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Showing 1401 - 1600 of 1720 Journals sorted alphabetically
Virus Genes     Hybrid Journal   (Followers: 1)
Virus Research     Hybrid Journal   (Followers: 1)
Visnyk of Dnipropetrovsk University. Biology, ecology     Open Access   (Followers: 2)
Visnyk of Dnipropetrovsk University. Biology, medicine     Open Access  
Walailak Journal of Science and Technology     Open Access  
Web Ecology     Open Access   (Followers: 5)
Weed Science     Full-text available via subscription   (Followers: 6)
Weed Technology     Full-text available via subscription   (Followers: 2)
West African Journal of Applied Ecology     Open Access  
Western Undergraduate Research Journal : Health and Natural Sciences     Open Access  
Wetlands     Hybrid Journal   (Followers: 24)
Wildlife Biology     Open Access   (Followers: 14)
Wildlife Research     Hybrid Journal   (Followers: 15)
Wiley Interdisciplinary Reviews - System Biology and Medicine     Hybrid Journal   (Followers: 5)
Wiley Interdisciplinary Reviews : Developmental Biology     Hybrid Journal   (Followers: 3)
Wiley Interdisciplinary Reviews : Membrane Transport and Signaling     Hybrid Journal  
Wiley Interdisciplinary Reviews : RNA     Hybrid Journal   (Followers: 3)
World Crop Pests     Full-text available via subscription   (Followers: 1)
World Mycotoxin Journal     Full-text available via subscription   (Followers: 6)
Xenobiotica     Hybrid Journal   (Followers: 9)
Yeast     Hybrid Journal   (Followers: 9)
Zebrafish     Hybrid Journal   (Followers: 1)
Zeitschrift für Evidenz, Fortbildung und Qualität im Gesundheitswesen     Full-text available via subscription   (Followers: 5)
Zeitschrift für Naturforschung C : A Journal of Biosciences     Open Access   (Followers: 2)

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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  [3043 journals]
  • Influence of spinal disc translational stiffness on the lumbar spinal
           loads, ligament forces and trunk muscle forces during upper body
           inclination
    • Authors: Rizwan Arshad; Thomas Zander; Maxim Bashkuev; Hendrik Schmidt
      Pages: 54 - 62
      Abstract: Publication date: August 2017
      Source:Medical Engineering & Physics, Volume 46
      Author(s): Rizwan Arshad, Thomas Zander, Maxim Bashkuev, Hendrik Schmidt
      Inverse dynamic musculoskeletal human body models are commonly used to predict the spinal loads and trunk muscle forces. These models include rigid body segments, mechanical joints, active and passive structural components such as muscles, tendons and ligaments. Several studies used simple definition of lumbar spinal discs idealized as spherical joints with infinite translational stiffness. The aim of the current sensitivity study was to investigate the influence of disc translational stiffness (shear and compressive stiffness) on the joint kinematics and forces in intervertebral discs (L1−L5), trunk muscles and ligaments for an intermediately flexed position (55°). Based on in vitro data, a range of disc shear stiffness (100−200N/mm) and compressive stiffness (1900−2700N/mm) was considered in the model using the technique of force dependent kinematics (FDK). Range of variation in spinal loads, trunk muscle forces and ligaments forces were calculated (with & without load in hands) and compared with the results of reference model (RM) having infinite translational stiffness. The discs’ centers of rotation (CoR) were computed for L3−L4 and L4−L5 motion segments. Between RM and FDK models, maximum differences in compressive forces were 7% (L1−L2 & L2−L3), 8% (L3−L4) and 6% (L4−L5) whereas in shear forces 35% (L1−L2), 47% (L2−L3), 45% (L3−L4) and more than 100% in L4−L5. Maximum differences in the sum of global and local muscle forces were approximately 10%, whereas in ligament forces were 27% (supraspinous), 40% (interspinous), 56% (intertransverse), 58% (lig. flavum) and 100% (lig. posterior). The CoRs were predicted posteriorly, below (L3−L4) and in the disc (L4−L5). FDK model predicted lower spinal loads, ligament forces and varied distribution of global and local muscle forces. Consideration of translational stiffnesses influenced the model results and showed increased differences with lower stiffness values.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.05.006
      Issue No: Vol. 46 (2017)
       
  • A mathematical method for precisely calculating the radiographic angles of
           the cup after total hip arthroplasty
    • Authors: Brian Derbyshire
      Pages: 110 - 111
      Abstract: Publication date: August 2017
      Source:Medical Engineering & Physics, Volume 46
      Author(s): Brian Derbyshire


      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.02.016
      Issue No: Vol. 46 (2017)
       
  • Image-based immersed boundary model of the aortic root
    • Authors: Ali Hasan; Ebrahim M. Kolahdouz; Andinet Enquobahrie; Thomas G. Caranasos; John P. Vavalle; Boyce E. Griffith
      Abstract: Publication date: Available online 2 August 2017
      Source:Medical Engineering & Physics
      Author(s): Ali Hasan, Ebrahim M. Kolahdouz, Andinet Enquobahrie, Thomas G. Caranasos, John P. Vavalle, Boyce E. Griffith
      Each year, approximately 300,000 heart valve repair or replacement procedures are performed worldwide, including approximately 70,000 aortic valve replacement surgeries in the United States alone. Computational platforms for simulating cardiovascular devices such as prosthetic heart valves promise to improve device design and assist in treatment planning, including patient-specific device selection. This paper describes progress in constructing anatomically and physiologically realistic immersed boundary (IB) models of the dynamics of the aortic root and ascending aorta. This work builds on earlier IB models of fluid–structure interaction (FSI) in the aortic root, which previously achieved realistic hemodynamics over multiple cardiac cycles, but which also were limited to simplified aortic geometries and idealized descriptions of the biomechanics of the aortic valve cusps. By contrast, the model described herein uses an anatomical geometry reconstructed from patient-specific computed tomography angiography (CTA) data, and employs a description of the elasticity of the aortic valve leaflets based on a fiber-reinforced constitutive model fit to experimental tensile test data. The resulting model generates physiological pressures in both systole and diastole, and yields realistic cardiac output and stroke volume at physiological Reynolds numbers. Contact between the valve leaflets during diastole is handled automatically by the IB method, yielding a fully competent valve model that supports a physiological diastolic pressure load without regurgitation. Numerical tests show that the model is able to resolve the leaflet biomechanics in diastole and early systole at practical grid spacings. The model is also used to examine differences in the mechanics and fluid dynamics yielded by fresh valve leaflets and glutaraldehyde-fixed leaflets similar to those used in bioprosthetic heart valves. Although there are large differences in the leaflet deformations during diastole, the differences in the open configurations of the valve models are relatively small, and nearly identical hemodynamics are obtained in all cases considered.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.05.007
       
  • In vitro performance of a shape memory polymer foam-coated coil
           embolization device
    • Authors: Anthony J. Boyle; Mark A. Wierzbicki; Scott Herting; Andrew C. Weems; Adam Nathan; Wonjun Hwang; Duncan J. Maitland
      Abstract: Publication date: Available online 31 July 2017
      Source:Medical Engineering & Physics
      Author(s): Anthony J. Boyle, Mark A. Wierzbicki, Scott Herting, Andrew C. Weems, Adam Nathan, Wonjun Hwang, Duncan J. Maitland
      Intracranial saccular aneurysm treatment using endovascular embolization devices are limited by aneurysm recurrence that can lead to aneurysm rupture. A shape memory polymer (SMP) foam-coated coil (FCC) embolization device was designed to increase packing density and improve tissue healing compared to current commercial devices. FCC devices were fabricated and tested using in vitro models to assess feasibility for clinical treatment of intracranial saccular aneurysms. FCC devices demonstrated smooth delivery through tortuous pathways similar to control devices as well as greater than 10 min working time for clinical repositioning during deployment. Furthermore, the devices passed pilot verification tests for particulates, chemical leachables, and cytocompatibility. Finally, devices were successfully implanted in an in vitro saccular aneurysm model with large packing density. Though improvements and future studies evaluating device stiffness were identified as a necessity, the FCC device demonstrates effective delivery and packing performance that provides great promise for clinical application of the device in treatment of intracranial saccular aneurysms.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.07.009
       
  • Does stabilization of the degenerative lumbar spine itself produce
           multifidus atrophy'
    • Authors: Young Eun Kim; Hae Won Choi
      Abstract: Publication date: Available online 31 July 2017
      Source:Medical Engineering & Physics
      Author(s): Young Eun Kim, Hae Won Choi
      The effect of stabilization of the degenerative segment on changes in the pattern of paraspinal muscle activity was investigated using a previously developed musculoskeletal model. Muscle activity change depending on L4-L5 segment stabilization with and without taking into account the presence of multifidus atrophy according to direct invasion of the back muscle during surgery (MADIBM) was analysed in erect standing and 20° flexed postures. For the stabilization of the degenerative segment, a fusion or non-fusion stabilization with a pedicle-based dynamic stabilization system (PBDS) was applied. During erect standing, fusion generated a 12% reduction in the total multifidus muscle force, while its reduction was 6.6% with PBDS application. The presence of MADIBM produced 23.0% and 22.5% reductions in fusion and with PBDS application, respectively. During 20° flexion, 10.5% and 9.3% reductions were produced for fusion and PBDS application, respectively, and the corresponding values were 23.4% and 23.0%, respectively, in the presence of MADIBM. Increased facet joint contact forces were produced at the non-stabilized levels after stabilization while in erect standing posture. Alterations in muscle activity, which could be regarded as adaptions to altered spinal stability, may generate unexpected secondary problems in the spine.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.07.008
       
  • The variation in frequency locations in Doppler ultrasound spectra for
           maximum blood flow velocities in narrowed vessels
    • Authors: Yingyun Zhang; Yufeng Zhang; Lian Gao; Li Deng; Xiao Hu; Kexin Zhang; Haiyan Li
      Abstract: Publication date: Available online 29 July 2017
      Source:Medical Engineering & Physics
      Author(s): Yingyun Zhang, Yufeng Zhang, Lian Gao, Li Deng, Xiao Hu, Kexin Zhang, Haiyan Li
      This study assessed the variation in the frequency locations in the Doppler ultrasound spectra for the maximum blood flow velocities of in vessels with different degrees of bilaterally axisymmetric stenosis. This was done by comparing the relationship between the velocity distributions and corresponding Doppler power spectra. First, a geometric vessel model with axisymmetric stenosis was established. This made it possible to obtain the blood flow velocity distributions for different degrees of stenosis from the solutions of the Navier–Stokes equations. Then, the Doppler spectra were calculated for the entire segment of the vessel that was covered by the sound field. Finally, the maximum frequency locations for the spectra were determined based on the intersections of the maximum values chosen from the calculated blood flow velocity distributions and their corresponding spectra. The computational analysis showed that the maximum frequencies, which corresponded to the maximum blood flow velocities for different degrees of stenosis, were located at different positions along the spectral falling edges. The location for a normal (stenosis free) vessel was in the middle of the falling edge. For vessels with increasing degrees of stenosis, this location shifted approximately linearly downward along the falling edge. For 40% stenosis, the location reached a position at the falling edge of 0.32. Results obtained using the Field II simulation tool demonstrated the validity of the theoretical analysis and calculations, and may help to improve the maximum velocity estimation accuracy for Doppler blood flow spectra in stenosed vessels.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.07.004
       
  • Development of an acoustic measurement protocol to monitor acetabular
           implant fixation in cementless total hip Arthroplasty: A preliminary study
           
    • Authors: Quentin Goossens; Steven Leuridan; Petr Henyš; Jorg Roosen; Leonard Pastrav; Michiel Mulier; Wim Desmet; Kathleen Denis; Jos Vander Sloten
      Abstract: Publication date: Available online 29 July 2017
      Source:Medical Engineering & Physics
      Author(s): Quentin Goossens, Steven Leuridan, Petr Henyš, Jorg Roosen, Leonard Pastrav, Michiel Mulier, Wim Desmet, Kathleen Denis, Jos Vander Sloten
      In cementless total hip arthroplasty (THA), the initial stability is obtained by press-fitting the implant in the bone to allow osseointegration for a long term secondary stability. However, finding the insertion endpoint that corresponds to a proper initial stability is currently based on the tactile and auditory experiences of the orthopedic surgeon, which can be challenging. This study presents a novel real-time method based on acoustic signals to monitor the acetabular implant fixation in cementless total hip arthroplasty. Twelve acoustic in vitro experiments were performed on three types of bone models; a simple bone block model, an artificial pelvic model and a cadaveric model. A custom made beam was screwed onto the implant which functioned as a sound enhancer and insertor. At each insertion step an acoustic measurement was performed. A significant acoustic resonance frequency shift was observed during the insertion process for the different bone models; 250 Hz (35%, second bending mode) to 180 Hz (13%, fourth bending mode) for the artificial bone block models and 120 Hz (11%, eighth bending mode) for the artificial pelvis model. No significant frequency shift was observed during the cadaveric experiment due to a lack of implant fixation in this model. This novel diagnostic method shows the potential of using acoustic signals to monitor the implant seating during insertion.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.07.006
       
  • Influence of design features of tibial stems in total knee arthroplasty on
           tibial bone remodeling behaviors
    • Authors: Zhengbin Jia; He Gong; Shimin Hu; Juan Fang; Ruoxun Fan
      Abstract: Publication date: Available online 29 July 2017
      Source:Medical Engineering & Physics
      Author(s): Zhengbin Jia, He Gong, Shimin Hu, Juan Fang, Ruoxun Fan
      In total knee arthroplasty, the optimal length and material of tibial stem remain controversial. This study aimed to evaluate influences of lengths and materials of cementless stems on tibial remodeling behaviors. Three groups of lengths were investigated (i.e., 110, 60, and 30 mm), and four materials (i.e., titanium, flexible ‘iso-elastic’ material, and two functionally graded materials [FGMs]) were selected for each group. FGM is a kind of material whose composition gradually varies in space. In this study, the compositions of two FGMs were Ti and hydroxyapatite (FGM I), and Ti and bioglass (FGM II), respectively. Tibial models were incorporated with finite element analysis to simulate bone remodeling. Distributions of bone mineral density, von Mises stress, and interface shear stress were obtained. For the length, the long stem produced more serious stress shielding and stress concentration than the short stem, but it could provide better mechanical stability. For the material, FGM I could reduce stress shielding and stress concentration and reduce the risk of loosening. Compared with the length, the material had a pronounced effect on remodeling. This study provided theoretical basis for optimal design of stem to improve service life of tibial components and to reduce pain of patients.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.06.046
       
  • What are the six degree-of-freedom errors of a robotically-machined
           femoral cavity in total hip arthroplasty and are they clinically
           important' An in-vitro study
    • Authors: Chih Ming Hsieh; Stephen M. Howell; Maury L. Hull
      Abstract: Publication date: Available online 26 July 2017
      Source:Medical Engineering & Physics
      Author(s): Chih Ming Hsieh, Stephen M. Howell, Maury L. Hull
      Errors during a robot-assisted THA may result in a femoral cavity with position and orientation different than planned. This can lead to a femoral component placement that inaccurately sets a patient's femoral anteversion (FA), femoral offset (FO), and vertical offset (VO). The objectives of this study were to determine the position and orientation errors of robotically-machined femoral cavities in six degrees of freedom and to determine how position and orientation errors translate into errors in the setting of FA, FO, and VO. After creating preoperative plans, robot-assisted THAs were performed on twelve cadaveric specimens. The position and orientation of the machined cavities were compared to those of the planned cavities to determine the errors in six degrees of freedom. Placement of femoral components into the machined cavities was simulated, and the differences in FA, FO, and VO between the simulated and planned component placement were computed. While bias (i.e. mean error) occurred for three of six degrees of freedom in femoral cavities machined by a robotic system, the root mean squared errors (RMSEs) when the placement of femoral component was simulated were limited to 1.9° for FA, 1.0mm for FO, and 2.1mm for VO and were clinically unimportant.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.06.016
       
  • A coupled mitral valve—left ventricle model with
           fluid–structure interaction
    • Authors: Hao Gao; Liuyang Feng; Nan Qi; Colin Berry; Boyce E. Griffith; Xiaoyu Luo
      Abstract: Publication date: Available online 25 July 2017
      Source:Medical Engineering & Physics
      Author(s): Hao Gao, Liuyang Feng, Nan Qi, Colin Berry, Boyce E. Griffith, Xiaoyu Luo
      Understanding the interaction between the valves and walls of the heart is important in assessing and subsequently treating heart dysfunction. This study presents an integrated model of the mitral valve (MV) coupled to the left ventricle (LV), with the geometry derived from in vivo clinical magnetic resonance images. Numerical simulations using this coupled MV–LV model are developed using an immersed boundary/finite element method. The model incorporates detailed valvular features, left ventricular contraction, nonlinear soft tissue mechanics, and fluid-mediated interactions between the MV and LV wall. We use the model to simulate cardiac function from diastole to systole. Numerically predicted LV pump function agrees well with in vivo data of the imaged healthy volunteer, including the peak aortic flow rate, the systolic ejection duration, and the LV ejection fraction. In vivo MV dynamics are qualitatively captured. We further demonstrate that the diastolic filling pressure increases significantly with impaired myocardial active relaxation to maintain a normal cardiac output. This is consistent with clinical observations. The coupled model has the potential to advance our fundamental knowledge of mechanisms underlying MV–LV interaction, and help in risk stratification and optimisation of therapies for heart diseases.

      PubDate: 2017-08-03T08:38:05Z
      DOI: 10.1016/j.medengphy.2017.06.042
       
  • Investigation of the feasibility of non-invasive optical sensors for the
           quantitative assessment of dehydration
    • Authors: Cobus Visser; Eduard Kieser; Kiran Dellimore; Dawie van den Heever; Johan Smith
      Abstract: Publication date: Available online 19 July 2017
      Source:Medical Engineering & Physics
      Author(s): Cobus Visser, Eduard Kieser, Kiran Dellimore, Dawie van den Heever, Johan Smith
      This study explores the feasibility of prospectively assessing infant dehydration using four non-invasive, optical sensors based on the quantitative and objective measurement of various clinical markers of dehydration. The sensors were investigated to objectively and unobtrusively assess the hydration state of an infant based on the quantification of capillary refill time (CRT), skin recoil time (SRT), skin temperature profile (STP) and skin tissue hydration by means of infrared spectrometry (ISP). To evaluate the performance of the sensors a clinical study was conducted on a cohort of 10 infants (aged 6–36 months) with acute gastroenteritis. High sensitivity and specificity were exhibited by the sensors, in particular the STP and SRT sensors, when combined into a fusion regression model (sensitivity: 0.90, specificity: 0.78). The SRT and STP sensors and the fusion model all outperformed the commonly used “gold standard” clinical dehydration scales including the Gorelick scale (sensitivity: 0.56, specificity: 0.56), CDS scale (sensitivity: 1.0, specificity: 0.2) and WHO scale (sensitivity: 0.13, specificity: 0.79). These results suggest that objective and quantitative assessment of infant dehydration may be possible using the sensors investigated. However, further evaluation of the sensors on a larger sample population is needed before deploying them in a clinical setting.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.036
       
  • A computational fluid–structure interaction analysis of coronary
           Y-grafts
    • Authors: Bruno Guerciotti; Christian Vergara; Sonia Ippolito; Alfio Quarteroni; Carlo Antona; Roberto Scrofani
      Abstract: Publication date: Available online 19 July 2017
      Source:Medical Engineering & Physics
      Author(s): Bruno Guerciotti, Christian Vergara, Sonia Ippolito, Alfio Quarteroni, Carlo Antona, Roberto Scrofani
      Coronary artery disease is one of the leading causes of death worldwide. The stenotic coronary vessels are generally treated with coronary artery bypass grafts (CABGs), which can be either arterial (internal mammary artery, radial artery) or venous (saphenous vein). However, the different mechanical properties of the graft can influence the outcome of the procedure in terms of risk of restenosis and subsequent graft failure. In this paper, we perform a computational fluid–structure interaction (FSI) analysis of patient-specific multiple CABGs (Y-grafts) with the aim of better understanding the influence of the choice of bypass (arterial vs venous) on the risk of graft failure. Our results show that the use of a venous bypass results in a more disturbed flow field at the anastomosis and in higher stresses in the vessel wall with respect to the arterial one. This could explain the better long-term patency of the arterial bypasses experienced in the clinical practice.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.05.008
       
  • Robotic assistants in personal care: A scoping review
    • Authors: A. Bilyea; N. Seth; S. Nesathurai; H.A. Abdullah
      Abstract: Publication date: Available online 19 July 2017
      Source:Medical Engineering & Physics
      Author(s): A. Bilyea, N. Seth, S. Nesathurai, H.A. Abdullah
      The aim of this study is to present an overview of the technological advances in the field of robotics developed for assistance with activities of daily living (ADL), and to present areas where further research is required. Four databases were searched for articles presenting either a novel design of one of these personal care robotic system or trial results relating to these systems. Articles presenting nine different robotic personal care systems were examined, six of which had been developed after 2005. These six also all have publications relating to their trials. In the majority of trials, patient independence was improved with operation of the robotic device for a specific subset of ADL. A map of the current state of the field of personal care robotics is presented in this study. Areas requiring further research include improving feedback and awareness, as well as refining control methods and pre-programmed behaviors. Developing an affordable, easy to use system would help fill the current gap in the commercial market.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.038
       
  • Modeling the cleavage of von Willebrand factor by ADAMTS13 protease in
           shear flow
    • Authors: Brooke Huisman; Masoud Hoore; Gerhard Gompper; Dmitry A. Fedosov
      Abstract: Publication date: Available online 19 July 2017
      Source:Medical Engineering & Physics
      Author(s): Brooke Huisman, Masoud Hoore, Gerhard Gompper, Dmitry A. Fedosov
      Von Willebrand factor (VWF) is a key protein in hemostasis as it mediates adhesion of blood platelets to a site of vascular injury. A proper distribution of VWF lengths is important for normal functioning of hemostatic processes, because a diminished number of long VWF chains may significantly limit blood clotting and lead to bleeding, while an abundant number of long VWFs may result in undesired thrombotic events. VWF size distribution is controlled by ADAMTS13 protease, which can cleave VWF chains beyond a critical shear rate when the chains are stretched enough such that cleavage sites become accessible. To better understand the cleavage process, we model VWF cleavage in shear flow using mesoscopic hydrodynamic simulations. Two cleavage models are proposed, a geometrical model based on the degree of local stretching of VWF, and a tension-force model based on instantaneous tension force within VWF bonds. Both models capture the susceptibility of VWF to cleavage at high shear rates; however, the geometrical model appears to be much more robust than the force model. Our simulations show that VWF susceptibility to cleavage in shear flow becomes a universal function of shear rate, independent of VWF length for long enough chains. Furthermore, VWF is cleaved with a higher probability close to its ends in comparison to cleaving in the middle, which results into longer circulation lifetimes of VWF multimers. Simulations of dynamic cleavage of VWF show an exponential distribution of chain lengths, consistently with available in vitro experiments. The proposed cleavage models can be used in realistic simulations of hemostatic processes in blood flow.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.044
       
  • A mechanistic force model for simulating haptics of hand-held bone burring
           operations
    • Authors: Avinash Danda; Mathew A. Kuttolamadom; Bruce L. Tai
      Abstract: Publication date: Available online 18 July 2017
      Source:Medical Engineering & Physics
      Author(s): Avinash Danda, Mathew A. Kuttolamadom, Bruce L. Tai
      This paper presents a mechanistic model to predict the forces experienced during bone burring with application to haptic feedback for virtual reality surgical simulations. Bone burring is a hand-held operation where the force perceived by the surgeon depends on the cutting tool orientation and motion. The model of this study adapted the concept of specific cutting energy and material removal rate based on machining theory to calculate force distribution on the spherical tool surface in a three-dimensional setting. A design of experiments with three tool cutting angles and three feed motions was performed to calibrate and validate the model. Despite some variance in the results, model predictions showed similar trends to experimental force patterns. While the actual force profile also exhibits significant oscillation, the dominant frequencies of this oscillating force component were found to be independent of cutting and non-cutting instances, and hence could be imposed as a uniform background signal. Though the presented model is primarily applicable to abrasive burrs, it has far-reaching applications within other types of surgical simulations as well.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.041
       
  • Development of a multi-DoF transhumeral robotic arm prosthesis
    • Authors: D.S.V. Bandara; R.A.R.C. Gopura; K.T.M.U. Hemapala; Kazuo Kiguchi
      Abstract: Publication date: Available online 18 July 2017
      Source:Medical Engineering & Physics
      Author(s): D.S.V. Bandara, R.A.R.C. Gopura, K.T.M.U. Hemapala, Kazuo Kiguchi
      An anthropomorphic transhumeral robotic arm prosthesis is proposed in this study. It is capable of generating fifteen degrees-of-freedom, seven active and eight passive. In order to realize wrist motions, a parallel manipulator-based mechanism is proposed. It simulates the human anatomical structure and generates motions in two axes. The hand-of-arm prosthesis consists of under-actuated fingers with intrinsic actuation. The finger mechanism is capable of generating three degrees of freedom, and it exhibits the capability of adjusting the joint angles passively according to the geometry of the grasping object. Additionally, a parameter to evaluate finger mechanisms is introduced, and it measures the adoptability of a finger mechanism. In order to verify the mechanism's efficacy in terms of motion generation, motion simulation and kinematic analysis were carried out. Results demonstrated that the mechanisms are capable of generating the required motions.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.034
       
  • Deformability- and size-based microcapsule sorting
    • Authors: Doriane Vesperini; Oriane Chaput; Nadège Munier; Pauline Maire; Florence Edwards-Lévy; Anne-Virginie Salsac; Anne Le Goff
      Abstract: Publication date: Available online 17 July 2017
      Source:Medical Engineering & Physics
      Author(s): Doriane Vesperini, Oriane Chaput, Nadège Munier, Pauline Maire, Florence Edwards-Lévy, Anne-Virginie Salsac, Anne Le Goff
      Biomedical applications often require to sort cells according to their physical properties, such as size, density or deformability. In recent years, microfluidics has provided a variety of tools to sort micro-objects. We present here a simple microfluidic device consisting of a channel containing a semi-cylindrical obstacle against which capsules are squeezed by the flow, followed by a diverging chamber where streamlines separate. We demonstrate that this basic system is capable of sorting elastic microcapsules according to their size at low flow strength, and according to the stiffness of their membrane at high flow strength. Contrary to most existing sorting devices, we show that the present one is very sensitive and capable of discriminating between capsules with differences in membrane elasticity of order unity.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.040
       
  • Finite element analysis of TAVI: Impact of native aortic root
           computational modeling strategies on simulation outcomes
    • Authors: Alice Finotello; Simone Morganti; Ferdinando Auricchio
      Abstract: Publication date: Available online 17 July 2017
      Source:Medical Engineering & Physics
      Author(s): Alice Finotello, Simone Morganti, Ferdinando Auricchio
      In the last few years, several studies, each with different aim and modeling detail, have been proposed to investigate transcatheter aortic valve implantation (TAVI) with finite elements. The present work focuses on the patient-specific finite element modeling of the aortic valve complex. In particular, we aim at investigating how different modeling strategies in terms of material models/properties and discretization procedures can impact analysis results. Four different choices both for the mesh size (from  20 k elements to  200 k elements) and for the material model (from rigid to hyperelastic anisotropic) are considered. Different approaches for modeling calcifications are also taken into account. Post-operative CT data of the real implant are used as reference solution with the aim of outlining a trade-off between computational model complexity and reliability of the results.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.045
       
  • Mass-spring models for the simulation of mitral valve function: Looking
           for a trade-off between reliability and time-efficiency
    • Authors: O.A. Pappalardo; F. Sturla; F. Onorati; G. Puppini; M. Selmi; G.B. Luciani; G. Faggian; A. Redaelli; E. Votta
      Abstract: Publication date: Available online 17 July 2017
      Source:Medical Engineering & Physics
      Author(s): O.A. Pappalardo, F. Sturla, F. Onorati, G. Puppini, M. Selmi, G.B. Luciani, G. Faggian, A. Redaelli, E. Votta
      Patient-specific finite element (FE) models can assess the impact of mitral valve (MV) repair on the complex MV anatomy and function. However, FE excessive time requirements hamper their use for surgical planning; mass-spring models (MSMs) represent a more approximate approach but can provide almost real-time simulations. On this basis, we implemented MSMs of three healthy MVs from cardiac magnetic resonance (cMR) imaging to simulate the systolic MV closure, including the in vivo papillary muscles and annular kinematics, and the anisotropic and non-linear mechanical response of MV tissues. To test MSM reliability we compared the systolic peak configurations computed by MSMs and FE: mismatches by less than twice the in-plane cMR image resolution were detected over 75% of the leaflets’ surface, independently of the MSM mesh refinement and of the specific MV anatomy. Data on MSMs time-efficiency and data from the comparison of MSMs vs. FE models suggest that MSM could represent a suitable trade-off between almost real-time simulations and reliability when computing MV systolic configuration, with the potential to be used in a clinical setting either as a support to the decisional process or as a virtual training tool.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.07.001
       
  • Three-dimensional computational model of a blood oxygenator reconstructed
           from micro-CT scans
    • Authors: C. D’Onofrio; R. van Loon; S. Rolland; R. Johnston; L. North; S. Brown; R. Phillips; J. Sienz
      Abstract: Publication date: Available online 14 July 2017
      Source:Medical Engineering & Physics
      Author(s): C. D’Onofrio, R. van Loon, S. Rolland, R. Johnston, L. North, S. Brown, R. Phillips, J. Sienz
      Cardiopulmonary bypass procedures are one of the most common operations and blood oxygenators are the centre piece for the heart-lung machines. Blood oxygenators have been tested as entire devices but intricate details on the flow field inside the oxygenators remain unknown. In this study, a novel method is presented to analyse the flow field inside oxygenators based on micro Computed Tomography (μCT) scans. Two Hollow Fibre Membrane (HFM) oxygenator prototypes were scanned and three-dimensional full scale models that capture the device-specific fibre distributions are set up for computational fluid dynamics analysis. The blood flow through the oxygenator is modelled as a non-Newtonian fluid. The results were compared against the flow solution through an ideal fibre distribution and show the importance of a uniform distribution of fibres and that the oxygenators analysed are not susceptible to flow directionality as mass flow versus area remain the same. However the pressure drop across the oxygenator is dependent on flow rate and direction. By comparing residence time of blood against the time frame to fully saturate blood with oxygen we highlight the potential of this method as design optimisation tool. In conclusion, image-based reconstruction is found to be a feasible route to assess oxygenator performance through flow modelling. It offers the possibility to review a product as manufactured rather than as designed, which is a valuable insight as a precursor to the approval processes. Finally, the flow analysis presented may be extended, at computational cost, to include species transport in further studies.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.035
       
  • Dynamic simulation of knee-joint loading during gait using force-feedback
           control and surrogate contact modelling
    • Authors: Jonathan P. Walter; Marcus G. Pandy
      Abstract: Publication date: Available online 13 July 2017
      Source:Medical Engineering & Physics
      Author(s): Jonathan P. Walter, Marcus G. Pandy
      The aim of this study was to perform multi-body, muscle-driven, forward-dynamics simulations of human gait using a 6-degree-of-freedom (6-DOF) model of the knee in tandem with a surrogate model of articular contact and force control. A forward-dynamics simulation incorporating position, velocity and contact force-feedback control (FFC) was used to track full-body motion capture data recorded for multiple trials of level walking and stair descent performed by two individuals with instrumented knee implants. Tibiofemoral contact force errors for FFC were compared against those obtained from a standard computed muscle control algorithm (CMC) with a 6-DOF knee contact model (CMC6); CMC with a 1-DOF translating hinge-knee model (CMC1); and static optimization with a 1-DOF translating hinge-knee model (SO). Tibiofemoral joint loads predicted by FFC and CMC6 were comparable for level walking, however FFC produced more accurate results for stair descent. SO yielded reasonable predictions of joint contact loading for level walking but significant differences between model and experiment were observed for stair descent. CMC1 produced the least accurate predictions of tibiofemoral contact loads for both tasks. Our findings suggest that reliable estimates of knee-joint loading may be obtained by incorporating position, velocity and force-feedback control with a multi-DOF model of joint contact in a forward-dynamics simulation of gait.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.043
       
  • Fixation strength of a polyetheretherketone femoral component in total
           knee arthroplasty
    • Authors: Lennert de Ruiter; Dennis Janssen; Adam Briscoe; Nico Verdonschot
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Lennert de Ruiter, Dennis Janssen, Adam Briscoe, Nico Verdonschot
      Introduction Introducing polyetheretherketone (PEEK) polymer as a material for femoral components in total knee arthroplasty (TKA) could potentially lead to a reduction of the cemented fixation strength. A PEEK implant is more likely to deform under high loads, rendering geometrical locking features less effective. Fixation strength may be enhanced by adding more undercuts or specific surface treatments. The aim of this study is to measure the initial fixation strength and investigate the associated failure patterns of three different iterations of PEEK-OPTIMA® implants compared with a Cobalt–Chromium (CoCr) component. Methods Femoral components were cemented onto trabecular bone analogue foam blocks and preconditioned with 86,400 cycles of compressive loading (2600 N–260 N at 1 Hz). They were then extracted while the force was measured and the initial failure mechanism was recorded. Four groups were compared: CoCr, regular PEEK, PEEK with an enhanced cement-bonding surface and the latter with additional surface primer. Results The mean pull-off forces for the four groups were 3814 N, 688 N, 2525 N and 2552 N, respectively. The initial failure patterns for groups 1, 3 and 4 were the same; posterior condylar foam fracture and cement–bone debonding. Implants from group 2 failed at the cement–implant interface. Conclusions This study has shown that a PEEK-OPTIMA® femoral TKA component with enhanced macro- and microtexture is able to replicate the main failure mechanism of a conventional CoCr femoral implant. The fixation strength is lower than for a CoCr implant, but substantially higher than loads occurring under in-vivo conditions.
      Graphical abstract image

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.039
       
  • A framework for computational fluid dynamic analyses of patient-specific
           stented coronary arteries from optical coherence tomography images
    • Authors: Susanna Migliori; Claudio Chiastra; Marco Bologna; Eros Montin; Gabriele Dubini; Cristina Aurigemma; Roberto Fedele; Francesco Burzotta; Luca Mainardi; Francesco Migliavacca
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Susanna Migliori, Claudio Chiastra, Marco Bologna, Eros Montin, Gabriele Dubini, Cristina Aurigemma, Roberto Fedele, Francesco Burzotta, Luca Mainardi, Francesco Migliavacca
      The clinical challenge of percutaneous coronary interventions (PCI) is highly dependent on the recognition of the coronary anatomy of each individual. The classic imaging modality used for PCI is angiography, but advanced imaging techniques that are routinely performed during PCI, like optical coherence tomography (OCT), may provide detailed knowledge of the pre-intervention vessel anatomy as well as the post-procedural assessment of the specific stent-to-vessel interactions. Computational fluid dynamics (CFD) is an emerging investigational tool in the setting of optimization of PCI results. In this study, an OCT-based reconstruction method was developed for the execution of CFD simulations of patient-specific coronary artery models which include the actual geometry of the implanted stent. The method was applied to a rigid phantom resembling a stented segment of the left anterior descending coronary artery. The segmentation algorithm was validated against manual segmentation. A strong correlation was found between automatic and manual segmentation of lumen in terms of area values. Similarity indices resulted >96% for the lumen segmentation and >77% for the stent strut segmentation. The 3D reconstruction achieved for the stented phantom was also assessed with the geometry provided by X-ray computed micro tomography scan, used as ground truth, and showed the incidence of distortion from catheter-based imaging techniques. The 3D reconstruction was successfully used to perform CFD analyses, demonstrating a great potential for patient-specific investigations. In conclusion, OCT may represent a reliable source for patient-specific CFD analyses which may be optimized using dedicated automatic segmentation algorithms.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.027
       
  • Large eddy simulations of blood dynamics in abdominal aortic aneurysms
    • Authors: Christian Vergara; Davide Le Van; Maurizio Quadrio; Luca Formaggia; Maurizio Domanin
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Christian Vergara, Davide Le Van, Maurizio Quadrio, Luca Formaggia, Maurizio Domanin
      We study the effects of transition to turbulence in abdominal aortic aneurysms (AAA). The presence of transitional effects in such districts is related to the heart pulsatility and the sudden change of diameter of the vessels, and has been recorded by means of clinical measures as well as of computational studies. Here we propose, for the first time, the use of a large eddy simulation (LES) model to accurately describe transition to turbulence in realistic scenarios of AAA obtained from radiological images. To this aim, we post-process the obtained numerical solutions to assess significant quantities, such as the ensemble-averaged velocity and wall shear stress, the standard deviation of the fluctuating velocity field, and vortical structures educed via the so-called Q-criterion. The results demonstrate the suitability of the considered LES model and show the presence of significant transitional effects around the impingement region during the mid-deceleration phase.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.030
       
  • Particle image velocimetry study of the celiac trunk hemodynamic induced
           by continuous-flow left ventricular assist device
    • Authors: Francesco Scardulla; Diego Bellavia; Leonardo D'Acquisto; Giuseppe M Raffa; Salvatore Pasta
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Francesco Scardulla, Diego Bellavia, Leonardo D'Acquisto, Giuseppe M Raffa, Salvatore Pasta
      Whereas left ventricular assist device (LVAD) is the gold-standard therapy for patients with heart failure, gastrointestinal bleeding is one of the most common complications. LVAD implantation may remarkably impact aortic hemodynamics so that experimental and computational flow analyses can be used to study the disease mechanisms. Here we present an experimentally-calibrated computational model of the celiac trunk hemodynamic of a LVAD-supported patient who experienced bleeding after device implantation. Specifically, both particle image velocimetry (PIV) and echocardiography were used to measure and compare flow distributions in each branch of a phantom model of the patient abdominal aorta. Then, the distribution of wall shear stress (WSS) was estimated by computational flow analysis. At a cardiac output of 5 L/min, the highest flow division was found in the mesenteric artery (13.6% for PIV and 14.6% for echocardiography), while the left renal artery exhibited the lowest amount in the celiac trunk model (2.6% for PIV and 2.4% for echocardiography). Bland–Altman analysis demonstrated a high agreement between echocardiographic and PIV-related flow measurements, while computational flow analysis revealed that WSS was high in the LVAD graft anastomosis site and just after the ostia of both the celiac trunk and mesenteric artery. This altered shear stress distribution in the celiac trunk may lead to a flow-mediated mechanism of adverse remodeling of the von Willebrand factor and ultimately to gastrointestinal bleeding as seen clinically in this patient.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.029
       
  • Improving the detection of evoked responses to periodic stimulation by
           using bivariate local spectral F-test – Application to EEG during photic
           stimulation
    • Authors: Leonardo Bonato Felix; Paulo Fábio Rocha; Eduardo Mazoni Andrade Marçal Mendes; Antonio Mauricio Ferreira Leite Miranda de Sá
      Abstract: Publication date: Available online 12 July 2017
      Source:Medical Engineering & Physics
      Author(s): Leonardo Bonato Felix, Paulo Fábio Rocha, Eduardo Mazoni Andrade Marçal Mendes, Antonio Mauricio Ferreira Leite Miranda de Sá
      The spectral local F-test has been applied for detecting evoked responses to rhythmic stimulation that are embedded in the ongoing electroencephalogram (EEG). Based on the sampling distribution of a flat spectrum at the neighbourhood of the stimulation frequency, spectral peaks in an EEG signal that are due to the stimulation may be readily assessed. Nevertheless, the performance of the technique is strongly affected by both the signal-to-noise ratio (SNR) of the responses and the number of data segments used in the estimation. The present work aims at both deriving and evaluating a multivariate extension of local F-test by including the EEG collected at a second distinct derivation. The detection rate with this multivariate detector was found to be greater than that using a single channel in case of equal SNR in both signals. Monte Carlo simulation results showed that the probability of detection with this new detector saturates for signal-to-noise ratios above 12 dB and indicated a greater detection rate in practical situations, even when smaller SNR-values are found in the added signal (e.g. 5 dB for 16 neighbouring frequencies used in the estimation). The technique was next applied to the EEG from 12 subjects during intermittent, photic stimulation leading to superior performance in comparison with the univariate local F-test. Since a higher detection rate with the proposed technique is achieved without the need of increasing the number of data segments, it allows evoked responses to be detected faster, once the same detection rate may be accomplished with less segments. This might be useful in clinical practice.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.032
       
  • A review of bioregulatory and coupled mechanobioregulatory mathematical
           models for secondary fracture healing
    • Authors: Monan Wang; Ning Yang
      Abstract: Publication date: Available online 11 July 2017
      Source:Medical Engineering & Physics
      Author(s): Monan Wang, Ning Yang
      Fracture healing is a complex biological process involving many cellular and molecular events. During fracture healing, biochemical signals play a regulatory role in promoting the healing process. Although many experiments have been conducted to study fracture healing, not all of the mechanisms are clearly understood. Over the past years, a lot of mathematical models and computational simulations have been established to investigate the fracture healing process. These models offer a powerful tool to study the interplay between cell behaviour, mechanical stimuli and biochemical signals and help design new treatment strategies. However, most of the mathematical models focus on the effect of mechanical stimuli and few models consider the important role of biochemical signals during fracture healing. In this review, we first emphasize the importance of biochemical signals during fracture healing. Then, existing bioregulatory and coupled mechanobioregulatory models are presented. Finally, some limitations and possible solutions are discussed.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.031
       
  • Non-invasive vibrometry-based diagnostic detection of acetabular cup
           loosening in total hip replacement (THR)
    • Authors: Abdullah A. Alshuhri; Timothy P. Holsgrove; Anthony W. Miles; James L. Cunningham
      Abstract: Publication date: Available online 11 July 2017
      Source:Medical Engineering & Physics
      Author(s): Abdullah A. Alshuhri, Timothy P. Holsgrove, Anthony W. Miles, James L. Cunningham
      Total hip replacement is aimed at relieving pain and restoring function. Currently, imaging techniques are primarily used as a clinical diagnosis and follow-up method. However, these are unreliable for detecting early loosening, and this has led to the proposal of novel techniques such as vibrometry. The present study had two aims, namely, the validation of the outcomes of a previous work related to loosening detection, and the provision of a more realistic anatomical representation of the clinical scenario. The acetabular cup loosening conditions (secure, and 1 and 2 mm spherical loosening) considered were simulated using Sawbones composite bones. The excitation signal was introduced in the femoral lateral condyle region using a frequency range of 100–1500 Hz. Both the 1 and 2 mm spherical loosening conditions were successfully distinguished from the secure condition, with a favourable frequency range of 500–1500 Hz. The results of this study represent a key advance on previous research into vibrometric detection of acetabular loosening using geometrically realistic model, and demonstrate the clinical potential of this technique.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.037
       
  • Multi-objective optimization of nitinol stent design
    • Authors: G. Alaimo; F. Auricchio; M. Conti; M. Zingales
      Abstract: Publication date: Available online 10 July 2017
      Source:Medical Engineering & Physics
      Author(s): G. Alaimo, F. Auricchio, M. Conti, M. Zingales
      Nitinol stents continuously experience loadings due to pulsatile pressure, thus a given stent design should possess an adequate fatigue strength and, at the same time, it should guarantee a sufficient vessel scaffolding. The present study proposes an optimization framework aiming at increasing the fatigue life reducing the maximum strut strain along the structure through a local modification of the strut profile.The adopted computational framework relies on nonlinear structural finite element analysis combined with a Multi Objective Genetic Algorithm, based on Kriging response surfaces. In particular, such an approach is used to investigate the design optimization of planar stent cell.The results of the strut profile optimization confirm the key role of a tapered strut design to enhance the stent fatigue strength, suggesting that it is possible to achieve a marked improvement of both the fatigue safety factor and the scaffolding capability simultaneously. The present study underlines the value of advanced engineering tools to optimize the design of medical devices.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.026
       
  • Effects of non-physiological blood pressure artefacts on cerebral
           autoregulation
    • Authors: Adam Mahdi; Erica M Rutter; Stephen J Payne
      Abstract: Publication date: Available online 8 July 2017
      Source:Medical Engineering & Physics
      Author(s): Adam Mahdi, Erica M Rutter, Stephen J Payne
      Cerebral autoregulation refers to the brain’s regulation mechanisms that aim to maintain the cerebral blood flow approximately constant. It is often assessed by the autoregulation index (ARI). ARI uses arterial blood pressure and cerebral blood flow velocity time series to produce a ten-scale index of autoregulation performance (0 denoting the absence of and 9 the strongest autoregulation). Unfortunately, data are rarely free from various artefacts. Here, we consider four of the most common non-physiological blood pressure artefacts (saturation, square wave, reduced pulse pressure and impulse) and study their effects on ARI for a range of different artefact sizes. We show that a sufficiently large saturation and square wave always result in ARI reaching the maximum value of 9. The pulse pressure reduction and impulse artefact lead to more diverse behaviour. Finally, we characterized the critical size of artefacts, defined as the minimum artefact size that, on average, leads to a 10% deviation of ARI.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.007
       
  • Mathematical modelling of the maternal cardiovascular system in the three
           stages of pregnancy
    • Authors: Chiara Corsini; Elena Cervi; Francesco Migliavacca; Silvia Schievano; Tain-Yen Hsia; Giancarlo Pennati
      Abstract: Publication date: Available online 8 July 2017
      Source:Medical Engineering & Physics
      Author(s): Chiara Corsini, Elena Cervi, Francesco Migliavacca, Silvia Schievano, Tain-Yen Hsia, Giancarlo Pennati
      In this study, a mathematical model of the female circulation during pregnancy is presented in order to investigate the hemodynamic response to the cardiovascular changes associated with each trimester of pregnancy. First, a preliminary lumped parameter model of the circulation of a non-pregnant female was developed, including the heart, the systemic circulation with a specific block for the uterine district and the pulmonary circulation. The model was first tested at rest; then heart rate and vascular resistances were individually varied to verify the correct response to parameter alterations characterising pregnancy. In order to simulate hemodynamics during pregnancy at each trimester, the main changes applied to the model consisted in reducing vascular resistances, and simultaneously increasing heart rate and ventricular wall volumes. Overall, reasonable agreement was found between model outputs and in vivo data, with the trends of the cardiac hemodynamic quantities suggesting correct response of the heart model throughout pregnancy. Results were reported for uterine hemodynamics, with flow tracings resembling typical Doppler velocity waveforms at each stage, including pulsatility indexes. Such a model may be used to explore the changes that happen during pregnancy in female with cardiovascular diseases.
      Graphical abstract image

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.025
       
  • Neural and non-neural related properties in the spastic wrist flexors: An
           optimization study
    • Authors: R. Wang; P. Herman; Ö. Ekeberg; J. Gäverth; A. Fagergren; H. Forssberg
      Abstract: Publication date: Available online 8 July 2017
      Source:Medical Engineering & Physics
      Author(s): R. Wang, P. Herman, Ö. Ekeberg, J. Gäverth, A. Fagergren, H. Forssberg
      Quantifying neural and non-neural contributions to increased joint resistance in spasticity is essential for a better understanding of its pathophysiological mechanisms and evaluating different intervention strategies. However, direct measurement of spasticity-related manifestations, e.g., motoneuron and biophysical properties in humans, is extremely challenging. In this vein, we developed a forward neuromusculoskeletal model that accounts for dynamics of muscle spindles, motoneuron pools, muscle activation and musculotendon of wrist flexors and relies on the joint angle and resistant torque as the only input measurement variables. By modeling the stretch reflex pathway, neural and non-neural related properties of the spastic wrist flexors were estimated during the wrist extension test. Joint angle and resistant torque were collected from 17 persons with chronic stroke and healthy controls using NeuroFlexor, a motorized force measurement device during the passive wrist extension test. The model was optimized by tuning the passive and stretch reflex-related parameters to fit the measured torque in each participant. We found that persons with moderate and severe spasticity had significantly higher stiffness than controls. Among subgroups of stroke survivors, the increased neural component was mainly due to a lower muscle spindle rate at 50% of the motoneuron recruitment. The motoneuron pool threshold was highly correlated to the motoneuron pool gain in all subgroups. The model can describe the overall resistant behavior of the wrist joint during the test. Compared to controls, increased resistance was predominantly due to higher elasticity and neural components. We concluded that in combination with the NeuroFlexor measurement, the proposed neuromusculoskeletal model and optimization scheme served as suitable tools for investigating potential parameter changes along the stretch-reflex pathway in persons with spasticity.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.023
       
  • Patient-specific biomechanical model of hypoplastic left heart to predict
           post-operative cardio-circulatory behaviour
    • Authors: Elena Cutrì; Alessio Meoli; Gabriele Dubini; Francesco Migliavacca; Tain-Yen Hsia; Giancarlo Pennati
      Abstract: Publication date: Available online 8 July 2017
      Source:Medical Engineering & Physics
      Author(s): Elena Cutrì, Alessio Meoli, Gabriele Dubini, Francesco Migliavacca, Tain-Yen Hsia, Giancarlo Pennati
      Hypoplastic left heart syndrome is a complex congenital heart disease characterised by the underdevelopment of the left ventricle normally treated with a three-stage surgical repair. In this study, a multiscale closed-loop cardio-circulatory model is created to reproduce the pre-operative condition of a patient suffering from such pathology and virtual surgery is performed. Firstly, cardio-circulatory parameters are estimated using a fully closed-loop cardio-circulatory lumped parameter model. Secondly, a 3D standalone FEA model is build up to obtain active and passive ventricular characteristics and unloaded reference state. Lastly, the 3D model of the single ventricle is coupled to the lumped parameter model of the circulation obtaining a multiscale closed-loop pre-operative model. Lacking any information on the fibre orientation, two cases were simulated: (i) fibre distributed as in the physiological right ventricle and (ii) fibre as in the physiological left ventricle. Once the pre-operative condition is satisfactorily simulated for the two cases, virtual surgery is performed. The post-operative results in the two cases highlighted similar hemodynamic behaviour but different local mechanics. This finding suggests that the knowledge of the patient-specific fibre arrangement is important to correctly estimate the single ventricle's working condition and consequently can be valuable to support clinical decision.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.024
       
  • Increased blood pressure variability upon standing up improves
           reproducibility of cerebral autoregulation indices
    • Authors: Adam Mahdi; Dragana Nikolic; Anthony A. Birch; Mette S. Olufsen; Ronney B. Panerai; David M. Simpson; Stephen J. Payne
      Abstract: Publication date: Available online 8 July 2017
      Source:Medical Engineering & Physics
      Author(s): Adam Mahdi, Dragana Nikolic, Anthony A. Birch, Mette S. Olufsen, Ronney B. Panerai, David M. Simpson, Stephen J. Payne
      Dynamic cerebral autoregulation, that is the transient response of cerebral blood flow to changes in arterial blood pressure, is currently assessed using a variety of different time series methods and data collection protocols. In the continuing absence of a gold standard for the study of cerebral autoregulation it is unclear to what extent does the assessment depend on the choice of a computational method and protocol. We use continuous measurements of blood pressure and cerebral blood flow velocity in the middle cerebral artery from the cohorts of 18 normotensive subjects performing sit-to-stand manoeuvre. We estimate cerebral autoregulation using a wide variety of black-box approaches (including the following six autoregulation indices ARI, Mx, Sx, Dx, FIR and ARX) and compare them in the context of reproducibility and variability. For all autoregulation indices, considered here, the intra-class correlation was greater during the standing protocol, however, it was significantly greater (Fisher’s Z-test) for Mx (p < 0.03), Sx (p < 0.003) and Dx (p < 0.03). In the specific case of the sit-to-stand manoeuvre, measurements taken immediately after standing up greatly improve the reproducibility of the autoregulation coefficients. This is generally coupled with an increase of the within-group spread of the estimates.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.006
       
  • A FSI computational framework for vascular physiopathology: A novel
           flow-tissue multiscale strategy
    • Authors: Daniele Bianchi; Elisabetta Monaldo; Alessio Gizzi; Michele Marino; Simonetta Filippi; Giuseppe Vairo
      Abstract: Publication date: Available online 6 July 2017
      Source:Medical Engineering & Physics
      Author(s): Daniele Bianchi, Elisabetta Monaldo, Alessio Gizzi, Michele Marino, Simonetta Filippi, Giuseppe Vairo
      A novel fluid-structure computational framework for vascular applications is herein presented. It is developed by combining the double multi-scale nature of vascular physiopathology in terms of both tissue properties and blood flow. Addressing arterial tissues, they are modelled via a nonlinear multiscale constitutive rationale, based only on parameters having a clear histological and biochemical meaning. Moreover, blood flow is described by coupling a three-dimensional fluid domain (undergoing physiological inflow conditions) with a zero-dimensional model, which allows to reproduce the influence of the downstream vasculature, furnishing a realistic description of the outflow proximal pressure. The fluid-structure interaction is managed through an explicit time-marching approach, able to accurately describe tissue nonlinearities within each computational step for the fluid problem. A case study associated to a patient-specific aortic abdominal aneurysmatic geometry is numerically investigated, highlighting advantages gained from the proposed multiscale strategy, as well as showing soundness and effectiveness of the established framework for assessing useful clinical quantities and risk indexes.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.028
       
  • Evaluating and improving the performance of thin film force sensors within
           body and device interfaces
    • Authors: Jirapat Likitlersuang; Matthew J. Leineweber; Jan Andrysek
      Abstract: Publication date: Available online 6 July 2017
      Source:Medical Engineering & Physics
      Author(s): Jirapat Likitlersuang, Matthew J. Leineweber, Jan Andrysek
      Thin film force sensors are commonly used within biomechanical systems, and at the interface of the human body and medical and non-medical devices. However, limited information is available about their performance in such applications. The aims of this study were to evaluate and determine ways to improve the performance of thin film (FlexiForce) sensors at the body/device interface. Using a custom apparatus designed to load the sensors under simulated body/device conditions, two aspects were explored relating to sensor calibration and application. The findings revealed accuracy errors of 23.3±17.6% for force measurements at the body/device interface with conventional techniques of sensor calibration and application. Applying a thin rigid disc between the sensor and human body and calibrating the sensor using compliant surfaces was found to substantially reduce measurement errors to 2.9±2.0%. The use of alternative calibration and application procedures is recommended to gain acceptable measurement performance from thin film force sensors in body/device applications.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.017
       
  • Geometry of an inflated membrane in elliptic bulge tests: Evaluation of an
           ellipsoidal shape approximation by stereoscopic digital image correlation
           measurements
    • Authors: C. Jayyosi; K. Bruyère-Garnier; M. Coret
      Abstract: Publication date: Available online 6 July 2017
      Source:Medical Engineering & Physics
      Author(s): C. Jayyosi, K. Bruyère-Garnier, M. Coret
      Elliptic bulge tests are conducted on liver capsule, a fibrous connective membrane, associated with a field measurement method to assess the global geometry of the samples during the tests. The experimental set up is derived from a previous experimental campaign of bulge tests under microscope. Here, a stereoscopic Digital Image Correlation (DIC) system is used to measure global parameters on the test and investigate some assumptions made on the testing conditions which could not been assessed with microscopic measurements. In particular, the assumption of an ellipsoidal shape of the inflated membrane is tested by comparing the actual sample shape measured by stereoscopic DIC with an idealized ellipsoidal shape. Results indicate that a rather constant gap exists between the idealized and actual position. The approximation in the calculation of a macroscopic strain through analytical modeling of the test is estimated here. The study of the liver capsule case shows that important differences can be observed in strain calculation depending on the method and assumptions taken. Therefore, analytical modeling of mechanical tests through ellipsoidal approximation needs to be carefully evaluated in every application. Here the field measurement allows assessing the validity of these modeling assumptions. Moreover, it gives precious details about the boundary conditions of the bulge test and revealed the heterogeneous clamping, highlighted by strain concentrations.

      PubDate: 2017-07-24T07:58:41Z
      DOI: 10.1016/j.medengphy.2017.06.020
       
  • Corrigendum to ‘A mathematical method for precisely calculating the
           radiographic angles of the cup after total hip arthroplasty’ Medical
           Engineering & Physics 38 (2016) 1376–1381
    • 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 22 June 2017
      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


      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.014
       
  • The taper corrosion pattern observed for one bi-modular stem design is
           related to geometry-determined taper mechanics
    • Authors: Dennis Buente; Michael Bryant; Michael Ward; Anne Neville; Michael Morlock; Gerd Huber
      Abstract: Publication date: Available online 21 June 2017
      Source:Medical Engineering & Physics
      Author(s): Dennis Buente, Michael Bryant, Michael Ward, Anne Neville, Michael Morlock, Gerd Huber
      Bi-modular primary hip stems exhibit high revision rates owing to corrosion at the stem-neck taper, and are associated with local adverse tissue reactions. The aim of this study was to relate the wear patterns observed for one bi-modular design to its design-specific stem-neck taper geometry. Wear patterns and initial geometry of the taper junctions were determined for 27 retrieved bi-modular primary hip arthroplasty stems (Rejuvenate, Stryker Orthopaedics) using a tactile coordinate-measuring device. Regions of high-gradient wear patterns were additionally analyzed via optical and electron microscopy. The determined geometry of the taper junction revealed design-related engagement at its opening (angle mismatch), concentrated at the medial and lateral apexes (axes mismatch). A patch of retained topography on the proximal medial neck-piece taper apex was observed, surrounded by regions of high wear. On the patch, a deposit from the opposing female stem taper—containing Ti, Mo, Zr, and O—was observed. High stress concentrations were focused at the taper apexes owing to the specific geometry. A medial canting of the components may have augmented the inhomogeneous stress distributions in vivo. In the regions with high normal loads interfacial slip and consequently fretting was inhibited, which explains the observed pattern of wear.
      Graphical abstract image

      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.003
       
  • Microwave thermal ablation: Effects of tissue properties variations on
           predictive models for treatment planning
    • Authors: Vanni Lopresto; Rosanna Pinto; Laura Farina; Marta Cavagnaro
      Abstract: Publication date: Available online 21 June 2017
      Source:Medical Engineering & Physics
      Author(s): Vanni Lopresto, Rosanna Pinto, Laura Farina, Marta Cavagnaro
      Microwave thermal ablation (MTA) therapy for cancer treatments relies on the absorption of electromagnetic energy at microwave frequencies to induce a very high and localized temperature increase, which causes an irreversible thermal damage in the target zone. Treatment planning in MTA is based on experimental observations of ablation zones in ex vivo tissue, while predicting the treatment outcomes could be greatly improved by reliable numerical models. In this work, a fully dynamical simulation model is exploited to look at effects of temperature-dependent variations in the dielectric and thermal properties of the targeted tissue on the prediction of the temperature increase and the extension of the thermally coagulated zone. In particular, the influence of measurement uncertainty of tissue parameters on the numerical results is investigated. Numerical data were compared with data from MTA experiments performed on ex vivo bovine liver tissue at 2.45GHz, with a power of 60W applied for 10min. By including in the simulation model an uncertainty budget (CI=95%) of ±25% in the properties of the tissue due to inaccuracy of measurements, numerical results were achieved in the range of experimental data. Obtained results also showed that the specific heat especially influences the extension of the thermally coagulated zone, with an increase of 27% in length and 7% in diameter when a variation of −25% is considered with respect to the value of the reference simulation model.

      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.008
       
  • Thermal management in closed incubators: New software for assessing the
           impact of humidity on the optimal incubator air temperature
    • Authors: Stéphane Delanaud; Pauline Decima; Amandine Pelletier; Jean-Pierre Libert; Estelle Durand; Erwan Stephan-Blanchard; Véronique Bach; Pierre Tourneux
      Abstract: Publication date: Available online 21 June 2017
      Source:Medical Engineering & Physics
      Author(s): Stéphane Delanaud, Pauline Decima, Amandine Pelletier, Jean-Pierre Libert, Estelle Durand, Erwan Stephan-Blanchard, Véronique Bach, Pierre Tourneux
      Background Low-birth-weight (LBW) neonates are nursed in closed incubators to prevent transcutaneous water loss. The RH's impact on the optimal incubator air temperature setting has not been studied. Methods On the basis of a clinical cohort study, we modelled all the ambient parameters influencing body heat losses and gains. The algorithm quantifies the change in RH on the air temperature, to maintain optimal thermal conditions in the incubator. Results Twenty-three neonates (gestational age (GA): 30.0 [28.9–31.6] weeks) were included. A 20% increase and a 20% decrease in the RH induced a change in air temperature of between −1.51 and +1.85°C for a simulated 650g neonate (GA: 26 weeks), between −1.66 and +1.87°C for a 1000g neonate (GA: 31 weeks), and between −1.77 and +1.97°C for a 2000g neonate (GA: 33 weeks) (p <0.001). According to regression analyses, the optimal incubator air temperature= a + b relative humidity +c age +d weight (p <0.001). Conclusions We have developed new mathematical equations for calculating the optimal temperature for the incubator air as a function of the latter's relative humidity. The software constitutes a decision support tool for improving patient care in routine clinical practice.

      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.002
       
  • FE and experimental study on how the cortex material properties of
           synthetic femurs affect strain levels
    • Authors: Vitor M.M. Lopes; Maria A. Neto; Ana M. Amaro; Luis M. Roseiro; M.F. Paulino
      Abstract: Publication date: Available online 20 June 2017
      Source:Medical Engineering & Physics
      Author(s): Vitor M.M. Lopes, Maria A. Neto, Ana M. Amaro, Luis M. Roseiro, M.F. Paulino
      The primary aim of this work was to validate the “numerical” cortex material properties (transversely isotropic) of synthetic femurs and to evaluate how the strain level of the cancellous bone can be affected by the FE modeling of the material's behavior. Sensitivity analysis was performed to find out if the parameters of the cortex material affect global strain results more than the Polyurethane (PU) foam used to simulate cancellous bone. Standard 4th generation composite femurs were made with 0.32g/cm3 solid PU foam to model healthy cancellous bone, while 0.2g/cm3 cellular PU was used to model unhealthy cancellous bone. Longitudinal and transversal Young's moduli of cortical bone were defined according the manufacturer data, while shear modulus and Poisson's ratios were defined from the literature. All femurs were instrumented with rosette strain gauges and loaded according to ISO7206 standards, simulating a one-legged stance. The experimental results were then compared with those from finite element analysis. When cortical bone was modelled as transversely isotropic, an overall FE/experimental error of 11% was obtained. However, with isotropic material the error rose to 20%. Strain field distributions predicted inside the two bone models were similar, but the strain state of a healthy cancellous bone was much more a compression state than that of unhealthy bone, the compression state decreased about 90%. Strain magnitudes show that average strain-levels of cancellous bone can be significantly affected by the properties of the cortical bone material and, therefore, simulations of femur-implanted systems must account for the composite behavior of the cortex, since small shear strains would develop near isotropic cancellous bone-implant interfaces. Moreover, the authors suggest that changing the volume fraction of glass fibers used to manufacture the cortical bone would allow a more realistic osteoporotic synthetic femurs to be produced.

      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.001
       
  • Biomechanical analysis using FEA and experiments of a standard plate
           method versus three cable methods for fixing acetabular fractures with
           simultaneous THA
    • Authors: Mina S.R. Aziz; Omar Dessouki; Saeid Samiezadeh; Habiba Bougherara; Emil H. Schemitsch; Radovan Zdero
      Abstract: Publication date: Available online 20 June 2017
      Source:Medical Engineering & Physics
      Author(s): Mina S.R. Aziz, Omar Dessouki, Saeid Samiezadeh, Habiba Bougherara, Emil H. Schemitsch, Radovan Zdero
      Acetabular fractures potentially account for up to half of all pelvic fractures, while pelvic fractures potentially account for over one-tenth of all human bone fractures. This is the first biomechanical study to assess acetabular fracture fixation using plates versus cables in the presence of a total hip arthroplasty, as done for the elderly. In Phase 1, finite element (FE) models compared a standard plate method versus 3 cable methods for repairing an acetabular fracture (type: anterior column plus posterior hemi-transverse) subjected to a physiological-type compressive load of 2207N representing 3 x body weight for a 75kg person during walking. FE stress maps were compared to choose the most mechanically stable cable method, i.e. lowest peak bone stress. In Phase 2, mechanical tests were then done in artificial hemipelvises to compare the standard plate method versus the optimal cable method selected from Phase 1. FE analysis results showed peak bone stresses of 255MPa (Plate method), 205MPa (Mears cable method), 250MPa (Kang cable method), and 181MPa (Mouhsine cable method). Mechanical tests then showed that the Plate method versus the Mouhsine cable method selected from Phase 1 had higher stiffness (662versus 385N/mm, p =0.001), strength (3210versus 2060N, p =0.009), and failure energy (8.8versus 6.2J, p =0.002), whilst they were statistically equivalent for interfragmentary sliding (p ≥0.179) and interfragmentary gapping (p ≥0.08). The Plate method had superior mechanical properties, but the Mouhsine cable method may be a reasonable alternative if osteoporosis prevents good screw thread interdigitation during plating.

      PubDate: 2017-06-27T04:18:45Z
      DOI: 10.1016/j.medengphy.2017.06.004
       
  • A custom-made temporomandibular joint prosthesis for fabrication by
           selective laser melting: Finite element analysis
    • Authors: Xiangliang Xu; Danmei Luo; Chuanbin Guo; Qiguo Rong
      Abstract: Publication date: Available online 17 June 2017
      Source:Medical Engineering & Physics
      Author(s): Xiangliang Xu, Danmei Luo, Chuanbin Guo, Qiguo Rong
      A novel and custom-made selective laser melting (SLM) 3D-printed alloplastic temporomandibular joint (TMJ) prosthesis is proposed. The titanium-6aluminium-4vanadium (Ti-6Al-4V) condyle component and ultra-high molecular weight polyethylene (UHMWPE) fossa component comprised the total alloplastic TMJ replacement prosthesis. For the condyle component, an optimized tetrahedral open-porous scaffold with combined connection structures, i.e. an inlay rod and an onlay plate, between the prosthesis and remaining mandible was designed. The trajectory of movement of the intact condyle was assessed via kinematic analysis to facilitate the design of the fossa component. The behaviours of the intact mandible and mandible with the prosthesis were compared. The biomechanical behaviour was analysed by assessing the stress distribution on the prosthesis and strain distribution on the mandible. After muscle force was applied, the magnitude of the compressive strain on the condyle neck of the mandible with the prosthesis was lower than that on the condyle neck of the intact mandible, with the exception of the area about the screws; additionally, the magnitude of the strain at the scaffold–bone interface was relatively high.

      PubDate: 2017-06-20T03:14:02Z
      DOI: 10.1016/j.medengphy.2017.04.012
       
  • Biomechanical evaluation of a novel pedicle screw-based interspinous
           spacer: A finite element analysis
    • Authors: Hsin-Chang Chen; Jia-Lin Wu; Shou-Chieh Huang; Zheng-Cheng Zhong; Shiu-Ling Chiu; Yu-Shu Lai; Cheng-Kung Cheng
      Abstract: Publication date: Available online 15 June 2017
      Source:Medical Engineering & Physics
      Author(s): Hsin-Chang Chen, Jia-Lin Wu, Shou-Chieh Huang, Zheng-Cheng Zhong, Shiu-Ling Chiu, Yu-Shu Lai, Cheng-Kung Cheng
      Interspinous spacers have been designed to provide a minimally invasive surgical technique for patients with lumbar spinal stenosis or foraminal stenosis. A novel pedicle screw-based interspinous spacer has been developed in this study, and the aim of this finite element experiment was to investigate the biomechanical differences between the pedicle screw-based interspinous spacer (M-rod system) and the typical interspinous spacer (Coflex-F™). A validated finite element model of an intact lumbar spine was used to analyze the insertions of the Coflex-F™, titanium alloy M-rod (M-Ti), and polyetheretherketone M-rod (M-PEEK), independently. The range of motion (ROM) between each vertebrae, stiffness of the implanted level, the peak stress at the intervertebral discs, and the contact forces on spinous process were analyzed. Of all three devices, the Coflex-F™ provided the largest restrictions in extension, flexion and lateral bending. For intervertebral disc, the peak stress at the implanted segment decreased by 81% in the Coflex-F™, 60.2% in the M-Ti and 46.7% in the M-PEEK when compared to the intact model. For the adjacent segments, while the Coflex-F™ caused considerable increases in the ROM and disc stress, the M-PEEK only had small changes.

      PubDate: 2017-06-20T03:14:02Z
      DOI: 10.1016/j.medengphy.2017.05.004
       
  • Precision and accuracy of consumer-grade motion tracking system for
           pedicle screw placement in pediatric spinal fusion surgery
    • Authors: Andrew Chan; Janelle Aguillon; Doug Hill; Edmond Lou
      Abstract: Publication date: Available online 9 June 2017
      Source:Medical Engineering & Physics
      Author(s): Andrew Chan, Janelle Aguillon, Doug Hill, Edmond Lou
      Adolescent idiopathic scoliosis (AIS) is a 3-dimensional spinal deformity involving lateral curvature and axial rotation. Surgical intervention involves insertion of pedicle screws into the spine, requiring accuracies of 1mm and 5° in translation and rotation to prevent neural and vascular complications. While commercial CT-navigation is available, the significant cost, bulk and radiation dose hinders their use in AIS surgery. The objective of this study was to evaluate a commercial-grade Optitrack Prime 13W motion capture cameras to determine if they can achieve adequate accuracy for screw insertion guidance in AIS. Static precision, camera and tracked rigid body configurations, translational and rotational accuracy were investigated. A 1-h camera warm-up time was required to achieve precisions of 0.13mm and 0.10°. A three-camera system configuration with cameras at equal height but staggered depth achieved the best accuracy. A triangular rigid body with 7.9mm markers had superior accuracy. The translational accuracy for motions up to 150mm was 0.25mm while rotational accuracy was 4.9° for rotations in two directions from 0° to 70°. Required translational and rotational accuracies were achieved using this motion capture system as well as being comparable to surgical-grade navigators.

      PubDate: 2017-06-15T02:27:05Z
      DOI: 10.1016/j.medengphy.2017.05.003
       
  • A novel flexible capacitive load sensor for use in a mobile
           unicompartmental knee replacement bearing: An in vitro proof of concept
           study
    • Authors: M J A Mentink; B H Van Duren; D W Murray; H S Gill
      Abstract: Publication date: Available online 9 June 2017
      Source:Medical Engineering & Physics
      Author(s): M J A Mentink, B H Van Duren, D W Murray, H S Gill
      Instrumented knee replacements can provide in vivo data quantifying physiological loads acting on the knee. To date instrumented mobile unicompartmental knee replacements (UKR) have not been realised. Ideally instrumentation would be embedded within the polyethylene bearing. This study investigated the feasibility of an embedded flexible capacitive load sensor. A novel flexible capacitive load sensor was developed which could be incorporated into standard manufacturing of compression moulded polyethylene bearings. Dynamic experiments were performed to determine the characteristics of the sensor on a uniaxial servo-hydraulic material testing machine. The instrumented bearing was measured at sinusoidal frequencies between 0.1 and 10Hz, allowing for measurement of typical gait load magnitudes and frequencies. These correspond to frequencies of interest in physiological loading. The loads that were applied were a static load of 390N, corresponding to an equivalent body weight load for UKR, and a dynamic load of ±293N. The frequency transfer response of the sensor suggests a low pass filter response with a −3dB frequency of 10Hz. The proposed embedded capacitive load sensor was shown to be applicable for measuring in vivo loads within a polyethylene mobile UKR bearing.

      PubDate: 2017-06-10T01:10:48Z
      DOI: 10.1016/j.medengphy.2017.05.002
       
  • MicroCT-based finite element models as a tool for virtual testing of
           cortical bone
    • Authors: Masoud Ramezanzadehkoldeh; Bjørn H. Skallerud
      Abstract: Publication date: Available online 18 May 2017
      Source:Medical Engineering & Physics
      Author(s): Masoud Ramezanzadehkoldeh, Bjørn H. Skallerud
      The aim of this study was to assess a virtual biomechanics testing approach purely based on microcomputed tomography (microCT or µCT) data, providing non-invasive methods for determining the stiffness and strength of cortical bone. Mouse femurs were µCT scanned prior to three-point-bend tests. Then microCT-based finite element models were generated with spatial variation in bone elastoplastic properties and subject-specific femur geometries. Empirical relationships of density versus Young's moduli and yield stress were used in assigning elastoplastic properties to each voxel. The microCT-based finite element modeling (µFEM) results were employed to investigate the model's accuracy through comparison with experimental tests. The correspondence of elastic stiffness and strength from the µFE analyses and tests was good. The interpretation of the derived data showed a 6.1%, 1.4%, 1.5%, and 1.6% difference between the experimental test result and µFEM output on global stiffness, nominal Young's modulus, nominal yield stress, and yield force, respectively. We conclude that virtual testing outputs could be used to predict global elastic-plastic properties and may reduce the cost, time, and number of test specimens in performing physical experiments.

      PubDate: 2017-05-20T21:56:27Z
      DOI: 10.1016/j.medengphy.2017.04.011
       
  • Biomechanical study on surgical fixation methods for minimally invasive
           treatment of hallux valgus
    • Authors: Rui Mao; Junchao Guo; Chenyu Luo; Yubo Fan; Jianmin Wen; Lizhen Wang
      Abstract: Publication date: Available online 17 May 2017
      Source:Medical Engineering & Physics
      Author(s): Rui Mao, Junchao Guo, Chenyu Luo, Yubo Fan, Jianmin Wen, Lizhen Wang
      Hallux valgus (HV) was one of the most frequent female foot deformities. The aim of this study was to evaluate mechanical responses and stabilities of the Kirschner, bandage and fiberglass fixations after the distal metatarsal osteotomy in HV treatment. Surface traction of different forefoot regions in bandage fixation and the biomechanical behavior of fiberglass bandage material were measured by a pressure sensor device and a mechanical testing, respectively. A three-dimensional foot finite element (FE) model was developed to simulate the three fixation methods (Kirschner, bandage and fiberglass fixations) in weight bearing. The model included 28 bones, sesamoids, ligaments, plantar fascia, cartilages and soft tissue. The peak Von Mises stress (MS) and compression stress (CS) of the distal fragment were predicted from the three fixation methods: Kirschner fixation (MS=6.71MPa, CS=1.232MPa); Bandage fixation (MS=14.90MPa, CS=9.642MPa); Fiberglass fixation (MS=15.83MPa, CS=19.70MPa). Compared with the Kirschner and bandage fixation, the fiberglass fixation reduced the relative movement of osteotomy fragments and obtained the maximum CS. We concluded that fiberglass fixation in HV treatment was helpful to the bone healing of distal fragment. The findings were expected to guide further therapeutic planning of HV patient.

      PubDate: 2017-05-20T21:56:27Z
      DOI: 10.1016/j.medengphy.2017.04.010
       
 
 
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