Haptic/VR Assessment Tool for Fine Motor Control

The Nine Hole Peg Test (NHPT) is routinely used in clinical environments to evaluate a patient’s fine hand control. A physician measures the total time required to insert nine pegs into nine holes and obtains information on the dexterity of the patient. Even though this method is simple and known to be reliable, using a virtual environment with haptic feedback instead of the classical device could give a more complete diagnosis which would isolate different constituting components of a pathology and objectively assess motor ability. Haptic devices enable extracting a large quantity of information by recording the position and the exerted forces at high frequency (1kHz). In addition to the creation of a realistic virtual counterpart of the NHPT, the present work also includes the implementation of real-time data analysis in order to extract meaningful and objective scores for the physician and the patient. A healthy group of volunteers performed the real and virtual tests which yielded a baseline for the scores of the different measured mobility parameters. Once calibrated, the virtual test successfully discriminates different mobility dysfunctions simulated by a healthy subject.

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

Exploitation de connaissances sémantiques externes dans les représentations vectorielles en recherche documentaire

Florian Seydoux

The work presented in this thesis deals with several problems met in information retrieval (IR), task which one can summarise as identifying, in a collection of "documents", a subset of documents carrying a sought information, i.e.. relevant for a request expressed by a user. In the case of textual documents, to which we limited ourselves within the framework of this thesis, a significant part of the difficulty lies in ambiguity inherent to human languages. The interaction with the user is also approached in our work, by studying a tool enabling a natural language access to a database. Finally, some techniques which permit the visualisation of large collections of documents are also presented. In this document we first of all describe the principal models of IR by highlighting the relations which exist with some manual technics of IR and document retrieval, developed during the past centuries. We present the principle of document indexing, allowing us to represent documents in a multidimensional space, and the use of this representation by a vectorial model. After having reviewed the principal improvements made these last years with vectorial research systems, including the preprocessings of collections, the indexing mechanism and measurements of similarities between documents, we detail some recent usecases of additional semantic resources (semantic dictionaries, thesaurus, networks, ontologies) reported in scientific literature for the indexing task. We then present more in detail the semantic indexing principle of textual documents by using a thesaurus, consisting in integrating in the document's representation space at least part of the informational contents of hierarchical semantic resources. We propose a general framework allowing us to describe and position various possible techniques to carry out the semantic indexing by adapting, if possible, the specificity of the descriptions resulting from the semantic resources to the data to be represented. We use this framework to describe three families of criteria usable for semantic indexing, each one having its own characteristics. For each of these families, we give the specific algorithms allowing the computation of the criteria. The first two families allow us to consider several criteria already known in feature selection. Moreover we show that, unfortunately, many of these criteria are in fact not very effective for the considered task. The third family allows us to introduce a completely new criterion, the Minimum Redundancy Cut criterion (MRC), built on the basis of the information theory and allowing us to obtain index terms having a probability of occurrence in the collection of documents as well balanced as possible. Finally, we treat the case of semantic index independent of the data (statically choosen), allowing a parameterisation of the level of generality of the index terms. Some of the criteria suggested for semantic indexing has been empirically evaluated. To judge their relevance, we used a well known vectorial system (the Smart IR system) and measured the performances of IR obtained with various reference collections. Those collections was indexed on the basis of the studied criterion, by taking into account the strongly structuring semantic relation of hyper/hyponymy ("is-a" relation), given by two different semantic resources. By comparing results obtained with the performances of a traditional indexing (using the lemmas of the words as representation space), we can show on one hand the relevance of the semantic indexings (in RD) and on the other hand the quality of the proposed criterion (MRC). Concerning man-machine interaction, we present a general outline allowing to build in a relatively fast and systematic way systems with mixed initiative, giving the human user a large (and natural) latitude in the control of the dialogue. This outline is usable in typical database research-task applications (where the database is hidden to the user, but the latter knows exactly which information they wish to find) as well as advice-task applications, for which the users does not necessarily have a precise idea of their needs, and uses the system not only for specifing their wishes, but also a set of propositions as a final result. We particularly stress the techniques allowing us to obtain a robust system, able to deal with speech recognizer failures. Concerning the visualisation of large textual data collections, we present an application of the correspondences analysis (allowing to highlight similarities and oppositions for various groups of entity, built on the basis of additional features present in the DB) to the case of patents data. In addition, we propose a method (based on the bootstrap replication principle) allowing us to determine a confidence interval for relative positionings of various groups, thus permit to immediately judge the reliability of the visually apparent similarities or oppositions.

EPFL2006

Generic and Systematic Evaluation of Haptic Interfaces Based on Testbeds

Hannes Bleuler, Evren Samur, Fei Wang

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.