Emmanuel Promayon

Medical Image Computing and Computer-Aided Medical Interventions Applied to Soft Tissues: Work in Progress in Urology

Until recently, computer-aided medical interventions (CAMI) and medical robotics have focused on rigid and nondeformable anatomical structures. Nowadays, special attention is paid to soft tissues, raising complex issues due to their mobility and deformation. Mini-invasive digestive surgery was probably one of the first fields where soft tissues were handled through the development of simulators, tracking of anatomical structures and specific assistance robots. However, other clinical domains, for instance urology, are concerned. Indeed, laparoscopic surgery, new tumour destruction techniques (e.g., HIFU, radiofrequency, or cryoablation), increasingly early detection of cancer, and use of interventional and diagnostic imaging modalities, recently opened new challenges to the urologist and scientists involved in CAMI. This resulted in the last five years in a very significant increase of research and developments of computer-aided urology systems. In this paper, we propose a description of the main problems related to computer-aided diagnostic and therapy of soft tissues and give a survey of the different types of assistance offered to the urologist: robotization, image fusion, surgical navigation. Both research projects and operational industrial systems are discussed

Simulating Prostate Surgical Procedures with a Discrete Soft Tissue Model

Simulating surgical procedures is still a complex challenge. Either modeling methods or simulators have to take into account specific geometries and properties of the patient organs. In this paper, a new soft tissue modeling method dedicated to prostate surgical interventions is presented. The chosen medical application requires the modeling of a complex anatomical environment including intricate interactions between organs and surgical instruments. We present a discrete model that has been specifically developed to fulfil these requirements. The influence of two particular instruments is studied: needles and ultrasound probe, according to two surgical interventions: biopsy and brachytherapy.

A virtual reality simulator combining a learning environment and clinical case database for image-guided prostate biopsy

The recent availability of navigation systems for mapping and targeting of transrectal ultrasound (TRUSS) guided prostate biopsies revealed new opportunities in training the clinician. This paper describes a simulator for TRUSS guided prostate biopsy that offers similar information, enhanced by a complete learning environment. Various exercises have been developed in accordance with a didactical study identifying the training needs. A dedicated clinical case database fed by a prostate navigation system provides a large patient prostate image database that covers the main situations encountered during clinical practice. A haptic device is used to enable complete biopsy procedures or practice specific tasks. This paper also presents work in progress of the evaluation of such a simulator.

Simulating complex organ interactions: evaluation of a soft tissue discrete model

Computer assisted procedures play a key role in the improvement of surgical operations. The current techniques in simulation potentially lead to more accuracy, more safety and more predictability in the surgical room. Despite the important number of algorithms proposed for interactively modelling deformable objects such as soft human tissues, very few methods have attempted to simulate complex anatomical configurations. In this paper, we present a new approach for soft tissue modelling whose novelty is to integrate the interactions between a given soft organ and its surrounding organs. The proposed discrete model is compared to finite element method in order to quantify its performance and physical realism. The model is applied to the simulation of the prostate-bladder set.

Using CamiTK for rapid prototyping of interactive Computer Assisted Medical Intervention applications

Computer Assisted Medical Intervention (CAMI hereafter) is a complex multi-disciplinary field. CAMI research requires the collaboration of experts in several fields as diverse as medicine, computer science, mathematics, instrumentation, signal processing, mechanics, modeling, automatics, optics, etc. CamiTK1 is a modular framework that helps researchers and clinicians to collaborate together in order to prototype CAMI applications by regrouping the knowledge and expertise from each discipline. It is an open-source, cross-platform generic and modular tool written in C++ which can handle medical images, surgical navigation, biomedicals simulations and robot control. This paper presents the Computer Assisted Medical Intervention ToolKit (CamiTK) and how it is used in various applications in our research team.

Hand-eye calibration of a robot--UltraSound probe system without any 3D localizers.

3D UltraSound (US) probes are used in clinical applications for their ease of use and ability to obtain intra-operative volumes. In surgical navigation applications a calibration step is needed to localize the probe in a general coordinate system. This paper presents a new hand-eye calibration method using directly the kinematic model of a robot and US volume registration data that does not require any 3D localizers. First results show a targeting error of 2.34 mm on an experimental setup using manual segmentation of five beads in ten US volumes.

Algebraic and analytic reconstruction methods for dynamic tomography

In this work, we discuss algebraic and analytic approaches for dynamic tomography. We present a framework of dynamic tomography for both algebraic and analytic approaches. We finally present numerical experiments.

Physical-object-oriented 3D Simulations of Cell Deformations and Migration

Many aspects of individual and collective cell motion are still poorly understood, and physical models dealing with both aspects appear clearly as valuable tools for understanding cell biomechanical behavior. We theoretically analyze and simulate individual cell mechanical properties and the related chemotactic behavior of single cells collectively involved in an aggregation process. Cell objects are defined as three-dimensional elastic bodies moving on a viscous medium and submitted both to internal cohesive and external attractive forces (gravity and chemoattraction). We first investigate individual cell mechanical response to externally applied forces and compare the simulated cell object deformations with experimental data obtained with optical tweezers. We then examine the simulated cell population reorganization submitted to a two-dimensional chemoattractant gradient over a solid plane simulating a glass coverslip. Simulations are carried out for different values of cell chemotactic response. We especially simulate cell sorting between pre-spore and pre-stalk cells duringDictyostelium discoideumaggregation process by considering two-cell populations exhibiting differential cell-cell interactions. We conclude that our physical-objectoriented (POO) approach for modeling individual cell cytomechanics also satisfactorily reproduces the two-dimensional aggregation at a cell population level. Because individual cell mechanical behavior can be compared to a wide range of cell microrheology experiments, the cell object parameters can be estimated. This framework should thus be adequate for biologically realistic multiscale analyses leading to a better understanding of how, through modulation of mechanical factors, individual cell behavior controls collective cell reorganization.

Modelling and Image Processing of Constriction and Proliferation in the Gastrulation Process of Drosophila melanogaster

The initial stage of gastrulation, an early stage of embryogenesis, is called invagination, or primitive streak formation. In the first part of the paper, we analyse by using image processing techniques the cell deformation and motion in he Drosophila melanogaster embryo searching to delimit the first period of invagination without proliferation. Then, in a second part, we propose a biomechanical model, based only on the consideration of elastic and contractile forces exerted on cell walls and on the centrosome through the combination of myosin contraction and cytoskeleton rigidity. Numerical simulations of this model made during the period of gastrulation without proliferation suggest that the model adequately simulates in-vivo cell behaviour, showing the start of the streak formation at the two extremities of the embryo cylinder, followed by a propagation of the invagination to its central part.

Virtual Adhesive: a Way to Handle Sticky Collisions in Surgical and Biological Simulators

A variety of methods have been proposed to efficiently process collisions between deformable objects. The method presented in this paper allows to model sticky states between deformable objects with triangulated surfaces. In contrast to an often used approach that consists of generating forces which eventually separate colliding objects, our method is based on the creation of an adhesive virtual object (virtual adhesive). This virtual adhesive is composed by clones of all particles locally in collision. Particle clones are used to gather forces on the virtual adhesive, which behaves like a rigid body. The resulting displacement of the virtual adhesive is used in turn to constrain the particles displacement: particles stick to their clone. As a result, no further interpenetration is possible and a sticky state is obtained in the considered zone. Moreover, the method correctly resolves contacts without introducing additional energy in the system. Results are presented through several simulations.