[robotics-worldwide][jobs] PhD proposal: Perception and rendering of tissues stiffness in minimally invasive medical and surgical procedures, in Strasbourg/Paris
Perception and rendering of tissues stiffness in minimally invasive medical and surgical procedures
Minimally invasive techniques have considerably modified surgery during the last three decades. Laparoscopic surgery, in particular, has been developing in many specialties, such as urology, digestive surgery, or gynecologic surgery. If they present numerous advantages for the patient (less scars, infection risks and a shorter recovery period), these surgical techniques have an influence on the surgeon perception. The natural perception of tissues properties resulting from palpation is no longer possible. The interactions are not direct and therefore less natural. This induces difficulties to perform the gestures and limits the use of laparoscopic access to rather simple interventions.
In endoscopic surgery, the introduction of rigid tools in the body comes with an artifact, the Fulcrum (or lever) effect. Because of the rotation of the tools about a fixed point, the motions inside and outside the body are in opposite directions, which requires a particular training. Also, the respective magnitude of the movements of the operator’s hand and of the surgical tool varies, depending on the tool insertion depth . Finally, the lever effect also modifies the forces, which leads to a distorted perception of stiffness. If li denotes the length of the tool within the body, and lo the length of the tool outside the body, it can be easily shown that the stiffness perceived at the tool is the real stiffness multiplied by (li/lo)^2. This naturally provides misleading feedback, and this is even amplified when the distal motions are observed on a screen, with and endoscope, whose amplification is fixed and does not depend on the lever.
To assist medical interventions, robotic means are proposed in the literature, where two main approaches exist (cf. Figure 1):
• Telemanipulation, which assumes that a slave arm manipulates the instrument, tracking the motions imposed by the surgeon on a master arm. This approach has proved successful because of its clinical development, but force feedback is not allowed by present commercial systems, used in the operating room. As a result, the available systems cannot solve the problems of stiffness perception;
• Collaborative manipulation (or comanipulation), a paradigm for which the surgeon and the robot jointly manipulate the tool, which allows the robot to apply forces to guide the surgeon. The interest of this approach lies in its simplicity and modularity. However, the choice of the robot impedance in order to take the lever effect into account remains an open problem.
Figure 1: two approaches for the assistance to surgical gestures in laparoscopic surgery
(left: telemanipulation; right: comanipulation)
In this thesis, we will compare two possible approaches:
• an approach for which the tool is manipulated through a variable stiffness device, allowing to correct the Fulcrum effect (comanipulation) ;
• an approach for which the manipulated tool has a constant stiffness, but is teleoperated in a way that the force feedback may restore the actual stiffness to the operator, removing the distortion due to the Fulcrum effect.
The study will explore the mechatronic design of variable stiffness systems, the control aspects, but also the sensorimotor behavior of the operator. It will consist, in particular to understand, if the operator can move the distal point of the instrument, in the same manner as it is performed in conventional open surgery. A possibility will be to use the analysis of gestures kinematics and stiffness perception. The influence of training (comparison between expert surgeons and beginers) will be a particular problem of interest.
This work is collaboration between ICUBE laboratory, in Strasbourg, and ISIR laboratory in Paris, within the frame of the Computer Assisted Medical Interventions excellence laboratory (CAMI LABEX). It takes place in the continuation of research led in Strasbourg on telemanipulation and variable stiffness robots, and in Paris on collaborative manipulation. The thesis will mostly take place in Strasbourg, but a significant stay in Paris will be considered.
The candidate will ideally have a multidisciplinary profile with skills in Control/Robotics but also in mechatronic design. Less polyvalent profiles, with a strong skill will however be considered. A real interest for experimentation is required.
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