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BIOLOGY (1323 journals)            First | 4 5 6 7 8 9 10 11 | Last

Journal of Biology and Earth Sciences     Open Access   (Followers: 1)
Journal of Biology and Life Science     Open Access   (Followers: 2)
Journal of Biology, Agriculture and Healthcare     Open Access   (Followers: 3)
Journal of Biomarkers     Open Access  
Journal of Biomechanics     Hybrid Journal   (Followers: 17)
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: 6)
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 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: 11)
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: 16)
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: 10)
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: 20)
Journal of Experimental and Clinical Anatomy     Full-text available via subscription  
Journal of Experimental Marine Biology and Ecology     Hybrid Journal   (Followers: 26)
Journal of Fish Biology     Hybrid Journal   (Followers: 24)
Journal of Functional Biomaterials     Open Access   (Followers: 1)
Journal of Genomes and Exomes     Open Access  
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: 4)
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: 2)
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: 6)
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: 6)
Journal of Mammalian Ova Research     Full-text available via subscription  
Journal of Mammalogy     Full-text available via subscription   (Followers: 6)
Journal of Mammary Gland Biology and Neoplasia     Hybrid Journal   (Followers: 1)
Journal of Marine Biology     Open Access   (Followers: 14)
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: 10)
Journal of Molecular Biology     Hybrid Journal   (Followers: 29)
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 Nanoparticles     Open Access  
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)

  First | 4 5 6 7 8 9 10 11 | Last

Journal Cover Medical Engineering & Physics
   Journal TOC RSS feeds Export to Zotero [11 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1350-4533
     Published by Elsevier Homepage  [2570 journals]   [SJR: 0.722]   [H-I: 57]
  • Feature dimensionality reduction for myoelectric pattern recognition: A
           comparison study of feature selection and feature projection methods
    • Abstract: Publication date: Available online 5 October 2014
      Source:Medical Engineering & Physics
      Author(s): Jie Liu
      This study investigates the effect of the feature dimensionality reduction strategies on the classification of surface electromyography (EMG) signals toward developing a practical myoelectric control system. Two dimensionality reduction strategies, feature selection and feature projection, were tested on both EMG feature sets, respectively. A feature selection based myoelectric pattern recognition system was introduced to select the features by eliminating the redundant features of EMG recordings instead of directly choosing a subset of EMG channels. The Markov random field (MRF) method and a forward orthogonal search algorithm were employed to evaluate the contribution of each individual feature to the classification, respectively. Our results from 15 healthy subjects indicate that, with a feature selection analysis, independent of the type of feature set, across all subjects high overall accuracies can be achieved in classification of seven different forearm motions with a small number of top ranked original EMG features obtained from the forearm muscles (average overall classification accuracy >95% with 12 selected EMG features). Compared to various feature dimensionality reduction techniques in myoelectric pattern recognition, the proposed filter-based feature selection approach is independent of the type of classification algorithms and features, which can effectively reduce the redundant information not only across different channels, but also cross different features in the same channel. This may enable robust EMG feature dimensionality reduction without needing to change ongoing, practical use of classification algorithms, an important step toward clinical utility.

      PubDate: 2014-10-09T11:21:43Z
  • Numerical analysis and experimental observation of guidewire motion in a
           blood vessel model
    • Abstract: Publication date: Available online 5 October 2014
      Source:Medical Engineering & Physics
      Author(s): Kazuto Takashima , Shotaro Tsuzuki , Atomu Ooike , Kiyoshi Yoshinaka , Kaihong Yu , Makoto Ohta , Koji Mori
      We have developed a computer-based system to simulate a guidewire in blood vessels for surgical planning, intra-operative assistance, and to facilitate the design of new guidewires. In this study, we compared simulation results with experimental results for validation of the simulation system. First, we inserted a commercial guidewire into a poly (vinyl alcohol) hydrogel blood vessel model using a two-axis automatic stage and measured the position of the guidewire tip and the contact force between the guidewire and the vessel. The experimental apparatus can be used not only for the validation of numerical analyses, but also as a simulation system. Second, similarly to the experiment, the motion of the guidewire in the blood vessel model was calculated when the proximal part of the guidewire model was pushed and twisted. The model of the guidewire is constructed with viscoelastic springs and segments, and the proximal part of the guidewire model is constrained by the fixed catheter model. Collisions between the guidewire and the vessel are calculated, and the contact forces are determined according to the stiffness of the vessel wall. The same tendency was seen in the trajectories and the contact force of both the experimental and simulated guidewire tips.

      PubDate: 2014-10-09T11:21:43Z
  • Rapid pressure-to-flow dynamics of cerebral autoregulation induced by
           instantaneous changes of arterial CO2
    • Abstract: Publication date: Available online 5 October 2014
      Source:Medical Engineering & Physics
      Author(s): Jia Liu , David M. Simpson , Hesam Kouchakpour , Ronney B. Panerai , Jie Chen , Shan Gao , Pandeng Zhang , Xinyu Wu
      Continuous assessment of CA is desirable in a number of clinical conditions, where cerebral hemodynamics may change within relatively short periods. In this work, we propose a novel method that can improve temporal resolution when assessing the pressure-to-flow dynamics in the presence of rapid changes in arterial CO2. A time-varying multivariate model is proposed to adaptively suppress the instantaneous effect of CO2 on CBFV by the recursive least square (RLS) method. Autoregulation is then quantified from the phase difference (PD) between arterial blood pressure (ABP) and CBFV by calculating the instantaneous PD between the signals using the Hilbert transform (HT). A Gaussian filter is used prior to HT in order to optimize the temporal and frequency resolution and show the rapid dynamics of cerebral autoregulation. In 13 healthy adult volunteers, rapid changes of arterial CO2 were induced by rebreathing expired air, while simultaneously and continuously recording ABP, CBFV and end-tidal CO2 (ETCO2). Both simulation and physiological studies show that the proposed method can reduce the transient distortion of the instantaneous phase dynamics caused by the effect of CO2 and is faster than our previous method in tracking time-varying autoregulation. The normalized mean square error (NMSE) of the predicted CBFV can be reduced significantly by 38.7% and 37.7% (p <0.001) without and with the Gaussian filter applied, respectively, when compared with the previous univariate model. These findings suggest that the proposed method is suitable to track rapid dynamics of cerebral autoregulation despite the influence of confounding covariates.

      PubDate: 2014-10-09T11:21:43Z
  • Computational modelling of the hybrid procedure in hypoplastic left heart
    • Abstract: Publication date: Available online 6 October 2014
      Source:Medical Engineering & Physics
      Author(s): Andrew Young , Terry Gourlay , Sean McKee , Mark H.D. Danton
      Previous studies have employed generic 3D-multiscale models to predict haemodynamic effects of the hybrid procedure in hypoplastic left heart syndrome. Patient-specific models, derived from image data, may allow a more clinically relevant model. However, such models require long computation times and employ internal pulmonary artery band [d int] dimension, which limits clinical application. Simpler, zero-dimensional models utilize external PAB diameters [d ext] and provide rapid analysis, which may better guide intervention. This study compared 0-D and 3-D modelling from a single patient dataset and investigated the relationship d int versus d ext and hemodynamic outputs of the two models. Optimum oxygen delivery defined at d int =2mm corresponded to d ext =3.1mm and 3.4mm when models were matched for cardiac output or systemic pressure, respectively. 0-D and 3-D models when matched for PAB dimension produced close equivalence of hemodynamics and ventricular energetics. From this study we conclude that 0-D model can provide a valid alternative to 3D-multiscale in the hybrid–HLHS circulation.

      PubDate: 2014-10-09T11:21:43Z
  • A method for carpal motion hysteresis quantification in 4-dimensional
           imaging of the wrist
    • Abstract: Publication date: Available online 29 September 2014
      Source:Medical Engineering & Physics
      Author(s): Ita Suzana Mat Jais , Xuan Liu , Kai-Nan An , Shian Chao Tay
      Introduction Carpal bones motions exhibit hysteresis that is dependent on the direction of wrist motion, which can be seen during 4-dimensional (3D plus time) imaging of the wrist. In vitro studies have demonstrated the phenomenon of carpal hysteresis and have reported that hysteresis area increases with carpal instabilities. However, their techniques required implantation of bone markers and thus cannot be used clinically. The objective of this study is to use noninvasive 4-dimensional computed tomography (4DCT) technique to quantify carpal hysteresis, and to determine the reliability of this method. Method A cadaveric wrist mounted on a custom motion simulator was imaged using a dual-source CT scanner while undergoing periodic radioulnar deviation. Ten image phases of this motion was reconstructed through retrospective cardiac gating. The rotational angles of scaphoid, lunate and triquetrum in each phase were derived through manual registration using Matlab after segmenting the bones in Analyze 8.1. These angles were then plotted against global wrist positional angles to produce the hysteresis curves and the area was calculated. The image segmentation and measurements were repeated by 2 raters to derive intra- and inter-rater reliability assessments. Results The hysteresis area was found to be larger in the lunate (96.5deg2) followed by triquetrum (92.3deg2) and scaphoid (67.5deg2). The measurement of the total hysteresis area of the scaphoid had the highest reliability with intra- and inter-rater reliability of 95.5% and 95.4% respectively. Discussion We have demonstrated that our approach of using 4DCT imaging can be used to assess and quantify the hysteresis of the carpal motion with good reliability.

      PubDate: 2014-10-03T10:36:06Z
  • Linear and nonlinear analyses of multi-channel mechanomyographic
           recordings reveal heterogeneous activation of wrist extensors in presence
           of delayed onset muscle soreness
    • Abstract: Publication date: Available online 30 September 2014
      Source:Medical Engineering & Physics
      Author(s): Pascal Madeleine , Ernst A. Hansen , Afshin Samani
      In this study, we applied multi-channel mechanomyographic (MMG) recordings in combination with linear and nonlinear analyses to investigate muscular and musculotendinous effects of high intensity eccentric exercise. Twelve accelerometers arranged in a 3×4 matrix over the dominant elbow muscles were used to detect MMG activity in 12 healthy participants. Delayed onset muscle soreness was induced by repetitive high intensity eccentric contractions of the wrist extensor muscles. Average rectified values (ARV) as well as percentage of recurrence (%REC) and percentage of determinism (%DET) extracted from recurrence quantification analysis were computed from data obtained during static–dynamic contractions performed before exercise, immediately after exercise, and in presence of muscle soreness. A linear mixed model was used for the statistical analysis. The ARV, %REC, and %DET maps revealed heterogeneous MMG activity over the wrist extensor muscles before, immediately after, and in presence of muscle soreness (P <0.01). The ARVs were higher while the %REC and %DET were lower in presence of muscle soreness compared with before exercise (P <0.05). The study provides new key information on linear and nonlinear analyses of multi-channel MMG recordings of the wrist extensor muscles following eccentric exercise that results in muscle soreness. Recurrence quantification analysis can be suggested as a tool for detection of MMG changes in presence of muscle soreness.

      PubDate: 2014-10-03T10:36:06Z
  • A novel system for automatic classification of upper limb motor function
           after stroke: An exploratory study
    • Abstract: Publication date: Available online 1 October 2014
      Source:Medical Engineering & Physics
      Author(s): Vítor Tedim Cruz , Virgílio Ferro Bento , David Dieteren Ribeiro , Isabel Araújo , Catarina Aguiar Branco , Paula Coutinho
      In the early post-stroke phase, when clinicians attempt to evaluate interventions and accurately measure motor performance, reliable tools are needed. Therefore, the development of a system capable of independent, repeated and automatic assessment of motor function is of increased importance. This manuscript explores the potential of a newly designed device for automatic assessment of motor impairment after stroke. A portable motion capture system was developed to acquire three-dimensional kinematics data of upper limb movements. These were then computed through an automatic decision tree classifier, with features inferred from the Functional Ability Score (FAS) of the Wolf Motor Function Test (WMFT). Five stroke patients were tested on both sides across five selected tasks. The system was compared against a trained clinician, operating simultaneously and blinded. Regarding performance time, the mean difference (system vs clinician) was 0.17s (sd=0.14s). For FAS evaluation, there was agreement in 4 out of 5 patients in the two tasks evaluated. The prototype tested was able to automatically classify upper limb movement, according to a widely used functional motor scale (WMFT) in a relevant clinical setting. These results represent an important step towards a system capable of precise and independent motor evaluation after stroke. The portability and low-cost design will contribute for its usability in ambulatory clinical settings and research trials.

      PubDate: 2014-10-03T10:36:06Z
  • In-vitro biomechanical evaluation of stress shielding and initial
           stability of a low-modulus hip stem made of β type Ti-33.6Nb-4Sn
    • Abstract: Publication date: Available online 1 October 2014
      Source:Medical Engineering & Physics
      Author(s): Go Yamako , Etsuo Chosa , Koji Totoribe , Shuji Hanada , Naoya Masahashi , Norikazu Yamada , Eiji Itoi
      Stress shielding-related proximal femoral bone loss after total hip arthroplasty occurs because of the different stiffness of metallic alloy stems and host bone. To overcome this, we fabricated a low-modulus cementless hip stem from β-type Ti-33.6Nb-4Sn alloy (TNS). Then we evaluated its stiffness, stress shielding, and initial stability compared with a similar Ti-6Al-4V alloy stem. Stiffness was determined by axial compression and cantilever-bending tests. Thirteen triaxial strain gages measured cortical strain. Stress shielding was defined as the percentage of intact strain after stem insertion. To evaluate initial stability, displacement transducers measured axial relative displacement and rotation. Intact and implanted femurs underwent single-leg-stance loading. Axial stiffness was 56% lower in the TNS stem than in the Ti-6Al-4V stem, and bending stiffness of the TNS stem decreased gradually from the proximal region to the distal region, being ≤53% that of the Ti-6Al-4V stem, indicating gradation of Young's modulus. The TNS stem decreased stress shielding in the proximal calcar region (A1: 83%, B1: 85% relative to intact cortical strain) without affecting the proximal lateral region (B3: 53%). The initial stabilities of the stems were comparable. These findings indicate that the TNS stem with gradation of Young's modulus minimizes proximal femoral bone loss and biological fixation, improving long-term stability.
      Graphical abstract image

      PubDate: 2014-10-03T10:36:06Z
  • Editorial
    • Abstract: Publication date: Available online 26 September 2014
      Source:Medical Engineering & Physics
      Author(s): Cheng-Kung Cheng , Yubo Fan

      PubDate: 2014-09-29T10:05:58Z
  • Effect of combining traction and vibration on back muscles, heart rate and
           blood pressure
    • Abstract: Publication date: Available online 26 September 2014
      Source:Medical Engineering & Physics
      Author(s): Lizhen Wang , Meiya Zhao , Jian Ma , Shan Tian , Pin Xiang , Wei Yao , Yubo Fan
      Eighty-five percentage of the population has ever experienced low back pain (LBP), which would result in decreasing of muscle strength and endurance, functional capacity of the spine and so on. Traction and vibration were commonly used to relieve the low back pain. It was investigated that the effect of the combing traction and vibration on back muscles, heart rate (HR) and blood pressure (BP) in this study. Thirty healthy subjects participated in 12 trials lying supine on the spine combing bed with different tilt angle (0°, 10°, 20° and 30°) and vibration modes (along with the sagittal and coronal axis with 0Hz, 2Hz and 12Hz separately). EMG was recorded during each trial. Power spectral frequency analysis was applied to evaluate muscle fatigue by the shift of median power frequency (MPF). Pulse pressure (PP) was calculated from BP. HR and PP were used to estimate the effect of the combination of traction and vibration on cardio-vascular system. It was shown that vibration could increase HR and decrease PP. The combination of traction and vibration (2Hz vibration along Z-axis and 12Hz vibration along Y-axis) might have no significant effect on cardio-vascular system. The MPF of LES and UT decreased significantly when the angle reached 20° under the condition of 2Hz vibration along Z-axis compared with it of 0°. What's more, the MPF also decreased significantly compared with it of static mode at 20° for LES and at 30° for UT. However at 12Hz vibration along Y-axis, the MPF had significant increase when the angle reached 20° in LES and 30° in UT compared to it of 0°. For LES, the MPF also had significant difference when the angle was added from 10° to 20°. Therefore, when the 2Hz vibration along Z-axis and traction (tilt angles that less than 20°) were combined, it was helpful to reduce muscle fatigue both for LES and UT compared with only vibration or traction. When the 12Hz vibration along Y-axis and traction (tilt angles that more than 10° for LES and more than 20° for UT) were combined, it could provide good treatment with lower muscle fatigue for back pain compared with only vibration or traction. It is helpful to provide biomechanical quantitative basis for the selection of the clinical treatment methods.

      PubDate: 2014-09-29T10:05:58Z
  • Assessing the bilateral geometrical differences of the tibia – Are
           they the same'
    • Abstract: Publication date: Available online 27 September 2014
      Source:Medical Engineering & Physics
      Author(s): S. Radzi , M. Uesugi , A. Baird , S. Mishra , M. Schuetz , B. Schmutz
      Contralateral bones are often used in many medical applications but it is assumed that their bilateral differences are insignificant. Previous studies used a limited number of distance measurements in quantifying the corresponding differences; therefore, little is known about their bilateral 3D surface asymmetries. The aim of the study is to develop a comprehensive method to quantify geometrical asymmetries between the left and right tibia in order to provide first results on whether the contralateral tibia can be used as an equivalent reference. In this study, 3D bone models were reconstructed from CT scans of seven tibiae pairs, and 34 variables consisting of 2D and 3D measurements were measured from various anatomical regions. All 2D measurements, and lateral plateau and distal subchondral bone surface measurements showed insignificant differences (p >0.05), but the rest of the surfaces showed significant differences (p <0.05). Our results suggest that the contralateral tibia can be used as a reference especially in surgical applications such as articular reconstructions since the bilateral differences in the subchondral bone surfaces were less than 0.3mm. The method can also be potentially transferable to other relevant studies that require the accurate quantification of bone bilateral asymmetries.

      PubDate: 2014-09-29T10:05:58Z
  • Automatic detection of wakefulness and rest intervals in actigraphic
           signals: A data-driven approach
    • Abstract: Publication date: Available online 26 September 2014
      Source:Medical Engineering & Physics
      Author(s): D. Martín-Martínez , P. Casaseca-de-la-Higuera , J.M. Andrés-de-Llano , J.R. Garmendia-Leiza , S. Alberola-López , C. Alberola-López
      Actigraphy is an useful tool for evaluating the activity pattern of a subject; activity registries are usually processed by first splitting the signal into its wakefulness and rest intervals and then analyzing each one in isolation. Consequently, a preprocessing stage for such a splitting is needed. Several methods have been reported to this end but they rely on parameters and thresholds which are manually set based on previous knowledge of the signals or learned from training. This compromises the general applicability of this methods. In this paper we propose a new method in which thresholds are automatically set based solely on the specific registry to be analyzed. The method consists of two stages: (1) estimation of an initial classification mask by means of the expectation maximization algorithm and (2) estimation of a final refined mask through an iterative method which re-estimates both the mask and the classifier parameters at each iteration step. Results on real data show that our methodology outperforms those so far proposed and can be more effectively used to obtain derived sleep quality parameters from actigraphy registries.

      PubDate: 2014-09-29T10:05:58Z
  • Image-based vs. mesh-based statistical appearance models of the human
           femur: Implications for finite element simulations
    • Abstract: Publication date: Available online 27 September 2014
      Source:Medical Engineering & Physics
      Author(s): Serena Bonaretti , Christof Seiler , Christelle Boichon , Mauricio Reyes , Philippe Büchler
      Statistical appearance models have recently been introduced in bone mechanics to investigate bone geometry and mechanical properties in population studies. The establishment of accurate anatomical correspondences is a critical aspect for the construction of reliable models. Depending on the representation of a bone as an image or a mesh, correspondences are detected using image registration or mesh morphing. The objective of this study was to compare image-based and mesh-based statistical appearance models of the femur for finite element (FE) simulations. To this aim, (i) we compared correspondence detection methods on bone surface and in bone volume; (ii) we created an image-based and a mesh-based statistical appearance models from 130 images, which we validated using compactness, representation and generalization, and we analyzed the FE results on 50 recreated bones vs. original bones; (iii) we created 1000 new instances, and we compared the quality of the FE meshes. Results showed that the image-based approach was more accurate in volume correspondence detection and quality of FE meshes, whereas the mesh-based approach was more accurate for surface correspondence detection and model compactness. Based on our results, we recommend the use of image-based statistical appearance models for FE simulations of the femur.

      PubDate: 2014-09-29T10:05:58Z
  • The role of coupled resistance–compliance in upper tracheobronchial
           airways under high frequency oscillatory ventilation
    • Abstract: Publication date: Available online 22 September 2014
      Source:Medical Engineering & Physics
      Author(s): Mohammed Alzahrany , Arindam Banerjee , Gary Salzman
      A large eddy simulation (LES) based computational fluid dynamics (CFD) study was conducted to investigate lung lobar ventilation and gas exchange under high frequency oscillatory ventilation conditions. Time-dependent pressure coupled with the airways resistance and compliance (R&C) were imposed as boundary conditions (BCs) in the upper tracheobronchial tree of patient-specific lung geometry. The flow distribution in the left and right lungs demonstrated significant variations compared to the case in which traditional BCs based on mass flow rate fractions was used and is in agreement with the in vivo data available in the literature. The gas transport due to the pendelluft mechanism was captured in the different lung lobes and units. The computed pendelluft elapsed time was consistent with available physiological data. In contrast to in vivo studies, our simulations were able to predict the volume associated with the pendelluft elapsed time at different frequencies. Significant differences in coaxial counter flow and flow structures were observed between different BCs. The consistency of the results with the physiological in vivo data indicates that computations with coupled R&C BCs provide a suitable alternative tool for understanding the gas transport, diagnosing lung pathway disease severity, and optimizing ventilation management techniques.

      PubDate: 2014-09-22T06:41:31Z
  • Baseline drift removal and denoising of MCG data using EEMD: Role of noise
           amplitude and the thresholding effect
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • Robust heart sound detection in respiratory sound using LRT with maximum a
           posteriori based online parameter adaptation
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      Author(s): Hamed Shamsi , I. Yucel Ozbek
      This paper investigates the utility of a likelihood ratio test (LRT) combined with an efficient adaptation procedure for the purpose of detecting the heart sound (HS) with lung sound and the lung sound only (non-HS) segments in a respiratory signal. The proposed detection method has four main stages: feature extraction, training of the models, detection, and adaptation of the model parameter. In the first stage, the logarithmic energy features are extracted for each frame of respiratory sound. In the second stage, the probabilistic models for HS and non-HS segments are constructed by training Gaussian mixture models (GMMs) with an expectation maximization algorithm in a subject-independent manner, and then the HS and non-HS segments are detected by the results of the LRT based on the GMMs. In the adaptation stage, the subject-independent trained model parameter is modified online using the observed test data to fit the model parameter of the target subject. Experiments were performed on the database from 24 healthy subjects. The experimental results indicate that the proposed heart sound detection algorithm outperforms two well-known heart sound detection methods in terms of the values of the normalized area under the detection error trade-off curve (NAUC), the false negative rate (FNR), and the false positive rate (FPR).

      PubDate: 2014-09-19T06:16:56Z
  • An algorithm to decompose ground reaction forces and moments from a single
           force platform in walking gait
    • Abstract: Publication date: Available online 16 September 2014
      Source:Medical Engineering & Physics
      Author(s): David Villeger , Antony Costes , Bruno Watier , Pierre Moretto
      In walking experimental conditions, subjects are sometimes unable to perform two steps on two different forceplates. This leads the authors to develop methods for discerning right and left ground reaction data while they are summed during the double support in walking. The aim of this study is to propose an adaptive transition function that considers the walking speed and ground reaction forces (GRF). A transition function is used to estimate left and right side GRF signals in double support. It includes a shape coefficient adjusted using single support GRF parameters. This shape coefficient is optimized by a non-linear least-square curve-fitting procedure to match the estimated signals with real GRF. A multiple regression is then performed to identify GRF parameters of major importance selected to compute the right and left GRF of the double support. Relative RMSE (RMSER), maximum GRF differences normalized to body mass and differences of center of pressure (CoP) are computed between real and decomposed signals. During double support, RMSER are 6%, 18%, 3.8%, 4.3%, 3%, and 12.3% for anterior force, lateral force, vertical force, frontal moment, sagittal moment and transverse moment, respectively. Maximum GRF differences normalized to body mass are lower than 1N/kg and mean CoP difference is 0.0135m, when comparing real to decomposed signals during double support. This work shows the accuracy of an adaptive transition function to decompose GRF and moment of right and left sides. This method is especially useful to accurately discern right and left GRF data in single force platform configurations.

      PubDate: 2014-09-19T06:16:56Z
  • In vivo measurements of patellar tracking and finite helical axis using a
           static magnetic resonance based methodology
    • Abstract: Publication date: Available online 18 September 2014
      Source:Medical Engineering & Physics
      Author(s): Jie Yao , Bin Yang , Wenxin Niu , Jianwei Zhou , Yuxing Wang , He Gong , Huasong Ma , Rong Tan , Yubo Fan
      Patellofemoral (PF) maltracking is a critical factor predisposing to PF pain syndrome. Many novel techniques of measuring patellar tracking remain research tools. This study aimed to develop a method to measure the in vivo patellar tracking and finite helical axis (FHA) by using a static magnetic resonance (MR) based methodology. The geometrical models of PF joint at 0°, 45°, 60°, 90°, and 120° of knee flexion were developed from MR images. The approximate patellar tracking was derived from the discrete PF models with a spline interpolation algorithm. The patellar tracking was validated with the previous in vitro and in vivo experiments. The patellar FHA throughout knee flexion was calculated. In the present case, the FHA drew an “L-shaped” curve in the sagittal section. This methodology could advance the examination of PF kinematics in clinics, and may also provide preliminary knowledge on patellar FHA study.

      PubDate: 2014-09-19T06:16:56Z
  • A new protocol from real joint motion data for wear simulation in total
           knee arthroplasty: Stair climbing
    • Abstract: Publication date: Available online 18 September 2014
      Source:Medical Engineering & Physics
      Author(s): Santina Battaglia , Claudio Belvedere , Sami Abdel Jaber , Saverio Affatato , Valentina D’Angeli , Alberto Leardini
      In its normal lifespan, a knee prosthesis must bear highly demanding loading conditions, going beyond the sole activity of level walking required by ISO standard 14243. We have developed a protocol for in vitro wear simulation of stair climbing on a displacement controlled knee simulator. The flexion/extension angle, intra/extra rotation angle, and antero/posterior translation were obtained in patients by three-dimensional video-fluoroscopy. Axial load data were collected by gait analysis. Kinematics and load data revealed a good consistence across patients, in spite of the different prosthesis size. The protocol was then implemented and tested on a displacement controlled knee wear simulator, showing an accurate reproduction of stair climbing waveforms with a relative error lower than 5%.

      PubDate: 2014-09-19T06:16:56Z
  • 3D printing of MRI compatible components: Why every MRI research group
           should have a low-budget 3D printer
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      Author(s): Karl-Heinz Herrmann , Clemens Gärtner , Daniel Güllmar , Martin Krämer , Jürgen R. Reichenbach
      Purpose To evaluate low budget 3D printing technology to create MRI compatible components. Material and methods A 3D printer is used to create customized MRI compatible components, a loop-coil platform and a multipart mouse fixation. The mouse fixation is custom fit for a dedicated coil and facilitates head fixation with bite bar, anesthetic gas supply and biomonitoring sensors. The mouse fixation was tested in a clinical 3T scanner. Results All parts were successfully printed and proved MR compatible. Both design and printing were accomplished within a few days and the final print results were functional with well defined details and accurate dimensions (Δ < 0.4mm). MR images of the mouse head clearly showed reduced motion artifacts, ghosting and signal loss when using the fixation. Conclusions We have demonstrated that a low budget 3D printer can be used to quickly progress from a concept to a functional device at very low production cost. While 3D printing technology does impose some restrictions on model geometry, additive printing technology can create objects with complex internal structures that can otherwise not be created by using lathe technology. Thus, we consider a 3D printer a valuable asset for MRI research groups.

      PubDate: 2014-09-19T06:16:56Z
  • In vitro dermal and epidermal cellular response to titanium alloy implants
           fabricated with electron beam melting
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      Author(s): Jessica Collins Springer , Ola L.A. Harrysson , Denis J. Marcellin-Little , Susan H. Bernacki
      Transdermal osseointegrated prostheses (TOPs) are emerging as an alternative to socket prostheses. Electron beam melting (EBM) is a promising additive manufacturing technology for manufacture of custom, freeform titanium alloy (Ti6Al4V) implants. Skin ongrowth for infection resistance and mechanical stability are critically important to the success of TOP, which can be influenced by material composition and surface characteristics. We assessed viability and proliferation of normal human epidermal keratinocytes (NHEK) and normal human dermal fibroblasts (NHDF) on several Ti6Al4V surfaces: solid polished commercial, solid polished EBM, solid unpolished EBM and porous unpolished EBM. Cell proliferation was evaluated at days 2 and 7 using alamarBlue® and cell viability was analyzed with a fluorescence-based live–dead assay after 1 week. NHDF and NHEK were viable and proliferated on all Ti6Al4V surfaces. NHDF proliferation was highest on commercial and EBM polished surfaces. NHEK was highest on commercial polished surfaces. All EBM Ti6Al4V discs exhibited an acceptable biocompatibility profile compared to solid Ti6Al4V discs from a commercial source for dermal and epidermal cells. EBM may be considered as an option for fabrication of custom transdermal implants.

      PubDate: 2014-09-19T06:16:56Z
  • Design and validation of a cadaveric knee joint loading device compatible
           with magnetic resonance imaging and computed tomography
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      Author(s): Larry Chen , Karen Gordon , Mark Hurtig
      Purpose Design and validation of a magnetic resonance and computed tomography compatible device capable of applying physiologically relevant muscle forces to cadaveric knee joints with high levels of repeatability and reproducibility. Methods Repeatability and reproducibility were assessed with two porcine stifle joints. Load was applied to joints at full extension, five and 15 degrees of flexion through two cables simulating the lines of action of the quadriceps and hamstrings muscles. Five repeatability and five reproducibility trials were performed at each flexion angle. Standard deviations (SDs) of joint angle and load were recorded. Results For repeatability, the maximum SDs for joint angle were 1.26° (flexion), 1.54° (ab/adduction) and 0.90° (in/external rotation). The maximum SDs for joint load were 4.60N (anterior/posterior), 7.36N (medial/lateral), and 42.6N (axial). For reproducibility, the maximum SDs for joint angle were 0.84° (flexion), 0.66° (ab/adduction) and 0.92° (in/external rotation). The maximum SDs for joint load were 6.40N (anterior/posterior), 11.7N (medial/lateral), and 39.7N (axial). Conclusions This level of repeatability and reproducibility is within intra-subject variability of measured gait kinematics. Therefore, this device is considered to be an effective tool for in vitro testing of knee soft tissue repair.

      PubDate: 2014-09-19T06:16:56Z
  • Automatic modeling of pectus excavatum corrective prosthesis using
           artificial neural networks
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • A novel stability and kinematics-driven trunk biomechanical model to
           estimate muscle and spinal forces
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • Arterial pulsatility improvement in a feedback-controlled continuous flow
           left ventricular assist device: An ex-vivo experimental study
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • 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: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • Editorial Board
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10

      PubDate: 2014-09-19T06:16:56Z
  • A neural network approach for determining gait modifications to reduce the
           contact force in knee joint implant
    • Abstract: Publication date: October 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 10
      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: 2014-09-19T06:16:56Z
  • Control strategies for effective robot assisted gait rehabilitation: The
           state of art and future prospects
    • Abstract: Publication date: Available online 7 September 2014
      Source:Medical Engineering & Physics
      Author(s): Jinghui Cao , Sheng Quan Xie , Raj Das , Guo L. Zhu
      A large number of gait rehabilitation robots, together with a variety of control strategies, have been developed and evaluated during the last decade. Initially, control strategies applied to rehabilitation robots were adapted from those applied to traditional industrial robots. However, these strategies cannot optimise effectiveness of gait rehabilitation. As a result, researchers have been investigating control strategies tailored for the needs of rehabilitation. Among these control strategies, assisted-as-needed (AAN) control is one of the most popular research topics in this field. AAN training strategies have gained the theoretical and practical evidence based backup from motor learning principles and clinical studies. Various approaches to AAN training have been proposed and investigated by research groups all around the world. This article presents a review on control algorithms of gait rehabilitation robots to summarise related knowledge and investigate potential trends of development. There are existing review papers on control strategies of rehabilitation robots. The review by Marchal-Crespo and Reinkensmeyer (2009) had a broad cover of control strategies of all kinds of rehabilitation robots. Hussain et al. (2011) had specifically focused on treadmill gait training robots and covered a limited number of control implementations on them. This review article encompasses more detailed information on control strategies for robot assisted gait rehabilitation, but is not limited to treadmill based training. It also investigates the potential to further develop assist-as-needed gait training based on assessments of patients’ ability. In this paper, control strategies are generally divided into the trajectory tracking control and AAN control. The review covers these two basic categories, as well as other control algorithm and technologies derived from them, such as biofeedback control. Assessments on human gait ability are also included to investigate how to further develop implementations based on assist-as-needed concept. For the consideration of effectiveness, clinical studies on robotic gait rehabilitation are reviewed and analysed from the viewpoint of control algorithm.

      PubDate: 2014-09-11T05:24:38Z
  • Static autoregulation in humans: a review and reanalysis
    • Abstract: Publication date: Available online 7 September 2014
      Source:Medical Engineering & Physics
      Author(s): Tianne Numan , Anthony R. Bain , Ryan L. Hoiland , Jonathan D. Smirl , Nia C. Lewis , Philip N. Ainslie
      Introduction Cerebral autoregulation (CA) is a theoretical construct characterized by the relationship between mean arterial pressure (MAP) and cerebral blood flow (CBF). We performed a comprehensive literature search to provide an up-to-date review on the static relationship between MAP and CBF. Methods The results are based on 40 studies (49 individual experimental protocols) in healthy subjects between 18 and 65 years. Exclusion criteria were: a ΔMAP <5%, hypoxia/hyperoxia or hypo/hypercapnia, and unstable levels (<2min stages). The partial pressure of arterial CO2 (PaCO2) was measured in a subset of the included studies (n =28); therefore, CBF was also adjusted to account for small changes in PaCO2. Results The linear regression coefficient between MAP and CBF (or velocity) of 0.82±0.77%ΔCBF/%ΔMAP during decreases in MAP (n =23 experiments) was significantly different than the relationship of 0.21±0.47%ΔCBF/%ΔMAP during increases (n =26 experiments; p <0.001). After correction for increases/decreases in PaCO2, the slopes were not significantly different: 0.64±1.16%ΔCBF/%ΔMAP (n =16) and 0.39±0.30%ΔCBF/%ΔMAP (n =12) for increased vs. decreased MAP changes, respectively (p =0.60). Conclusion The autoregulatory ability of the cerebral circulation appears to be more active in buffering increases in MAP as compared to reductions in MAP. However, the statistical finding of hysteresis is lost following an attempt to correct for PaCO2.

      PubDate: 2014-09-11T05:24:38Z
  • What if you stretch the IFU' A mechanical insight into stent graft
           instructions for use in angulated proximal aneurysm necks
    • Abstract: Publication date: Available online 10 September 2014
      Source:Medical Engineering & Physics
      Author(s): S. De Bock , F. Iannaccone , M. De Beule , F. Vermassen , P. Segers , B. Verhegghe
      Endovascular treatment for patients with a proximal neck anatomy outside instructions for use is an ongoing topic of debate in endovascular aneurysm repair. This paper employs the finite element method to offer insight into possible adverse effects of deploying a stent graft into an angulated geometry. The effect of angulation, straight neck length and device oversize was investigated in a full factorial parametric analysis. Stent apposition, area reduction of the graft, asymmetry of contact forces and the ability to find a good seal were investigated. Most adverse effects are expected for combinations of high angulation and short straight landing zones. Higher oversize has a beneficiary effect, but not enough to compensate the adverse effects of (very) short and angulated angles. Our analysis shows that for an angle between the suprarenal aorta and proximal neck above 60°, proximal kinking of the device can occur. The method used offers a engineering view on the morphological limits of EVAR for a clinically used device.

      PubDate: 2014-09-11T05:24:38Z
  • Walking speed estimation using foot-mounted inertial sensors: Comparing
           machine learning and strap-down integration methods
    • Abstract: Publication date: Available online 5 September 2014
      Source:Medical Engineering & Physics
      Author(s): Andrea Mannini , Angelo Maria Sabatini
      In this paper we implemented machine learning (ML) and strap-down integration (SDI) methods and analyzed them for their capability of estimating stride-by-stride walking speed. Walking speed was computed by dividing estimated stride length by stride time using data from a foot mounted inertial measurement unit. In SDI methods stride-by-stride walking speed estimation was driven by detecting gait events using a hidden Markov model (HMM) based method (HMM-based SDI); alternatively, a threshold-based gait event detector was investigated (threshold-based SDI). In the ML method a linear regression model was developed for stride length estimation. Whereas the gait event detectors were a priori fixed without training, the regression model was validated with leave-one-subject-out cross-validation. A subject-specific regression model calibration was also implemented to personalize the ML method. Healthy adults performed over-ground walking trials at natural, slower-than-natural and faster-than-natural speeds. The ML method achieved a root mean square estimation error of 2.0% and 4.2%, with and without personalization, against 2.0% and 3.1% by HMM-based SDI and threshold-based SDI. In spite that the results achieved by the two approaches were similar, the ML method, as compared with SDI methods, presented lower intra-subject variability and higher inter-subject variability, which was reduced by personalization.

      PubDate: 2014-09-06T04:51:13Z
  • Nonlinear properties of cardiac rhythm and respiratory signal under paced
           breathing in young and middle-aged healthy subjects
    • Abstract: Publication date: Available online 4 September 2014
      Source:Medical Engineering & Physics
      Author(s): Ana Kapidžić , Mirjana M Platiša , Tijana Bojić , Aleksandar Kalauzi
      We examined the effects of gender and age in young and middle-aged subjects on the level of cardio-respiratory interaction by analyzing properties of cardiac, respiratory and cardiac-respiratory regulatory mechanisms under paced breathing. In 56 healthy subjects, ECG (RR interval) and respiratory signal were simultaneously acquired in supine position at paced (0.1–0.45Hz, steps of 0.05Hz) and spontaneous breathing. The participants were divided into gender matched group of young adults (19–25 years old) and middle-aged adults (35–44 years old). Power spectral analysis was applied on RR interval time series and spectral components in very low frequency (VLF), low frequency (LF) and high frequency (HF) ranges were computed. We also calculated sample entropy of RR interval series (SampEnRR), respiratory series (SampEnResp), and their cross-sample entropy (cross-SampEn). Under paced breathing, reduction of all spectral powers with age (p <0.05) is not gender dependent but reduction of some entropy measures is; SampEnRR and SampEnResp were lower only in men (p <0.05). In the middle-aged subjects, effect of gender on spectral measures is significant; males had lower HF (p <0.05). Pattern of dependencies of SampEn and cross-SampEn on paced breathing frequency were significantly different in men (young vs. middle-aged, p =0.001 and p =0.037) and in middle-aged subjects (females vs. males, p =0.011 and p =0.008). In middle-aged males, lower entropy measures indicated reduced and less complex partial cardiac and respiratory control, and central cardio-respiratory control. In conclusion, in healthy middle-aged subjects changes in cardio-respiratory coupling are detectable only in males.

      PubDate: 2014-09-06T04:51:13Z
  • Computer-aided surgical planner for a new bone deformity correction device
           using axis-angle representation
    • Abstract: Publication date: Available online 4 September 2014
      Source:Medical Engineering & Physics
      Author(s): Ying Ying Wu , Anton Plakseychuk , Kenji Shimada
      Current external fixators for distraction osteogenesis (DO) are unable to correct all types of deformities in the lower limb and are difficult to use because of the lack of a pre-surgical planning system. We propose a DO system that consists of a surgical planner and a new, easy-to-setup unilateral fixator that not only corrects all lower limb deformity, but also generates the contralateral/predefined bone shape. Conventionally, bulky constructs with six or more joints (six degrees of freedom, 6DOF) are needed to correct a 3D deformity. By applying the axis-angle representation, we can achieve that with a compact construct with only two joints (2DOF). The proposed system makes use of computer-aided design software and computational methods to plan and simulate the planned procedure. Results of our stress analysis suggest that the stiffness of our proposed fixator is comparable to that of the Orthofix unilateral external fixator. We tested the surgical system on a model of an adult deformed tibia and the resulting bone trajectory deviates from the target bone trajectory by 1.8mm, which is below our defined threshold error of 2mm. We also extracted the transformation matrix that defines the deformity from the bone model and simulated the planned procedure.

      PubDate: 2014-09-06T04:51:13Z
  • Comprehensive evaluation of PCA-based finite element modelling of the
           human femur
    • Abstract: Publication date: Available online 14 August 2014
      Source:Medical Engineering & Physics
      Author(s): Lorenzo Grassi , Enrico Schileo , Christelle Boichon , Marco Viceconti , Fulvia Taddei
      Computed tomography (CT)-based finite element (FE) reconstructions describe shape and density distribution of bones. Both shape and density distribution, however, can vary a lot between individuals. Shape/density indexation (usually achieved by principal component analysis—PCA) can be used to synthesize realistic models, thus overcoming the shortage of CT-based models, and helping e.g. to study fracture determinants, or steer prostheses design. The aim of this study was to describe a PCA-based statistical modelling algorithm, and test it on a large CT-based population of femora, to see if it can accurately describe and reproduce bone shape, density distribution, and biomechanics. To this aim, 115 CT-datasets showing normal femoral anatomy were collected and characterized. Isotopological FE meshes were built. Shape and density indexation procedures were performed on the mesh database. The completeness of the database was evaluated through a convergence study. The accuracy in reconstructing bones not belonging to the indexation database was evaluated through (i) leave-one-out tests (ii) comparison of calculated vs. in-vitro measured strains. Fifty indexation modes for shape and 40 for density were necessary to achieve reconstruction errors below pixel size for shape, and below 10% for density. Similar errors for density, and slightly higher errors for shape were obtained when reconstructing bones not belonging to the database. The in-vitro strain prediction accuracy of the reconstructed FE models was comparable to state-of-the-art studies. In summary, the results indicate that the proposed statistical modelling tools are able to accurately describe a population of femora through finite element models.

      PubDate: 2014-08-17T03:03:44Z
  • Subject-specific evaluation of patellofemoral joint biomechanics during
           functional activity
    • Abstract: Publication date: September 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 9
      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: 2014-08-17T03:03:44Z
  • Comparative study of corneal tangent elastic modulus measurement using
           corneal indentation device
    • Abstract: Publication date: September 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 9
      Author(s): Match W.L. Ko , Leo K.K. Leung , David C.C. Lam
      The aim of this study is to examine the corneal tangent modulus measurement repeatability and performance of the corneal indentation device (CID). Twenty enucleated porcine eyes were measured and the eyes were pressurized using saline solution-filled manometer to 15 and 30mmHg. Corneal tangent moduli measured using the CID were compared with those measured using high precision universal testing machine (UTM). The within-subject standard deviation (Sw), repeatability (2.77×Sw), coefficient of variation (CV) (Sw/overall mean), and intraclass correlation coefficient (ICC) were determined. The mean corneal tangent moduli measured using UTM and CID were 0.094±0.030 and 0.094±0.028MPa at 15mmHg, and 0.207±0.056 and 0.207±0.055MPa at 30mmHg, respectively, with a difference less than 0.13%. The 95% limit of agreement was between −0.009 and 0.009MPa. The Sw, repeatability, CV and ICC of corneal tangent moduli measured by the CID were 0.006MPa, 0.015MPa, 4.3% and 0.993, respectively. The results showed that the corneal tangent moduli measured by the CID are repeatable and are in good agreement with the results measured by the high precision UTM.

      PubDate: 2014-08-17T03:03:44Z
  • Effect of pulsatile swirling flow on stenosed arterial blood flow
    • Abstract: Publication date: September 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 9
      Author(s): Hojin Ha , Sang Joon Lee
      The existence of swirling flow phenomena is frequently observed in arterial vessels, but information on the fluid-dynamic roles of swirling flow is still lacking. In this study, the effects of pulsatile swirling inlet flows with various swirling intensities on the flow field in a stenosis model are experimentally investigated using a particle image velocimetry velocity field measurement technique. A pulsatile pump provides cyclic pulsating inlet flow and spiral inserts with two different helical pitches (10D and 10/3D) induce swirling flow in the stenosed channel. Results show that the pulsatile swirling flow has various beneficial effects by reducing the negative wall shear stress, the oscillatory shear index, and the flow reverse coefficient at the post-stenosis channel. Temporal variations of vorticity fields show that the short propagation length of the jet flow and the early breakout of turbulent flow are initiated as the swirling flow disturbs the symmetric development of the shear layer. In addition, the overall energy dissipation rate of the flow is suppressed by the swirling component of the flow. The results will be helpful for elucidating the hemodynamic characteristics of atherosclerosis and discovering better diagnostic procedures and clinical treatments.

      PubDate: 2014-08-17T03:03:44Z
  • Editorial Board
    • Abstract: Publication date: September 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 9

      PubDate: 2014-08-17T03:03:44Z
  • Optimal needle design for minimal insertion force and bevel length
    • Abstract: Publication date: September 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 9
      Author(s): Yancheng Wang , Roland K. Chen , Bruce L. Tai , Patrick W. McLaughlin , Albert J. Shih
      This research presents a methodology for optimal design of the needle geometry to minimize the insertion force and bevel length based on mathematical models of cutting edge inclination and rake angles and the insertion force. In brachytherapy, the needle with lower insertion force typically is easier for guidance and has less deflection. In this study, the needle with lancet point (denoted as lancet needle) is applied to demonstrate the model-based optimization for needle design. Mathematical models to calculate the bevel length and inclination and rake angles for lancet needle are presented. A needle insertion force model is developed to predict the insertion force for lancet needle. The genetic algorithm is utilized to optimize the needle geometry for two cases. One is to minimize the needle insertion force. Using the geometry of a commercial lancet needle as the baseline, the optimized needle has 11% lower insertion force with the same bevel length. The other case is to minimize the bevel length under the same needle insertion force. The optimized design can reduce the bevel length by 46%. Both optimized needle designs were validated experimentally in ex vivo porcine liver needle insertion tests and demonstrated the methodology of the model-based optimal needle design.

      PubDate: 2014-08-17T03:03:44Z
  • Characterization of robotic system passive path repeatability during
           specimen removal and reinstallation for in vitro knee joint testing
    • Abstract: Publication date: Available online 12 August 2014
      Source:Medical Engineering & Physics
      Author(s): Mary T. Goldsmith , Sean D. Smith , Kyle S. Jansson , Robert F. LaPrade , Coen A. Wijdicks
      Robotic testing systems are commonly utilized for the study of orthopaedic biomechanics. Quantification of system error is essential for reliable use of robotic systems. Therefore, the purpose of this study was to quantify a 6-DOF robotic system's repeatability during knee biomechanical testing and characterize the error induced in passive path repeatability by removing and reinstalling the knee. We hypothesized removing and reinstalling the knee would substantially alter passive path repeatability. Testing was performed on four fresh-frozen cadaver knees. To determine repeatability and reproducibility, the passive path was collected three times per knee following the initial setup (intra-setup), and a single time following two subsequent re-setups (inter-setup). Repeatability was calculated as root mean square error. The intra-setup passive path had a position repeatability of 0.23mm. In contrast, inter-setup passive paths had a position repeatability of 0.89mm. When a previously collected passive path was replayed following re-setup of the knee, resultant total force repeatability across the passive path increased to 28.2N (6.4N medial–lateral, 25.4N proximal–distal, and 10.5N anterior–posterior). This study demonstrated that removal and re-setup of a knee can have substantial, clinically significant changes on our system's repeatability and ultimately, accuracy of the reported results.

      PubDate: 2014-08-14T02:43:52Z
  • First in vivo application and evaluation of a novel method for
           non-invasive estimation of cardiac output
    • Abstract: Publication date: Available online 6 August 2014
      Source:Medical Engineering & Physics
      Author(s): Theodore G. Papaioannou , Dimitrios Soulis , Orestis Vardoulis , Athanase Protogerou , Petros P. Sfikakis , Nikolaos Stergiopulos , Christodoulos Stefanadis
      Surgical or critically ill patients often require continuous assessment of cardiac output (CO) for diagnostic purposes or for guiding therapeutic interventions. A new method of non-invasive CO estimation has been recently developed, which is based on pressure wave analysis. However, its validity has been examined only in silico. Aim of this study was to evaluate in vivo the reproducibility and accuracy of the “systolic volume balance” method (SVB). Twenty two subjects underwent 2-D transthoracic echocardiography for CO measurement (reference value of CO). The application of SVB method required aortic pressure wave analysis and estimation of total arterial compliance. Aortic pulses were derived by mathematical transformation of radial pressure waves recorded by applanation tonometry. Total compliance was estimated by the “pulse pressure” method. The agreement, association, variability, bias and precision between Doppler and SVB measures of CO were evaluated by intraclass correlation coefficient (ICC), mean difference, SD of differences, percentage error (PR) and Bland–Altman analysis. SVB yielded very reproducible CO estimates (ICC=0.84, mean difference 0.27±0.73L/min, PR=16.7%). SVB-derived CO was comparable with Doppler measurements, indicating a good agreement and accuracy (ICC=0.74, mean difference=−0.22±0.364L/min, PR≈15). The basic mathematical and physical principles of the SVB method provide highly reproducible and accurate estimates of CO compared with echocardiography.

      PubDate: 2014-08-09T02:28:26Z
  • Finite element analysis of three commonly used external fixation devices
           for treating Type III pilon fractures
    • Abstract: Publication date: Available online 7 August 2014
      Source:Medical Engineering & Physics
      Author(s): Muhammad Hanif Ramlee , Mohammed Rafiq Abdul Kadir , Malliga Raman Murali , Tunku Kamarul
      Pilon fractures are commonly caused by high energy trauma and can result in long-term immobilization of patients. The use of an external fixator i.e. the (1) Delta, (2) Mitkovic or (3) Unilateral frame for treating type III pilon fractures is generally recommended by many experts owing to the stability provided by these constructs. This allows this type of fracture to heal quickly whilst permitting early mobilization. However, the stability of one fixator over the other has not been previously demonstrated. This study was conducted to determine the biomechanical stability of these external fixators in type III pilon fractures using finite element modelling. Three-dimensional models of the tibia, fibula, talus, calcaneus, navicular, cuboid, three cuneiforms and five metatarsal bones were reconstructed from previously obtained CT datasets. Bones were assigned with isotropic material properties, while the cartilage was assigned as hyperelastic springs with Mooney–Rivlin properties. Axial loads of 350N and 70N were applied at the tibia to simulate the stance and the swing phase of a gait cycle. To prevent rigid body motion, the calcaneus and metatarsals were fixed distally in all degrees of freedom. The results indicate that the model with the Delta frame produced the lowest relative micromovement (0.03mm) compared to the Mitkovic (0.05mm) and Unilateral (0.42mm) fixators during the stance phase. The highest stress concentrations were found at the pin of the Unilateral external fixator (509.2MPa) compared to the Mitkovic (286.0MPa) and the Delta (266.7MPa) frames. In conclusion, the Delta external fixator was found to be the most stable external fixator for treating type III pilon fractures.

      PubDate: 2014-08-09T02:28:26Z
  • In vitro measurements of velocity and wall shear stress in a novel
    • Abstract: Publication date: Available online 4 August 2014
      Source:Medical Engineering & Physics
      Author(s): Foad Kabinejadian , Dhanjoo N. Ghista , Boyang Su , Mercedeh Kaabi Nezhadiana , Leok Poh Chua , Joon Hock Yeo , Hwa Liang Leo
      This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo.

      PubDate: 2014-08-06T02:06:05Z
  • Biomechanical evaluation of two commonly used external fixators in the
           treatment of open subtalar dislocation—A finite element analysis
    • Abstract: Publication date: Available online 2 August 2014
      Source:Medical Engineering & Physics
      Author(s): Muhammad Hanif Ramlee , Mohammed Rafiq Abdul Kadir , Malliga Raman Murali , Tunku Kamarul
      Subtalar dislocation is a rare injury caused by high-energy trauma. Current treatment strategies include leg casts, internal fixation and external fixation. Among these, external fixators are the most commonly used as this method is believed to provide better stabilization. However, the biomechanical stability provided by these fixators has not been demonstrated. This biomechanical study compares two commonly used external fixators, i.e. Mitkovic and Delta. CT imaging data were used to reconstruct three-dimensional models of the tibia, fibula, talus, calcaneus, navicular, cuboid, three cuneiforms and five metatarsal bones. The 3D models of the bones and cartilages were then converted into four-noded linear tetrahedral elements, whilst the ligaments were modelled with linear spring elements. Bones and cartilage were idealized as homogeneous, isotropic and linear. To simulate loading during walking, axial loading (70N during the swing and 350N during the stance phase) was applied at the end of diaphyseal tibia. The results demonstrate that the Mitkovic fixator produced greater displacement (peak 3.0mm and 15.6mm) compared to the Delta fixator (peak 0.8mm and 3.9mm), in both the swing and stance phase, respectively. This study demonstrates that the Delta external fixator provides superior stability over the Mitkovic fixator. The Delta fixator may be more effective in treating subtalar dislocation.

      PubDate: 2014-08-06T02:06:05Z
  • Representation of fluctuation features in pathological knee joint
           vibroarthrographic signals using kernel density modeling method
    • Abstract: Publication date: Available online 3 August 2014
      Source:Medical Engineering & Physics
      Author(s): Shanshan Yang , Suxian Cai , Fang Zheng , Yunfeng Wu , Kaizhi Liu , Meihong Wu , Quan Zou , Jian Chen
      This article applies advanced signal processing and computational methods to study the subtle fluctuations in knee joint vibroarthrographic (VAG) signals. Two new features are extracted to characterize the fluctuations of VAG signals. The fractal scaling index parameter is computed using the detrended fluctuation analysis algorithm to describe the fluctuations associated with intrinsic correlations in the VAG signal. The averaged envelope amplitude feature measures the difference between the upper and lower envelopes averaged over an entire VAG signal. Statistical analysis with the Kolmogorov–Smirnov test indicates that both of the fractal scaling index (p =0.0001) and averaged envelope amplitude (p =0.0001) features are significantly different between the normal and pathological signal groups. The bivariate Gaussian kernels are utilized for modeling the densities of normal and pathological signals in the two-dimensional feature space. Based on the feature densities estimated, the Bayesian decision rule makes better signal classifications than the least-squares support vector machine, with the overall classification accuracy of 88% and the area of 0.957 under the receiver operating characteristic (ROC) curve. Such VAG signal classification results are better than those reported in the state-of-the-art literature. The fluctuation features of VAG signals developed in the present study can provide useful information on the pathological conditions of degenerative knee joints. Classification results demonstrate the effectiveness of the kernel feature density modeling method for computer-aided VAG signal analysis.

      PubDate: 2014-08-06T02:06:05Z
  • 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
  • Soft wearable contact lens sensor for continuous intraocular pressure
    • 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
  • 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
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