Medical Engineering & Physics RSS feed: Current Issue. Medical Engineering & Physics provides a forum for the publication of the latest developments in biomedical engineering, and reflects the essential multidisciplinary nature of the subject. The journal publishes in-depth critical reviews, scientific papers and technical notes. Our focus encompasses the application of the basic principles of physics and engineering to the development of medical devices and technology, with the ultimate aim of producing improvements in the quality of health care. Topics covered include biomechanics, biomaterials, mechanobiology, rehabilitation engineering, biomedical signal processing and medical device development. Medical Engineering & Physics aims to keep both engineers and clinicians abreast of the latest applications of technology to health care. http://www.medengphys.com/?rss=yesElsevier Inc.en © 2012 Published by Elsevier Inc. All rights reserved. Medical Engineering & Physics1350-4533345June 2012 © 2012 Published by Elsevier Inc. All rights reserved. healthpermissions@elsevier.comhttp://www.medengphys.com/article/PIIS1350453312001166/abstract?rss=yesEditorial Board10.1016/S1350-4533(12)00116-6Medical Engineering & Physics 34, 5 (2012)2012-06-01Medical Engineering & Physics2012-06-01345S1350-4533(12)X0005-5CO2CO2http://www.medengphys.com/article/PIIS1350453311002220/abstract?rss=yesAbstract: An EMG-driven musculoskeletal model is implemented to estimate subject-specific musculoskeletal parameters such as the optimal physiological muscle length, the tendon slack length and the maximum isometric muscle force of flexor and extensor muscle groups crossing the wrist, as well as biomechanical indexes to quantify the muscle operating range, the stiffness of the musculotendon actuators, and the contribution of the muscle fibres to the joint moment.Twelve healthy subjects (11 males and 1 female, mean age 31.1±8.7 years) were instructed to perform isometric maximum voluntary contractions of wrist flexors and extensors. Recorded EMGs were used as input to the model and the root mean square error (RMSE) between measured and predicted torque was minimised to estimate the subject-specific musculotendon parameters. The model was validated and the RMSE and the normalised RMSE calculated during estimation and validation phases are compared.Estimated subject-specific musculoskeletal parameters vary in a physiological range, while the biomechanical indexes are in agreement with previously published data.The proposed methodology proved to be effective for the in vivo estimation of physiological parameters of the musculotendon complex and has potential as an investigative tool to distinguish aetiological differences among subjects affected by musculoskeletal disorders.Subject-specific musculoskeletal parameters of wrist flexors and extensors estimated by an EMG-driven musculoskeletal modelFrancesco M. Colacino, Rustighi Emiliano, Brian R. Mace10.1016/j.medengphy.2011.08.012Medical Engineering & Physics 34, 5 (2012)2011-09-21Medical Engineering & Physics2011-09-21345S1350-4533(12)X0005-5Papers531540http://www.medengphys.com/article/PIIS1350453311002232/abstract?rss=yesAbstract: In motor-vehicle crashes, young school-aged children restrained by vehicle seat belt systems often suffer from abdominal injuries due to submarining. However, the current anthropomorphic test device, so-called “crash dummy”, is not adequate for proper simulation of submarining. In this study, a modified Hybrid-III six-year-old dummy model capable of simulating and predicting submarining was developed using MADYMO (TNO Automotive Safety Solutions). The model incorporated improved pelvis and abdomen geometry and properties previously tested in a modified physical dummy. The model was calibrated and validated against four sled tests under two test conditions with and without submarining using a multi-objective optimization method. A sensitivity analysis using this validated child dummy model showed that dummy knee excursion, torso rotation angle, and the difference between head and knee excursions were good predictors for submarining status. It was also shown that restraint system design variables, such as lap belt angle, D-ring height, and seat coefficient of friction (COF), may have opposite effects on head and abdomen injury risks; therefore child dummies and dummy models capable of simulating submarining are crucial for future restraint system design optimization for young school-aged children.Development and validation of a modified Hybrid-III six-year-old dummy model for simulating submarining in motor-vehicle crashesJingwen Hu, Kathleen D. Klinich, Matthew P. Reed, Michael Kokkolaras, Jonathan D. Rupp10.1016/j.medengphy.2011.08.013Medical Engineering & Physics 34, 5 (2012)2011-09-19Medical Engineering & Physics2011-09-19345S1350-4533(12)X0005-5Papers541551http://www.medengphys.com/article/PIIS1350453311002244/abstract?rss=yesAbstract: Disc degeneration (DD) is often accompanied by a height reduction of the anterior and posterior discs (AD and PD, respectively), and this affect the way in which articulating posterior facets (PFs) come into contact during physiological motions. Any increase in the contact between overlapping articulating facet surfaces increases PF loading. Development of adjacent segment disease is a significant clinical concern. It still is not clear how degenerative motion changes in AD and PD heights affect the mechanics of adjacent segment discs and facets. We hypothesized that changes in axial height patterns (in the AD and PD) at the degenerated C5–C6 disc-segment would affect axial height patterns (in the AD and PD) above and below the degenerated disc-segment. A previously validated poroelastic three-dimensional finite element (FE) model of a normal C3–T1 segment was used. Two additional C3–T1 models were built with moderate and severe DD at C5–C6. The three FE models were evaluated in flexion and extension. With progressive C5–C6 DD, AD and PD flexibility (axial deformation or elongation per unit load) at C5–C6 decrease with a compensatory corresponding flexibility increase in adjacent segments (normal), whereas PF loading increased at all segments only during extension. Changes in AD and PD flexibility and PF loading were higher at inferior segments than at superior segments. This study confirmed the hypothesis that the anterior and posterior discs and articulating facets of cervical spine segments are affected during flexion and extension motions when a disc-segment degenerates. Motion changes involving a higher PD height loss, both at the degenerated and adjacent segments, would further increase PF loading along the posterior spinal column – a possible mechanism for the dysfunctioning of the facet joints. The current data should be compared to other multi-segmental cervical spine experiments.Progressive disc degeneration at C5–C6 segment affects the mechanics between disc heights and posterior facets above and below the degenerated segment: A flexion–extension investigation using a poroelastic C3–T1 finite element modelMozammil Hussain, Raghu N. Natarajan, Howard S. An, Gunnar B.J. Andersson10.1016/j.medengphy.2011.08.014Medical Engineering & Physics 34, 5 (2012)2011-09-19Medical Engineering & Physics2011-09-19345S1350-4533(12)X0005-5Papers552558http://www.medengphys.com/article/PIIS1350453311002256/abstract?rss=yesAbstract: Hip resurfacing (HR) is a highly attractive option for young and active patients. Some surgeons have advocated cementing the metaphyseal stem of the femoral component to improve fixation and survivorship of HR. However, extending component fixation to the metaphysis may promote femoral head strain shielding, which in turn may reduce survival of the femoral component. Replacing the metallic metaphyseal stem by a composite material with bone-matching properties could help to alleviate this phenomenon. This study uses finite element analysis to examine the strain state in the femoral head for three types of implant fixation: an unfixed metallic stem, an osseointegrated biomimetic stem and a cemented metallic stem. Bone remodeling is also simulated to evaluate long-term bone resorption due to strain shielding. Results show that the unfixed stem causes strain shielding in the femoral head, and that cementing the stem increases strain shielding. The biomimetic stem does not eliminate the strain shielding effect, but reduces it significantly versus the metallic cemented version. The current finite element study suggests that an osseointegrated metaphyseal stem made of biomimetic material in hip resurfacing implants could become an interesting alternative when fixation extension is desired.Anisotropic bone remodeling of a biomimetic metal-on-metal hip resurfacing implantC. Caouette, M.N. Bureau, P.-A. Vendittoli, M. Lavigne, N. Nuño10.1016/j.medengphy.2011.08.015Medical Engineering & Physics 34, 5 (2012)2011-09-26Medical Engineering & Physics2011-09-26345S1350-4533(12)X0005-5Papers559565http://www.medengphys.com/article/PIIS1350453311002268/abstract?rss=yesAbstract: Fetal movement is one index of fetal well-being. We designed and built a new recorder based on fetal movement acceleration measurement (FMAM). The FMAM recorder has a newly developed, capacitive acceleration sensor that can detect the oscillations of the maternal abdominal wall caused by fetal movements. In this study, the recorder was examined for its suitability for long-term home monitoring of fetal movement by pregnant women themselves.Experiment I: Fourteen pregnant women underwent 45 examinations in the laboratory at gestational 20–39 weeks. We simultaneously recorded fetal movement as detected by the recorder, ultrasonography, and maternal perception, and then calculated agreement among the three methods. We evaluated agreement using prevalence-adjusted bias-adjusted kappa (PABAK). Agreement for gross fetal movement as detected by FMAM and ultrasonography was substantial or almost perfect, while agreement between maternal perception and ultrasonography was moderate or substantial. Experiment II: Six pregnant women undertook 53 experiments at home by themselves. Fetal movement during maternal nocturnal sleep was successfully recorded 50 out of 53 times at home.In conclusion, there was high agreement for gross fetal movement between FMAM and ultrasonography. The recorder is promising for objective, accurate, and long-term home monitoring of gross fetal movement by pregnant women themselves.A new method for long-term home monitoring of fetal movement by pregnant women themselvesEiji Ryo, Kyoko Nishihara, Sachiyo Matsumoto, Hideo Kamata10.1016/j.medengphy.2011.09.001Medical Engineering & Physics 34, 5 (2012)2011-10-03Medical Engineering & Physics2011-10-03345S1350-4533(12)X0005-5Papers566572http://www.medengphys.com/article/PIIS1350453311002281/abstract?rss=yesAbstract: This study was conducted to study the influence of design parameters namely; the head/neck ratio (R), neck-shaft angle (NSA), oscillation angle (OsA) and stem offset (Sθ) on cup–stem orientations namely; the cup inclination (CI), cup anteversion (CA) and stem antetorsion (SA). R is often linked to influence NSA, OsA and impingement. An effort has been made to analyze range of motion (RoM) with NSA greater than 135° and R lower than 2.3 that may produce impingement. This study attempted to answer the following assumptions whether (a) implants with higher H–N ratio can achieve higher oscillations and higher stem antetorsion, (b) stems with higher neck shaft angle can achieve higher cup anteversion with lower stem offset and stem antetorsion, (c) stem with higher offsets can achieve lower cup anteversion with higher stem antetorsion, and (d) lower cup anteversion can be achieved when stem antetorsion is higher. A theoretical and a simulated method were implemented to anaylze RoM until impingement between cup and neck occurred. Cup abduction and anterior opening were held constant for this study. Multivariate prediction models were developed to predict optimal cup–stem orientations for the chosen design parameters of 12 hip implants. Optimal design parameters to achieve an impingement free RoM were as follows: NSA=139.25°, R=3.08, OsA=119.83°, Sθ=34.45mm, CApredicted=16.26°, CIpredicted=42.77° and SApredicted=30.37°, respectively. Multivariate models may be further developed for use in surgery planning to achieve optimal component placement.Influence of design parameters on cup–stem orientations for impingement free RoM in hip implantsDishita Patel, Tarun Goswami10.1016/j.medengphy.2011.09.003Medical Engineering & Physics 34, 5 (2012)2011-10-05Medical Engineering & Physics2011-10-05345S1350-4533(12)X0005-5Papers573578http://www.medengphys.com/article/PIIS1350453311002293/abstract?rss=yesAbstract: Fetal welfare during labor and delivery is commonly monitored through the cardiotocogram (CTG), the combined registration of uterus contractions and fetal heart rate (FHR). The CTG gives an indication of the main determinant of the acute fetal condition, namely its oxygen state. However, interpretation is complicated by the complex relationship between the two.Mathematical models can be used to assist with the interpretation of the CTG, since they enable quantitative modeling of the cascade of events through which uterine contractions affect fetal oxygenation and FHR. We developed a mathematical model to simulate ‘early decelerations’, i.e. variations in FHR originating from caput compression during uterine contractions, as mediated by cerebral flow reduction, cerebral hypoxia and a vagal nerve response to hypoxia.Simulation results show a realistic response, both for fetal and maternal hemodynamics at term, as for FHR variation during early decelerations.The model is intended to be used as a training tool for gynaecologists. Therefore 6 clinical experts were asked to rate 5 real and 5 model-generated CTG tracings on overall realism and realism of selected aspects. Results show no significant differences between real and computer-generated CTG tracings.A mathematical model for simulation of early decelerations in the cardiotocogram during laborM. Beatrijs van der Hout-van der Jagt, S. Guid Oei, Peter H.M. Bovendeerd10.1016/j.medengphy.2011.09.004Medical Engineering & Physics 34, 5 (2012)2011-10-31Medical Engineering & Physics2011-10-31345S1350-4533(12)X0005-5Papers579589http://www.medengphys.com/article/PIIS135045331100230X/abstract?rss=yesAbstract: Accelerometers are seemingly a criterion standard of real-life walking mobility and this is supported by assumptions and empirical data. This application would be strengthened by including objective measures of walking mobility along with a matched control sample for verifying specificity versus generality in accelerometer output.We compared associations among accelerometer output, walking mobility, and physical activity between persons with multiple sclerosis (MS) and controls without a neurological disorder. Sixty-six persons (33 MS, 33 matched controls) completed a battery of questionnaires, performed the six-minute walk (6MW) and timed-up-and-go (TUG), and wore an accelerometer for a 7-day period. After this period, participants completed the Godin Leisure-Time Exercise Questionnaire (GLTEQ) and International Physical Activity Questionnaire (IPAQ). Accelerometer output was significantly correlated with only mobility measures (6MW, ρ=.78; TUG, ρ=−.68) in MS, whereas it correlated with both mobility (6MW, ρ=.58; TUG, ρ=−.49) and physical activity (GLTEQ, ρ=.56; IPAQ, ρ=.53) measures in controls. Regression analysis indicated that only 6MW explained variance in accelerometer output in MS (β=.65, R2=.43). These findings support the possibility that accelerometers primarily and specifically measure real-life walking mobility, not physical activity, in persons with MS.Accelerometry is associated with walking mobility, not physical activity, in persons with multiple sclerosisMadeline Weikert, Yoojin Suh, Abbi Lane, Brian Sandroff, Deirdre Dlugonski, Bo Fernhall, Robert W. Motl10.1016/j.medengphy.2011.09.005Medical Engineering & Physics 34, 5 (2012)2011-10-04Medical Engineering & Physics2011-10-04345S1350-4533(12)X0005-5Papers590597http://www.medengphys.com/article/PIIS1350453311002311/abstract?rss=yesAbstract: In this study the relationship between the mean intercept length (MIL) method – the current standard histomorphometric method of assessing structural anisotropy and an alternative method of the gray-level structure tensor (GST) is investigated. Both methods are applied to a set of 25 three-dimensional binary μCT images of trabecular bone. It is shown that there is a very strong correlation between the logarithms of the principal values of the MIL and the GST fabric tensors (Pearson's coefficient of correlation higher than 0.98) and between the logarithms of the invariants of the MIL and the GST fabric tensors (Pearson's coefficient of correlation higher than 0.999). There is also a good correlation between the degree of anisotropy calculated from the MIL and from the GST tensors (Pearson's coefficient of correlation equal to 0.90). The principal anisotropy directions of the MIL and the GST fabric tensors coincide at the 5% significance level. Additionally, the performance of both methods is tested, based on a set of artificial structures with prescribed orientations.Equivalence of mean intercept length and gradient fabric tensors – 3d studyZbisław Tabor10.1016/j.medengphy.2011.09.006Medical Engineering & Physics 34, 5 (2012)2011-10-04Medical Engineering & Physics2011-10-04345S1350-4533(12)X0005-5Papers598604http://www.medengphys.com/article/PIIS1350453311002347/abstract?rss=yesAbstract: A primary etiological factor underlying chronic middle ear disease is an inability to open the collapsible Eustachian tube (ET). However, the structure–function relationships responsible for ET dysfunction in patient populations at risk for developing otitis media (OM) are not known. In this study, three-dimensional (3D) finite element (FE) modeling techniques were used to investigate how changes in biomechanical and anatomical properties influence opening phenomena in three populations: normal adults, young children and infants with cleft palate. Histological data was used to create anatomically accurate models and FE techniques were used to simulate tissue deformation and ET opening. Lumen dilation was quantified using a computational fluid dynamic (CFD) technique and a sensitivity analysis was performed to ascertain the relative importance of the different anatomical and tissue mechanical properties. Results for adults suggest that ET function is highly sensitive to tensor veli palatini muscle (TVPM) forces and to periluminal mucosal tissue (PMT) elasticity. Young children and cleft palate subjects exhibited reduced sensitivity to TVPM forces while changes in PMT stiffness continued to have a significant impact on ET function. These results suggest that reducing PMT stiffness might be an effective way to restore ET function in these populations. Varying TVPM force vector relationships via changes in hamulus location had no effect on ET opening in young children and cleft palate subjects but did alter force transmission to the ET lumen during conditions of elevated adhesion. These models have therefore provided important new insights into the biomechanical mechanisms responsible for ET dysfunction.Three-dimensional finite element analysis of Eustachian tube function under normal and pathological conditionsF.J. Sheer, J.D. Swarts, S.N. Ghadiali10.1016/j.medengphy.2011.09.008Medical Engineering & Physics 34, 5 (2012)2011-10-13Medical Engineering & Physics2011-10-13345S1350-4533(12)X0005-5Papers605616http://www.medengphys.com/article/PIIS1350453311002359/abstract?rss=yesAbstract: Repetitive reaching movements to a fixed target can be generally characterized by bell-shaped velocity profiles and sigmoidal trajectories with variable morphologies across multiple repetitions. A neuromuscular correspondence of these kinematic variations has thus far eluded electromyographic (EMG) analysis. We recorded EMG and elbow kinematics from fourteen healthy individuals performing repetitive, self-paced, isolated elbow flexions, with their arms supported against gravity. The global kinematic pattern of each flexion was classified as either sigmoidal (S) or non-sigmoidal (NS), based on goodness of fit with analytical curves. Ten of the fourteen subjects generated an approximately equal number of S and NS types (383 movement cycles). Trajectories of the other four subjects were not classifiable or did not vary sufficiently and were excluded from subsequent analysis. A post hoc predictor of trajectory type was derived by testing linear support vector machines trained with a strategically selected 3-feature sub-space of the early phase of enveloped biceps EMG during a leave-one-out cross-validation paradigm. Results showed that EMG features predicted kinematic morphology with sensitivity and specificity both exceeding 80%. The high predictive accuracy suggests neuromotor signals coding for subtle variations in elbow kinematics during self-paced, unloaded motions, can be deciphered from the biceps EMG.Relating biceps EMG to elbow kinematics during self-paced arm flexionsGautam S. Natarajan, Michael Wininger, Nam H. Kim, William Craelius10.1016/j.medengphy.2011.09.009Medical Engineering & Physics 34, 5 (2012)2011-10-13Medical Engineering & Physics2011-10-13345S1350-4533(12)X0005-5Papers617624http://www.medengphys.com/article/PIIS1350453312000574/abstract?rss=yesAbstract: This paper presented an effective method for the 3D heterogeneous porous scaffold design of human tissue using triply periodic minimal surface (TPMS) internal pore architectures. First, an implicit solid representing the smooth 3D scalar field for the porosity distribution was reconstructed by interpolating the geometric positions of control points and porosity values defined at those points using an implicit interpolation algorithm based on the thin-plate radial basis function. After generating the implicit solid representing the smooth 3D scalar field for the porosity distribution, a functionally graded tissue scaffold with accurately controlled porosity distribution was designed using the TPMS-based unit cell libraries. Numerical results showed that the proposed scaffold design method has the potential benefits for accurately controlling the spatial porosity distribution within an arbitrarily shaped scaffold while keeping the advantage of the TPMS-based unit cell libraries.Heterogeneous minimal surface porous scaffold design using the distance field and radial basis functionsDongjin Yoo10.1016/j.medengphy.2012.03.009Medical Engineering & Physics 34, 5 (2012)2012-04-10Medical Engineering & Physics2012-04-10345S1350-4533(12)X0005-5Papers625639http://www.medengphys.com/article/PIIS1350453311003146/abstract?rss=yesAbstract: Linked-segment representations of human body dynamics have been used extensively in biomechanics, ergonomics, and rehabilitation research to systemize thinking, make predictions, and suggest novel experiments. In the scope of upper body biomechanics, these models play an even more essential role as the human spine dynamics are difficult to study in vivo. No study exists to date, however, that specifically disseminates the technical details of a comprehensive three-dimensional model of the upper body for the purpose of estimating spinal joint torques and forces for a wide range of scenarios. Consequently, researchers are still bound to develop and implement their own models. Therefore, the objective of this study was to design a dynamic model of the upper body that can comprehensively estimate spinal joint torques and forces from upper body kinematics. The proposed three-dimensional model focuses on the actions of the lumbar and cervical vertebrae and consists of five lumbar segments (L1 to L5), the thorax, six cervical segments (C2 to C7), and the head. Additionally, the model: (1) is flexible regarding the kinematic nature of the spinal joints (free, constrained, or fixed); (2) incorporates all geometric and mass-inertia parameters from a single, high-resolution source; and (3) can be feasibly implemented via different inverse dynamics formulations. To demonstrate its practicality, the model was finally employed to estimate the lumbar and cervical joint torques during perturbed sitting using experimental motion data. Considering the growing importance of mathematical predictions, the developed model should become an important resource for researchers in different fields.A comprehensive three-dimensional dynamic model of the human head and trunk for estimating lumbar and cervical joint torques and forces from upper body kinematicsAlbert H. Vette, Takashi Yoshida, T. Adam Thrasher, K. Masani, Milos R. Popovic10.1016/j.medengphy.2011.11.023Medical Engineering & Physics 34, 5 (2012)2012-01-03Medical Engineering & Physics2012-01-03345S1350-4533(12)X0005-5Technical Notes640649http://www.medengphys.com/article/PIIS1350453312000288/abstract?rss=yesAbstract: Previous studies have demonstrated the possibility of using functional MRI to control a robot arm through a brain–machine interface by directly coupling haemodynamic activity in the sensory–motor cortex to the position of two axes. Here, we extend this work by implementing interaction at a more abstract level, whereby imagined actions deliver structured commands to a robot arm guided by a machine vision system. Rather than extracting signals from a small number of pre-selected regions, the proposed system adaptively determines at individual level how to map representative brain areas to the input nodes of a classifier network. In this initial study, a median action recognition accuracy of 90% was attained on five volunteers performing a game consisting of collecting randomly positioned coloured pawns and placing them into cups. The “pawn” and “cup” instructions were imparted through four mental imaginery tasks, linked to robot arm actions by a state machine. With the current implementation in MatLab language the median action recognition time was 24.3s and the robot execution time was 17.7s. We demonstrate the notion of combining haemodynamic brain–machine interfacing with computer vision to implement interaction at the level of high-level commands rather than individual movements, which may find application in future fMRI approaches relevant to brain-lesioned patients, and provide source code supporting further work on larger command sets and real-time processing.Thoughts turned into high-level commands: Proof-of-concept study of a vision-guided robot arm driven by functional MRI (fMRI) signalsLudovico Minati, Anna Nigri, Cristina Rosazza, Maria Grazia Bruzzone10.1016/j.medengphy.2012.02.004Medical Engineering & Physics 34, 5 (2012)2012-03-14Medical Engineering & Physics2012-03-14345S1350-4533(12)X0005-5Technical Notes650658http://www.medengphys.com/article/PIIS1350453312000252/abstract?rss=yesAbstract: In this contribution, we present and evaluate a method for characterizing stapes prostheses by their mechanical transfer function. The measurements were carried out after a stapedotomy surgery was performed in three human temporal bones conserved in 4% formaldehyde. The inner ear was drained of fluid. Successively, one of three different stapes prostheses was inserted. After such preparation, the prosthesis piston movement compared to the incus movement is measured with laser vibrometry. The magnitude transfer function considered is defined as the amplitude of the prosthesis piston movement compared to the amplitude of the incus movement. Measurements were made in a frequency range from 500Hz to 4kHz. The measured amplitudes roughly ranged between 10nm and 100nm. A great advantage of the presented method is the fact that only a small portion of the ossicular chain influences the measurement, mainly the joint between the prosthesis and the incus. Furthermore, the usage of cadaver temporal bones allows for an automated measurement setup, long term experiments and the access of measurement positions inapproachable during in vivo measurements. With this method, the different kinds of prostheses could be evaluated on incuses of different diameters.A method for characterizing stapes prostheses by their mechanical transfer functionAlexander Sutor, Joachim Hornung, Julian Gossler, Michael Doellinger, Reinhard Lerch10.1016/j.medengphy.2012.02.001Medical Engineering & Physics 34, 5 (2012)2012-03-15Medical Engineering & Physics2012-03-15345S1350-4533(12)X0005-5Communication659663