Walaa Khaled

Palpation imaging using a haptic system for virtual reality applications in medicine.

In the field of medical diagnosis, there is a strong need to determine mechanical properties of biological tissue, which are of histological and pathological relevance. Malignant tumors are significantly stiffer than surrounding healthy tissue. One of the established diagnosis procedures is the palpation of body organs and tissue. Palpation is used to measure swelling, detect bone fracture, find and measure pulse, or to locate changes in the pathological state of tissue and organs. Current medical practice routinely uses sophisticated diagnostic tests through magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US) imaging. However, they cannot provide direct measure of tissue elasticity. Last year we presented the concept of the first haptic sensor actuator system to visualize and reconstruct mechanical properties of tissue using ultrasonic elastography and a haptic display with electrorheological fluids. We developed a real time strain imaging system for tumor diagnosis. It allows biopsies simultaneously to conventional ultrasound B-Mode and strain imaging investigations. We deduce the relative mechanical properties by using finite element simulations and numerical solution models solving the inverse problem. Various modifications on the haptic sensor actuator system have been investigated. This haptic system has the potential of inducing real time substantial forces, using a compact lightweight mechanism which can be applied to numerous areas including intraoperative navigation, telemedicine, teaching and telecommunication.

P1C-1 Evaluation of Material Parameters of PVA Phantoms for Reconstructive Ultrasound Elastography

The real-time ultrasound elastography system presented in Pesavento, A. et al., (1999) allows the use of elastography in a clinical study for the early detection of prostate cancer during conventional transrectal ultrasound examinations. Since tumors often consist of hard tissue structures, imaging the elastic properties promises to increase the ability to detect prostate cancer. In the frame of reconstructive elastography it is important to understand more about material properties and boundary conditions. Thus in freehand elastography, the compression is manually induced by the conducting physician leading to unstable strain image sequences. Therefore we present in this work a new designed phantom with known target E-modulus and boundary data to help physicians get used to real time elastography systems and to solve the forward and inverse problems respectively.

A NEW ER FLUID BASED HAPTIC ACTUATOR SYSTEM FOR VIRTUAL REALITY

The concept and some steps in the development of a new actuator system which enables the haptic perception of mechanically inhomogeneous virtual objects are introduced. The system consists of a two-dimensional planar array of actuator elements containing an electrorheological (ER) fluid. When a user presses his fingers onto the surface of the actuator array, he perceives locally variable resistance forces generated by vertical pistons which slide in the ER fluid through the gaps between electrode pairs. The voltage in each actuator element can be individually controlled by a novel sophisticated switching technology based on optoelectric gallium arsenide elements. The haptic information which is represented at the actuator array can be transferred from a corresponding sensor system based on ultrasonic elastography. The combined sensor-actuator system may serve as a technology platform for various applications in virtual reality, like telemedicine where the information on the consistency of tissue of a real patient is detected by the sensor part and recorded by the actuator part at a remote location.

The inverse problem of elasticity: a reconstruction procedure to determine the shear modulus of tissue

In the field of medical diagnosis, there is a strong need to determine mechanical properties of biological tissue, which are of histological and pathological relevance. In order to obtain noninvasively quantitative mechanical properties of tissue, we propose in this work an inverse approach by which the spatial distribution of the relative shear modulus of tissue can be estimated from the measured axial deformation only. First, during the solution of the mechanical forward problem the biological tissue was modeled as a linear isotropic incompressible elastic medium and a 2-D plane strain state model was used. Furthermore, to develop an inverse elastography reconstruction procedure, finite element simulations were performed for a number of biological tissue object models. The results obtained from finite element analysis were confirmed in the ultrasonic experiments on a set of tissue-like phantoms with known acoustical and mechanical properties. These phantoms were produced using PVA-Materials with different thaw and freeze cycles. Finally, using numerical solution models and solving the inverse problem using two different methods we deduce the relative shear modulus of the sample. The first method is a modified direct method based on solving the equations of equilibrium. The second method is an iterative method for solving the inverse elasticity problem and is based on recasting the problem as a non-linear optimization problem. The proposed methods were compared with respect to the stability of algorithms using numerical simulations and ultrasound measurements. Based on this comparison, an approach is introduced, which is capable of taking into account large deformations, whereas other existing methods are generally based on the theory of linear elasticity. KeywordsReal time Ultrasound Elastography; Reconstruction of Elasticity; Inverse Problem

A New Haptic Sensor Actuator System for Virtual Reality Applications in Medicine

The pathological state of soft tissues is often correlated with changes in stiffness. Malignant tumors are significantly stiffer and more immobile than surrounding healthy tissue. (hard lesions, “nodes” in organs: tumors; calcifications in vessels: arteriosclerosis). The main problem is, that such information is usually not available or can only be obtained by manual palpation, which is subjective and limited in sensitivity. It requires intuitive assessment and does not allow quantitative documentation. On the one hand a suitable sensor is required for quantitative measurement of mechanical tissue properties. On the other hand, there is also a need for a realistic mechanical display of such tissue properties. Suitable actuator arrays with high spatial resolution acting in real time are required. A haptic sensor actuator system is presented in this paper including a sensitive sensor part and an actuator array for different applications. The mechanical consistency of an object is to be locally specified using a sensor system and represented perceptibly in a remote position on a tactile display (actuator system) for the user. The sensor system uses ultrasound (US) elastography, whereas the actuator array is based on electrorheological (ER) fluids.

P5D-6 Displacement Estimators Using Angular Insonifications for Reconstructive Elastography

In order to obtain quantitative mechanical properties of tissue non-invasively, we propose in this work an inverse approach by which the spatial distribution of the relative shear modulus of tissue can be estimated from the measured axial and lateral deformation using angular insonifications. Measurements on PVA phantoms and the procedure to obtain the shear modulus are described.

P1D-8 Strain Imaging with Intravascular Ultrasound: An In Vivo Study

Coronary atherosclerosis is a common disease in industrialized countries. Acute coronary syndromes are associated with a high mortality rate. They are usually caused by a sudden occlusion of the coronary lumen due to rupture of unstable plaques in the vessel wall, often with less than 50 % stenosis. Thus, plaque morphology does not give sufficient information for determining the risk of an acute syndrome. However, the mechanical properties of vulnerable coronary plaques were shown to be different from other plaque types. Therefore, IVUS strain imaging can be an important imaging tool for risk assessment of plaques

Entwicklung eines haptischen Sensor-Aktor-Systems für Anwendungen in der virtuellen Realität

Die mechanischen Eigenschaften des biologischen Gewebes stellen wichtige Diagnoseinformationen dar und sind von groser histologischer und pathologischer Bedeutung. Insbesondere Tumoren stel- len sich oft als Gewebeverhartungen dar. Das Problem ist, dass konven- tionelle bildgebende Verfahren (Ultraschall, Computertomographie, Ma- gnetresonanztomographie) oftmals keine pathologische Verhartungen im Gewebe (wie z. B. in Brust- oder Prostatakrebs) erkennen konnen. In diesem Projekt wird ein neuartiges System fur die Erfassung und Darstellung haptischer Informationen in der virtuellen Realitat entwickelt. Mit einem haptischen Sensor-Aktor-System soll die Konsistenz eines Objektes ortsaufgelost erfasst und an anderer Stelle fur den Benutzer tastbar dargestellt werden. Das haptische System wird als eine Technologieplattform angesehen, auf der anschliesend verschiedene Produkte fur die Medizintechnik, die Unter-haltungsindustrie oder den Ausbildungssektor entwickelt werden konnen.

A Haptic System for Virtual Reality Applications Based on Ultrasound Elastography and Electro-Rheological Fluids

Mechanical properties of biological tissue represent important diagnostic information and are of histological and pathological relevance. Malignant tumors are significantly stiffer and more immobile than surrounding healthy tissue. Hard calcifications in vessels occur due to arteriosclerosis. The problem is, that such information is usually not available or can only be obtained by manual palpation, which is subjective and limited in sensitivity. It requires intuitive assessment and does not allow quantitative documentation. Unfortunately, none of the established medical imaging equipment such as magnetic resonance imaging (MRI) or X-ray computed tomography (CT) can provide direct measure of tissue elasticity. On the one hand a suitable sensor is required for quantitative measurement of mechanical tissue properties. On the other hand there is also some need for a realistic haptic display of such tissue properties. Suitable actuator arrays with high spatial resolution acting in real time are required. A haptic sensor actuator system is presented in this paper including a sensitive sensor part and an actuator array for different applications. The mechanical consistency of an object is to be locally specified using a sensor system and represented perceptibly in a remote position on an actuator system for the user. The sensor system uses ultrasound (US) elastography, whereas the actuator array is based on electrorheological (ER) fluids.