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16:00   Poster Session II AN INNOVATIVE SETTING FOR THE IMPROVEMENT OF ULTRASOUND ERGONOMICS Jesse Bosma, Marjan Leerkes, Wendy Manten, Joris Jaspers Abstract: Objective: To design and investigate a new setting for the improvement of ultrasound ergonomics. Background: Musculoskeletal disorders pose a great problem for obstetric ultrasound departments. A main cause appears to be the right arm position that requires prolonged, extensive muscle effort [1]. Although many adjustments of ultrasound equipment have been applied [2], the prevalence of musculoskeletal complaints among sonographers remains high. We propose an innovative approach to the problem by developing an ‘extended arm’, that changes the posture of sonographers. Methods: The Department of Obstetrics and Gynaecology and the Medical Technology & Clinical Physics department worked closely together during the design of a new device, using a co-creation design method. With the aid of the device, the traditional position of the sonographer -sitting alongside of the patient- was changed to a frontal working area. The setting was tested with several sonographers to evaluate the change of posture. Results: We developed a dedicated extended arm, with facilitates placement of the ultrasound keyboard above the patient. Moreover, the display can be positioned in line with the neutral viewing position. This setting enables the sonographer to perform all ultrasound probe manipulation in front of him/her, instead of sideways. The new setting was tested with 5 experienced sonographers. With the new setting, a more neutral posture could be achieved, which was perceived to be less fatiguing by the sonographers. All sonographers indicated that they preferred the new setting over the conventional setting. Conclusion: Using a co-creation design method, we created an unconventional frontal workspace that enables a more ergonomic posture for obstetric sonographers. Performing ultrasound procedures in a frontal position, supported by an extended arm seems to be a promising new strategy for the improvement of ultrasound ergonomics. More research has to be done to acquire comparative test results between the new and the conventional setting. QUANTITATIVE POWER DOPPLER ANALYSIS OF SKELETON MUSCLE PERFUSION Benjamin Tchang, Maarten Heres, Richard Lopata, Sigrid Pillen, Marco van Brussel Abstract: Juvenile polymyositis is a rare systemic autoimmune vasculopathy that is characterized by loss of muscle mass and weakness in the proximal muscles, leading to generalized fatigue. Symptoms include pain in the neck, torso and upper arms and legs. [1]. Juvenile polymysositis has two different stages; the inflammatory state where there is a higher blood perfusion, and the chronicle state, which has a lower blood perfusion. Krix et al. showed that it is possible to detect the difference between the resting state and the exercise state with use of contrast-enhanced ultrasonography and Power Doppler [2]. In this study, a protocol was devised to induce enhanced blood flow in skeletal muscle in healthy volunteers using Power Doppler. Power Doppler is a known feature on the US system, but is not often used in the medical workflow. The advantage of this technique is that it can detect small vessels or low blood flow with high sensitivity and without aliasing, which makes it a powerful tool to detect variations in blood flow perfusion. Quantification of Power Doppler signal is important to determine the difference between blood flow perfusion. Therefore, a custom made algorithm was developed to optimize the Power Doppler signal for quantification. Pre-clinical data was collected in 15 healthy adolescents (20 - 25 years). A protocol was development, which includes 2 different contractions exercises of the rectus femoris and the gastrocnemius, each with 3, 10 and 20 times repetition. Both blood vessel perfusion and blood vessel dilatation increased during all the exercises and decreased during the resting state, which was specific for each subject. A reproducibility test was performed to validate our protocol. Power Doppler images were acquired using a Mylab70 (Esaote, Genoa, Italy) with a linear array transducer (fc = 5.6 MHz, PRF = 2.5 kHz, Gain = 63%). The datasets were post-processed using a custom developed algorithm to optimize the PD signal for further analysis. Next, both slope determination of the resting state and calculation of the fractional moving blood volume were performed [2]. An independent-samples Student’s t-test was conducted to compare the first set with the second set of measurements. An average decay time of 40 s ± 2 s and 52 s ± 10 s was found for the rectus femoris and the gastrocnemius, respectively. The slopes of the 3x, 10x and 20x repetition were 0.063 ± 0.087; 0.064 ± 0.058; 0.088 ± 0.127; 0.098 ± 0.0194; 0.0634 ± 0.0621; 0.033 ± 0.05 for the rectus femoris 0.057 ± 0.052; 0.038 ± 0.056; 0.029 ± 0.031; 0.097 ± 0.0626, 0.0843 ± 0.0592; 0.059 ± 0.044 for the gastrocnemius, respectively. A significant difference in slope was found for the gastrocnemius (10x and 20x). Further research will include a patient study to conclude if our methods can differentiate between healthy person and patients with myositis at different disease states. Furthermore, 3D ultrasound imaging will be explored to improve field-of-view. REFERENCES [1] Marinos C Dakakas, Reindhard Hohlfeld, “Polymyositis and dermatomyositis”, Lancet; page 971-982, (2003). [2] Krix M, Weber MA, Assessment of skeletal muscle perfusion using contrast-enhanced ultrasonography. Journal of Ultrasound in Medicine, page 431-41, (2005) [3] J M Rubin, R S Adler et al, Fractional moving blood volume: estimation with power Doppler US, Vol. 197, Radiology, 1995 CHANGES IN BLOOD FLOW-INDUCED SHEAR STRESS DURING PLAQUE PROGRESSION R. Xing, L. Winkel, David de Wilde, R.Y. Ridwan, Anton van der Steen, Jolanda Wentzel, Frank Gijsen, K. van der Heiden Abstract: Accumulation of lipids and inflammatory cells in the arterial wall gives rise to formation of atherosclerotic plaques. As the disease advances, plaques can progress into two distinctive types: a stable or a vulnerable plaque. Rupture of a vulnerable plaque is the main cause of stroke and myocardial infarction. It is known that hemodynamic shear stress plays a role in the initiation of atherosclerotic plaques. However, factors determining plaque progression/vulnerability remain unclear. We will study this by analyzing the spatial and temporal changes of shear stress over growing plaques using a mouse model in which both a stable and a vulnerable plaque are present. Our initial experiments focused on creating a 3D shear stress map using an atherosclerotic mouse model. A tapering cast was placed around the carotid artery of ApoE-/- mice fed a high fat diet. The geometry of the cast is designed to produce low and oscillatory shear stress downstream of the cast, forming stable plaques, while upstream it creates low shear stress, forming vulnerable plaques. Five weeks after cast placement, blood flow velocity through the right common carotid artery was measured with ultrasound (VEVO 2100, VisualSonics). Vessel geometry was obtained using contrast-enhanced micro-CT (Quantum FX microCT, PerkinElmer) with high resolution. The respiratory gated in vivo acquisition and reconstruction was performed in less than 5 minutes. From stacks of 550 CT images, manual segmentation was performed using ITK-SNAP, creating a 3D model of the right common carotid artery. A 3D mesh for computational fluid dynamics (CFD) was then generated. Finally, CFD simulation was performed to create a 3D shear stress map using the CFD software Fluent (Ansys). As inlet boundary condition, parabolic velocity profile was imposed. Distribution of shear stress and oscillatory index (OSI) were characterized. Shear stress was low at the upstream of the cast, while maximum shear stress was observed in the cast region where lumen narrowed, corresponding to the designed geometry of the tapering cast. Streamline analysis revealed flow reversal downstream of the cast where OSI was high. However, only a single vortex was identified, demonstrating that the downstream vessel wall was exposed to an uneven oscillatory shear stress pattern. Our preliminary data demonstrate the possibility to create a detailed 3D shear stress map, by using fast and high quality micro-CT imaging to capture vessel geometry of the mouse carotid artery. To the best of our knowledge, it is the first study that reports in vivo 3D shear stress map using a cast-induced atherosclerotic mouse model. Our future work will aim at analysing the spatial and temporal changes of shear stress over the stable and vulnerable plaque in our cast model. OPTICAL ABSORBANCE MEASUREMENTS AND PHOTOACOUSTIC EVALUATION OF FREEZE-THAWED POLYVINYL-ALCOHOL VESSEL PHANTOMS Ümit Arabul, Maarten Heres, Marcel Rutten, Frans van de Vosse, Richard Lopata Abstract: Multispectral photoacoustic (MPA) imaging is a promising tool for the diagnosis of atherosclerotic carotid. Exciting the different constituents of a plaque with different wavelengths may provide morphological information to evaluate plaque vulnerability. Preclinical validation of in vivo photoacoustic (PA) imaging requires a comprehensive phantom study. In this study, the design of optically realistic vessel phantoms for photoacoustics was examined by characterizing their optical properties for different dye concentrations and mechanical properties, and comparing those to PA measurements. Four different concentrations of Indian ink and molecular dye were added to a 13 wt% PVA and 0.86 wt% orgasol mixture. Next, the homogeneously mixed gels were subjected to five freeze-thaw cycles to increase the stiffness of vessel phantoms (r_inner = 2.5 mm, r_outer = 4 mm). For each cycle, the optical absorbance was measured between 400 nm – 990 nm using a plate reader. Additionally, photoacoustic responses of each vessel phantom at 808 nm were tested with a novel, hand-held, integrated PA probe (Esaote). Measurements show that the PA signal intensity increases with the optical absorber concentration (0.3 to 0.9) in close agreement with the absorbance measurements. The freeze - thaw process has no significant effect on PA intensity. Although the total attenuation of optical energy increases after each freeze-thaw cycles, which is primarily due to the increase in the scattering coefficient. In future work, the complexity of these phantoms will be increased to examine the feasibility of distinguishing different constituents with MPA imaging. TOWARDS THE CONTROL OF A WEARABLE ACTIVE ARM SUPPORT FOR MEN WITH DUCHENNE MUSCULAR DYSTROPHY: ARE EMG AND FORCE SUITABLE CONTROL INTERFACES? Joan Lobo-Prat, Peter Kooren, Mariska Janssen, Arvid Keemink, Micha Paalman, Arno Stienen, Peter Veltink, Bart Koopman Abstract: Currently, a considerable group of men with Duchenne Muscular Dystrophy (DMD) lives with severe physical impairments and strong dependency on care. Active arm supports can improve their quality of life by augmenting their arm's residual motor capabilities. In the Flextension A-Gear project we have the goal of developing a wearable five degree-of-freedom active arm support that adapts to the time-varying needs of DMD patients. The selection of the most suitable control interface for the A-Gear arm support required a better understanding of the limitations and capabilities of different control strategies, through objective and quantitative evaluations during functional tasks. We built an experimental active elbow support to investigate the performance of EMG- and force-based control interfaces in men with DMD. The system was tested in three volunteers with DMD (21-23 years) with almost no arm function left. The participants were asked to perform a one-dimensional discrete position-tracking task in which they had to bring the forearm to a target angle and remain there for 2 seconds. The control performance of the EMG- and force-based control interfaces were evaluated in terms of rising time, settling time and overshoot, and the results were compared with the design requirements. We found that the system was capable of successfully supporting the elbow flexion-extension movements during the discrete position-tracking task using the low-amplitude EMG and force signals that still remain measurable in man with DMD. We conclude that both interfaces are suitable and should be investigated further in the final design of the arm support. MINIMIZING FRICTION IN A CABLE ACTUATED STEERABLE CATHETER FOR CARDIAC INTERVENTIONS Awaz Ali, Aimee Sakes, Paul Breedveld Abstract: Catheters are among the most versatile and fundamental instruments used in cardiology. State-of-the-art catheters in cardiology have limited functionality as a result of both environmental factors in the cardiovascular system and instrument limitations. To overcome these limitations, ideally, the catheter tip must be accurately steered towards and positioned at the required location. Implementing mechanically actuated cables for precise steering of the catheter offers a solution, however, cables tend to align against the outer sleeve of the catheter during bending. As a result, high normal forces are caused between the sleeve and cables, in turn causing high friction forces, and altogether increasing the required steering forces. The aim of this study is to minimize friction forces with special focus on material optimization, cable guidance, and prevention of cable buckling. A number of different cable materials is combined with a number of different low friction guide structure materials. The design of the guide structures allows for guidance of one cable. Several guide structures are fixated on a background plate following a pre-determined curve. For this purpose four different background plates are designed: a first pilot plate for initial friction measurements following a straight path and three additional plates representing cardiovascular curves crucial to cardiac interventions. Friction forces are measured with a tensile tester setup. Additionally, the number of required guide structures, for prevention of cable buckling, is determined. Both guide structures and plates are designed successfully. Significant differences are found between measured friction forces for different material combinations. Least average friction forces are measured for Polytetrafluoroethylene (PTFE) and High-Density Polyethylene (HDPE) guide structures. Promising results are found for these materials when combined with stainless steel cables. Highest average friction forces are measured for Titanium and Aluminium guide structures. Measurements of friction forces in cardiovascular curve representations result in additional insight into applicable material combinations. Additionally, cable buckling can be prevented by use of cable guidance structures. Significant differences are found in friction force for different material combinations for application in a cable actuated steerable catheter. Since friction is a major problem in cable actuated catheters, conventionally applied material combinations may not be optimal. This approach allows for comparative evaluation of material combinations in cable actuated cardiac catheters with regard to low friction, and is applicable for future device optimization and design. SELECTIVE STIMULATION OF THE SUBTHALAMIC NUCLEUS USING A HIGH DENSITY DBS LEAD. Kees van Dijk, Rens Verhagen, Lo Bour, Peter Veltink, Ciska Heida Abstract: Deep brain stimulation (DBS) is widely used in advanced stages of Parkinson’s disease (PD) and has proven to be an effective treatment of various motor symptoms. The clinical procedure involves the implantation of a DBS lead through which continuous high frequency electric pulses are delivered in a the subthalamic nucleus (STN). The clinical outcome of the therapy is rather sensitive to the precise location of the DBS lead within the STN. Unfortunately, despite careful planning and precise stereotactic surgery, a lead displacement may occur. The conventional cylindrical contact (CC) lead is only able to correct for a displacement in dorsal-ventral direction by using one or a combination of the 4 cylindrical contacts. Interestingly, a new high density (HD) lead, which consist of 40 individual circular contacts, facing different directions, has been created. This lead design provides additional degrees of freedom in steering the stimulating electric field and can be used to increase the selectivity of the stimulation. With this increased selectivity it is in principle possible to compensate to a certain extend for a lead displacement without the need to reposition the DBS lead. In this study, we assess selective stimulation of STN cells using the CC lead and the HD lead. To evaluate the two leads a computational model was used, consisting of a finite element method electric field model (SCIRun v3.0.2) combined with neuron and axon models (NEURON 6.2) of three neural populations in the subthalamic region [1]. We compared four-contact steering-mode stimulation with the HD lead to single-contact stimulation with the CC lead. The leads were targeting the centroid of the STN. Under these conditions, we adjusted the contact configurations and stimulation amplitudes until we maximized the number of activated STN cells without stimulating any of the axon fibers of the two other neural populations. The results of this model showed that the CC lead, with a stimulation current of 1.5 mA, was able to stimulate a maximum of 26.5±2.5 % of the STN cells. The HD lead, with a stimulation current of 2.3±0.45 mA, was able to stimulate 43.8±5.4 % of the STN cells. A t-test showed there was a significant difference (p<0.05) between the amount of activated STN cells. However, there was an increase of stimulation current. In conclusion, in this model with optimized stimulation parameter selection the HD lead compared to the CC lead in theory should have a better clinical effect, however, at the expense of more energy consumption. POSTURAL ADAPTATION STRATEGIES TO UNEXPECTED PLATFORM TRANSLATIONS IN DIFFERENT DIRECTIONS AND OF DIFFERENT INTENSITIES Lianne de Vries, Simone Caljouw, Mike van Diest, Helco van Keeken, Klaas Postema, Bart Verkerke, Claudine Lamoth Abstract: INTRODUCTION: In daily life activities, balance is continuously disturbed by all kinds of perturbations, for example when tripping or slipping while walking. Age-related deterioration of neural, sensory and musculoskeletal systems affects postural control, which hampers adequate postural adaptations in response to perturbations and consequently increases fall risk in older adults [1]. To examine age-related deficits in postural control, balance perturbations, by translating the surface, are often applied in controlled experimental environments [2]. The focus in these kind of studies is mainly on the step characteristics in response to the perturbation [2], but what remains unknown is whether there is a kind of ‘critical’ perturbation intensity at which a transition takes place in postural adaptation strategies used to recover balance. METHODS: 20 healthy adults (age ranging between 20 and 60 years old) participated in the study. Horizontal platform perturbations of different intensities were applied by suddenly translating the platform with eight different peak velocities and in four different directions (forward, backward, right, left) over 0.1 m. It was determined whether the participants used a stepping strategy or an in-place strategy (% of trials) in response to each perturbation. For the trials in which a step was detected, it was determined with which leg the participants took a step. For the trials in which an in-place strategy was detected, the size of the weight-shift was calculated in terms of the force distribution over both legs, where 0% indicates that the distribution over both force plates is equal, and 100% indicates that all force is on one of both force plates. RESULTS: The percentage of steps increased with increasing perturbation intensity until a ‘critical’ perturbation intensity after a forward (16% to 47% of all trials) and rightward (5% to 30% of all trials) perturbation, after which the number of times a step strategy was detected remained constant. For leftward and rightward directed perturbations it was found that the size of the weight-shift increased with increasing perturbation intensity until it reached a maximum value of 90% at a ‘critical’ perturbation intensity. CONCLUSION: For forward and rightward directed perturbations, there seems to be a ‘critical’ perturbation intensity for which a transition takes place from an in-place strategy to a stepping strategy. For perturbations to the left and the right a ‘critical’ perturbation intensity was found at which the size of the weight-shift reaches a maximum. Platform perturbations with intensities around this value can be used in future platform perturbation experiments, to examine age-related declines in postural control and causes of falls in older adults. [1] I. Melzer, N. Benjuya N and J. Kaplanski, “Postural stability in the elderly: A comparison between fallers and non-fallers”, Age Ageing, Vol.33(6), pp. 602-607, (2004). [2] W.E. McIlroy and B.E. Maki, “Age-related changes in compensatory stepping in response to unpredictable perturbations”, J Gerontol A Biol Sci Med Sci, Vol. 51(6), pp. M289-M296, (1996). MONITORING THE USE OF ELECTROSURGERY DEVICES Annetje Guédon, Frederique Meeuwsen, Marcel Paalvast, Arjan van Dijke, Linda Wauben, Joleen Blok, Maarten van der Elst, Jenny Dankelman, John van den Dobbelsteen Abstract: Introduction Insights in the progress of surgical procedures is needed to improve the scheduling and optimal use of operating rooms (OR). Moreover, monitoring the use of surgical devices is desired to create a safer environment in terms of competences and qualifications of the OR staff. The aim of this study was to develop a monitoring system for electrosurgical devices. The data collected with the monitoring system is used subsequently to research the differences in use of electrosurgical devices and to recognize the progress of surgery. Methods An electric current measurement device that enables recording the amount of current delivered to an electrosurgical device (Valleylab, Force FX) was developed. Measurements were done during 25 laparoscopic cholecystectomies that were performed by five different surgeons, each of them assisted by a surgeon in training. The surgeons and assistants had different levels of experience. Patients’ characteristics such as BMI and age were registered as well as an indication of the difficulty of the surgery. The differences in use of the electrosurgical device were measured in terms of total time of surgery and time of activation of the device. Furthermore, the activation of the device within the first 15 minutes of the surgery, the level of experience of the surgeon and the patient’s BMI and age were used to predict the end time of surgery using Support Vector Machine as a prediction method. Results The activation and power level of electrosurgical devices during the procedure could reliably be detected. Regarding the differences in the use of the device, surgeons in training were taking more time to perform the surgery but used less activation of the electrosurgical device than experienced surgeons. Regarding the prediction of the end time of surgery, the prediction was correct for 80% of the surgeries. Conclusion and future research Electric current measurement is a promising method for monitoring the use of electrosurgical devices. Differences in use are detectable and their effect on the clinical outcome may be interesting to research. Besides, it may be used as an objective measurement of the handling of the surgeon for training purposes. Concerning the prediction of the end time of surgery, future work will focus on gathering a larger data set to improve the prediction methods and research the usability of such a prediction in the OR. USING EEG TO UNDERSTAND THE ROLE OF THE BRAIN IN STABILIZING HUMAN GAIT Sjoerd Bruijn, Jaap van Dieën, Andreas Daffertshofer Abstract: Walking on two legs is inherently unstable, and how we are able to do it so well is still a matter of research. Still, the consequences of unstable gait, that is, falls, come with an enormous personal costs, and socioeconomic burden on society. To overcome this burden a fundamental understanding about how humans stabilize gait is pivotal. While the influence of peripheral factors on gait stability has received ample attention in the literature, the research on central processing for gait stability is still in its infancy [1]. To gain more understanding of the role of the brain in gait stability, we measured brain activity using Electro Encephalo Graphy (EEG) during stabilized and normal walking in healthy young subjects. Subjects walked on treadmill in two conditions, each lasting 10 minutes; normal, and while being stabilized by elastic cords [2]. Kinematics of trunk and foot clustermarkers were sampled at 100 samples/s by an optoelectronic system (Optotrack, Northern Digital, Waterloo, ON, Canada), and EEG was recorded at 2048 samples/s by means of a 64-channel cap, amplified by a TMSI Refa amplifier (TMSI, Enschede, The Netherlands). To assess differences in gait stability, local divergence exponents were calculated from the kinematic data. The EEG data were preprocessed using Independent Component Analysis (ICA) [3] to remove movement, EMG and eyeblink artifacts. Stabilized walking led to significant increases in gait stability (i.e. lower local divergence exponents). Moreover, beamforming at the beta band yielded significant sources in supplementary motor areas. In these areas, beta band activity was increased during stabilized walking. These findings suggest that supplementary motor areas are involved even in unperturbed walking. Future work will focus on brain activity during perturbed gait. This work was previously presented at the ICCS-SHA 2014 in Groningen. Acknowledgments SMB was funded by a grant from the Netherlands Organisation for Scientific Research (NWO #451-12-041). References [1] Bakker et al (2007) J Neural Transm. 114(10):1323-31. [2] Dean et al. (2007) Trans Biomed Eng. 54(11):1919-26. [3] Gwin et al. (2010) J Neurophysiol. 103(6):3526-34. SPRINT@WORK: SUSTAINABLE EMPLOYMENT OF OLDER WORKERS Charissa Roossien, Michiel Reneman, Bart Verkerke, Jan Stegenga Abstract: The last decades, the demographic trend is towards a small workforce and comparatively large retired population. Consequently, the Dutch government has increased the retirement age to reduce the costs of ageing. At the same time it is vital that older workers retain their productivity. Ageing comes with physical and cognitive decline, such as muscle strength, balance and attention mechanisms which will affect the wellbeing, workability and work performance of employees. Without countermeasures, more health care problems of workers and absenteeism costs for companies, the government and the Dutch (working) population, are to be expected. The recently started SPRINT@Work project will investigate solutions that enhance the sustainable employment of older workers. In cooperation with (local) companies and with four different fields of expertise (social health, technical business management, behavioral and social sciences and rehabilitation medicine), the cognitive and physical state of employees will be monitored. The last topic, and subject of this contribution, will focus on the development of sensor systems that monitor mechanical and energetic workload, and intervention products for improving physical state. These tools will be applied and evaluated in daily work and we will focus both on physically active and inactive (blue- and white-collar) workers. Real-time feedback about individual performance may be an important source of information that can be used to optimize work output. At the moment, monitoring health status and working condition involve self-assessment tools based on questionnaires. New monitoring technologies provide the opportunity to unobtrusively, and more accurately, assess the individual performance, during normal work. This information may provide an indication of unsafe or unhealthy circumstances. Current techniques to measure energetic workload either interfere with the workability of the user or are inaccurate because they rely on a statistical relationship between the measured parameter and energetic workload that is only true for populations. By focusing first on alternatives to such sensor systems, such as mask less breathing gas analysis or diaphragm and lung muscle activity, more accurate results will be achieved while also being unobtrusive. Secondly, the focus will be on the working posture, duration and force exerted in the postures and its effect on the well-being of the worker. With these monitoring tools, the relation between the energetic and mechanical workload of physical active workers will be investigated, as well as the influence of cognitive aspects on the workings postures, (physical) fatigue and overall physical functioning of workers in their natural working environment. WHERE ARE MY INSTRUMENTS? HAZARDS IN DELIVERY OF SURGICAL INSTRUMENTS Annetje Guédon, Linda Wauben, Anne van der Eijk, Alex Vernooij, Maarten van der Elst, Jenny Dankelman, John van den Dobbelsteen Abstract: Nowadays, tracking medical devices is required by the Food and Drug Administration (FDA) in order to recall a device when it presents a serious risk. Tracking may also present a great opportunity to get insights in the logistics and processes involved. Currently, little is known on the issues concerning the delivery of surgical instruments and it is unclear if the introduction of tracking methods will improve the situation. It is assumed that many issues are occurring regarding planning, human error, communication and lack of information. However, a quantification in terms of frequency and severity of those issues is lacking and would be valuable to introduce well addressed solutions. This work aims to provide an overview of the processes and hazards involved in the delivery of surgical instruments, in three different organizational situations. A Failure Mode and Effects Analysis (FMEA) was conducted by multidisciplinary teams in two hospitals, for three different organizational situations. The first situation was a hospital with a sterilization department situated internally. The second was a hospital with an external sterilization department situated a few kilometers from the hospital. In both situations, the sterilized instruments were stocked in the OR complex. In the third situation, they were stocked in the external sterilization department and were delivered daily on a just-in-time manner to the OR complex. With the FMEA, each team provided an overview of the processes divided in 10 main steps (planning, order, delivery, cleaning and sterilization, transport to OR, preparation, surgery, transport to sterilization department, cleaning and sterilization, return). Each main step was again divided in several sub-steps, varying from 4 to 11 sub-steps. For each of them, a list of hazards has been identified, evaluated and prioritized. Preliminary results show that a large amount of personnel is involved in the processes, which requires a surplus of double checks and communication efforts to create a sense of safety. We conclude that information technology can reduce the amount of process steps and therefore the potential hazards due to communication errors and lack of information. ESTIMATION OF HUMAN ARM DYNAMIC DURING PLANAR ARM MOVEMENTS Nurhan Gursel Ozmen, Frans van der Helm, Alfred Schouten Abstract: Background: The human body can perform many movements and maintain its posture during everyday life acting. To hold a glass or to wave your hand, we need to compensate for the forces arising from interaction with the physical environment [1-2]. The multijoint dynamic compliance of the human arm can be estimated by analysing its behaviour under different types of disturbances and environments. In a previous study we introduced a multivariable closed-loop system identification method to estimate multijoint dynamic compliance [3]. However, in that study the system was assumed to be stationary. Goal: This study aims to develop a novel closed-loop system identification method to analyse human arm dynamics under non-stationary conditions like goal-directed arm movement. Methods: The dynamic compliance of multijoint human arm will be estimated under different experimental conditions such as different movement velocities and different viscous force fields. In the first stage, simulation studies will be carried out to technically validate the proposed closed-loop system identification method. Later, the method will be applied in a human experiment. The experiment will be conducted with healthy subjects while holding the handle of a planar 2DOF manipulator and performing continuous forward and backward arm movement task. During the movement task, continuous force perturbations in the two planar directions will be imposed. Motion of the robot handle, interaction forces, and electromyography (EMG) from shoulder and elbow muscles will be recorded. A previously developed nonparametric matrix frequency response function (MFRF) estimator will be used [3]. Desired result: It is expected that the novel closed loop method would produce a reliable estimation of multijoint arm dynamics during human arm movement. BRAIN STIMULATION IN EPILEPSY. WHAT IS ACTUALLY HAPPENING? Debby Klooster, Anton de Louw, Svitlana Zinger, Paul Boon, Bert Aldenkamp Abstract: Epilepsy is one of the most common neurological disorders affecting more than 50 million people worldwide. Nowadays, different brain stimulation modalities are available for epilepsy patients who do not respond to medication and are unsuitable candidates for epilepsy surgery [1]. Complete seizure freedom is hardly ever achieved, but brain stimulation has been shown to decrease seizure frequency and also seizure severity in epilepsy patients. Although the clinical benefits have been proven, the mechanism of action of different brain stimulation techniques are not yet known. Moreover, the additional, often positive, side effects in mood and cognition are not well understood. Knowledge about the exact mechanism of action is crucial for further improvement of stimulation techniques in clinical practice. For example, it is important to know what type of patient responds best to a certain type of stimulation and what stimulation parameters are optimal. Multiple studies attempted to model the induced electrical field in the brain [2], [3]. Furthermore, studies combining stimulation with imaging have been performed [4]. These studies show that at least some of the effect of stimulation is via the thalamus. Together with the fact that positive effects from stimulation are obtained after stimulating different targets (for example deep brain structures for deep brain stimulation [1] or cortical structures for magnetic stimulation [5]), this might suggest that epilepsy is a network disease. In this paper, an overview of brain stimulation techniques and their influence on epilepsy patients is presented with the main focus on the mechanism of action. Based on this overview, future research goals have been defined. Future work of our study aims at further specifying the mechanism of action of neurostimulation. An extensive protocol is set up, combining noninvasive brain stimulation with MRI and EEG recordings. The acute and chronic effects of stimulation will be investigated, based on detailed network analyses. DIFFERENTIATING NOCICEPTIVE MECHANISMS USING ELECTROCUTANEOUS DETECTION THRESHOLDS Robert-Jan Doll, Peter Veltink, Jan Buitenweg Abstract: Chronic pain after surgery is a frequent problem and difficult to treat. Patients at risk are not identified until early treatment is no longer effective. Persisting and chronic pain can be the result of the malfunctioning of nociceptive mechanisms; both ascending and descending pathways can, individually, attribute to chronic pain development [1]. Pain thresholds measured before and after surgery demonstrated a predictability for post-surgical chronic pain [2], but more evidence is required before it can be used for identification of patients at risk in clinical practice. Moreover, existing methodology does not discriminate between ascending and descending mechanisms. Here, we present psychophysical methods which could help improve the understanding of nociceptive malfunction in persistent post-surgical pain. Single nociceptive detection thresholds can be estimated from (binary) responses to electrical stimuli and are useful to obtain information about the current state of the nociceptive system [3]. As the processing of a stimulus depends on its temporal parameters (such as pulse width, number of pulses, or inter-pulse interval), different parameters results in different detection thresholds, governed by the processing characteristics [4]. Hence, simultaneous estimation of multiple thresholds could provide information about underlying processing mechanisms. In previous studies, we demonstrated that our multiple thresholds tracking paradigm is capable of observing several nociceptive phenomena. Varying temporal stimulus properties resulted in different psychophysical functions, each related to different underlying mechanisms. A temporary change in central mechanisms was observed during the application of a painful conditioning stimulus. Moreover, long lasting peripheral and central changes were observed after epidermal nerve defunctionalisation caused by temporary application of a high dose capsaicin patch. REFERENCES 1. Wilder-Smith, O.H., et al., Patients with chronic pain after abdominal surgery show less preoperative endogenous pain inhibition and more postoperative hyperalgesia: a pilot study. Journal of pain & palliative care pharmacotherapy, 2010. 24(2): p. 119-28. 2. Yarnitsky, D., Conditioned pain modulation (the diffuse noxious inhibitory control-like effect): its relevance for acute and chronic pain states. Current Opinion in Anesthesiology, 2010. 23(5): p. 611-615. 3. Pud, D., Y. Granovsky, and D. Yarnitsky, The methodology of experimentally induced diffuse noxious inhibitory control (DNIC)-like effect in humans. Pain, 2009. 144(1-2): p. 16-9. 4. van der Heide, E.M., et al., Single pulse and pulse train modulation of cutaneous electrical stimulation: a comparison of methods. Journal of Clinical Neurophysiology, 2009. 26(1): p. 54-60. EFFECT OF SCAPULA LOCATOR DOUBLE CALIBRATION ON MEASUREMENT OF SCAPULAR KINEMATICS WITH INERTIAL AND MAGNETIC SENSORS IN SCAPULAR DYSKINESIS Josien van den Noort, Suzanne Wiertsema, Karin Hekman, Casper Schönhuth, Joost Dekker, Jaap Harlaar Abstract: 3D scapular kinematics in patients with scapular dyskinesis [1] can be measured using an inertial and magnetic measurement system (IMMS) sensor on the spina scapulae (ISEO protocol [2]). However, skin movement artefacts and a fixation offset might cause inaccuracies. To improve the anatomical calibration, double calibration at two elevation angles with a scapula locator can be used, by correcting for underestimation of motion at higher elevation angles [3,4]. The aim of this study is to evaluate the effect of double anatomical calibration (at 0 and 120deg anteflexion and abduction) with the scapula locator on 3D scapular kinematics in patients with scapular dyskinesis. 3D scapular kinematics were measured during humeral anteflexion and abduction movements in ten patients with scapular dyskinesis (BMI 24±3, age 45±14y). IMMS sensors were placed on the thorax, spina scapulae and upper arm (ISEO protocol [2]). Additionally, the scapula locator (with IMMS) was positioned on the scapula, while holding the upper arm at 0deg and 120deg anteflexion and abduction postures. The scapular kinematics during the movement trials as measured with the skin sensor (from ISEO) were anatomically calibrated using single (0deg) and double calibration (using quaternion interpolation between 0-120deg [4,5]). Statistical differences between the joint angles of the different methods (skin fixed, single and double calibration at 0,30,60,90,120deg elevation) were tested using a Linear Mixed Model. Both single and double calibration resulted in a significant increase of scapular anterior tilt (14-30deg, P<0.001) for all elevation angles during humeral anteflexion and abduction with respect to the skin fixed sensor. Protraction was not significantly different between methods. During anteflexion, double calibration did not show a significant higher increase in lateral rotation compared to single calibration (<4deg, P>0.99). During abduction of >90deg, double calibration showed 9-12deg increased lateral rotation with respect to the skin fixed sensor and single calibration, although these differences were not significant (P>0.07). In conclusion, calibration with a scapula locator yields higher measures of scapular anterior tilt compared to the ISEO protocol. For shoulder movements that exceed 90deg elevation, double calibration prevents underestimation of lateral rotation. Enhanced evaluation is needed to show when application of double calibration is required, e.g. in patients with high BMI. REFERENCES [1] Ludewig et al. (2009), J.Bone Joint Surg.Am. 91:378-389; [2] Cutti et al. (2008), Med.Biol.Eng.Comput. 46:169-178; [3] Meskers et al. (2007), J.Biomech. 40:941-946; [4] Brochard et al. (2011), J.Biomech. 44 :751-754; [5] Kuipers,J.B. (2002), Quaternions and Rotation Sequences FINGER-INTERDEPENDENCY IN YOUNG HEALTHY SUBJECTS MEASURED WITH THE POWERGLOVE Josien van den Noort, Nathalie van Beek, Dick Stegeman, DirkJan Veeger, Huub Maas, Peter Veltink Abstract: In elderly the independency to move individual fingers may decrease as a consequence of changes in neural control and mechanical characteristics of skeletal muscles [1]. To understand the changing neuromechanics of the hand with aging (MOVE-AGE project), we aim to investigate the finger interdependency during various finger tasks in healthy young and aged subjects. In the first part of the study 13 young healthy subjects performed flexion of each finger separately and in different finger combinations through the full range of motion (ROM) with a movement frequency of 0.5Hz (single: index(i), middle(m), ring(r), little(l); combined: im, mr, rl, imr, mrl). Three different conditions were measured: (1) active flexion, (2) passive flexion using a Kleinert splint and (3) active flexion with the non-instructed finger(s) constrained in extension. The PowerGlove, which includes miniature inertial and magnetic sensors placed on finger segments [2] (PowerSensor project), was used to measure kinematics of metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of each finger individually. Up to now, kinematic data of three subjects have been analysed. Individuation indices (II=1-(mean ROMnoninstructed finger(s) / mean ROMinstructed finger(s)) , based on [3], excluding the thumb) of the MCP, PIP and DIP joints have been calculated to evaluate finger interdependency. For passive flexion of the MCP joint the finger-interdependency is higher (i.e. lower value II, 0.18-0.83) compared to active (II: 0.50-0.88), especially for the ring finger (II: 0.18 vs. 0.59). However, the PIP and DIP joints show similar or lower interdependency for passive flexion (II: PIP 0.73-0.90; DIP 0.60-0.83) compared to active (II: PIP 0.54-0.92; DIP 0.30-0.83). For some of the combined movements a higher finger-interdependency compared to single finger movements was found, particularly for active flexion of the PIP joint (II: single 0.65-0.92; combined 0.54-0.77). These differences may be explained by different neuromuscular control and/or mechanical coupling within the multi-tendoned muscles that move the fingers [3]. Future studies will include more in-debt analyses of kinematic data, integrating EMG and ultrasound data and comparisons between young and aged healthy subjects. REFERENCES [1] Cole, K.J. et al. (2010). Exp Brain Res. 201(2):239–247 [2] Kortier, H.G., et al. (2014). J Neuroeng Rehabil. 11(1):70 [3] Lang, C.E. and Schieber, M.B. (2004). J Neurophysiol. 92(5):2802-2810 AN AUTOMATED METHOD TO PLAN SAFE ELECTRODE TRAJECTORIES FOR EPILEPSY SURGERY Martin Visser, Johannes Baaijen, Theo Faes, Pepijn van Horssen, Jan de Munck Abstract: ABSTRACT Patients suffering from drug resistant focal epilepsy, can be candidates for the placement of depth electrodes in their brain, in order to find the epileptogenic zone.This requires a meticulous pre-operative planning, as it is common that more than 10 electrodes are placed per patient, but avoids more invasive procedures as craniotomy, which is required for ECoG. This pre-operative planning is a demanding and time consuming process for the neurosurgeon. It is paramount that no blood vessels are damaged during the placement and removal of the depth electrodes. The methods used in current practice can take up several hours, and require a skilled neurosurgeon to perform this planning. We propose a computer driven solution to this problem to reduce planning time. Planning is based on two MR scans: an anatomical MRI scan containing structural information and a MRA scan containing vascular information of the brain. Both scans are matched and the MRA data is cleaned with a filter that emphasizes the vascular tree [1]. We have developed an algorithm that computes all possible and safe trajectories using the target region, where epileptic activity is suspected, as specified by the neurosurgeon. The algorithm provides a list of trajectories that can be sorted on the preferences of the neurosurgeon. Procedures performed on patients in the past are used to show that the computer generated list of trajectories contains at least the trajectory used by the concerning neurosurgeon on that specific patient. We have shown a posterior that for a specific trajectory our solution set contains a solution that conforms to a previously performed procedure, confirming the veracity of the suggested solution. The remaining solutions in the solution set for a specific trajectory still need to be confirmed in a simulated pre-operative planning. We expect that our algorithm is also applicable for deep brain stimulation electrode planning[2] in patients with Parkinson’s disease. REFERENCES [1] AF. Frangi et al. – Multiscalevesselenhancement filtering. Medical image computing and computer assisted intervention – MICCAI 1998, W.M. Wells, A. Colchester and S.L. Delp (Eds.), lecture notes in computer science, vol. 1496 – Springer Verlag, Berlin, Germany, pp. 130-137 [2] EJL. Brunenberg et al. - Automatic Trajectory Planning for Deep Brain Stimulation: A Feasibility Study. MICCAI 2007, Part I, LNCS 4791, pp. 584–592, 2007. DIIRECT 3-D PRINTING OF 70S30C BIOACTIVE GLASS SCAFFOLDS FOR BONE REGENERATION Christina Miss Topouzeli, J. Jones, G. Poologasundarampillai Abstract: A sol-gel derived bioactive glass scaffold fabricated with traditional techniques satisfy only some of the criteria of an ideal scaffold, including bioactivity, osteoconductivity, biodegradability and surface topography. However, scaffolds generated with traditional techniques lack a well interconnected pore network with sufficient mechanical properties [1,2]. Solid fabrication techniques (SFF) can fabricate an irregular shape scaffold layer-by-layer according to computer aided design data (CAD) obtained from patient’s medical scans. All the attempts published utilizing SFF to fabricate bioactive glass scaffolds, needed sintering either to remove organic binders or to fuse particles together and enhance mechanical properties [3,4]. However, sintering causes crystallization, which impairs the bioactivity of the scaffolds. The current aimed to produce 70S30C sol-gel derived bioactive glass scaffolds by three dimensional (3D) printing directly from sol. In this study, the effect of different molar ratio (R=molH2O:mol TEOS=12,8,4,2) on the surface area of 70S30C glass powders was investigated. It was found that samples of R=8 showed the highest surface area without gelling before heating at 60oC. This composition was chosen for further experiments. The rheological properties of the sol heated at 60oC were mapped against solvent evaporation percentage using a hybrid rheometer. The sol obtained shear thinning properties after evaporation of ~60% wt of solvents. Printing attempts from sol were run using an Ultimaker printer. A variety of unanswered questions were investigated, which were related not only to computational printing parameters but also to the rheology behind the process of extruding a 70S30C sol-gel paste. Initiating the printing process when ~70% wt of solvents had been evaporated, prolonged the printing process to 55-60 minutes. Although this project succeeded in printing well defined 70S30C bioactive glass scaffolds from sol, cracking issues after drying suggested further research. This issue can be overcome by extruding a material that turns into a gel as soon as it is extruded from the printing orifice. REFERENCES [1] Jones JR, Hench LL. Factors affecting the structure and properties of bioactive foam scaffolds for tissue engineering. J Biomed Mater Res Part B 2004;68B:36–44. [2] Fu Q, Saiz E, Tomsia AP. Bioinspired strong and highly porous glass scaffolds. Adv Funct Mater 2011;21:1058–63. [3] Saiz E, Tomsia AP. Direct ink writing of highly porous and strong glass scaffolds for load-bearing bone defects repair and regeneration. Acta Biomaterialia 2011;7(10): 3547–3554. [4] Wu C, Luo Y, Guniberti G, Xiao Y, Gelinsky M. Three-dimensional printing of hierarchical and tough mesoporous bioactive glass scaffolds with a controllable pore architecture, excellent mechanical strength and mineralization ability. Acta Biomaterialia 2011; 7(6): 2644–2650. ASSESSMENT AND VISUALISATION OF DAILY-LIFE ARM MOVEMENTS AFTER STROKE Fokke van Meulen, Bart Klaassen, Jasper Reenalda, Jaap Buurke, Peter Veltink Abstract: For an optimal guidance of the rehabilitation therapy of stroke patients in an in-home setting, objective, and patient specific assessment of upper extremity task performance is needed. Towards this goal, metrics of hand position relative to the pelvis were estimated and visualized. Using a body-worn ambulatory movement analysis system [1], hand positions were estimated in 13 stroke subjects while performing a simulated daily-life task [2]. Hand positions were visualized and derived metrics were correlated with results of the upper extremity part of the Fugl-Meyer Assessment scale (uFMA). These metrics, including work area and maximum reaching distance, appeared to strongly correlate with uFMA scores (r > 0.84, p < 0.001). Proposed metrics and visualisation can be used to objectively assess the arm movement performance over a longer period of time in a daily-life setting, if combined with info about performed task derived from a activity monitor. Further developments are on the body-worn sensing system for a more general acceptance of the system in a daily-life setting and testing the new system with stroke subjects in a daily-life setting [3]. SCALP TOPOGRAPHY OF NONLINEAR COMPONENTS OF SOMATOSENSORY STEADY-STATE RESPONSES TO MECHANICAL WRIST STIMULATION Teodoro Solis-Escalante, Yuan Yang, Alfred Schouten, Frans van der Helm Abstract: Classical paradigms for studying somatosensory function stimulate the peripheral nervous system to elicit time- and phase-locked responses in the brain. The electroencephalogram (EEG) measures electrical potentials at the scalp. These potentials represent electrical activity of neuronal groups in the brain. Averaging the EEG across multiple repetitions of the stimulus reduces the contribution of spontaneous brain activity and reveals stimulus-related responses. Rhythmic stimulation evokes steady-state responses at the stimulation rate and its harmonics [1, 2], indicating the nonlinear behavior of the nervous system. Steady-state responses have a higher signal-to-noise ratio than the responses evoked by transient stimuli, thus fewer repetitions of the stimulus are needed and the recording time is reduced. Lesion to the central or peripheral nervous system may alter the characteristics of the evoked responses, e.g., its topography; which highlights the clinical relevance of somatosensory evoked responses. Noteworthy, the absence of evoked responses following electrical stimulation of the median nerve successfully predicts poor recovery of upper limb function in acute stroke patients [3]. The goal of this work is to map the topography of nonlinear (frequency) components of somatosensory steady-state responses. Using a periodic stimulus with multiple frequency components, we evoked responses in harmonics and intermodulation products of the stimulation frequencies; effectively increasing the amount of information that can be retrieved. Analyzing the nonlinear components has the potential to enhance the signal-to-noise ratio (in the frequency domain) and to reveal interactions between brain structures. We analyzed high-density EEG recordings (126 channels) from eleven healthy young volunteers (right-handed), while a robotic manipulator (Wristalyzer, Moog Inc., The Netherlands) applied a mechanical stimulation to their right wrist. The participants’ task was to relax with eyes open. Using three frequency components (7, 13, and 29 Hz) we retrieved steady-state responses from a total of 30 frequencies, i.e., the three stimulation frequencies, and their second and third order harmonics and intermodulation products. We calculated inter-trial phase-coherence (ITPC) [4] for each electrode (563 ± 207 epochs), and obtained the average scalp topography for each frequency across participants. Our results show frequency specific scalp topographies consistent across participants. Main responses occur at the (i) contralateral hemisphere and in (ii) midfrontal areas. These can be found one at the time or in combination, with variations on the ITPC strength of each area. The variations on scalp topography could be explained by the response of underlying sources to specific frequencies, but also to varying levels of noise across frequencies. Due to the large number of epochs and the computation of phase-coherence, the former explanation seems more plausible. Future analysis will apply this methodology to EEG recordings of stroke patients to study neurophysiological changes linked to recovery of motor function. A 21-BIT COMPANDING TWO-STEP ANALOG-TO-DIGITAL CONVERTER USING A MINIMUM AMOUNT OF HIGH VOLTAGE DEVICES FOR RECORDING NEURAL RE-SPONSES IN COCHLEAR IMPLANTS Cees-Jeroen Bes, Reza Lotfi, Wouter Serdijn, Jeroen Briaire, Johan Frijns Abstract: Modern Cochlear implants (CIs) are equipped with a neural response recording system to record neural responses evoked by the stimulus applied to the auditory nerve by the implant. These recording systems are perfectly able to record neural responses once the stimulus and artifact (due to the residual charge at the electrode after stimulus) are over, but are not able to record during stimulus and artifact. This implies that the implant can neither check whether the stimulus is applied properly nor how the nerve fibers respond to the stimulus during stimulation and artifact. Moreover, medical scientists are not able to fine-tune the implant to the patient specific needs accurately. In the future, it is foreseen that CIs will be able to adjust their stimulation based on the neural response during and directly after stimulation [1]. The dynamic range of existing neural recording systems is thus limited and smaller than desired. As the stimulus can be as high as 20 Volt while neural responses can be as small as 10µV, a dynamic range of 126-dB is required. A solution to fulfill the dynamic range requirement can be found by using a 21-bit two-step Analog-to-Digital Converter (ADC) system based on a technique called Additive Instantaneous Companding [2]. The two-step ADC system consists of two stages; The first stage contains a 5-bit coarse ADC and DAC able to capture a high voltage input signal, compressing the signal to the low voltage domain and generating the 5 Most Significant Bits (MSBs) of the two-step ADC system. An Analog Charge Domain Offsetting System is proposed as implementation of the first stage. This system can be realized using switched capacitor (SC) circuits. As high voltage capacitors occupy a much larger physical area than their low voltage counterparts, by the use of only one high voltage capacitor, the circuit can be made very compact, i.e., with a small form factor, yet sufficiently low noise [3]. The second stage contains a 16-bit fine ADC for converting the remaining low voltage compressed signal to the digital domain and generating the 16 Least Significant Bits (LSBs) of the two-step ADC. The 16-bit ADC can be completely implemented in using low voltage components. The MSBs and LSBs will be digitally added in order to expand (reconstruct) the original signal in the digital domain. NOVEL EXPERIMENT DESIGN TO EXPLORE THE INTERACTION BETWEEN SPASTICITY AND ABNORMAL SYNERGIES IN INDIVIDUALS WITH CHRONIC HEMIPARETIC STROKE Nishant Jain, Jun Yao, Teodoro Solis-Escalante, Yuan Yang, Paul Krueger, Carolina Carmona, Alfred Schouten, Frans van der Helm, Julius Dewald Abstract: The two most prevalent motor impairments in the paretic upper limb following stroke are stretch reflex hyper-excitability (i.e., spasticity) and the expression of the flexion synergy (i.e., unintended coactivation between shoulder abduction (SABD) with elbow/wrist and finger flexion). The flexion synergy and spasticity may be related to an ipsilateral shift of cortical activity due to stroke-induced lesions [1]. However, the extent of our understanding of synergies and its link with altered stretch reflex activation is limited by the methodologies commonly used to study their interaction in individuals with stroke. This study uses novel multisine perturbations at the elbow joint during different motor tasks; namely SABD, elbow flexion or a passive relax task. During the experiment, a robotic device (ACT2D [3]) displaced participants’ elbow, while participants were asked to maintain various predefined level of shoulder abduction or elbow flexion torque with the aid of visual feedback. Reflexive behaviour was quantified by measuring the reaction torque of the elbow joint against the elbow angle, across a wide range of frequencies [2]. When fitted to a physiological model, this measure of the elbow admittance can describe the differences in reflexive behaviour with various synergetic activation levels between stroke patients and healthy persons. Our experimental setup incorporates high-density electroencephalogram (EEG) and electromyogram (EMG) of the relevant arm muscles (intermediate deltoid, bracheoradialis, biceps and triceps). These measures allow for quantifying the cortical activity and cortico-muscular connectivity during the motor tasks, and the differences across tasks as well as subject groups. Two stroke patients and two healthy age-matched controls participated in our pilot study. These preliminary data provide initial results that demonstrate the feasibility of this novel experiment methodology. This method can be used to assess the relation between stretch reflex behaviour and the flexion synergy, as a means to better understand the interaction between these two motor impairments in individuals with chronic stroke by physiological modelling of mechanical as well as muscular and cortical activity. REFERENCES [1] Albert Chen, Jun Yao, Julius P. A. Dewald, “Increased ipsilateral cortical activity as a function of shoulder abduction loading: evidence for an increased reliance on reticulospinal pathways”, 36th Annual International IEEE EMBS Conference, Chicago, USA (2014). [2] A. C. Schouten, W. Mugge, Frans v. d. Helm, “NMCLab, a model to assess the contributions of muscle visco-elasticity and afferent feedback to joint dynamics”, J. Biomech., Vol. 41, pp. 1659−67, (2008). [3] J. McPherson, A. Stienen, J. Drogos and Julius P. A. Dewald, “The relationship between the flexion synergy and stretch reflexes in individuals with chronic hemiparetic stroke”, IEEE International Conference on Rehabilitation Robotics, Zurich, Switzerland (2011). NON-INVASIVE UTERINE CONTRACTION DETECTION IN TERM LABOR USING ELECTROHYSTEROGRAPHY Galin Bajlekov, Chiara Rabotti, Guid Oei, Massimo Mischi Abstract: Uterine activity assessment is essential for evaluating labor progress. The use of electrohysterography (EHG) is becoming a viable alternative to the invasive intrauterine pressure (IUP) measurements [1]. For this purpose, a quantity strongly correlating with the IUP is derived from the EHG signal, an estimated IUP (eIUP). Uterine contractions are detected based on increased uterine activity. However, current criteria for contraction detection are often based on amplitude thresholds analogous to those used for IUP assessment, not taking into account the different content of the derived eIUP signal [2]. We propose a method for uterine contraction detection based on the eIUP using a template-matching algorithm. Gaussian templates adapted to relevant characteristics are compared to the eIUP, resulting in a set of features indicating their similarity to the signal. These features are evaluated in their ability to predict uterine contractions from the eIUP signal using manually annotated contraction events. The obtained weights are applied to features calculated similarly from a novel eIUP signal, resulting in a predictor of uterine contractions. The template-matching method is based on Bayesian evidence using a Gaussian likelihood function [3]. Compared to convolution template-matching, this allows for a non-linear relationship between the feature amplitude and resulting similarity. The proposed method was applied to a set of term labor data as described in [1], from which the eIUP was estimated by the Teager energy operator [4]. Contraction events were annotated by three independent observers based on a synchronized IUP signal. As reference, the results were compared to those obtained from a method by [2]. Both methods were adjusted to a sample-wise false-positive rate of 5.1%. We observed a true-positive rate of 58.4% (95%CI: 55.8%–62.7%) for the proposed method compared to 45.2% (95%CI: 39.8%–51.0%) for the reference one. Applied to 64 annotated contraction events, the proposed method resulted in 1 false-positive and 1 false-negative detections, compared to 5 false-positive and 12 false-negative detections using the reference method. The template-matching method outperforms previously employed methods. Its adaptive nature makes it more suitable to a wide range of problems. This could be beneficial for contraction detection in preterm pregnancy, where features in the EHG signals are less robust. ASSOCIATION BETWEEN PLAQUE COMPOSITION AND SHEAR STRESS IN ATHEROSCLEROTIC CAROTID ARTERIES Annelies Tuenter, Mariana Selwaness, Hans Schuurbiers, Andres Arias Lorza, Marleen de Bruijne, Meike Vernooij, Jolanda Wentzel Abstract: Rupture of an atherosclerotic plaque in the carotid arteries is a major cause of cerebrovascular events (1)(2). Plaques that are prone to rupture are characterized by the presence of certain plaque components including intraplaque haemorrhage (IPH), or a lipid rich necrotic core (LRNC)(3). The shear stress, this is the frictional force of the blood at the endothelium, is known to influence plaque initiation and progression(4). However, little research has been performed to study the association between plaque composition and shear stress. This study aims at investigating the association between plaque components and shear stress in carotid arteries of healthy subjects. This cross-sectional study consists of participants from the population-based Rotterdam Study(5). All participants with a carotid artery wall thickness of more than 2.5 mm based on ultrasound were invited for MR imaging of both carotid arteries (1.5T). These MRI images were used to evaluate the presence of intraplaque haemorrhage, lipid rich necrotic core and/or calcifications. In a random subgroup of participants additional shear stress measurements were performed. Lumen contours and outer vessel walls were detected by automated segmentation (6) and were used for wall thickness and shear stress calculations. In the 3D lumen reconstruction shear stresses were calculated using computational fluid dynamics (FIDAP). As inflow conditions at the common carotid artery, patient specific parabolic inflow was used, whereas the outflow at the external carotid artery was determined being 40% of the inflow. Based on the wall thickness measurements, plaques with a wall thickness > 1.5 mm were detected and minimal, mean and maximum shear stress was determined at those locations. Associations between plaque composition and shear stress across the plaque were studied using linear regression analysis. A general linear model was used with shear stress as outcome and plaque composition as determinant; associations were adjusted for age, gender and wall thickness. The study group consisted of 70 participants and 84 carotid arteries. In 29 (34.5%) carotid arteries, plaque with a lipid rich necrotic core was present, in 60 (71.4%) calcifications were seen and in 18 (21.4%) IPH. Atherosclerotic plaques with IPH, were exposed to a maximum shear stress, which was higher (2.57 Pa (IQR: 1,86 – 3.61) than plaques without IPH (1.62 Pa (IQR: 0.92 – 2.98), p=0.005. No significant difference in shear stress exposure was observed for plaques with and without a lipid rich necrotic core or calcifications. Conclusion: The presence of intraplaque haemorrhage in plaque of carotid arteries of healthy subjects is associated with higher shear stress. INFLUENCE OF TUNING PARAMETERS IN THE MOMENTUM-BASED BALANCE CONTROL FRAMEWORK Amber Emmens, Gijs van Oort, Herman van der Kooij Abstract: In the field of wearable exoskeletons and humanoid robotics, balance still is a difficult subject to tackle. Recent research has shown the benefit of controlling linear and angular momentum of a robot to obtain human-like balance [1]. This contribution focuses on balance control of a human model in the sagittal plane in the presence of an external perturbation using a momentum-based controller. A slightly modified version of the momentum-based controller proposed in [1,2] is implemented, with differences in the optimization method. In brief, the controller tries to find joint torques such that a certain desired momentum rate change is obtained, which is a function of the desired center of mass (CoM) position, CoM velocity and angular momentum. These variables are weighted with tuning parameters Γ_1,2,Γ_1,1 and Γ_2,1 respectively. Our goal is to investigate the influence of these parameters on the joint angle trajectories in simulations of human-like balancing on one leg. For the simulations a two-leg plus HAT (head-arms-trunk) model was created in the sagittal plane. Each leg has a thigh, shank and foot segment. As an external perturbation, a force was applied on the trunk above the CoM. Multiple simulations were executed where each tuning parameter was varied while the others remained constant. Outputs were the center of pressure (CoP), the error between the desired and real CoM in horizontal direction, the upper body rotation, the swing leg rotation and the absolute joint angle of the ankle of the stance leg. The results show that in particular Γ_1,1 has influence on keeping the CoP away from the edges of the base of support and therefore away from instability. Raising Γ_2,1 leads to more damping of the joint trajectories and has little influence on the CoP and the CoM error. Increasing Γ_1,1 as well as Γ_1,2 increases the leg swing in order to obtain the desired CoM, instead of decreasing the upper body rotation. Multiple Γ_(i,j) can have similar effects on one joint, but generally their influence on other outputs is different. Though varying the tuning parameters in other circumstances may lead to different effects, this research provides a good picture of how the tuning parameters influence a certain motion. In future work we will compare the momentum-based balancing control method with real human balancing. USE OF MULTIPLE DISTRIBUTED FORCE SENSING ARRAYS IN AN ANTHROPOCENTRIC EXOSKELETAL LIFTING SYSTEM Jack Schorsch, Arvid Keemink, Arno Stienen, Frans van der Helm, David Abbink Abstract: To support the more accurate estimation of human-machine and human-environmental force interactions, a method is proposed where a flexible distributed force sensing array (TactArray, Pressure Profile Systems) is embedded in the human-machine interface, as well as being embedded in a flexible membrane which is suspended and transposed between the human operator and the environment. With the addition of accurate accelerometer data, an accurate estimation of both the operator and environment can be obtained, for the control of the robotic support system OVERVIEW OF STATE-OF-THE-ART GUIDEWIRE’S PROXIMAL CONNECTORS Hoda Sharei Amarghan, Jenny Dankelman Abstract: Many intravascular procedures use a guidewire as an initial approach of accessing a particular vessel. There is an increasing trend to not only use it to guide other instruments, but also to measure physical quantities like flow, pressure and vessel diameter at the place of interest. Therefore, sensors need to be integrated at the tip of guidewires. Once the distal tip of a guidewire has been located at the place of interest, it will be able to detect (changes in) these quantities. The corresponding output data need to be sent through the guidewire to the proximal side and finally from the proximal side to a monitoring system for data processing. For this, it becomes necessary to establish a suitable connector between the proximal tip of the guidewire and the monitoring system. Because of the small size of the guidewire (less than 1 mm), we encounter two important challenges. First, communication between the distal tip of the guidewire to the proximal side and second, communication from the proximal side to monitoring system. When high speed data communication is required, these two challenges become much more serious. A good example of such a challenge appears by using the intravascular ultrasound (IVUS) system where an electrical data connection of 500 Mbit/s is required. To overcome the first problem (distal tip-proximal side), using an optical fiber (80µm) instead of coaxial cable as data link is proposed. In this method, a multimode optical fiber is used to transport the data and several insulated wires to power the device; all of them are running through the guidewire (360 µm) from the distal tip to the proximal side. Further research has been performed to determine the state-of-the-art of existing connectors to address the second problem, the connection from the proximal side to the monitoring system. TARGET ACCURACY OF PROSTATE BIOPSIES GUIDED BY MRI/US FUSION IMAGES Kirsten Henken, Olivier Wegelin, Frans Breuking, Harm van Melick, Ruud Bosch, Christiaan van Swol Abstract: Prostate cancer is the most common malignancy among men [1]. The standard technique for detection of prostate cancer is transrectal ultrasound (TRUS) guided biopsy. However, TRUS is not able to clearly visualize suspected lesions in the prostate. Therefore, systematic biopsies throughout the prostate are taken rather than a specific biopsy from the suspected lesion. Magnetic Resonance Imaging (MRI) has a higher sensitivity for suspected lesions, but MRI-guided interventions are expensive, time-consuming, and require equipment that is compatible with MRI. Fusion of pre-operative MRI-images with inter-operative TRUS-images combines the best of both imaging techniques. The fused images provide accurate spatial information about the target based on the MR-images as well as real-time information about the position of the needle with TRUS. This study aims to quantify the accuracy with which a target can be reached guided by fusion images from MRI and US, similarly to the study presented in [2]. Therefore, lesions in a phantom (Tissue Equivalent Prostate Phantom, CIRS) are targeted with a needle (Puncture Biopsy 18G Cannulas, Uromed) guided by a MRI/US fusion system (Biopsee, Medcom [3]). First, a T2-weighted image of the phantom is made. This image is fused with TRUS-images after which the trajectory is planned. Then the needle is inserted transperineally through a grid, while the real-time fusion images are displayed. Once the target has been reached, the needle is replaced by an MRI-safe guidewire to mark the needle trajectory. Afterwards, a second T2-weighted image of the phantom is made. The target accuracy is determined by comparing the target position with the actual needle position that is marked by means of the guidewire on MRI. The results of this study will be presented at the conference. HAPTIC INTERFACE FOR SHOULDER CONTROL OF AN UPPER LIMB PROSTHESIS Alistair Vardy, Dick Plettenburg Abstract: Body-powered prostheses remain the most cost-effective upper limb prosthesis to date. One of the main advantages over externally-powered prostheses is that it provides proprioceptive feedback to the user and thereby a high level of control. However, users abandonment rate remains high [1]. Common complaints include the high control forces required to operate the device. Forces exerted by the shoulders are transferred to a terminal device through a Bowden cable. The cable forces required to open commercially available terminal devices are so high [2,3] that powerful shoulder movements typically involving both sides of the body are required to operate the device. This study investigates a novel prosthetic interface designed to provide the same level of feedback but can be operated at much lower force levels provided by a single shoulder. The interface utilizes skin anchors [4]; two plastic adhesive patches connected by sensors and an actuator to record force/displacement and to provide feedback from sensors in the terminal device. Two experiments were performed to answer the following questions: 1) which locations on the back/shoulder will provide the largest displacement between during shoulder movements? 2) which force levels can be used that provide accurate and comfortable control. Importantly, we limit this study to movements of only one shoulder enabling the use of the other shoulder as an additional means of control for flexion/extension of the wrist or pronation/supination. To answer the first question, 26 points covering the area over the shoulder blade were tracked using a motion capture system. Five motions: elevation, depression, protraction, retraction, and a combination of elevation and protraction were investigated. As expected, the combination of elevation and protraction yielded the largest displacements between points crossing the shoulder blade from the spine to the acromion. To answer the second question, a different set of participants were asked to match a target force using elevation and protraction. A Bowden cable connecting the T7 and the acromion enabled transmission of force to a force sensor. Forces ranged from 2 to 10 N. All forces could be easily attained for trials lasting 8 seconds. The force production was most comfortable for 4 and 6 N. We conclude that force control using single-shoulder movements can readily be used to control a prosthetic device. Current efforts are underway to determine the best feedback level for feedback from a prosthetic device. REFERENCES [1] E. A. Biddiss and T. T. Chau, “Upper limb prosthesis use and abandonment: A survey of the last 25 years,” Prosthetics and Orthotics International, vol. 31, pp. 236-257, 2007. [2] G. Smit, R.M. Bongers, C.K. van der Sluis, and D.H. Plettenburg, “Efficiency of voluntary opening hand and hook prosthetic devices: 24 years of development?,” Journal of Rehabilitation Research and Development, vol. 49, pp. 523-34, 2012. [3] G. Smit, D.H. Plettenburg, “Efficiency of voluntary closing hand and hook prostheses”. Prosthetics and orthotics international vol. 34 (4), pp 411-427, 2010 [4] D. Latour, T Sabolevski, K Lajoie-Weaver. “Ipsilateral scapular cutaneous anchor” 12th World Congress of the International Society for Prosthetics and Orthotics, Vancouver Canada , July 29 - August 3, 2007 HOW THE PARAMETERS AFFECT THE DYNAMIC BEHAVIOUR OF AN INVERTED PENDULUM BALANCE CONTROL MODEL Vasiliki Spyropoulou, Tjitske Boonstra, Alfred Schouten Abstract: ABSTRACT During bipedal stance, humans generate corrective joint torques to counteract the destabilizing gravitational torque in order to maintain an upright posture. To investigate how this is achieved and to identify possible causes of balance disorders, neuromuscular modelling is employed. The developed balance control models consist of various parameters able to describe balance behaviour. Theoretically, differences in the values of these parameters could provide insight into pathophysiological changes in certain patient groups. However, even after fitting a model to experimental data, it is hard to recognize the relative contribution of each parameter in specific frequency points. Therefore, a sensitivity analysis was performed in an inverted pendulum balance control model [1],[2], with the goal to identify the unique contribution and the relative importance of the model parameters. In the model the dynamic balance behaviour was expressed with frequency response functions (FRFs), representing the relationship between external perturbations and the response (i.e. body sway), in terms of amplitude and timing. The analysed FRF included the following parameters: the human body mass (m), moment of inertia (J) and centre-of-mass height (h); the intrinsic muscle stiffness (K) and damping (B); the sensory weighting factor (W); the neural controller’s proportional and derivative feedback gains (KP, KD) and time delay (τd); the muscle activation dynamics’ eigen-frequency (ω0) and relative damping (β) and the force feedback’s gain and time constant (KF, τF). The sensitivity of each model parameter was determined for both the FRF magnitude and phase through the analytically obtained partial derivative, using the Matlab symbolic toolbox (Mathworks). The results for the main feedback parameters showed that: a) both K and KP shape the FRF in the lower frequencies (0.1-1 Hz); b) KD has a distinct influence on the FRF, by shaping the peak and slope in the 0.5-0.9 Hz range; c) W influences the overall magnitude of the FRF, without any apparent frequency dependency, and does not have any effect on the phase; d) the effect of τd is difficult to detect in the FRF magnitude, but becomes apparent in the phase above 0.6 Hz. In conclusion, it is possible to uniquely determine the value of the sensory weighting factor, the time delay, the derivative gain, and the lumped sum of the passive and active stiffness, making the used balance control model suitable to determine differences in these parameters in different patient groups. REFERENCES [1] R. J. Peterka, “Sensorimotor integration in human postural control,” J. Neurophysiol., vol. 88, no. 3, pp. 1097–1118, Sep. 2002. [2] M. Cenciarini and R. J. Peterka, “Stimulus-dependent changes in the vestibular contribution to human postural control,” J. Neurophysiol., vol. 95, no. 5, pp. 2733–2750, May 2006.