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  Subjects -> BIOLOGY (Total: 2590 journals)
    - BIOCHEMISTRY (192 journals)
    - BIOENGINEERING (60 journals)
    - BIOLOGY (1320 journals)
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BIOLOGY (1320 journals)            First | 4 5 6 7 8 9 10 11 | Last

Journal of Biology and Life Science     Open Access   (Followers: 2)
Journal of Biology, Agriculture and Healthcare     Open Access   (Followers: 3)
Journal of Biomechanics     Hybrid Journal   (Followers: 16)
Journal of Biomedical Discovery and Collaboration     Open Access   (Followers: 1)
Journal of Biomedical Education     Open Access   (Followers: 1)
Journal of Biomedical Informatics     Partially Free   (Followers: 13)
Journal of Biomedical Materials Research Part A     Hybrid Journal   (Followers: 1)
Journal of Biomedical Materials Research Part B : Applied Biomaterials     Hybrid Journal   (Followers: 1)
Journal of Biomedical Nanotechnology     Full-text available via subscription   (Followers: 5)
Journal of Biomedical Physics and Engineering     Open Access  
Journal of Biomedical Science and Engineering     Open Access   (Followers: 2)
Journal of Biomedical Sciences     Open Access   (Followers: 2)
Journal of Biomolecular Screening     Hybrid Journal   (Followers: 4)
Journal of Bionic Engineering     Full-text available via subscription  
Journal of Biorheology     Hybrid Journal  
Journal of Bioscience and Bioengineering     Full-text available via subscription   (Followers: 15)
Journal of Biosocial Science     Hybrid Journal   (Followers: 4)
Journal of Biotechnology and Biodiversity     Open Access  
Journal of Bryology     Hybrid Journal   (Followers: 1)
Journal of Cell and Plant Sciences     Open Access   (Followers: 3)
Journal of Cell Communication and Signaling     Hybrid Journal  
Journal of Cell Death     Open Access   (Followers: 1)
Journal of Cell Science     Full-text available via subscription   (Followers: 10)
Journal of Cellular Biochemistry     Hybrid Journal   (Followers: 3)
Journal of Cellular Physiology     Hybrid Journal   (Followers: 2)
Journal of Cerebral Blood Flow & Metabolism     Hybrid Journal   (Followers: 1)
Journal of Chromatography B     Hybrid Journal   (Followers: 15)
Journal of Clinical Bioinformatics     Open Access   (Followers: 5)
Journal of Communications Technology and Electronics     Hybrid Journal   (Followers: 1)
Journal of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 1)
Journal of Contradicting Results in Science     Open Access   (Followers: 2)
Journal of Crustacean Biology     Full-text available via subscription   (Followers: 2)
Journal of Developmental Biology     Open Access   (Followers: 2)
Journal of Ecosystems     Open Access   (Followers: 4)
Journal of Electrical Bioimpedance     Full-text available via subscription   (Followers: 2)
Journal of Electromyography and Kinesiology     Hybrid Journal   (Followers: 3)
Journal of Environment and Ecology     Open Access   (Followers: 9)
Journal of Environmental Radioactivity     Hybrid Journal   (Followers: 2)
Journal of Environmental Science and Natural Resources     Open Access   (Followers: 2)
Journal of Ethnobiology     Full-text available via subscription   (Followers: 4)
Journal of Ethnobiology and Ethnomedicine     Open Access  
Journal of Ethology     Hybrid Journal   (Followers: 1)
Journal of Evolutionary Biology     Hybrid Journal   (Followers: 18)
Journal of Experimental and Clinical Anatomy     Full-text available via subscription  
Journal of Experimental Marine Biology and Ecology     Hybrid Journal   (Followers: 23)
Journal of Fish Biology     Hybrid Journal   (Followers: 23)
Journal of Functional Biomaterials     Open Access   (Followers: 1)
Journal of Great Lakes Research     Hybrid Journal   (Followers: 7)
Journal of Health and Biological Sciences     Open Access  
Journal of Health Sciences     Open Access   (Followers: 5)
Journal of Heredity     Hybrid Journal   (Followers: 2)
Journal of Herpetology     Full-text available via subscription   (Followers: 3)
Journal of Huazhong University of Science and Technology [Medical Sciences]     Hybrid Journal  
Journal of Human Evolution     Hybrid Journal   (Followers: 9)
Journal of Hymenoptera Research     Open Access   (Followers: 2)
Journal of Ichthyology     Hybrid Journal   (Followers: 3)
Journal of Insect Behavior     Hybrid Journal   (Followers: 6)
Journal of Insect Biodiversity     Open Access   (Followers: 1)
Journal of Insect Conservation     Hybrid Journal   (Followers: 5)
Journal of Integrated OMICS     Open Access  
Journal of Integrated Pest Management     Open Access   (Followers: 2)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 3)
Journal of Intelligent Transportation Systems: Technology, Planning, and Operations     Hybrid Journal   (Followers: 5)
Journal of Invertebrate Pathology     Hybrid Journal   (Followers: 3)
Journal of Landscape Ecology     Open Access   (Followers: 5)
Journal of Law and the Biosciences     Open Access  
Journal of Leukocyte Biology     Open Access   (Followers: 5)
Journal of Life and Earth Science     Open Access  
Journal of Lipid Research     Full-text available via subscription   (Followers: 3)
Journal of Lipids     Open Access   (Followers: 1)
Journal of Luminescence     Hybrid Journal   (Followers: 2)
Journal of Mammalian Evolution     Hybrid Journal   (Followers: 5)
Journal of Mammalian Ova Research     Full-text available via subscription  
Journal of Mammalogy     Full-text available via subscription   (Followers: 5)
Journal of Mammary Gland Biology and Neoplasia     Hybrid Journal  
Journal of Marine Biology     Open Access   (Followers: 13)
Journal of Mathematical Biology     Hybrid Journal   (Followers: 12)
Journal of Mechanics in Medicine and Biology     Hybrid Journal  
Journal of Medical Primatology     Hybrid Journal   (Followers: 1)
Journal of Medical Toxicology     Hybrid Journal   (Followers: 4)
Journal of Medicine and Philosophy     Hybrid Journal   (Followers: 6)
Journal of Membrane Biology     Hybrid Journal   (Followers: 2)
Journal of Membrane Science     Hybrid Journal   (Followers: 9)
Journal of Molecular Biology     Hybrid Journal   (Followers: 27)
Journal of Molecular Biology Research     Open Access   (Followers: 1)
Journal of Molecular Catalysis B: Enzymatic     Hybrid Journal  
Journal of Molecular Cell Biology     Hybrid Journal   (Followers: 8)
Journal of Molecular Evolution     Hybrid Journal   (Followers: 8)
Journal of Molecular Signaling     Open Access  
Journal of Molecular Structure     Hybrid Journal   (Followers: 3)
Journal of Molluscan Studies     Hybrid Journal   (Followers: 2)
Journal of Muscle Research and Cell Motility     Hybrid Journal   (Followers: 1)
Journal of Nanoparticle Research     Hybrid Journal   (Followers: 3)
Journal of Natural History     Hybrid Journal   (Followers: 4)
Journal of Natural Products     Full-text available via subscription   (Followers: 8)
Journal of Natural Science, Biology and Medicine     Open Access   (Followers: 2)
Journal of Natural Sciences Research     Open Access   (Followers: 3)
Journal of Negative Results in BioMedicine     Open Access   (Followers: 2)
Journal of Nematology     Open Access   (Followers: 2)
Journal of Neuroscience and Behavioral Health     Open Access  

  First | 4 5 6 7 8 9 10 11 | Last

Journal Cover Medical Engineering & Physics
   [11 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1350-4533
     Published by Elsevier Homepage  [2563 journals]   [SJR: 0.722]   [H-I: 57]
  • Effect of an exclusion range of jaw movement data from the intercuspal
           positionon the estimation of the kinematic axis point
    • Abstract: Publication date: Available online 19 July 2014
      Source:Medical Engineering & Physics
      Author(s): Shuji Shigemoto , Nobuyuki Bando , Keisuke Nishigawa , Yoshitaka Suzuki , Toyoko Tajima , Kazuo Okura , Yoshizo Matsuka
      In patients who have lost natural occlusal contacts, the centric relation is usually estimated based on several anatomical factors such as the temporomandibular joint and masticatory muscles except dental arch. The clinical procedure to record the centric relation often depends on the clinician's expertise and technique; an objective method to determine proper occlusal position is desirable. The kinematic axis point (KAP) is kinematically estimated from sagittal movements and is an ideal posterior reference point that is used in dental articulators for reproducing jaw movement. Occlusal registration using the KAP may serve as a definite objective technique. The aim of this study is to investigate the effect of the exclusion range of sagittal jaw movement data from the intercuspal position (ICP) on the estimation of the KAP. The complete and incomplete sagittal border movement data of dentate subjects were used to estimate the KAPs. The locations of the estimated KAPs were compared. The results indicate that the incomplete sagittal border jaw movement data set does not include data points inside a 7mm distance from the ICP can be used for estimation of the KAP. In conclusion, the sagittal border jaw movement data around the ICP is not indispensable in the valid identification of the KAP.


      PubDate: 2014-07-28T01:17:01Z
       
  • Arterial pulsatility improvement in a feedback-controlled continuous flow
           left ventricular assist device: An ex-vivo experimental study
    • Abstract: Publication date: Available online 25 July 2014
      Source:Medical Engineering & Physics
      Author(s): Selim Bozkurt , Sjoerd van Tuijl , Stephanie Schampaert , Frans N. van de Vosse , Marcel C.M. Rutten
      Continuous flow left ventricular assist devices (CF-LVADs) reduce arterial pulsatility, which may cause long-term complications in the cardiovascular system. The aim of this study is to improve the pulsatility by driving a CF-LVAD at a varying speed, synchronous with the cardiac cycle in an ex-vivo experiment. A Micromed DeBakey pump was used as CF-LVAD. The heart was paced at 140bpm to obtain a constant cardiac cycle for each heartbeat. First, the CF-LVAD was operated at a constant speed. At varying-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. For synchronization purposes, an algorithm was developed to trigger the CF-LVAD each heartbeat. The pump flow rate was selected as the control variable and a reference model was used for regulating the CF-LVAD speed. Continuous and varying-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility doubled in both arterial pressure and pump flow rate signals under pulsatile pump speed support. This study shows the possibility of improving the pulsatility in CF-LVAD support by regulating pump speed over a cardiac cycle without compromising the overall level of support.


      PubDate: 2014-07-28T01:17:01Z
       
  • A neural network approach for determining gait modifications to reduce the
           contact force in knee joint implant
    • Abstract: Publication date: Available online 25 July 2014
      Source:Medical Engineering & Physics
      Author(s): Marzieh Mostafavizadeh Ardestani , Zhenxian Chen , Ling Wang , Qin Lian , Yaxiong Liu , Jiankang He , Dichen Li , Zhongmin Jin
      There is a growing interest in non-surgical gait rehabilitation treatments to reduce the loading in the knee joint. In particular, synergetic kinematic changes required for joint offloading should be determined individually for each subject. Previous studies for gait rehabilitation designs are typically relied on a “trial-and-error” approach, using multi-body dynamic (MBD) analysis. However MBD is fairly time demanding which prevents it to be used iteratively for each subject. This study employed an artificial neural network to develop a cost-effective computational framework for designing gait rehabilitation patterns. A feed forward artificial neural network (FFANN) was trained based on a number of experimental gait trials obtained from literature. The trained network was then hired to calculate the appropriate kinematic waveforms (output) needed to achieve desired knee joint loading patterns (input). An auxiliary neural network was also developed to update the ground reaction force and moment profiles with respect to the predicted kinematic waveforms. The feasibility and efficiency of the predicted kinematic patterns were then evaluated through MBD analysis. Resuls showed that FFANN-based predicted kinematics could effectively decrease the total knee joint reaction forces. Peak values of the resultant knee joint forces, with respect to the bodyweight (BW), were reduced by 20% BW and 25% BW in the midstance and the terminal stance phases. Impulse values of the knee joint loading patterns were also decreased by 17% BW*s and 24%BW*s in the corresponding phases. The FFANN-based framework suggested a cost-effective forward solution which directly calculated the kinematic variations needed to implement a given desired knee joint loading pattern. It is therefore expected that this approach provides potential advantages and further insights into knee rehabilitation designs.


      PubDate: 2014-07-28T01:17:01Z
       
  • Automatic modeling of pectus excavatum corrective prosthesis using
           artificial neural networks
    • Abstract: Publication date: Available online 26 July 2014
      Source:Medical Engineering & Physics
      Author(s): Pedro L. Rodrigues , Nuno F. Rodrigues , ACM Pinho , Jaime C. Fonseca , Jorge Correia-Pinto , João L. Vilaça
      Pectus excavatum is the most common deformity of the thorax. Pre-operative diagnosis usually includes Computed Tomography (CT) to successfully employ a thoracic prosthesis for anterior chest wall remodeling. Aiming at the elimination of radiation exposure, this paper presents a novel methodology for the replacement of CT by a 3D laser scanner (radiation-free) for prosthesis modeling. The complete elimination of CT is based on an accurate determination of ribs position and prosthesis placement region through skin surface points. The developed solution resorts to a normalized and combined outcome of an artificial neural network (ANN) set. Each ANN model was trained with data vectors from 165 male patients and using soft tissue thicknesses (STT) comprising information from the skin and rib cage (automatically determined by image processing algorithms). Tests revealed that ribs position for prosthesis placement and modeling can be estimated with an average error of 5.0±3.6mm. One also showed that the ANN performance can be improved by introducing a manually determined initial STT value in the ANN normalization procedure (average error of 2.82±0.76mm). Such error range is well below current prosthesis manual modeling (approximately 11mm), which can provide a valuable and radiation-free procedure for prosthesis personalization.


      PubDate: 2014-07-28T01:17:01Z
       
  • Biomechanical evaluation of bending strength of spinal pedicle screws,
           including cylindrical, conical, dual core and double dual core designs
           using numerical simulations and mechanical tests
    • Abstract: Publication date: Available online 21 July 2014
      Source:Medical Engineering & Physics
      Author(s): Yongyut Amaritsakul , Ching-Kong Chao , Jinn Lin
      Pedicle screws are used for treating several types of spinal injuries. Although several commercial versions are presently available, they are mostly either fully cylindrical or fully conical. In this study, the bending strengths of seven types of commercial pedicle screws and a newly designed double dual core screw were evaluated by finite element analyses and biomechanical tests. All the screws had an outer diameter of 7mm, and the biomechanical test consisted of a cantilever bending test in which a vertical point load was applied using a level arm of 45mm. The boundary and loading conditions of the biomechanical tests were applied to the model used for the finite element analyses. The results showed that only the conical screws with fixed outer diameter and the new double dual core screw could withstand 1,000,000 cycles of a 50–500N cyclic load. The new screw, however, exhibited lower stiffness than the conical screw, indicating that it could afford patients more flexible movements. Moreover, the new screw produced a level of stability comparable to that of the conical screw, and it was also significantly stronger than the other screws. The finite element analysis further revealed that the point of maximum tensile stress in the screw model was comparable to the point at which fracture occurred during the fatigue test.


      PubDate: 2014-07-28T01:17:01Z
       
  • Predicting flow in aortic dissection: Comparison of computational model
           with PC-MRI velocity measurements
    • Abstract: Publication date: Available online 26 July 2014
      Source:Medical Engineering & Physics
      Author(s): Z. Cheng , C. Juli , N.B. Wood , R.G.J. Gibbs , X.Y. Xu
      Aortic dissection is a life-threatening process in which the weakened wall develops a tear, causing separation of wall layers. The dissected layers separate the original true aortic lumen and a newly created false lumen. If untreated, the condition can be fatal. Flow rate in the false lumen is a key feature for false lumen patency, which has been regarded as one of the most important predictors of adverse early and later outcomes. Detailed flow analysis in the dissected aorta may assist vascular surgeons in making treatment decisions, but computational models to simulate flow in aortic dissections often involve several assumptions. The purpose of this study is to assess the computational models adopted in previous studies by comparison with in vivo velocity data obtained by means of phase-contrast magnetic resonance imaging (PC-MRI). Aortic dissection geometry was reconstructed from computed tomography (CT) images, while PC-MRI velocity data were used to define inflow conditions and to provide distal velocity components for comparison with the simulation results. The computational fluid dynamics (CFD) simulation incorporated a laminar–turbulent transition model, which is necessary for adequate flow simulation in aortic conditions. Velocity contours from PC-MRI and CFD in the two lumens at the distal plane were compared at four representative time points in the pulse cycle. The computational model successfully captured the complex regions of flow reversal and recirculation qualitatively, although quantitative differences exist. With a rigid wall assumption and exclusion of arch branches, the CFD model over-predicted the false lumen flow rate by 25% at peak systole. Nevertheless, an overall good agreement was achieved, confirming the physiological relevance and validity of the computational model for type B aortic dissection with a relatively stiff dissection flap.


      PubDate: 2014-07-28T01:17:01Z
       
  • An in vitro investigation of the influence of stenosis severity on the
           flow in the ascending aorta
    • Abstract: Publication date: Available online 25 July 2014
      Source:Medical Engineering & Physics
      Author(s): Utku Gülan , Beat Lüthi , Markus Holzner , Alex Liberzon , Arkady Tsinober , Wolfgang Kinzelbach
      Cardiovascular diseases can lead to abnormal blood flows, some of which are linked to hemolysis and thrombus formation. Abnormal turbulent flows of blood in the vessels with stenosis create strong shear stresses on blood elements and may cause blood cell destruction or platelet activation. We implemented a Lagrangian (following the fluid elements) measurement technique of three dimensional particle tracking velocimetry that provides insight on the evolution of viscous and turbulent stresses along blood element trajectories. We apply this method to study a pulsatile flow in a compliant phantom of an aorta and compare the results in three cases: the reference case (called “healthy” case), and two cases of abnormal flows due to mild and severe stenosis, respectively. The chosen conditions can mimic a clinical application of an abnormal flow due to a calcific valve. We estimate the effect of aortic stenosis on the kinetic energy of the mean flow and the turbulent kinetic energy, which increases about two orders of magnitude as compared with the healthy flow case. Measuring the total flow stress acting on a moving fluid element that incorporates viscous stresses and the apparent turbulent-induced stresses (the so-called Reynolds stresses) we find out similar increase of the stresses with the increased severity of the stenosis. Furthermore, these unique Lagrangian measurements provide full acceleration and, consequently, the forces acting on the blood elements that are estimated to reach the level that can considerably deform red blood cells. These forces are strong and abrupt due to the contribution of the turbulent fluctuations which is much stronger than the typically measured phase-averaged values.


      PubDate: 2014-07-28T01:17:01Z
       
  • A novel stability and kinematics-driven trunk biomechanical model to
           estimate muscle and spinal forces
    • Abstract: Publication date: Available online 26 July 2014
      Source:Medical Engineering & Physics
      Author(s): M. Hajihosseinali , N. Arjmand , A. Shirazi-Adl , F. Farahmand , M.S. Ghiasi
      An anatomically detailed eighteen-rotational-degrees-of-freedom model of the human spine using optimization constrained to equilibrium and stability requirements is developed and used to simulate several symmetric tasks in upright and flexed standing postures. Predictions of this stability and kinematics-driven (S+KD) model for trunk muscle forces and spine compressive/shear loads are compared to those of our existing kinematics-driven (KD) model where both translational and rotational degrees-of-freedom are included but redundancy is resolved using equilibrium conditions alone. Unlike the KD model, the S+KD model predicted abdominal co-contractions that, in agreement with electromyography data, increased as lifting height increased at a constant horizontal moment arm. The S+KD model, however, could not fully explain the CNS strategy in activating antagonistic muscles for most of the remaining tasks. Despite quite distinct activities in individual muscles, both models predicted L4-L5 intradiscal pressure that matched the in vivo data, the L4-S1 compression loads, and the sum of all trunk muscle forces. For modeling applications in ergonomics, where the compressive spine loads are of interest, the two models yielded <15% difference. In the field of rehabilitation, where detailed muscle forces are required, the S+KD model explained more properly the CNS strategy in activating the antagonistic muscles for some tasks.


      PubDate: 2014-07-28T01:17:01Z
       
  • Changes in dissipated energy and contact pressure after osteochondral
           graft transplantation
    • Abstract: Publication date: Available online 25 July 2014
      Source:Medical Engineering & Physics
      Author(s): Evgenij Bobrowitsch , Andrea Lorenz , Johanna Jörg , Ulf G. Leichtle , Nikolaus Wülker , Christian Walter
      Osteochondral autologous transplantation is frequently used to repair small cartilage defects. Incongruence between the osteochondral graft surface and the adjacent cartilage leads to changed friction and contact pressure. The present study wanted to analyze the differences between intact and surgically treated cartilage surface in respect to contact pressure and frictional characteristic (dissipated energy). Six ovine carpometacarpal joints were used in the present study. Dissipated energy during instrumentally controlled joint movement as well as static contact pressure were measured in different cartilage states (intact, defect, deep-, flush-, high-implanted osteochondral graft and cartilage failure simulation on a high-implanted graft). The best contact area restoration was observed after the flush implantation. However, the dissipated energy measurements did not reveal an advantage of the flush implantation compared to the defect and deep-implanted graft states. The high-implanted graft was associated with a significant increase of the mean contact pressure and decrease of the contact area but the dissipated energy was on the level of intact cartilage in contrast to other treatments where the dissipated energy was significantly higher as in the intact state. However the cartilage failure simulation on the high-implanted graft showed the highest increase of the dissipated energy.


      PubDate: 2014-07-28T01:17:01Z
       
  • Baseline drift removal and denoising of MCG data using EEMD: Role of noise
           amplitude and the thresholding effect
    • Abstract: Publication date: Available online 26 July 2014
      Source:Medical Engineering & Physics
      Author(s): N. Mariyappa , S. Sengottuvel , C. Parasakthi , K. Gireesan , M.P. Janawadkar , T.S. Radhakrishnan , C.S. Sundar
      We adopt the Ensemble Empirical Mode Decomposition (EEMD) method, with an appropriate thresholding on the Intrinsic Mode Functions (IMFs), to denoise the magnetocardiography (MCG) signal. To this end, we discuss the two associated problems that relate to: (i) the amplitude of noise added to the observed signal in the EEMD method with a view to prevent mode mixing and (ii) the effect of direct thresholding that causes discontinuities in the reconstructed denoised signal. We then denoise the MCG signals, having various signal-to-noise ratios, by using this method and compare the results with those obtained by the standard wavelet based denoising method. We also address the problem of eliminating the high frequency baseline drift such as the sudden and discontinuous changes in the baseline of the experimentally measured MCG signal using the EEMD based method. We show that the EEMD method used for denoising and the elimination of baseline drift is superior in performance to other standard methods such as wavelet based techniques and Independent Component Analysis (ICA).


      PubDate: 2014-07-28T01:17:01Z
       
  • Screening of obstructive sleep apnea with empirical mode decomposition of
           pulse oximetry
    • Abstract: Publication date: August 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 8
      Author(s): Gastón Schlotthauer , Leandro E. Di Persia , Luis D. Larrateguy , Diego H. Milone
      Detection of desaturations on the pulse oximetry signal is of great importance for the diagnosis of sleep apneas. Using the counting of desaturations, an index can be built to help in the diagnosis of severe cases of obstructive sleep apnea–hypopnea syndrome. It is important to have automatic detection methods that allows the screening for this syndrome, reducing the need of the expensive polysomnography based studies. In this paper a novel recognition method based on the empirical mode decomposition of the pulse oximetry signal is proposed. The desaturations produce a very specific wave pattern that is extracted in the modes of the decomposition. Using this information, a detector based on properly selected thresholds and a set of simple rules is built. The oxygen desaturation index constructed from these detections produces a detector for obstructive sleep apnea–hypopnea syndrome with high sensitivity (0.838) and specificity (0.855) and yields better results than standard desaturation detection approaches.


      PubDate: 2014-07-28T01:17:01Z
       
  • Subject-specific evaluation of patellofemoral joint biomechanics during
           functional activity
    • Abstract: Publication date: Available online 3 July 2014
      Source:Medical Engineering & Physics
      Author(s): Massoud Akbarshahi , Justin W. Fernandez , Anthony G. Schache , Marcus G. Pandy
      Patellofemoral joint pain is a common problem experienced by active adults. However, relatively little is known about patellofemoral joint load and its distribution across the medial and lateral facets of the patella. In this study, biomechanical experiments and computational modeling were used to study patellofemoral contact mechanics in four healthy adults during stair ambulation. Subject-specific anatomical and gait data were recorded using magnetic resonance imaging, dynamic X-ray fluoroscopy, video motion capture, and multiple force platforms. From these data, in vivo tibiofemoral joint kinematics and knee muscle forces were computed and then applied to a deformable finite-element model of the patellofemoral joint. The contact force acting on the lateral facet of the patella was 4–6 times higher than that acting on the medial facet. The peak average patellofemoral contact stresses were 8.2±1.0MPa and 5.9±1.3MPa for the lateral and medial patellar facets, respectively. Peak normal compressive stress and peak octahedral shear stress occurred near toe-off of the contralateral leg and were higher on the lateral facet than the medial facet; furthermore, the peak compressive stress (11.5±3.0MPa) was higher than the peak octahedral shear stress (5.2±0.9MPa). The dominant stress pattern on the lateral patellar facet corresponded well to the location of maximum cartilage thickness. Higher loading of the lateral facet is also consistent with the clinical observation that the lateral compartment of the patellofemoral joint is more prone to osteoarthritis than the medial compartment. Predicted cartilage contact stress maps near contralateral toe-off showed three distinctly different patterns: peak stresses located on the lateral patellar facet; peak stresses located centrally between the medial and lateral patellar facets; and peak stresses located superiorly on both the medial and lateral patellar facets.


      PubDate: 2014-07-28T01:17:01Z
       
  • Exploiting parameter sparsity in model-based reconstruction to accelerate
           proton density and T2 mapping
    • Abstract: Publication date: Available online 3 July 2014
      Source:Medical Engineering & Physics
      Author(s): Xi Peng , Xin Liu , Hairong Zheng , Dong Liang
      T2 mapping is a powerful noninvasive technique providing quantitative biological information of the inherent tissue properties. However, its clinical usage is limited due to the relative long scanning time. This paper proposed a novel model-based method to address this problem. Typically, we directly estimated the relaxation values from undersampled k-space data by exploiting the sparse property of proton density and T2 map in a penalized maximum likelihood formulation. An alternating minimization approach was presented to estimate the relaxation maps separately. Both numerical phantom and in vivo experiment dataset were used to demonstrate the performance of the proposed method. We showed that the proposed method outperformed the state-of-the-art techniques in terms of detail preservation and artifact suppression with various reduction factors and in both moderate and heavy noise circumstances. The superior reconstruction performance validated its promising potential in fast T2 mapping applications.


      PubDate: 2014-07-28T01:17:01Z
       
  • Computational fluid dynamics analysis of balloon-expandable coronary
           stents: Influence of stent and vessel deformation
    • Abstract: Publication date: August 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 8
      Author(s): David M. Martin , Eoin A. Murphy , Fergal J. Boyle
      In many computational fluid dynamics (CFD) studies of stented vessel haemodynamics, the geometry of the stented vessel is described using non-deformed (NDF) geometrical models. These NDF models neglect complex physical features, such as stent and vessel deformation, which may have a major impact on the haemodynamic environment in stented coronary arteries. In this study, CFD analyses were carried out to simulate pulsatile flow conditions in both NDF and realistically-deformed (RDF) models of three stented coronary arteries. While the NDF models were completely idealised, the RDF models were obtained from nonlinear structural analyses and accounted for both stent and vessel deformation. Following the completion of the CFD analyses, major differences were observed in the time-averaged wall shear stress (TAWSS), time-averaged wall shear stress gradient (TAWSSG) and oscillatory shear index (OSI) distributions predicted on the luminal surface of the artery for the NDF and RDF models. Specifically, the inclusion of stent and vessel deformation in the CFD analyses resulted in a 32%, 30% and 31% increase in the area-weighted mean TAWSS, a 3%, 7% and 16% increase in the area-weighted mean TAWSSG and a 21%, 13% and 21% decrease in the area-weighted mean OSI for Stents A, B and C, respectively. These results suggest that stent and vessel deformation are likely to have a major impact on the haemodynamic environment in stented coronary arteries. In light of this observation, it is recommended that these features are considered in future CFD studies of stented vessel haemodynamics.


      PubDate: 2014-07-28T01:17:01Z
       
  • Characterization of a CMOS sensing core for ultra-miniature wireless
           implantable temperature sensors with application to cryomedicine
    • Abstract: Publication date: Available online 4 July 2014
      Source:Medical Engineering & Physics
      Author(s): Ahmad Khairi , Chandrajit Thaokar , Gary Fedder , Jeyanandh Paramesh , Yoed Rabin
      In effort to improve thermal control in minimally invasive cryosurgery, the concept of a miniature, wireless, implantable sensing unit has been developed recently. The sensing unit integrates a wireless power delivery mechanism, wireless communication means, and a sensing core—the subject matter of the current study. The current study presents a CMOS ultra-miniature PTAT temperature sensing core and focuses on design principles, fabrication of a proof-of-concept, and characterization in a cryogenic environment. For this purpose, a 100μm×400μm sensing core prototype has been fabricated using a 130nm CMOS process. The senor has shown to operate between −180°C and room temperature, to consume power of less than 1μW, and to have an uncertainty range of 1.4°C and non-linearity of 1.1%. Results of this study suggest that the sensing core is ready to be integrated in the sensing unit, where system integration is the subject matter of a parallel effort.


      PubDate: 2014-07-28T01:17:01Z
       
  • Inter-scanner differences in in vivo QCT measurements of the density and
           strength of the proximal femur remain after correction with
           anthropomorphic standardization phantoms
    • Abstract: Publication date: Available online 4 July 2014
      Source:Medical Engineering & Physics
      Author(s): R. Dana Carpenter , Isra Saeed , Serena Bonaretti , Carole Schreck , Joyce H. Keyak , Timothy Streeper , Tamara B. Harris , Thomas F. Lang
      In multicenter studies and longitudinal studies that use two or more different quantitative computed tomography (QCT) imaging systems, anthropomorphic standardization phantoms (ASPs) are used to correct inter-scanner differences and allow pooling of data. In this study, in vivo imaging of 20 women on two imaging systems was used to evaluate inter-scanner differences in hip integral BMD (iBMD), trabecular BMD (tBMD), cortical BMD (cBMD), femoral neck yield moment (M y ) and yield force (F y ), and finite-element derived strength of the femur under stance (FEstance) and fall (FEfall) loading. Six different ASPs were used to derive inter-scanner correction equations. Significant (p <0.05) inter-scanner differences were detected in all measurements except M y and FEfall, and no ASP-based correction was able to reduce inter-scanner variability to corresponding levels of intra-scanner precision. Inter-scanner variability was considerably higher than intra-scanner precision, even in cases where the mean inter-scanner difference was statistically insignificant. A significant (p <0.01) effect of body size on inter-scanner differences in BMD was detected, demonstrating a need to address the effects of body size on QCT measurements. The results of this study show that significant inter-scanner differences in QCT-based measurements of BMD and bone strength can remain even when using an ASP.


      PubDate: 2014-07-28T01:17:01Z
       
  • An MRI compatible loading device for the reconstruction of clinically
           relevant plantar pressure distributions and loading scenarios of the
           forefoot
    • Abstract: Publication date: Available online 7 July 2014
      Source:Medical Engineering & Physics
      Author(s): Panagiotis E. Chatzistergos , Roozbeh Naemi , Nachiappan Chockalingam
      The purpose of this study is to demonstrate a new MRI compatible loading device capable of reconstructing realistic loading scenarios of the human foot for research in the field of foot biomechanics. This device has two different configurations: one used to compress the forefoot and one to bend the metatarsophalangeal joints. Required plantar pressure distribution under the metatarsal heads can be achieved by modifying the distribution of the dorsally applied forces. To validate the device, subject-specific plantar pressures were measured and then reconstructed using the device. For quiet stance the peak pressure reconstruction error was 3% while for mid-stance phase of gait it was 8%. The device was also used to measure the passive bending stiffness of the metatarsophalangeal joints of one subject with low intra-subject variability. A series of preliminary MRI scans confirmed that the loading device can be used to produce static weight-bearing images of the foot (voxel size: 0.23mm×0.23mm×1.00mm). The results indicate that the device presented here can accurately reconstruct subject specific plantar pressure distributions and measure the foot's metatarsophalangeal passive stiffness. Possible future applications include the validation of finite element models, the investigation of the relationship between plantar pressure and internal stresses/strains and the study of the foot's inter-segmental passive stiffness.


      PubDate: 2014-07-28T01:17:01Z
       
  • Fast computation of voxel-level brain connectivity maps from resting-state
           functional MRI using l1-norm as approximation of Pearson's temporal
           correlation: Proof-of-concept and example vector hardware implementation
    • Abstract: Publication date: Available online 8 July 2014
      Source:Medical Engineering & Physics
      Author(s): Ludovico Minati , Domenico Zacà , Ludovico D’Incerti , Jorge Jovicich
      An outstanding issue in graph-based analysis of resting-state functional MRI is choice of network nodes. Individual consideration of entire brain voxels may represent a less biased approach than parcellating the cortex according to pre-determined atlases, but entails establishing connectedness for 19–111 links, with often prohibitive computational cost. Using a representative Human Connectome Project dataset, we show that, following appropriate time-series normalization, it may be possible to accelerate connectivity determination replacing Pearson correlation with l1-norm. Even though the adjacency matrices derived from correlation coefficients and l1-norms are not identical, their similarity is high. Further, we describe and provide in full an example vector hardware implementation of l1-norm on an array of 4096 zero instruction-set processors. Calculation times <1000s are attainable, removing the major deterrent to voxel-based resting-sate network mapping and revealing fine-grained node degree heterogeneity. L1-norm should be given consideration as a substitute for correlation in very high-density resting-state functional connectivity analyses.


      PubDate: 2014-07-28T01:17:01Z
       
  • A tissue stabilization device for MRI-guided breast biopsy
    • Abstract: Publication date: Available online 8 July 2014
      Source:Medical Engineering & Physics
      Author(s): Alexandru Patriciu , Maggie Chen , Behzad Iranpanah , Shahin Sirouspour
      We present a breast tissue stabilization device that can be used in magnetic resonance imaging-guided biopsy. The device employs adjustable support plates with an optimized geometry to minimize the biopsy target displacement using smaller compression than the conventional parallel plates approach. It is expected that the reduced compression will cause less patient discomfort and improve image quality by enhancing the contrast intake. Precomputed optimal positions of the stabilization plates for a given biopsy target location are provided in a look-up table. The results of several experiments with a prototype of the device carried out on chicken breast tissue demonstrate the effectiveness of the new design when compared with conventional stabilization methods. The proposed stabilization mechanism provides excellent flexibility in selecting the needle insertion point and can be used in manual as well as robot-assisted biopsy procedures.


      PubDate: 2014-07-28T01:17:01Z
       
  • Soft wearable contact lens sensor for continuous intraocular pressure
           monitoring
    • Abstract: Publication date: Available online 14 July 2014
      Source:Medical Engineering & Physics
      Author(s): Guo-Zhen Chen , Ion-Seng Chan , Leo K.K. Leung , David C.C. Lam
      Intraocular pressure (IOP) is a primary indicator of glaucoma, but measurements from a single visit to the clinic miss the peak IOP that may occur at night during sleep. A soft chipless contact lens sensor that allows the IOP to be monitored throughout the day and at night is developed in this study. A resonance circuit composed of a thin film capacitor coupled with a sensing coil that can sense corneal curvature deformation is designed, fabricated and embedded into a soft contact lens. The resonance frequency of the sensor is designed to vary with the lens curvature as it changes with the IOP. The frequency responses and the ability of the sensor to track IOP cycles were tested using a silicone rubber model eye. The results showed that the sensor has excellent linearity with a frequency response of ∼8kHz/mmHg, and the sensor can accurately track fluctuating IOP. These results showed that the chipless contact lens sensor can potentially be used to monitor IOP to improve diagnosis accuracy and treatment of glaucoma.


      PubDate: 2014-07-28T01:17:01Z
       
  • Design of tissue engineering scaffolds based on hyperbolic surfaces:
           Structural numerical evaluation
    • Abstract: Publication date: August 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 8
      Author(s): Henrique A. Almeida , Paulo J. Bártolo
      Tissue engineering represents a new field aiming at developing biological substitutes to restore, maintain, or improve tissue functions. In this approach, scaffolds provide a temporary mechanical and vascular support for tissue regeneration while tissue in-growth is being formed. These scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and distribution, and optimal vascularization with both surface and structural compatibility. The challenge is to establish a proper balance between porosity and mechanical performance of scaffolds. This work investigates the use of two different types of triple periodic minimal surfaces, Schwarz and Schoen, in order to design better biomimetic scaffolds with high surface-to-volume ratio, high porosity and good mechanical properties. The mechanical behaviour of these structures is assessed through the finite element method software Abaqus. The effect of two parametric parameters (thickness and surface radius) is also evaluated regarding its porosity and mechanical behaviour.


      PubDate: 2014-07-28T01:17:01Z
       
  • Early detection of abnormal left ventricular relaxation in acute
           myocardial ischemia with a quadratic model
    • Abstract: Publication date: Available online 16 July 2014
      Source:Medical Engineering & Physics
      Author(s): Philippe Morimont , Antoine Pironet , Thomas Desaive , Geoffrey Chase , Bernard Lambermont
      Aims The time constant of left ventricular (LV) relaxation derived from a monoexponential model is widely used as an index of LV relaxation rate, although this model does not reflect the non-uniformity of ventricular relaxation. This study investigates whether the relaxation curve can be better fitted with a “quadratic” model than with the “conventional” monoexponential model and if changes in the LV relaxation waveform due to acute myocardial ischemia could be better detected with the quadratic model. Methods and results Isovolumic relaxation was assessed with quadratic and conventional models during acute myocardial ischemia performed in 6 anesthetized pigs. Mathematical development indicates that one parameter (Tq) of the quadratic model reflects the rate of LV relaxation, while the second parameter (K) modifies the shape of the relaxation curve. Analysis of experimental data obtained in anesthetized pigs showed that the shape of LV relaxation consistently deviates from the conventional monoexponential decay. During the early phase of acute myocardial ischemia, the rate and non-uniformity of LV relaxation, assessed with the quadratic function, were significantly enhanced. Tq increased by 16% (p <0.001) and K increased by 12% (p <0.001) within 30 and 60min, respectively, after left anterior descending (LAD) coronary artery occlusion. However, no significant changes were observed with the conventional monoexponential decay within 60min of ischemia. Conclusions The quadratic model better fits LV isovolumic relaxation than the monoexponential model and can detect early changes in relaxation due to acute myocardial ischemia that are not detectable with conventional methods.


      PubDate: 2014-07-28T01:17:01Z
       
  • Low torque levels can initiate a removal of the passivation layer and
           cause fretting in modular hip stems
    • Abstract: Publication date: Available online 19 July 2014
      Source:Medical Engineering & Physics
      Author(s): S.Y. Jauch , L.G. Coles , L.V. Ng , A.W. Miles , H.S. Gill
      Taper connections of modular hip prostheses are at risk of fretting and corrosion, which can result in reduced implant survival. The purpose of this study was to identify the minimum torque required to initiate a removal of the passivation layer at the taper interface as a function of assembly force and axial load. Titanium stems and cobalt–chromium heads were assembled with peak impaction forces of 4.5kN or 6.0kN and then mounted on a materials testing machine whilst immersed in Ringer's solution. The stems were subjected to a static axial load (1kN or 3kN) along the taper axis. After a period of equilibration, a torque ramp from 0 to 15Nm was manually applied and the galvanic potential was continuously recorded. Prostheses assembled with a force of 6kN required a significantly higher torque to start a removal of the passivation layer compared to those assembled with 4.5kN (7.23±0.55Nm vs. 3.92±0.97Nm, p =0.029). No influence of the axial load on the fretting behaviour was found (p =0.486). The torque levels, which were demonstrated to initiate surface damage under either assembly force, can be readily reached during activities of daily living. The damage will be intensified in situations of large weight and high activity of the patient or malpositioning of the prosthesis.


      PubDate: 2014-07-28T01:17:01Z
       
  • Editorial Board
    • Abstract: Publication date: August 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 8




      PubDate: 2014-07-28T01:17:01Z
       
  • The effects of implant angulation on the resonance frequency of a dental
           implant
    • Abstract: Publication date: August 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 8
      Author(s): R. Harirforoush , S. Arzanpour , B. Chehroudi
      Dental implants are ideally placed in an orientation that allows vertical transfer of occlusal forces along their long axis. Nevertheless, optimal situations for implant placement are seldom encountered resulting in implants placement in angulated positions, which may affect their long-term success. The resonance frequency (RF) is an objective tool used to monitor stability of the implant tissue integration; however, little is known of the effect of the implant orientation in bone on the RF and its potential significance. The purpose of this research was to determine the relation between the dental implant orientation and the corresponding RF of implant. Three-dimensional (3D) modelling software was used to construct a 3D model of a pig mandible from computed tomography (CT) images. The RF of the implant was analysed using finite element (FE) modal analysis in software ANSYS (v.12). In addition, a cubical model was also developed in MIMICS to investigate the parameters affecting the relationship between RF and implant orientation in a simplified environment. The orientation angle was increased from 0 to 10 degrees in 1 degree increments and the resulting RF was analysed using correlation analysis and one-way ANOVA. Our analysis illustrated that the RF fluctuation following altering implant orientation was strongly correlated (r =0.97) with the contacting cortical to cancellous bone ratio (CCBR) at the implant interface. The most extreme RF change (from 9.81kHz to 10.07kHz) occurred when the implant was moved 0.5mm in positive z-direction, which resulted in the maximum change of CCBR from 52.9 to 54.8.


      PubDate: 2014-07-28T01:17:01Z
       
  • Prediction of structural failure of tibial bone models under physiological
           loads: Effect of CT density–modulus relationships
    • Abstract: Publication date: Available online 3 June 2014
      Source:Medical Engineering & Physics
      Author(s): Mahmut Tuncer , Ulrich N. Hansen , Andrew A. Amis
      Although finite element (FE) models can provide distinct benefits in understanding knee biomechanics, in particular the response of the knee to implants, their usefulness is limited by the modelling assumptions and input parameters. This study highlights the uncertainty of material input parameters derived from the literature and its limitation on the accuracy and usefulness of FE models of the tibia. An FE model of the intact human knee and a database of knee forces (muscles, ligaments and medial and lateral tibio-femoral contacts) were developed for walking and stair-descent activities. Ten models were constructed from ten different combinations of apparent bone density to elastic modulus material property relationships, published in the literature. Some of the published material property relationships led to predictions of bone strains in the proximal tibia which exceeded published failure criteria under loads imposed by normal activities. These relationships appear not to be applicable for the human tibia. There is a large discrepancy in proposed relationships that cover the cancellous bone density range. For FE models of the human tibia, the material relationship proposed by Morgan et al., which assumed species and anatomic site dependence, produced the most believable results for cancellous bone. In addition to casting doubt on the use of some of the published density–modulus relationships for analysis of the human proximal tibia, this study highlights the need for further experimental work to characterise the behaviour of bone with intermediate densities.


      PubDate: 2014-06-10T18:38:57Z
       
  • Evaluation of a CT-based technique to measure the transfer accuracy of a
           virtually planned osteotomy
    • Abstract: Publication date: Available online 6 June 2014
      Source:Medical Engineering & Physics
      Author(s): J.G.G. Dobbe , A.J. Kievit , M.U. Schafroth , L. Blankevoort , G.J. Streekstra
      Accurate transfer of a preoperatively planned osteotomy plane to the bone is of significance for corrective surgery, tumor resection, implant positioning and evaluation of new osteotomy techniques. Methods for comparing a preoperatively planned osteotomy plane with a surgical cut exist but the accuracy of these techniques are either limited or unknown. This paper proposes and evaluates a CT-based technique that enables comparing virtual with actual osteotomy planes. The methodological accuracy and reproducibility of the technique is evaluated using CT-derived volume data of a cadaver limb, which serves to plan TKA osteotomies in 3-D space and to simulate perfect osteotomies not hampered by surgical errors. The methodological variability of the technique is further investigated with repeated CT scans after actual osteotomy surgery of the same cadaver specimen. Plane displacement (d err ) and angulation errors in the sagittal and coronal plane (β err , γ err ) are measured with high accuracy and reproducibility (d err =−0.11±0.06mm; β err =0.08±0.04°, γ err =−0.03±0.03°). The proposed method for evaluating an osteotomy plane position and orientation has a high intrinsic accuracy and reproducibility. The method can be of great value for measuring the transfer accuracy of new techniques for positioning and orienting a surgical cut in 3-D space.


      PubDate: 2014-06-10T18:38:57Z
       
  • A viscoelastic poromechanical model of the knee joint in large compression
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): M. Kazemi , L.P. Li
      The elastic response of the knee joint in various loading and pathological conditions has been investigated using anatomically accurate geometry. However, it is still challenging to predict the poromechanical response of the knee in realistic loading conditions. In the present study, a viscoelastic, poromechanical model of the knee joint was developed for soft tissues undergoing large deformation. Cartilages and menisci were modeled as fibril-reinforced porous materials and ligaments were considered as fibril-reinforced hyperelastic solids. Quasi-linear viscoelasticty was formulated for the collagen network of these tissues and nearly incompressible Neo-Hookean hyperelasticity was used for the non-fibrillar matrix. The constitutive model was coded with a user defined FORTRAN subroutine, in order to use ABAQUS for the finite element analysis. Creep and stress relaxation were investigated with large compression of the knee in full extension. The contact pressure distributions were found similar in creep and stress relaxation. However, the load transfer in the joint was completely different in these two loading scenarios. During creep, the contact pressure between cartilages decreased but the pressure between cartilage and meniscus increased with time. This led to a gradual transfer of some loading from the central part of cartilages to menisci. During stress relaxation, however, both contact pressures decreased monotonically.


      PubDate: 2014-06-10T18:38:57Z
       
  • In vivo application of an optical segment tracking approach for bone
           loading regimes recording in humans: A reliability study
    • Abstract: Publication date: Available online 3 June 2014
      Source:Medical Engineering & Physics
      Author(s): Peng-Fei Yang , Maximilian Sanno , Bergita Ganse , Timmo Koy , Gert-Peter Brüggemann , Lars Peter Müller , Jörn Rittweger
      This paper demonstrates an optical segment tracking (OST) approach for assessing the in vivo bone loading regimes in humans. The relative movement between retro-reflective marker clusters affixed to the tibia cortex by bone screws was tracked and expressed as tibia loading regimes in terms of segment deformation. Stable in vivo fixation of bone screws was tested by assessing the resonance frequency of the screw-marker structure and the relative marker position changes after hopping and jumping. Tibia deformation was recorded during squatting exercises to demonstrate the reliability of the OST approach. Results indicated that the resonance frequencies remain unchanged prior to and after all exercises. The changes of Cardan angle between marker clusters induced by the exercises were rather minor, maximally 0.06°. The reproducibility of the deformation angles during squatting remained small (0.04°/m–0.65°/m). Most importantly, all surgical and testing procedures were well tolerated. The OST method promises to bring more insights of the mechanical loading acting on bone than in the past.


      PubDate: 2014-06-10T18:38:57Z
       
  • Validation of a numerical FSI simulation of an aortic BMHV by in vitro PIV
           experiments
    • Abstract: Publication date: Available online 10 June 2014
      Source:Medical Engineering & Physics
      Author(s): S. Annerel , T. Claessens , J. Degroote , P. Segers , J. Vierendeels
      In this paper, a validation of a recently developed fluid–structure interaction (FSI) coupling algorithm to simulate numerically the dynamics of an aortic bileaflet mechanical heart valve (BMHV) is performed. This validation is done by comparing the numerical simulation results with in vitro experiments. For the in vitro experiments, the leaflet kinematics and flow fields are obtained via the particle image velocimetry (PIV) technique. Subsequently, the same case is numerically simulated by the coupling algorithm and the resulting leaflet kinematics and flow fields are obtained. Finally, the results are compared, revealing great similarity in leaflet motion and flow fields between the numerical simulation and the experimental test. Therefore, it is concluded that the developed algorithm is able to capture very accurately all the major leaflet kinematics and dynamics and can be used to study and optimize the design of BMHVs.


      PubDate: 2014-06-10T18:38:57Z
       
  • Fatigue behaviour of Nitinol peripheral stents: The role of plaque shape
           studied with computational structural analyses
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Elena Dordoni , Alessio Meoli , Wei Wu , Gabriele Dubini , Francesco Migliavacca , Giancarlo Pennati , Lorenza Petrini
      Fatigue resistance of Nitinol stents implanted into femoro-popliteal arteries is a critical issue for the particular biomechanical environment of this district. Hip and knee joint movements due to the cyclic daily activity expose the superficial femoral artery (SFA), and therefore the implanted stents, to quite large and cyclic deformations influencing stent fatigue resistance. Objective of this work is to provide a tool based on finite element analysis able to evaluate the biomechanical effect of SFA on stent fatigue resistance. Computer simulations of the treatment of stenotic vessel by angioplasty and stenting and of the subsequent in vivo loading conditions (axial compression and bending) were carried out. Three different stenotic vessel models were defined, by keeping a constant stenosis rate and changing the plaque sharpness and number of stenoses. The fatigue behaviour was analysed comparing the amplitude and mean value distribution of the first principal strain in the whole stent for the different simulated conditions. Results showed that the maximum mean strain is similar in all the models, while the alternating strain is related to both plaque shape and loading conditions. In conclusion, this study confirms the requisite of replicating in vivo loading conditions. It also reveals the importance of taking into account the thickness variation of the vessel in the stenotic zone in the assessment of the stent fatigue resistance.


      PubDate: 2014-06-03T12:08:17Z
       
  • Automation of a portable extracorporeal circulatory support system with
           adaptive fuzzy controllers
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): A. Mendoza García , M. Krane , B. Baumgartner , N. Sprunk , U. Schreiber , S. Eichhorn , R. Lange , A. Knoll
      The presented work relates to the procedure followed for the automation of a portable extracorporeal circulatory support system. Such a device may help increase the chances of survival after suffering from cardiogenic shock outside the hospital, additionally a controller can provide of optimal organ perfusion, while reducing the workload of the operator. Animal experiments were carried out for the acquisition of haemodynamic behaviour of the body under extracorporeal circulation. A mathematical model was constructed based on the experimental data, including a cardiovascular model, gas exchange and the administration of medication. As the base of the controller fuzzy logic was used allowing the easy integration of knowledge from trained perfusionists, an adaptive mechanism was included to adapt to the patient's individual response. Initial simulations show the effectiveness of the controller and the improvements of perfusion after adaptation.


      PubDate: 2014-06-03T12:08:17Z
       
  • Hemodynamics in the cephalic arch of a brachiocephalic fistula
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): M. Boghosian , K. Cassel , M. Hammes , B. Funaki , S. Kim , X. Qian , X. Wang , P. Dhar , J. Hines
      The care and outcome of patients with end stage renal disease (ESRD) on chronic hemodialysis is directly dependent on their hemodialysis access. A brachiocephalic fistula (BCF) is commonly placed in the elderly and in patients with a failed lower-arm, or radiocephalic, fistula. However, there are numerous complications such that the BCF has an average patency of only 3.6 years. A leading cause of BCF dysfunction and failure is stenosis in the arch of the cephalic vein near its junction with the axillary vein, which is called cephalic arch stenosis (CAS). Using a combined clinical and computational investigation, we seek to improve our understanding of the cause of CAS, and to develop a means of predicting CAS risk in patients with a planned BCF access. This paper details the methodology used to determine the hemodynamic consequences of the post-fistula environment and illustrates detailed results for a representative sample of patient-specific anatomies, including a single, bifurcated, and trifurcated arch. It is found that the high flows present due to fistula creation lead to secondary flows in the arch owing to its curvature with corresponding low wall shear stresses. The abnormally low wall shear stress locations correlate with the development of stenosis in the singular case that is tracked in time for a period of one year.


      PubDate: 2014-06-03T12:08:17Z
       
  • Analysis of the effects of surface stiffness on the contact interaction
           between a finger and a cylindrical handle using a three-dimensional hybrid
           model
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): John Z. Wu , Ren G. Dong , Christopher M. Warren , Daniel E. Welcome , Thomas W. McDowell
      Contact interactions between the hand and handle, such as the contact surface softness and contact surface curvature, will affect both physical effort and musculoskeletal fatigue, thereby the comfort and safety of power tool operations. Previous models of hand gripping can be categorized into two groups: multi-body dynamic models and finite element (FE) models. The goal of the current study is to develop a hybrid FE hand gripping model, which combines the features of conventional FE models and multi-body dynamic models. The proposed model is applied to simulate hand-gripping on a cylindrical handle with covering materials of different softness levels. The model included three finger segments (distal, middle, and proximal phalanxes), three finger joints (the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joint), and major anatomical substructures. The model was driven by joint moments, which are the net effects of all passive and active muscular forces acting about the joints. The finger model was first calibrated by using experimental data of human subject tests, and then applied to investigate the effects of surface softness on contact interactions between a finger and a cylindrical handle. Our results show that the maximal compressive stress and strain in the soft tissues of the fingers can be effectively reduced by reducing the stiffness of the covering material.


      PubDate: 2014-06-03T12:08:17Z
       
  • Bioelectric signal detrending using smoothness prior approach
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): Fan Zhang , Shixiong Chen , Haoshi Zhang , Xiufeng Zhang , Guanglin Li
      Bioelectric signals such as electromyogram (EMG) and electrocardiogram (ECG) are often affected by various low-frequency trending interferences. It is critical to remove these interferences from the recordings so that the critical features of the bioelectric signals could be clearly observed. In this study, an advanced method based on smoothness prior approach (SPA) was proposed to solve this problem. EMG and ECG signals from both the MIT-BIH database and the experiments were employed to evaluate the detrending performance of the proposed method. For comparison purposes, a conventional high-pass Butterworth filter was also used for the detrending of the EMG and ECG signals. Two numerical measures, the correlation coefficient (CC) and root mean square error (RMSE) between the clean data and the detrended data, were calculated to evaluate the detrending performance. The results showed that the proposed SPA method outperformed the high-pass filtering method in reducing various kinds of trending interferences and preserving the desired frequency contents of the EMG and ECG signals. The study suggested that the SPA method might be a promising approach in detrending bioelectric signals.


      PubDate: 2014-06-03T12:08:17Z
       
  • A new paradigm of electrical stimulation to enhance sensory neural
           function
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): Paul P. Breen , Gearóid ÓLaighin , Caroline McIntosh , Sean F. Dinneen , Leo R. Quinlan , Jorge M. Serrador
      The ability to improve peripheral neural transmission would have significant therapeutic potential in medicine. A technology of this kind could be used to restore and/or enhance sensory function in individuals with depressed sensory function, such as older adults or patients with peripheral neuropathies. The goal of this study was to investigate if a new paradigm of subsensory electrical noise stimulation enhances somatosensory function. Vibration (50Hz) was applied with a Neurothesiometer to the plantar aspect of the foot in the presence or absence of subsensory electrical noise (1/f type). The noise was applied at a proximal site, on a defined region of the tibial nerve path above the ankle. Vibration perception thresholds (VPT) of younger adults were measured in control and experimental conditions, in the absence or presence of noise respectively. An improvement of ∼16% in VPT was found in the presence of noise. These are the first data to demonstrate that modulation of axonal transmission with externally applied electrical noise improves perception of tactile stimuli in humans.


      PubDate: 2014-06-03T12:08:17Z
       
  • Non-intrusive real-time breathing pattern detection and classification for
           automatic abdominal functional electrical stimulation
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): E.J. McCaughey , A.J. McLachlan , H. Gollee
      Abdominal Functional Electrical Stimulation (AFES) has been shown to improve the respiratory function of people with tetraplegia. The effectiveness of AFES can be enhanced by using different stimulation parameters for quiet breathing and coughing. The signal from a spirometer, coupled with a facemask, has previously been used to differentiate between these breath types. In this study, the suitability of less intrusive sensors was investigated with able-bodied volunteers. Signals from two respiratory effort belts, positioned around the chest and the abdomen, were used with a Support Vector Machine (SVM) algorithm, trained on a participant by participant basis, to classify, in real-time, respiratory activity as either quiet breathing or coughing. This was compared with the classification accuracy achieved using a spirometer signal and an SVM. The signal from the belt positioned around the chest provided an acceptable classification performance compared to the signal from a spirometer (mean cough (c) and quiet breath (q) sensitivity (Se) of Se c =92.9% and Se q =96.1% vs. Se c =90.7% and Se q =98.9%). The abdominal belt and a combination of both belt signals resulted in lower classification accuracy. We suggest that this novel SVM classification algorithm, combined with a respiratory effort belt, could be incorporated into an automatic AFES device, designed to improve the respiratory function of the tetraplegic population.


      PubDate: 2014-06-03T12:08:17Z
       
  • Influence of 3D QCT scan protocol on the QCT-based finite element models
           of human vertebral cancellous bone
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): Yongtao Lu , Klaus Engelke , Klaus Püschel , Michael M. Morlock , Gerd Huber
      Quantitative computed tomography (QCT)-based finite element (FE) models provide a better prediction of vertebral strength than dual-energy X-ray absorptiometry. However, FE models are often created from datasets acquired at different CT scan protocols and it is unclear whether this influences the FE results. The aim of this paper was to investigate whether there was an effect of the CT scan protocol on the FE models. 12 human thoracolumbar vertebrae were scanned on top of a calcium hydroxyapatite calibration phantom using a standard QCT scan protocol – 120kV, 100mAs (PA); and a low dose protocol – 90kV, 150mAs (PB). FE cancellous models with cuboid volume of interest and inhomogeneous nonlinear bone properties were created. Axial compression was simulated. The apparent BMD, modulus and yield strength showed significant differences between the two scan protocols. The apparent BMD, the modulus and yield strength between the two groups were highly linearly correlated. This paper indicated that the FE models created from image datasets acquired at different X-ray tube voltage settings would give significantly different results and this effect could be possibly corrected using a linear correction approach.


      PubDate: 2014-06-03T12:08:17Z
       
  • Uncertainty assessment of imaging techniques for the 3D reconstruction of
           stent geometry
    • Abstract: Publication date: Available online 2 June 2014
      Source:Medical Engineering & Physics
      Author(s): Daria Cosentino , Iwona Zwierzak , Silvia Schievano , Vanessa Díaz-Zuccarini , John W. Fenner , Andrew J. Narracott
      This paper presents a quantitative assessment of uncertainty for the 3D reconstruction of stents. This study investigates a CP stent (Numed, USA) used in congenital heart disease applications with a focus on the variance in measurements of stent geometry. The stent was mounted on a model of patient implantation site geometry, reconstructed from magnetic resonance images, and imaged using micro-computed tomography (CT), conventional CT, biplane fluoroscopy and optical stereo-photogrammetry. Image data were post-processed to retrieve the 3D stent geometry. Stent strut length, separation angle and cell asymmetry were derived and repeatability was assessed for each technique along with variation in relation to μCT data, assumed to represent the gold standard. The results demonstrate the performance of biplanar reconstruction methods is comparable with volumetric CT scans in evaluating 3D stent geometry. Uncertainty on the evaluation of strut length, separation angle and cell asymmetry using biplanar fluoroscopy is of the order ±0.2mm, 3° and 0.03, respectively. These results support the use of biplanar fluoroscopy for in vivo measurement of 3D stent geometry and provide quantitative assessment of uncertainty in the measurement of geometric parameters.


      PubDate: 2014-06-03T12:08:17Z
       
  • Application of an asymmetric finite element model of the C2-T1 cervical
           spine for evaluating the role of soft tissues in stability
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): D.U. Erbulut , I. Zafarparandeh , I. Lazoglu , A.F. Ozer
      Different finite element models of the cervical spine have been suggested for evaluating the roles of ligaments, facet joints, and disks in the stability of cervical spine under sagittal moments. However, no comprehensive study on the response of the full cervical spine that has used a detailed finite element (FE) model (C2-T1) that considers the asymmetry about the mid-sagittal plane has been reported. The aims of this study were to consider asymmetry in a FE model of the full cervical spine and to investigate the influences of ligaments, facet joints, and disk nucleus on the stability of the asymmetric model during flexion and extension. The model was validated against various published in vitro studies and FE studies for the three main loading planes. Next, the C4-C5 level was modified to simulate different cases to investigate the role of the soft tissues in segmental stability. The FE model predicted that excluding the interspinous ligament (ISL) from the index level would cause excessive instability during flexion and that excluding the posterior longitudinal ligament (PLL) or the ligamentum flavum (LF) would not affect segmental rotation. During extension, motion increased when the facet joints were excluded. The model without disk nucleus was unstable compared to the intact model at lower loads and exhibited a similar rotation response at higher loads.


      PubDate: 2014-06-03T12:08:17Z
       
  • Design considerations and quantitative assessment for the development of
           percutaneous mitral valve stent
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Gideon Praveen Kumar , Fangsen Cui , Hui Qun Phang , Boyang Su , Hwa Liang Leo , Jimmy Kim Fatt Hon
      Percutaneous heart valve replacement is gaining popularity, as more positive reports of satisfactory early clinical experiences are published. However this technique is mostly used for the replacement of pulmonary and aortic valves and less often for the repair and replacement of atrioventricular valves mainly due to their anatomical complexity. While the challenges posed by the complexity of the mitral annulus anatomy cannot be mitigated, it is possible to design mitral stents that could offer good anchorage and support to the valve prosthesis. This paper describes four new Nitinol based mitral valve designs with specific features intended to address migration and paravalvular leaks associated with mitral valve designs. The paper also describes maximum possible crimpability assessment of these mitral stent designs using a crimpability index formulation based on the various stent design parameters. The actual crimpability of the designs was further evaluated using finite element analysis (FEA). Furthermore, fatigue modeling and analysis was also done on these designs. One of the models was then coated with polytetrafluoroethylene (PTFE) with leaflets sutured and put to: (i) leaflet functional tests to check for proper coaptation of the leaflet and regurgitation leakages on a phantom model and (ii) anchorage test where the stented valve was deployed in an explanted pig heart. Simulations results showed that all the stents designs could be crimped to 18F without mechanical failure. Leaflet functional test results showed that the valve leaflets in the fabricated stented valve coapted properly and the regurgitation leakage being within acceptable limits. Deployment of the stented valve in the explanted heart showed that it anchors well in the mitral annulus. Based on these promising results of the one design tested, the other stent models proposed here were also considered to be promising for percutaneous replacement of mitral valves for the treatment of mitral regurgitation, by virtue of their key features as well as effective crimping. These models will be fabricated and put to all the aforementioned tests before being taken for animal trials.


      PubDate: 2014-06-03T12:08:17Z
       
  • Empirical Mode Decomposition of simulated and real ultrasonic Doppler
           signals of periodic fetal activity
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Krzysztof Kaluzynski
      Simulated signals comprising components (trains of Gaussian packets) resulting from cardiac movements and from pseudorespiratory movements with added white noise were submitted to Empirical Mode Decomposition. The increase of sampling frequency fs (from 0.5kHz to 5kHz) for given signal to noise ratio SNR moves signal components toward higher order intrinsic mode functions (IMFs) and increases their number. The increase of the SNR (from −5dB to 10dB, fixed fs) moves the signal components to lower order IMFs. The separation of components is most efficient for SNR≥5dB and fs not exceeding 1kHz, for lower SNRs fs should be at least 2kHz. SNR=∞ results in erroneous decomposition and therefore limited noise level is beneficial. Recommended number of sifting iterations is 10. Fetal data obtained using 2MHz emission frequency and sampled at 2kHz were decomposed. The cardiac signal always appears in IMF3, frequently also in IMF1 and IMF2. The pseudobreathing signal, appearing mainly in IMF4-6, is easy to separate. Signals resulting from fetal displacements due to maternal respiration appear in IMF7 or IMF8. The EMD performs better than the classic linear filtering as a tool for separation of the pseudorespiration signals and provides inferior results in terms of separation of the cardiac signals.


      PubDate: 2014-06-03T12:08:17Z
       
  • Editorial Board
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7




      PubDate: 2014-06-03T12:08:17Z
       
  • Poroelastic response of articular cartilage by nanoindentation creep tests
           at different characteristic lengths
    • Abstract: Publication date: Available online 10 May 2014
      Source:Medical Engineering & Physics
      Author(s): M. Taffetani , D. Gastaldi , R. Gottardi , D. Gastaldi , R. Raiteri , P. Vena
      Nanoindentation is an experimental technique which is attracting increasing interests for the mechanical characterization of articular cartilage. In particular, time dependent mechanical responses due to fluid flow through the porous matrix can be quantitatively investigated by nanoindentation experiments at different penetration depths and/or by using different probe sizes. The aim of this paper is to provide a framework for the quantitative interpretation of the poroelastic response of articular cartilage subjected to creep nanoindentation tests. To this purpose, multiload creep tests using spherical indenters have been carried out on saturated samples of mature bovine articular cartilage achieving two main quantitative results. First, the dependence of indentation modulus in the drained state (at equilibrium) on the tip radius: a value of 500kPa has been found using the large tip (400μm radius) and of 1.7MPa using the smaller one (25μm). Secon, the permeability at microscopic scale was estimated at values ranging from 4.5×10−16 m4/Ns to 0.1×10−16 m4/Ns, from low to high equivalent deformation. Consistently with a poroelastic behavior, the size-dependent response of the indenter displacement disappears when characteristic size and permeability are accounted for. For comparison purposes, the same protocol was applied to intrinsically viscoelastic homogeneous samples of polydimethylsiloxane (PDMS): both indentation modulus and time response have been found size-independent.


      PubDate: 2014-05-13T03:44:18Z
       
  • EP-based wavelet coefficient quantization for linear distortion ECG data
           compression
    • Abstract: Publication date: Available online 29 April 2014
      Source:Medical Engineering & Physics
      Author(s): King-Chu Hung , Tsung-Ching Wu , Hsieh-Wei Lee , Tung-Kuan Liu
      Reconstruction quality maintenance is of the essence for ECG data compression due to the desire for diagnosis use. Quantization schemes with non-linear distortion characteristics usually result in time-consuming quality control that blocks real-time application. In this paper, a new wavelet coefficient quantization scheme based on an evolution program (EP) is proposed for wavelet-based ECG data compression. The EP search can create a stationary relationship among the quantization scales of multi-resolution levels. The stationary property implies that multi-level quantization scales can be controlled with a single variable. This hypothesis can lead to a simple design of linear distortion control with 3-D curve fitting technology. In addition, a competitive strategy is applied for alleviating data dependency effect. By using the ECG signals saved in MIT and PTB databases, many experiments were undertaken for the evaluation of compression performance, quality control efficiency, data dependency influence. The experimental results show that the new EP-based quantization scheme can obtain high compression performance and keep linear distortion behavior efficiency. This characteristic guarantees fast quality control even for the prediction model mismatching practical distortion curve.


      PubDate: 2014-05-03T06:21:40Z
       
  • Adding “hemodynamic and fluid leads” to the ECG. Part I: The
           electrical estimation of BNP, chronic heart failure (CHF) and
           extracellular fluid (ECF) accumulation
    • Abstract: Publication date: Available online 30 April 2014
      Source:Medical Engineering & Physics
      Author(s): Falko Skrabal , Georg P. Pichler , Gerfried Gratze , Albert Holler
      Objectives In primary care the diagnosis of CHF and ECF accumulation is no triviality. We aimed to predict plasma BNP, CHF and ECF accumulation with segmental impedance spectroscopy while using and extending the electrodes of the conventional electrocardiography. Methods Three combined multiple electrodes were added to the 15 lead ECG for segmental impedance spectroscopy and for measuring the maximal rate of segmental fluid volume change with heart action at the thorax and the legs. The obtained signals were analyzed by partial correlation analyses in comparison with plasma BNP, CHF classes, ejection fraction by echocardiography and cardiac index by double gas re-breathing. 119 subjects (34 healthy volunteers, 50 patients with CHF, NYHA classes II to IV and 35 patients without CHF) were investigated. Results The maximal rate of volume change with heart action at the thorax and at the legs, as well as the ECF/ICF ratio at the legs contribute equally and independently to the prediction of BNP and heart failure in an unknown test sample of 49 patients (multiple r =0.88, p <0.001). The ROC-curve for the predicted plasma BNP>400pg/ml gave an AUC=0.93. The absence or the presence of heart failure could be predicted correctly by a binomial logistic regression in 92.9 and 87.5% of cases, respectively. Conclusion The methodology, which is based on inverse coupling of BNP release and of maximal blood acceleration and on sensitive detection of ECF overload, could enable the diagnosis of CHF with useful sensitivity and specificity while writing a routine-ECG.


      PubDate: 2014-05-03T06:21:40Z
       
  • Comparison of mechanical and ultrasound elastic modulus of ovine tibial
           cortical bone
    • Abstract: Publication date: Available online 1 May 2014
      Source:Medical Engineering & Physics
      Author(s): Caroline A. Grant , Lance J. Wilson , Christian Langton , Devakar Epari
      Finite element models of bones can be created by deriving geometry from an X-ray CT scan. Material properties such as the elastic modulus can then be applied using either a single or set of homogeneous values, or individual elements can have local values mapped onto them. Values for the elastic modulus can be derived from the CT density values using an elasticity versus density relationship. Many elasticity–density relationships have been reported in the literature for human bone. However, while ovine in vivo models are common in orthopaedic research, no work has been done to date on creating FE models of ovine bones. To create these models and apply relevant material properties, an ovine elasticity–density relationship needs to be determined. Using fresh frozen ovine tibias the apparent density of regions of interest was determined from a clinical CT scan. The bones were the sectioned into cuboid samples of cortical bone from the regions of interest. Ultrasound was used to determine the elastic modulus in each of three directions – longitudinally, radially and tangentially. Samples then underwent traditional compression testing in each direction. The relationships between apparent density and both ultrasound, and compression modulus in each direction were determined. Ultrasound testing was found to be a highly repeatable non-destructive method of calculating the elastic modulus, particularly suited to samples of this size. The elasticity–density relationships determined in the longitudinal direction were very similar between the compression and ultrasound data over the density range examined. A clear difference was seen in the elastic modulus between the longitudinal and transverse directions of the bone samples, and a transverse elasticity–density relationship is also reported.


      PubDate: 2014-05-03T06:21:40Z
       
  • A preliminary study on atrial epicardial mapping signals based on Graph
           Theory
    • Abstract: Publication date: Available online 24 April 2014
      Source:Medical Engineering & Physics
      Author(s): Liqian Sun , Cuiwei Yang , Lin Zhang , Ying Chen , Zhong Wu , Jun Shao
      In order to get a better understanding of atrial fibrillation, we introduced a method based on Graph Theory to interpret the relations of different parts of the atria. Atrial electrograms under sinus rhythm and atrial fibrillation were collected from eight living mongrel dogs with cholinergic AF model. These epicardial signals were acquired from 95 unipolar electrodes attached to the surface of the atria and four pulmonary veins. Then, we analyzed the electrode correlations using Graph Theory. The topology, the connectivity and the parameters of graphs during different rhythms were studied. Our results showed that the connectivity of graphs varied from sinus rhythm to atrial fibrillation and there were parameter gradients in various parts of the atria. The results provide spatial insight into the interaction between different parts of the atria and the method may have its potential for studying atrial fibrillation.


      PubDate: 2014-04-28T06:22:18Z
       
  • Towards understanding knee joint laxity: Errors in non-invasive assessment
           of joint rotation can be corrected
    • Abstract: Publication date: Available online 26 April 2014
      Source:Medical Engineering & Physics
      Author(s): P. Moewis , H. Boeth , M.O. Heller , C. Yntema , T. Jung , R. Doyscher , R.M. Ehrig , Y. Zhong , W.R. Taylor
      The in vivo quantification of rotational laxity of the knee joint is of importance for monitoring changes in joint stability or the outcome of therapies. While invasive assessments have been used to study rotational laxity, non-invasive methods are attractive particularly for assessing young cohorts. This study aimed to determine the conditions under which tibio-femoral rotational laxity can be assessed reliably and accurately in a non-invasive manner. The reliability and error of non-invasive examinations of rotational joint laxity were determined by comparing the artefact associated with surface mounted markers against simultaneous measurements using fluoroscopy in five knees including healthy and ACL deficient joints. The knees were examined at 0°, 30°, 60° and 90° flexion using a device that allows manual axial rotation of the joint. With a mean RMS error of 9.6°, the largest inaccuracy using non-invasive assessment was present at 0° knee flexion, whereas at 90° knee flexion, a smaller RMS error of 5.7° was found. A Bland and Altman assessment indicated that a proportional bias exists between the non-invasive and fluoroscopic approaches, with limits of agreement that exceeded 20°. Correction using average linear regression functions resulted in a reduction of the RMS error to below 1° and limits of agreement to less than ±1° across all knees and flexion angles. Given the excellent reliability and the fact that a correction of the surface mounted marker based rotation values can be achieved, non-invasive evaluation of tibio-femoral rotation could offer opportunities for simplified devices for use in clinical settings in cases where invasive assessments are not justified. Although surface mounted marker based measurements tend to overestimate joint rotation, and therefore joint laxity, our results indicate that it is possible to correct for this error.


      PubDate: 2014-04-28T06:22:18Z
       
  • The influence of an unilateral carotid artery stenosis on brain
           oxygenation
    • Abstract: Publication date: Available online 26 April 2014
      Source:Medical Engineering & Physics
      Author(s): T. Köppl , M. Schneider , U. Pohl , B. Wohlmuth
      We study the impact of varying degrees of unilateral stenoses of an carotid artery on pulsatile blood flow and oxygen transport from the heart to the brain. For the numerical simulation a model reduction approach is used involving non-linear 1-D transport equation systems, linear 1-D transport equations and 0-D models. The haemodynamic effects of vessels beyond the outflow boundaries of the 1-D models are accounted for using a 0-D lumped three element windkessel model. At the cerebral outflow boundaries the 0-D windkessel model is extended by metabolic autoregulation, based on the cerebral oxygen supply. Additionally lumped parameter models are applied to incorporate the impact of the carotid stenosis. Our model suggests that for a severe unilateral stenosis in the right carotid artery the partial pressure of oxygen in the brain area at risk can only be restored, if the corresponding cerebral resistance is significantly decreased and if the circle of Willis (CoW) is complete.


      PubDate: 2014-04-28T06:22:18Z
       
 
 
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