Section: New Results

Medical robotics

Ultrasound image-based visual servoing

Participants : Rafik Mebarki, Alexandre Krupa, François Chaumette.

We continue our works dedicated to controlling the motion of a 2D ultrasound probe actuated by a medical robot in order to reach and to track a desired cross-section image. The visual servoing techniques available in the literature are devoted to optical systems that differ completely from 2D ultrasound ones in the sense that the latters provide full information in their observation plane but none at all outside. Furthermore, the variation of the ultrasound cross-section image due to the probe out-of-plane motion strongly depends on the 3D shape of the observed object with which the 2D ultrasound probe is interacting.

This year, we proposed in [38] a new technique affording visual servoing without the knowledge of a 3D model of the soft tissue of interest. In that work, we made use of the image moments of the cross-section as visual features by deriving the analytical form of the interaction matrix relating their variation to the probe motion. To afford model-free control, the object surface normal vector is estimated on line. We obtained satisfactory results in simulations, experiments on an ultrasound phantom, and ex-vivo experiments on a motionless kidney immersed in a water-filled tank.

3D robot registration from ultrasound images

Participants : Caroline Nadeau, Alexandre Krupa.

We have studied a new approach for rigid registration of a per-operative 2D ultrasound image and a pre-operative 3D image. A visual servoing strategy is used to perform the matching of both image coordinate systems. In this case, the desired image is provided by the ultrasound probe used in the operating room and the current one is obtained by the intersection of a virtual probe with the pre-operative volume. Visual servoing enables then to move this virtual probe to minimize the error of features extracted from both images. To reduce the presence of local minima during the algorithm convergence, a virtual bi-plane probe providing two slides is considered. Preliminary simulation results, obtained by considering non-deformable soft tissue structures, demonstrate the feasibility of this approach.

Autonomous control modes for ultrasound probe guidance

Participants : Tao Li, Alexandre Krupa.

This study is realized within the ANR Contint Prosit project (see Section 8.2.6 ). It consists in developing several autonomous control modes based on ultrasound visual servoing that will assist the physician during a robotized and teleoperated ultrasound examination (tele-echography). The objective of the first autonomous control mode we will develop is to guarantee the visibility of an anatomical element of interest while the physician is teleoperating the robotized probe.