Annual Report Department

2.12Biomedical engineering

bone structure and bone properties

2.12.1Bone mechanical properties (structure-properties relations)

Osteoporosis deteriorates the bone structure gradually, resulting in a fracture at a relatively late stage of the disease, after a severe loss of bone mass. The determination of the risk factors is essential to target patients at risk, and to deal with the disease preventively. The ultrasound velocity and attenuation through trabecular bone is studied. The aim is to determine how the architecture and material properties of this highly porous structure influence the ultrasonic parameters. The theory developed by Biot is applied on bone, and used for simulations. Methods have been developed for velocity determination from phase spectra and for the quantification of the dispersion of ultrasonic waves in trabecular bone. This additional information is broadening our understanding of the mechanisms of propagation of ultrasound through bone, and may improve our ability to characterise trabecular bone in terms of its structural and mechanical properties. Modifications to the existing ultrasonic system will allow an extended range of frequencies to be studied, and also permit the use of continuous wave and toneburst signals in addition to pulses.

Related projects: IDO

Publications and reports: 03PB21, 03PB34, 03PB50

Scientific staff: G. Van der Perre, R. Van Audekercke, J. Vander Sloten, V. Pattijn, P. Spaepen

2.12.2High-resolution finite element models of cancellous bone and bone scaffold design

High-resolution finite element modelling is a powerful tool in the analysis of the mechanical properties of trabecular bone tissue. Microfocus computed tomography (µCT) images of cancellous bone samples have been taken, providing cross-sectional images of high-resolution. These images are used to generate finite element models of the exact three-dimensional trabecular structure. Two methods for finite element modelling have been developed, one which models the structure with tetrahedral elements, and one using hexahedrons. An optimisation algorithm has been developed to increase the model accuracy and the models have been subjected to mechanical analyses. The software for model generation is written in a mathematical software environment.

In a next stage, the results from the mechanical analyses will be used to design scaffolds for the repair of large bone defects. After bone tumor resection the remaining cavity will be filled with a porous artificial structure (a so-called ‘scaffold’). This structure takes over the load-bearing function of the bone tissue until the scaffold is broken down and replaced by newly formed bone. Comparison of the mechanical properties of the designed scaffold and the finite element model of trabecular bone allows the design of a scaffold with mechanical properties that match those of cancellous bone. This results in an optimal load-bearing structure for the temporary replacement of bone tissue.

Bone cells are also believed to have mechanosensing properties. Different loading patterns are being applied either to cancellous bone samples or scaffold structures filled with bone cells in a bioreactor environment. Bone growth is measured by means of histology (fluorescent double labeling) and compared to the µCT based finite element models. In this way a validation of the computer models can be performed for the bone adaptive response to mechanical loading.

This research topic investigates the potential of mechanical stimulation on the biological response of trabecular bone. The mechanical stimulation will be applied using an extended version of the ZETOS setup (zetos.mech.kuleuven.ac.be): a in-vitro culture and loading system for trabecular bone samples of ±1 cm³. The biological response will be evaluated using µ-CT based FE element models, stiffness measurements, histological sections and information from biochemical markers in the medium. By measuring the outcome for a variety of mechanical loading conditions (frequency: 1 to 50Hz, amplitude 100 to 5000 µε, nr of cycles, inserted rest periods) the effect of the individual loading parameters will be determined. Quantified knowledge of this response will enable physicians to apply new (drugless) treatments to prevent bone loss due to osteoporosis or weightlessness.

Related projects: ESA-Prodex, Brite-Euram PISA, GBE

Publications and reports: 03PB33, 03PB54

Scientific staff: J. Vander Sloten, T. Van Cleynenbreugel, G. Van der Perre, Koen Dierckx, Pieter Spaepen

computer aided engineering

2.12.3Personalized mechanical guiding systems for surgery

Although conventional surgical instruments for the alignment and placement of screws and prostheses are widely used, there is still much room for improvement with regard to safety and placement accuracy. As an alternative to conventional surgical instruments and camera-based navigation systems, personalised templates have been developed for the accurate placement of screws in the spine and for the guiding of critical drill actions in total shoulder arthroplasty.  The template obtains a correct fit to the application area by incorporating the 3D surface information of the bone and provides guidance according to a pre-operative planning.

The presence of soft tissue gives a particular problem for templates to find a stable, unique and correct position on anatomical structures of the human body.  The occurrence of soft tissue on the bony surface introduces position errors and even can make the positioning of the tool on the bone impossible. Therefore, special 2D-support structures have been developed based on the 3D-surface description of the bone.  The support structures are implemented as a combination of wedge-shaped knife-edges that are extruded along a curve of the bony surface.  While soft tissue remainders obstruct a correct fit of a 3D-surface contact, almost no influence is observed on the quality of the fit using the knife-edges.  The drill guides are manufactured using rapid prototyping techniques such as stereolithography and selective laser sintering.

Using this support technique drill guide templates have been developed for the placement of atlanto-axial screws in cervical vertebrae, pedicle screws in lumbar vertebrae and glenoid components of shoulder prostheses.  The drill guides for the spine have been optimised in cadaver experiments and clinically applied in 10 patients.  In a clinical validation study the atlanto-axial drill guides show sub-millimetre accuracy whilst the pedicle screws are placed within a range of 2 mm.  The drill guide for the placement of glenoid components is still under development.

Collaborating surgeons: Prof. Dr. Rozing, Prof. Dr. Goffin and Prof. Dr. Lauweryns.

Related projects: Brite-Euram PISA and VLIR - ASIMED

Publication and reports: 03PB39

Scientific staff: J. Vander Sloten, R. Van Audekercke, V. Pattijn

Related Spin-off company:  Custom8 NV

2.12.4Custom implants for hard tissue surgery

In hard tissue surgery a lot of standard implants are used to restore bones, but the fit and fill of these devices is often not satisfactory. Nowadays personalized implants can be designed starting from digital medical images. The medical images yield the geometry of the bone as well as an indication for the bone quality. The objective of this research is to optimise the design of the custom implants biomechanically so that a perfect contact between bone and implant is assured and also an optimal stability and bone loading is obtained. Two case studies are being investigated. First the application of a preformed titanium membrane for bone reconstruction after tumour surgery in the proximal tibia is studied, in collaboration with the Orthopaedic Department of K.U.L (Dr. Samson). This reconstruction method is biomechanically evaluated by performing finite element analyses. Such a titanium membrane is first clinically applied for the specific case of a juxta-cortical cartilaginous tumour in the left distal femur. The membrane is produced using rapid prototyping technology (Materialise NV) and hydroforming (Ceka NV). Second the application of a preformed titanium membrane in trauma surgery is studied. For the production of the membrane a 3D-model of the bone is needed. Therefore software is written to reposition the fracture elements as to reconstruct the bone. The next step is the biomechanical evaluation of a titanium membrane for the specific case of an articular fracture of the proximal tibia.

Related projects: Brite-Euram PISA, VLIR - ASIMED

Publications and reports: 03PB01, 03PB02, 03PB10, 03PB25, 03PB39, 03PB44, 03PB53, 03PB59

Scientific staff: J. Vander Sloten, R. Van Audekercke, V. Pattijn, F. Gelaude

2.12.5Computer aided planning of cranial vault remodelling

Craniosynostosis is caused by premature closure of one or more sutures of the skull. It affects children during the first months after birth and can cause severe deformation of the head. The possibility for the surgeon to plan the operation on a computer system not only reduces operation time, but also gives the surgeon the opportunity to compare different solutions and choose the most optimal approach for each individual case. This planning system has been developed in a CAD environment, in collaboration with Dr. Mommaerts (A.Z. Sint Jan, Bruges). A classification of all surgical techniques was carried out resulting in 6 basic actions out of which all other techniques could be derived. The use of CAD offers the possibility to incorporate material properties and to simulate bending, one of the most important surgical actions, with feedback to the surgeon about the feasibility of the simulation. Mechanical tests on segments of cranial bone were carried out to obtain these material properties. A database with characteristic distances of the skull of healthy children was incorporated into the program. Since some operations involve harvesting bone on other parts of the skull, a module to optimise the area in which the bone will be harvested was also added to the program. So far, six operations have been planned on the system and these were performed according to the planning.

Publications and reports: 03PB12

Scientific staff: J. Vander Sloten, R. Gobin, G. Van der Perre, G. Janssens

2.12.6Robotic tools in orthopaedic surgery

Robot-assistance to prepare the bone surfaces in total knee replacement (TKR) and total hip replacement (THR) enables to increase the accuracy of the location of the bone cuts and the fit between prosthesis and bone, so enhancing the chances for proper long term functionality of the prosthesis. We developed an operation strategy to prepare the tibia in TKR by means of a force-controlled robot. Hereby the surgeon moves the robot-arm to which the cutting tool is attached and the robot constrains the motion to the predefined trajectory. Measuring on line the milling forces yields an indication about the local bone quality. The surgeon can use this additional input to decide on the fixation technique to be used. A key component in any robot-assisted operation procedure is to determine the position and the orientation of the bone with respect to the robot. For locating the tibia in TKR, we have introduced registration based upon locating an intramedullary pin in the tibia. Validation of this procedure showed that it is fast and quite accurate. An alternative location procedure based on surface matching techniques was developed for locating the acetabulum in THR. This technique is accurate, but rather time-consuming at the moment. In addition, machining experiments are performed to determine the optimal machining parameters of bone e.g. yielding maximal surface quality and minimal temperature rise.

Related projects: FWO G.0419.98

Publications and reports: 03PB11, 03PB19, 03PB20, 03PB37, 03PB42, 03PB58, 03R66

Scientific staff: J. Vander Sloten, J. De Schutter, G. Van der Perre, R. Van Audekercke, K. Denis, A. Ranftl

mechanical analysis of bone-implANt structures

2.12.7Analysis of bone loading in oral rehabilitation

Endosseous oral implants are used to restore a patient's masticatory function. Although high success rates are achieved, failures still occur. Clinical and animal experimental research have demonstrated the important role of mechanical load in interfacial bone resorption, however the exact mechanisms are not yet fully understood. In these projects the finite element (FE) method is applied to study bone loading patterns around oral implants and to simulate mechanically-induced bone adaptation and resorption. The calculated stress and strain patterns are compared with animal experimental and clinical data in order to gain insight in the bone adaptive response. Finite element models were created of implant-bone systems at different modelling levels. A first modelling level consisted of non-anatomical FE models of a solitary screw-shaped implant, surrounded by a cylindrical bone volume. The influence of interfacial parameters on the stresses and strains in the vicinity of the implant were studied. Finite element results demonstrated that relative motion occurs at the implant-bone interface, even for physiological loads. At a second level patient-dependent anatomical FE models of a complete mandible with implants and prosthesis were constructed. A procedure was developed to derive the model from medical CT images. Relations between Hounsfield value and E-modulus were applied in order to implement CT-based bone elastic properties. In vivo bone stress and strain distributions corresponding to in vivo measured implant loads were calculated. At a third level microfocus computerized tomographic images were used to develop detailed models of the (trabecular) bone structure around oral implants. The developed FE models were applied to relate calculated bone loading patterns with observed bone resorption in an animal experiment in which controlled cyclic loading was applied to oral implants. Once the initial stress and strain distribution is calculated, bone resorption (e.g. due to fatigue failure) can be simulated. Software routines were developed that simulate the bone adaptive (or resorptive) response according to a mathematical remodelling (or failure) criterion. This process is then iterated until equilibrium is reached (or until osseointegration is completely lost).

These projects are in collaboration with the Division of Prosthetic Dentistry and the Division ESAT-MICAS.

Related projects: OT 95/27, OT 98/30, FWO G.0180.96, PISA co-financing COF/97/04

Publications and reports: 03PB40, 03PB62, 03PB63

Scientific staff: J. Vander Sloten, G. Van der Perre, H. Van Oosterwyck, L. Geris

2.12.8Tissue differentiation and bone adaptation around implants

The aim of the research is to quantify the influence of mechanical and biological parameters on tissue differentiation and bone adaptation around loaded implants. The research consists of an experimental and a numerical part. For the experimental part a bone chamber was designed. In this mechanically isolated (in vivo) environment the influence of different loading regimes on the differentiation and adaptation process can be tested. The mathematical modelling aims at the numerical simulation and prediction of events in the bone chamber. By comparing the mathematical models to the results of animal experiments, the models can be optimised. At the other hand, simulation results can reveal plausible causes and explanations for experimental observations.

Publications and reports: 03PB04, 03PB06, 03PB07, 03PB08, 03PB09, 03PB28, 03PB32, 03PB36, 03PB47, 03PB48, 03R68

Scientific staff: J. Vander Sloten, H. Van Oosterwyck, L. Geris

2.12.9Monitoring of hip implant loosening by vibration analysis

The functional life of orthopaedic implants is generally limited to 10-15 years due to aseptic loosening and mechanical failure. Vibration analysis is proposed as a diagnostic method for the monitoring of hip implant loosening. A well-fixed implant and the surrounding bone behave as a linear dynamic system when subjected to a mechanical stimulus. When the implant loosens, non-linear behaviour develops. Within the Biomed II “STIMuLus” project, loosening was diagnosed by detecting distortion of a sinusoidal excitation signal applied externally to the condyle. Detection was by means of a prosthesis head with a built-in accelerometer, avoiding distortions introduced by soft tissue interposed between the prosthesis and an externally applied accelerometer. A large number of experiments have been performed in vitro, on cadavers and on volunteers, to design a complete measurement protocol. For these experiments, a specific test set-up with related acquisition devices and software were developed. Because excitation is a critical point, a large effort was spent on development and evaluation of different support and excitation systems. Finally, a handheld shaker system was retained for clinical measurements. The feasibility of the measurement protocol was proven by intra-operative pilot measurements on patients undergoing total hip replacement surgery. Loosening was quantified by means of the harmonic distortion, measured as the sigf-function in the time domain and as the ratio of the amplitudes of the harmonics in the frequency spectrum. A finite element (FE) study revealed that higher bending modes are more sensitive than lower bending modes to the rigidity of implant fixation. As an alternative approach, resonant frequency analysis was evaluated on cadaver bones. Implementation in vivo will require additional development work. A prosthesis fixation model based on standardised artificial bones (Sawbone® composite femora) was developed to facilitate further experimental work. Current work focuses on modal analysis of Sawbones implanted with customised cementless hip stems in various stages of fixation. FE simulations of modal behaviour are validated by experimental vibration analyses.

This research is currently done in collaboration with the Orthopaedic Surgery division and the company Advanced Custom Made Implants.

Related projects: OT/03/31

Publications and reports: 03PB22

Scientific staff: G. Van der Perre, S. Jaecques, C. Pastrav, M. Zeman-Borden

2.12.10Improving implant fixation by mechanical stimulation

This research addresses problems associated with permucosal or trans-cutaneous fixation of prostheses, using osseointegrated implants. These problems are most often found in the older population or due to trauma, where this technology is able to yield significant improvements in function. Bone anchored prostheses are now being fixed to the implants after a period of unloaded healing and osseointegration. One-stage placement of implants and immediate implant loading through the connection of a prosthesis, are slowly emerging in the clinical field. This has important functional and social benefits for the patients, since they can return sooner to their social and economic life. The scientific rationale behind this new approach is however not properly understood. This research studies the effects of immediate mechanical loading on bone reaction and implant fixation. A guinea pig model was developed to study bone reaction and implant fixation under immediate mechanical stimulation in vivo. In several pilot studies, the guinea pig model was refined. A mechanical stimulator and a guinea pig “sample holder” for in vivo microfocus computed tomography (µCT) were produced. Implantation technique, mechanical stimulation, in vivo µCT and anaesthesia protocols were continuously improved. Feasibility of monitoring bone remodelling in vivo by µCT was proven. This research is performed in collaboration with the Division of Prosthetic Dentistry and the Department of Metallurgy and Materials Engineering. An EC project (IMLOAD) was started in 2003. The methodology to derive individualised finite element (FE) models of bone and implant structures was refined in collaboration with project partners (Materialise and MSC.Software). The guinea pig model was used in full-scale experiments to study the stimulus-response relation between strain rate amplitude and peri-implant bone density.

Related projects: VIS/99/12, IMLOAD QLK6-CT-2002-02442

Publications and reports: 03PB29, 03PB30, 03PB35, 03PB38, 03PB52, 03PB55, 03RB65

Scientific staff: J. Vander Sloten, G. Van der Perre, S. Jaecques, O. Muraru

2.12.11Innovative coating of temperature sensitive medical implants with biofunctional materials using Electron Beam Ablation (INCOMED)

The objective is to develop a low temperature electron beam ablation (ELBA) coating procedure of biofunctional materials with good homogeneity, stoichiometry, substrate adhesion etc. By using targets with mixtures of bioactive or bioactive/bioinert materials, new biologically functional surfaces can be realised. The work plan is modular. First, coated samples will be made, then the coatings will be analysed on two or three substrates for two coating materials (hydroxylapatite (HA) and bioactive glass (BAG)). They will then be tested in vitro and in vivo to determine how the development of adverse biological phenomena is inhibited. With optimal coating parameters, implants will be prepared that include three substrate materials with two coating materials (HA and BAG). The results of the characterisation work and the in vivo tests will be used to validate the computer models for the prediction of coating properties from deposition parameters. Once validated, the deposition model will allow the prediction of coating properties from deposition parameters, thus reducing future experimental work. After evaluation of in vivo tests, a bench scale ELBA system will be developed including functional testing. “Typical” implant parts will be coated on the bench-scale system. In vivo evaluation will be by subcutaneous implantation in rats and rabbits and histological evaluation.

Related projects: INCOMED G5RD-CT-2001-00533

Publications and reports: 03PB23, 03PB41, 03PB56, 03PB64

Scientific staff: J. Vander Sloten, S. Jaecques

Rehabilitation and prevention biomechanics

2.12.12Biomechanics of body support on mattresses

We spend approximately one third of our lives in bed, while our inactive body depends on the sleeping system (i.e. mattress + supporting structure) we are lying and relying on. The need for an objective method to determine the most suited sleeping system for each individual is met by an intelligent database that is founded on measurements and on computer simulations. Video rasterstereography is a technique for the assessment of 3D objects that permits to reconstruct the entire vertebral column in a numeric format and to evaluate its characteristics when lying on a specific sleeping system. These measurements and pressure distribution measurements during sleep produce the first building stone of the database. The second building stone is a 3D parametric finite element model that is able to model any combination individual-sleeping system: the model is first parameterised in CAD and further assimilated in a finite element model predicting both back support and pressure relieving qualities. Finally an algorithm assesses the measured and simulated spinal deformations and pressures, and defines the best mattress with regard to a person. Based on all acquired data neural networks and statistical methods are used to put a link between anthropometrical characteristics and standardised mattress properties. Both methods are able to evaluate any existing mattress and are powerful tools for the development of adequate future sleeping systems.

Related projects:

Publications and reports: 03PB14

Scientific staff: R. Van Audekercke, G. Van der Perre, J. Vander Sloten, B. Haex, T. Huysmans, T. De Wilde

Related Spin-off company:  Custom8 NV

2.12.13The influence of whole-body vibrations on the human spine

Low back pain presents a common problem in occupational health, where the excess of back pain in drivers is often considered to be due to exposure to whole-body vibration. It is not yet understood what injury mechanisms are responsible for this, but it is clear that an improved understanding of the spinal movements caused by vibrations is necessary to identify the importance of the different vibration frequencies and body postures. Only observing the spine deformations will however not reveal the effects of cumulative trauma induced by certain frequency combinations and amplitude patterns; the interaction with the entire body through non-linear whole body modelling (e.g. combined full spine-buttocks model) and through observing tendon and muscle behaviour (e.g. physiological changes through heat development) gives a better idea of the vulnerability of the spine. State of the art EMG data processing techniques, wavelet tools and classification schemes are used for this purpose.

Related projects: Vibracom

Publications and reports: 03PB16, 03PB17, 03PB18

Scientific staff: R. Van Audekercke, B. Haex

2.12.14Prevention of head injuries by bicycle helmets

Epidemiological studies on bicycle accidents show that a substantial fraction of the cyclists that call for medical aid, are suffering from skull and brain damage; furthermore, cranio-cerebral traumas are a direct cause for the majority of the fatal accidents. Earlier investigations have shown that conventional bicycle helmets already give a significant reduction in the acceleration of the brain and thus a reduction in brain damage. In order to further improve the helmet it is necessary to fully understand the physical background of injuries during an impact on the head.

Firstly, epidemiological studies are carried out to assess the frequency of different types of skull and brain damage, and the relation with other parameters. In order to reconstruct these accidents, mathematical models are developed (e.g. a 3D multi-body model of a cyclist for collisions with a motorized vehicle). The simulated mechanical input on the head is compared to the actual injuries, and the type of impact and the calculated head and brain response are interpreted together with the medical consequences hence contributing to the understanding of skull and brain injuries in bicycle accidents.

Secondly, mathematical simulations are applied to study biological responses. More specifically, a model of a virtual human head is developed, consisting of two parts, namely a model describing the thermal responses of the head and a model describing the mechanical responses. Next to this mathematical modelling, experiments are carried out to investigate the pathogenesis of neurotrauma in cycling accidents.

Related projects: FWO-project (levenslijn)

Publications and reports: 03PB05, 03PB15, 03PB27, 03PB45, 03PB46, 03RB68, 03RB69, 03RB70

Scientific staff: G. Van der Perre, J. Vander Sloten, R. Van Audekercke, B. Haex, C. Van Lierde, N. Bogaert

2.12.15Dynamic biomechanical reconstruction of the musculo-skeletal system

The amount of people suffering from different musculo-skeletal complaints, such as low back pain or knee problems, is huge, and is by far the most important cause for work absenteeism. Orthopaedic physicians and physiotherapists are required to analyse a variety of movements to diagnose pathological or abnormal changes of the human body.

The aim is to develop an optical contact-free measuring system for various body surfaces, which is suited for dynamical applications, in order to be able to analyse a variety of movements, e.g. to diagnose pathological or abnormal changes in the human body. Various biomechanical models are developed for this purpose.

Related projects: 4D Bodyscan (EU Fifth framework)

Publications and reports: 4D Bodyscan year report (september 2003), 03PB13, 03PB51

Scientific staff: J. Vander Sloten, R. Van Audekercke, B. Haex, T. De Wilde, T. Huysmans, C. Forausberger, K. Denis, W. Rapp, N. Bogaert

2.12.16Innovation in Engineering Education

Engineering education at the K.U.Leuven has always been evaluated (e.g. by visitation commissions) to be of a very high level, with the remark, however, that knowledge is overemphasised compared to skills. This is also true for most of the other university educations. Therefore, K.U.Leuven has made an effort to rethink its teaching strategy and has developed the concept of “tutored self-study”. Essentially, the goal is to strengthen the link between education and research and, thus, enable students to actively incorporate newly acquired knowledge in a research environment. Our division is involved in the engineering education of first and second year freshmen and tries to implement this educational concept in its teaching tasks. Two projects started last academic year.

a) In the course of engineering design, so-called 'open' engineering design problems were developed for second year engineering students. This was their first exercise in the area of design methodology. The students worked in small groups, and the method of tutored self-study was used to teach them the principles of good engineering design practice. The specific difficulty of this project was the definition of the project subjects. On the one hand they had to take into account the limited technological background of these students, but on the other hand the problems had to feature enough challenges. Dedicated documentation files were developed for the students, and tutors monitored the student's progress. At the end of the design project, the students wrote a report and presented it orally.

b) In the second project we want to link the mechanics teaching in the second year of engineering. In the academic year 2003-2004 the Faculty of Engineering launches its new partly problem-based curriculum. The dicision has played and will play an instrumental role in the design, development and implementation of its curriculum (G. Van der Perre, Programme Director and J. Vander Sloten, Project Leader "Problems and Projects"). The conventional problem solving sessions were changed into sessions in which student teams analyze and discuss cases. Students were expected to extract relevant mechanical aspects from realistic technological cases and make simple mechanical models of them, which they then analysed. The lectures were divided in lectures to teach basic principles and methodologies, and lectures on demand, according to the needs of the students. Students were evaluated, both permanently, based on their work during the sessions and at the end of the year based on a report and an exam. The new approach is being fine-tuned during the following years with a project funded by the university. The first goal is the adaptation of existing and the development of new cases. A second goal is the development of ICT-support (case-presentation, selftests, applications in nowadays technolgoy…).

Related projects: K.U.Leuven – OOI – Convenant Vlaamse Regering

Publications and reports: 03PB03, 03PB24, 03PB26, 03PB31, 03PB43, 03PB49, 03PB57, 03PB60, 03PB61, 03RB71, 03RB72

Scientific staff: G. Van der Perre, J. Vander Sloten, R. Van Audekercke, L. Labey, C. Heylen

SURGICAL INSTRUMENTS

2.12.17Force feedback for telesurgical manipulator

Before robotised laparoscopic surgery can become an accepted technique in clinical practice, some human/machine interface problems have to be solved. One of them is the improvement of the haptic perception by the surgeon by implementing good feedback of the interaction forces between the laparoscopic tool and the body tissue to the surgeon through a haptic interface.

In the project, optimal bilateral force reflection with respect to the correct transmission of the environment stiffness has been implemented. Stiffness of the tissue serves as the basis for the surgeon to decide wether the tissue is healty or tumorous, or wether an artery is hidden underneath or not. This is a quite challenging problem in view of the small magnitude of those forces with respect to other disturbing forces like friction in robot joints. Moreover, to be able to discriminate better than through direct manipulation, a new method to provide enhanced sensitivity has been developed and implemented. In order to be able to provide valuable information to the surgeon, comparison of different control architectures showed that the direct measurement of the interaction forces with the tissue is absolutely necessary. Therefore, a miniature optical force sensor has been developed and tested.

Related projects: FWO336-W (07)

Publications and reports: 2003PP130, 2003PP180

Scientific staff: H. Van Brussel, D. Reynaerts, J. Vander Sloten, G. De Gersem

2.12.18Biomechanical properties of tissue and enhanced safety within robotic surgery

The safety of surgical operations with medical robots still is an open research field: how to define 'safety', how to assure safe interaction, and how to enhance safety using robotic technology. In joint research with the Centre of Surgical Techniques, the possibilities to assure the safety within telesurgical procedures are analysed, with a special focus on the information content of the interaction forces and the benifits of force feedback.

Stretching of biological tissue leads to internal damage, even long before little cracks or tears are visible or a force change can be felt by our natural touch sense. However, accurate measurement of the interaction forces shows multiple sudden force drops. By using this knowledge, the robot could give the surgeon extra information about his actions and thus reduce the unneeded trauma for the patient and enhance the safety during the intervention.

Related projects: FWO336-W (07)

Scientific staff: J. Vander Sloten, H. Van Brussel, G. De Gersem, G. De Win

2.12.19A laparoscopic robot with intuitive writing interface for gynecological laser laparoscopy

Minimal invasive surgery (MIS) becomes increasingly popular in recent years, as well as in gynaecology. Although smaller traumas lead to better postoperative quality and less pain and hospital stay, the complexity is also increasing for surgeons due to the restricted field of vision, limited degrees of freedom (DoFs) and the disparity in hand eye coordination. The CO₂ laser, coupled with an operative laparoscope, through an offset channel can be used to evaporate soft-tissues. The innovative combination provides surgeon to identify the ill tissues by inspection through laparoscope and ablate the lesion simultaneously in one laparoscope attempt. The demanding trajectory of laser ablation is commanded by surgeon to perform coordinated 7 DoFs arm movement. In view of the analogous visual behaviour of human handwriting and laser-assisted laparoscopic surgery, we introduced an Intuitive Writing Interface (IWI) for surgeons to perform What-You-Draw-Is-What-You-Cut (WYDIWYC) together with any laparoscope robot capable of dealing with specific 4 MIS instrument’s DoFs. A laparoscopic distance sensor had been developed based on optics and triangulation. The Auto-focus functionality employed the distance information to maintain laser ablating at its focal position. An evaluation with 34 subjects from the Faculty of Medicine and Biomedical Science to examine the performance of IWI was carried out and proved the short completion time and less error compared to manual manipulation of the application. Recently, a methodology to reconstruct the 3D surface contour is under investigation, using structured lighting and 3D modelling from a series of images.

Related projects: FWO336-W (07)

Publications and reports: 2003PP165

Scientific staff: H. Van Brussel, J. Vander Sloten, D. Reynaerts, J. Peirs, G. De Gersem, H.W. Tang