the case in mini-invasive interventions. Moreover, the planned results should not only guarantee a collision free operation, but should also target a maximum separation from the surrounding obstacles, since this is a critical application, and since the positioning is done in an error prone environment. In this paper we propose a systematic method for the positioning of the passive dofs of a robotic system; i.e., those that are not under direct tele-operation or autonomous control. Optimality is translated by the separation between the different manipulators, as well as with the surrounding obstacles. These requirements am formulated as an optimization problem, and an interference measurement method is presented to allow for an efficient solution. Results on the daVinci/spl trade/ system am presented to illustrate the proposed approach.

Concerns telerobotic microsurgery. Existing systems offer tremor elimination and scaling of motions. This article goes beyond the strict master/slave scheme to the enhancement of the operator's capabilities during teleoperation. It is focused on the implementation of three types of constraints for the operators' movements: constrained movement (along a curve or on a predefined surface); virtual obstacle avoidance; and geometric constraints to limit the robots workspace. Constraints for the operator's movements can be implemented mechanically. Our approach uses a haptic master robot, and consists in adding constraint forces to its control scheme. Constraint forces are computed according to attractive or repulsive potential fields placed around constraints. This article presents the principles of these control enhancements which, we believe, will raise dramatically the level of safety and precision that a surgeon can achieve, but those principles can also be applied to a wide variety of teleoperation applications.

Architectures form the backbone of complete robotic systems. The right choice of architecture can go a long way in facilitating the specification, implementation and validation of robotic systems. Conversely, of course, the wrong choice can make one's life miserable. We present some of the needs of robotic systems, describe some general classes of robot architectures, and discuss how different architectural styles can help in addressing those needs. The paper, like the field itself, is somewhat preliminary, yet it is hoped that it will provide guidance for those who use, or develop, robot architectures.

We present a generic and yet efficient mission programming method for robotic systems. The MAESTRO programming language, directed towards the end-user, is defined to be integrated into various existing control architectures. Its development is based on the use of formal methods to fully benefit from their mathematical foundations. Subsequently, programs written in MAESTRO can be proven to be in conformity with their specification before they are executed. The programming of a representative underwater mission illustrates the features of MAESTRO and of its companion environment for specification, verification, simulation and control of robotic missions.

Underwater robotic systems require a control architecture that handles automatic control aspects and discrete-event management while considering real-time issues within a formalized framework in order to achieve a high degree of autonomy and robustness while performing missions. To extract generic characteristics of working implementations, we examine two methodologies developed independently by French and American research organizations to control their underwater robots. In particular, we study how a specific reactive and complex mission is encoded under the two different methodologies. Details of the methodologies along with mission programs created by each team to accomplish the evaluation mission are presented.

Presents a coherent approach for visual servoing tasks that consists of following the contours of unknown objects using a hand-eye robotic system. The motion of the contour relative to the camera sensor is estimated in real-time by processing the measured optical flow of a set of relevant feature points. The desired motion of the end-effector is then computed to minimize the displacements of the feature points with respect to a reference configuration in the image. Control schemes are used in order to stabilize the robot and enhance tracking performances. The authors illustrate the approach by experimental results acquired with a real-time environment, where their CMU-Direct-Drive Arm II follows the boundaries of motionless objects positioned in a plane parallel to the image plane. Three degrees of freedom of planar motions are thus servoed to perform the contour-following task.

The authors present some design issues for a task-level controller based on a specific control approach. The achievement of a robotic application requires the use of a large set of cooperating devices such as manipulators and sensors. An application is performed by scheduling several actions of the system. Each action is modeled with a functional aspect (control law) and a behavioral one (reactions on events). These two aspects are combined in a single object, the robot-task. An object-oriented approach was used to model these actions. The synchronous language Esterel was used both to program an application at the end-user level and to program the behavioral part of the robot-tasks at the control level. The main design issues of a real-time controller able to implement and perform these actions are outlined.>