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BIOLOGY (1385 journals)            First | 4 5 6 7 8 9 10 11 | Last

Journal of Applied Phycology     Hybrid Journal   (Followers: 9)
Journal of Applied Virology     Open Access   (Followers: 7)
Journal of Aquatic Sciences     Full-text available via subscription   (Followers: 1)
Journal of Arachnology     Full-text available via subscription  
Journal of Asia-Pacific Biodiversity     Open Access  
Journal of Astrobiology & Outreach     Open Access  
Journal of Avian Biology     Hybrid Journal   (Followers: 19)
Journal of Bacteriology     Full-text available via subscription   (Followers: 17)
Journal of Basic Microbiology     Hybrid Journal   (Followers: 3)
Journal of Bio-Science     Open Access   (Followers: 1)
Journal of Biobased Materials and Bioenergy     Full-text available via subscription  
Journal of Biodiversity & Endangered Species     Open Access  
Journal of Biodiversity Management & Forestry     Hybrid Journal   (Followers: 1)
Journal of Bioenergetics and Biomembranes     Hybrid Journal  
Journal of Biogeography     Hybrid Journal   (Followers: 22)
Journal of Bioinformatics and Computational Biology     Hybrid Journal   (Followers: 13)
Journal of Bioinformatics and Intelligent Control     Full-text available via subscription  
Journal of Biological and Information Sciences     Open Access   (Followers: 2)
Journal of Biological Dynamics     Open Access   (Followers: 1)
Journal of Biological Education     Hybrid Journal   (Followers: 1)
Journal of Biological Engineering     Open Access   (Followers: 4)
Journal of Biological Methods     Open Access  
Journal of Biological Physics     Hybrid Journal  
Journal of Biological Research - Thessaloniki     Open Access  
Journal of Biological Sciences     Open Access   (Followers: 4)
Journal of Biological Systems     Hybrid Journal   (Followers: 2)
Journal of Biology and Earth Sciences     Open Access   (Followers: 1)
Journal of Biology and Life Science     Open Access   (Followers: 2)
Journal of Biology, Agriculture and Healthcare     Open Access   (Followers: 5)
Journal of Biomarkers     Open Access  
Journal of Biomechanics     Hybrid Journal   (Followers: 29)
Journal of Biomedical Discovery and Collaboration     Open Access   (Followers: 1)
Journal of Biomedical Education     Open Access   (Followers: 1)
Journal of Biomedical Informatics     Partially Free   (Followers: 14)
Journal of Biomedical Materials Research Part A     Hybrid Journal   (Followers: 1)
Journal of Biomedical Materials Research Part B : Applied Biomaterials     Hybrid Journal   (Followers: 1)
Journal of Biomedical Nanotechnology     Full-text available via subscription   (Followers: 6)
Journal of Biomedical Physics and Engineering     Open Access  
Journal of Biomedical Science and Engineering     Open Access   (Followers: 2)
Journal of Biomolecular Screening     Hybrid Journal   (Followers: 5)
Journal of Bionic Engineering     Full-text available via subscription  
Journal of Biorheology     Hybrid Journal  
Journal of Bioscience and Bioengineering     Full-text available via subscription   (Followers: 17)
Journal of Biosciences and Medicines     Open Access  
Journal of Biosocial Science     Hybrid Journal   (Followers: 4)
Journal of Biotechnology and Biodiversity     Open Access   (Followers: 1)
Journal of Bryology     Hybrid Journal   (Followers: 1)
Journal of Cell and Plant Sciences     Open Access   (Followers: 4)
Journal of Cell Communication and Signaling     Hybrid Journal  
Journal of Cell Death     Open Access   (Followers: 1)
Journal of Cell Science     Full-text available via subscription   (Followers: 11)
Journal of Cellular Biochemistry     Hybrid Journal   (Followers: 3)
Journal of Cellular Physiology     Hybrid Journal   (Followers: 5)
Journal of Cerebral Blood Flow & Metabolism     Hybrid Journal   (Followers: 1)
Journal of Chromatography B     Hybrid Journal   (Followers: 23)
Journal of Clinical Bioinformatics     Open Access   (Followers: 6)
Journal of Clinical Toxicology     Open Access   (Followers: 1)
Journal of Communications Technology and Electronics     Hybrid Journal   (Followers: 1)
Journal of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 1)
Journal of Contradicting Results in Science     Open Access   (Followers: 2)
Journal of Crustacean Biology     Hybrid Journal   (Followers: 3)
Journal of Developmental Biology     Open Access   (Followers: 2)
Journal of Ecosystems     Open Access   (Followers: 4)
Journal of Education, Health and Sport     Open Access   (Followers: 5)
Journal of Electrical Bioimpedance     Full-text available via subscription   (Followers: 2)
Journal of Electromyography and Kinesiology     Hybrid Journal   (Followers: 4)
Journal of Environment and Ecology     Open Access   (Followers: 13)
Journal of Environmental Radioactivity     Hybrid Journal   (Followers: 3)
Journal of Environmental Science and Natural Resources     Open Access   (Followers: 3)
Journal of Ethnobiology     Full-text available via subscription   (Followers: 5)
Journal of Ethnobiology and Ethnomedicine     Open Access  
Journal of Ethology     Hybrid Journal   (Followers: 2)
Journal of Evolutionary Biology     Hybrid Journal   (Followers: 23)
Journal of Experimental and Clinical Anatomy     Open Access   (Followers: 1)
Journal of Experimental Marine Biology and Ecology     Hybrid Journal   (Followers: 27)
Journal of Fish Biology     Hybrid Journal   (Followers: 25)
Journal of Functional Biomaterials     Open Access   (Followers: 1)
Journal of Fungi     Open Access  
Journal of Genomes and Exomes     Open Access  
Journal of Great Lakes Research     Hybrid Journal   (Followers: 7)
Journal of Green Science and Technology     Full-text available via subscription  
Journal of Health and Biological Sciences     Open Access  
Journal of Heredity     Hybrid Journal   (Followers: 3)
Journal of Herpetology     Full-text available via subscription   (Followers: 4)
Journal of Histology & Histopathology     Open Access  
Journal of Huazhong University of Science and Technology [Medical Sciences]     Hybrid Journal  
Journal of Human Evolution     Hybrid Journal   (Followers: 12)
Journal of Hymenoptera Research     Open Access   (Followers: 1)
Journal of Ichthyology     Hybrid Journal   (Followers: 4)
Journal of Insect Behavior     Hybrid Journal   (Followers: 6)
Journal of Insect Biodiversity     Open Access   (Followers: 3)
Journal of Insect Conservation     Hybrid Journal   (Followers: 5)
Journal of Integrated OMICS     Open Access  
Journal of Integrated Pest Management     Open Access   (Followers: 2)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Intelligent Transportation Systems: Technology, Planning, and Operations     Hybrid Journal   (Followers: 4)
Journal of Invertebrate Pathology     Hybrid Journal   (Followers: 3)
Journal of Landscape Ecology     Open Access   (Followers: 8)
Journal of Law and the Biosciences     Open Access   (Followers: 2)
Journal of Leukocyte Biology     Open Access   (Followers: 3)

  First | 4 5 6 7 8 9 10 11 | Last

Journal Cover   Medical Engineering & Physics
  [SJR: 0.871]   [H-I: 64]   [9 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1350-4533
   Published by Elsevier Homepage  [2799 journals]
  • A technique for developing CAD geometry of long bones using clinical CT
    • Abstract: Publication date: Available online 1 October 2015
      Source:Medical Engineering & Physics
      Author(s): Matthew L. Davis, Nicholas A. Vavalle, Joel D. Stitzel, F. Scott Gayzik
      Computed tomography scans are a valuable tool for developing computational models of bones. The objective of this study is to present a method to generate CAD representations of long bones from clinically based CT scans. A secondary aim is to apply the method to six long bones from a sample of three individuals. Periosteal and endosteal bone surfaces were segmented and used to calculate the characteristic cortical thickness, T c, at 1 mm increments along the bone axis. In the epiphyses where the value of T c fell below the scanner threshold, the endosteal bone layer was replaced using literature values projected inward from the periosteal surface. On average, 74.7 ± 7.4% of the bone geometry was above the scanner cut-off and was therefore derived from the CT scan data. The thickness measurement was also compared to experimental measurements of cadaveric bone and was found to predict T c with an error of 3.1%. This method presents a possible solution for the characterization of characteristic thickness along the length of the bone and may also aid in the development of orthopedic implant design and subject specific finite element models.

      PubDate: 2015-10-02T04:54:29Z
  • Wavelet analysis of skin perfusion to assess the effects of FREMS therapy
           before and after occlusive reactive hyperemia
    • Abstract: Publication date: Available online 29 September 2015
      Source:Medical Engineering & Physics
      Author(s): Stefan Octavian Popa, Myriam Ferrari, Giuseppe Maria Andreozzi, Romeo Martini, Andrea Bagno
      Laser Doppler Fluxmetry is used to evaluate the hemodynamics of skin microcirculation. Laser Doppler signals contain oscillations due to fluctuations of microvascular perfusion. By performing spectral analysis, six frequency intervals from 0.005 to 2 Hz have been identified and assigned to distinct cardiovascular structures: heart, respiration, vascular myocites, sympathetic terminations and endothelial cells (dependent and independent on nitric oxide). Transcutaneous electrical pulses are currently applied to treat several diseases, i.e. neuropathies and chronic painful leg ulcers. Recently, FREMS (Frequency Rhythmic Electrical Modulation System) has been applied to vasculopathic patients, too. In this study Laser Doppler signals of skin microcirculation were measured in five patients with intermittent claudication, before and after the FREMS therapy. Changes in vascular activities were assessed by wavelet transform analysis. Preliminary results demonstrate that FREMS induces alterations in vascular activities.

      PubDate: 2015-10-02T04:54:29Z
  • The effect of load obliquity on the strength of locking and nonlocking
           constructs in synthetic osteoporotic bone
    • Abstract: Publication date: Available online 29 September 2015
      Source:Medical Engineering & Physics
      Author(s): Daniel F. Tensmeyer, Peter A. Gustafson, James R. Jastifer, Bipin Patel, Joseph L. Chess
      The biomechanical performance of internal fracture fixation depends on several factors. One measure of performance is the strength of the construct. The objective of this biomechanical study was to identify the effect of load obliquity on the strength of locking and nonlocking plate and screw constructs. For this study, plates and screws were fixed to synthetic osteoporotic bone that had a 1 mm thick synthetic cortical shell. An 8-hole, 3.5 mm thick hybrid plate was fixed with either two 3.5 mm major diameter locking screws or two 4.0 mm major diameter cancellous screws. Forces were applied at 0, 45, and 90 degrees to the plate normal. Eight specimens were loaded to failure for each group. When loads were applied normal to the plate, the nonlocking construct failed initially at higher loads (123.2 ± 13.2 N) than the locking construct (108.7 ± 7.6 N, P = 0.020). For oblique loads, the locking construct failed at higher mean loads but the difference of means was not statistically significant (167.7 ± 14.9 N compared to 154.2 ± 9.4 N, P = 0.052). For loads parallel to the plate, the locking construct was much stronger than the nonlocking construct (1591 ± 227 N compared to 913 ± 237 N, P < 0.001). Stiffness and Energy outcomes are also compared.

      PubDate: 2015-10-02T04:54:29Z
  • Evaluation of in-vivo measurement errors associated with micro-computed
           tomography scans by means of the bone surface distance approach
    • Abstract: Publication date: Available online 1 October 2015
      Source:Medical Engineering & Physics
      Author(s): Yongtao Lu, Maya Boudiffa, Enrico Dall'Ara, Ilaria Bellantuono, Marco Viceconti
      In vivo micro-computed tomography (µCT) scanning is an important tool for longitudinal monitoring of the bone adaptation process in animal models. However, the errors associated with the usage of in vivo µCT measurements for the evaluation of bone adaptations remain unclear. The aim of this study was to evaluate the measurement errors using the bone surface distance approach. The right tibiae of eight 14-week-old C57BL/6 J female mice were consecutively scanned four times in an in vivo µCT scanner using a nominal isotropic image voxel size (10.4 µm) and the tibiae were repositioned between each scan. The repeated scan image datasets were aligned to the corresponding baseline (first) scan image dataset using rigid registration and a region of interest was selected in the proximal tibia metaphysis for analysis. The bone surface distances between the repeated and the baseline scan datasets were evaluated. It was found that the average (±standard deviation) median and 95th percentile bone surface distances were 3.10 ± 0.76 µm and 9.58 ± 1.70 µm, respectively. This study indicated that there were inevitable errors associated with the in vivo µCT measurements of bone microarchitecture and these errors should be taken into account for a better interpretation of bone adaptations measured with in vivo µCT.

      PubDate: 2015-10-02T04:54:29Z
  • The development and testing of a system for wheelchair stability
    • Abstract: Publication date: Available online 26 September 2015
      Source:Medical Engineering & Physics
      Author(s): Dimitar Stefanov, Alexander Avtanski, Nigel Shapcott, Paul Magee, Paul Dryer, Simon Fielden, Mike Heelis, Jill Evans, Louise Moody
      Wheelchair stability has an impact on safety as well as wheelchair performance, propulsion and manoeuvrability. Wheelchair stability is affected by the addition of life-supporting heavy equipment, e.g. ventilators and oxygen cylinders, as well as the characteristics of the user e.g. limb amputations, obesity. The aim of the research described here was to develop and test a stability assessment system that would guide and support the adjustment of wheelchairs to individual needs, characteristics and lifestyles. The resulting system provides assessment of centre of gravity and wheelchair stability and calculates the wheelchair tipping angles. The system consists of a force platform that senses the weight distribution of the wheelchair and calculates the centres of the contact points of the wheels and the distances between them. The measurement data are transferred via a WiFi connection to a portable tablet computer where wheelchair stability parameters are calculated. A touchscreen GUI provides visualization of the stability results and navigation through the measurement modes. The developed new concept has been evaluated through technical laboratory-based testing to determine the validity of the data collected. Initial testing has been undertaken within the clinical setting in 3 large hospitals in the UK. Initial results suggest that Wheelsense® provides a valuable tool to support clinical judgement.

      PubDate: 2015-09-28T04:21:26Z
  • Modeling of unstable pelvic fractures for 20 ° sagittally
           rotated pelvic displacement
    • Abstract: Publication date: Available online 19 September 2015
      Source:Medical Engineering & Physics
      Author(s): Xinbao Wu, Yu'neng Li, Xu Sun, Jianshun Wang, Chunpeng Zhao, Minghui Yang, Shiwen Zhu, Qiyong Cao, Honghua Wu, Manyi Wang
      Early and accurate assessment of unstable pelvic fractures decreases mortality and morbidity by improving the outcomes of closed reduction surgery. In some circumstances (such as in developing countries or in acute trauma), accurate computed tomography (CT) 3D reconstructions are difficult to obtain and plain radiography must be relied upon for surgical planning. Therefore, a simulation model of pelvic displacement was evaluated as a basis for improving the assessment of pelvic fracture displacement from plain radiography images. The simulated model was based on a modified anteroposterior (AP) view of the pelvis constructed using anatomical data. Plain radiography imaging data of sagittal 20 ° hemipelvic rotation, similar to that observed in trauma, was obtained from the simulated model and were compared with normal pelvic rings from 10 cadaveric specimens (actual model). For each data set, the anterior superior iliac spine and ipsilateral pubic symphysis were measured on both sides. There was no significant difference between pelvic sides in the simulated and actual models (P = 0.870). Furthermore, no significant difference was found between the rotational degree of each pelvis based on calculated or simulated degrees and the 20 ° rotational angle (P = 0.322). A simulation model based on plain radiography of pelvic displacement could contribute to the optimal surgical management of unstable pelvic fractures without relying on CT.

      PubDate: 2015-09-24T04:03:30Z
  • Rolling resistance and propulsion efficiency of manual and power-assisted
    • Abstract: Publication date: Available online 12 September 2015
      Source:Medical Engineering & Physics
      Author(s): Efthymia Pavlidou, Marieke G.M. Kloosterman, Jaap H. Buurke, Johan S. Rietman, Thomas W.J. Janssen
      Rolling resistance is one of the main forces resisting wheelchair propulsion and thus affecting stress exerted on the upper limbs. The present study investigates the differences in rolling resistance, propulsion efficiency and energy expenditure required by the user during power-assisted and manual propulsion. Different tire pressures (50%, 75%, 100%) and two different levels of motor assistance were tested. Drag force, energy expenditure and propulsion efficiency were measured in 10 able-bodied individuals under different experimental settings on a treadmill. Results showed that drag force levels were significantly higher in the 50%, compared to the 75% and 100% inflation conditions. In terms of wheelchair type, the manual wheelchair displayed significantly lower drag force values than the power-assisted one. The use of extra-power-assisted wheelchair appeared to be significantly superior to conventional power-assisted and manual wheelchairs concerning both propulsion efficiency and energy expenditure required by the user. Overall, the results of the study suggest that the use of power-assisted wheelchair was more efficient and required less energy input by the user, depending on the motor assistance provided.

      PubDate: 2015-09-16T02:50:17Z
  • Automatic detection of selective arterial devices for advanced
           visualization during abdominal aortic aneurysm endovascular repair
    • Abstract: Publication date: Available online 9 September 2015
      Source:Medical Engineering & Physics
      Author(s): Simon Lessard, Claude Kauffmann, Marcus Pfister, Guy Cloutier, Éric Thérasse, Jacques A. de Guise, Gilles Soulez
      Here we address the automatic segmentation of endovascular devices used in the endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) that deform vascular tissues. Using this approach, the vascular structure is automatically reshaped solving the issue of misregistration observed on 2D/3D image fusion for EVAR guidance. The endovascular devices we considered are the graduated pigtail catheter (PC) used for contrast injection and the stent-graft delivery device (DD). The segmentation of the DD was enhanced using an asymmetric Frangi filter. The segmented geometries were then analysed using their specific features to remove artefacts. The radiopaque markers of the PC were enhanced using a fusion of Hessian and newly introduced gradient norm shift filters. Extensive experiments were performed using a database of images taken during 28 AAA-EVAR interventions. This dataset was divided into two parts: the first half was used to optimize parameters and the second to compile performances using optimal values obtained. The radiopaque markers of the PC were detected with a sensitivity of 88.3% and a positive predictive value (PPV) of 96%. The PC can therefore be positioned with a majority of its markers localized while the artefacts were all located inside the vessel lumen. The major parts of the DD, the dilatator tip and the pusher surfaces, were detected accurately with a sensitivity of 85.9% and a PPV of 88.7%. The less visible part of the DD, the stent enclosed within the sheath, was segmented with a sensitivity of 63.4% because the radiopacity of this region is low and uneven. The centreline of the DD in this stent region was alternatively traced within a 0.74 mm mean error. The automatic segmentation of endovascular devices during EVAR is feasible and accurate; it could be useful to perform elastic registration of the vascular lumen during endovascular repair.

      PubDate: 2015-09-11T20:00:51Z
  • Exploring inter-subject anatomic variability using a population of
           patient-specific femurs and a statistical shape and intensity model
    • Abstract: Publication date: Available online 9 September 2015
      Source:Medical Engineering & Physics
      Author(s): Mamadou T. Bah, Junfen Shi, Martin Browne, Yanneck Suchier, Fabien Lefebvre, Philippe Young, Leonard King, Doug G. Dunlop, Markus O. Heller
      This paper is motivated by the need to accurately and efficiently measure key periosteal and endosteal parameters of the femur, known to critically influence hip biomechanics following arthroplasty. The proposed approach uses statistical shape and intensity models (SSIMs) to represent the variability across a wide range of patients, in terms of femoral shape and bone density. The approach feasibility is demonstrated by using a training dataset of computer tomography scans from British subjects aged 25–106 years (75 male and 34 female). For each gender, a thousand new virtual femur geometries were generated using a subset of principal components required to capture 95% of the variance in both female and male training datasets. Significant differences were found in basic anatomic parameters between females and males: anteversion, CCD angle, femur and neck lengths, head offsets and radius, cortical thickness, densities in both Gruen and neck zones. The measured anteversion for female subjects was found to be twice as high as that for male subjects: 13 ± 6.4° vs. 6.3 ± 7.8° using the training datasets compared to 12.96 ± 6.68 vs. 5.83 ± 9.2 using the thousand virtual femurs. No significant differences were found in canal flare indexes. The proposed methodology is a valuable tool for automatically generating a large specific population of femurs, targeting specific patients, supporting implant design and femoral reconstructive surgery.

      PubDate: 2015-09-11T20:00:51Z
  • Influence of dual-task on sit-to-stand-to-sit postural control in
           Parkinson's disease
    • Abstract: Publication date: Available online 9 September 2015
      Source:Medical Engineering & Physics
      Author(s): Ângela Fernandes, Andreia S.P. Sousa, Joana Couras, Nuno Rocha, João Manuel R.S. Tavares
      Postural control deficits are the most disabling aspects of Parkinson's disease (PD), resulting in decreased mobility and functional independence. The aim of this study was to assess the postural control stability, revealed by variables based on the centre of pressure (CoP), in individuals with PD while performing a sit-to-stand-to-sit sequence under single- and dual-task conditions. An observational, analytical and cross-sectional study was performed. The sample consisted of 9 individuals with PD and 9 healthy controls. A force platform was used to measure the CoP displacement and velocity during the sit-to-stand-to-sit sequence. The results were statistically analysed. Individuals with PD required greater durations for the sit-to-stand-to-sit sequence than the controls (p < 0.05). The anteroposterior and mediolateral CoP displacement were higher in the individuals with PD (p < 0.05). However, only the anteroposterior CoP velocity in the stand-to-sit phase (p = 0.006) was lower in the same individuals. Comparing the single- and dual-task conditions in both groups, the duration, the anteroposterior CoP displacement and velocity were higher in the dual-task condition (p < 0.05). The individuals with PD presented reduced postural control stability during the sit-to-stand-to-sit sequence, especially when under the dual-task condition. These individuals have deficits not only in motor performance, but also in cognitive performance when performing the sit-to-stand-to-sit sequence in their daily life tasks. Moreover, both deficits tend to be intensified when two tasks are performed simultaneously.

      PubDate: 2015-09-11T20:00:51Z
  • Understanding particle margination in blood flow – A step toward
           optimized drug delivery systems
    • Abstract: Publication date: Available online 4 September 2015
      Source:Medical Engineering & Physics
      Author(s): Kathrin Müller, Dmitry A. Fedosov, Gerhard Gompper
      Targeted delivery of drugs and imaging agents is very promising to develop new strategies for the treatment of various diseases such as cancer. For an efficient targeted adhesion, the particles have to migrate toward the walls in blood flow – a process referred to as margination. Due to a huge diversity of available carriers, a good understanding of their margination properties in blood flow depending on various flow conditions and particle properties is required. We employ a particle-based mesoscopic hydrodynamic simulation approach to investigate the margination of different carriers for a wide range of hematocrits (volume fraction of red blood cells) and flow rates. Our results show that margination strongly depends on the thickness of the available free space close to the wall, the so-called red blood cell-free layer (RBC-FL), in comparison to the carrier size. The carriers with a few micrometers in size are comparable with the RBC-FL thickness and marginate better than their sub-micrometer counterparts. Deformable carriers, in general, show worse margination properties than rigid particles. Particle margination is also found to be most pronounced in small channels with a characteristic size comparable to blood capillaries. Finally, different margination mechanisms are discussed.

      PubDate: 2015-09-08T07:59:14Z
  • Determination of pulse profile characteristics of multi spot retinal
           photocoagulation lasers
    • Abstract: Publication date: Available online 4 September 2015
      Source:Medical Engineering & Physics
      Author(s): Douglas McG. Clarkson, Osama Makhzoum, John Blackburn
      A system is described for determination of discrete pulse train characteristics of multi spot laser delivery systems for retinal photocoagulation. While photodiodes provide an ideal detection mechanism, measurement artifacts can potentially be introduced by the spatial pattern of the delivered beam relative to a discrete photodiode element. This problem was overcome by use of an integrating sphere to produce a uniform light field at the site of the photodiode detector. A basic current driven photodiode detection circuit incorporating an operational amplifier was used to generate a signal captured by a commercially available USB interface device at a rate of 10 kHz. Studies were undertaken of a Topcon Pascal Streamline laser system with output at a wavelength of 577 nm (yellow). This laser features the proprietary feature of ‘Endpoint Management’ ™ where pulses can be delivered as 100% of set energy levels with visible reaction on the retina and also at a reduced energy level to create potentially non visible but clinically effective lesions. Using the pulse train measurement device it was identified that the ‘Endpoint Management’ ™ delivery mode of pulses of lower energy was achieved by reducing the pulse duration of pulses for non-visible effect pulses while maintaining consistent beam power levels within the delivered pulse profile. The effect of eye geometry in determining safety and effectiveness of multi spot laser delivery for retinal photocoagulation is discussed.

      PubDate: 2015-09-08T07:59:14Z
  • The effect of cup outer sizes on the contact mechanics and cement fixation
           of cemented total hip replacements
    • Abstract: Publication date: Available online 4 September 2015
      Source:Medical Engineering & Physics
      Author(s): Xijin Hua, Junyan Li, Ling Wang, Ruth Wilcox, John Fisher, Zhongmin Jin
      One important loosening mechanism of the cemented total hip arthroplasty is the mechanical overload at the bone-cement interface and consequent failure of the cement fixation. Clinical studies have revealed that the outer diameter of the acetabular component is a key factor in influencing aseptic loosening of the hip arthroplasty. The aim of the present study was to investigate the influence of the cup outer diameter on the contact mechanics and cement fixation of a cemented total hip replacement (THR) with different wear penetration depths and under different cup inclination angles using finite element (FE) method. A three-dimensional FE model was developed based on a typical Charnley hip prosthesis. Two acetabular cup designs with outer diameters of 40 and 43 mm were modelled and the effect of cup outer diameter, penetration depth and cup inclination angle on the contact mechanics and cement fixation stresses in the cemented THR were studied. The results showed that for all penetration depths and cup inclination angles considered, the contact mechanics in terms of peak von Mises stress in the acetabular cup and peak contact pressure at the bearing surface for the two cup designs were similar (within 5%). However, the peak von Mises stress, the peak maximum principal stress and peak shear stress in the cement mantle at the bone-cement interface for the 43 mm diameter cup design were predicted to be lower compared to those for the 40 mm diameter cup design. The differences were predicted to be 15–19%, 15–22% and 18–20% respectively for different cup penetration depths and inclination angles, which compares to the clinical difference of aseptic loosening incidence of about 20% between the two cup designs.

      PubDate: 2015-09-08T07:59:14Z
  • A device for characterising the mechanical properties of the plantar soft
           tissue of the foot
    • Abstract: Publication date: Available online 4 September 2015
      Source:Medical Engineering & Physics
      Author(s): D Parker, G Cooper, S Pearson, G Crofts, D Howard, P. Busby, C Nester
      The plantar soft tissue is a highly functional viscoelastic structure involved in transferring load to the human body during walking. A Soft Tissue Response Imaging Device was developed to apply a vertical compression to the plantar soft tissue whilst measuring the mechanical response via a combined load cell and ultrasound imaging arrangement. Accuracy of motion compared to input profiles; validation of the response measured for standard materials in compression; variability of force and displacement measures for consecutive compressive cycles; and implementation in vivo with five healthy participants. Static displacement displayed average error of 0.04 mm (range of 15 mm), and static load displayed average error of 0.15 N (range of 250 N). Validation tests showed acceptable agreement compared to a Houndsfield tensometer for both displacement (CMC > 0.99 RMSE > 0.18 mm) and load (CMC > 0.95 RMSE < 4.86 N). Device motion was highly repeatable for bench-top tests (ICC = 0.99) and participant trials (CMC = 1.00). Soft tissue response was found repeatable for intra (CMC > 0.98) and inter trials (CMC > 0.70). The device has been shown to be capable of implementing complex loading patterns similar to gait, and of capturing the compressive response of the plantar soft tissue for a range of loading conditions in vivo.

      PubDate: 2015-09-08T07:59:14Z
  • Implementation of boundary conditions in modeling the femur is critical
           for the evaluation of distal intramedullary nailing
    • Abstract: Publication date: Available online 2 September 2015
      Source:Medical Engineering & Physics
      Author(s): Riza Bayoglu, A. Fethi Okyar
      In previous numerical and experimental studies of the intramedullary nail-implanted human femur several simplifications to model the boundary and loading conditions during pre-clinical testing have been proposed. The distal end of the femur was fixed in the majority of studies dealing with the biomechanics of the lower extremity, be it numerical or experimental, which resulted in obviously non-physiological deflections. Per contra, Speirs et al. (2007) proclaimed physiological deflections as a result of constraining the femur in a novel statically determinate fashion in combination with using a complex set of muscle forces. In tandem with this, we have shown that not only the deflections but also the stress and strain predictions turn out to be much lower in magnitude, as a result of using the latter approach. To illustrate the dramatic change in results, we compared these results with those of two other models employing commonly used boundary and loading conditions in retrograde stabilization of a distal diaphyseal fracture. The model used herewith resulted in more realistic femoral cortical strains, lower stresses on both the nail and the screws, as well as such deflections in the overall structure.

      PubDate: 2015-09-04T07:31:27Z
  • Effects of frontal and sagittal thorax attitudes in gait on trunk and
           pelvis three-dimensional kinematics
    • Abstract: Publication date: Available online 31 August 2015
      Source:Medical Engineering & Physics
      Author(s): Mickaël Begon, Alberto Leardini, Claudio Belvedere, Nader Farahpour, Paul Allard
      While sagittal trunk inclinations alter upper body biomechanics, little is known about the extent of frontal trunk bending on upper body and pelvis kinematics in adults during gait and its relation to sagittal trunk inclinations. The objective was to determine the effect of the mean lateral trunk attitude on upper body and pelvis three-dimensional kinematics during gait in asymptomatic subjects. Three gait cycles were collected in 30 subjects using a motion analysis system (Vicon 612) and an established protocol. Sub-groups were formed based on the mean thorax lateral bending angle, bending side, and also sagittal tilt. These were compared based on 38 peak angles identified on pelvis, thorax and shoulder kinematics using MANOVAs. A main effect for bending side (p = 0.038) was found, especially for thorax peak angles. Statistics revealed also a significant interaction (p = 0.04993) between bending side and tilt for the thorax sagittal inclination during body-weight transfer. These results reinforce the existence of different gait patterns, which correlate upper body and pelvis motion measures. The results also suggest that frontal and sagittal trunk attitude should be considered carefully when treating a patient with impaired gait.

      PubDate: 2015-09-04T07:31:27Z
  • Numerical analysis of the V-Y advancement flap
    • Abstract: Publication date: Available online 2 September 2015
      Source:Medical Engineering & Physics
      Author(s): D. Remache, J. Chambert, J. Pauchot, E. Jacquet
      The V-Y advancement flap is a usual technique for the closure of skin defects. A triangular flap is incised adjacent to a skin defect of rectangular shape. As the flap is advanced to close the initial defect, two smaller defects in the shape of a parallelogram are formed with respect to a reflection symmetry. The height of the defects depends on the apex angle of the flap and the closure efforts are related to the defects height. Andrades et al. [1] have performed a geometrical analysis of the V-Y flap technique in order to reach a compromise between the flap size and the defects width. However, the geometrical approach does not consider the mechanical properties of the skin. The present analysis based on the finite element method is proposed as a complement to the geometrical one. This analysis aims to highlight the major role of the skin elasticity for a full analysis of the V-Y advancement flap. Furthermore, the study of this technique shows that closing at the flap apex seems mechanically the most interesting step. Thus different strategies of defect closure at the flap apex stemming from surgeon’s know-how have been tested by numerical simulations.

      PubDate: 2015-09-04T07:31:27Z
  • New equations to calculate 3D joint centres in the lower extremities
    • Abstract: Publication date: Available online 28 August 2015
      Source:Medical Engineering & Physics
      Author(s): Martin Sandau, Rikke V. Heimbürger, Chiara Villa, Karl E. Jensen, Thomas B. Moeslund, Henrik Aanæs, Tine Alkjær, Erik B. Simonsen
      Biomechanical movement analysis in 3D requires estimation of joint centres in the lower extremities and this estimation is based on extrapolation from markers placed on anatomical landmarks. The purpose of the present study was to quantify the accuracy of three established set of equations and provide new improved equations to predict the joint centre locations. The ‘true’ joint centres of the knee and ankle joint were obtained in vivo by MRI scans on 10 male subjects whereas the ‘true’ hip joint centre was obtained in 10 male and 10 female cadavers by CT scans. For the hip joint the errors ranged from 26.7 (8.9) to 29.6 (7.5) mm, for the knee joint 5.8 (3.1) to 22.6 (3.3) mm and for the ankle joint 14.4 (2.2) to 27.0 (4.6) mm. This differed significantly from the improved equations by which the error for the hip joint ranged from 8.2 (3.6) to 11.6 (5.6) mm, for the knee joint from 2.9 (2.1) to 4.7 (2.5) mm and for the ankle joint from 3.4 (1.3) to 4.1 (2.0) mm. The coefficients in the new hip joint equations differed significantly between sexes. This difference depends on anatomical differences of the male and female pelvis.

      PubDate: 2015-08-30T07:17:05Z
  • Radio frequency energy harvesting from a feeding source in a passive deep
           brain stimulation device for murine preclinical research
    • Abstract: Publication date: Available online 28 August 2015
      Source:Medical Engineering & Physics
      Author(s): Md Kamal Hosain, Abbas Z. Kouzani, Susannah J. Tye, Mst Fateha Samad, Rajas P. Kale, Kevin E. Bennet, Felicia S. Manciu, Michael Berk
      This paper presents the development of an energy harvesting circuit for use with a head-mountable deep brain stimulation (DBS) device. It consists of a circular planar inverted-F antenna (PIFA) and a Schottky diode-based Cockcroft-Walton 4-voltage rectifier. The PIFA has the volume of π × 102 × 1.5 mm3, resonance frequency of 915 MHz, and bandwidth of 16 MHz (909–925 MHz) at a return loss of −10 dB. The rectifier offers maximum efficiency of 78% for the input power of −5 dBm at a 5 kΩ load resistance. The developed rectenna operates efficiently at 915 MHz for the input power within −15 dBm to +5 dBm. For operating a DBS device, the DC voltage of 2 V is recorded from the rectenna terminal at a distance of 55 cm away from a 26.77 dBm transmitter in free space. An in-vitro test of the DBS device is presented.

      PubDate: 2015-08-30T07:17:05Z
  • Distraction osteogenesis device to estimate the axial stiffness of the
           callus in Vivo
    • Abstract: Publication date: Available online 28 August 2015
      Source:Medical Engineering & Physics
      Author(s): J. Mora-Macías, E. Reina-Romo, J. Domínguez
      Knowing the evolution of callus stiffness is very important in distraction osteogenesis and bone healing. It allows the characterization of the bone maturation process and the assessment of the moment to retire the fixator. A new distractor device that monitors the callus axial stiffness is presented in this study. It quantifies the callus stiffness during the bone transport process with some advantages over previous methods to assess stiffness during simple distraction and bone healing. This device avoids a misalignment between bone segments, uses real load conditions, monitors forces continuously, does not involve radiation for patients, and allows the study of the complete distraction process, i.e., the distraction and consolidation phases. The device was calibrated in vitro simulating different real bone load conditions depending on the stage of the process. The stiffness of the callus could be estimated for values between 4.2 N/mm and 9066.8 N/mm. The average relative error in measurements carried out in in vitro calibration tests was 7.8% during the distraction phase and 9.5% during the consolidation phase. These results improve the accuracy and increase the callus stiffness range of estimation with respect to other devices in the literature. In addition, the device was used successfully in vivo in a preliminary experiment.

      PubDate: 2015-08-30T07:17:05Z
  • Editorial Board
    • Abstract: Publication date: September 2015
      Source:Medical Engineering & Physics, Volume 37, Issue 9

      PubDate: 2015-08-30T07:17:05Z
  • Novel real function based method to construct heterogeneous porous
           scaffolds and additive manufacturing for use in medical engineering
    • Abstract: Publication date: Available online 29 August 2015
      Source:Medical Engineering & Physics
      Author(s): Nan Yang, Yanling Tian, Dawei Zhang
      Heterogeneous porous scaffolds have important applications in biomedical engineering, as they can mimic the structures of natural tissues to achieve the corresponding properties. Here, we introduce a new and easy to implement real function based method for constructing complex, heterogeneous porous structures, including hybrid structures, stochastic structures, functionally gradient structures, and multi-scale structures, or their combinations (e.g., hybrid multi-scale structures). Based on micro-CT data, a femur-mimetic structure with gradient morphology was constructed using our method and fabricated using stereolithography. Results showed that our method could generate gradient porosity or gradient specific surfaces and be sufficiently flexible for use with micro-CT data and additive manufacturing (AM) techniques.

      PubDate: 2015-08-30T07:17:05Z
  • A review of the functionalities of smart walkers
    • Abstract: Publication date: Available online 22 August 2015
      Source:Medical Engineering & Physics
      Author(s): Maria Martins, Cristina Santos, Anselmo Frizera, Ramón Ceres
      There is a need to conceptualize and improve the investigation and developments in assistive devices, focusing on the design and effectiveness of walkers in the user's rehabilitation process and functional compensation. This review surveys the importance of smart walkers in maintaining mobility and discusses their potential in rehabilitation and their demands as assistive devices. It also presents related research in addressing and quantifying the smart walker's efficiency and influence on gait. Besides, it discusses smart walkers focusing on studies related to the concept of autonomous and shared-control and manual guidance, the use of smart walkers as personal helpers to sit-to-stand and diagnostic tools for patients' rehabilitation through the evaluation of their gait.

      PubDate: 2015-08-26T06:59:30Z
  • Effect of power-assisted hand-rim wheelchair propulsion on shoulder load
           in experienced wheelchair users: A pilot study with an instrumented
    • Abstract: Publication date: Available online 22 August 2015
      Source:Medical Engineering & Physics
      Author(s): Marieke G.M. Kloosterman, Jaap H. Buurke, Wiebe de Vries, Lucas H.V. Van der Woude, Johan S. Rietman
      This study aims to compare hand-rim and power-assisted hand-rim propulsion on potential risk factors for shoulder overuse injuries: intensity and repetition of shoulder loading and force generation in the extremes of shoulder motion. Eleven experienced hand-rim wheelchair users propelled an instrumented wheelchair on a treadmill while upper-extremity kinematic, kinetic and surface electromyographical data was collected during propulsion with and without power-assist. As a result during power-assisted propulsion the peak resultant force exerted at the hand-rim decreased and was performed with significantly less abduction and internal rotation at the shoulder. At shoulder level the anterior directed force and internal rotation and flexion moments decreased significantly. In addition, posterior and the minimal inferior directed forces and the external rotation moment significantly increased. The stroke angle decreased significantly, as did maximum shoulder flexion, extension, abduction and internal rotation. Stroke-frequency significantly increased. Muscle activation in the anterior deltoid and pectoralis major also decreased significantly. In conclusion, compared to hand-rim propulsion power-assisted propulsion seems effective in reducing potential risk factors of overuse injuries with the highest gain on decreased range of motion of the shoulder joint, lower peak propulsion force on the rim and reduced muscle activity.

      PubDate: 2015-08-26T06:59:30Z
  • Response of single cell with acute angle exposed to an external electric
    • Abstract: Publication date: Available online 22 August 2015
      Source:Medical Engineering & Physics
      Author(s): Saber Sarbazvatan, Dariush Sardari, Nahid Taheri, Kamran Sepanloo
      It is known that the electric field incurs effects on the living cells. Predicting the response of single cell or multilayer cells to induced alternative or static eclectic field has permanently been a challenge. In the present study a first order single cell with acute angle under the influence of external electric field is considered. The cell division stage or the special condition of reshaping is modelled with a cone being connected. In the case of cell divisions, anaphase, it can be considered with two cones that connected nose-to-nose. Each cone consists of two regions. The first is the membrane modelled with a superficial layer, and the second is cytoplasm at the core. A Laplace equation is written for this model and the distribution of its electric field is a sharp point in the single cell for which an acute angle model is calculated.

      PubDate: 2015-08-26T06:59:30Z
  • A time-dependent model for improved biogalvanic tissue characterisation
    • Abstract: Publication date: Available online 19 August 2015
      Source:Medical Engineering & Physics
      Author(s): J.H. Chandler, P.R. Culmer, D.G. Jayne, A. Neville
      Measurement of the passive electrical resistance of biological tissues through biogalvanic characterisation has been proposed as a simple means of distinguishing healthy from diseased tissue. This method has the potential to provide valuable real-time information when integrated into surgical tools. Characterised tissue resistance values have been shown to be particularly sensitive to external load switching direction and rate, bringing into question the stability and efficacy of the technique. These errors are due to transient variations observed in measurement data that are not accounted for in current electrical models. The presented research proposes the addition of a time-dependent element to the characterisation model to account for losses associated with this transient behaviour. Influence of switching rate has been examined, with the inclusion of transient elements improving the repeatability of the characterised tissue resistance. Application of this model to repeat biogalvanic measurements on a single ex vivo human colon tissue sample with healthy and cancerous (adenocarcinoma) regions showed a statistically significant difference (p < 0.05) between tissue types. In contrast, an insignificant difference (p > 0.05) between tissue types was found when measurements were subjected to the current model, suggesting that the proposed model may allow for improved biogalvanic tissue characterisation.

      PubDate: 2015-08-22T06:19:53Z
  • Validation of a method for combining biplanar radiography and magnetic
           resonance imaging to estimate knee cartilage contact
    • Abstract: Publication date: Available online 21 August 2015
      Source:Medical Engineering & Physics
      Author(s): Eric Thorhauer, Scott Tashman
      Combining accurate bone kinematics data from biplane radiography with cartilage models from magnetic resonance imaging, it is possible to estimate tibiofemoral cartilage contact area and centroid location. Proper validation of such estimates, however, has not been performed under loading conditions approximating functional tasks, such as gait, squatting, and stair descent. The goal of this study was to perform an in vitro validation to resolve the accuracy of cartilage contact estimations in comparison to a laser scanning gold standard. Results demonstrated acceptable reliability and accuracy for both contact area and centroid location estimates. Root mean square errors in contact area averaged 8.4% and 4.4% of the medial and lateral compartmental areas, respectively. Modified Sorensen-Dice agreement scores of contact regions averaged 0.81 ± 0.07 for medial and 0.83 ± 0.07 for lateral compartments. These validated methods have applications for in vivo assessment of a variety of patient populations and physical activities, and may lead to greater understanding of the relationships between knee cartilage function, effects of joint injury and treatment, and the development of osteoarthritis.

      PubDate: 2015-08-22T06:19:53Z
  • Influence of contextual task constraints on preferred stride parameters
           and their variabilities during human walking
    • Abstract: Publication date: Available online 4 August 2015
      Source:Medical Engineering & Physics
      Author(s): Lauro V. Ojeda, John R. Rebula, Arthur D. Kuo, Peter G. Adamczyk
      Walking is not always a free and unencumbered task. Everyday activities such as walking in pairs, in groups, or on structured walkways can limit the acceptable gait patterns, leading to motor behavior that differs from that observed in more self-selected gait. Such different contexts may lead to gait performance different than observed in typical laboratory experiments, for example, during treadmill walking. We sought to systematically measure the impact of such task constraints by comparing gait parameters and their variability during walking in different conditions over-ground, and on a treadmill. We reconstructed foot motion from foot-mounted inertial sensors, and characterized forward, lateral and angular foot placement while subjects walked over-ground in a straight hallway and on a treadmill. Over-ground walking was performed in three variations: with no constraints (self-selected, SS); while deliberately varying walking speed (self-varied, SV); and while following a toy pace car programmed to vary speed (externally-varied, EV). We expected that these conditions would exhibit a statistically similar relationship between stride length and speed, and between stride length and stride period. We also expected treadmill walking (TM) would differ in two ways: first, that variability in stride length and stride period would conform to a constant-speed constraint opposite in slope from the normal relationship; and second, that stride length would decrease, leading to combinations of stride length and speed not observed in over-ground conditions. Results showed that all over-ground conditions used similar stride length-speed relationships, and that variability in treadmill walking conformed to a constant-speed constraint line, as expected. Decreased stride length was observed in both TM and EV conditions, suggesting adaptations due to heightened awareness or to prepare for unexpected changes or problems. We also evaluated stride variability in constrained and unconstrained tasks. We observed that in treadmill walking, lateral variability decreased while forward variability increased, and the normally-observed correlation between wider foot placement and external foot rotation was eliminated. Preferred stride parameters and their variability appear significantly influenced by the context and constraints of the walking task.

      PubDate: 2015-08-06T03:53:11Z
  • A comparison of public datasets for acceleration-based fall detection
    • Abstract: Publication date: Available online 29 July 2015
      Source:Medical Engineering & Physics
      Author(s): Raul Igual, Carlos Medrano, Inmaculada Plaza
      Falls are one of the leading causes of mortality among the older population, being the rapid detection of a fall a key factor to mitigate its main adverse health consequences. In this context, several authors have conducted studies on acceleration-based fall detection using external accelerometers or smartphones. The published detection rates are diverse, sometimes close to a perfect detector. This divergence may be explained by the difficulties in comparing different fall detection studies in a fair play since each study uses its own dataset obtained under different conditions. In this regard, several datasets have been made publicly available recently. This paper presents a comparison, to the best of our knowledge for the first time, of these public fall detection datasets in order to determine whether they have an influence on the declared performances. Using two different detection algorithms, the study shows that the performances of the fall detection techniques are affected, to a greater or lesser extent, by the specific datasets used to validate them. We have also found large differences in the generalization capability of a fall detector depending on the dataset used for training. In fact, the performance decreases dramatically when the algorithms are tested on a dataset different from the one used for training. Other characteristics of the datasets like the number of training samples also have an influence on the performance while algorithms seem less sensitive to the sampling frequency or the acceleration range.
      Graphical abstract image

      PubDate: 2015-08-02T03:33:52Z
  • Failure location prediction by finite element analysis for an additive
           manufactured mandible implant
    • Abstract: Publication date: Available online 27 July 2015
      Source:Medical Engineering & Physics
      Author(s): Jinxing Huo, Per Dérand, Lars-Erik Rännar, Jan-Michaél Hirsch, E. Kristofer Gamstedt
      In order to reconstruct a patient with a bone defect in the mandible, a porous scaffold attached to a plate, both in a titanium alloy, was designed and manufactured using additive manufacturing. Regrettably, the implant fractured in vivo several months after surgery. The aim of this study was to investigate the failure of the implant and show a way of predicting the mechanical properties of the implant before surgery. All computed tomography data of the patient were preprocessed to remove metallic artefacts with metal deletion technique before mandible geometry reconstruction. The three-dimensional geometry of the patient's mandible was also reconstructed, and the implant was fixed to the bone model with screws in Mimics medical imaging software. A finite element model was established from the assembly of the mandible and the implant to study stresses developed during mastication. The stress distribution in the load-bearing plate was computed, and the location of main stress concentration in the plate was determined. Comparison between the fracture region and the location of the stress concentration shows that finite element analysis could serve as a tool for optimizing the design of mandible implants.

      PubDate: 2015-07-28T20:58:54Z
  • Tailoring the hybrid palliation for hypoplastic left heart syndrome: A
           simulation study using a lumped parameter model
    • Abstract: Publication date: Available online 26 July 2015
      Source:Medical Engineering & Physics
      Author(s): A. Di Molfetta, M. Pilati, M.G. Gagliardi, L. Fresiello, A. Amodeo, A. Cristofaletti, G. Pongiglione, G. Ferrari
      The results of Hybrid procedure (HP) for the hypoplastic left heart syndrome (HLHS) depend on several variables: pulmonary artery banding tightness (PAB), atrial septal defect size (ASD) and patent ductus arteriosus stent size (PDA). A HP complication could be the aortic coarctaction (CoAo). The reverse Blalock–Taussig shunt (RevBT) placement was proposed to avoid CoAo effects. This work aims at developing a lumped parameter model (LPM) to investigate the effects of the different variables on HP haemodynamics. A preliminary verification was performed collecting measurements on a newborn HLHS patient to calculate LPM input parameters to reproduce patient's baseline. Results suggest that haemodynamics is affected by ASD (ASD: 0.15–0.55 cm, pulmonary to systemic flow ratio Q p/Q s: 0.73–1, cardiac output (CO): 1–1.5 l/min and ventricular stroke work SW: 336–577 ml mmHg) and by the PAB diameter (PAB: 0.07–0.2 cm, Q p/Q s: 0.46–2.1, CO: 1.3–1.6 l/min and SW: 591–535 ml mmHg). Haemodynamics was neither affected by RevBT diameter nor by PDA diameter higher than 0.2 cm. RevBT implantation does not change the HP haemodynamics, but it can make the CoAo effect negligible. LPM could be useful to support clinical decision in complex physiopathology and to calibrate and personalise the parameters that play a role on flow distribution.

      PubDate: 2015-07-28T20:58:54Z
  • Surrogate modeling of deformable joint contact using artificial neural
    • Abstract: Publication date: Available online 26 July 2015
      Source:Medical Engineering & Physics
      Author(s): Ilan Eskinazi, Benjamin J. Fregly
      Deformable joint contact models can be used to estimate loading conditions for cartilage–cartilage, implant–implant, human–orthotic, and foot–ground interactions. However, contact evaluations are often so expensive computationally that they can be prohibitive for simulations or optimizations requiring thousands or even millions of contact evaluations. To overcome this limitation, we developed a novel surrogate contact modeling method based on artificial neural networks (ANNs). The method uses special sampling techniques to gather input–output data points from an original (slow) contact model in multiple domains of input space, where each domain represents a different physical situation likely to be encountered. For each contact force and torque output by the original contact model, a multi-layer feed-forward ANN is defined, trained, and incorporated into a surrogate contact model. As an evaluation problem, we created an ANN-based surrogate contact model of an artificial tibiofemoral joint using over 75,000 evaluations of a fine-grid elastic foundation (EF) contact model. The surrogate contact model computed contact forces and torques about 1000 times faster than a less accurate coarse grid EF contact model. Furthermore, the surrogate contact model was seven times more accurate than the coarse grid EF contact model within the input domain of a walking motion. For larger input domains, the surrogate contact model showed the expected trend of increasing error with increasing domain size. In addition, the surrogate contact model was able to identify out-of-contact situations with high accuracy. Computational contact models created using our proposed ANN approach may remove an important computational bottleneck from musculoskeletal simulations or optimizations incorporating deformable joint contact models.

      PubDate: 2015-07-28T20:58:54Z
  • An integrated CAD/CAM/robotic milling method for custom cementless femoral
    • Abstract: Publication date: Available online 22 July 2015
      Source:Medical Engineering & Physics
      Author(s): Xi Wen-ming, Wang Ai-min, Wu Qi, Liu Chang-Hua, Zhu Jian-fei, Xia Fang-fang
      Aseptic loosening is the primary cause of cementless femoral prosthesis failure and is related to the primary stability of the cementless femoral prosthesis in the femoral cavity. The primary stability affects both the osseointegration and the long-term stability of cementless femoral prostheses. A custom cementless femoral prosthesis can improve the fit and fill of the prosthesis in the femoral cavity and decrease the micromotion of the proximal prosthesis such that the primary stability of the custom prosthesis can be improved, and osseointegration of the proximal prosthesis is achieved. These results will help to achieve long-term stability in total hip arthroplasty (THA). In this paper, we introduce an integrated CAD/CAM/robotic method of milling custom cementless femoral prostheses. The 3D reconstruction model uses femoral CT images and 3D design software to design a CAD model of the custom prosthesis. After the transformation matrices between two units of the robotic system are calibrated, consistency between the CAM software and the robotic system can be achieved, and errors in the robotic milling can be limited. According to the CAD model of the custom prosthesis, the positions of the robotic tool points are produced by the CAM software of the CNC machine. The normal vector of the three adjacent robotic tool point positions determines the pose of the robotic tool point. In conclusion, the fit rate of custom pig femur stems in the femoral cavities was 90.84%. After custom femoral prostheses were inserted into the femoral cavities, the maximum gaps between the prostheses and the cavities measured less than 1 mm at the diaphysis and 1.3 mm at the metaphysis.

      PubDate: 2015-07-24T10:56:39Z
  • Comparison of the bending performance of solid and cannulated spinal
           pedicle screws using finite element analyses and biomechanical tests
    • Abstract: Publication date: Available online 21 July 2015
      Source:Medical Engineering & Physics
      Author(s): Kao-Shang Shih, Ching-Chi Hsu, Sheng-Mou Hou, Shan-Chuen Yu, Chen-Kun Liaw
      Spinal pedicle screw fixations have been used extensively to treat fracture, tumor, infection, or degeneration of the spine. Cannulated spinal pedicle screws with bone cement augmentation might be a useful method to ameliorate screw loosening. However, cannulated spinal pedicle screws might also increase the risk of screw breakage. Thus, the purpose of this study was to investigate the bending performance of different spinal pedicle screws with either solid design or cannulated design. Three-dimensional finite element models, which consisted of the spinal pedicle screw and the screw's hosting material, were first constructed. Next, monotonic and cyclic cantilever bending tests were both applied to validate the results of the finite element analyses. Finally, both the numerical and experimental approaches were evaluated and compared. The results indicated that the cylindrical spinal pedicle screws with a cannulated design had significantly poorer bending performance. In addition, conical spinal pedicle screws maintained the original bending performance, whether they were solid or of cannulated design. This study may provide useful recommendations to orthopedic surgeons before surgery, and it may also provide design rationales to biomechanical engineers during the development of spinal pedicle screws.

      PubDate: 2015-07-24T10:56:39Z
  • Detection of central fixation using short-time autoregressive spectral
           estimation during retinal birefringence scanning
    • Abstract: Publication date: Available online 23 July 2015
      Source:Medical Engineering & Physics
      Author(s): Boris I. Gramatikov
      The manuscript reports on the implementation of autoregressive spectral estimation aimed at improving the accuracy of detecting short-lasting events in signals acquired by a retinal birefringence scanning device that was reported earlier. A signal consisting of two frequency components is generated, where each frequency is a multiple of the scanning frequency. One frequency is produced during central fixation, while another one prevails during off-central fixation. These components may be of a very short duration, presenting a challenge for the FFT to identify them with sufficient time- and frequency resolution. Autoregressive spectral estimation using the Burg algorithm provided a satisfactory solution, capable of reliably differentiating between the two frequency components (96 and 192 Hz) on signal segments of duration as short as 5 ms. The device and the signal analysis methods were developed originally with the purpose of checking for eye alignment and strabismus – a major risk factor for amblyopia. The method enables the technology to work with less-cooperative patients, such as young children. Other medical and non-medical applications are possible.

      PubDate: 2015-07-24T10:56:39Z
  • Accuracy assessment of 3D bone reconstructions using CT: an intro
    • Abstract: Publication date: August 2015
      Source:Medical Engineering & Physics, Volume 37, Issue 8
      Author(s): Emily A. Lalone, Ryan T. Willing, Hannah L. Shannon, Graham J.W. King, James A. Johnson
      Computed tomography provides high contrast imaging of the joint anatomy and is used routinely to reconstruct 3D models of the osseous and cartilage geometry (CT arthrography) for use in the design of orthopedic implants, for computer assisted surgeries and computational dynamic and structural analysis. The objective of this study was to assess the accuracy of bone and cartilage surface model reconstructions by comparing reconstructed geometries with bone digitizations obtained using an optical tracking system. Bone surface digitizations obtained in this study determined the ground truth measure for the underlying geometry. We evaluated the use of a commercially available reconstruction technique using clinical CT scanning protocols using the elbow joint as an example of a surface with complex geometry. To assess the accuracies of the reconstructed models (8 fresh frozen cadaveric specimens) against the ground truth bony digitization—as defined by this study—proximity mapping was used to calculate residual error. The overall mean error was less than 0.4 mm in the cortical region and 0.3 mm in the subchondral region of the bone. Similarly creating 3D cartilage surface models from CT scans using air contrast had a mean error of less than 0.3 mm. Results from this study indicate that clinical CT scanning protocols and commonly used and commercially available reconstruction algorithms can create models which accurately represent the true geometry.

      PubDate: 2015-07-24T10:56:39Z
  • Editorial Board
    • Abstract: Publication date: August 2015
      Source:Medical Engineering & Physics, Volume 37, Issue 8

      PubDate: 2015-07-24T10:56:39Z
  • Numerical evaluation of sequential bone drilling strategies based on
           thermal damage
    • Abstract: Publication date: Available online 7 July 2015
      Source:Medical Engineering & Physics
      Author(s): Bruce L. Tai , Andrew C. Palmisano , Barry Belmont , Todd A Irwin , James Holmes , Albert J. Shih
      Sequentially drilling multiple holes in bone is used clinically for surface preparation to aid in fusion of a joint, typically under non-irrigated conditions. Drilling induces a significant amount of heat and accumulates after multiple passes, which can result in thermal osteonecrosis and various complications. To understand the heat propagation over time, a 3D finite element model was developed to simulate sequential bone drilling. By incorporating proper material properties and a modified bone necrosis criteria, this model can visualize the propagation of damaged areas. For this study, comparisons between a 2.0 mm Kirschner wire and 2.0 mm twist drill were conducted with their heat sources determined using an inverse method and experimentally measured bone temperatures. Three clinically viable solutions to reduce thermally-induced bone damage were evaluated using finite element analysis, including tool selection, time interval between passes, and different drilling sequences. Results show that the ideal solution would be using twist drills rather than Kirschner wires if the situation allows. A shorter time interval between passes was also found to be beneficial as it reduces the total heat exposure time. Lastly, optimizing the drilling sequence reduced the thermal damage of bone, but the effect may be limited. This study demonstrates the feasibility of using the proposed model to study clinical issues and find potential solutions prior to clinical trials.

      PubDate: 2015-07-12T10:07:23Z
  • Breakdown of deterministic lateral displacement efficiency for non-dilute
           suspensions: A numerical study
    • Abstract: Publication date: Available online 2 July 2015
      Source:Medical Engineering & Physics
      Author(s): R. Vernekar , T. Krüger
      We investigate the effect of particle volume fraction on the efficiency of deterministic lateral displacement (DLD) devices. DLD is a popular passive sorting technique for microfluidic applications. Yet, it has been designed for treating dilute suspensions, and its efficiency for denser samples is not well known. We perform 3D simulations based on the immersed-boundary, lattice-Boltzmann and finite-element methods to model the flow of red blood cells (RBCs) in different DLD devices. We quantify the DLD efficiency in terms of appropriate “failure” probabilities and RBC counts in designated device outlets. Our main result is that the displacement mode breaks down upon an increase of RBC volume fraction, while the zigzag mode remains relatively robust. This suggests that the separation of larger particles (such as white blood cells) from a dense RBC background is simpler than separating smaller particles (such as platelets) from the same background. The observed breakdown stems from non-deterministic particle collisions interfering with the designed deterministic nature of DLD devices. Therefore, we postulate that dense suspension effects generally hamper efficient particle separation in devices based on deterministic principles.

      PubDate: 2015-07-07T15:00:04Z
  • Design and testing of a high-speed treadmill to measure ground reaction
           forces at the limit of human gait
    • Abstract: Publication date: Available online 2 July 2015
      Source:Medical Engineering & Physics
      Author(s): Matthew W. Bundle , Michael O. Powell , Laurence J. Ryan
      Investigations focused on the gait and physiological limits of human speed have been on-going for more than a century. However, due to measurement limitation a kinetic understanding of the foot-ground collision and how these dynamics differ between individuals to confer speed and limit gait has only recently begun to come forth. Therefore, we designed and tested an instrumented high-speed force treadmill to measure the forces occurring at the limits of human performance. The treadmill was designed to maximize flexural stiffness and natural frequency by using a honeycomb sandwich panel as the bed surface and a flexible drive shaft between the drive roller and servo motor to reduce the mass of the supported elements which contribute to the system's response frequency. The functional performance of the force treadmill met or exceeded the measurement criteria established for ideal force plates: high natural frequency (z-axis = 113 Hz), low crosstalk between components of the force (Fx /Fz = 0.0020[SD = 0.0010]; Fy /Fz = 0.0016[SD = 0.0003]), a linear response (R 2 > 0.999) for loading with known weights (range: 44–3857 N), and an accuracy of 2.5[SD = 1.7] mm and 2.8[SD = 1.5] mm in the x and y-axes, respectively, for the point of force application. In dynamic testing at running speeds up to 10 m s−1, the measured durations and magnitudes of force application were similar between the treadmill and over-ground running using a force platform. This design provides a precise instrumented treadmill capable of recording multi-axis ground reaction forces applied during the foot ground contacts of the fastest men and animals known to science.

      PubDate: 2015-07-07T15:00:04Z
  • Influence of proximal drug eluting stent (DES) on distal bare metal stent
           (BMS) in multi-stent implantation strategies in coronary arteries
    • Abstract: Publication date: Available online 3 July 2015
      Source:Medical Engineering & Physics
      Author(s): Anqiang Sun , Zhenze Wang , Zhenmin Fan , Xiaopeng Tian , Fan Zhan , Xiaoyan Deng , Xiao Liu
      The aim of this study was to investigate the drug distribution in arteries treated with DES-BMS stenting strategy and to analyze the influence of proximal DES on distal segments of BMS. A straight artery model (Straight Model) and a branching artery model (Branching Model) were constructed in this study. In each model, the DES was implanted at the proximal position and the BMS was implanted distally. Hemodynamic environments, drug delivery and distribution features were simulated and analyzed in each model. The results showed that blood flow would contribute to non-uniform drug distribution in arteries. In the Straight Model the proximal DES would cause drug concentration in BMS segments. While in the Branching Model the DES in the main artery has slight influence on the BMS segments in the branch artery. In conclusion, due to the blood flow washing effect the uniformly released drug from DES would distribute focally and distally. The proximal DES would have greater influence on the distal BMS in straight artery than that in branching artery. This preliminary study would provide good reference for atherosclerosis treatment, especially for some complex cases, like coronary branching stenting.

      PubDate: 2015-07-07T15:00:04Z
  • Realistic glottal motion and airflow rate during human breathing
    • Abstract: Publication date: Available online 7 July 2015
      Source:Medical Engineering & Physics
      Author(s): Adam Scheinherr , Lucie Bailly , Olivier Boiron , Aude Lagier , Thierry Legou , Marine Pichelin , Georges Caillibotte , Antoine Giovanni
      The glottal geometry is a key factor in the aerosol delivery efficiency for treatment of lung diseases. However, while glottal vibrations were extensively studied during human phonation, the realistic glottal motion during breathing is poorly understood. Therefore, most current studies assume an idealized steady glottis in the context of respiratory dynamics, and thus neglect the flow unsteadiness related to this motion. This is particularly important to assess the aerosol transport mechanisms in upper airways. This article presents a clinical study conducted on 20 volunteers, to examine the realistic glottal motion during several breathing tasks. Nasofibroscopy was used to investigate the glottal geometrical variations simultaneously with accurate airflow rate measurements. In total, 144 breathing sequences of 30s were recorded. Regarding the whole database, two cases of glottal time-variations were found: “static” or “dynamic” ones. Typically, the peak value of glottal area during slow breathing narrowed from 217 ± 54 mm2 (mean ± STD) during inspiration, to 178 ± 35 mm2 during expiration. Considering flow unsteadiness, it is shown that the harmonic approximation of the airflow rate underevaluates the inertial effects as compared to realistic patterns, especially at the onset of the breathing cycle. These measurements provide input data to conduct realistic numerical simulations of laryngeal airflow and particle deposition.

      PubDate: 2015-07-07T15:00:04Z
  • Individual and combined effects of OA-related subchondral bone alterations
           on proximal tibial surface stiffness: a parametric finite element modeling
    • Abstract: Publication date: Available online 12 June 2015
      Source:Medical Engineering & Physics
      Author(s): Morteza Amini , S. Majid Nazemi , Joel L. Lanovaz , Saija Kontulainen , Bassam A. Masri , David R. Wilson , Walerian Szyszkowski , James D. Johnston
      The role of subchondral bone in OA pathogenesis is unclear. While some OA-related changes to morphology and material properties in different bone regions have been described, the effect of these alterations on subchondral bone surface stiffness has not been investigated. The objectives of this study were to characterize the individual (Objective 1) and combined (Objective 2) effects of OA-related morphological and mechanical alterations to subchondral and epiphyseal bone on surface stiffness of the proximal tibia. We developed and validated a parametric FE model of the proximal tibia using quantitative CT images of 10 fresh-frozen cadaveric specimens and in situ macro-indentation testing. Using this validated FE model, we estimated the individual and combined roles of OA-related alterations in subchondral cortical thickness and elastic modulus, and subchondral trabecular and epiphyseal trabecular elastic moduli on local surface stiffness. A 20% increase in subchondral cortical or subchondral trabecular elastic moduli resulted in little change in stiffness (1% increase). A 20% reduction in epiphyseal trabecular elastic modulus, however, resulted in an 11% reduction in stiffness. Our parametric analysis suggests that subchondral bone stiffness is affected primarily by epiphyseal trabecular bone elastic modulus rather than subchondral cortical and trabecular morphology or mechanical properties. Our results suggest that observed OA-related alterations to epiphyseal trabecular bone (e.g., lower mineralization, bone volume fraction, density and elastic modulus) may contribute to OA proximal tibiae being less stiff than normal.

      PubDate: 2015-06-28T14:01:24Z
  • From mechanical stimulus to bone formation: A review
    • Abstract: Publication date: Available online 25 June 2015
      Source:Medical Engineering & Physics
      Author(s): Natacha Rosa , Ricardo Simoes , Fernão D. Magalhães , Antonio Torres Marques
      Bone is a remarkable tissue that can respond to external stimuli. The importance of mechanical forces on the mass and structural development of bone has long been accepted. This adaptation behaviour is very complex and involves multidisciplinary concepts, and significant progress has recently been made in understanding this process. In this review, we describe the state of the art studies in this area and highlight current insights while simultaneously clarifying some basic yet essential topics related to the origin of mechanical stimulus in bone, the biomechanisms associated with mechanotransduction, the nature of physiological bone stimuli and the test systems most commonly used to study the mechanical stimulation of bone.

      PubDate: 2015-06-28T14:01:24Z
  • Low-intensity functional electrical stimulation can increase
           multidirectional trunk stiffness in able-bodied individuals during sitting
    • Abstract: Publication date: Available online 10 June 2015
      Source:Medical Engineering & Physics
      Author(s): Albert H. Vette , Noel Wu , Kei Masani , Milos R. Popovic
      The inability to voluntarily control the trunk musculature is a major problem following spinal cord injury as it can compromise functional independence and produce unwanted secondary complications. Recent developments suggest that neuroprostheses utilizing functional electrical stimulation (FES) may be able to facilitate or restore trunk control during sitting, standing, and other tasks involving postural control. In spite of these efforts, no study to date has used low-intensity FES to increase multidirectional trunk stiffness and damping in an attempt to bolster stability while minimizing muscle fatigue. Therefore, we set out to investigate how multidirectional trunk stiffness changes in response to low-intensity FES of a few selected trunk muscles. Fifteen healthy participants sitting naturally were randomly perturbed in eight horizontal directions. Trunk stiffness and damping during natural and FES-supported sitting conditions were quantified using force and trunk kinematics in combination with two models of a mass-spring-damper system. Our results indicate that low-intensity FES can increase trunk stiffness in healthy individuals, and this specifically for directions associated with the stimulated muscles. In contrast, trunk damping was not found to be altered during FES. The presented results suggest that low-intensity FES is a simple and effective method for increasing trunk stiffness on demand.

      PubDate: 2015-06-28T14:01:24Z
  • Development of a non-invasive diagnostic technique for acetabular
           component loosening in total hip replacements
    • Abstract: Publication date: Available online 6 June 2015
      Source:Medical Engineering & Physics
      Author(s): Abdullah A. Alshuhri , Timothy P. Holsgrove , Anthony W. Miles , James L. Cunningham
      Current techniques for diagnosing early loosening of a total hip replacement (THR) are ineffective, especially for the acetabular component. Accordingly, new, accurate, and quantifiable methods are required. The aim of this study was to investigate the viability of vibrational analysis for accurately detecting acetabular component loosening. A simplified acetabular model was constructed using a Sawbones® foam block. By placing a thin silicone layer between the acetabular component and the Sawbones block, 2- and 4-mm soft tissue membranes were simulated representing different loosening scenarios. A constant amplitude sinusoidal excitation with a sweep range of 100–1500 Hz was used. Output vibration from the model was measured using an accelerometer and an ultrasound probe. Loosening was determined from output signal features such as the number and relative strength of observed harmonic frequencies. Both measurement methods were sufficient to measure the output vibration. Vibrational analysis reliably detected loosening corresponding to both 2 and 4 mm tissue membranes at driving frequencies between 100 and 1000 Hz (p < 0.01) using the accelerometer. In contrast, ultrasound detected 2-mm loosening at a frequency range of 850–1050 Hz (p < 0.01) and 4-mm loosening at 500–950 Hz (p < 0.01).

      PubDate: 2015-06-28T14:01:24Z
  • Effect of different radial hole designs on pullout and structural strength
           of cannulated pedicle screws
    • Abstract: Publication date: Available online 6 June 2015
      Source:Medical Engineering & Physics
      Author(s): Hsin-Chang Chen , Yu-Shu Lai , Wen-Chuan Chen , Jou-Wen Chen , Chia-Ming Chang , Yi-Long Chen , Shih-Tien Wang , Cheng-Kung Cheng
      Cannulated pedicle screws are designed for bone cement injection to enhance fixation strength in severely osteoporotic spines. However, the screws commonly fracture during insertion. This study aims to evaluate how different positions/designs of radial holes may affect the pullout and structural strength of cannulated pedicle screws using finite element analysis. Three different screw hole designs were evaluated under torsion and bending conditions. The pullout strength for each screw was determined by axial pullout failure testing. The results showed that when the Von Mises stress reached the yield stress of titanium alloy the screw with four radial holes required a greater torque or bending moment than the nine and twelve hole screws. In the pullout test, the strength and stiffness of each screw with cement augmentation showed no significant differences, but the screw with four radial holes had a greater average pullout strength, which probably resulted from the significantly greater mean maximum lengths of cement augmentation. Superior biomechanical responses, with lower stress around the radial holes and greater pullout strength, represented by cannulated pedicle screw with four radial holes may worth recommending for clinical application.

      PubDate: 2015-06-28T14:01:24Z
  • Biomechanical properties of the Marfan's aortic root and ascending aorta
           before and after personalised external aortic root support surgery
    • Abstract: Publication date: Available online 6 June 2015
      Source:Medical Engineering & Physics
      Author(s): S.D. Singh , X.Y. Xu , J.R. Pepper , T. Treasure , R.H. Mohiaddin
      Marfan syndrome is an inherited systemic connective tissue disease which may lead to aortic root disease causing dilatation, dissection and rupture of the aorta. The standard treatment is a major operation involving either an artificial valve and aorta or a complex valve repair. More recently, a personalised external aortic root support (PEARS) has been used to strengthen the aorta at an earlier stage of the disease avoiding risk of both rupture and major surgery. The aim of this study was to compare the stress and strain fields of the Marfan aortic root and ascending aorta before and after insertion of PEARS in order to understand its biomechanical implications. Finite element (FE) models were developed using patient-specific aortic geometries reconstructed from pre and post-PEARS magnetic resonance images in three Marfan patients. For the post-PEARS model, two scenarios were investigated—a bilayer model where PEARS and the aortic wall were treated as separate layers, and a single-layer model where PEARS was incorporated into the aortic wall. The wall and PEARS materials were assumed to be isotropic, incompressible and linearly elastic. A static load on the inner wall corresponding to the patients’ pulse pressure was applied. Results from our FE models with patient-specific geometries show that peak aortic stresses and displacements before PEARS were located at the sinuses of Valsalva but following PEARS surgery, these peak values were shifted to the aortic arch, particularly at the interface between the supported and unsupported aorta. Further studies are required to assess the statistical significance of these findings and how PEARS compares with the standard treatment.

      PubDate: 2015-06-28T14:01:24Z
  • Evaluating the effect of increasing ceramic content on the mechanical
           properties, material microstructure and degradation of selective laser
           sintered polycaprolactone/β-tricalcium phosphate materials
    • Abstract: Publication date: Available online 6 June 2015
      Source:Medical Engineering & Physics
      Author(s): Heather Doyle , Stefan Lohfeld , Peter McHugh
      Orthopaedic scaffold materials were fabricated from polycaprolactone (PCL) and composite PCL–β-tricalcium phosphate (PCL/β-TCP) powders using selective laser sintering (SLS). Incorporating β-TCP particles is desirable to promote osteogenesis. The effects of increasing β-TCP content on the material's mechanical properties and microstructure were evaluated. The wt% of β-TCP and PCL particle sizes were found to influence material microstructure and mechanical properties, with increasing ceramic content causing a small but significant increase in stiffness but significant reductions in strength. Degradation of materials was achieved using accelerated ageing methods. The influence of β-TCP content on degradation at 7 weeks was evaluated through changes in mechanical properties and microstructure, and the ceramic particles were found to reduce elastic modulus and increase strength. The results of this study highlight the influence of ceramic content on mechanical properties and degradation behaviour of PCL/β-TCP SLS materials, and indicate that these changes must be considered in the design of scaffolds for critical-sized defects.

      PubDate: 2015-06-28T14:01:24Z
  • A model of lung parenchyma stress relaxation using fractional
    • Abstract: Publication date: Available online 3 June 2015
      Source:Medical Engineering & Physics
      Author(s): Zoujun Dai , Ying Peng , Hansen A. Mansy , Richard H. Sandler , Thomas J. Royston
      Some pulmonary diseases and injuries are believed to correlate with lung viscoelasticity changes. Hence, a better understanding of lung viscoelastic models could provide new perspectives on the progression of lung pathology and trauma. In the presented study, stress relaxation measurements were performed to quantify relaxation behavior of pig lungs. Results have uncovered certain trends, including an initial steep decay followed by a slow asymptotic relaxation, which would be better described by a power law than exponential decay. The fractional standard linear solid (FSLS) and two integer order viscoelastic models – standard linear solid (SLS) and generalized Maxwell (GM) – were used to fit the stress relaxation curves; the FSLS was found to be a better fit. It is suggested that fractional order viscoelastic models, which have nonlocal, multi-scale attributes and exhibit power law behavior, better capture the lung parenchyma viscoelastic behavior.

      PubDate: 2015-06-28T14:01:24Z
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