Mechatronic elements and haptic rendering for computer-assisted minimally invasive surgery training

Technological advances of the last decades enabled the development of a set of new medical techniques that differ from traditional open surgery. These techniques, referred to as minimally invasive surgery (MIS), involve complex instruments and imaging devices to reach and treat anatomical regions through small incisions or natural entry points resulting in reduced trauma and shorter recovery time. For the surgeons, MIS introduces unnatural hand-eye coordination and anatomical representation that require specific training. One alternative is the use of virtual reality (VR) simulations of MIS procedures coupled to input devices mimicking instruments used by surgeons. To achieve high-fidelity with such a computer-assisted training system, the input device also provides the sensations experienced during a procedure with force reflective technology, often referred to as haptics. This work explores the mechatronic aspects implied in the realization of such a haptic device for MIS training applications. An analysis of different MIS procedures enables to draw two categories: lumen-guided and cavity procedures. A simple classification of the required mechanism can be extracted from these observations. To fulfil the requirements, an implementation should follow a series of guidelines in terms of actuation and power transmission that are presented. The interactions between a human operator and a haptic interface involve both force and motion. Impedance control generates a force command based on the position of the haptic interface. This process, called haptic rendering, is an integrate part of the VR environment. This work proposes to extend impedance control with model-based compensation of the dynamics and non-linearities (such as friction) of the haptic device. Due to sensitivity to model uncertainties, the proposed control architecture is completed by a parallel implicit force controller. Since the computational load of VR simulation for complex anatomies is high, update rates reach 20 to 30 Hz. These frequencies are not sufficient to control a haptic device and meet the sensitivity requirements of the human sensory system. Therefore, in such system a multirate approach is introduced. A model is proposed for the dynamics of a haptic interface and its user. Based on this model, the effect of the introduced implicit force controller is studied and different interfacing techniques between the VR simulation and the haptic controller are evaluated. Since force sensing is a requirement for the implementation of the proposed implicit forcecontroller, a technique using infrared reflective sensors is proposed. A modelling method for such sensors is introduced and implementation issues for force sensing are discussed. Finally, the topics discussed in this work are applied to the development of a computer-assisted training system for Interventional Radiology.

Haptic instrumentation for an interventional radiology simulator

Dejan Ilic

Low trauma, reduced costs and fast recovery are only a few factors why minimally invasive surgery (MIS) is taking over classical surgical methods. Interventional Radiology (IR) is a minimally invasive procedure where thin tubular instruments are steered through the patient's vascular system under X-ray imaging. In order to perform these procedures, a radiologist has to be trained to master hand-eye coordination, instrument manipulation and procedure protocols. The importance of training IR procedures rises with the increasing variety and sophistication of the procedures performed using this approach. Apart from the traditional "see one, do one, teach one" model, radiologists have only had few mock devices with limitations in practical use. Training on animals is an alternative, but its use is hindered by high costs and ethical issues. The existing simulation systems all have major drawbacks: the requirement to use modified instruments, high inertia of the haptic feedback that creates a noticeably degraded dynamic behavior, or excessive friction that is not properly compensated. In this thesis we propose a quality training environment dedicated to IR. The system is composed of a virtual reality (VR) simulation of the patients anatomy linked to a robotic interface providing haptic force feedback. This thesis focuses on the requirements, design and prototyping of a specific haptic interface for the manipulation of catheters and guide wires. Translational tracking and force feedback on the catheter are provided by two cylinders forming a friction drive arrangement. The complete friction drive can be set in rotation with an additional motor providing torque feedback. A force and a torque sensor are integrated in the cylinders for direct measurement on the catheter enabling disturbance cancellation with a closed-loop force control strategy. One of the specific requirements during a simulated intervention is to measure the position of the tip of a guide wire inside a catheter. This is a so called "tube in tube" problem. The guide wire is detected at the entrance of the simulator and then grasped by a micro-gripper. Forces and movements of the guidewire moving inside the catheter are then transmitted through a gripper and along a rod to an external unit. This thesis also reports a study of several micro-gripper designs developed and tested on a haptic force feedback interface developed at the LSRO-EPFL. A virtual reality environment has been developed to provide real-time visualisation and force feedback. Several different software routines are integrated in the system. During an IR procedure the tip of an employed instrument interacts with a wall of blood vessels and a repulsive force is transmitted to the user. Force feedback helps radiologist to orient and navigate the inserted instrument in the vessel. This thesis presents a novel method for measurement of internal constraints during an IR procedure. The measurements help to determine the maximum interaction forces between the catheter and the wall of the blood vessel and to observe the shape of dynamic interaction during manipulation. In order to recreate a realistic simulation environment it is necessary to derive the elastic properties and behavior of arteries when contact with an instrument occurs. A novel method for measurement of mechanical properties of blood vessels is proposed in this work. Information derived with this method is also very useful to determine coherent boundary conditions for hemodynamic simulations. Measurements of the modulus of elasticity of an artery are carried out by measuring the deformations due to the inflation of an angioplasty balloon catheter used for IR procedures. A test bench, consisting of an angioplasty balloon, a PVA model and an actuator used to inflate the balloon, is developed for realization of experiments. The pressure-volume curve during the inflation of the balloon is observed. The Young's modulus is derived with an analytical model of the measurement system. The results are then analyzed and compared to existing data from literature.

EPFL2005

Haptic interface design and control with application to surgery simulation

Ulrich Spälter

This thesis proposes a framework for haptic devices interacting with virtual environments. As application of the theoretical results a haptic device for the surgical training of hysteroscopy, a gynecologic intervention, is presented. Surgery simulators, which can be described as 'flight simulators for surgeons', comprise a virtual reality for modeling and visualization of organs, and the haptic device: While the surgeon interactively follows the scene on the computer screen, he perceives the contact forces at the tool handle of the surgical instrument. The haptic device tracks the position of the surgery tool and transforms the virtual contact forces to real forces, which can be actually felt by the surgeon. This thesis treats haptic devices with application to surgery simulators for minimally-invasive surgery. Haptic interfaces are complex mechatronic systems and show inherent trade-offs between haptic realism and system stability. Human factors play an important role, as the human operator can both stabilize or destabilize the system. The haptic perception, which can vary between individuals, as a criterion for haptic rendering quality is still not formalized. The optimization of haptic interfaces, within focus of research since 15 years ago, has remained a complex task. However, with look at the emerging applications for haptics, it has become an even more important topic. For this reason it is necessary to integrate mechanical design, control design, mechatronic elements and human factors in a unifying approach. This thesis highlights the principal trade-offs of haptic interfaces and works out design guidelines for new developments and quantitative information on where and how to optimize haptic systems. As application example a haptic interface for the simulation of hysteroscopy, a gynecologic intervention on the female uterus, has been realized as prototype. The device takes the characteristics of hysteroscopy into account and introduces features like insertion and complete removal of the surgery tool from the haptic interface. A design methodology is proposed, which combines aspects of theoretical kinematics based on Lie-Groups with integrated product development – a systematic approach for engineering tasks. The result, a novel kinematic design, has been realized as haptic interface prototype. The well-known affine parameterization for all stabilizing controllers is shown to be a well-suited tool for haptic control synthesis. It provides insights into the control trade-offs and allows to integrate human factors at controller design stage. The resulting controller, demonstrated by experimental results, can reduce parasitic effects (friction, device dynamics) close to and below the human perception threshhold, thus making the device transparent within the specified bandwidth and suitable for real-time implementation. For numerical controller representation the δ-operator is discussed. It unifies continuous and discrete time domain and has beneficial numerical properties. As there is still no standardized procedure for technical performance evaluation of haptic interfaces methods proposed in literature are summarized. In the near future a large market for haptic technology can be expected with applications from surgery-assist devices and drive-by-wire interfaces in automobiles to entertainment, which highlights the relevance of the treated topic.

EPFL2006

On the Importance of Providing a Tangible Haptic Response for Training Cardiopulmonary Resuscitation in Virtual Reality

Ronan Boulic, Mathias Guy Delahaye, Bruno Herbelin

The current approach to train Cardiopulmonary Resuscitation (CPR) is to employ a mannequin device replicating the physical properties of a real human head and torso. This aims to ensure a correct transfer of the cardiac massage location, amplitude and frequency in a real situation. However, this type of training does not replicate the stress that may be elicited in the presence of a real victim ; this may result in reduced CPR performances or even errors. Virtual Reality (VR) may alleviate this lack by adding visual immersion with a Head-Mounted Display (HMD) so that the trainee is cut from the potential distractions of the real surrounding and can fully engage in a more faithful training scenario. However, one must ensure in the first place that using this technology maintains the quality of the CPR. Hence, we have conducted an experimental study to evaluate the potential of visual immersion in such a training context (limited to the cardiac massage). One important requirement was to ensure a correct hand tracking while executing the standard CPR two-hands pose. In the present paper we describe first how we assessed a simple approach using two HTC-Vive trackers. Results show that the proposed minimal setup based on a single hand tracking is validated for frequency and, with correction, for amplitude. Then, to assess the quality of the training, we performed an evaluation study considering the following two factors: Haptic feedback with the mannequin device (with/out) and Real-time Performance feedback (with/out) in the HMD. We observed that the visually immersive experience proposed in this paper delivers a sufficient level of spatial presence, involvement and agency. Integrating the real CPR mannequin in VR has a significantly positive impact on the massage performance quality whereas displaying the real-time performance in the virtual environment tends to be only useful for the frequency when no mannequin is used.

The Eurographics Association2021