Hannes Bleuler

A 2-DOF fMRI compatible haptic interface to investigate the neural control of arm movements

This paper describes a two-degrees-of-freedom haptic interface to investigate the brain mechanisms of human motor control, which is capable of safely and gently interacting with human arm motion during functional magnetic resonance imaging (fMRI). A hydrostatic transmission separates the interface into a master and an MR compatible slave system, allowing the placement of all interfering components outside the electromagnetic shield of the MR room. The transmission mirrors force and motion of the master actuators on the slave system placed close to the MR scanner. The parallel architecture takes advantage of the linear MR compatible actuators and allows human subjects to perform reaching movements comfortably in the small workspace limited by the dimensions of the MR scanner and the biomechanics of the arm. The kinematic structure of the slave interface was optimized with respect to the available space and types of movements to be investigated. Materials were chosen based on their MR compatibility, their stiffness and weight. The interaction force with the subject is measured over two optical force sensors, located close to the output of the interface. Two shielded optoelectronic encoders measure the extension of the slave hydraulic pistons. Detailed tests demonstrated the fMRI compatibility even during movement of the interface

Dynamics and control of an MRI compatible master-slave system with hydrostatic transmission

We analyze the dynamics of an MR-compatible hydrostatic transmission designed to transfer power over distances of up to 10 m. In this system, a master actuates a passive slave connected by two hydrostatic lines in a cyclic arrangement. We derive a nonlinear model of this system and use it to analyze the systems behavior and the design parameters. The transmission acts as a low-pass filter with cut-off frequency decreasing for longer hoses. Even for a length of 10 m the cut-off frequency is about 20 Hz, resulting in a bandwidth that suffices for haptic interfaces interacting with human motion as well as for medical robots. A pragmatic control delivered free movements, position and velocity dependent force fields and trajectory control suitable to investigate how the brain controls movements in interaction with the environment. For short hose lengths (/spl les/1 m) the dynamics can be well approximated by a linear model, and the system is dynamic and stiff. The hydraulic transmission can produce force and motion in any orientation, enabling a more flexible design than other types of transmissions such as by cables.

A Computer-Based Real-Time Simulation of Interventional Radiology

Interventional radiology is a minimally invasive procedure where thin instruments, guidewires and catheters or stents are steered through the patients vascular system under X-ray imaging for treatment of vascular diseases. The complexity of these procedures makes training in order to master hand-eye coordination, instrument manipulation and procedure protocols for each radiologist mandatory. In this paper, we present a computer-based real-time simulation of interventional radiology procedures, which deploys a very efficient physics-based thread model to simulate the elastic behavior of guidewires and catheters. A fast collision detection scheme provides continuous collision response, which reveals more details of arterial walls than a center/line approach. Furthermore rendering techniques for realistic X-ray effect have been implemented. Our simulation structure is updated at a haptic rate of 500 Hz, thus contributing to physical realism.

Generic and systematic evaluation of haptic interfaces based on testbeds

The purpose of evaluation procedures is to achieve both qualitative and quantitative statements on haptic rendering realism and performance. Since a haptic interface provides an interaction between a user and a virtual environment, fidelity of a haptic interface directly affects the performance. To our knowledge, a standard, generic and reusable validation method which comprehensively addresses all the attributes of haptic feedback has not been realized yet. Despite the large number of human factor studies, only few of them have been proposed as well for haptic interface performance measurements. For this reason, we review validation procedures for haptic rendering and propose an evaluation method based on testbeds to obtain a systematic haptic interface assessment. We integrated the approaches of human factor studies into the testbeds to obtain a simple and yet complete measure of human-machine interaction performance. The testbeds were tested on a haptic interface, the IHP of Xitact SA, and performance results are presented. In the testbeds, performance metrics for generic haptic interaction tasks are expressed in terms of information transfer (bits) and sensory thresholds which are indeed device specific benchmark metrics. Thus, the suitability of a haptic interface for a defined task can be verified, device comparisons become possible and the obtained information can be used to identify possible improvements.

Investigation of a Cable Transmission for the Actuation of MR Compatible Haptic Interfaces

This paper investigates a cable transmission to remotely actuate MR compatible robots over a distance of several meters. Such a transmission could be an interesting solution for haptic interfaces for neuroscience studies performing force feedback during functional magnetic resonance imaging (fMRI), as well as for robots for interventional MRI. MR compatible components, transmission length and bandwidth as well as cable properties are discussed. Experiments performed on an MR compatible test bench allowing variable transmission length up to 9 meters show a mechanical bandwidth of over 30 Hz. Transmission performances and flexibility are compared with those of a hydrostatic transmission

Design and Evaluation of a Novel Haptic Interface for Endoscopic Simulation

Inspection of the colon with an endoscope for early signs of cancer (colonoscopy) has become an extremely widespread procedure, since early treatment radically improves the outlook of patients. The procedure requires a close coordination between the sense of touch and vision to navigate the endoscope along the colon. This raises the need to develop efficient training methods for physicians. Training simulators based on virtual reality, where realistic graphics are combined with a mechatronic system providing haptic feedback, are alternative to traditional training methods. To provide physicians with realistic haptic sensations of an endoscopic procedure, we have designed a haptic interface, instrumented a clinical endoscope and combined them with a simulation software for colonoscopy. In this contribution, we present the mechatronic components of the simulator. The haptic interface is able to generate high forces using the combination of electrical motors and brakes in a compact design. Experiments were performed to determine the characteristics of the device. A model-based control has been implemented and the results show that the control successfully compensates for the device nonlinearities, such as friction. The proposed haptic interface, together with the virtual reality, form a highly realistic training simulator for endoscopic surgeons, applicable not only to colonoscopy, but also to similar interventions.

Design and control of a novel thermo-tactile multimodal display

This paper describes the design and control of a water-based multimodal haptic display. The system is able to provide temperature and pressure (pulse) cues through a finger-sized display. Temperature feedback is obtained by mixing hot and cold water stored in two water tanks. The heating and cooling of the water is performed with a Peltier whose two surfaces are used, thus increasing the energetic efficiency of the system. Mixing the hot and cold water allows for very rapid temperature changes essential in applications such as object discrimination. The device can provide cooling rates sufficient to mimic the contact with any object found in our daily lives. Tactile (pulse) feedback is achieved by closing the circuit with a valve while building up the pressure with the pump. Results show that temperature is controlled with a precision of ±1°C in the range of 20°C to 40°C while simultaneously generating sensible pulses. In addition, this display is MRI-compatible as it is remotely actuated using water. These characteristics make the system suitable for psychophysics experiments, which are considered to be one of the goals and the next logic step of this work.

Position feedback for microrobots based on scanning probe microscopy

A cluster of small cooperative robots capable of executing measurement and manipulation tasks is being developed within the scope of a European project. The robots are autonomous and have an overall dimension in the order of 1 cm/sup 3/. In this paper we present the concept of the robots, along with possible locomotion modules based on piezoelectric stick-slip actuators. Tools can be added to the robot for different measurements and manipulations. The integration of an AFM probe on the robot has been realized as a high resolution sensor for localization purposes and for measurements. First experimental results are shown.

A hybrid ultrasonic motor and electrorheological fluid clutch actuator for force-feedback in MRI/fMRI

This paper presents a safe, electrically powered MR-compatible actuator with a large range of output impedance, which can be used at the entry of the scanner bore. This actuator is composed of an ultrasonic motor (USM) and a torque-controlled electrorheological fluid clutch which modulates the output torque of the USM. This paper describes the developments on the electrorheological fluid (ERF) clutch and its high voltage driver. The performances of the ERF brake constituting the clutch are evaluated, and its torque range is adapted using an epicyclic differential. The transmissible torque of the ERF clutch, i.e., the maximum system output torque, is 94.4 mNm and its drag torque is 2.6 mNm. The MR compatibility of the complete hybrid actuator is shown in extensive tests including subtraction of images and comparison of signal-to-noise ratios in powered and unpowered conditions. This novel MR-compatible actuator may be used to study the neural control of the hand.

Combined tendon vibration and virtual reality for post-stroke hand rehabilitation

Sensory function is essential for functional post-stroke recovery and control of basic hand movements like grasping. Despite this fact, therapy focuses strongly on motor aspects of rehabilitation, requiring active participation and thus excluding stroke patients with severe paresis. The aim of our novel therapeutic approach combining virtual reality, based on clinically proven mirror therapy, and tendon vibration of hand and wrist muscles is to induce neuroplastic changes leading to improved hand function. This paper presents the further development and evaluation of a robotic device, which can apply vibrations at precise locations on the finger flexor tendons to create illusions of extension movements and visualize the movements with a virtual hand. A preliminary study including 16 healthy subjects investigated the influence of the virtual reality on the perception of proprioceptive illusory movements. The experimental results provided evidence that the addition of the virtual reality enhanced the perception of the illusory movement generated by tendon vibration, by inducing movements with significantly higher extension (+4.5%, p <; 0.05). Furthermore, the virtual reality allowed a better controlled temporal elicitation of the illusion. These findings indicate the potential of this novel strategy for a more effective therapy, especially for severely impaired patients.