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Medical Engineering & Physics

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ISSN (Print) 1350-4533
Published by Elsevier

[2556 journals]

DXA predictions of human femoral mechanical properties depend on the load configuration
- Abstract: Publication date: Available online 16 May 2013
  Source:Medical Engineering & Physics
  Author(s): E. Dall’Ara , B. Luisier , R. Schmidt , M. Pretterklieber , F. Kainberger , P. Zysset , D. Pahr
  The aim of this study was to evaluate the ability of dual energy X-rays absorptiometry (DXA) areal bone mineral density (aBMD) measured in different regions of the proximal part of the human femur for predicting the mechanical properties of matched proximal femora tested in two different loading configurations. 36 pairs of fresh frozen femora were DXA scanned and tested until failure in two loading configurations: a fall on the side or a one-legged standing. The ability of the DXA output from four different regions of the proximal femur in predicting the femoral mechanical properties was measured and compared for the two loading scenarios. The femoral neck DXA BMD was best correlated to the femoral ultimate force for both configurations and predicted significantly better femoral failure load (R 2 =0.80 vs. R 2 =0.66, P <0.05) when simulating a side than when simulating a standing configuration. Conversely, the work to failure was predicted similarly for both loading configurations (R 2 =0.54 vs. R 2 =0.53, P >0.05). Therefore, neck BMD should be considered as one of the key factors for discriminating femoral fracture risk in vivo. Moreover, the better predictive ability of neck BMD for femoral strength if tested in a fall compared to a one-legged stance configuration suggests that DXA's clinical relevance may not be as high for spontaneous femoral fractures than for fractures associated to a fall.
  
  PubDate: 2013-05-17T21:23:33Z
Thermal model to investigate the temperature in bone grinding for skull base neurosurgery
- Abstract: Publication date: Available online 15 May 2013
  Source:Medical Engineering & Physics
  Author(s): Lihui Zhang , Bruce L. Tai , Guangjun Wang , Kuibang Zhang , Stephen Sullivan , Albert J. Shih
  This study develops a thermal model utilizing the inverse heat transfer method (IHTM) to investigate the bone grinding temperature created by a spherical diamond tool used for skull base neurosurgery. Bone grinding is a critical procedure in the expanded endonasal approach to remove the cranial bone and access to the skull base tumor via nasal corridor. The heat is generated during grinding and could damage the nerve or coagulate the blood in the carotid artery adjacent to the bone. The finite element analysis is adopted to investigate the grinding-induced bone temperature rise. The heat source distribution is defined by the thermal model, and the temperature distribution is solved using the IHTM with experimental inputs. Grinding experiments were conducted on a bovine cortical bone with embedded thermocouples. Results show significant temperature rise in bone grinding. Using 50°C as the threshold, the thermal injury can propagate about 3mm in the traverse direction, and 3mm below the ground surface under the dry grinding condition. The presented methodology demonstrated the capability of being a thermal analysis tool for bone grinding study.
  
  PubDate: 2013-05-17T21:23:33Z
Validity and reliability of measuring activities, movement intensity and energy expenditure with the DynaPort MoveMonitor
- Abstract: Publication date: Available online 16 May 2013
  Source:Medical Engineering & Physics
  Author(s): Sonja de Groot , Mieke G. Nieuwenhuizen
  The purpose of this study was to evaluate the validity and reliability of assessing activities, movement intensity (MI) and energy expenditure (EE) measured by accelerometry. 28 Able-bodied participants performed standardized tasks while an accelerometer was worn and oxygen uptake was measured. After uploading the accelerometer data to the manufacturer's website, a report was received that gave minute-by-minute MI and EE of the performed activities. Validity was assessed by comparing reported activities and EE with the actual performed activities and calculated EE from the oxygen uptake, and by testing whether MI differed between walking velocities and cycling resistances. Reliability was assessed by performing the protocol twice. Except for standing (classified predominantly (82%) as sitting), most activities were categorized mainly correctly (93–100%). A difference in MI was detected between walking speeds but not between cycling resistances. EE was overestimated for walking (ICC=0.54) and underestimated for cycling (ICC=0.03). Reliability of MI was high (ICC=0.91) but reliability for the relative time spent in activities or the step count was weak to moderate. In conclusion, most activities were categorized correctly, MI seemed to be valid and reliable but reliability is low for relative time spent in activities and EE cannot be estimated well.
  
  PubDate: 2013-05-17T21:23:33Z
TETRA mobile radios interfere with electroencephalography recording equipment
- Abstract: Publication date: Available online 16 May 2013
  Source:Medical Engineering & Physics
  Author(s): Nathalie C. Fouquet , Malcolm B. Hawken , Paul Elliott , Adrian P. Burgess
  We observed an anomaly in the human electroencephalogram (EEG) associated with exposure to terrestrial trunked radio (TETRA) Radiofrequency Fields (RF). Here, we characterize the time and frequency components of the anomaly and demonstrate that it is an artefact caused by TETRA RF interfering with the EEG recording equipment and not by any direct or indirect effect on the brain.
  
  PubDate: 2013-05-17T21:23:33Z
Reproducible metacarpal joint space width measurements using 3D analysis of images acquired with high-resolution peripheral quantitative computed tomography
- Abstract: Publication date: Available online 14 May 2013
  Source:Medical Engineering & Physics
  Author(s): Cheryl Barnabe , Helen Buie , Michelle Kan , Eva Szabo , Susan G. Barr , Liam Martin , Steven K. Boyd
  Objective Joint space narrowing is an important feature of progressive joint damage and functional impairment in rheumatoid arthritis (RA). Methods to provide a continuous measurement of joint space width have not been adopted in research or clinical settings. High-resolution peripheral quantitative computed tomography (HR-pQCT) (Scanco Medical AG, Brüttisellen, Switzerland) accurately and reproducibly images bone microstructure at a nominal isotropic voxel dimension of 82μm. Given the ability of HR-pQCT to detect bone margins with high precision, we developed methodology to measure a three-dimensional (3D) metacarpophalangeal (MCP) joint space width and tested the reproducibility of the scan protocol with hand repositioning. Materials and methods Consecutive HR-pQCT scans of the 2nd and 3rd MCP joints of ten subjects with early RA (70% female, mean age 45 years), with repositioning between scans, were obtained. The periosteal edges of the metacarpal head and proximal phalanx base were detected using the μCT Evaluation Program V6.0 (Scanco Medical AG). Using the method of ‘fitting maximal spheres’, the joint space width and distribution of joint space thickness was estimated. Results The mean minimum joint space width of the 2nd MCP was 1.82mm (SD 0.20) and of the 3rd MCP 1.84mm (SD 0.23). Reproducibility with repositioning was reliable, with overlapping filtered histograms and a root square mean coefficient of variance of 4.8%. Conclusions We provide reproducible methodology for evaluating the joint space width of the MCP joints. When combined with the assessment of erosions and periarticular bone density, HR-pQCT may be the ideal technology to assess disease activity and progression in RA.
  
  PubDate: 2013-05-14T21:20:34Z
A sensitivity analysis of a personalized pulse wave propagation model for arteriovenous fistula surgery. Part B: Identification of possible generic model parameters
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): W. Huberts , C. de Jonge , W.P.M. van der Linden , M.A. Inda , K. Passera , J.H.M. Tordoir , F.N. van de Vosse , E.M.H. Bosboom
  Decision-making in vascular access surgery for hemodialysis can be supported by a pulse wave propagation model that is able to simulate pressure and flow changes induced by the creation of a vascular access. To personalize such a model, patient-specific input parameters should be chosen. However, the number of input parameters that can be measured in clinical routine is limited. Besides, patient data are compromised with uncertainty. Incomplete and uncertain input data will result in uncertainties in model predictions. In part A, we analyzed how the measurement uncertainty in the input propagates to the model output by means of a sensitivity analysis. Of all 73 input parameters, 16 parameters were identified to be worthwhile to measure more accurately and 51 could be fixed within their measurement uncertainty range, but these latter parameters still needed to be measured. Here, we present a methodology for assessing the model input parameters that can be taken constant and therefore do not need to be measured. In addition, a method to determine the value of this parameter is presented. For the pulse wave propagation model applied to vascular access surgery, six patient-specific datasets were analyzed and it was found that 47 out of 73 parameters can be fixed on a generic value. These model parameters are not important for personalization of the wave propagation model. Furthermore, we were able to determine a generic value for 37 of the 47 fixable model parameters.
  
  PubDate: 2013-05-11T21:22:07Z
A sensitivity analysis of a personalized pulse wave propagation model for arteriovenous fistula surgery. Part A: Identification of most influential model parameters
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): W. Huberts , C. de Jonge , W.P.M. van der Linden , M.A. Inda , J.H.M. Tordoir , F.N. van de Vosse , E.M.H. Bosboom
  Previously, a pulse wave propagation model was developed that has potential in supporting decision-making in arteriovenous fistula (AVF) surgery for hemodialysis. To adapt the wave propagation model to personalized conditions, patient-specific input parameters should be available. In clinics, the number of measurable input parameters is limited which results in sparse datasets. In addition, patient data are compromised with uncertainty. These uncertain and incomplete input datasets will result in model output uncertainties. By means of a sensitivity analysis the propagation of input uncertainties into output uncertainty can be studied which can give directions for input measurement improvement. In this study, a computational framework has been developed to perform such a sensitivity analysis with a variance-based method and Monte Carlo simulations. The framework was used to determine the influential parameters of our pulse wave propagation model applied to AVF surgery, with respect to parameter prioritization and parameter fixing. With this we were able to determine the model parameters that have the largest influence on the predicted mean brachial flow and systolic radial artery pressure after AVF surgery. Of all 73 parameters 51 could be fixed within their measurement uncertainty interval without significantly influencing the output, while 16 parameters importantly influence the output uncertainty. Measurement accuracy improvement should thus focus on these 16 influential parameters. The most rewarding are measurement improvements of the following parameters: the mean aortic flow, the aortic windkessel resistance, the parameters associated with the smallest arterial or venous diameters of the AVF in- and outflow tract and the radial artery windkessel compliance.
  
  PubDate: 2013-05-11T21:22:07Z
New insights into the understanding of flow dynamics in an in vitro model for abdominal aortic aneurysms
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Valérie Deplano , Clark Meyer , Carine Guivier-Curien , Eric Bertrand
  An in vitro dynamics set-up of the flow in a compliant abdominal aortic aneurysm (AAA) model with an anterior posterior asymmetry, aorto-iliac bifurcation, and physiological inlet flow rate and outlet pressure waveforms was developed. The aims were first to show that the structural mechanical behavior of the used material to mimic the AAA wall was similar to this of patients with AAA and then to study the influence of the aorto-iliac bifurcation presence and to study the influence of the imbalanced flow rate in the iliac branches on the AAA flow field. 3D visualizations, never performed in the literature, have clearly put into evidence the development of a vortex ring generated at the AAA proximal neck during the decelerating phase of flow rate, which detaches and progresses downstream during the cardiac cycle, impinges on the anterior wall in the distal AAA region, breaks up, and separates into two vortices of which one rolls on upstream along the anterior wall. 2D particle image velocimetry measurements, swirling strength and enstrophy calculations allowed quantification of the vorticity, vortex trajectory and energy for the different geometrical and hydrodynamical conditions. The main results show that the instant and the intensity of the vortex ring impingement depend on the presence of the aorto-iliac bifurcation, with higher intensity, by about 90%, for an AAA without bifurcation. The imbalance of the flow rates into the iliac branches induces different propagation velocities of the vortex ring and lowers the intensity of the vortex impact by about 60%. The potential influence of the AAA dynamics is discussed in terms of AAA remodeling and rupture.
  
  PubDate: 2013-05-11T21:22:07Z
Permeability studies of artificial and natural cancellous bone structures
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Ardiyansyah Syahrom , Mohammed Rafiq Abdul Kadir , Jaafar Abdullah , Andreas Öchsner
  In the development of artificial cancellous bones, two major factors need to be considered: the integrity of the overall structure and its permeability. Whilst there have been many studies analysing the mechanical properties of artificial and natural cancellous bones, permeability studies, especially those using numerical simulation, are scarce. In this study, idealised cancellous bones were simulated from the morphological indices of natural cancellous bone. Three different orientations were also simulated to compare the anisotropic nature of the structure. Computational fluid dynamics methods were used to analyse fluid flow through the cancellous structures. A constant mass flow rate was used to determine the intrinsic permeability of the virtual specimens. The results showed similar permeability of the prismatic plate-and-rod model to the natural cancellous bone. The tetrakaidecahedral rod model had the highest permeability under simulated blood flow conditions, but the plate counterpart had the lowest. Analyses on the anisotropy of the virtual specimens showed the highest permeability for the horizontal orientation. Linear relationships were found between permeability and the two physical properties, porosity and bone surface area.
  
  PubDate: 2013-05-11T21:22:07Z
Physiological simulation of blood flow in the aorta: Comparison of hemodynamic indices as predicted by 3-D FSI, 3-D rigid wall and 1-D models
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Philippe Reymond , Paolo Crosetto , Simone Deparis , Alfio Quarteroni , Nikos Stergiopulos
  Interest in patient-specific blood-flow circulation modeling has increased substantially in recent years. The availability of clinical data for geometric and elastic properties together with efficient numerical methods has now made model rendering feasible. This work uses 3-D fluid–structure interaction (FSI) to provide physiological simulation resulting in modeling with a high level of detail. Comparisons are made between results using FSI and rigid wall models. The relevance of wall compliance in determining parameters of clinical importance, such as wall shear stress, is discussed together with the significance of differences found in the pressure and flow waveforms when using the 1-D model. Patient-specific geometry of the aorta and its branches was based on MRI angiography data. The arterial wall was created with a variable thickness. The boundary conditions for the fluid domain were pressure waveform at the ascending aorta and flow for each outlet. The waveforms were obtained using a 1-D model validated by in vivo measurements performed on the same person. In order to mimic the mechanical effect of surrounding tissues in the simulation, a stress–displacement relation was applied to the arterial wall. The temporal variation and spatial patterns of wall shear stress are presented in the aortic arch and thoracic aorta together with differences using rigid wall and FSI models. A comparison of the 3-D simulations to the 1-D model shows good reproduction of the pressure and flow waveforms.
  
  PubDate: 2013-05-11T21:22:07Z
An SEMG computer interface using three myoelectric sites for proportional two-dimensional cursor motion control and clicking for individuals with spinal cord injuries
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Changmok Choi , Youngjin Na , Byeongcheol Rim , Youngkyung Kim , Sangkuk Kang , Jung Kim
  We developed an alternative computer interface using surface electromyography (sEMG) for individuals with spinal cord injuries (SCI) to access a computer. We designed this interface to make a cursor move on a two-dimensional screen and to click using only three muscles for each subject. In addition, a user can voluntarily control cursor movement speed by modulating muscle contraction levels. Three SCI patients and 10 healthy subjects volunteered to evaluate the performance of this interface using Fitts’ law test in a two-dimensional testing setup. The throughputs (TP) of our interface were 0.1962±0.0562b/s for the SCI patients and 0.4356±0.0706b/s for the healthy subjects. This interface could help SCI patients handle a wider range of activities such as browsing the Internet and communicating with others.
  
  PubDate: 2013-05-11T21:22:07Z
Fibre orientation of fresh and frozen porcine aorta determined non-invasively using diffusion tensor imaging
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Vittoria Flamini , Christian Kerskens , Ciaran Simms , Caitríona Lally
  Diffusion tensor imaging analysis was applied to fresh and frozen porcine aortas in order to determine fibre orientation. Fresh and stored frozen porcine aortas were imaged in a 7T scanner with a diffusion weighted spin echo sequence (six gradient directions, matrix 128×128 pixels, 2.8cm×2.8cm field of view). The images were taken for different b values, ranging from 200s/mm2 to 1600s/mm2. For each dataset the diffusion tensor was evaluated, fractional anisotropy (FA) maps were calculated, and the fibres mapped. The arterial fibres resulting were postprocessed and their fibre angle evaluated. The FA maps, the dominant fibre angle, and the fibre pattern in the arterial wall thickness were compared in the fresh and in the stored frozen aortas. The technique was able to determine a fibre pattern in the fresh healthy aorta that is in accordance with the data available in literature and to identify an alteration in the fibre pattern caused by freezing. This study shows that this technique has potential for studying fibre orientation and fibre distribution in humans and could be further developed to diagnose fibre alterations due to cardiovascular diseases. In fact, our results suggest that DTI has the potential to determine the fibrous structure of arteries non-invasively. This capability could be further developed to study the natural remodelling of the aorta in vivo due to age and/or gender or to obtain information on aortic diseases at an early stage of their evolution.
  
  PubDate: 2013-05-11T21:22:07Z
A novel non-linear recursive filter design for extracting high rate pulse features in nuclear medicine imaging and spectroscopy
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Salar Sajedi , Alireza Kamal Asl , Mohammad R. Ay , Mohammad H. Farahani , Arman Rahmim
  Applications in imaging and spectroscopy rely on pulse processing methods for appropriate data generation. Often, the particular method utilized does not highly impact data quality, whereas in some scenarios, such as in the presence of high count rates or high frequency pulses, this issue merits extra consideration. In the present study, a new approach for pulse processing in nuclear medicine imaging and spectroscopy is introduced and evaluated. The new non-linear recursive filter (NLRF) performs nonlinear processing of the input signal and extracts the main pulse characteristics, having the powerful ability to recover pulses that would ordinarily result in pulse pile-up. The filter design defines sampling frequencies lower than the Nyquist frequency. In the literature, for systems involving NaI(Tl) detectors and photomultiplier tubes (PMTs), with a signal bandwidth considered as 15MHz, the sampling frequency should be at least 30MHz (the Nyquist rate), whereas in the present work, a sampling rate of 3.3MHz was shown to yield very promising results. This was obtained by exploiting the known shape feature instead of utilizing a general sampling algorithm. The simulation and experimental results show that the proposed filter enhances count rates in spectroscopy. With this filter, the system behaves almost identically as a general pulse detection system with a dead time considerably reduced to the new sampling time (300ns). Furthermore, because of its unique feature for determining exact event times, the method could prove very useful in time-of-flight PET imaging.
  
  PubDate: 2013-05-11T21:22:07Z
Mesenchymal stem cells increase collagen infiltration and improve wound healing response to porous titanium percutaneous implants
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Dorthyann Isackson , Kevin J. Cook , Lawrence D. McGill , Kent N. Bachus
  Epidermal downgrowth, commonly associated with long-term percutaneous implants, weakens the skin-implant seal and greatly increases the vulnerability of the site to infection. To improve the skin attachment and early tissue integration with porous metal percutaneous implants, we evaluated the effect of bone marrow-derived mesenchymal stem cells (BMMSCs) to provide wound healing cues and vascularization to the dermal and epidermal tissues in establishing a barrier with the implant. Two porous metal percutaneous implants, one treated with BMMSCs and one untreated, were placed subdermally on the dorsum of Lewis rats. Implants were evaluated at 0, 3, 7, 28, and 56 days after implantation. Histological analyses evaluated cellular infiltrates, vascularization, quantity and quality of tissue ingrowth, epidermal downgrowth, and fibrous encapsulation. The amount of collagen infiltrating the porous coating was significantly greater for the BMMSC-treated implants at 3 and 28 days post implantation compared to untreated implants. There was an early influx and resolution of cellular inflammatory infiltrates in the treated implants compared to the untreated, though not statistically significant. Vascularization increased over time in both treated and untreated implants, with no statistical significance. Epidermal downgrowth was minimally observed in all implants with or without the BMMSC treatment. Our results suggest that BMMSCs can influence an early and rapid resolution of acute and chronic inflammation in wound healing, and can stimulate early collagen deposition and granulation tissue associated with later stages of wound repair. These findings provide evidence that BMMSCs can stimulate a more rapid and improved barrier between the skin and porous metal percutaneous implant.
  
  PubDate: 2013-05-11T21:22:07Z
Investigation of metallic and carbon fibre PEEK fracture fixation devices for three-part proximal humeral fractures
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Emer M. Feerick , Jim Kennedy , Hannan Mullett , David FitzPatrick , Patrick McGarry
  A computational investigation of proximal humeral fracture fixation has been conducted. Four devices were selected for the study; a locking plate, intramedullary nail (IM Nail), K-wires and a Bilboquet device. A 3D model of a humerus was created using a process of thresholding based on the grayscale values of a CT scan of an intact humerus. An idealised three part fracture was created in addition to removing a standard volume from the humeral head as a representation of bone voids that occur as a result of the injury. All finite element simulations conducted represent 90° arm abduction. Simulations were conducted to investigate the effect of filling this bone void with calcium phosphate cement for each device. The effect of constructing devices from carbon fibre polyetheretherketone (CFPEEK) was investigated. Simulations of cement reinforced devices predict greater stability for each device. The average unreinforced fracture line opening (FLO) is reduced by 48.5% for metallic devices with a lesser effect on composite devices with FLO reduced by 23.6%. Relative sliding (shear displacement) is also reduced between fracture fragments by an average of 58.34%. CFPEEK device simulations predict reduced stresses at the device–bone interface.
  
  PubDate: 2013-05-11T21:22:07Z
Evaluation of a minimally invasive renal cooling device using heat transfer analysis and an in vivo porcine model
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Thomas M. Cervantes , Edward K. Summers , Rachel Batzer , Christie Simpson , Raymond Lewis , Nadeem N. Dhanani , Alexander H. Slocum
  Partial nephrectomy is the gold standard treatment for renal cell carcinoma. This procedure requires temporary occlusion of the renal artery, which can cause irreversible damage due to warm ischemia after 30min. Open surgical procedures use crushed ice to induce a mild hypothermia of 20°C in the kidney, which can increase allowable ischemia time up to 2.5h. The Kidney Cooler device was developed previously by the authors to achieve renal cooling using a minimally invasive approach. In the present study an analytical model of kidney cooling in situ was developed using heat transfer equations to determine the effect of kidney thickness on cooling time. In vivo porcine testing was conducted to evaluate the cooling performance of this device and to identify opportunities for improved surgical handling. Renal temperature was measured continuously at 6 points using probes placed orthogonally to each other within the kidney. Results showed that the device can cool the core of the kidney to 20°C in 10–20min. Design enhancements were made based on surgeon feedback; it was determined that the addition of an insulating air layer below the device increased difficulty of positioning the device around the kidney and did not significantly enhance cooling performance. The Kidney Cooler has been shown to effectively induce mild renal hypothermia of 20°C in an in vivo porcine model.
  
  PubDate: 2013-05-11T21:22:07Z
Including aortic valve morphology in computational fluid dynamics simulations: Initial findings and application to aortic coarctation
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): David C. Wendell , Margaret M. Samyn , Joseph R. Cava , Laura M. Ellwein , Mary M. Krolikowski , Kimberly L. Gandy , Andrew N. Pelech , Shawn C. Shadden , John F. LaDisa Jr.
  Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality.
  
  PubDate: 2013-05-11T21:22:07Z
Editorial Board
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  
  PubDate: 2013-05-11T21:22:07Z
Electrocardiogram beat detection enhancement using Independent Component Analysis
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Jakub Kuzilek , Lenka Lhotska
  Beat detection is a basic and fundamental step in electrocardiogram (ECG) processing. In many ECG applications strong artifacts from biological or technical sources could appear and cause distortion of ECG signals. Beat detection algorithm desired property is to avoid these distortions and detect beats in any situation. Our developed method is an extension of Christov's beat detection algorithm, which detects beat using combined adaptive threshold on transformed ECG signal (complex lead). Our offline extension adds estimation of independent components of measured signal into the transformation of ECG creating a signal called complex component, which enhances ECG activity and enables beat detection in presence of strong noises. This makes the beat detection algorithm much more robust in cases of unpredictable noise appearances, typical for holter ECGs and telemedicine applications of ECG. We compared our algorithm with the performance of our implementation of the Christov's and Hamilton's beat detection algorithm.
  
  PubDate: 2013-05-11T21:22:07Z
Variable stiffness actuated prosthetic knee to restore knee buckling during stan A modeling study
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): E.C. Wentink , H.F.J.M. Koopman , S. Stramigioli , J.S. Rietman , P.H. Veltink
  Most modern intelligent knee prosthesis use dampers to modulate dynamic behavior and prevent excessive knee flexion, but they dissipate energy and do not assist in knee extension. Energy efficient variable stiffness control (VSA) can reduce the energy consumption yet effectively modulate the dynamic behavior and use stored energy during flexion to assist in subsequent extension. A principle design of energy efficient VSA in a prosthetic knee is proposed and analyzed for the specific case of rejection of a disturbed stance phase. The concept is based on the principle that the output stiffness of a spring can be changed without changing the energy stored in the elastic elements of the spring. The usability of this concept to control a prosthetic knee is evaluated using a model. Part of the stance phase of the human leg was modeled by a double pendulum. Specifically the rejection of a common disturbance of transfemoral prosthetic gait, an unlocked knee at heel strike, was evaluated. The ranges of spring stiffnesses were determined such that the angular characteristics of a normal stance phase were preserved, but disturbances could also be rejected. The simulations predicted that energy efficient VSA can be useful for the control of prosthetic knees.
  
  PubDate: 2013-05-11T21:22:07Z
Contractions, a risk for premature rupture of fetal membranes: A new protocol with cyclic biaxial tension
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Michela Perrini , Wilfried Bürzle , Claudia Haller , Nicole Ochsenbein-Kölble , Jan Deprest , Roland Zimmermann , Edoardo Mazza , Martin Ehrbar
  This study aims at investigating the effect of repeated mechanical loading on the rupture and deformation properties of fetal membranes. Ten membranes delivered by cesarean sections were tested using a custom-built inflation device which provides a multi-axial stress state. For each membrane, a group of samples was first cyclically stretched by application of pressure ranging between 10 and 40mmHg. After cycles, samples were subjected to inflation up to rupture. Differences between mechanical parameters from cycled and uncycled samples were analyzed. Ten cycles at 40% of mean critical membrane tension—representative of mean physiologic contractions—did not affect strength and stiffness of fetal membranes but reduced the work to rupture, thus indicating that contractions might increase the risk of premature rupture of the membrane. Cyclic testing demonstrated a large hysteresis loop and irreversible deformation on the first cycle, followed by rapid stabilization on subsequent cycles. In 80% of tests, amnion ruptured first and at the periphery of the sample, under uniaxial strain state. Chorion ruptured at higher deformation levels in the middle, under biaxial strain state.
  
  PubDate: 2013-05-11T21:22:07Z
Suitability of DCPs with Screw Locking Elements to allow sufficient interfragmentary motion to promote secondary bone healing of osteoporotic fractures
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): A. Cuadrado , A. Yánez , J.A. Carta , G. Garcés
  This paper analyses the suitability of a system comprising a Dynamic Compression Plate (DCP) and Screw Locking Elements (SLEs) to allow sufficient interfragmentary motion to promote secondary bone healing in osteoporotic fractures. Four fixation systems were mounted on bone-simulating reinforced epoxy bars filled with solid rigid polyurethane foam. Group 1, used for comparison purposes, represents a system comprised of a Locking Compression Plate (LCP) and eight locking screws. Groups 2 and 3 represent a system comprised of a DCP plate with eight cortical screws and two SLEs placed on the screws furthest from (group 2) and nearest to (group 3) the fracture. Group 4 represents the system comprised of a DCP plate with SLEs placed on all eight cortical screws. Cyclic compression tests of up to 10,000 load cycles were performed in order to determine the parameters of interest, namely the stiffnesses and the interfragmentary motion of the various configurations under consideration. Tukey's multiple comparison test was used to analyse the existence or otherwise of significant differences between the means of the groups. At 10,000 cycles, interfragmentary motion at the far cortex for group 2 was 0.60±0.04mm and for group 3 0.59±0.03mm (there being no significant differences: p =0.995). The mean interfragmentary motion at the far cortex of the LCP construct was 70% less than that of the two groups with 2SLEs (there being significant differences: p =1.1×10−8). In the case of group 4 this figure was 45% less than in groups 2 and 3 (there being significant differences: p =5.6×10−6). At 10,000 cycles, interfragmentary motion at the near cortex for group 2 was 0.24±0.06mm and for group 3 0.24±0.03mm (there being no significant differences: p =1.000). The mean interfragmentary motion at the near cortex of the LCP construct was 70.8% less than that of the two groups with 2SLEs (there being significant differences: p =0.011). In the case of group 4 this figure was 66.7% less than in groups 2 and 3 (there being significant differences: p =0.016). The mean stiffness at 10,000 cycles was 960±110Nmm−1 for group 2 and 969±53Nmm−1 for group 3 (there being no significant differences: p =1.000). For group 1 (the LCP construct) the mean stiffness at 10,000 cycles was 3144±446Nmm−1, 3.25 times higher than that of groups 2 and 3 (there being significant differences: p =0.00002), and 1.6 times higher than that of the DCP+8SLEs construct (1944±408Nmm−1, there being significant differences: p =0.007). It is concluded that using the DCP+2SLEs construct sufficient interfragmentary motion is ensured to promote secondary bone healing. However, if too many SLEs are used the result may be, as with the LCP, an excessively rigid system for callus formation.
  
  PubDate: 2013-05-11T21:22:07Z
Patient-specific finite element modeling for femoral bone augmentation
- Abstract: Publication date: June 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 6
  Author(s): Ehsan Basafa , Robert S. Armiger , Michael D. Kutzer , Stephen M. Belkoff , Simon C. Mears , Mehran Armand
  The aim of this study was to provide a fast and accurate finite element (FE) modeling scheme for predicting bone stiffness and strength suitable for use within the framework of a computer-assisted osteoporotic femoral bone augmentation surgery system. The key parts of the system, i.e. preoperative planning and intraoperative assessment of the augmentation, demand the finite element model to be solved and analyzed rapidly. Available CT scans and mechanical testing results from nine pairs of osteoporotic femur bones, with one specimen from each pair augmented by polymethylmethacrylate (PMMA) bone cement, were used to create FE models and compare the results with experiments. Correlation values of R 2 =0.72–0.95 were observed between the experiments and FEA results which, combined with the fast model convergence (∼3min for ∼250,000 degrees of freedom), makes the presented modeling approach a promising candidate for the intended application of preoperative planning and intraoperative assessment of bone augmentation surgery.
  
  PubDate: 2013-05-11T21:22:07Z
Biomechanical analysis of different types of pedicle screw augmentation: A cadaveric and synthetic bone sample study of instrumented vertebral specimens
- Abstract: Publication date: Available online 11 May 2013
  Source:Medical Engineering & Physics
  Author(s): Kuo-Hua Chao , Yu-Shu Lai , Wen-Chuan Chen , Chia-Ming Chang , Colin J. McClean , Chang-Yuan Fan , Chia-Hao Chang , Leou-Chyr Lin , Cheng-Kung Cheng
  This study aims to determine the pull-out strength, stiffness and failure pull-out energy of cement-augmented, cannulated-fenestrated pedicle screws in an osteoporotic cadaveric thoracolumbar model, and to determine, using synthetic bone samples, the extraction torques of screws pre-filled with cement and those with cement injected through perforations. Radiographs and bone mineral density measurements from 32 fresh thoracolumbar vertebrae were used to define specimen quality. Axial pull-out strength of screws was determined through mechanical testing. Mechanical pull-out strength, stiffness and energy-to-failure ratio were recorded for cement-augmented and non-cement-augmented screws. Synthetic bone simulating a human spinal bone with severe osteoporosis was used to measure the maximum extraction torque. The pull-out strength and stiffness-to-failure ratio of cement pre-filled and cement-injected screws were significantly higher than the non-cement-augmented control group. However, the cement pre-filled and cement-injected groups did not differ significantly across these values (p =0.07). The cement pre-filled group had the highest failure pull-out energy, approximately 2.8 times greater than that of the cement-injected (p <0.001), and approximately 11.5 times greater than that of the control groups (p <0.001). In the axial pull-out test, the cement-injected group had a greater maximum extraction torque than the cement pre-filled group, but was statistically insignificant (p =0.17). The initial fixation strength of cannulated screws pre-filled with cement is similar to that of cannulated screws injected with cement through perforations. This comparable strength, along with the heightened pull-out energy and reduced extraction torque, indicates that pedicle screws pre-filled with cement are superior for bone fixation over pedicle screws injected with cement.
  
  PubDate: 2013-05-11T21:22:07Z
Assessment of gait sensitivity norm as a predictor of risk of falling during walking in a neuromusculoskeletal model
- Abstract: Publication date: Available online 11 May 2013
  Source:Medical Engineering & Physics
  Author(s): Sayed Naseel Mohamed Thangal , Mukul Talaty , Sriram Balasubramanian
  Quantifying the risk of falling (falls risk) would be helpful in treating people with gait disorders. The gait sensitivity norm (GSN) is a stability measure that correlates well to risk of falling in passive dynamic walkers but has not been evaluated on humans or human-like walking models. We assessed the correlation of GSN to risk of falling in a neuromusculoskeletal (NMS) walking model. Specifically, we evaluated the correlation of GSN to the actual disturbance rejection (ADR) of the model and the sensitivity of this relationship to gait parameter, Poincaré section selection and steady state variability correction. Statistically significant results at p <0.05 were obtained for some of the gait indicators evaluated at the point in the gait cycle where they were most variable. The correlation between GSN and ADR was sensitive to gait indicator and Poincaré sections evaluated but not to steady state variability correction. The current work suggests some simple steps to reduce the sensitivity of GSN to arbitrary and subjective factors. Overall, the findings support the potential of GSN to be a clinically applicable measure of falls risk. Further study is required to identify methods to more definitively select the various factors within the GSN calculation and to confirm its ability to predict falls risk in human subjects.
  
  PubDate: 2013-05-11T21:22:07Z
Evaluating and improving the quality of time-dependent, diffuse reflectance spectroscopic signals measured from in vivo brain during craniotomy
- Abstract: Publication date: Available online 10 May 2013
  Source:Medical Engineering & Physics
  Author(s): Nitin Yadav , Sanjiv Bhatia , John Ragheb , Yinchen Song , Adrian Romero , Sanghoon Oh , Wei-Chiang Lin
  Background Optical spectroscopy can be used to assess the pathophysiological characteristics of diseased and injured biological tissue in vivo in a non-destructive way. It is often used in conjunction with a contact optical probe for the purposes of operating and sensing in a sterile field. Since the probe is often held by the hand of an investigator during data acquisition, any hand instability can affect the quality of acquired data and, hence, degrade the accuracy of diagnosis. This study was designed to quantitatively characterize these artifacts, and then propose an effective engineering solution to remove them. Methods Time-dependent diffuse reflectance spectra (Rd(λ,t)) were acquired from the normal cortex region of pediatric patients undergoing epilepsy surgery. They were acquired at a rate of 33Hz, and their range was 400 and 900nm. Two distinct ways of collecting data were tested: one with the fiber optical probe held by the surgeon's hand during data acquisition, and the other with the probe held by a specially designed probe holder. The probe holder was designed and constructed to minimize the variations in probe contact pressure and contact point for the full duration of any given investigation. Spectral data acquired using versus not using the probe holder were characterized and compared in the time, wavelength, and frequency domains, using both descriptive and inferential statistics. Results Hand motion manifested as strong random variations in Rd(λ,t) which impacted temporal and frequency characteristics of Rd(λ,t). The percentage standard deviation %STD of Rd(λ,t) acquired without probe holder could be as high as 60%, and they are significantly higher than those with probe holder at all wavelengths. This difference is especially prominent between 400 and 600nm. Rd(λ,t) acquired without the probe holder also processed a higher spectral power energy in the frequency domain than those with the probe holder. The correlation analysis revealed that the hand motions induced synchronistic variations in Rd(λ,t) between 600 and 800nm, but this synchronicity is not obvious between 400 and 600nm. Conclusion The results of this investigation demonstrate the nature and the magnitude of hand motion induced artifacts in in vivo diffuse reflectance spectra and propose one potential solution (i.e., a probe holder) to remove them. These findings allow us to improve the quality of time-dependent, diffuse reflectance signals acquired to study the dynamic characteristics of biological tissues, like brain, in vivo.
  
  PubDate: 2013-05-11T21:22:07Z
Spectral analysis of intracranial pressure signals recorded during infusion studies in patients with hydrocephalus
- Abstract: Publication date: Available online 9 May 2013
  Source:Medical Engineering & Physics
  Author(s): María García , Jesús Poza , David Santamarta , Daniel Abásolo , Patricia Barrio , Roberto Hornero
  Hydrocephalus includes a number of disorders characterised by clinical symptoms, enlarged ventricles (observable using neuroimaging techniques) and altered cerebrospinal fluid (CSF) dynamics. Infusion tests are one of the available procedures to study CSF circulation in patients with clinical and radiological features of hydrocephalus. In them, intracranial pressure (ICP) is deliberately raised and CSF circulation disorders evaluated through measurements of the resulting ICP. In this study, we analysed seventy-seven ICP signals recorded during infusion tests using four spectral-based parameters: median frequency (MF) and relative power (RP) in three frequency bands. These measures provide a novel perspective for the analysis of ICP signals in the frequency domain. Each signal was divided into four artefact-free epochs (corresponding to the basal, early infusion, plateau and recovery phases of the infusion study). The four spectral parameters were calculated for each epoch. We analysed differences between epochs of the infusion test and correlations between these epochs and patient data. Statistically significant differences (p <1.7×10−3, Bonferroni-corrected Wilcoxon signed-rank tests) were found between epochs of the infusion test using MF and RP. Furthermore, some spectral parameters (MF in the basal phase, RP for the first frequency band and in the early infusion phase, RP for the second frequency band and in all phases of the infusion study and RP in the third frequency band and in the basal phase) revealed significant correlations (p <0.01) between epochs of the infusion test and signal amplitude in the basal and plateau phases. Our results suggest that spectral analysis of ICP signals could be useful for understanding CSF dynamics in hydrocephalus.
  
  PubDate: 2013-05-11T21:22:07Z
The influence of elastic upstream artery length on fluid–structure interaction modeling: A comparative study using patient-specific cerebral aneurysm
- Abstract: Publication date: Available online 7 May 2013
  Source:Medical Engineering & Physics
  Author(s): C.J. Lee , Y. Zhang , H. Takao , Y. Murayama , Y. Qian
  Fluid–structure interaction (FSI) simulations using a patient-specific geometry are carried out to investigate the influence the length of elastic parent artery and the position of constraints in the solid domain on the accuracy of patient-specific FSI simulations. Three models are tested: Long, Moderate, and Short, based on the length of the elastic parent artery. All three models use same wall thickness (0.5mm) and the elastic modulus (5MPa). The maximum mesh displacement is the largest for the Long model (0.491mm) compared to other models (0.3mm for Moderate, and 0.132mm for Short). The differences of hemodynamic and mechanical variables, aneurysm volume and cross-sectional area between three models are all found to be minor. In addition, the Short model takes the least amount of computing time of the three models (11h compared to 21h for Long and 19h for Moderate). The present results indicate that the use of short elastic upstream artery can shorten the time required for patient-specific FSI simulations without impacting the overall accuracy of the results.
  
  PubDate: 2013-05-08T21:21:52Z
Grip and pinch capability assessment system for children
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Silvia R.M.S. Boschi , Annie F. Frère
  The grip movement is essential for performing daily activities. However, the assessment of this movement is currently made subjectively, due to the lack of appropriate quantification equipment. The objective of this study was to develop, validate and test a virtual environment controlled by five trigger devices used to analyse cylindrical, spherical and hook grips as well as tip-to-tip pinch and pulp-to-side movements. Sensors and electronic circuits that detect the correct grip, the threshold of grip strength and the range of motion were inserted into the devices. To validate this system, tests were conducted with 20 children while being evaluated by three physical therapists, all specialists in neurology. The results from the evaluators and the system agreed to an extent of 86.6%. Following validation, the system was used by 35 children with no motor impairment and by 10 children with mild motor abnormalities in an upper limb; these assessments provided efficient and reliable results. The developments presented in this study may help to assess grip and pinch movements and facilitate the choice of strategies in therapeutic processes.
  
  PubDate: 2013-05-05T19:00:16Z
Investigation of intracranial aneurysm hemodynamics following flow diverter stent treatment
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Y. Zhang , W. Chong , Y. Qian
  Flow diverters (FDs) are high density meshed stents designed to reduce blood flow into intra-cranial aneurysms. Though the FD is one of many intracranial aneurysm (IA) treatments, FD implantation may also result in the growth and rupture of residual aneurysms. The purpose of this research is to investigate the effect of FD implantation on IA hemodynamics. Computational fluid dynamics (CFD) was conducted to analyze dynamic and resistance forces after FD deployment. Simulation results for the successful case (patient A) showed that FD flow resistance force was higher than dynamic force. This indicated that the FD provided sufficient resistance to reduce flow into the aneurysm. As a result, flow velocity magnitude at the aneurysm neck was reduced by 95%. On the other hand, the flow velocity magnitude at the aneurysm neck was reduced by about 50% for the unsuccessful case (patient B). The reason was that the flow resistance force at the aneurysm neck section was calculated to be lower than the flow driving force. In order to completely occlude the aneurysm, a higher resistance FD stent is to be required to suppress the dynamic forces. Patient-specific hemodynamic simulations offer means of quantitative estimation FD treatment outcomes.
  
  PubDate: 2013-05-05T19:00:16Z
A critical analysis of whole body bioimpedance spectroscopy (BIS) for the estimation of body compartments in health and disease
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Georg P. Pichler , Omid Amouzadeh-Ghadikolai , Albrecht Leis , Falko Skrabal
  Aim of the study was to assess the accuracy and precision of a BIS device and the relative contribution of BIS beyond the anthropometric parameters. The output of the Impedimed device (SFB7) and the relative contribution of height, weight, age, sex and resistance values at zero and infinite frequency (R zero and R inf respectively) to the prediction of total body water (TBWd, deuterium space), of extracellular fluid (ECFbr, sodium bromide space) and of fat mass (FMDXA) were assessed in 116 subjects (32 healthy subjects and 84 patients with disorders of body composition). Using a repeated randomization procedure, new equations for TBW, ECF and FM were derived. The SFB7 gave measures of determination similar to those obtained with equations that included only anthropometric data. The SFB7, but not the newly derived regression equations, underestimated TBW and ECF by 3.82±3.37 (mean±SD) and by 0.93±2.62l and overestimated FM by 6.55±3.86kg. Nine of 16 patients with ECF overload as detected by ECFbr were also detected by BIS. BIS measurements contribute marginally but not significantly beyond anthropometric data to the prediction of TBW, ECF and FM, either in healthy subjects or in patients with disturbed body composition.
  
  PubDate: 2013-05-05T19:00:16Z
Changes in permeability of the plasma membrane of myoblasts to fluorescent dyes with different molecular masses under sustained uniaxial stretching
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Efrat Leopold , Amit Gefen
  Deep tissue injury (DTI) is a serious pressure ulcer which onsets in skeletal muscle tissues adjacent to weight-bearing bony prominences. Recent literature points at sustained large deformations in muscle tissue, which translate to static stretching of the plasma membrane (PM) at the cell-scale, as the primary cause of accumulated cell death in DTI. It has been specifically suggested that prolonged exposure to large tensional PM strains interferes with normal cellular homeostasis, primarily by affecting transport through the PM which could become more permeable when stretched. In this context, using confocal imaging and fluorescence-activated cell sorter (FACS), we visualized and quantified here the uptake of fluorescent Dextran dye by myoblasts that were statically stretched uniaxially, up to physiological strains of 3%, 6% and 9%, using two different molecular masses for the Dextran (4kDa and 20kDa). The confocal and FACS studies provided consistent evidence that the permeability of the PM increased at large static deformations. Furthermore, the FACS data indicated that the kinetics of the PM permeability very likely depends on the size of the biomolecular marker. Both results were consistent with reports published in the neurotrauma literature on the kinetics of uptake of fluorescent biomolecules by dynamically stretched neurons; hence there are some analogues in the biomechanical pathways of cellular-level injury between DTI and impact insults. The present work provides additional empirical support to the theory of cell-scale deformation-diffusion damage in the etiology of DTI, and may lead to better understanding of time courses for onset of cellular damage in DTI, by exploring mass transport processes across the PM of the involved cells.
  
  PubDate: 2013-05-05T19:00:16Z
Validation of multiple subject-specific finite element models of unicompartmental knee replacement
- Abstract: Publication date: Available online 3 May 2013
  Source:Medical Engineering & Physics
  Author(s): Mahmut Tuncer , Justin P. Cobb , Ulrich N. Hansen , Andrew A. Amis
  Accurate computer modelling of the fixation of unicompartmental knee replacements (UKRs) is a valuable design tool. However, models must be validated with in vitro mechanical tests to have confidence in the results. Ten fresh-frozen cadaveric knees with differing bone densities were CT-scanned to obtain geometry and bone density data, then implanted with cementless medial Oxford UKRs by an orthopaedic surgeon. Five strain gauge rosettes were attached to the tibia and femur of each knee and the bone constructs were mechanically tested. They were re-tested following implanting the cemented versions of the implants. Finite element models of four UKR tibiae and femora were developed. Sensitivity assessments and convergence studies were conducted to optimise modelling parameters. The cemented UKR pooled R 2 values for predicted versus measured bone strains were 0.85 and 0.92 for the tibia and femur respectively. The cementless UKR pooled R 2 values were slightly lower at 0.62 and 0.73 which may have been due to the irregularity of bone resections. The correlation of the results was attributed partly to the improved material property prediction method used in this project. This study is the first to validate multiple UKR tibiae and femora for bone strain across a range of specimen bone densities.
  
  PubDate: 2013-05-05T19:00:16Z
Definition and evaluation of testing scenarios for knee wear simulation under conditions of highly demanding daily activities
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Jens Schwiesau , Carolin Schilling , Christian Kaddick , Sandra Utzschneider , Volkmar Jansson , Bernhard Fritz , Wilhelm Blömer , Thomas M. Grupp
  The objective of our study was the definition of testing scenarios for knee wear simulation under various highly demanding daily activities of patients after total knee arthroplasty. This was mainly based on a review of published data on knee kinematics and kinetics followed by the evaluation of the accuracy and precision of a new experimental setup. We combined tibio-femoral load and kinematic data reported in the literature to develop deep squatting loading profiles for simulator input. A servo-hydraulic knee wear simulator was customised with a capability of a maximum flexion of 120°, a tibio-femoral load of 5000N, an anterior–posterior (AP) shear force of ±1000N and an internal–external (IE) rotational torque of ±50Nm to simulate highly demanding patient activities. During the evaluation of the newly configurated simulator the ability of the test machine to apply the required load and torque profiles and the flexion kinematics in a precise manner was examined by nominal–actual profile comparisons monitored periodically during subsequent knee wear simulation. For the flexion kinematics under displacement control a delayed actuator response of approximately 0.05s was inevitable due to the inertia of masses in movement of the coupled knee wear stations 1–3 during all applied activities. The axial load and IE torque is applied in an effective manner without substantial deviations between nominal and actual load and torque profiles. During the first third of the motion cycle a marked deviation between nominal and actual AP shear load profiles has to be noticed but without any expected measurable effect on the latter wear simulation due to the fact that the load values are well within the peak magnitude of the nominal load amplitude. In conclusion the described testing method will be an important tool to have more realistic knee wear simulations based on load conditions of the knee joint during activities of daily living.
  
  PubDate: 2013-05-05T19:00:16Z
Controlling horizontal deceleration during gait termination in transfemoral amputees: Measurements and simulations
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Helco G. van Keeken , Aline H. Vrieling , At L. Hof , Klaas Postema , Bert Otten
  In this study we investigated how leading limb angles combined with active ankle moments of a sound ankle or passive stiffness of a prosthetic ankle, influence the center of mass (CoM) velocity during the single limb support phase in gait termination. Also, we studied how the trailing limb velocity influences the CoM velocity during this phase. We analyzed force plate data from a group of experienced transfermoral (TF) amputee subjects using a prosthetic limb, and the outcome from a two-dimensional mathematical forward dynamics model. We found that when leading with the sound limb, the subjects came almost to a full stop in the single limb support phase, without the use of the prosthetic limb. When leading with the prosthetic limb, the CoM deceleration was less in a relatively short single limb support phase, with a fast forward swing of the trailing sound limb. Slowing down the heavier trailing sound limb, compared to the prosthetic limb, results in a relatively larger braking force at the end of the swing phase. The simulations showed that only narrow ranges of leading limb angle and ankle moments could be used to achieve the same CoM velocities with the mathematical model as the average start and end velocities of the prosthetic limb user. We conclude that users of prosthetic limbs have a narrow range of options for the dynamics variables to achieve a target CoM velocity. The lack of active control in the passive prosthetic ankle prevents the TF amputee subjects from producing sufficient braking force when terminating gait with the prosthetic limb leading, forcing the subjects to use both limbs as a functional unit, in which the sound limb is mostly responsible for the gait termination.
  
  PubDate: 2013-05-05T19:00:16Z
Fractal dimension and mechanical properties of human cortical bone
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): David Sanchez-Molina , Juan Velazquez-Ameijide , Víctor Quintana , Carlos Arregui-Dalmases , Jeff R. Crandall , Damien Subit , Jason R. Kerrigan
  Fractal dimension (FD) can be used to characterize microstructure of porous media, particularly bone tissue. The porous microstructure of cortical bone is observable in micro-CT (μCT) images. Estimations of fractal dimensions of μCT images of coupons of human cortical bone are obtained. The same samples were tested on a tensile test machine and Young's modulus (YM) and Failure stress were obtained. When both types of measures were compared, a clear correlation was found (R =−81%, P <0.01). Young's modulus of each sample and the FD of its μCT images are correlated. From the assumption that cortical bone is approximately a fractal set, a non-linear constitutive relation involving FD is obtained for YM. Experimental results show good agreement with this constitutive relation. Additional parameters in the non-linear relation between YM and FD have been estimated from experimental results and related to physical parameters.
  
  PubDate: 2013-05-05T19:00:16Z
Biomechanical consideration of total hip arthroplasty following failed fixation of femoral intertrochanteric fractures – A finite element analysis
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Dave W. Chen , Chun-Li Lin , Chih-Chien Hu , Ming-Feng Tsai , Mel S. Lee
  Objective The current study aimed to perform a biomechanical analysis of the effect and distribution of stress and strain values in the femur and its residual screw holes from the implantation of different lengths of total hip prostheses following failed dynamic hip screw (DHS) fixation of AO type A1.1 and A1.3 intertrochanteric fractures. Methods Medical image processing, computer-assisted engineering design, and finite element analysis were combined for the analysis and the reliability of the model confirmed by convergence testing and comparison with a physical model. Using finite element analysis, patterns of stress from implantation of total hip prostheses with different stem length were obtained. Results Stress distribution was concentrated over the third and fourth residual screw holes, especially in the models with shorter stem length. Fracture type (AO type A1.1 or A1.3) did not alter its distribution. In proximal cancellous bone, a stress-shielding effect was seen at the region of the residual fracture fragment, especially in the A1.1 fracture. In the fracture fixed with 2 cable wires, the maximum von Mises stress was in the proximal cable wire. Conclusion The results suggest that an increase in the original stem length equal to the diameter of the femoral isthmus, or a distance between the most distal residual screw hole and the end of the femoral prosthesis, provide improved stress distribution.
  
  PubDate: 2013-05-05T19:00:16Z
Comparison of different methods of heart rate entropy analysis during acute anoxia superimposed on a chronic rat model of pulmonary hypertension
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Hernâni Gonçalves , Tiago Henriques-Coelho , Ana Paula Rocha , André P. Lourenço , Adelino Leite-Moreira , João Bernardes
  Acute life-threatening situations are particularly critical when superimposed on chronic diseases. The objective of this study was the assessment of heart rate (HR) dynamics during episodes of acute anoxia superimposed on a rat model of chronic pulmonary hypertension. In 10 adult Wistar rats, five weeks after pulmonary hypertension induction with Monocrotaline, we analysed eight 1-min HR segments, during episodes of baseline, mechanical ventilation and acute anoxia, using linear indices, approximate entropy (ApEn), sample entropy (SampEn) and multiscale entropy (MSE). The transition from baseline or mechanical ventilation to early anoxia was identified through almost all indices, but SampEn(2,0.6) was the index that better identified all the transitions. MSE presented limited performance, possibly due to the non-stationary nature and short duration of the acute anoxia episodes. A systematic evaluation of all computed HR indices may help to identify which indices or combination of indices more adequately discriminates and monitors critical acute events superimposed on chronic clinical conditions.
  
  PubDate: 2013-05-05T19:00:16Z
Editorial Board
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  
  PubDate: 2013-05-05T19:00:16Z
A statistical finite element model of the knee accounting for shape and alignment variability
- Abstract: Publication date: Available online 3 May 2013
  Source:Medical Engineering & Physics
  Author(s): Chandreshwar Rao , Clare K. Fitzpatrick , Paul J. Rullkoetter , Lorin P. Maletsky , Raymond H. Kim , Peter J. Laz
  By characterizing anatomical differences in size and shape between subjects, statistical shape models enable population-based evaluations in biomechanics. Statistical models have largely focused on individual bones with application to implant sizing, bone fracture and osteoarthritis; however, in joint mechanics applications, the statistical models must consider the geometry of multiple structures of a joint and their relative position. Accordingly, the objectives of this study were to develop a statistical shape and alignment modeling (SSAM) approach to characterize the intersubject variability in bone morphology and alignment for the structures of the knee, to demonstrate the statistical model's ability to describe variability in a training set and to generate realistic instances for use in finite element evaluation of joint mechanics. The statistical model included representations of the bone and cartilage for the femur, tibia and patella from magnetic resonance images and relative alignment of the structures at a known, loaded position in an experimental knee simulator for a training set of 20 specimens. The statistical model described relationships or modes of variation in shape and relative alignment of the knee structures. By generating new ‘virtual subjects’ with physiologically realistic knee anatomy, the modeling approach can efficiently perform investigations into joint mechanics and implant design which benefit from population-based considerations.
  
  PubDate: 2013-05-05T19:00:16Z
Time-lapsed imaging of implant fixation failure in human femoral heads
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Thomas L. Mueller , Samuel E. Basler , Ralph Müller , G. Harry van Lenthe
  The failure mechanisms of bone–implant constructs are still incompletely understood, because the role of the peri-implant bone in implant stability is unclear. We hypothesized that implant fixation failure is preceded by substantial peri-implant bone failure. A new device was developed that combines mechanical testing of large bone–implant constructs with high-resolution peripheral quantitative computed tomography, following the principles of image-guided failure assessment (IGFA). In this study, we investigated the push-in failure behavior of dynamic hip screws (DHS) implanted in human cadaveric femoral heads. For the first time the fixation failure of a clinically used implant in human trabecular bone could be experimentally visualized at the microstructural level. The ultimate force was highly correlated with the peri-implant bone volume fraction (R 2 =0.85). We demonstrated that primary fixation failure of DHS implants was accompanied by trabecular bone failure in the immediate peri-implant bone region only. Such experimental data are crucial to enhance the understanding on the quality of the bone–implant interface and of the trabecular bone in the process of implant fixation failure. We believe that this newly developed device will be beneficial for the development of new implant designs, especially for use in osteoporotic bone.
  
  PubDate: 2013-05-05T19:00:16Z
Generation, absorption, and transfer of mechanical energy during walking in children
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Brian R. Umberger , Sam Augsburger , JoAnne Resig , Donna Oeffinger , Robert Shapiro , Chester Tylkowski
  The purpose of this study was to characterize the manner in which net joint moments and non-muscular forces generate, absorb, and transfer mechanical energy during walking in able-bodied children. Standard gait data from seven healthy subjects between 6 and 17 years of age were combined with a dynamic model of the whole body to perform a power analysis based on induced acceleration techniques. These data were used to determine how each moment and force generates energy to, absorbs energy from, and transfers energy among the major body segments. The joint moments were found to induce transfers of mechanical energy between body segments that generally exceeded the magnitudes of energy generation and absorption. The amount of energy transferred by gravitational and velocity-dependent forces was considerably less than for the joint moments. The hip and ankle joint moments had relatively simple power patterns that tended to oppose each other, particularly over the stance phase. The knee joint moment had a more complex power pattern that appeared distinct from the hip and ankle moments. The general patterns of mechanical energy flow were similar to previous reports in adults. The approach described in this paper should provide a useful complement to standard clinical gait analysis procedures.
  
  PubDate: 2013-05-05T19:00:16Z
A dimensionally-heterogeneous closed-loop model for the cardiovascular system and its applications
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): P.J. Blanco , R.A. Feijóo
  In the present work a computational model of the entire cardiovascular system is developed using heterogeneous mathematical representations. This model integrates different levels of detail for the blood circulation. The arterial tree is described by a one dimensional model in order to simulate the wave propagation phenomena that take place at the larger arterial vessels. The inflow and outflow locations of this 1D model are coupled with lumped parameter descriptions of the remainder part of the circulatory system, closing the loop. The four cardiac valves are considered using a valve model which allows for stenoses and regurgitation phenomena. In addition, full 3D geometrical models of arterial districts are embedded in this closed-loop circuit to model the local blood flow in specific vessels. This kind of detailed closed-loop network for the cardiovascular system allows hemodynamics analyses of patient-specific arterial district, delivering naturally the appropriate boundary conditions for different cardiovascular scenarios. An example of application involving the effect of aortic insufficiency on the local hemodynamics of a cerebral aneurism is provided as a motivation to reproduce, through numerical simulation, the hemodynamic environment in patients suffering from infective endocarditis and mycotic aneurisms. The need for incorporating homeostatic control mechanisms is also discussed in view of the large sensitivity observed in the results, noting that this kind of integrative modeling allows such incorporation.
  
  PubDate: 2013-05-05T19:00:16Z
Predicting atrial fibrillation inducibility in a canine model by multi-threshold spectra of the recurrence complex network
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Baodan Bai , Yuanyuan Wang , Cuiwei Yang
  The purpose of this study is to predict atrial fibrillation (AF) from epicardial signals by investigating the recurrence property of atrial activity dynamic system before AF. A novel scheme is proposed to predict AF by using multi-threshold spectra of the recurrence complex network. Firstly, epicardial signals are transformed into the recurrence complex network to quantify structural properties of the recurrence in the phase space. Spectral parameters with multi-threshold are used to characterize the global structure of the network. Then the feature sequential forward searching algorithm and mutual information based Maximum Relevance Minimum Redundancy criterion are used to find the optimal feature set. Finally, a support vector machine is used to predict the occurrence of AF. This method is assessed on the pre-AF epicardial signals of canine which includes the normal group A (no further AF will happen), the mild group B (the following AF time is less than 180s) and the severe group C (the following AF time is more than 180s). 25 optimal features are selected out of 180 features from each sample. With these features, sensitivity, specificity and accuracy are 99.40%, 99.70% and 99.60%, respectively, which are the best among the recurrence based methods. The results suggest that the proposed method can predict AF accurately and thus can be prospectively used in the postoperative evaluation.
  
  PubDate: 2013-05-05T19:00:16Z
The influence of contact conditions and micromotions on the fretting behavior of modular titanium alloy taper connections
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): M. Baxmann , S.Y. Jauch , C. Schilling , W. Blömer , T.M. Grupp , M.M. Morlock
  Modularity of femoral stems and neck components has become a more frequently used tool for an optimized restoration of the hip joint center and improvement of patient biomechanics. The additional taper interface increases the risk of mechanical failure due to fretting and crevice corrosion. Several failures of titanium alloy neck adapters have been documented in case-reports. An experimental fretting device was developed in this study to systematically investigate the effect of micromotion and contact pressure on fretting damage in contact situations similar to taper interfaces of modular hip prostheses under cyclic loading representative of in vivo load conditions. As a first application, the fretting behavior of Ti–6Al–4V titanium alloy components was investigated. Micromotions were varied between 10μm and 50μm, maximum contact pressures between 400 and 860N/mm2. All modes of fretting damage were observed: Fretting wear was found for high micromotions in combination with low contact pressures. Fretting fatigue occurred with reduced movement or increased contact pressures. With small micromotions or high normal pressures, low fretting damage was observed. The developed device can be used to evaluate taper design (and especially contact geometry) as well as different materials prior to clinical use.
  
  PubDate: 2013-05-05T19:00:16Z
Use of puncture force measurement to investigate the conditions of blood vessel needle insertion
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Yo Kobayashi , Ryutaro Hamano , Hiroki Watanabe , Jaesung Hong , Kazutaka Toyoda , Makoto Hashizume , Masakatsu G. Fujie
  Central venous catheterization involves venous puncture and catheter insertion for transfusions. Quantitative conditions that facilitate insertion of the needle, such as the angle and velocity of insertion, have not been clarified. We previously developed a robotic system for guiding the needle along a specified puncture path with high precision and are currently implementing a hardware design for a robotic system to assist in blood vessel puncture. In this study, we proposed the insertion angle and velocity for stopping the needle in a blood vessel, assuming that a robotic system such as ours is used during the procedure. We inserted a needle into a segment of porcine jugular vein and obtained the puncture reaction force. Evaluation indices were the magnitude of the sudden decrease in reaction force at the point at which the needle advances and the length of time that the needle is present within the vein. Results indicated that the conditions under which it was easiest to stop the needle inside the vein were an insertion angle range of 10–20 and an insertion velocity of 3mm/s.
  
  PubDate: 2013-05-05T19:00:16Z
Measurement of transmission of vibration through the human spine using skin-mounted inertial sensors
- Abstract: Publication date: May 2013
  Source:Medical Engineering & Physics, Volume 35, Issue 5
  Author(s): Dafne Z. Morgado Ramírez , Siobhan Strike , Raymond Y.W. Lee
  The purpose of this study was to examine the feasibility of measuring the transmission of vibration using skin mounted inertial sensors and to assess the dynamic properties of the human spine during activities of daily living. Two inertial sensors were attached to skin overlying the first thoracic vertebra (T1) and another one over the first sacral vertebra (S1) with double sided adhesive tape. Subjects walked along a straight line, and up and down stairs at a self selected, comfortable speed. Transmissibility of vertical vibration was calculated as the ratio of the power spectral density of the acceleration signal at T1 over that at S1, over the frequency range of 0.5–12Hz. Cross correlation and coherence of the acceleration signals between the two T1 sensors were performed to evaluate the similarity of the data after correction. Cross correlation of signals between trials was also performed to examine the repeatability of the signals. Cross correlation coefficients were found to be very high (>0.9). Inter-trial consistency of the signals of all sensors was also high (>0.9). It is concluded that skin measurement of transmission of vertical vibration is feasible with the inertial sensors and correction method presented. Different physical activities seem to elicit different frequency characteristics of vibration.
  
  PubDate: 2013-05-05T19:00:16Z
Effect of wheelchair mass, tire type and tire pressure on physical strain and wheelchair propulsion technique
- Abstract: Publication date: Available online 1 May 2013
  Source:Medical Engineering & Physics
  Author(s): Sonja de Groot , Riemer J.K. Vegter , Lucas H.V. van der Woude
  The purpose of this study was to evaluate the effect of wheelchair mass, solid vs. pneumatic tires and tire pressure on physical strain and wheelchair propulsion technique. 11 Able-bodied participants performed 14 submaximal exercise blocks on a treadmill with a fixed speed (1.11m/s) within 3 weeks to determine the effect of tire pressure (100%, 75%, 50%, 25% of the recommended value), wheelchair mass (0kg, 5kg, or 10kg extra) and tire type (pneumatic vs. solid). All test conditions (except pneumatic vs. solid) were performed with and without instrumented measurement wheels. Outcome measures were power output (PO), physical strain (heart rate (HR), oxygen uptake (VO2), gross mechanical efficiency (ME)) and propulsion technique (timing, force application). At 25% tire pressure PO and subsequently VO2 were higher compared to 100% tire pressure. Furthermore, a higher tire pressure led to a longer cycle time and contact angle and subsequently lower push frequency. Extra mass did not lead to an increase in PO, physical strain or propulsion technique. Solid tires led to a higher PO and physical strain. The solid tire effect was amplified by increased mass (tire×mass interaction). In contrast to extra mass, tire pressure and tire type have an effect on PO, physical strain or propulsion technique of steady-state wheelchair propulsion. As expected, it is important to optimize tire pressure and tire type.
  
  PubDate: 2013-05-02T21:22:49Z
Peri-implant bone microstructure determines dynamic implant cut-out
- Abstract: Publication date: Available online 25 April 2013
  Source:Medical Engineering & Physics
  Author(s): Samuel E. Basler , John Traxler , Ralph Müller , G. Harry van Lenthe
  Dynamic implant cut-out is a frequent complication associated with surgical fracture fixation. In this in vitro study, we investigated the influence of the local trabecular bone microstructure on the rate and path of implant migration. Dynamic hip screws were implanted into six human femoral head specimens with a wide range of bone volume fractions. The specimens were subjected to image-guided failure assessment using physiological dynamic hip loading. Mechanical testing was used intermittently with high-resolution computed tomography scanning. A high correlation was found between the bone volume fraction and implant migration (R 2 =0.95). Profiles of the bone-implant interface were computed based on the positions of the screw and the femoral head. With a larger interface, the implant migration rate was smaller. The bone-implant interface was significantly smaller on the approximated screw migration path than if it had been on a straight line in loading direction. We thus hypothesize that implants migrate on a path of least resistance. This would indicate a relevant mechanism for targeted surgical intervention.
  
  PubDate: 2013-04-26T21:18:50Z
Clinical evaluation of a wireless ECG sensor system for arrhythmia diagnostic purposes
- Abstract: Available online 3 April 2013
  Publication year: 2013
  Source:Medical Engineering & Physics
  
  In a clinical study, a novel wireless electrocardiogram (ECG) recorder has been evaluated with regard to its ability to perform arrhythmia diagnostics. As the ECG recorder will detect a “non-standard” ECG signal, it has been necessary to compare those signals to “standard” ECG recording signals in order to evaluate the arrhythmia detection ability of the new system. Simultaneous recording of ECG signals from both the new wireless ECG recorder and a conventional Holter recorder was compared by two independent cardiology specialists with regard to signal quality for performing arrhythmia diagnosis. In addition, calculated R–R intervals from the two systems were correlated. A total number of 16 patients participated in the study. It can be considered that recorded ECG signals obtained from the wireless ECG system had an acceptable quality for arrhythmia diagnosis. Some of the patients used the wireless sensor while doing physical sport activities, and the quality of the recorded ECG signals made it possible to perform arrhythmia diagnostics even under such conditions. Consequently, this makes possible improvements in correlating arrhythmias to physical activities.
  
  PubDate: 2013-04-05T11:15:29Z