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Биологический вестник МГПУ имени Богдана Хмельницкого     Open Access   (Followers: 1)

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Journal Cover Medical Engineering & Physics
  [SJR: 0.784]   [H-I: 76]   [9 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1350-4533
   Published by Elsevier Homepage  [3038 journals]
  • The mechanobiology of wounds: The science of preventing pain and suffering
    • Authors: Amit Gefen
      First page: 827
      Abstract: Publication date: September 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 9
      Author(s): Amit Gefen

      PubDate: 2016-08-21T17:00:20Z
      DOI: 10.1016/j.medengphy.2016.08.001
  • Cytoskeleton and plasma-membrane damage resulting from exposure to
           sustained deformations: A review of the mechanobiology of chronic wounds
    • Authors: Amit Gefen; Daphne Weihs
      Pages: 828 - 833
      Abstract: Publication date: September 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 9
      Author(s): Amit Gefen, Daphne Weihs
      The purpose of this review paper is to summarize the current knowledge on cell-scale mechanically-inflicted deformation-damage, which is at the frontier of cell mechanobiology and biomechanics science, specifically in the context of chronic wounds. The dynamics of the mechanostructure of cells and particularly, the damage occurring to the cytoskeleton and plasma-membrane when cells are chronically deformed (as in a weight-bearing static posture) is correlated to formation of the most common chronic wounds and injuries, such as pressure ulcers (injuries). The first occurrence is microscopic injury which onsets as damage in individual cells and then progresses macroscopically to the tissue-scale. Here, we specifically focus on sub-catastrophic and catastrophic damage to cells that can result from mechanical loads that are delivered statically or at physiological rates; this results in apoptosis at prolonged times or necrosis, rapidly. We start by providing a basic background of cell mechanics and dynamics, focusing on the plasma-membrane and the cytoskeleton, and discuss approaches to apply and estimate deformations in cells. We then consider the effects of different levels of mechanical loads, i.e. low, high and intermediate, and describe the expected damage in terms of time-scales of application and in terms of cell response, providing experimental examples where available. Finally, we review different theoretical and computational modeling approaches that have been used to describe cell responses to sustained deformation. We highlight the insights that those models provide to explain, for example, experimentally observed variabilities in cell damage and death under loading.
      Graphical abstract image

      PubDate: 2016-08-21T17:00:20Z
      DOI: 10.1016/j.medengphy.2016.05.014
  • Asymmetry in traction forces produced by migrating preadipocytes is
           bounded to 33%
    • Authors: Shada Abuhattum; Daphne Weihs
      Pages: 834 - 838
      Abstract: Publication date: September 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 9
      Author(s): Shada Abuhattum, Daphne Weihs
      Wound healing by gap closure is accomplished by the migratory cells within tissues. In fat tissue, the preadipocytes, stem cells committed to the adipose (fat) lineage, typically migrate into the wound area, and then differentiate into mature adipocytes to facilitate tissue repair and regeneration. While cell migration has previously been characterized, typically for fibroblasts, little is known about the dynamic, mechanical interactions of migrating cells with their microenvironment; cells crawl on a two-dimensional (2D) substrate by attaching and applying forces that allow them to extend leading edges and retract their rear. Moreover, preadipocytes, the highly migratory precursors of fat cells, have not been studied from this aspect. Here, we have evaluated the migration of preadipocytes, through their speed and directionality as well as the magnitude of the lateral forces applied during their migration on a 2D gel with Young's modulus of 2.44 kPa. We have found that the preadipocytes migrate non-directionally in the absence of chemoattractant, at an average rate of 0.27 µm/min, similar to fibroblasts. The preadipocytes exhibited a wide range of total traction forces (100–800 nN), and migrated along the long axis of their elongated morphology. Interestingly, we have observed an asymmetry in the location of force application between the lead and rear of the cells that was bounded in magnitude, where cells applied only up to 33% more force on either side; cell sides were defined relative to the minor axis of a bounding ellipse. These quantitative mechanobiological aspects of natural preadipocyte migration may shed light on the wound healing processes occurring in adipose tissue.

      PubDate: 2016-08-21T17:00:20Z
      DOI: 10.1016/j.medengphy.2016.05.013
  • Feasibility of freehand ultrasound to measure anatomical features
           associated with deep tissue injury risk
    • Authors: Jonathan S. Akins; Jaxon J. Vallely; Patricia E. Karg; Kara Kopplin; Amit Gefen; Prerna Poojary-Mazzotta; David M. Brienza
      Pages: 839 - 844
      Abstract: Publication date: Available online 4 July 2016
      Source:Medical Engineering & Physics
      Author(s): Jonathan S. Akins, Jaxon J. Vallely, Patricia E. Karg, Kara Kopplin, Amit Gefen, Prerna Poojary-Mazzotta, David M. Brienza
      Deep tissue injuries (DTI) are severe forms of pressure ulcers that start internally and are difficult to diagnose. Magnetic resonance imaging (MRI) is the currently preferred imaging modality to measure anatomical features associated with DTI, but is not a clinically feasible risk assessment tool. B-mode ultrasound (US) is proposed as a practical, alternative technology suitable for bedside or outpatient clinic use. The goal of this research was to confirm US as an imaging modality for acquiring measurements of anatomical features associated with DTI. Tissue thickness measurements using US were reliable (ICC=.948) and highly correlated with MRI measurements (muscle r =.988, p ≤ .001; adipose r =.894, p ≤ .001; total r =.919; p ≤ .001). US measures of muscle tissue thickness were 5.4mm (34.1%) higher than MRI, adipose tissue thickness measures were 1.6mm (11.9%) lower, and total tissue thickness measures were 3.8mm (12.8%) higher. Given the reliability and ability to identify high-risk anatomies, as well as the cost effectiveness and availability, US measurements show promise for use in future development of a patient-specific, bedside, biomechanical risk assessment tool to guide clinicians in appropriate interventions to prevent DTI.

      PubDate: 2016-07-18T06:41:29Z
      DOI: 10.1016/j.medengphy.2016.04.026
  • Fixation strength of four headless compression screws
    • Authors: Adam Hart; Edward J. Harvey; Reza Rabiei; Francois Barthelat; Paul A. Martineau
      Pages: 1037 - 1043
      Abstract: Publication date: Available online 29 August 2016
      Source:Medical Engineering & Physics
      Author(s): Adam Hart, Edward J. Harvey, Reza Rabiei, Francois Barthelat, Paul A. Martineau
      To promote a quicker return to function, an increasing number of patients are treated with headless screws for acute displaced and even non-displaced scaphoid fractures. Therefore, it is imperative to understand and optimize the biomechanical characteristics of different implants to support the demands of early mobilization. The objective of this study was to evaluate the biomechanical fixation strength of 4 headless compression screws under distracting and bending forces. The Acutrak Standard, Acutrak Mini, Synthes 3.0, and Herbert-Whipple screws were tested using a polyurethane foam scaphoid fracture model. Implants were inserted into the foam blocks across a linear osteotomy. Custom fixtures applied pull-apart and four-point bending forces until implant failure. Pull-apart testing was performed in three different foam densities in order to simulate osteoporotic, osteopenic, and normal bone. The peak pull-apart forces varied significantly between implants and were achieved by (from greatest to least): the Acutrak Standard, Synthes 3.0, Acutrak Mini, and Herbert-Whipple screws. The fully threaded screws (Acutrak) failed at their proximal threads while the shanked screw (Synthes and Herbert Whipple) failed at their distal threads. Similarly, the screws most resistant to bending were (from greatest to least): the Acutrak Standard, Acutrak Mini, Herbert-Whipple, and Synthes. Although the amount of force required for pull-apart failure increased with each increasing simulated bone density (a doubling in density required triple the amount of pull apart force), the mode and sequence of failure was the same. Overall, the fully threaded, conical design of the Acutrak screws demonstrated superior fixation against pull-apart and bending forces than the shanked designs of the Synthes and Herbert-Whipple. We also found a strong relationship between simulated bone density and pull-apart force.

      PubDate: 2016-08-30T18:33:10Z
      DOI: 10.1016/j.medengphy.2016.06.025
  • Mechanical and material properties of cortical and trabecular bone from
           cannabinoid receptor-1-null (Cnr1−/−) mice
    • Authors: Aysha B. Khalid; Simon R. Goodyear; Ruth A. Ross; Richard M. Aspden
      Pages: 1044 - 1054
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Aysha B. Khalid, Simon R. Goodyear, Ruth A. Ross, Richard M. Aspden
      The endocannabinoid system is known for its regulatory effects on bone metabolism through the cannabinoid receptors, Cnr1 and Cnr2. In this study we analysed the mechanical and material properties of long bones from Cnr1−/− mice on a C57BL/6 background. Tibiae and femora from 5- and 12-week-old mice were subjected to three-point bending to measure bending stiffness and yield strength. Elastic modulus, density and mineral content were measured in the diaphysis. Second moment of area (MOA2), inner and outer perimeters of the cortical shaft and trabecular fractional bone volume (BV/TV) were measured using micro-CT. In Cnr1−/− males and females at both ages the bending stiffness was reduced due to a smaller MOA2. Bone from Cnr1−/− females had a greater modulus than wild-type controls, although no differences were observed in males. BV/TV of 12-week-old Cnr1−/− females was greater than controls, although no difference was seen at 5-weeks. On the contrary, Cnr1−/− males had the same BV/TV as controls at 12-weeks while they had significantly lower values at 5-weeks. This study shows that deleting Cnr1 decreases the amount of cortical bone in both males and females at 12-weeks, but increases the amount of trabecular bone only in females.
      Graphical abstract image

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.024
  • In vivo tissue interaction between the transverse carpal ligament and
           finger flexor tendons
    • Authors: Joseph N. Gabra; Joshua L. Gordon; Tamara L. Marquardt; Zong-Ming Li
      Pages: 1055 - 1062
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Joseph N. Gabra, Joshua L. Gordon, Tamara L. Marquardt, Zong-Ming Li
      The transverse carpal ligament (TCL) is a component of the flexor pulley system of the wrist, keeping the flexor tendons in place by resisting their volar displacement. The purpose of this study was to investigate the in vivo biomechanical interaction between the TCL and flexor tendons in response to tendon tensioning with the wrist at various postures. In eight healthy subjects, the flexor digitorum superficialis and profundus tendons were tensioned by isometrically applying loads (5, 10, and 15N) to the index finger while the wrist posture was at 20° extension, neutral, 20° flexion, and 40° flexion. The TCL and flexor tendons were imaged at the distal carpal tunnel cross section using ultrasound. The volar-dorsal positions of the tendons, TCL arch height, and TCL-tendon distances were calculated. With increasing wrist flexion, the flexor tendons moved volarly, the TCL arch height increased, and the TCL-tendon distances decreased, indicating that the flexor tendons contacted the TCL and pushed it volarly. The TCL-tendon interaction was amplified by the combination of finger loading and wrist flexion. This study provides in vivo evidence of the biomechanical interaction between the TCL and flexor tendons. Repetitive TCL-tendon interactions may implicate the interacting tissues and the median nerve resulting in tissue maladaptation and nerve compression.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.023
  • In vivo evaluation of a novel, wrist-mounted arterial pressure sensing
           device versus the traditional hand-held tonometer
    • Authors: Orestis Vardoulis; T. Scott Saponas; Dan Morris; Nicolas Villar; Greg Smith; Shwetak Patel; Desney Tan
      Pages: 1063 - 1069
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Orestis Vardoulis, T. Scott Saponas, Dan Morris, Nicolas Villar, Greg Smith, Shwetak Patel, Desney Tan
      Although hemodynamic parameters can be assessed non-invasively, state-of-the-art non-invasive systems generally require an expert operator and are not applicable for ambulatory measurements. These limitations have restricted our understanding of the continuous behavior of hemodynamic parameters. In this manuscript, we introduce a novel wrist-mounted device that incorporates an array of pressure sensors which can be used to extract arterial waveforms and relevant pulse wave analysis biomarkers. In vivo evaluation is performed with Bland–Altman analysis to compare the novel sensor to a gold-standard hand-held tonometer by assessing their reproducibility and agreement in peripheral augmentation index (AIx) estimation at the radial artery. Arterial waves from 28 randomly selected participants were recorded in a controlled environment. Initially we assess the reproducibility of AIx results for both devices. The intra-class correlation coefficient (ICC) and mean difference ± SD were [0.913, 0.033±0.048] and [0.859, 0.039±0.076] for the hand-held and the wrist-mounted tonometer respectively. We then show that the AIx values derived from the novel tonometer have good agreement, accuracy, and precision when compared against the AIx values derived from the reference hand-held tonometer (ICC 0.927, mean difference 0.026±0.049). In conclusion, we have presented evidence that the new wrist-mounted arterial pressure sensor records arterial waveforms that can be processed to yield AIx values that are in good agreement with its traditional hand-held counterpart.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.022
  • Conceptual finite element study for comparison among superior, anterior,
           and spiral clavicle plate fixations for midshaft clavicle fracture
    • Authors: Teng-Le Huang; Wen-Chuan Chen; Kun-Jhih Lin; Cheng-Lun Tsai; Kang-Ping Lin; Hung-Wen Wei
      Pages: 1070 - 1075
      Abstract: Publication date: Available online 8 August 2016
      Source:Medical Engineering & Physics
      Author(s): Teng-Le Huang, Wen-Chuan Chen, Kun-Jhih Lin, Cheng-Lun Tsai, Kang-Ping Lin, Hung-Wen Wei
      Open reduction internal fixation technique has been generally accepted for treatment of midshaft clavicle fractures. Both superior and anterior clavicle plates have been reported in clinical or biomechanical researches, while presently the spiral clavicle plate design has been introduced improved biomechanical behavior over conventional designs. In order to objectively realize the multi-directional biomechanical performances among the three geometries for clavicle plate designs, a current conceptual finite element study has been conducted with identical cross-sectional features for clavicle plates. The conceptual superior, anterior, and spiral clavicle plate models were constructed for virtual reduction and fixation to an OTA 15-B1.3 midshaft transverse fracture of clavicle. Mechanical load cases including cantilever bending, axial compression, inferior bending, and axial torsion have been applied for confirming the multi-directional structural stability and implant safety in biomechanical perspective. Results revealed that the anterior clavicle plate model represented lowest plate stress under all loading cases. The superior clavicle plate model showed greater axial compressive stiffness, while the anterior clavicle plate model performed greater rigidity under cantilever bending load. Three model represented similar structural stiffness under axial torsion. Played as a transition structure between superior and anterior clavicle plate, the spiral clavicle plate model revealed comparable results with acceptable multi-directional biomechanical behavior. The concept of spiral clavicle plate design is worth considering in practical application in clinics. Implant safety should be further investigated by evidences in future mechanical tests and clinical observations.

      PubDate: 2016-08-09T16:13:49Z
      DOI: 10.1016/j.medengphy.2016.06.021
  • A model for flexi-bar to evaluate intervertebral disc and muscle forces in
    • Authors: Masoud Abdollahi; Mohammad Nikkhoo; Sajad Ashouri; Mohsen Asghari; Mohamad Parnianpour; Kinda Khalaf
      Pages: 1076 - 1082
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Masoud Abdollahi, Mohammad Nikkhoo, Sajad Ashouri, Mohsen Asghari, Mohamad Parnianpour, Kinda Khalaf
      This study developed and validated a lumped parameter model for the FLEXI-BAR, a popular training instrument that provides vibration stimulation. The model which can be used in conjunction with musculoskeletal-modeling software for quantitative biomechanical analyses, consists of 3 rigid segments, 2 torsional springs, and 2 torsional dashpots. Two different sets of experiments were conducted to determine the model's key parameters including the stiffness of the springs and the damping ratio of the dashpots. In the first set of experiments, the free vibration of the FLEXI-BAR with an initial displacement at its end was considered, while in the second set, forced oscillations of the bar were studied. The properties of the mechanical elements in the lumped parameter model were derived utilizing a non-linear optimization algorithm which minimized the difference between the model's prediction and the experimental data. The results showed that the model is valid (8% error) and can be used for simulating exercises with the FLEXI-BAR for excitations in the range of the natural frequency. The model was then validated in combination with AnyBody musculoskeletal modeling software, where various lumbar disc, spinal muscles and hand muscles forces were determined during different FLEXI-BAR exercise simulations.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.07.006
  • Comparison of adaptive neuro-fuzzy inference system (ANFIS) and Gaussian
           processes for machine learning (GPML) algorithms for the prediction of
           skin temperature in lower limb prostheses
    • Authors: Neha Mathur; Ivan Glesk; Arjan Buis
      Pages: 1083 - 1089
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Neha Mathur, Ivan Glesk, Arjan Buis
      Monitoring of the interface temperature at skin level in lower-limb prosthesis is notoriously complicated. This is due to the flexible nature of the interface liners used impeding the required consistent positioning of the temperature sensors during donning and doffing. Predicting the in-socket residual limb temperature by monitoring the temperature between socket and liner rather than skin and liner could be an important step in alleviating complaints on increased temperature and perspiration in prosthetic sockets. In this work, we propose to implement an adaptive neuro fuzzy inference strategy (ANFIS) to predict the in-socket residual limb temperature. ANFIS belongs to the family of fused neuro fuzzy system in which the fuzzy system is incorporated in a framework which is adaptive in nature. The proposed method is compared to our earlier work using Gaussian processes for machine learning. By comparing the predicted and actual data, results indicate that both the modeling techniques have comparable performance metrics and can be efficiently used for non-invasive temperature monitoring.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.07.003
  • Measurement and modelling the sensitivity of tetrapolar transfer impedance
    • Authors: E. Naydenova; S. Cavendish; A.J. Wilson
      Pages: 1090 - 1099
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): E. Naydenova, S. Cavendish, A.J. Wilson
      Finite element method (FEM) modelling of a small disk in a homogeneous saline medium showed that the sensitivity distribution for tetrapolar transfer impedance measurements was dependant on the ratio, σ disk/σ saline, and not absolute conductivity values. In addition, the amplitude of the negative sensitivity regions between the drive and receive electrodes decreased non-linearly with σ disk/σ saline for σ disk/σ saline < 1, eventually becoming zero. This non-linear behaviour determined the limit of the assumption of a small change in conductivity in Geselowitz’s lead theorem with 0.5 <σ disk/σ saline <1.5 for the measurements reported. The modelling supported the design of a sensitivity measurement system using an insulating support and a metal disk in a saline filled tank. Measurements were shown to give good agreement with sensitivity predictions from Geselowitz's lead theorem. Replacing the homogeneous medium in the FEM model with layers of different conductivity parallel to the plane of the electrodes changed the sensitivity distribution when the thickness of the layers adjacent to the electrodes were less than ½ the electrode spacing. A layer of greater conductivity over a layer of lesser conductivity next to the electrodes gave a peak in the sensitivity distribution and extended regions of negative sensitivity further into the tissue.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.07.005
  • Influence of fracture geometry on bone healing under locking plate
           fixations: A comparison between oblique and transverse tibial fractures
    • Authors: Saeed Miramini; Lihai Zhang; Martin Richardson; Priyan Mendis; Peter R. Ebeling
      Pages: 1100 - 1108
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Saeed Miramini, Lihai Zhang, Martin Richardson, Priyan Mendis, Peter R. Ebeling
      Mechano-regulation plays a crucial role in bone healing and involves complex cellular events. In this study, we investigate the change of mechanical microenvironment of stem cells within early fracture callus as a result of the change of fracture obliquity, gap size and fixation configuration using mechanical testing in conjunction with computational modelling. The research outcomes show that angle of obliquity (θ) has significant effects on interfragmentary movement (IFM) which influences mechanical microenvironment of the callus cells. Axial IFM at near cortex of fracture decreases with θ, while shear IFM significantly increases with θ. While a large θ can increase shear IFM by four-fold compared to transverse fracture, it also result in the tension–stress effect at near cortex of fracture callus. In addition, mechanical stimuli for cell differentiation within the callus are found to be strongly negatively correlated to angle of obliquity and gap size. It is also shown that a relatively flexible fixation could enhance callus formation in presence of a large gap but could lead to excessive callus strain and interstitial fluid flow when a small transverse fracture gap is present. In conclusion, there appears to be an optimal fixation configuration for a given angle of obliquity and gap size.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.07.007
  • Vector-based forearm rotation moment arms – A sensitivity analysis
    • Authors: Desney Greybe; Michael R. Boland; Kumar Mithraratne
      Pages: 1109 - 1114
      Abstract: Publication date: Available online 10 August 2016
      Source:Medical Engineering & Physics
      Author(s): Desney Greybe, Michael R. Boland, Kumar Mithraratne
      All existing moment arm data for muscles of the forearm derive from tendon excursion experiments. Moment arms determined this way are only valid for movement about the same generalised coordinate system as was used during the tendon excursion, which makes their implementation in more complex or realistic joint models problematic. This study used a vector-based method to calculate muscle moment arms in a three dimensional model of forearm rotation. It also evaluated the sensitivity of this method to errors in the input data. There was reasonably close agreement between the moment arms calculated in this study and those published using tendon excursion methods. Six out of eight muscles had moment arms within the range of values reported previously. However, the vector-based method was sensitive to the accuracy of the input data. This sensitivity varied between muscles and input variables. Generally, the calculations were more robust to the point of force application than the muscle lines of action and the joint's axis of rotation. A small change in these variables could produce substantial changes in the calculated moment arms. Consequently, accurate input data is important when using the vector-based method in a joint model.

      PubDate: 2016-08-13T16:33:34Z
      DOI: 10.1016/j.medengphy.2016.07.012
  • In vitro osteocytic microdamage and viability quantification using a
           microloading platform
    • Authors: S.L. York; P. Sethu; M.M. Saunders
      Pages: 1115 - 1122
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): S.L. York, P. Sethu, M.M. Saunders
      Bone remodeling is a process in which bone is resorbed by osteoclasts and formed by osteoblasts. This is normally a paired process, although it can be disrupted by changes in mechanical load. One theory is that osteocytes play a key role in the cellular regulation of this process. Mechanotransduction studies, which investigate how cells convert mechanical stimuli into biophysical effects and cellular activity, offer one way to investigate this theory. Mechanotransduction work is commonly done by applying an isolated mechanical load to cells grown in vitro, and quantifying the response. While in vitro work does not fully replicate the natural environment, it does allow the study of isolated factors. In this study, a mechanical loading platform was designed, fabricated, and characterized for bone mechanotransduction studies. This platform was designed to tent cell-seeded substrates from below, loading using out of plane distension. This introduced a nonuniform strain profile, enabling the study of cells cultured under identical conditions and variable strains as a function of substrate location. An alphanumerically gridded polydimethylsiloxane well substrate was designed and fabricated for cellular loading experiments. Following initial characterization, a study was run to quantify the cellular activity of osteocyte-like MLO-Y4 cells as a function of strain field. The results indicated that regions with lower strains led to an increase in cellular activity while higher strains led to a reduction in cellular activity. This demonstrated that cells could be exposed to mechanically-induced microdamage using the microloading platform.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.002
  • A comparison between dynamic implicit and explicit finite element
           simulations of the native knee joint
    • Authors: Hamid Naghibi Beidokhti; Dennis Janssen; Mehdi Khoshgoftar; Andre Sprengers; Emin Semih Perdahcioglu; Ton Van den Boogaard; Nico Verdonschot
      Pages: 1123 - 1130
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Hamid Naghibi Beidokhti, Dennis Janssen, Mehdi Khoshgoftar, Andre Sprengers, Emin Semih Perdahcioglu, Ton Van den Boogaard, Nico Verdonschot
      The finite element (FE) method has been widely used to investigate knee biomechanics. Time integration algorithms for dynamic problems in finite element analysis can be classified as either implicit or explicit. Although previously both static/dynamic implicit and dynamic explicit method have been used, a comparative study on the outcomes of both methods is of high interest for the knee modeling community. The aim of this study is to compare static, dynamic implicit and dynamic explicit solutions in analyses of the knee joint to assess the prediction of dynamic effects, potential convergence problems, the accuracy and stability of the calculations, the difference in computational time, and the influence of mass-scaling in the explicit formulation. The heel-strike phase of fast, normal and slow gait was simulated for two different body masses in a model of the native knee. Our results indicate that ignoring the dynamic effect can alter joint motion. Explicit analyses are suitable to simulate dynamic loading of the knee joint in high-speed simulations, as this method offers a substantial reduction of the computational time with a similar prediction of cartilage stresses and meniscus strains. Although mass-scaling can provide even more gain in computational time, it is not recommended for high-speed activities, in which inertial forces play a significant role.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.001
  • Accuracy of model-based tracking of knee kinematics and cartilage contact
           measured by dynamic volumetric MRI
    • Authors: Jarred Kaiser; Arezu Monawer; Rajeev Chaudhary; Kevin M. Johnson; Oliver Wieben; Richard Kijowski; Darryl G. Thelen
      Pages: 1131 - 1135
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Jarred Kaiser, Arezu Monawer, Rajeev Chaudhary, Kevin M. Johnson, Oliver Wieben, Richard Kijowski, Darryl G. Thelen
      The purpose of this study was to determine the accuracy of knee kinematics and cartilage contact measured by volumetric dynamic MRI. A motor-actuated phantom drove femoral and tibial bone segments through cyclic 3D motion patterns. Volumetric images were continuously acquired using a 3D radially undersampled cine spoiled gradient echo sequence (SPGR-VIPR). Image data was binned based on position measured via a MRI-compatible rotary encoder. High-resolution static images were segmented to create bone models. Model-based tracking was performed by optimally registering the bone models to the volumetric images at each frame of the SPGR-VIPR series. 3D tibiofemoral translations and orientations were reconstructed, and compared to kinematics obtained by tracking fiducial markers. Imaging was repeated on a healthy subject who performed cyclic knee flexion-extension. Cartilage contact for the subject was assessed by measuring the overlap between articular cartilage surfaces. Model-based tracking was able to track tibiofemoral angles and translations with precisions less than 0.8° and 0.5mm. These precisions resulted in an uncertainty of less than 0.5mm in cartilage contact location. Dynamic SPGR-VIPR imaging can accurately assess in vivo knee kinematics and cartilage contact during voluntary knee motion performed in a MRI scanner. This technology could facilitate the quantitative investigation of links between joint mechanics and the development of osteoarthritis.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.016
  • Experimental determination of the emissivity of bone
    • Authors: Arne Feldmann; Philippe Zysset
      Pages: 1136 - 1138
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Arne Feldmann, Philippe Zysset
      Cutting and drilling operations in bone are involved in many orthopedic and otolaryngological surgeries. The temperature elevation of these procedures is potentially harmful to bone and soft tissue cells. The research on this topic aims therefore at minimizing temperature elevation and finding optimal process parameters. Experimental studies are mostly carried out on ex vivo setups using bovine bone material. For temperature measurements, either thermocouples or infrared cameras are used. Infrared cameras have potential advantages, but the emissivity value of the material has to be known. Literature values are scattered and vary within a wide range. An experimental study was carried out to quantify the emissivity using freshly frozen bovine and human bone, as well as human bone samples which were either fixed with Formalin or Thiel solution. Additionally, different surface finishes were used and emissivity was evaluated at different temperatures. The mean emissivity of bone was determined to be ɛ = 0.96 ± 0.01 for temperature elevations up to 60 °C. A slightly higher value of ɛ = 0.97 ± 0.01 was found for temperatures around 80 °C. No significant differences for human or bovine bone samples, preparation or fixation techniques were found.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.06.019
  • On the use of a Euclidean norm function for the estimation of local
    • Authors: Shawn M. Beaudette; Samuel J. Howarth; Ryan B. Graham; Stephen H.M. Brown
      Pages: 1139 - 1145
      Abstract: Publication date: October 2016
      Source:Medical Engineering & Physics, Volume 38, Issue 10
      Author(s): Shawn M. Beaudette, Samuel J. Howarth, Ryan B. Graham, Stephen H.M. Brown
      Several different state-space reconstruction methods have been employed to assess the local dynamic stability (LDS) of a 3D kinematic system. One common method is to use a Euclidean norm ( N ) transformation of three orthogonal x, y, and z time-series’ followed by the calculation of the maximum finite-time Lyapunov exponent (λ max) from the resultant N waveform (using a time-delayed state space reconstruction technique). By essentially acting as a weighted average, N has been suggested to account for simultaneous expansion and contraction along separate degrees of freedom within a 3D system (e.g. the coupling of dynamic movements between orthogonal planes). However, when estimating LDS using N , non-linear transformations inherent within the calculation of N should be accounted for. Results demonstrate that the use of N on 3D time-series data with arbitrary magnitudes of relative bias and zero-crossings cause the introduction of error in estimates of λ max obtained through N . To develop a standard for the analysis of 3D dynamic kinematic waveforms, we suggest that all dimensions of a 3D signal be independently shifted to avoid the incidence of zero-crossings prior to the calculation of N and subsequent estimation of LDS through the use of λ max.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.07.001
  • Can a single lower trunk body-fixed sensor differentiate between
           level-walking and stair descent and ascent in older adults'
           Preliminary findings
    • Authors: Aner Weiss; Marina Brozgol; Nir Giladi; Jeffrey M. Hausdorff
      Pages: 1146 - 1151
      Abstract: Publication date: Available online 12 August 2016
      Source:Medical Engineering & Physics
      Author(s): Aner Weiss, Marina Brozgol, Nir Giladi, Jeffrey M. Hausdorff
      Stair ascent and descent are common forms of ambulation that may be challenging to detect. Here, we propose the first step towards differentiating between stair negotiation and level-walking using a single body-fixed sensor. Seventeen healthy older adults (age: 79.3±4.2 years, 47% women) wore a body-fixed sensor on the lower-back while performing level-walking and stair negotiation. Measures derived from the 3D acceleration and angular-velocity signals included medians, ranges, step duration, step and stride regularity, filtered vertical to horizontal acceleration ratio (VAF/HAF), and wavelet-based features. Friedman's and Wilcoxon tests compared between conditions. Stepwise-binary logistic-regression evaluated classification accuracy. During level-walking, yaw range was lowest and anterior–posterior and vertical step and stride regularity were highest (p ≤0.007). Anterior–posterior step regularity (p =0.003), VAF/HAF (p =0.094), and yaw range (p =0.105) identified level-walking (92.2% accuracy). During stair ascent, roll range, median anterior–posterior acceleration and anterior–posterior wavelet-coefficient were lowest (p ≤0.006), while VAF/HAF was highest (p =0.0029). Anterior posterior wavelet coefficient (p =0.038) and VAF/HAF (p =0.018) identified stair ascent (94.3% accuracy). During stair descent, vertical and medio-lateral ranges were highest and medio-lateral stride regularity and VAF/HAF were lowest (p ≤0.006). VAF/HAF (p =0.01), medio-lateral acceleration range (p =0.069), and medio-lateral stride regularity (p =0.072) identified stair descent (90.2% accuracy). These findings suggest that a single worn body-fixed sensor can be used to differentiate between level-walking and stair negotiation.

      PubDate: 2016-08-13T16:33:34Z
      DOI: 10.1016/j.medengphy.2016.07.008
  • The influence of high-heeled shoes on strain and tension force of the
           anterior talofibular ligament and plantar fascia during balanced standing
           and walking
    • Authors: Jia Yu; Duo Wai-Chi Wong; Hongtao Zhang; Zong-Ping Luo; Ming Zhang
      Pages: 1152 - 1156
      Abstract: Publication date: Available online 4 August 2016
      Source:Medical Engineering & Physics
      Author(s): Jia Yu, Duo Wai-Chi Wong, Hongtao Zhang, Zong-Ping Luo, Ming Zhang
      High-heeled shoes have the capability to alter the strain and tension of ligamentous structures between the foot and ankle, which may result in ankle instability. However, high-heeled shoes can also reduce the strain on plantar fascia, which may be beneficial for the treatment of plantar fasciitis. In this study, the influence of heel height on strain and tension force applied to the anterior talofibular ligament (ATL) and plantar fascia were investigated. A three-dimensional finite element model of coupled foot–ankle–shoe complex was constructed. Four heel heights were studied in balanced standing: 0 in. (0cm), 1 in. (2.54cm), 2 in. (5.08cm), and 3 in. (7.62cm). A walking analysis was performed using 2-in. (5.08cm) high-heeled shoes. During balanced standing, the tension force on the ATL increased from 14.8N to 97.0N, with a six-fold increase in strain from 0 in. to 3 in. (0–7.62cm). The tension force and the average strain on the plantar fascia decreased from 151.0N (strain: 0.74%) to 59.6N (strain: 0.28%) when the heel height increased from 0 in. to 2 in. (0–5.08cm). When heel height reached 3 in. (7.62cm), the force and average strain increased to 278.3N (strain: 1.33%). The walking simulation showed that the fascia stretched out while the ATL loading decreased during push off. The simulation outcome demonstrated the influence of heel height on ATL alteration and plantar fascia strain, which implies risks for ankle injury and suggests guidance for the treatment of plantar fasciitis.

      PubDate: 2016-08-05T15:12:13Z
      DOI: 10.1016/j.medengphy.2016.07.009
  • A theoretical computerized study for the electrical conductivity of
           arterial pulsatile blood flow by an elastic tube model
    • Authors: Hua Shen; Yong Zhu; Kai-Rong Qin
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Hua Shen, Yong Zhu, Kai-Rong Qin
      The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell–Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.013
  • Stress shielding in periprosthetic bone following a total knee
           replacement: Effects of implant material, design and alignment
    • Authors: Qing-Hang Zhang; Andrew Cossey; Jie Tong
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Qing-Hang Zhang, Andrew Cossey, Jie Tong
      Periprosthetic bone strain distributions in some of the typical cases of total knee replacement (TKR) were studied with regard to the selection of material, design and the alignments of tibial components to examine which conditions are more forgiving than the others to stress shielding post a TKR. Four tibial components with two implant designs (cruciate sacrificing and cruciate retaining) and material properties (metal-backed (MB) and all-polyethylene (AP)) were considered in a specimen-specific finite element tibia bone model loaded in a neutral position. The influence of tibial material and design on the periprosthetic bone strain response was investigated under the peak loads of walking and stair descending/ascending. Two of the models were also modified to examine the effect of selected implant malalignment conditions (7° posterior, 5° valgus and 5° varus) on stress shielding in the bone, where the medio-lateral load share ratios were adjusted accordingly. The predicted increases of bone density due to implantation for the selected cases studied were also presented. For the cases examined, the effect of stress shielding on the periprosthetic bone seems to be more significantly influenced by the implant material than by the implant geometry. Significant stress shielding is found in MB cases, as opposed to increase in bone density found in AP cases, particularly in the bones immediately beneath the baseplate. The effect of stress shielding is reduced somewhat for the MB components in the malaligned positions compared with the neutral case. In AP cases, the effect of stress shielding is mostly low except in the varus position, possibly due to off-loading of lateral condyle. Increases in bone density are found in both MB and AP cases for the malaligned conditions.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.018
  • Discrete sensors distribution for accurate plantar pressure analyses
    • Authors: Laetitia Claverie; Anne Ille; Pierre Moretto
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Laetitia Claverie, Anne Ille, Pierre Moretto
      The aim of this study was to determine the distribution of discrete sensors under the footprint for accurate plantar pressure analyses. For this purpose, two different sensor layouts have been tested and compared, to determine which was the most accurate to monitor plantar pressure with wireless devices in research and/or clinical practice. Ten healthy volunteers participated in the study (age range: 23–58 years). The barycenter of pressures (BoP) determined from the plantar pressure system (W-inshoe®) was compared to the center of pressures (CoP) determined from a force platform (AMTI) in the medial-lateral (ML) and anterior-posterior (AP) directions. Then, the vertical ground reaction force (vGRF) obtained from both W-inshoe® and force platform was compared for both layouts for each subject. The BoP and vGRF determined from the plantar pressure system data showed good correlation (SCC) with those determined from the force platform data, notably for the second sensor organization (ML SCC= 0.95; AP SCC=0.99; vGRF SCC=0.91). The study demonstrates that an adjusted placement of removable sensors is key to accurate plantar pressure analyses. These results are promising for a plantar pressure recording outside clinical or laboratory settings, for long time monitoring, real time feedback or for whatever activity requiring a low-cost system.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.021
  • Evaluation of the SMALL nail: Drive technology and behavior in situ
    • Authors: L.H. Dünnweber; R. Rödl; G. Gosheger; F.M. Schiedel
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): L.H. Dünnweber, R. Rödl, G. Gosheger, F.M. Schiedel
      Although clear advances have been made during the last 5 years, practical difficulties persist for patients and surgeons in procedures for intramedullary lengthening of long bones. In particular, precise adjustment of the desired amount of lengthening and technically reliable checking of the length actually achieved are problematic. An intramedullary nail with a new type of drive that exploits the shape memory effect has been constructed. The drive technology and the behavior of the intramedullary nail in situ were evaluated in a cadaver experiment. Three shape memory alloy limb lengthening (SMALL) nails were implanted in a body donor. The SMALL nail contains a spring coupled to a shape memory element consisting of a nickel–titanium alloy. This shape memory element “remembers” its initial state before the lengthening through the spring and can return to it when it is warmed. A cartridge heater inside the lengthening nail is warmed using transcutaneous induction with high-frequency energy via a subcutaneously implanted coil. For evaluation, two SMALL nails were implanted into the femora (antegrade on the left and retrograde on the right) and one SMALL nail was implanted into the left tibia. Lengthening by 50mm was attempted using repeated activation of the drive mechanism. At the same time, test parameters for temperature increases and cooling periods were continually monitored and the data were subsequently analyzed. The nail's mechanism worked in principle, but was inadequate in view of success rates (number of lengthening steps attempted versus number of lengthening steps achieved) of 21% for the SMALL nail in the tibia and left femur and 14% for the nail in the right femur. The temperature values measured during the distraction experiments show that high-frequency energy induction in the SMALL nail gives no cause for concern for patients.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.020
  • Anisotropic abdominal aortic aneurysm replicas with biaxial material
    • Authors: Sergio Ruiz de Galarreta; Raúl Antón; Aitor Cazon; Gorka S. Larraona; Ender A. Finol
      Abstract: Publication date: Available online 10 October 2016
      Source:Medical Engineering & Physics
      Author(s): Sergio Ruiz de Galarreta, Raúl Antón, Aitor Cazon, Gorka S. Larraona, Ender A. Finol
      An Abdominal Aortic Aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta at least 1.5 times its normal diameter. The criterion of maximum diameter is still used in clinical practice, although numerical studies have demonstrated the importance of other biomechanical factors. Numerical studies, however, must be validated experimentally before they can be clinically implemented. We have developed a methodology for manufacturing anisotropic AAA replicas with non-uniform wall thickness. Different composites were fabricated and tested, and one was selected in order to manufacture a phantom with the same properties. The composites and the phantom were characterized by biaxial tensile tests and a material model was fit to the experimental data. The experimental results were compared with data from the literature, and similar responses were obtained. The anisotropic AAA replicas with non-uniform wall thickness can be used in benchtop experiments to validate deformations obtained with numerical simulations or for pre-intervention testing of endovascular grafts. This is a significant step forward considering the importance of anisotropy in numerical simulations.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.010
  • Motor unit firing rates and synchronisation affect the fractal dimension
           of simulated surface electromyogram during isometric/isotonic contraction
           of vastus lateralis muscle
    • Authors: Luca Mesin; Davide Dardanello; Alberto Rainoldi; Gennaro Boccia
      Abstract: Publication date: Available online 12 October 2016
      Source:Medical Engineering & Physics
      Author(s): Luca Mesin, Davide Dardanello, Alberto Rainoldi, Gennaro Boccia
      During fatiguing contractions, many adjustments in motor units behaviour occur: decrease in muscle fibre conduction velocity; increase in motor units synchronisation; modulation of motor units firing rate; increase in variability of motor units inter-spike interval. We simulated the influence of all these adjustments on synthetic EMG signals in isometric/isotonic conditions. The fractal dimension of the EMG signal was found mainly influenced by motor units firing behaviour, being affected by both firing rate and synchronisation level, and least affected by muscle fibre conduction velocity. None of the calculated EMG indices was able to discriminate between firing rate and motor units synchronisation.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.022
  • Fully automatic segmentation of femurs with medullary canal definition in
           high and in low resolution CT scans
    • Authors: Diogo F. Almeida; Rui B. Ruben; João Folgado; Paulo R. Fernandes; Emmanuel Audenaert; Benedict Verhegghe; Matthieu De Beule
      Abstract: Publication date: Available online 15 October 2016
      Source:Medical Engineering & Physics
      Author(s): Diogo F. Almeida, Rui B. Ruben, João Folgado, Paulo R. Fernandes, Emmanuel Audenaert, Benedict Verhegghe, Matthieu De Beule
      Femur segmentation can be an important tool in orthopedic surgical planning. However, in order to overcome the need of an experienced user with extensive knowledge on the techniques, segmentation should be fully automatic. In this paper a new fully automatic femur segmentation method for CT images is presented. This method is also able to define automatically the medullary canal and performs well even in low resolution CT scans. Fully automatic femoral segmentation was performed adapting a template mesh of the femoral volume to medical images. In order to achieve this, an adaptation of the active shape model (ASM) technique based on the statistical shape model (SSM) and local appearance model (LAM) of the femur with a novel initialization method was used, to drive the template mesh deformation in order to fit the in-image femoral shape in a time effective approach. With the proposed method a 98% convergence rate was achieved. For high resolution CT images group the average error is less than 1mm. For the low resolution image group the results are also accurate and the average error is less than 1.5mm. The proposed segmentation pipeline is accurate, robust and completely user free. The method is robust to patient orientation, image artifacts and poorly defined edges. The results excelled even in CT images with a significant slice thickness, i.e., above 5mm. Medullary canal segmentation increases the geometric information that can be used in orthopedic surgical planning or in finite element analysis.

      PubDate: 2016-10-15T13:02:11Z
      DOI: 10.1016/j.medengphy.2016.09.019
  • Rôle of contrast media viscosity in altering vessel wall shear stress and
           relation to the risk of contrast extravasations
    • Authors: Sophia Sakellariou; Wenguang Li; Manosh C Paul; Giles Roditi
      Abstract: Publication date: Available online 8 October 2016
      Source:Medical Engineering & Physics
      Author(s): Sophia Sakellariou, Wenguang Li, Manosh C Paul, Giles Roditi
      Iodinated contrast media (CM) are the most commonly used injectables in radiology today. A range of different media are commercially available, combining various physical and chemical characteristics (ionic state, osmolality, viscosity) and thus exhibiting distinct in vivo behaviour and safety profiles. In this paper, numerical simulations of blood flow with contrast media were conducted to investigate the effects of contrast viscosity on generated vessel wall shear stress and vessel wall pressure to elucidate any possible relation to extravasations. Five different types of contrast for Iodine fluxes ranging at 1.5–2.2gI/s were modelled through 18G and 20G cannulae placed in an ideal vein at two different orientation angles. Results demonstrate that the least viscous contrast media generate the least maximum wall shear stress as well as the lowest total pressure for the same flow rate. This supports the empirical clinical observations and hypothesis that more viscous contrast media are responsible for a higher percentage of contrast extravasations. In addition, results support the clinical hypothesis that a catheter tip directed obliquely to the vein wall always produces the highest maximum wall shear stress and total pressure due to impingement of the contrast jet on the vessel wall.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.016
  • Advances in Functional Electrical Stimulation modelling and control
    • Authors: Thomas Schauer; Christopher Freeman
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Thomas Schauer, Christopher Freeman

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.004
  • Improved Rubin–Bodner model for the prediction of soft tissue
    • Authors: Guangming Zhang; James J. Xia; Michael Liebschner; Xiaoyan Zhang; Daeseung Kim; Xiaobo Zhou
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Guangming Zhang, James J. Xia, Michael Liebschner, Xiaoyan Zhang, Daeseung Kim, Xiaobo Zhou
      In craniomaxillofacial (CMF) surgery, a reliable way of simulating the soft tissue deformation resulted from skeletal reconstruction is vitally important for preventing the risks of facial distortion postoperatively. However, it is difficult to simulate the soft tissue behaviors affected by different types of CMF surgery. This study presents an integrated bio-mechanical and statistical learning model to improve accuracy and reliability of predictions on soft facial tissue behavior. The Rubin–Bodner (RB) model is initially used to describe the biomechanical behavior of the soft facial tissue. Subsequently, a finite element model (FEM) computers the stress of each node in soft facial tissue mesh data resulted from bone displacement. Next, the Generalized Regression Neural Network (GRNN) method is implemented to obtain the relationship between the facial soft tissue deformation and the stress distribution corresponding to different CMF surgical types and to improve evaluation of elastic parameters included in the RB model. Therefore, the soft facial tissue deformation can be predicted by biomechanical properties and statistical model. Leave-one-out cross-validation is used on eleven patients. As a result, the average prediction error of our model (0.7035mm) is lower than those resulting from other approaches. It also demonstrates that the more accurate bio-mechanical information the model has, the better prediction performance it could achieve.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.008
  • Probabilistic finite element method for large tumor radiofrequency
           ablation simulation and planning
    • Authors: Bin Duan; Rong Wen; Yabo Fu; Kian-Jon Chua; Chee-Kong Chui
      Abstract: Publication date: Available online 4 October 2016
      Source:Medical Engineering & Physics
      Author(s): Bin Duan, Rong Wen, Yabo Fu, Kian-Jon Chua, Chee-Kong Chui
      A challenging problem of radiofrequency ablation (RFA) in liver surgery is to accurately estimate the shapes and sizes of RFA lesions whose formation depends on intrinsic variations of the thermal–electrical properties of soft tissue. Large tumors, which can be as long as 10 cm or more, further complicate the problem. In this paper, a probabilistic bio-heating finite element (FE) model is proposed and developed to predict RFA lesions. Uncertainties of RFA lesions are caused by the probabilistic nature of five thermal–electrical liver properties: thermal conductivity, liver tissue density, specific heat, blood perfusion rate and electrical conductivity. Confidence levels of shapes and sizes of lesions are generated by the FE model incorporated with the mean-value first-order second-moment (MVFOSM) method. Based on the probabilistic FE method, a workflow of RFA planning is introduced to enable clinicians to preoperatively view the predicted RFA lesions in three-dimension (3D) within a hepatic environment. Accurate planning of the RFA needle placements can then be achieved based on the interactive simulation and confidence level selection.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.08.007
  • A mathematical method for precisely calculating the radiographic angles of
           the cup after total hip arthroplasty
    • Authors: Jing-Xin Zhao; Xiu-Yun Su; Ruo-Xiu Xiao; Zhe Zhao; Li-Hai Zhang; Li-Cheng Zhang; Pei-Fu Tang
      Abstract: Publication date: Available online 5 October 2016
      Source:Medical Engineering & Physics
      Author(s): Jing-Xin Zhao, Xiu-Yun Su, Ruo-Xiu Xiao, Zhe Zhao, Li-Hai Zhang, Li-Cheng Zhang, Pei-Fu Tang
      We established a mathematical method to precisely calculate the radiographic anteversion (RA) and radiographic inclination (RI) angles of the acetabular cup based on anterior–posterior (AP) pelvic radiographs after total hip arthroplasty. Using Mathematica software, a mathematical model for an oblique cone was established to simulate how AP pelvic radiographs are obtained and to address the relationship between the two-dimensional and three-dimensional geometry of the opening circle of the cup. In this model, the vertex was the X-ray beam source, and the generatrix was the ellipse in radiographs projected from the opening circle of the acetabular cup. Using this model, we established a series of mathematical formulas to reveal the differences between the true RA and RI cup angles and the measurements results achieved using traditional methods and AP pelvic radiographs and to precisely calculate the RA and RI cup angles based on post-operative AP pelvic radiographs. Statistical analysis indicated that traditional methods should be used with caution if traditional measurements methods are used to calculate the RA and RI cup angles with AP pelvic radiograph. The entire calculation process could be performed by an orthopedic surgeon with mathematical knowledge of basic matrix and vector equations.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.007
  • Isolated effects of external bath osmolality, solute concentration, and
           electrical charge on solute transport across articular cartilage
    • Authors: Behdad Pouran; Vahid Arbabi; Amir A. Zadpoor; Harrie Weinans
      Abstract: Publication date: Available online 6 October 2016
      Source:Medical Engineering & Physics
      Author(s): Behdad Pouran, Vahid Arbabi, Amir A. Zadpoor, Harrie Weinans
      The metabolic function of cartilage primarily depends on transport of solutes through diffusion mechanism. In the current study, we use contrast enhanced micro-computed tomography to determine equilibrium concentration of solutes through different cartilage zones and solute flux in the cartilage, using osteochondral plugs from equine femoral condyles. Diffusion experiments were performed with two solutes of different charge and approximately equal molecular weight, namely iodixanol (neutral) and ioxaglate (charge=−1) in order to isolate the effects of solute’s charge on diffusion. Furthermore, solute concentrations as well as bath osmolality were changed to isolate the effects of steric hindrance on diffusion. Bath concentration and bath osmolality only had minor effects on the diffusion of the neutral solute through cartilage at the surface, middle and deep zones, indicating that the diffusion of the neutral solute was mainly Fickian. The negatively charged solute diffused considerably slower through cartilage than the neutral solute, indicating a large non-Fickian contribution in the diffusion of charged molecules. The numerical models determined maximum solute flux in the superficial zone up to a factor of 2.5 lower for the negatively charged solutes (charge=−1) as compared to the neutral solutes confirming the importance of charge-matrix interaction in diffusion of molecules across cartilage.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.003
  • Design and biomechanical study of a novel adjustable hemipelvic prosthesis
    • Authors: Dongxu Liu; Zikai Hua; Xinyi Yan; Zhongmin Jin
      Abstract: Publication date: Available online 6 October 2016
      Source:Medical Engineering & Physics
      Author(s): Dongxu Liu, Zikai Hua, Xinyi Yan, Zhongmin Jin
      A pelvic endoprosthesis is commonly used in orthopedic surgeries to reconstruct the pelvis after internal hemipelvectomy. This study presents the detailed design of a novel type I+II+III adjustable hemipelvic prosthesis based on the geometrical features of massive human pelvises. Finite element analysis is conducted to estimate the biomechanical performance of the newly designed adjustable hemipelvic prosthesis. Detailed numerical models of the natural and reconstructed pelvises including related soft tissues are developed. Hip contact forces during normal walking, which is one of the most frequent dynamic activities in daily living, are imposed on the pelvis. Results show that the peak stress observed in the reconstructed pelvis model is still within a low and elastic range below the yielding strength of the cortical bone and Ti6Al4V. No significant difference of the stress transferring route, displacement distributions and principal stress vectors is observed between the reconstructed and natural pelvises. The results indicate that the load transferring function of the partially resected pelvis is able to be reliably recovered by the adjustable hemipelvic prosthesis. The principal stress vectors in both pelvis models predict that bone absorption may not apparently occur in the long run. Long-term biomechanical performance of this newly designed prosthesis may be stability.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.017
  • Cone-beam micro computed tomography dedicated to the breast
    • Authors: Antonio Sarno; Giovanni Mettivier; Francesca Di Lillo; Mario Cesarelli; Paolo Bifulco; Paolo Russo
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): Antonio Sarno, Giovanni Mettivier, Francesca Di Lillo, Mario Cesarelli, Paolo Bifulco, Paolo Russo
      We developed a scanner for micro computed tomography dedicated to the breast (BµCT) with a high resolution flat-panel detector and a microfocus X-ray tube. We evaluated the system spatial resolution via the 3D modulation transfer function (MTF). In addition to conventional absorption-based X-ray imaging, such a prototype showed capabilities for propagation-based phase-contrast and related edge enhancement effects in 3D imaging. The system limiting spatial resolution is 6.2mm−1 (MTF at 10%) in the vertical direction and 3.8mm−1 in the radial direction, values which compare favorably with the spatial resolution reached by mini focus breast CT scanners of other groups. The BµCT scanner was able to detect both microcalcification clusters and masses in an anthropomorphic breast phantom at a dose comparable to that of two-view mammography. The use of a breast holder is proposed in order to have 1–2min long scan times without breast motion artifacts.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.012
  • Study of the transdentinal diffusion of bioactive molecules
    • Authors: A.D. Passos; D. Tziafas; A.A. Mouza; S.V. Paras
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): A.D. Passos, D. Tziafas, A.A. Mouza, S.V. Paras
      In this work the mass transfer characteristics in a µ-tube that simulates a simplified dentinal tubule geometry are numerically investigated. The aim is to assess the key features that affect transdentinal diffusion of substances and consequently to define the necessary quantitative and qualitative issues related to a specific bioactive agent before its potential application in clinical practice. CFD simulations were performed in an S-shaped tapered micro-tube, while the code was validated using the non-intrusive optical measuring technique Laser Induced Fluorescence (LIF). As the phenomenon is one-dimensional, diffusion dominated and strongly dependent on the molecular size, the time needed for the concentration of released molecules to attain a required value can be controlled by their initial concentration. Thus, we propose a model, which is successfully verified by experimental data using a dentinal disc and which given the type of applied molecules and their critical pulpal concentration is able to estimate the initial concentration to be imposed.
      Graphical abstract image

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.005
  • Comparison of algorithms to quantify muscle fatigue in upper limb muscles
           based on sEMG signals
    • Authors: Lorenz Kahl; Ulrich G. Hofmann
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): Lorenz Kahl, Ulrich G. Hofmann
      This work compared the performance of six different fatigue detection algorithms quantifying muscle fatigue based on electromyographic signals. Surface electromyography (sEMG) was obtained by an experiment from upper arm contractions at three different load levels from twelve volunteers. Fatigue detection algorithms mean frequency (MNF), spectral moments ratio (SMR), the wavelet method WIRM1551, sample entropy (SampEn), fuzzy approximate entropy (fApEn) and recurrence quantification analysis (RQA%DET) were calculated. The resulting fatigue signals were compared considering the disturbances incorporated in fatiguing situations as well as according to the possibility to differentiate the load levels based on the fatigue signals. Furthermore we investigated the influence of the electrode locations on the fatigue detection quality and whether an optimized channel set is reasonable. The results of the MNF, SMR, WIRM1551 and fApEn algorithms fell close together. Due to the small amount of subjects in this study significant differences could not be found. In terms of disturbances the SMR algorithm showed a slight tendency to out-perform the others.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.009
  • Bone cement flow analysis by stepwise injection through medical cannulas
    • Authors: Ivan Zderic; Philipp Steinmetz; Markus Windolf; R. Geoff Richards; Andreas Boger; Boyko Gueorguiev
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): Ivan Zderic, Philipp Steinmetz, Markus Windolf, R. Geoff Richards, Andreas Boger, Boyko Gueorguiev
      Cement leakage is a serious adverse event potentially occurring during vertebroplasty. Pre-operative in-silico planning of the cement filling process can help reducing complication rates related to leakage. This requires a better understanding of the cement flow along the whole injection path. Therefore, the aim of the present study was to analyze bone cement flow behavior by stepwise injections through medical cannulas. Sixteen cannulas were assigned to four groups for stepwise injection of differently colored cement portions of 1ml volume. Each group differed in the amount of injected cement portions with a range of 1–4ml. After cement curing longitudinal cross-sections of the cannulas were performed and high-resolution pictures taken. Based on these pictures, quadratic polynomial interpolation was applied to the marked intersections between the last two injected cement portions to calculate the leading coefficients. Leading coefficients in the groups with three cement portions (0.287 ± 0.078), four portions (0.243 ± 0.041) and two portions (0.232 ± 0.050) were comparable and significantly higher than the group with one cement portion (0.0032 ± 0.0004), p ≤ 0.016. Based on these findings, cement flow through medical cannulas can be considered as predictable and can therefore be excluded as a source of risk for possible cement leakage complications during vertebroplasty procedures.

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.015
  • Three-dimensional measurement technique to assess implant position and
           orientation after total knee arthroplasty
    • Authors: Filip Jonkergouw; Florence Allé; Karim Chellaoui; Jos Vander Sloten; Dieter Vangeneugden
      Abstract: Publication date: Available online 7 October 2016
      Source:Medical Engineering & Physics
      Author(s): Filip Jonkergouw, Florence Allé, Karim Chellaoui, Jos Vander Sloten, Dieter Vangeneugden
      The performance of implant placement technologies are often evaluated based on their achieved post-operative implant alignment. Therefore accurate assessment techniques are necessary to compare pre-operatively planned implant positions with the corresponding post-operatively placed implant positions in total knee arthroplasty. This paper describes a CT based 3D measurement method for evaluation of implant positioning accuracy comparing post-operative implant position to the corresponding pre-operative planned implant position using 3D virtual models. TKAs were carried out on three phantoms and processed three times to investigate the accuracy of the method. The measurements were then assessed against measurements taken through an optical scan. The results indicate that an average measurement error less than 1 ° and 0.5mm can be obtained except in the proximal–distal direction where the error was up to 1.34mm. The accuracy of this 3D measurement technique is sufficiently reliable to enable reporting on implant position and orientation in the same coordinate system as pre-operatively defined independently of the planning system or the surgical implant placement technology (patient-specific guides, robotics, and navigation).

      PubDate: 2016-10-09T12:41:42Z
      DOI: 10.1016/j.medengphy.2016.09.006
  • A new 3D center of mass control approach for FES-assisted standing: First
           experimental evaluation with a humanoid robot
    • Authors: J. Jovic; V. Bonnet; C. Fattal; P. Fraisse; Ch. Azevedo Coste
      Abstract: Publication date: Available online 28 September 2016
      Source:Medical Engineering & Physics
      Author(s): J. Jovic, V. Bonnet, C. Fattal, P. Fraisse, Ch. Azevedo Coste
      This paper proposes a new control framework to restore the coordination between upper (functional) and lower (paralyzed) limbs in the context of functional electrical stimulation in completely paraplegic individuals. A kinematic decoupling between the lower and upper limbs controls the 3D whole-body center of mass location and the relative foot positions by acting only on the lower-limb joints. The upper limbs are free to move under voluntary control, and are seen as a perturbation for the lower limbs. An experimental validation of this paradigm using a humanoid robot demonstrates the real-time applicability and robustness of the method. Different scenarios mimicking the motion of a healthy subject are investigated. The proposed method can maintain bipedal balance and track the desired center of mass trajectories under movement disturbances of the upper limbs with an error inferior to 0.01 m under any conditions.

      PubDate: 2016-10-01T11:48:04Z
      DOI: 10.1016/j.medengphy.2016.09.002
  • Hybrid robotic systems for upper limb rehabilitation after stroke: A
    • Authors: Francisco Resquín; Alicia Cuesta Gómez; Jose Gonzalez-Vargas; Fernando Brunetti; Diego Torricelli; Francisco Molina Rueda; Roberto Cano de la Cuerda; Juan Carlos Miangolarra; José Luis Pons
      Abstract: Publication date: Available online 29 September 2016
      Source:Medical Engineering & Physics
      Author(s): Francisco Resquín, Alicia Cuesta Gómez, Jose Gonzalez-Vargas, Fernando Brunetti, Diego Torricelli, Francisco Molina Rueda, Roberto Cano de la Cuerda, Juan Carlos Miangolarra, José Luis Pons
      In recent years the combined use of functional electrical stimulation (FES) and robotic devices, called hybrid robotic rehabilitation systems, has emerged as a promising approach for rehabilitation of lower and upper limb motor functions. This paper presents a review of the state of the art of current hybrid robotic solutions for upper limb rehabilitation after stroke. For this aim, studies have been selected through a search using web databases: IEEE-Xplore, Scopus and PubMed. A total of 10 different hybrid robotic systems were identified, and they are presented in this paper. Selected systems are critically compared considering their technological components and aspects that form part of the hybrid robotic solution, the proposed control strategies that have been implemented, as well as the current technological challenges in this topic. Additionally, we will present and discuss the corresponding evidences on the effectiveness of these hybrid robotic therapies. The review also discusses the future trends in this field.

      PubDate: 2016-10-01T11:48:04Z
      DOI: 10.1016/j.medengphy.2016.09.001
  • Experimental investigation and statistical modeling of temperature rise in
           rotary ultrasonic bone drilling
    • Authors: Vishal Gupta; Pulak M. Pandey
      Abstract: Publication date: Available online 14 September 2016
      Source:Medical Engineering & Physics
      Author(s): Vishal Gupta, Pulak M. Pandey
      Thermal necrosis is one of the major problems associated with the bone drilling process in orthopedic/trauma surgical operations. To overcome this problem a new bone drilling method has been introduced recently. Studies have been carried out with rotary ultrasonic drilling (RUD) on pig bones using diamond coated abrasive hollow tools. In the present work, influence of process parameters (rotational speed, feed rate, drill diameter and vibrational amplitude) on change in the temperature was studied using design of experiment technique i.e., response surface methodology (RSM) and data analysis was carried out using analysis of variance (ANOVA). Temperature was recorded and measured by using embedded thermocouple technique at a distance of 0.5mm, 1.0mm, 1.5mm and 2.0mm from the drill site. Statistical model was developed to predict the maximum temperature at the drill tool and bone interface. It was observed that temperature increased with increase in the rotational speed, feed rate and drill diameter and decreased with increase in the vibrational amplitude.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.012
  • A review of the design and clinical evaluation of the ShefStim array-based
           functional electrical stimulation system
    • Authors: Laurence P. Kenney; Ben W. Heller; Anthony T. Barker; Mark L. Reeves; Jamie Healey; Timothy R. Good; Glen Cooper; Ning Sha; Sarah Prenton; Anmin Liu; David Howard
      Abstract: Publication date: Available online 14 September 2016
      Source:Medical Engineering & Physics
      Author(s): Laurence P. Kenney, Ben W. Heller, Anthony T. Barker, Mark L. Reeves, Jamie Healey, Timothy R. Good, Glen Cooper, Ning Sha, Sarah Prenton, Anmin Liu, David Howard
      Functional electrical stimulation has been shown to be a safe and effective means of correcting foot drop of central neurological origin. Current surface-based devices typically consist of a single channel stimulator, a sensor for determining gait phase and a cuff, within which is housed the anode and cathode. The cuff-mounted electrode design reduces the likelihood of large errors in electrode placement, but the user is still fully responsible for selecting the correct stimulation level each time the system is donned. Researchers have investigated different approaches to automating aspects of setup and/or use, including recent promising work based on iterative learning techniques. This paper reports on the design and clinical evaluation of an electrode array-based FES system for the correction of drop foot, ShefStim. The paper reviews the design process from proof of concept lab-based study, through modelling of the array geometry and interface layer to array search algorithm development. Finally, the paper summarises two clinical studies involving patients with drop foot. The results suggest that the ShefStim system with automated setup produces results which are comparable with clinician setup of conventional systems. Further, the final study demonstrated that patients can use the system without clinical supervision. When used unsupervised, setup time was 14min (9min for automated search plus 5min for donning the equipment), although this figure could be reduced significantly with relatively minor changes to the design.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.005
  • Morphology based anisotropic finite element models of the proximal femur
           validated with experimental data
    • Authors: W.S. Enns-Bray; O. Ariza; S. Gilchrist; R.P. Widmer Soyka; P.J. Vogt; H. Palsson; S.K. Boyd; P. Guy; P.A. Cripton; S.J. Ferguson; B. Helgason
      Abstract: Publication date: Available online 15 September 2016
      Source:Medical Engineering & Physics
      Author(s): W.S. Enns-Bray, O. Ariza, S. Gilchrist, R.P. Widmer Soyka, P.J. Vogt, H. Palsson, S.K. Boyd, P. Guy, P.A. Cripton, S.J. Ferguson, B. Helgason
      Finite element analysis (FEA) of bones scanned with Quantitative Computed Tomography (QCT) can improve early detection of osteoporosis. The accuracy of these models partially depends on the assigned material properties, but anisotropy of the trabecular bone cannot be fully captured due to insufficient resolution of QCT. The inclusion of anisotropy measured from high resolution peripheral QCT (HR-pQCT) could potentially improve QCT-based FEA of the femur, although no improvements have yet been demonstrated in previous experimental studies. This study analyzed the effects of adding anisotropy to clinical resolution femur models by constructing six sets of FE models (two isotropic and four anisotropic) for each specimen from a set of sixteen femurs that were experimentally tested in sideways fall loading with a strain gauge on the superior femoral neck. Two different modulus–density relationships were tested, both with and without anisotropy derived from mean intercept length analysis of HR-pQCT scans. Comparing iso- and anisotropic models to the experimental data resulted in nearly identical correlation and highly similar linear regressions for both whole bone stiffness and strain gauge measurements. Anisotropic models contained consistently greater principal compressive strains, approximately 14% in magnitude, in certain internal elements located in the femoral neck, greater trochanter, and femoral head. In summary, anisotropy had minimal impact on macroscopic measurements, but did alter internal strain behavior. This suggests that organ level QCT-based FE models measuring femoral stiffness have little to gain from the addition of anisotropy, but studies considering failure of internal structures should consider including anisotropy to their models.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.010
  • Numerical prediction of peri-implant bone adaptation: Comparison of
           mechanical stimuli and sensitivity to modeling parameters
    • Authors: Marco Piccinini; Joel Cugnoni; John Botsis; Patrick Ammann; Anselm Wiskott
      Abstract: Publication date: Available online 15 September 2016
      Source:Medical Engineering & Physics
      Author(s): Marco Piccinini, Joel Cugnoni, John Botsis, Patrick Ammann, Anselm Wiskott
      Long term durability of osseointegrated implants depends on bone adaptation to stress and strain occurring in proximity of the prosthesis. Mechanical overloading, as well as disuse, may reduce the stability of implants by provoking bone resorption. However, an appropriate mechanical environment can improve integration. Several studies have focused on the definition of numerical methods to predict bone peri-implant adaptation to the mechanical environment. Existing adaptation models differ notably in the type of mechanical variable adopted as stimulus but also in the bounds and shape of the adaptation rate equation. However, a general comparison of the different approaches on a common benchmark case is still missing and general guidelines to determine physically sound parameters still need to be developed. This current work addresses these themes in two steps. Firstly, the histograms of effective stress, strain and strain energy density are compared for rat tibiae in physiological (homeostatic) conditions. According to the Mechanostat, the ideal stimulus should present a clearly defined, position and tissue invariant lazy zone in homeostatic conditions. Our results highlight that only the octahedral shear strain presents this characteristic and can thus be considered the optimal choice for implementation of a continuum level bone adaptation model. Secondly, critical modeling parameters such as lazy zone bounds, type of rate equation and bone overloading response are classified depending on their influence on the numerical predictions of bone adaptation. Guidelines are proposed to establish the dominant model parameters based on experimental and simulated data.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.008
  • Effects of implant drilling parameters for pilot and twist drills on
           temperature rise in bone analog and alveolar bones
    • Authors: Yung-Chuan Chen; Chih-Kun Hsiao; Ji-Sih Ciou; Yi-Jung Tsai; Yuan-Kun Tu
      Abstract: Publication date: Available online 16 September 2016
      Source:Medical Engineering & Physics
      Author(s): Yung-Chuan Chen, Chih-Kun Hsiao, Ji-Sih Ciou, Yi-Jung Tsai, Yuan-Kun Tu
      This study concerns the effects of different drilling parameters of pilot drills and twist drills on the temperature rise of alveolar bones during dental implant procedures. The drilling parameters studied here include the feed rate and rotation speed of the drill. The bone temperature distribution was analyzed through experiments and numerical simulations of the drilling process. In this study, a three dimensional (3D) elasto-plastic dynamic finite element model (DFEM) was proposed to investigate the effects of drilling parameters on the bone temperature rise. In addition, the FE model is validated with drilling experiments on artificial human bones and porcine alveolar bones. The results indicate that 3D DFEM can effectively simulate the bone temperature rise during the drilling process. During the drilling process with pilot drills or twist drills, the maximum bone temperature occurred in the region of the cancellous bones close to the cortical bones. The feed rate was one of the important factors affecting the time when the maximum bone temperature occurred. Our results also demonstrate that the elevation of bone temperature was reduced as the feed rate increased and the drill speed decreased, which also effectively reduced the risk region of osteonecrosis. These findings can serve as a reference for dentists in choosing drilling parameters for dental implant surgeries.

      PubDate: 2016-09-17T20:56:52Z
      DOI: 10.1016/j.medengphy.2016.08.009
  • Termination of atrial spiral waves by traction into peripheral non 1:1
           conducting regions – A numerical study
    • Authors: Amit Rozner; Sharon Zlochiver
      Abstract: Publication date: Available online 7 September 2016
      Source:Medical Engineering & Physics
      Author(s): Amit Rozner, Sharon Zlochiver
      Atrial ablation has been recently utilized to treat atrial fibrillation (AF) by isolation or destruction of arrhythmia drivers. In chronic or persistent AF patients these drivers often consist of one or few rotors at unknown locations, and several ablations are commonly conducted before arrhythmia is terminated. However, the irreversible damage done to the tissue may lead to AF recurrence. We propose an alternative strategy to terminate rotor activity by its attraction into a non 1:1 conducting region. The feasibility of the method was numerically tested in 2D models of chronic AF human atrial tissue. Left-to-right gradients of either acetylcholine (ACh) or potassium conductance were employed to generate regions of 1:1 and non 1:1 conduction, characterized by their dominant frequency (DF) ratios. Spiral waves were established in the 1:1 conducting region and raster scanning was employed using a stimulating probe to attract the spiral wave tip. The probe was then linearly moved towards the boundary between the two regions. Successful attraction of spiral waves to the probe was demonstrated when the probe was <8mm from the spiral wave tip. Maximal traction velocity without loss of anchoring increased in a non-linear way with increasing values of ACh. Success rate of spiral wave termination was over 90% for regional DF ratios of as low as 1:1.2. Given that normally much higher ratios are measured in physiological atrial tissues, we envision this technique to provide a feasible, safer alternative to ablation procedures performed in persistent AF patients.

      PubDate: 2016-09-08T19:50:19Z
      DOI: 10.1016/j.medengphy.2016.08.006
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