6th Dutch Bio-Medical Engineering Conference
26 & 27 January 2017, Egmond aan Zee, The Netherlands
13:30   Medical Instruments II
Chair: Jenny Dankelman
15 mins
ADAPTIVE power converter for wireADAPTIVE POWER CONVERTER FOR WIRELESS POWER TRANSFER IN BIOMEDICAL APPLICATIONSless power transfer in biomedical applications
Gustavo Martins, Wouter Serdijn
Abstract: Wireless power transfer is a suitable method for powering electronic devices implanted in the human body or attached to the skin, as it prevents the need for inconvenient cables or surgeries to replace batteries. The power received by the device varies due to antenna misalignment, distance from the power source and objects present in the environment that reflect the electromagnetic waves. In addition, different applications have different power requirements, e.g., a neural stimulator usually requires more power than a temperature sensor. RF power receivers designed to operate at a specific minimum input power do not perform well at different available power levels [1]. Therefore, the power conversion chain must be adaptive to the changing power in order to present better overall efficiency. Since the rectifier is the most inefficient block in the chain [1], it is interesting to not add extra switches to it to keep its efficiency as high as possible. Thus, we can apply two techniques to compensate for the power variations: change the matching network between the antenna and the rectifier [2] (adaptive matching network) and the rectifier's output load [3] (adaptive DC-DC converter). To modulate the rectifier's DC load, a buck-boost converter is proposed. Because this type of converter isolates its input from its output when operating in open-loop DCM (Discontinuous Conduction Mode), it is suitable in applications in which a storage capacitor is employed (since the voltage over it varies considerably) [4]. The designed converter can be dynamically adjusted for 1-μW to 1-mW available input power, being able to supply a multitude of biomedical devices, and 0.38 to 1.3-V input voltage levels. Its peak efficiency is 76.3% at an input power of 1 μW and 86.3% at 1 mW. This was achieved by using pulse frequency modulation, reconfigurable power switches and adaptively biased zero-current-detection comparator. In order to dynamically select the best switching frequency of the converter, an MPPT (Maximum Power Point Tracking) circuit was designed. It employs a timing scheme that enables the entire circuit to be switched off for a long time, decreasing its average power consumption, and a novel input power estimation circuit that measures the input power indirectly, without sensing the input current and avoiding extra losses. With these characteristics, the proposed power converter is suitable for several low-power biomedical devices or devices that require higher instantaneous power but can be duty-cycled. REFERENCES [1] H. J. Visser and R. J. M. Vullers, “RF energy harvesting and transport for wireless sensor network applications: Principles and requirements”. Proceedings of the IEEE, 101(6), 1410–1423, 2013. [2] G. C. Martins and W. A. Serdijn, “Rectifier Automatic Impedance Matching For Biomedical Implants”, 5th Dutch Bio-Medical Engineering Conference, 2015. [3] T. Paing, J. Shin, R. Zane, and Z. Popovic, “Resistor Emulation Approach to Low-Power RF Energy Harvesting,” IEEE Trans. Power Electron., vol. 23, no. 3, pp. 1494-1501, 2008. [4] G. C. Martins and W. A. Serdijn, “Adaptive Buck-Boost Converter for RF Energy Harvesting and Transfer in Biomedical Applications,” 2016 IEEE BioCAS Conf., Oct. 2016.
15 mins
Sasa Kenjeres, Jimmy Leroy Tjin
Abstract: Numerical simulations of the upper airways in humans can be a powerful tool for prediction of the distribution of different classes of inhaled particles or droplets. Furthermore, computer studies can improve various strategies to deliver medical drug aerosols to specific locations within the human respiratory system to fight respiratory diseases, [1], [2]. A novel experimental technique of targeted delivery of magnetic aerosol droplets to intact mice lungs was reported in [3]. It was demonstrated that by imposing sufficiently strong magnetic field gradients close to the main trachea bifurcation, steering of magnetic droplets towards the right lung can be achieved, resulting in an overall 400% increase in the drug deposition compared to the neutral situation. In conclusion, it is suggested that this approach should be applied to human lungs. In the present study, we analyze drug-aerosol distribution in the realistic human respiratory system (which was experimentally studied in [4]) that includes up to the 8th bronchial generations. We performed the air flow simulations in the Eulerian framework by using wall-resolving Large-Eddy Simulation (LES) approach, whereas the dynamics of the aerosols is done in the Lagrangian framework. The optimization of the unstructured numerical mesh is performed by performing RANS-type pre-simulations from which values of the dissipation rate of the turbulent kinetic energy are used to estimate the Kolmogorov length scales. The final mesh size of approximately 15x106 control volumes, proved to be sufficient for LES for inlet Reynolds number of Re=5000. The simulations are validated against recent Magnetic Resonance Velocimetry (MRV) measurements for identical geometry, [4]. An overall good agreement between MRV measurements and simulations are obtained. After detailed validation of the flow fields, we focus on the Lagrangian dynamics of the different classes of aerosols and their distribution within the airway geometry. Finally, concept of the magnetic steering and capturing is analyzed for different classes of spherical particles with paramagnetic core and different orientation/location of the imposed magnetic field gradients, [5]. The results confirmed that a significant enhancement (more than 500% increase) of the local deposition of the aerosols at specific predefined targeted locations can be achieved. REFERENCES [1] Kleinstreuer C., Zhang Z., Donohue J. F.,”Targeted drug-aerosol delivery in the human respiratory system”, Annual Review of Biomedical Engineering 10:195-220 (2008) [2] Grotberg J. B.,”Respiratory fluid mechanics”, Physics of Fluids 23, 021301: 1-15 (2011) [3] Dames P., Gleich B., Flemmer A., Hajek K., Seidl N., Wiekhorst F., Eberbeck D., Bittmann I.,Bergemann C., Weyh T., Trahms L., Rosenecker J., Rudolph C.,”Targeted delivery of magnetic aerosol droplets to the lung”, Nature Nanotechnology 2 (8): 495–499 (2007) [4] Banko AJ, Coletti F, Schiavazzi D, Elkins CJ, Eaton JK, 2015. Three-dimensional inspiratory flow in the upper and central human airways. Exp. Fluids 56 (117): 1–12. [5] Kenjeres S., Righolt B.W.,”Simulations of magnetic capturing of drug carriers in the brain vascular system”, Int. J. Heat and Fluid Flow 35(3): 68–75 (2012)
15 mins
Fouzia Khan, Roy Roesthuis, Sarthak Misra
Abstract: Minimally invasive procedure is the preferred option for many treatments because compared to open procedures they lead to less complications, reduced blood loss and shorter recovery time for the patient [1]. The procedures can be safer when devices equipped with force sensors are used. This is because the operator is aware of the force exerted thus can avoid excess force minimizing the chance of tissue damage [2]. As a result, there exists a research effort to develop force sensors for minimally invasive devices. This abstract presents work that uses optical fibers with Fiber Bragg Gratings (FBGs) for sensing forces at the tip of a flexible minimally invasive device. The work is directly applicable to devices such as catheters and flexible needles. Optical fibers are used because they are small in diameter, capable of withstanding high temperatures and are compatible with imaging modality such as MRI [3]. FBGs are etched on short segments of the optical fiber, and they behave as strain sensor for those segments [4]. Shape reconstruction of a flexible needle has been successfully conducted using FBGs [3]. This work focuses on detecting forces at the tip of a flexible device based on measurement from FBGs. Two methods have been developed; one utilizes a Cosserat rod model and the other a rigid link model. Both methods were tested using a flexible continuum manipulator that was 210 mm in length and had a 3 mm diameter backbone. Two tests were conducted; one involved moving the robot linearly towards a commercial force sensor (ATI Nano43) such that the tip of the robot exerts force on the force sensor and the other test involved applying a pull force at the tip of the robot by attaching a string from the commercial force sensor to the tip of the robot. The method using the Cosserat rod theory could calculate force along the longitudinal axis of the robot and the moment along one transverse axis. The average error between the measurement from the commercial force sensor and the force calculation using Cosserat rod theory was 0.089 N (30%) for the force along the longitudinal axis and 0.366 Nm (25%) for the moment around one transverse axis. The method using rigid link model could calculate force along the two transverse axis. The average error, calculated the same manner as the results for the previous model, in the two transverse direction was 0.010 N (45%) and 0.008 N (16%), respectively. These results show that force measurement is possible using Fiber Bragg Gratings as sensors. For future work, the current methods will be further developed and the force/moment calculations will be used to control continuum manipulators. REFERENCES [1] A. J. Koffron, G. Auffenberg, R. Kung, and M. Abecassis, "Evaluation of 300 minimally invasive liver resections at a single institution: less is more." Annals of Surgery, 385-394 (2007). [2] C. R. Wagner, N. Stylopoulos, and R. D. Howe, “The role of force feedback in surgery: Analysis of blunt dissection.” Haptic Interfaces for Virtual Environment and Teleoperator Systems, 68–74, (2002). [3] R. J. Roesthuis, S. Janssen, and S. Misra, “On using an array of fiber Bragg grating sensors for closed-loop control of flexible minimally invasive surgical instruments.” IEEE/RSJ International Conference on Intelligent Robots and Systems, 2545–2551, (2013). [4] R. Kashyap, “Fiber Bragg Gratings” Elsevier, (2010).
15 mins
Marta Scali, Tim Pusch, Paul Breedveld, Dimitra Dodou
Abstract: Medical needles are commonly used in percutaneous procedures, such as localized therapeutic drug delivery and tissue sample removal (biopsy). Reaching the target with high accuracy and precision is important for the success of these procedures. However, this might be challenging, or even not possible, when the target is located deep inside the body. Flexible steerable needles may allow the surgeon to reach these areas while avoiding sensitive structure located along the path [1]. Needle steering can be achieved by means of pre-defined shapes, such as bevel-tip [2], or by means of actuated elements, such as cables [3]. To steer a bevel-tip needle in multiple directions, a rotation around the longitudinal axis of the needle is needed, which may induce a risk of tissue damage. Needles that include cables or other types of actuators do allow steering to all directions, but their miniaturization is difficult. In nature, several species of parasitic wasps have a thin and flexible needle-like structure, called ovipositor, used for laying eggs inside larvae hidden inside fruits or tree trunks. The ovipositor consists of three longitudinal segments, called valves, that are actuated independently of each other by musculature located in the abdomen of the insect. The valves themselves do not possess muscles. The ovipositor advances into the substrate by reciprocally sliding the valves along each other. One valve is moved forward at a time, whereas the other two valves are pulled backwards, anchoring against the substrate thanks to protrusions on their surface. This reciprocal motion of the valves allows the wasp to penetrate deep into solid structures without buckling [4]. Moreover, the wasp is able to steer the ovipositor along curved trajectories, without the need of rotatory motion. Instead, the offset between the sliding valves defines the steering direction of the tip [5]. Inspired by the anatomy and the steering mechanism of the wasp ovipositor we designed and fabricated a multi-part needle prototype with an outer diameter of 1.2 mm, in which each body part is actuated independently. The prototype was tested in gelatine. Results showed that the prototype was able to cut both straight and curved trajectories by varying the actuation sequence of the body parts. REFERENCES [1] N. Abolhassani, R. Patel and M. Moallem, “Needle insertion into soft-tissue: a survey”, Med. Eng. Phys., vol. 28 (4), pp. 413-431, 2007. [2] P. J. Swaney, J. Burgner, H. B. Gilbert, et al. “A flexure-based steerable needle: high curvature with reduced tissue damage”, IEEE Trans. Biomed. Eng., vol. 60 (4), pp. 906-909, 2013. [3] N. J. Van de Berg, J. Dankelman and J. J. Van den Dobbelsteen, “Design of an actively controlled steerable needle with tendon actuation and FBG-based shape sensing”, Med. Eng. Phys., vol. 37 (6), pp. 617-622, 2015. [4] J. F. V. Vincent and M.J. King, “The mechanism of drilling by wood wasp ovipositors”, Biomim., vol. 3, pp. 187-201, 1995. [5] D. L. Quicke, M. G. Fitton and J. Harris, “Ovipositor steering mechanisms in braconid wasps”, J. Hymenopt. Res., vol. 4, pp. 110-120, 1995.
15 mins
Lisette Tas, John van den Dobbelsteen, Alex Eggink, Dick Oepkes
Abstract: Introduction: In spina bifida there is, due to incomplete formation of the vertebral arches, a failure of closure of the neural tube during the embryonic period. This failure of closure causes a defect, through which the spinal cord, nerves and meninges can protrude. [1][2] The defect in the formation of the spinal cord has a direct influence on the nerves. [3] On top of this initial deformation, the defect results in the nerves being unprotected and in direct contact with the amniotic fluid in the uterus, causing neurologic degeneration of the nerves during pregnancy, called the second hit. [4] By operating prenatally the damage of the second hit can be prevented. In this treatment the foetus is reached with the aid of a laparotomy and hysterotomy. Unfortunately, this open prenatal surgery can lead to complications, like preterm rupture of membranes, resulting in preterm delivery. [5] Based on a literature study the following design goal is formulated: To develop a method for minimal invasive prenatal surgery of spina bifida as well as the required instrumentation. In this method the damage to the uterine wall must be minimized. Method: From this design goal it can be deduced that the most optimal method to reach the foetus in the uterus is by one port with the smallest possible diameter. Moreover, a simple method to close the defect is preferred to limit the amount of movements and operating time. A literature study showed that the use of a patch is the most promising method to close the defect. Therefore a material is selected that can be injected in a liquid state and becomes solid in the uterus, forming a watertight layer. The instrumentation and equipment needed to perform this operation will be designed and elaborated upon. For each step of the function analysis several concepts or solutions are explored. These concepts can be based on already existing instrumentation or especially designed for this application. Based on the requirements and in some parts testing, a selection is made. Results: Based on these findings a prototype is developed with which functional tests and user tests will be performed. Discussion & conclusion: Based on the test results recommendations will be made for an improved design of the instrument. This project will be an addition to the research into a successful minimal invasive prenatal surgery method for spina bifida in the future.
15 mins
Thomas Plaisier, Joris Jaspers, Victor Sluiter
Abstract: Given that more and more tasks are augmented with robots the amount of interfaces between humans and robots increases as well. In many cases these robots are meant to alter the ‘kinetic shape’ of the task, a field of study called ‘haptics’. Such devices can provide the user with a tactile response that is quite different from the natural dynamics of the system [1]. An interesting application of such a haptic system is an inertia compensator: a haptic interface that does not serve to replace all aspects of the plant’s dynamics (such as damping and springlike behavior) but only to reduce the mass that the plant presents to the human user/operator [2]. Reducing the apparent mass can make manipulation easier and faster, but it is harder for the designer of the interface to stabilize the control loop that runs in the background. In a different field, that of minimally invasive surgery, new devices and techniques are developed to improve the accuracy, speed, and reduce errors, of the surgeon. Recently the Universitair Medisch Centrum Utrecht (UMCU) has crafted a prototype of a passive structure (the MIST) that can assist in positioning and balancing of surgical tools while allowing the surgeon to work from a more ergonomic posture. Because it is passive and lacks actuators it trades these benefits for one major flaw: the inertia that needs to be overcome when manipulating the tool is greatly increased. By combining these two fields a novel system for compensating inertia in human-machine interactions is created. It employs an impedance controller, avoiding costly force sensors, to estimate the user’s movement intent and amplifies the applied acceleration to reduce the apparent inertia of the tool equipped by the MIST. Comprehensive dynamic and kinematic models are used to estimate the inertia to be compensated in real-time for every possible configuration. A 3-DOF MARA-sensor (magnetometer, angular rate, and acceleration) is used to detect user input. Appropriate safeguards are implemented to keep the total system (human plus robot) passive when needed in order to guarantee stability. The result is a setup that allows for dynamically adjusted inertia compensation in a 3-degree of freedom device. Augmentation of the compensator with additional actuators allows for a fully configurable inertia profile of the surgical tool. REFERENCES [1] Zeng, G. & Hemami, A., “An Overview of Robot Force Control”, Robotica, Cambridge University Press, 1997, 15, 473-482. [2] Aguirre-Ollinger, G.; Colgate, J. E.; Peshkin, M. A. & Goswami, A., “Design of an active one-degree-of-freedom lower-limb exoskeleton with inertia compensation”, The International Journal of Robotics Research, Sage Publications, 2011, 30, 486-499