7th Dutch Bio-Medical Engineering Conference
January 24th & 25th 2019, Egmond aan Zee, the Netherlands
10:30   Neuromuscular – upper extremities
Chair: Joleen Blok
15 mins
Miniaturization of Hydraulic Components
Ronald Bos, Dick Plettenburg
Abstract: A lot of knowledge is available on hydraulics, where applications can range from micro-scale lab-on-chips to large-scale construction equipment. In between these two scales lies the millimeter-range of applications and is not explored as much. The goal of this study is to analyze whether this scale (miniature hydraulics) can be an interesting method of actuation in prosthetics, orthotics and other robotic applications, and how dimensional scaling of this method can be leveraged. In order to assess the state-of-the-art of miniature hydraulics, both miniature pneumatic and hydraulic actuators were searched in scientific literature due to their similar working principles. Additionally, products from Festo, SMC, Parker and Airpot were also scanned for actuators that fall within the miniature scale (<20 mm). Using performance indices that were normalized to scale [1], their performance relating to stroke and output force were assessed. The most suitable type of actuator for prosthetic and orthotic applications was further examined. A total of 39 different actuators were found originating from 18 scientific articles and 7 product lines from industry. Piston-type actuators with a contact seal (e.g., O-rings) were most suitable for prosthetic and orthotic applications due to their large relative strokes, high attainable pressures and a force output that is independent on stroke position. Only 9 actuators were hydraulic, which showed little difference in performance with pneumatic actuators of similar type. This is mostly because the working pressures were similar as well (<1.7 MPa), whereas hydraulic actuators have the potential to function at much higher pressures [2]. In fact, if miniaturization is coupled with an increase in pressure to reach a desired output force, efficiency is able to increase for smaller diameters. From these results, it can be concluded that piston-type actuators with O-ring seals are the most suitable method of miniature hydraulic actuation in applications that require high forces and strokes in small volumes. However, the state-of-the-art of miniature hydraulics can benefit from much higher pressures (>2 MPa) to achieve higher efficiencies. [1] Huber, J. E., Fleck, N. a., & Ashby, M. F. (1997). The selection of mechanical actuators based on performance indices. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 453(1965), 2185–2205. [2] Xia, J., & Durfee, W. K. (2013). Analysis of Small-Scale Hydraulic Actuation Systems. Journal of Mechanical Design, 135(9), 091001.
15 mins
It Takes a Week to Obtain Reliable Estimates of Tremor Characteristics: a Pilot Study in Organic and Functional Tremor Patients
Zeus Tlaltecutli Dominguez Vega, Gerrit Kramer, Jan Willem Elting, Marina A J Tijssen, Natasha M Maurits
Abstract: Background: Visual assessment of a patient’s tremor during a visit to the outpatient clinic can be considered only a snapshot. Sometimes electromyography or accelerometry can be used for longer offline assessment of tremor characteristics such as intensity, frequency and occurrence, which are the most common tremor characteristics used for tremor quantification. Despite that some investigations have studied these characteristics with long-term tremor recordings, inconsistencies in recording times have not been addressed. Objective: To determine the minimum number of days needed to obtain reliable estimates of quantified tremor presence and frequency variability from long-term tremor recordings using accelerometry. Methods: Inertial sensor data were recorded from 34 tremor patients (16 functional tremor (FT), 18 organic tremor (OT)) during unconstrained activities of daily living during 30 days, each day over a 10-hour period. Sensors were attached to the dorsal side of the forearm. Start and end of recording per day were obtained from electronic patient diaries. The accelerometer signal and a tremor identification algorithm [1] implementing the periodogram were used to identify time windows with tremor, from which the percentage of tremor and tremor frequency variability were calculated per patient across all days. Non-parametric distributions were generated and Z-tests performed to determine whether estimates of tremor characteristics obtained from one up to fifteen days were representative of estimates obtained from any one up to fifteen days within the entire thirty days. Results: Tremor percentage as estimated from the full 30 days ranged from 11.17 to 31.17% for FT patients and from 10.17 to 70.0% for OT patients. Frequency variability ranged from 0.73 to 2.0 Hz for FT patients and from 0.4 to 1.5 Hz for OT patients. The shortest period of time needed to obtain reliable estimates of these tremor characteristics was found to be seven days for FT patients and one day for OT patients. Conclusions: While one day suffices for OT patients, seven days are needed to obtain reliable estimates of tremor presence in FT patients. This is likely due to higher tremor variability in FT patients. Our findings have potential impact for future diagnostic and monitoring purposes in tremor disorders.
15 mins
Evaluating Time-Varying System Identification Methods to Assess Joint Impedance: a Simulation Study and Experimental Validation
Mark van de Ruit, Winfred Mugge, Alfred Schouten
Abstract: Humans optimally interact with their environment by adapting mechanical properties of their joints to successfully execute movements e.g. knee stiffness is modulated during the gait cycle. Time-varying system identification (TV-SysID) allows to quantify joint mechanics during dynamic motor tasks, useful when mimicking human joint behaviour in active prostheses. In recent years numerous TV-SysID methods have been developed, each with their own properties. In this study six methods are compared using simulations and experimental data. Available TV-SysID methods that were tested are: (1) Linear Parameter Varying (LPV) method; (2) Kernel Based Regression (KBR); (3) Ensemble Impulse Response Function (eIRF); (4) Basis Impulse Response Function (bIRF); (5) Short Data Segments (SDS); and (6) Ensemble Spectral Method (ESM). The limitations of each method to estimate joint stiffness were verified with simulations, where the underlying system is known. For the experiments, six healthy human participants were seated with their ankle strapped to a manipulator (Achilles, MOOG). The manipulator imposed ankle rotations (filtered Gaussian white noise: 0.1-40 Hz – RMS of ~1 deg) while participants performed a torque task by tracking a 0.5 Hz sinusoid (5 to 50% of dorsiflexion MVC). The simulations demonstrated that LPV and eIRF can identify instantaneous adaptations in joint stiffness, at the cost of requiring a lot of data. SDS, ESM, KBR and bIRF are able to identify rapid - but not instantaneous - changes in joint stiffness with less data, as they possess some smoothing. For the experiments, the joint stiffness estimated by SDS, ESM, bIRF and eIRF has a comparable sinusoidal pattern, as expected from the participants’ task. Whereas the TV-SysID methods provided similar estimates of joint stiffness, their robustness to noise and amount of data differs. Ideally, a TV-SysID method: (1) tracks rapid changes, at least as fast as humans can adapt; (2) can be applied on a single trial of data to investigate trial-by-trial variability; and (3) requires little to no prior information. To facilitate comparison of TV-SysID methods authors should publish their algorithm as well as their experimental data so new methods can be validated and compared to existing methods.
15 mins
Studying Single Nerve Cells in Humans by Integrating Multichannel Surface-EMG with Exctabiltiy Testing
Boudewijn T.H.M. Sleutjes, Ernest Boskovic, Leonard J. van Schelven, Leonard H. van den Berg, Hessel Franssen
Abstract: Amyotrophic lateral sclerosis (ALS) is a devastating neurological disorder characterized by the progressive loss of motor neurons that innervate muscles leading to muscle weakness and, ultimately, death. A major challenge is to identify the pathophysiological mechanisms that contribute to the disease, and find sensitive markers to measure treatment efficacy. A promising target for disease-modifying treatment involves ion channels of which their dysfunction has been associated with motor neuron degeneration in ALS. Studying ionic processes in motor neurons (= nerve cells) however often remains limited to basic cellular or animal studies while sensitive markers of their dysfunction in humans are strongly needed. Therefore, we recently developed a new tool that enables recording single motor neuron ion channel functioning in humans directly [1]. Using multichannel surface-EMG, we identified single motor unit potentials (MUPs), generated by the muscle fibers innervated by single motor neurons. Excitability testing applied on single MUPs allowed assessment of their ion channel function. The aim of this study is to show the current state of this new tool and practical aspects for further development. With multichannel surface-EMG a 9-by-14 multi-electrode array is placed on the skin overlying the thenar muscles. This records 126 surface-EMG signals, providing spatial information which aids single MUP detection. In 10 healthy subjects, we have successfully obtained excitability measures from 14 single MUPs. From the 126 EMG signals, one EMG signal, most selective for a single motor neuron, was transferred to the excitability testing setup. To ensure that changes in single MUPs can be ascribed to pathophysiological changes, further implementation requires assessing the physiological variability of single MUPs, and standardization of the set-up to allow their redetection in subsequent sessions. This promising tool has the potential to identify new targets for treatment when monitoring the disease process in single motor neurons. It may further be used to determine biological target engagement of candidate drugs on single motor neurons in patients directly. This will bridge the gap between cellular based studies and large clinical trials accelerating the development of new treatments. [1] BTHM Sleutjes, J Drenthen, E Boskovic, LJ van Schelven, MO Kovalchuk, PGE Lumens, LH van den Berg, H Franssen. Excitability tests using high-density surface-EMG: A novel approach to studying single motor units, Clinical Neurophysiology, 129 (8): 1634 – 1641, 2018
15 mins
Motor Axon Loss in Patients with SMA
Boudewijn T.H.M. Sleutjes, Camiel A. Wijngaarde, H. Stephan Goedee, Louise A.M. Otto, Renske I. Wadman, Inge Cuppen, Leonard H. van den Berg, W. Ludo van der Pol
Abstract: Spinal muscular atrophy (SMA) is a monogenetic neurological disorder that predominantly affects children. SMA presents with a wide range in severity and a high degree of morbidity. A reduced production of the SMN-protein (survival motor neuron) leads to the progressive loss of motor axons causing loss of motor function and muscle strength. The recent introduction of the drug Spinraza (Nusinersen) marked a breakthrough as it showed efficacy in severely affected childhood-onset patients. Most of clinical trials rely on measures of gross motor function. Sensitive outcome measures that can capture subtle, but highly relevant therapeutic effects are therefore highly warranted. Treatments aiming to reduce loss of motor axons require objective tools to quantify such an effect. Therefore, we applied the compound muscle action potential (CMAP) scan, which is a electrophysiological tool that successively activates all motor axons innervating the muscle by increasing transcutaneous stimulus-currents. It captures the contribution of enlarged motor units (MUs; increased muscle fiber number per axon) due to reinnervation by the presence of relative large discontinuities in the scan. The aim of this study was to identify pathophysiological changes of axon loss and reinnervation in SMA using the CMAP scan. Recordings were obtained from 21 patients with SMA (median age 39, range 12 – 67). Stimulus-currents were applied on the left and right median nerve at the wrist and motor responses were recorded from the thenar muscles. The largest discontinuities in the CMAP scan were quantified by means of a novel marker, D50, where a low number is indicative of axon loss and enlarged MUs. The median maximum CMAP amplitude was 8.4 mV (range 0.9 – 14.6 mV) and median D50 was 31 (range 3 – 57). Nine SMA patients with a normal CMAP amplitude (> 3.5 mV) had a reduced D50 (< 25), which is indicative of axon loss and enlarged MUs. These findings suggest that the CMAP scan is a promising tool in detecting pathological changes in SMA, more so than standard maximum CMAP. It is quick and easy to perform, and has the potential to be useful for follow-up studies to monitor treatment efficacy and natural disease course.
15 mins
A Semi-Automatic Workflow for CT-MRI Registration of Complex Deformations Induced by Interscan Radio-Ulnar Rotations
Ruurd Kuiper, Marijn van Stralen, Frank Zijlstra, Harrie Weinans, Kasper Roth, Joost Colaris, Ralph Sakkers, Peter Seevinck
Abstract: Purpose: The nature of the radio-ulnar joint introduces large nonlinear deformation fields caused by radio-ulnar rotation and elbow extension-flexion motion. The purpose of this work is to register CT to MR images of the forearm region, subjected to these large interscan deformations. We propose a stepwise approach, by first using a rigid body registration and subsequently applying an interpolation step for the soft tissue registration. The registered images can then be used to assist orthopaedic surgeons in pre-operative planning for radio-ulnar osteotomies or to train machine learning techniques that require paired data, such as methods performing automatic registration or to generate synthetic CT contrast images from MR images. Methods: MRI and CT scans were obtained in 15 patients suffering from both-bone forearm fractures. Dixon water-fat reconstruction was used to reconstruct water, fat and in-phase images. A two-step workflow was designed consisting of: 1) deformable BSpline registrations, initialized using rigid body transformations for bone tissue, and 2) a dual quaternion based interpolation scheme for soft tissue. Rigid body transformations were calculated using an Iterative Closest Point (ICP) algorithm applied to segmentations of the humerus, radius and ulna. Results of this workflow were compared to a traditional workflow consisting of rigid and deformable BSpline registration peformed with the widely used software package elastix. The registrations were evaluated quantitatively by segmenting water, fat and bone tissue on both CT and Dixon-reconstructed MR images in order to calculate Dice similarity coefficient. Results: Preliminary results using the proposed workflow showed a Dice coefficient of 0.79, 0.68 and 0.79 for the water, fat and bone tissue respectively, averaging 0.75 over all tissue. For comparison, Dice coefficients using the traditional workflow were 0.74, 0.68 and 0.42, averaging 0.62. Conclusion: The preliminary results showed an increase in Dice coefficient when using the proposed method. Due to the lack of a gold standard for the segmentation of the CT and MR images the results could only be interpreted relative to each other. Qualitative inspection of the results of the proposed workflow indicate regions with considerable registration errors at locations that are distant from the bone. Registration errors also occur close to the edge of the image, caused by a difference in field of view between the CT and MR images. However, tissue close to the bone is generally well registered.