Home Realtime assessment of foot orientation by Accelerometers and Gyroscopes
Article Open Access

Realtime assessment of foot orientation by Accelerometers and Gyroscopes

  • Thomas Seel EMAIL logo , David Graurock and Thomas Schauer
Published/Copyright: September 12, 2015
Download Article (PDF)
Become an author with De Gruyter Brill
Author Information Explore this Subject
Current Directions in Biomedical Engineering
From the journal Current Directions in Biomedical Engineering Volume 1 Issue 1

Abstract

Foot orientation can be assessed in realtime by means of a foot-mounted inertial sensor. We consider a method that uses only accelerometer and gyroscope readings to calculate the foot pitch and roll angle, i.e. the foot orientation angle in the sagittal and frontal plane, respectively. Since magnetometers are avoided completely, the method can be used indoors as well as in the proximity of ferromagnetic material and magnetic disturbances. Furthermore, we allow for almost arbitrary mounting orientation in the sense that we only assume one of the local IMU coordinate axes to lie in the sagittal plane of the foot. The method is validated with respect to a conventional optical motion capture system in trials with transfemoral amputees walking with shoes and healthy subjects walking barefoot, both at different velocities. Root mean square deviations of less than 4° are found in all scenarios, while values near 2° are found in slow shoe walking. This demonstrates that the proposed method is suitable for realtime application such as the control of FES-based gait neuroprostheses and active orthoses.

Keywords: Biomedical Engineering; Rehabilitation Engineering; Inertial Measurement Unit; Accelerometers, Gyroscopes; Realtime Motion Assessment; Foot Orientation

1 Introduction

Foot motion assessment plays a central role in diagnosis and treatment of walking disabilities. Functional electrical stimulation (FES) and active orthoses represent effective tools for online gait support. Both technologies rely on realtime foot motion assessment. The conventional method for motion assessment is optical motion capture (OMC), which has the decisive disadvantage that it is not suitable for realtime applications. Furthermore, it is an expensive technology and strictly limiting in space and time, as it restricts the analysis to a laboratory environment. Ambulatory realtime motion capture can be performed by the use of inertial measurement units (IMU), which typically comprise accelerometers, gyroscopes, and magnetometers. They represent an inexpensive and easy-to-handle technology without any of the mentioned limitations of OMC. There are a number of standard methods that estimate the orientation of the foot based on measurement data of an IMU attached to the foot, see for example [1, 3, 7]. Since, in indoor environments, the magnetic field is often heavily disturbed and far from homogeneous, we consider an IMU-based method that completely avoids to use magnetometer readings to calculate pitch and roll angles. Furthermore, we allow for almost arbitrary mounting orientation in the sense that we only assume one of the local IMU coordinate axes to lie in the sagittal plane of the foot.

In this contribution, we focus on the question how accurate the obtained orientation measurements are with respect to the conventional OMC method under different walking conditions. Unlike most IMU validation studies, e.g. [1], we place the optical markers on anatomical landmarks instead of attaching them to the IMUs. Thereby, we compare the entire gait analysis methods instead of comparing only the measurement systems. In the following, we briefly explain the method, before we validate it in trials with transfemoral amputees walking with shoes and in trials with healthy subjects walking barefoot.

2 Methods

The measured angular rates and accelerations of the paretic foot are used to detect the gait eventstoe-off and initial contact, which mark the beginning and the end of the swing phase, as well as full contact and heel-rise, which mark the beginning and the end of thefoot-flat phase. In the following,tto,tic, tfc and thr will denote the according time instants of the considered step, respectively. As depicted in Figure 1, the period of time between heel-rise and toe-off is referred to aspre-swing, and the phase between initial contact and full contact is calledloading response. This is in accordance with standard literature, see e.g. [2]. The employed gait phase detection algorithm is described in [5] and, for the sake of brevity, is not further discussed here. Instead, we assume that we have realtime information of the current gait phase and consider the task of foot orientation angle measurement in the following.

Figure 1 Employed finite state automaton model (phases and transitions) of the gait cycle of one side. During foot-flat phase, the foot rests on the ground, while it has no ground contact during swing phase.
Figure 1

Employed finite state automaton model (phases and transitions) of the gait cycle of one side. During foot-flat phase, the foot rests on the ground, while it has no ground contact during swing phase.

Figure 2 The angle α that the foot’s posterior-anterior axisxfoot and its projection into the horizontal plane (dotted lines) confine is a proper measure of foot pitch, while foot roll can be quantified analogously using the foot’s mediolateral axis yfoot. The local coordinate axes of the IMU are not parallel to any anatomical axis, but the local x-axis lies in the sagittal plane of the foot.
Figure 2

The angle α that the foot’s posterior-anterior axisxfoot and its projection into the horizontal plane (dotted lines) confine is a proper measure of foot pitch, while foot roll can be quantified analogously using the foot’s mediolateral axis yfoot. The local coordinate axes of the IMU are not parallel to any anatomical axis, but the local x-axis lies in the sagittal plane of the foot.

The foot’s pitch angle α and roll angle β are defined in Figure 2. The local(By ”local” we denote the coordinates in the moving sensor coordinate system.) coordinates of xfoot,yfoot ∈ ℝ3×1 are unknown because the sensor cannot be attached such that the local coordinate axes coincide with the anatomical axes of the foot, as Figure 3 illustrates. However, it is possible to assure that the local axis xlocal = (1, 0, 0)T of the IMU lies in the sagittal plane of the foot. We therefore assume that this is assured and determine the local coordinates of the foot’s posterior-anterior and mediolateral axis as follows: During every foot-flat phase, the local accelerometer readings a(t) are integrated over time, and the resulting vector is normalized to unit length:

(1)z^ff:=∑t∈foot-flata(t), zff:=z^ff/||z^ff||2,

where ‖·‖2 denotes the Euclidean norm. Since gravitational acceleration dominates when the foot is (almost) at rest, zff is (almost) vertical. Therefore, we calculate the local coordinates of the mediolateral axis yfoot as follows:

(2)y^foot:=zff×χlocal,yfoot:=+y^foot/||y^foot||2for a left foot,
(3)and yfoot:=−y^foot/||y^foot||2for a right foot.

Likewise, we calculate the local coordinates of the posterior-anterior axis xfoot as follows:

(4)x^foot:=zff×xlocal×zff,x^foot:=x^foot/||x^foot||2.

Please note that, by construction, xfoot and yfoot are horizontal during stance and their local coordinates do not change with time, since the sensor moves along with the foot, see Figure 3 for illustration.

For each step, a strap-down integration [4] of the angular rates is started at heel-risethr that yields the rotation matrix Rff(t). This matrix transforms the local measurement vectors a(t) and g(t) of any time instantt between two foot-flat phases to the local coordinate system of the preceding foot-flat phase, which we refer to as the reference coordinate system of that step. By transforming xfoot to the reference coordinate system, in which the vertical axis zff is known, we calculate the time-dependent foot orientation angle in pitch direction:

(5)α(t):=π2−∢(zff,Rff(t)xfoot),
(6)=arcsin(zffTRff(t)xfoot) ∈[−π2,+π2].

Please note that the pitch angle is positive when the toes are above the heel and negative when vice versa. Likewise, we calculate the time-dependent foot orientation angle β in roll direction:

(7)β(t):=π2−∢(zff,Rff(t)yfoot),
(8)=arcsin(zffTRff(t)yfoot) ∈[−π2,+π2].

Due to the side-dependent axis definition (3), the roll angle β is always positive when the foot’s outer edge is above the inner edge, both for a right and a left foot.

However, it is important to note that orientation strap-down integration is always subject to drift, since, even with proper calibration, the gyroscopes have non-zero bias. Therefore, α(t) and β(t) also drift(For example, with the employed sensor hardware, we found that, at the end of a step, α(tfc) is typically in the range of 2°.) between each two foot-flat phases. At every full contact tfc, however, we can remove the drift from α(t), β(t) on the time interval t ∈ [thr,tfc] by assuming that neither the gyroscope bias nor the slope of the ground changed significantly during the swing phase:

(9)α˜(t):=α(t)−t−thrtfc−thr(α(tfc)−α(thr)),
(10)β˜(t):=β(t)−t−thrtfc−thr(β(tfc)−β(thr)).

In the following, we validate these IMU-based angles with respect to optical motion capture. Since the standard setup with only one optical marker on the forefoot and one on the ankle does not permit the calculation of roll orientation angles, we restrict the validation to foot pitch angles.

3 Experimental procedure and results of the validation

Figure 3 Experimental Setup with IMUs and optical markers attached to shoes and bare feet. Note that the data of the depicted IMUs on the shanks (upper photos) wasnot used in this study.
Figure 3

Experimental Setup with IMUs and optical markers attached to shoes and bare feet. Note that the data of the depicted IMUs on the shanks (upper photos) wasnot used in this study.

For evaluation of the proposed methods, the recorded data of two different experiments is processed. In both trial series, a wireless IMU was attached dorsally on the instep of each foot and optical markers of a visual motion capture system were attached to the lateral malleolus and the head of the fifth metatarsal (see Figure 3). In the first experiment, two healthy subjects walked barefoot at slow and fast pace, whereas in the second one, two transfemoral amputees walked with a leg prosthesis at self-assessed speed while wearing shoes on both the prosthetic and the contralateral foot. At least six trials were completed by each subject, for each of which the foot pitch angle is computed according to (6). For the sake of comparison, we also calculate the foot pitch from the three-dimensional optical marker positions.

Table 1

Deviations between inertial and optical measurements. Columns show the walking velocity (vel.), the average root mean square error (RMSE) with its standard deviation with and without drift correction. Averages are taken over several steps. The rows refer to different subjects and their different footwear – barefoot (baref.), shoe and shoe on the prosthetic side (prosth.).

walking vel.[ms]RMSE α [°] drift not removedRMSEα˜[°]drift removed
Subj.1-shoe0.812.66 ± 0.732.24 ± 0.41
Subj.1-prosth.0.811.40 ± 0.211.20 ± 0.26
Subj.2-shoe1.425.78 ± 1.493.97 ± 0.51
Subj.2-prosth.1.423.97 ± 1.312.93 ± 0.75
Subj.3-baref.1.623.61 ± 0.873.63 ± 0.83
Subj.3-baref.0.853.14 ± 0.393.09 ± 0.36
Subj.4-baref.1.523.90 ± 0.913.79 ± 0.73
Subj.4-baref.0.783.37 ± 0.373.41 ± 0.31

The root mean square error (RMSE) with and without drift correction is determined for each trial of each subject. We then calculate the average and standard deviations over all trials for each foot. Table 1 shows the results, as well as corresponding walking velocities. In Figure 4a, the pitch angles of Subject 2 (cf. Table 1) are plotted over one step for both the prosthetic and the contralateral side. Furthermore, pitch angles for different walking velocities of the barefoot walking Subject 3 are presented in Figure 4b.

4 Discussion

We first analyze the influence of the footwear. It is evident that deviations between the results of both measurement systems are larger in barefoot trials than in trials with shoes. This is most likely due to slight deformations of the foot during stance-phase and push-off, which lead to relative motion of the IMU and the optical markers with respect to each other. Since the IMU was attached directly to the skin in the barefoot trials, the effect is stronger therein than in the shoe-trials, in which the shoe dampens this effect. Likewise, the data in Table 1 demonstrates that the deviations are slightly smaller on the prosthetic side, which is more rigid and allows for less relative motion of the markers and IMU with respect to each other.

If we furthermore compare RMSEs between the slow and fast trials of Subject 3 and 4, it is noticeable that the deviations are significantly smaller in slower walking. The same observation is also made when comparing (the prosthetic or contralateral foot of) Subject 1 and Subject 2, the latter of which walked at a much faster pace.

Figure 4 IMU-based foot pitch (solid) and reference angles (dashed) from an optical motion capture system. (a) for a prosthetic and a contralateral foot and in (b) for slow and fast walking. Plus markers indicate gait phase transitions (see Figure 1).
Figure 4

IMU-based foot pitch (solid) and reference angles (dashed) from an optical motion capture system. (a) for a prosthetic and a contralateral foot and in (b) for slow and fast walking. Plus markers indicate gait phase transitions (see Figure 1).

By applying the periodic online drift correction proposed in (9), the RMSE was reduced by more than 15% in the shoe-walkers. In the barefoot walkers, this correction had no significant effect.

5 Conclusion

A method for realtime foot pitch and roll angle estimation was considered that avoids magnetometers and copes with almost arbitrary mounting orientation. It was validated with respect to a conventional optical motion capture method in subjects with different footwear. Results indicate that deformations of the foot and shoe during foot-flat and push-off lead to relative motion of the optical markers and the IMUs with respect to each other, which are strongest in barefoot walking and weakest in prosthetic feet. Nevertheless, the deviation between inertial and optical measurements are in the few-degrees range under all tested conditions. For slow walking with shoes, accuracies below 2° were obtained.

With respect to the intended application in FES-based gait neuroprostheses and active orthoses, we conclude that the obtained deviations are small enough to facilitate precise feedback control of the foot motion.

Acknowledgment:

We would like to express our deep gratitude to Julius Thiele from TU Berlin as well as to Noelia Chia Bejarano and Simona Ferrante from Politecnico di Milano for providing the datasets that were analyzed in this study. Furthermore, we thank Sebastian Scheel and Dirk Reinhardt for their skillful support in automatic data evaluation.

Funding: Being conducted in the research project BeMobil, this work is funded by the German Federal Ministry of Research and Education (FKZ 16SV7069K).

Author’s Statement

  1. Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use has been complied with all the relevant national regulations, institutional policies and in accordance the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

References

[1] van den Noort JC, Ferrari A, Cutti AG, Becher JG, Harlaar J. Gait analysis in children with cerebral palsy via inertial and magnetic sensors. Med Biol Eng Comput 2013; 51:377–386.10.1007/s11517-012-1006-5Search in Google Scholar

[2] Perry J, Burnfield JM. Gait Analysis: Normal and Pathological Function. SLACK Incorporated 201010.1097/01241398-199211000-00023Search in Google Scholar

[3] Sabatini AM, Martelloni C, Scapellato S, Cavallo F. Assessment of walking features from foot inertial sensing. Biomedical Engineering 2005; 52(3): 486-49410.1109/TBME.2004.840727Search in Google Scholar

[4] Savage PG. Strapdown Inertial Navigation Integration Algorithm Design – Part 1: Attitude Algorithms. Journal of guidance, control, and dynamics 1998; 21(1):19–28.10.2514/2.4228Search in Google Scholar

[5] Seel T, Landgraf L, Schauer T. Online Gait Phase Detection with Automatic Adaption to Gait Velocity Changes Using Accelerometers and Gyroscopes. Biomedical Engineering / Biomedizinische Technik 2014; 59(S1):795–798.Search in Google Scholar

[6] Seel T, Raisch J, Schauer T. IMU-based joint angle measurement for gait analysis. Sensors 2014; 14(4):6891-909.10.3390/s140406891Search in Google Scholar

[7] Veltink PH, Slycke P, Hemssems J, Buschman R, Bulstra G, Her-mens H. Three dimensional intertial sensing of foot movements for automatic tuning of a two-channel implantable drop-foot stimulator. Medical Engineering & Physics 2003; 25(1): 21-28.10.1016/S1350-4533(02)00041-3Search in Google Scholar

Published Online: 2015-9-12
Published in Print: 2015-9-1

© 2015 by Walter de Gruyter GmbH, Berlin/Boston

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Articles in the same Issue

  1. Research Article
  2. Development and characterization of superparamagnetic coatings
  3. Research Article
  4. The development of an experimental setup to measure acousto-electric interaction signal
  5. Research Article
  6. Stability analysis of ferrofluids
  7. Research Article
  8. Investigation of endothelial growth using a sensors-integrated microfluidic system to simulate physiological barriers
  9. Research Article
  10. Energy harvesting for active implants: powering a ruminal pH-monitoring system
  11. Research Article
  12. New type of fluxgate magnetometer for the heart’s magnetic fields detection
  13. Research Article
  14. Field mapping of ballistic pressure pulse sources
  15. Research Article
  16. Development of a new homecare sleep monitor using body sounds and motion tracking
  17. Research Article
  18. Noise properties of textile, capacitive EEG electrodes
  19. Research Article
  20. Detecting phase singularities and rotor center trajectories based on the Hilbert transform of intraatrial electrograms in an atrial voxel model
  21. Research Article
  22. Spike sorting: the overlapping spikes challenge
  23. Research Article
  24. Separating the effect of respiration from the heart rate variability for cases of constant harmonic breathing
  25. Research Article
  26. Locating regions of arrhythmogenic substrate by analyzing the duration of triggered atrial activities
  27. Research Article
  28. Combining different ECG derived respiration tracking methods to create an optimal reconstruction of the breathing pattern
  29. Research Article
  30. Atrial and ventricular signal averaging electrocardiography in pacemaker and cardiac resynchronization therapy
  31. Research Article
  32. Estimation of a respiratory signal from a single-lead ECG using the 4th order central moments
  33. Research Article
  34. Compressed sensing of multi-lead ECG signals by compressive multiplexing
  35. Research Article
  36. Heart rate monitoring in ultra-high-field MRI using frequency information obtained from video signals of the human skin compared to electrocardiography and pulse oximetry
  37. Research Article
  38. Synchronization in wireless biomedical-sensor networks with Bluetooth Low Energy
  39. Research Article
  40. Automated classification of stages of anaesthesia by populations of evolutionary optimized fuzzy rules
  41. Research Article
  42. Effects of sampling rate on automated fatigue recognition in surface EMG signals
  43. Research Article
  44. Closed-loop transcranial alternating current stimulation of slow oscillations
  45. Research Article
  46. Cardiac index in atrio- and interventricular delay optimized cardiac resynchronization therapy and cardiac contractility modulation
  47. Research Article
  48. The role of expert evaluation for microsleep detection
  49. Research Article
  50. The impact of baseline wander removal techniques on the ST segment in simulated ischemic 12-lead ECGs
  51. Research Article
  52. Metal artifact reduction by projection replacements and non-local prior image integration
  53. Research Article
  54. A novel coaxial nozzle for in-process adjustment of electrospun scaffolds’ fiber diameter
  55. Research Article
  56. Processing of membranes for oxygenation using the Bellhouse-effect
  57. Research Article
  58. Inkjet printing of viable human dental follicle stem cells
  59. Research Article
  60. The use of an icebindingprotein out of the snowflea Hypogastrura harveyi as a cryoprotectant in the cryopreservation of mesenchymal stem cells
  61. Research Article
  62. New NIR spectroscopy based method to determine ischemia in vivo in liver – a first study on rats
  63. Research Article
  64. QRS and QT ventricular conduction times and permanent pacemaker therapy after transcatheter aortic valve implantation
  65. Research Article
  66. Adopting oculopressure tonometry as a transient in vivo rabbit glaucoma model
  67. Research Article
  68. Next-generation vision testing: the quick CSF
  69. Research Article
  70. Improving tactile sensation in laparoscopic surgery by overcoming size restrictions
  71. Research Article
  72. Design and control of a 3-DOF hydraulic driven surgical instrument
  73. Research Article
  74. Evaluation of endourological tools to improve the diagnosis and therapy of ureteral tumors – from model development to clinical application
  75. Research Article
  76. Frequency based assessment of surgical activities
  77. Research Article
  78. “Hands free for intervention”, a new approach for transoral endoscopic surgery
  79. Research Article
  80. Pseudo-haptic feedback in medical teleoperation
  81. Research Article
  82. Feasibility of interactive gesture control of a robotic microscope
  83. Research Article
  84. Towards structuring contextual information for workflow-driven surgical assistance functionalities
  85. Research Article
  86. Towards a framework for standardized semantic workflow modeling and management in the surgical domain
  87. Research Article
  88. Closed-loop approach for situation awareness of medical devices and operating room infrastructure
  89. Research Article
  90. Kinect based physiotherapy system for home use
  91. Research Article
  92. Evaluating the microsoft kinect skeleton joint tracking as a tool for home-based physiotherapy
  93. Research Article
  94. Integrating multimodal information for intraoperative assistance in neurosurgery
  95. Research Article
  96. Respiratory motion tracking using Microsoft’s Kinect v2 camera
  97. Research Article
  98. Using smart glasses for ultrasound diagnostics
  99. Research Article
  100. Measurement of needle susceptibility artifacts in magnetic resonance images
  101. Research Article
  102. Dimensionality reduction of medical image descriptors for multimodal image registration
  103. Research Article
  104. Experimental evaluation of different weighting schemes in magnetic particle imaging reconstruction
  105. Research Article
  106. Evaluation of CT capability for the detection of thin bone structures
  107. Research Article
  108. Towards contactless optical coherence elastography with acoustic tissue excitation
  109. Research Article
  110. Development and implementation of algorithms for automatic and robust measurement of the 2D:4D digit ratio using image data
  111. Research Article
  112. Automated high-throughput analysis of B cell spreading on immobilized antibodies with whole slide imaging
  113. Research Article
  114. Tissue segmentation from head MRI: a ground truth validation for feature-enhanced tracking
  115. Research Article
  116. Video tracking of swimming rodents on a reflective water surface
  117. Research Article
  118. MR imaging of model drug distribution in simulated vitreous
  119. Research Article
  120. Studying the extracellular contribution to the double wave vector diffusion-weighted signal
  121. Research Article
  122. Artifacts in field free line magnetic particle imaging in the presence of inhomogeneous and nonlinear magnetic fields
  123. Research Article
  124. Introducing a frequency-tunable magnetic particle spectrometer
  125. Research Article
  126. Imaging of aortic valve dynamics in 4D OCT
  127. Research Article
  128. Intravascular optical coherence tomography (OCT) as an additional tool for the assessment of stent structures
  129. Research Article
  130. Simple concept for a wide-field lensless digital holographic microscope using a laser diode
  131. Research Article
  132. Intraoperative identification of somato-sensory brain areas using optical imaging and standard RGB camera equipment – a feasibility study
  133. Research Article
  134. Respiratory surface motion measurement by Microsoft Kinect
  135. Research Article
  136. Improving image quality in EIT imaging by measurement of thorax excursion
  137. Research Article
  138. A clustering based dual model framework for EIT imaging: first experimental results
  139. Research Article
  140. Three-dimensional anisotropic regularization for limited angle tomography
  141. Research Article
  142. GPU-based real-time generation of large ultrasound volumes from freehand 3D sweeps
  143. Research Article
  144. Experimental computer tomograph
  145. Research Article
  146. US-tracked steered FUS in a respiratory ex vivo ovine liver phantom
  147. Research Article
  148. Contribution of brownian rotation and particle assembly polarisation to the particle response in magnetic particle spectrometry
  149. Research Article
  150. Preliminary investigations of magnetic modulated nanoparticles for microwave breast cancer detection
  151. Research Article
  152. Construction of a device for magnetic separation of superparamagnetic iron oxide nanoparticles
  153. Research Article
  154. An IHE-conform telecooperation platform supporting the treatment of dementia patients
  155. Research Article
  156. Automated respiratory therapy system based on the ARDSNet protocol with systemic perfusion control
  157. Research Article
  158. Identification of surgical instruments using UHF-RFID technology
  159. Research Article
  160. A generic concept for the development of model-guided clinical decision support systems
  161. Research Article
  162. Evaluation of local alterations in femoral bone mineral density measured via quantitative CT
  163. Research Article
  164. Creating 3D gelatin phantoms for experimental evaluation in biomedicine
  165. Research Article
  166. Influence of short-term fixation with mixed formalin or ethanol solution on the mechanical properties of human cortical bone
  167. Research Article
  168. Analysis of the release kinetics of surface-bound proteins via laser-induced fluorescence
  169. Research Article
  170. Tomographic particle image velocimetry of a water-jet for low volume harvesting of fat tissue for regenerative medicine
  171. Research Article
  172. Wireless medical sensors – context, robustness and safety
  173. Research Article
  174. Sequences for real-time magnetic particle imaging
  175. Research Article
  176. Speckle-based off-axis holographic detection for non-contact photoacoustic tomography
  177. Research Article
  178. A machine learning approach for planning valve-sparing aortic root reconstruction
  179. Research Article
  180. An in-ear pulse wave velocity measurement system using heart sounds as time reference
  181. Research Article
  182. Measuring different oxygenation levels in a blood perfusion model simulating the human head using NIRS
  183. Research Article
  184. Multisegmental fusion of the lumbar spine a curse or a blessing?
  185. Research Article
  186. Numerical analysis of the biomechanical complications accompanying the total hip replacement with NANOS-Prosthetic: bone remodelling and prosthesis migration
  187. Research Article
  188. A muscle model for hybrid muscle activation
  189. Research Article
  190. Mathematical, numerical and in-vitro investigation of cooling performance of an intra-carotid catheter for selective brain hypothermia
  191. Research Article
  192. An ideally parameterized unscented Kalman filter for the inverse problem of electrocardiography
  193. Research Article
  194. Interactive visualization of cardiac anatomy and atrial excitation for medical diagnosis and research
  195. Research Article
  196. Virtualizing clinical cases of atrial flutter in a fast marching simulation including conduction velocity and ablation scars
  197. Research Article
  198. Mesh structure-independent modeling of patient-specific atrial fiber orientation
  199. Research Article
  200. Accelerating mono-domain cardiac electrophysiology simulations using OpenCL
  201. Research Article
  202. Understanding the cellular mode of action of vernakalant using a computational model: answers and new questions
  203. Research Article
  204. A java based simulator with user interface to simulate ventilated patients
  205. Research Article
  206. Evaluation of an algorithm to choose between competing models of respiratory mechanics
  207. Research Article
  208. Numerical simulation of low-pulsation gerotor pumps for use in the pharmaceutical industry and in biomedicine
  209. Research Article
  210. Numerical and experimental flow analysis in centifluidic systems for rapid allergy screening tests
  211. Research Article
  212. Biomechanical parameter determination of scaffold-free cartilage constructs (SFCCs) with the hyperelastic material models Yeoh, Ogden and Demiray
  213. Research Article
  214. FPGA controlled artificial vascular system
  215. Research Article
  216. Simulation based investigation of source-detector configurations for non-invasive fetal pulse oximetry
  217. Research Article
  218. Test setup for characterizing the efficacy of embolic protection devices
  219. Research Article
  220. Impact of electrode geometry on force generation during functional electrical stimulation
  221. Research Article
  222. 3D-based visual physical activity assessment of children
  223. Research Article
  224. Realtime assessment of foot orientation by Accelerometers and Gyroscopes
  225. Research Article
  226. Image based reconstruction for cystoscopy
  227. Research Article
  228. Image guided surgery innovation with graduate students - a new lecture format
  229. Research Article
  230. Multichannel FES parameterization for controlling foot motion in paretic gait
  231. Research Article
  232. Smartphone supported upper limb prosthesis
  233. Research Article
  234. Use of quantitative tremor evaluation to enhance target selection during deep brain stimulation surgery for essential tremor
  235. Research Article
  236. Evaluation of adhesion promoters for Parylene C on gold metallization
  237. Research Article
  238. The influence of metallic ions from CoCr28Mo6 on the osteogenic differentiation and cytokine release of human osteoblasts
  239. Research Article
  240. Increasing the visibility of thin NITINOL vascular implants
  241. Research Article
  242. Possible reasons for early artificial bone failure in biomechanical tests of ankle arthrodesis systems
  243. Research Article
  244. Development of a bending test procedure for the characterization of flexible ECoG electrode arrays
  245. Research Article
  246. Tubular manipulators: a new concept for intracochlear positioning of an auditory prosthesis
  247. Research Article
  248. Investigation of the dynamic diameter deformation of vascular stents during fatigue testing with radial loading
  249. Research Article
  250. Electrospun vascular grafts with anti-kinking properties
  251. Research Article
  252. Integration of temperature sensors in polyimide-based thin-film electrode arrays
  253. Research Article
  254. Use cases and usability challenges for head-mounted displays in healthcare
  255. Research Article
  256. Device- and service profiles for integrated or systems based on open standards
  257. Research Article
  258. Risk management for medical devices in research projects
  259. Research Article
  260. Simulation of varying femoral attachment sites of medial patellofemoral ligament using a musculoskeletal multi-body model
  261. Research Article
  262. Does enhancing consciousness for strategic planning processes support the effectiveness of problem-based learning concepts in biomedical education?
  263. Research Article
  264. SPIO processing in macrophages for MPI: The breast cancer MPI-SNLB-concept
  265. Research Article
  266. Numerical simulations of airflow in the human pharynx of OSAHS patients
https://doi.org/10.1515/cdbme-2015-0112
Keywords for this article
Biomedical Engineering; Rehabilitation Engineering; Inertial Measurement Unit; Accelerometers, Gyroscopes; Realtime Motion Assessment; Foot Orientation
Creative Commons
BY-NC-ND 3.0

Articles in the same Issue

  1. Research Article
  2. Development and characterization of superparamagnetic coatings
  3. Research Article
  4. The development of an experimental setup to measure acousto-electric interaction signal
  5. Research Article
  6. Stability analysis of ferrofluids
  7. Research Article
  8. Investigation of endothelial growth using a sensors-integrated microfluidic system to simulate physiological barriers
  9. Research Article
  10. Energy harvesting for active implants: powering a ruminal pH-monitoring system
  11. Research Article
  12. New type of fluxgate magnetometer for the heart’s magnetic fields detection
  13. Research Article
  14. Field mapping of ballistic pressure pulse sources
  15. Research Article
  16. Development of a new homecare sleep monitor using body sounds and motion tracking
  17. Research Article
  18. Noise properties of textile, capacitive EEG electrodes
  19. Research Article
  20. Detecting phase singularities and rotor center trajectories based on the Hilbert transform of intraatrial electrograms in an atrial voxel model
  21. Research Article
  22. Spike sorting: the overlapping spikes challenge
  23. Research Article
  24. Separating the effect of respiration from the heart rate variability for cases of constant harmonic breathing
  25. Research Article
  26. Locating regions of arrhythmogenic substrate by analyzing the duration of triggered atrial activities
  27. Research Article
  28. Combining different ECG derived respiration tracking methods to create an optimal reconstruction of the breathing pattern
  29. Research Article
  30. Atrial and ventricular signal averaging electrocardiography in pacemaker and cardiac resynchronization therapy
  31. Research Article
  32. Estimation of a respiratory signal from a single-lead ECG using the 4th order central moments
  33. Research Article
  34. Compressed sensing of multi-lead ECG signals by compressive multiplexing
  35. Research Article
  36. Heart rate monitoring in ultra-high-field MRI using frequency information obtained from video signals of the human skin compared to electrocardiography and pulse oximetry
  37. Research Article
  38. Synchronization in wireless biomedical-sensor networks with Bluetooth Low Energy
  39. Research Article
  40. Automated classification of stages of anaesthesia by populations of evolutionary optimized fuzzy rules
  41. Research Article
  42. Effects of sampling rate on automated fatigue recognition in surface EMG signals
  43. Research Article
  44. Closed-loop transcranial alternating current stimulation of slow oscillations
  45. Research Article
  46. Cardiac index in atrio- and interventricular delay optimized cardiac resynchronization therapy and cardiac contractility modulation
  47. Research Article
  48. The role of expert evaluation for microsleep detection
  49. Research Article
  50. The impact of baseline wander removal techniques on the ST segment in simulated ischemic 12-lead ECGs
  51. Research Article
  52. Metal artifact reduction by projection replacements and non-local prior image integration
  53. Research Article
  54. A novel coaxial nozzle for in-process adjustment of electrospun scaffolds’ fiber diameter
  55. Research Article
  56. Processing of membranes for oxygenation using the Bellhouse-effect
  57. Research Article
  58. Inkjet printing of viable human dental follicle stem cells
  59. Research Article
  60. The use of an icebindingprotein out of the snowflea Hypogastrura harveyi as a cryoprotectant in the cryopreservation of mesenchymal stem cells
  61. Research Article
  62. New NIR spectroscopy based method to determine ischemia in vivo in liver – a first study on rats
  63. Research Article
  64. QRS and QT ventricular conduction times and permanent pacemaker therapy after transcatheter aortic valve implantation
  65. Research Article
  66. Adopting oculopressure tonometry as a transient in vivo rabbit glaucoma model
  67. Research Article
  68. Next-generation vision testing: the quick CSF
  69. Research Article
  70. Improving tactile sensation in laparoscopic surgery by overcoming size restrictions
  71. Research Article
  72. Design and control of a 3-DOF hydraulic driven surgical instrument
  73. Research Article
  74. Evaluation of endourological tools to improve the diagnosis and therapy of ureteral tumors – from model development to clinical application
  75. Research Article
  76. Frequency based assessment of surgical activities
  77. Research Article
  78. “Hands free for intervention”, a new approach for transoral endoscopic surgery
  79. Research Article
  80. Pseudo-haptic feedback in medical teleoperation
  81. Research Article
  82. Feasibility of interactive gesture control of a robotic microscope
  83. Research Article
  84. Towards structuring contextual information for workflow-driven surgical assistance functionalities
  85. Research Article
  86. Towards a framework for standardized semantic workflow modeling and management in the surgical domain
  87. Research Article
  88. Closed-loop approach for situation awareness of medical devices and operating room infrastructure
  89. Research Article
  90. Kinect based physiotherapy system for home use
  91. Research Article
  92. Evaluating the microsoft kinect skeleton joint tracking as a tool for home-based physiotherapy
  93. Research Article
  94. Integrating multimodal information for intraoperative assistance in neurosurgery
  95. Research Article
  96. Respiratory motion tracking using Microsoft’s Kinect v2 camera
  97. Research Article
  98. Using smart glasses for ultrasound diagnostics
  99. Research Article
  100. Measurement of needle susceptibility artifacts in magnetic resonance images
  101. Research Article
  102. Dimensionality reduction of medical image descriptors for multimodal image registration
  103. Research Article
  104. Experimental evaluation of different weighting schemes in magnetic particle imaging reconstruction
  105. Research Article
  106. Evaluation of CT capability for the detection of thin bone structures
  107. Research Article
  108. Towards contactless optical coherence elastography with acoustic tissue excitation
  109. Research Article
  110. Development and implementation of algorithms for automatic and robust measurement of the 2D:4D digit ratio using image data
  111. Research Article
  112. Automated high-throughput analysis of B cell spreading on immobilized antibodies with whole slide imaging
  113. Research Article
  114. Tissue segmentation from head MRI: a ground truth validation for feature-enhanced tracking
  115. Research Article
  116. Video tracking of swimming rodents on a reflective water surface
  117. Research Article
  118. MR imaging of model drug distribution in simulated vitreous
  119. Research Article
  120. Studying the extracellular contribution to the double wave vector diffusion-weighted signal
  121. Research Article
  122. Artifacts in field free line magnetic particle imaging in the presence of inhomogeneous and nonlinear magnetic fields
  123. Research Article
  124. Introducing a frequency-tunable magnetic particle spectrometer
  125. Research Article
  126. Imaging of aortic valve dynamics in 4D OCT
  127. Research Article
  128. Intravascular optical coherence tomography (OCT) as an additional tool for the assessment of stent structures
  129. Research Article
  130. Simple concept for a wide-field lensless digital holographic microscope using a laser diode
  131. Research Article
  132. Intraoperative identification of somato-sensory brain areas using optical imaging and standard RGB camera equipment – a feasibility study
  133. Research Article
  134. Respiratory surface motion measurement by Microsoft Kinect
  135. Research Article
  136. Improving image quality in EIT imaging by measurement of thorax excursion
  137. Research Article
  138. A clustering based dual model framework for EIT imaging: first experimental results
  139. Research Article
  140. Three-dimensional anisotropic regularization for limited angle tomography
  141. Research Article
  142. GPU-based real-time generation of large ultrasound volumes from freehand 3D sweeps
  143. Research Article
  144. Experimental computer tomograph
  145. Research Article
  146. US-tracked steered FUS in a respiratory ex vivo ovine liver phantom
  147. Research Article
  148. Contribution of brownian rotation and particle assembly polarisation to the particle response in magnetic particle spectrometry
  149. Research Article
  150. Preliminary investigations of magnetic modulated nanoparticles for microwave breast cancer detection
  151. Research Article
  152. Construction of a device for magnetic separation of superparamagnetic iron oxide nanoparticles
  153. Research Article
  154. An IHE-conform telecooperation platform supporting the treatment of dementia patients
  155. Research Article
  156. Automated respiratory therapy system based on the ARDSNet protocol with systemic perfusion control
  157. Research Article
  158. Identification of surgical instruments using UHF-RFID technology
  159. Research Article
  160. A generic concept for the development of model-guided clinical decision support systems
  161. Research Article
  162. Evaluation of local alterations in femoral bone mineral density measured via quantitative CT
  163. Research Article
  164. Creating 3D gelatin phantoms for experimental evaluation in biomedicine
  165. Research Article
  166. Influence of short-term fixation with mixed formalin or ethanol solution on the mechanical properties of human cortical bone
  167. Research Article
  168. Analysis of the release kinetics of surface-bound proteins via laser-induced fluorescence
  169. Research Article
  170. Tomographic particle image velocimetry of a water-jet for low volume harvesting of fat tissue for regenerative medicine
  171. Research Article
  172. Wireless medical sensors – context, robustness and safety
  173. Research Article
  174. Sequences for real-time magnetic particle imaging
  175. Research Article
  176. Speckle-based off-axis holographic detection for non-contact photoacoustic tomography
  177. Research Article
  178. A machine learning approach for planning valve-sparing aortic root reconstruction
  179. Research Article
  180. An in-ear pulse wave velocity measurement system using heart sounds as time reference
  181. Research Article
  182. Measuring different oxygenation levels in a blood perfusion model simulating the human head using NIRS
  183. Research Article
  184. Multisegmental fusion of the lumbar spine a curse or a blessing?
  185. Research Article
  186. Numerical analysis of the biomechanical complications accompanying the total hip replacement with NANOS-Prosthetic: bone remodelling and prosthesis migration
  187. Research Article
  188. A muscle model for hybrid muscle activation
  189. Research Article
  190. Mathematical, numerical and in-vitro investigation of cooling performance of an intra-carotid catheter for selective brain hypothermia
  191. Research Article
  192. An ideally parameterized unscented Kalman filter for the inverse problem of electrocardiography
  193. Research Article
  194. Interactive visualization of cardiac anatomy and atrial excitation for medical diagnosis and research
  195. Research Article
  196. Virtualizing clinical cases of atrial flutter in a fast marching simulation including conduction velocity and ablation scars
  197. Research Article
  198. Mesh structure-independent modeling of patient-specific atrial fiber orientation
  199. Research Article
  200. Accelerating mono-domain cardiac electrophysiology simulations using OpenCL
  201. Research Article
  202. Understanding the cellular mode of action of vernakalant using a computational model: answers and new questions
  203. Research Article
  204. A java based simulator with user interface to simulate ventilated patients
  205. Research Article
  206. Evaluation of an algorithm to choose between competing models of respiratory mechanics
  207. Research Article
  208. Numerical simulation of low-pulsation gerotor pumps for use in the pharmaceutical industry and in biomedicine
  209. Research Article
  210. Numerical and experimental flow analysis in centifluidic systems for rapid allergy screening tests
  211. Research Article
  212. Biomechanical parameter determination of scaffold-free cartilage constructs (SFCCs) with the hyperelastic material models Yeoh, Ogden and Demiray
  213. Research Article
  214. FPGA controlled artificial vascular system
  215. Research Article
  216. Simulation based investigation of source-detector configurations for non-invasive fetal pulse oximetry
  217. Research Article
  218. Test setup for characterizing the efficacy of embolic protection devices
  219. Research Article
  220. Impact of electrode geometry on force generation during functional electrical stimulation
  221. Research Article
  222. 3D-based visual physical activity assessment of children
  223. Research Article
  224. Realtime assessment of foot orientation by Accelerometers and Gyroscopes
  225. Research Article
  226. Image based reconstruction for cystoscopy
  227. Research Article
  228. Image guided surgery innovation with graduate students - a new lecture format
  229. Research Article
  230. Multichannel FES parameterization for controlling foot motion in paretic gait
  231. Research Article
  232. Smartphone supported upper limb prosthesis
  233. Research Article
  234. Use of quantitative tremor evaluation to enhance target selection during deep brain stimulation surgery for essential tremor
  235. Research Article
  236. Evaluation of adhesion promoters for Parylene C on gold metallization
  237. Research Article
  238. The influence of metallic ions from CoCr28Mo6 on the osteogenic differentiation and cytokine release of human osteoblasts
  239. Research Article
  240. Increasing the visibility of thin NITINOL vascular implants
  241. Research Article
  242. Possible reasons for early artificial bone failure in biomechanical tests of ankle arthrodesis systems
  243. Research Article
  244. Development of a bending test procedure for the characterization of flexible ECoG electrode arrays
  245. Research Article
  246. Tubular manipulators: a new concept for intracochlear positioning of an auditory prosthesis
  247. Research Article
  248. Investigation of the dynamic diameter deformation of vascular stents during fatigue testing with radial loading
  249. Research Article
  250. Electrospun vascular grafts with anti-kinking properties
  251. Research Article
  252. Integration of temperature sensors in polyimide-based thin-film electrode arrays
  253. Research Article
  254. Use cases and usability challenges for head-mounted displays in healthcare
  255. Research Article
  256. Device- and service profiles for integrated or systems based on open standards
  257. Research Article
  258. Risk management for medical devices in research projects
  259. Research Article
  260. Simulation of varying femoral attachment sites of medial patellofemoral ligament using a musculoskeletal multi-body model
  261. Research Article
  262. Does enhancing consciousness for strategic planning processes support the effectiveness of problem-based learning concepts in biomedical education?
  263. Research Article
  264. SPIO processing in macrophages for MPI: The breast cancer MPI-SNLB-concept
  265. Research Article
  266. Numerical simulations of airflow in the human pharynx of OSAHS patients
Sign up now to receive a 20% welcome discount
Institutional Access
How does access work?
Have an idea on how to improve our website?
Please write us.
© 2025 De Gruyter Brill
Downloaded on 7.9.2025 from https://www.degruyterbrill.com/document/doi/10.1515/cdbme-2015-0112/html
Scroll to top button