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  Subjects -> BIOLOGY (Total: 2575 journals)
    - BIOCHEMISTRY (190 journals)
    - BIOENGINEERING (58 journals)
    - BIOLOGY (1316 journals)
    - BIOPHYSICS (39 journals)
    - BIOTECHNOLOGY (144 journals)
    - BOTANY (192 journals)
    - CYTOLOGY AND HISTOLOGY (25 journals)
    - ENTOMOLOGY (52 journals)
    - GENETICS (136 journals)
    - MICROBIOLOGY (208 journals)
    - MICROSCOPY (9 journals)
    - ORNITHOLOGY (23 journals)
    - PHYSIOLOGY (64 journals)
    - ZOOLOGY (119 journals)

BIOLOGY (1316 journals)            First | 4 5 6 7 8 9 10 11 | Last

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: 4)
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  
Journal of New Seeds     Hybrid Journal  
Journal of Nucleic Acids     Open Access   (Followers: 2)
Journal of Parasitology     Full-text available via subscription   (Followers: 11)

  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]
  • 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
       
  • Experimental investigations and finite element simulation of cutting heat
           in vibrational and conventional drilling of cortical bone
    • Abstract: Publication date: Available online 4 June 2014
      Source:Medical Engineering & Physics
      Author(s): Yu Wang , Meng Cao , Xiangrui Zhao , Gang Zhu , Colin McClean , Yuanyuan Zhao , Yubo Fan
      Heat generated during bone drilling could cause irreversible thermal damage, which can lead to bone necrosis or even osteomyelitis. In this study, vibrational drilling was applied to fresh bovine bones to investigate the cutting heat in comparison with conventional drilling through experimental investigation and finite element analysis (FEA). The influence of vibrational frequency and amplitude on cutting heat generation and conduction were studied. The experimental results showed that, compared with the conventional drilling, vibrational drilling could significantly reduce the cutting temperature in drilling of cortical bone (P <0.05): the cutting temperature tended to decrease with increasing vibrational frequency and amplitude. The FEA results also showed that the vibrational amplitude holds a significant effect on the cutting heat conduction.


      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
       
  • Biomechanical study of expandable pedicle screw fixation in severe
           osteoporotic bone comparing with conventional and cement-augmented pedicle
           screws
    • Abstract: Publication date: Available online 3 June 2014
      Source:Medical Engineering & Physics
      Author(s): Yi-Long Chen , Wen-Chuan Chen , Chi-Wei Chou , Jou-Wen Chen , Chia-Ming Chang , Yu-Shu Lai , Cheng-Kung Cheng , Shih-Tien Wang
      Pedicle screws are widely utilized to treat the unstable thoracolumbar spine. The superior biomechanical strength of pedicle screws could increase fusion rates and provide accurate corrections of complex deformities. However, osteoporosis and revision cases of pedicle screw substantially reduce screw holding strength and cause loosening. Pedicle screw fixation becomes a challenge for spine surgeons in those scenarios. The purpose of this study was to determine if an expandable pedicle screw design could be used to improve biomechanical fixation in osteoporotic bone. Axial mechanical pull-out test was performed on the expandable, conventional and augmented pedicle screws placed in a commercial synthetic bone block which mimicked a human bone with severe osteoporosis. Results revealed that the pull-out strength and failure energy of expandable pedicle screws were similar with conventional pedicle screws augmented with bone cement by 2ml. The pull-out strength was 5-fold greater than conventional pedicle screws and the failure energy was about 2-fold greater. Besides, the pull-out strength of expandable screw was reinforced by the expandable mechanism without cement augmentation, indicated that the risks of cement leakage from vertebral body would potentially be avoided. Comparing with the biomechanical performances of conventional screw with or without cement augmentation, the expandable screws are recommended to be applied for the osteoporotic vertebrae.


      PubDate: 2014-06-10T18:38:57Z
       
  • Leg general muscle moment and power patterns in able-bodied subjects
           during recumbent cycle ergometry with ankle immobilization
    • Abstract: Publication date: Available online 10 June 2014
      Source:Medical Engineering & Physics
      Author(s): J. Szecsi , A. Straube , C. Fornusek
      Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads. Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60rpm during passive cycling and at two workloads (low 15W and high 40W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations. During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0–258°) hip extension moment and a shortened range (350–150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase. For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.


      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
       
  • Prophylactic vertebroplasty can decrease the fracture risk of adjacent
           vertebrae: An in vitro cadaveric study
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): René Aquarius , Jasper Homminga , Allard Jan Frederik Hosman , Nico Verdonschot , Esther Tanck
      Adjacent level vertebral fractures are common in patients with osteoporotic wedge fractures, but can theoretically be prevented with prophylactic vertebroplasty. Previous tests on prophylactic vertebroplasties have been performed under axial loading, while in vivo changes in spinal alignment likely cause off-axis loads. In this study we determined whether prophylactic vertebroplasty can also reduce the fracture risk under off-axis loads. In a previous study, we tested vertebral bodies that were loaded axially or 20° off-axis representing vertebrae in an unfractured spine or vertebrae adjacent to a wedge fracture, respectively. In the current study, vertebral failure load and stiffness of our previously tested vertebral bodies were compared to those of a new group of vertebral bodies that were filled with bone cement and then loaded 20° off-axis. These vertebral bodies represented adjacent-level vertebrae with prophylactic bone cement filling. Prophylactic augmentation resulted in failure loads that were comparable to those of the 0° group, and 32% greater than the failure loads of the 20° group. The stiffness of the prophylacticly augmented vertebrae was 21% lower than that of the 0° group, but 27% higher than that of the 20° group. We conclude that prophylactic augmentation can decrease the fracture risk in a malaligned, osteoporotic vertebra. Whether this is enough to actually prevent additional vertebral fractures in vivo remains subject of further study.


      PubDate: 2014-06-03T12:08:17Z
       
  • 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
       
  • Biomechanical responses due to discitis infection of a juvenile
           thoracolumbar spine using finite element modeling
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): D. Davidson Jebaseelan , C. Jebaraj , N. Yoganandan , S. Rajasekaran , J. Yerramshetty
      Growth modulation changes occur in pediatric spines and lead to kyphotic deformity during discitis infection from mechanical forces. The present study was done to understand the consequences of discitis by simulating inflammatory puss at the T12/L1 disc space using a validated eight-year-old thoracolumbar spine finite element model. Changes in the biomechanical responses of the bone, disc and ligaments were determined under physiological compression and flexion loads in the intact and discitis models. During flexion, the angular-displacement increased by 3.33 times the intact spine and localized at the infected junction (IJ). The IJ became a virtual hinge. During compression loading, higher stresses occurred in the growth plate superior to the IJ. The components of the principal stresses in the growth plates at the T12/L1 junction indicated differential stresses. The strain increased by 143% during flexion loading in the posterior ligaments. The study indicates that the flexible pediatric spine increases the motion of the infected spine during physiological loadings. Understanding intrinsic responses around growth plates is important within the context of growth modulation in children. These results are clinically relevant as it might help surgeons to come up with better decisions while developing treatment protocols or performing surgeries.


      PubDate: 2014-06-03T12:08:17Z
       
  • MR-compatible pedal ergometer for reproducible exercising of the human
           calf muscle
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Kevin Tschiesche , Markus Rothamel , Reinhard Rzanny , Alexander Gussew , Patrick Hiepe , Jürgen R. Reichenbach
      A pneumatic MR-compatible pedal ergometer was designed to perform dynamic contraction exercises of the human calf muscle in a whole-body 3T MR scanner. The set-up includes sensors for monitoring mechanical parameters, such as pedal angle, cadence as well as applied force and power. Actual parameter values during the exercise were presented to the volunteer as a visual feedback to enable real-time self-adjustment of pedal deflection and cadence to the target reference value. Time-resolved dynamic 31P-MR spectroscopic measurements of phosphocreatine (PCr), inorganic phosphate (Pi) and pH were performed in a pilot experiment before, during, and after the exercise by a single volunteer. Two different load strengths were applied in these experiments (15% and 25% of the maximum voluntary contraction, MVC). As expected, mechanical and metabolic parameters differed for the two load levels. Small variations of the cadence, power and metabolic changes (time constants of PCr depletion and Pi accumulation) during the experiments demonstrate a highly reproducible mechanical output by the volunteer mediated by the ergometer.


      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
       
  • Development of a novel pulse wave velocity measurement system: Using dual
           piezoelectric elements
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Kei-ichiro Kitamura , Ryuya Takeuchi , Kazuhiro Ogai , Zhu Xin , Wenxi Chen , Tetsu Nemoto
      The aim of this study is to develop a painless system of measuring the brachial-ankle arterial pulse wave velocity (baPWV) without compression cuffs. The PWV reflects the compliance of the artery and is measured for the early diagnosis of arteriosclerotic vascular diseases. However, the conventional baPWV system, which measures four cuff pressures simultaneously, easily causes circulation block and tightening pain at the extremities. In addition, approximately 15min are required to stabilise the blood pressure for re-examination. Therefore, we developed a novel baPWV measurement system using dual piezoelectric sensor elements. The principle of this high-sensitivity pressure pulse detection system is based on adding the two in-phase outputs from the coaxially arranged dual piezoelectric sensor. As our system facilitates the measurement of the baPWV by detecting the pulsation of an artery using sensors fixed on the skin where the pulse is palpable, it does not cause pain and reduces examination time. The coefficients of correlation between the baPWV values obtained from the conventional and present methods were 0.93 (right side) and 0.90 (left side). The results suggest that our system can be used to measure the baPWV without pressure cuffs as accurately as the conventional method.


      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
       
  • Objective diagnosis of ADHD using IMUs
    • Abstract: Publication date: July 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 7
      Author(s): Niamh O’Mahony , Blanca Florentino-Liano , Juan J. Carballo , Enrique Baca-García , Antonio Artés Rodríguez
      This work proposes the use of miniature wireless inertial sensors as an objective tool for the diagnosis of ADHD. The sensors, consisting of both accelerometers and gyroscopes to measure linear and rotational movement, respectively, are used to characterize the motion of subjects in the setting of a psychiatric consultancy. A support vector machine is used to classify a group of subjects as either ADHD or non-ADHD and a classification accuracy of greater than 95% has been achieved. Separate analyses of the motion data recorded during various activities throughout the visit to the psychiatric consultancy show that motion recorded during a continuous performance test (a forced concentration task) provides a better classification performance than that recorded during “free time”.


      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
       
  • Validity of using tri-axial accelerometers to measure human movement
           – Part II: Step counts at a wide range of gait velocities
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Emma Fortune , Vipul Lugade , Melissa Morrow , Kenton Kaufman
      A subject-specific step counting method with a high accuracy level at all walking speeds is needed to assess the functional level of impaired patients. The study aim was to validate step counts and cadence calculations from acceleration data by comparison to video data during dynamic activity. Custom-built activity monitors, each containing one tri-axial accelerometer, were placed on the ankles, thigh, and waist of 11 healthy adults. ICC values were greater than 0.98 for video inter-rater reliability of all step counts. The activity monitoring system (AMS) algorithm demonstrated a median (interquartile range; IQR) agreement of 92% (8%) with visual observations during walking/jogging trials at gait velocities ranging from 0.1 to 4.8m/s, while FitBits (ankle and waist), and a Nike Fuelband (wrist) demonstrated agreements of 92% (36%), 93% (22%), and 33% (35%), respectively. The algorithm results demonstrated high median (IQR) step detection sensitivity (95% (2%)), positive predictive value (PPV) (99% (1%)), and agreement (97% (3%)) during a laboratory-based simulated free-living protocol. The algorithm also showed high median (IQR) sensitivity, PPV, and agreement identifying walking steps (91% (5%), 98% (4%), and 96% (5%)), jogging steps (97% (6%), 100% (1%), and 95% (6%)), and less than 3% mean error in cadence calculations.


      PubDate: 2014-05-22T04:03:52Z
       
  • A microfluidic device for continuous manipulation of biological cells
           using dielectrophoresis
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Debanjan Das , Karabi Biswas , Soumen Das
      The present study demonstrates the design, simulation, fabrication and testing of a label-free continuous manipulation and separation micro-device of particles/biological cells suspended on medium based on conventional dielectrophoresis. The current dielectrophoretic device uses three planner electrodes to generate non-uniform electric field and induces both p-DEP and n-DEP force simultaneously depending on the dielectric properties of the particles and thus influencing at least two types of particles at a time. Numerical simulations were performed to predict the distribution of non-uniform electric field, DEP force and particle trajectories. The device is fabricated utilizing the advantage of bonding between PDMS and SU8 polymer. The p-DEP particles move away from the center of the streamline, while the n-DEP particles will follow the central streamline along the channel length. Dielectrophoretic effects were initially tested using polystyrene beads followed by manipulation of HeLa cells. In the experiment, it was observed that polystyrene beads in DI water always response as n-DEP up to 1MHz frequency, whereas HeLa cells in PBS medium response as n-DEP up to 400kHz frequency and then it experiences p-DEP up to 1MHz. Further, the microscopic observations of DEP responses of HeLa cells were verified by performing trapping experiment at static condition.


      PubDate: 2014-05-22T04:03:52Z
       
  • EMG feature assessment for myoelectric pattern recognition and channel
           selection: A study with incomplete spinal cord injury
    • Abstract: Publication date: Available online 17 May 2014
      Source:Medical Engineering & Physics
      Author(s): Jie Liu , Xiaoyan Li , Guanglin Li , Ping Zhou
      Myoelectric pattern recognition with a large number of electromyogram (EMG) channels provides an approach to assessing motor control information available from the recorded muscles. In order to develop a practical myoelectric control system, a feature dependent channel reduction method was developed in this study to determine a small number of EMG channels for myoelectric pattern recognition analysis. The method selects appropriate raw EMG features for classification of different movements, using the minimum Redundancy Maximum Relevance (mRMR) and the Markov random field (MRF) methods to rank a large number of EMG features, respectively. A k-nearest neighbor (KNN) classifier was used to evaluate the performance of the selected features in terms of classification accuracy. The method was tested using 57 channels’ surface EMG signals recorded from forearm and hand muscles of individuals with incomplete spinal cord injury (SCI). Our results demonstrate that appropriate selection of a small number of raw EMG features from different recording channels resulted in similar high classification accuracies as achieved by using all the EMG channels or features. Compared with the conventional sequential forward selection (SFS) method, the feature dependent method does not require repeated classifier implementation. It can effectively reduce redundant information not only cross different channels, but also cross different features in the same channel. Such hybrid feature-channel selection from a large number of EMG recording channels can reduce computational cost for implementation of a myoelectric pattern recognition based control system.


      PubDate: 2014-05-22T04:03:52Z
       
  • Smart instrumentation for determination of ligament stiffness and ligament
           balance in total knee arthroplasty
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): W. Hasenkamp , J. Villard , J.R. Delaloye , A. Arami , A. Bertsch , B.M. Jolles , K. Aminian , P. Renaud
      Ligament balance is an important and subjective task performed during total knee arthroplasty (TKA) procedure. For this reason, it is desirable to develop instruments to quantitatively assess the soft-tissue balance since excessive imbalance can accelerate prosthesis wear and lead to early surgical revision. The instrumented distractor proposed in this study can assist surgeons on performing ligament balance by measuring the distraction gap and applied load. Also the device allows the determination of the ligament stiffness which can contribute a better understanding of the intrinsic mechanical behavior of the knee joint. Instrumentation of the device involved the use of hall-sensors for measuring the distractor displacement and strain gauges to transduce the force. The sensors were calibrated and tested to demonstrate their suitability for surgical use. Results show the distraction gap can be measured reliably with 0.1mm accuracy and the distractive loads could be assessed with an accuracy in the range of 4N. These characteristics are consistent with those have been proposed, in this work, for a device that could assist on performing ligament balance while permitting surgeons evaluation based on his experience. Preliminary results from in vitro tests were in accordance with expected stiffness values for medial collateral ligament (MCL) and lateral collateral ligament (LCL).


      PubDate: 2014-05-22T04:03:52Z
       
  • Comparison of dental implant stabilities by impact response and resonance
           frequencies using artificial bone
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Dae-Seung Kim , Woo-Jin Lee , Soon-Chul Choi , Sam-Sun Lee , Min-Suk Heo , Kyung-Hoe Huh , Tae-Il Kim , Won-Jin Yi
      Purpose We compared implant stability as determined by the peak frequency from the impact response with the implant stability quotient (ISQ) by resonance frequency analysis (RFA) in various artificial bone conditions. The clinical bone conditions were simulated using an artificial bone material with different cortical thicknesses and trabecular densities. Materials and methods The artificial bone material was solid, rigid polyurethane. The polyurethane foam of 0.8g/cm3 density was used for the cortical bone layer, and that of 0.08, 0.16, 0.24, 0.32, and 0.48g/cm3 densities for the trabecular bone layer. The cortical bone material of 4 different thicknesses (1.4, 1.6, 1.8, and 2.0mm) was attached to the trabecular bone with varying density. Two types of dental implants (10 and 13mm lengths of 4.0mm diameter) were placed into the artificial bone blocks. An inductive sensor was used to measure the vibration caused by tapping the adapter–implant assembly. The peak frequency of the power spectrum of the impact response was used as the criterion for implant stability. The ISQ value was also measured for the same conditions. Results The stability, as measured by peak frequency (SPF) and ISQ value, increased as the trabecular density and the cortical density increased in linear regression analysis. The SPF and ISQ values were highly correlated with each other when the trabecular bone density and cortical bone thickness changed (Pearson correlation=0.90, p <0.01). The linear regression of the SPF with the cortical bone thickness showed higher goodness of fit (R 2 measure) than the ISQ value with the cortical bone thickness. The SPF could differentiate implantation conditions as many as the ISQ value when the trabecular bone density and the cortical density changed. However, the ISQ value was not consistent with the general stability tendency in some conditions. Conclusion The SPF showed better consistency and differentiability with implant stability than the ISQ value by resonance frequency analysis in the various implantation conditions.


      PubDate: 2014-05-22T04:03:52Z
       
  • Optical tracking of local surface wave for skin viscoelasticity
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Yubo Guan , Mingzhu Lu , Zhilong Shen , Mingxi Wan
      Rapid and effective determination of biomechanical properties is important in examining and diagnosing skin thermal injury. Among the methods used, viscoelasticity quantification is one of the most effective methods in determining such properties. This study aims to rapidly determine skin viscoelasticity by optically tracking the local surface wave. New elastic and viscous coefficients were proposed to indicate skin viscoelasticity based on a single impulse response of the skin. Experiments were performed using fresh porcine skin samples. Surface wave was generated in a single impulse using a vibrator with a ball-tipped device and was detected using a laser Doppler vibrometer. The motions along the depth direction were monitored using an ultrasound system. The ultrasound monitoring results indicated the multi-layered viscoelasticity of the epidermis and dermis. The viscoelastic coefficients from four healthy samples show a potential viscoelasticity variation of porcine skin. In one sample, the two coefficients were evidently higher than those in a healthy area if the skin was slightly burned. These results indicate that the proposed method is sensitive, effective, and quick in determining skin viscoelasticity.


      PubDate: 2014-05-22T04:03:52Z
       
  • Generating finite element models of the knee: How accurately can we
           determine ligament attachment sites from MRI scans'
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): H.H. Rachmat , D. Janssen , W.J. Zevenbergen , G.J. Verkerke , R.L. Diercks , N. Verdonschot
      In this study, we evaluated the intra- and inter-observer variability when determining the insertion and origin sites of knee ligaments on MRI scan images. We collected data of five observers with different backgrounds, who determined the ligament attachment sites in an MRI scan of a right knee of a 66-year-old male cadaver donor. We evaluated the intra- and inter-observer differences between the ligament attachment center points, and also determined the differences relative to a physical measurement performed on the same cadaver. The largest mean intra- and inter-observer differences were 4.30mm (ACL origin) and 16.81mm (superficial MCL insertion), respectively. Relative to the physical measurement, the largest intra- and inter-observer differences were 31.84mm (superficial MCL insertion) and 23.39mm (deep MCL insertion), respectively. The results indicate that, dependent on the location, a significant variation can occur when identifying the attachment site of the knee ligaments. This finding is of particular importance when creating computational models based on MRI data, as the variations in attachment sites may have a considerable effect on the biomechanical behavior of the human knee joint.


      PubDate: 2014-05-22T04:03:52Z
       
  • Load-transfer analysis after insertion of cementless anatomical femoral
           stem using pre- and post-operative CT images based patient-specific finite
           element analysis
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Go Yamako , Etsuo Chosa , Xin Zhao , Koji Totoribe , Shinji Watanabe , Takero Sakamoto , Nobutake Nakane
      Periprosthetic bone remodeling is commonly seen after total hip arthroplasty, but the remodeling pattern differs among patients even in those implanted with the same stem. Remodeling occurs mainly because of the difference in load transmitted from the stem to the femur. In this study, we evaluated the load-transfer pattern in eight female patients implanted with an anatomical stem on an individual basis by patient-specific finite element analysis that is based on pre- and postoperative computed tomography images. Load transfer was evaluated using interface stress between the stem and bone. One of eight patients demonstrated proximal dominant load transfer, while the other patients demonstrated a distal dominant pattern. The results of our biomechanical simulations reveal the differences in load-transfer pattern after surgery among patients with the same anatomical stem.


      PubDate: 2014-05-22T04:03:52Z
       
  • A micro-optical system for endoscopy based on mechanical compensation
           paradigm using miniature piezo-actuation
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Pietro Cerveri , Cynthia Corinna Zazzarini , Paolo Patete , Guido Baroni
      The goal of the study was to investigate the feasibility of a novel miniaturized optical system for endoscopy. Fostering the mechanical compensation paradigm, the modeled optical system, composed by 14 lenses, separated in 4 different sets, had a total length of 15.55mm, an effective focal length ranging from 1.5 to 4.5mm with a zoom factor of about 2.8×, and an angular field of view up to 56°. Predicted maximum lens travel was less than 3.5mm. The consistency of the image plane height across the magnification range testified the zoom capability. The maximum predicted achromatic astigmatism, transverse spherical aberration, longitudinal spherical aberration and relative distortion were less than or equal to 25μm, 15μm, 35μm and 12%, respectively. Tests on tolerances showed that the manufacturing and opto-mechanics mounting are critical as little deviations from design dramatically decrease the optical performances. However, recent micro-fabrication technology can guarantee tolerances close to nominal design. A closed-loop actuation unit, devoted to move the zoom and the focus lens sets, was implemented adopting miniaturized squiggle piezo-motors and magnetic position encoders based on Hall effect. Performance results, using a prototypical test board, showed a positioning accuracy of less than 5μm along a lens travel path of 4.0mm, which was in agreement with the lens set motion features predicted by the analysis. In conclusion, this study demonstrated the feasibility of the optical design and the viability of the actuation approach while tolerances must be carefully taken into account.


      PubDate: 2014-05-22T04:03:52Z
       
  • Activity recognition with smartphone support
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): John J. Guiry , Pepijn van de Ven , John Nelson , Lisanne Warmerdam , Heleen Riper
      In this paper, the authors describe a method of accurately detecting human activity using a smartphone accelerometer paired with a dedicated chest sensor. The design, implementation, testing and validation of a custom mobility classifier are also presented. Offline analysis was carried out to compare this custom classifier to de-facto machine learning algorithms, including C4.5, CART, SVM, Multi-Layer Perceptrons, and Naïve Bayes. A series of trials were carried out in Ireland, initially involving N =6 individuals to test the feasibility of the system, before a final trial with N =24 subjects took place in the Netherlands. The protocol used and analysis of 1165min of recorded activities from these trials are described in detail in this paper. Analysis of collected data indicate that accelerometers placed in these locations, are capable of recognizing activities including sitting, standing, lying, walking, running and cycling with accuracies as high as 98%.


      PubDate: 2014-05-22T04:03:52Z
       
  • Flow transport and gas mixing during invasive high frequency oscillatory
           ventilation
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6
      Author(s): Mohammed Alzahrany , Arindam Banerjee , Gary Salzman
      A large Eddy simulation (LES) based computational fluid dynamics study was performed to investigate gas transport and mixing in patient specific human lung models during high frequency oscillatory ventilation. Different pressure-controlled waveforms (sinusoidal, exponential and square) and ventilator frequencies (15, 10 and 6Hz) were used (tidal volume=50mL). The waveforms were created by solving the equation of motion subjected to constant lung wall compliance and flow resistance. Simulations were conducted with and without endotracheal tube to understand the effect of invasive management device. Variation of pressure-controlled waveform and frequency exhibits significant differences on counter flow pattern, which could lead to a significant impact on the gas mixing efficiency. Pendelluft-like flow was present for the sinusoidal waveform at all frequencies but occurred only at early inspiration for the square waveform at highest frequency. The square waveform was most efficient for gas mixing, resulting in the least wall shear stress on the lung epithelium layer thereby reducing the risk of barotrauma to both airways and the alveoli for patients undergoing therapy.


      PubDate: 2014-05-22T04:03:52Z
       
  • Editorial Board
    • Abstract: Publication date: June 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 6




      PubDate: 2014-05-22T04:03:52Z
       
  • Stress distributions in maxillary central incisors restored with various
           types of post materials and designs
    • Abstract: Publication date: Available online 14 May 2014
      Source:Medical Engineering & Physics
      Author(s): A.A. Madfa , M.R. Abdul Kadir , J. Kashani , S. Saidin , E. Sulaiman , J. Marhazlinda , R. Rahbari , B.J.J. Abdullah , H. Abdullah , N.H. Abu Kasim
      Different dental post designs and materials affect the stability of restoration of a tooth. This study aimed to analyse and compare the stability of two shapes of dental posts (parallel-sided and tapered) made of five different materials (titanium, zirconia, carbon fibre and glass fibre) by investigating their stress transfer through the finite element (FE) method. Ten three-dimensional (3D) FE models of a maxillary central incisor restored with two different designs and five different materials were constructed. An oblique loading of 100N was applied to each 3D model. Analyses along the centre of the post, the crown-cement/core and the post-cement/dentine interfaces were computed, and the means were calculated. One-way ANOVAs followed by post hoc tests were used to evaluate the effectiveness of the post materials and designs (p =0.05). For post designs, the tapered posts introduced significantly higher stress compared with the parallel-sided post (p <0.05), especially along the centre of the post. Of the materials, the highest level of stress was found for stainless steel, followed by zirconia, titanium, glass fibre and carbon fibre posts (p <0.05). The carbon and glass fibre posts reduced the stress distribution at the middle and apical part of the posts compared with the stainless steel, zirconia and titanium posts. The opposite results were observed at the crown-cement/core interface.


      PubDate: 2014-05-17T04:05:33Z
       
  • X-ray image calibration and its application to clinical orthopedics
    • Abstract: Publication date: Available online 14 May 2014
      Source:Medical Engineering & Physics
      Author(s): Steffen Schumann , Benedikt Thelen , Steven Ballestra , Lutz-P. Nolte , Philippe Büchler , Guoyan Zheng
      X-ray imaging is one of the most commonly used medical imaging modality. Albeit X-ray radiographs provide important clinical information for diagnosis, planning and post-operative follow-up, the challenging interpretation due to its 2D projection characteristics and the unknown magnification factor constrain the full benefit of X-ray imaging. In order to overcome these drawbacks, we proposed here an easy-to-use X-ray calibration object and developed an optimization method to robustly find correspondences between the 3D fiducials of the calibration object and their 2D projections. In this work we present all the details of this outlined concept. Moreover, we demonstrate the potential of using such a method to precisely extract information from calibrated X-ray radiographs for two different orthopedic applications: post-operative acetabular cup implant orientation measurement and 3D vertebral body displacement measurement during preoperative traction tests. In the first application, we have achieved a clinically acceptable accuracy of below 1° for both anteversion and inclination angles, where in the second application an average displacement of 8.06±3.71mm was measured. The results of both applications indicate the importance of using X-ray calibration in the clinical routine.


      PubDate: 2014-05-17T04:05:33Z
       
  • 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
       
  • Segmentation accuracy of long bones
    • Abstract: Publication date: Available online 24 April 2014
      Source:Medical Engineering & Physics
      Author(s): Joyce Van den Broeck , Evie Vereecke , Roel Wirix-Speetjens , Jos Vander Sloten
      The use of three-dimensional imaging methodologies in new applications in the orthopaedic field has introduced a need for high accuracy, in addition to a correct diagnosis. The aim of this study was to quantify the absolute dimensional errors between models reconstructed from computed tomography and magnetic resonance images compared to a ground truth for various regions of the bone. Clinical CT and MRI scans were acquired from nine lower leg cadavers and the bones were subsequently cleaned from soft tissues. 3D models of the tibia were created from the segmented CT and MRI images and compared to optical scans of the cleaned bones (considered as ground truth). The 3D reconstruction using CT images resulted in an RMS error of 0.55mm, corresponding to an overestimated CT bone model compared to the cleaned bone. MR imaging resulted in an RMS error of 0.56mm; however, the MRI bone model was on average a small underestimation of the cleaned bone. Different regions of the bones were analysed, indicating a difference in accuracy between diaphysis and epiphysis. This study demonstrates a high accuracy for both CT and MRI imaging, supporting the feasibility of using MRI technology for the 3D reconstruction of bones in medical applications.


      PubDate: 2014-04-28T06:22:18Z
       
  • 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
       
  • An improved algorithm for the automatic detection and characterization of
           slow eye movements
    • Abstract: Publication date: Available online 25 April 2014
      Source:Medical Engineering & Physics
      Author(s): Filippo Cona , Fabio Pizza , Federica Provini , Elisa Magosso
      Slow eye movements (SEMs) are typical of drowsy wakefulness and light sleep. SEMs still lack of systematic physical characterization. We present a new algorithm, which substantially improves our previous one, for the automatic detection of SEMs from the electro-oculogram (EOG) and extraction of SEMs physical parameters. The algorithm utilizes discrete wavelet decomposition of the EOG to implement a Bayes classifier that identifies intervals of slow ocular activity; each slow activity interval is segmented into single SEMs via a template matching method. Parameters of amplitude, duration, velocity are automatically extracted from each detected SEM. The algorithm was trained and validated on sleep onsets and offsets of 20 EOG recordings visually inspected by an expert. Performances were assessed in terms of correctly identified slow activity epochs (sensitivity: 85.12%; specificity: 82.81%), correctly segmented single SEMs (89.08%), and time misalignment (0.49s) between the automatically and visually identified SEMs. The algorithm proved reliable even in whole sleep (sensitivity: 83.40%; specificity: 72.08% in identifying slow activity epochs; correctly segmented SEMs: 93.24%; time misalignment: 0.49s). The algorithm, being able to objectively characterize single SEMs, may be a valuable tool to improve knowledge of normal and pathological sleep.


      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
       
  • The effect of signal acquisition and processing choices on ApEn values:
           Towards a “gold standard” for distinguishing effort levels
           from isometric force records
    • Abstract: Publication date: Available online 13 April 2014
      Source:Medical Engineering & Physics
      Author(s): Sarah M. Forrest , John H. Challis , Samantha L. Winter
      Approximate entropy (ApEn) is frequently used to identify changes in the complexity of isometric force records with ageing and disease. Different signal acquisition and processing parameters have been used, making comparison or confirmation of results difficult. This study determined the effect of sampling and parameter choices by examining changes in ApEn values across a range of submaximal isometric contractions of the first dorsal interosseus. Reducing the sample rate by decimation changed both the value and pattern of ApEn values dramatically. The pattern of ApEn values across the range of effort levels was not sensitive to the filter cut-off frequency, or the criterion used to extract the section of data for analysis. The complexity increased with increasing effort levels using a fixed ‘r’ value (which accounts for measurement noise) but decreased with increasing effort level when ‘r’ was set to 0.1 of the standard deviation of force. It is recommended isometric force records are sampled at frequencies >200Hz, template length (‘m’) is set to 2, and ‘r’ set to measurement system noise or 0.1SD depending on physiological process to be distinguished. It is demonstrated that changes in ApEn across effort levels are related to changes in force gradation strategy.


      PubDate: 2014-04-18T06:33:00Z
       
 
 
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