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BIOLOGY (1342 journals)            First | 4 5 6 7 8 9 10 11 | Last

Journal of Bioenergetics and Biomembranes     Hybrid Journal  
Journal of Biogeography     Hybrid Journal   (Followers: 18)
Journal of Bioinformatics and Computational Biology     Hybrid Journal   (Followers: 13)
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: 3)
Journal of Biomarkers     Open Access  
Journal of Biomechanics     Hybrid Journal   (Followers: 22)
Journal of Biomedical Discovery and Collaboration     Open Access   (Followers: 1)
Journal of Biomedical Education     Open Access   (Followers: 1)
Journal of Biomedical Informatics     Partially Free   (Followers: 13)
Journal of Biomedical Materials Research Part A     Hybrid Journal   (Followers: 1)
Journal of Biomedical Materials Research Part B : Applied Biomaterials     Hybrid Journal   (Followers: 1)
Journal of Biomedical Nanotechnology     Full-text available via subscription   (Followers: 6)
Journal of Biomedical Physics and Engineering     Open Access  
Journal of Biomedical Science and Engineering     Open Access   (Followers: 2)
Journal of Biomedical Sciences     Open Access   (Followers: 2)
Journal of Biomolecular Screening     Hybrid Journal   (Followers: 4)
Journal of Bionic Engineering     Full-text available via subscription  
Journal of Biorheology     Hybrid Journal  
Journal of Bioscience and Bioengineering     Full-text available via subscription   (Followers: 15)
Journal of Biosciences and Medicines     Open Access  
Journal of Biosocial Science     Hybrid Journal   (Followers: 4)
Journal of Biotechnology and Biodiversity     Open Access  
Journal of Cell and Plant Sciences     Open Access   (Followers: 3)
Journal of Cell Communication and Signaling     Hybrid Journal  
Journal of Cell Death     Open Access   (Followers: 1)
Journal of Cell Science     Full-text available via subscription   (Followers: 10)
Journal of Cellular Biochemistry     Hybrid Journal   (Followers: 3)
Journal of Cellular Physiology     Hybrid Journal   (Followers: 2)
Journal of Cerebral Blood Flow & Metabolism     Hybrid Journal   (Followers: 2)
Journal of Chromatography B     Hybrid Journal   (Followers: 16)
Journal of Clinical Bioinformatics     Open Access   (Followers: 5)
Journal of Communications Technology and Electronics     Hybrid Journal   (Followers: 1)
Journal of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 1)
Journal of Contradicting Results in Science     Open Access   (Followers: 2)
Journal of Crustacean Biology     Full-text available via subscription   (Followers: 2)
Journal of Developmental Biology     Open Access   (Followers: 2)
Journal of Ecosystems     Open Access   (Followers: 4)
Journal of Electrical Bioimpedance     Full-text available via subscription   (Followers: 2)
Journal of Electromyography and Kinesiology     Hybrid Journal   (Followers: 3)
Journal of Environment and Ecology     Open Access   (Followers: 10)
Journal of Environmental Radioactivity     Hybrid Journal   (Followers: 2)
Journal of Environmental Science and Natural Resources     Open Access   (Followers: 2)
Journal of Ethnobiology     Full-text available via subscription   (Followers: 5)
Journal of Ethnobiology and Ethnomedicine     Open Access  
Journal of Ethology     Hybrid Journal   (Followers: 1)
Journal of Evolutionary Biology     Hybrid Journal   (Followers: 22)
Journal of Experimental and Clinical Anatomy     Full-text available via subscription  
Journal of Experimental Marine Biology and Ecology     Hybrid Journal   (Followers: 26)
Journal of Fish Biology     Hybrid Journal   (Followers: 24)
Journal of Functional Biomaterials     Open Access   (Followers: 1)
Journal of Genomes and Exomes     Open Access  
Journal of Great Lakes Research     Hybrid Journal   (Followers: 7)
Journal of Health and Biological Sciences     Open Access  
Journal of Health Sciences     Open Access   (Followers: 5)
Journal of Heredity     Hybrid Journal   (Followers: 2)
Journal of Herpetology     Full-text available via subscription   (Followers: 4)
Journal of Huazhong University of Science and Technology [Medical Sciences]     Hybrid Journal  
Journal of Human Evolution     Hybrid Journal   (Followers: 9)
Journal of Hymenoptera Research     Open Access   (Followers: 2)
Journal of Ichthyology     Hybrid Journal   (Followers: 3)
Journal of Insect Behavior     Hybrid Journal   (Followers: 6)
Journal of Insect Biodiversity     Open Access   (Followers: 2)
Journal of Insect Conservation     Hybrid Journal   (Followers: 5)
Journal of Integrated OMICS     Open Access  
Journal of Integrated Pest Management     Open Access   (Followers: 2)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Intelligent Transportation Systems: Technology, Planning, and Operations     Hybrid Journal   (Followers: 5)
Journal of Invertebrate Pathology     Hybrid Journal   (Followers: 3)
Journal of Landscape Ecology     Open Access   (Followers: 6)
Journal of Law and the Biosciences     Open Access  
Journal of Leukocyte Biology     Open Access   (Followers: 5)
Journal of Life and Earth Science     Open Access  
Journal of Lipid Research     Full-text available via subscription   (Followers: 3)
Journal of Lipids     Open Access   (Followers: 1)
Journal of Luminescence     Hybrid Journal   (Followers: 2)
Journal of Mammalian Evolution     Hybrid Journal   (Followers: 6)
Journal of Mammalian Ova Research     Full-text available via subscription  
Journal of Mammalogy     Full-text available via subscription   (Followers: 6)
Journal of Mammary Gland Biology and Neoplasia     Hybrid Journal   (Followers: 1)
Journal of Marine Biology     Open Access   (Followers: 14)
Journal of Mathematical Biology     Hybrid Journal   (Followers: 13)
Journal of Mechanics in Medicine and Biology     Hybrid Journal  
Journal of Medical Primatology     Hybrid Journal   (Followers: 1)
Journal of Medical Toxicology     Hybrid Journal   (Followers: 5)
Journal of Medicine and Philosophy     Hybrid Journal   (Followers: 7)
Journal of Membrane Biology     Hybrid Journal   (Followers: 2)
Journal of Membrane Science     Hybrid Journal   (Followers: 11)
Journal of Molecular Biology     Hybrid Journal   (Followers: 29)
Journal of Molecular Biology Research     Open Access   (Followers: 1)

  First | 4 5 6 7 8 9 10 11 | Last

Journal Cover Medical Engineering & Physics
   [11 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1350-4533
     Published by Elsevier Homepage  [2575 journals]   [SJR: 0.722]   [H-I: 57]
  • Biomechanics of first ray hypermobility: An investigation on joint force
           during walking using finite element analysis
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Duo Wai-Chi Wong , Ming Zhang , Jia Yu , Aaron Kam-Lun Leung
      Hypermobility of the first ray is suggested to contribute to hallux valgus. The investigation of first ray hypermobility focused on the mobility and range of motion that based on manual examination. The load transfer mechanism of the first ray is important to understand the development and pathomechanism of hallux valgus. In this study, we investigated the immediate effect of the joint hypermobility on the metatarsocuneiform and metatarsophalangeal joint loading through a reduction of the stiffness of the foot ligaments. A three-dimensional foot model was constructed from a female aged 28 via MRI. All foot and ankle bones, including two sesamoids and the encapsulated bulk tissue were modeled as 3D solid parts, linking with ligaments of shell elements and muscles connectors. The stance phase of walking was simulated by the boundary and loading conditions obtained from gait analysis of the same subject. Compared with the normal foot, the hypermobile foot had higher resultant metatarsocuneiform and metatarsophalangeal joint forces. The increases accounted for 18.6% and 3.9% body weight. There was also an abrupt change of metatarsocuneiform joint force in the medial–lateral direction. The predicted results represented possible risk of joint problems and metatarsus primus varus.

      PubDate: 2014-12-16T04:42:30Z
  • A non-invasive, 3D, dynamic MRI method for measuring muscle moment arms in
           vivo: Demonstration in the human ankle joint and Achilles tendon
    • Abstract: Publication date: Available online 26 November 2014
      Source:Medical Engineering & Physics
      Author(s): E.C. Clarke , J.H. Martin , A.G. d’Entremont , M.G. Pandy , D.R. Wilson , R.D. Herbert
      Muscle moment arms are used widely in biomechanical analyses. Often they are measured in 2D or at a series of static joint positions. In the present study we demonstrate a simple MRI method for measuring muscle moment arms dynamically in 3D from a single range-of-motion cycle. We demonstrate this method in the Achilles tendon for comparison with other methods, and validate the method using a custom apparatus. The method involves registration of high-resolution joint geometry from MRI scans of the stationary joint with low-resolution geometries from ultrafast MRI scans of the slowly moving joint. Tibio-talar helical axes and 3D Achilles tendon moment arms were calculated throughout passive rotation for 10 adult subjects, and compared with recently published data. A simple validation was conducted by comparing MRI measurements with direct physical measurements made on a phantom. The moment arms measured using our method and those of others were similar and there was good agreement between physical measurements (mean 41.0mm) and MRI measurements (mean 39.5mm) made on the phantom. This new method can accurately measure muscle moment arms from a single range-of-motion cycle without the need to control rotation rate or gate the scanning. Supplementary data includes custom software to assist implementation.

      PubDate: 2014-12-16T04:42:30Z
  • Wiener filtering of surface EMG with a priori SNR estimation toward
           myoelectric control for neurological injury patients
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12
      Author(s): Jie Liu , Dongwen Ying , Ping Zhou
      Voluntary surface electromyogram (EMG) signals from neurological injury patients are often corrupted by involuntary background interference or spikes, imposing difficulties for myoelectric control. We present a novel framework to suppress involuntary background spikes during voluntary surface EMG recordings. The framework applies a Wiener filter to restore voluntary surface EMG signals based on tracking a priori signal to noise ratio (SNR) by using the decision-directed method. Semi-synthetic surface EMG signals contaminated by different levels of involuntary background spikes were constructed from a database of surface EMG recordings in a group of spinal cord injury subjects. After the processing, the onset detection of voluntary muscle activity was significantly improved against involuntary background spikes. The magnitude of voluntary surface EMG signals can also be reliably estimated for myoelectric control purpose. Compared with the previous sample entropy analysis for suppressing involuntary background spikes, the proposed framework is characterized by quick and simple implementation, making it more suitable for application in a myoelectric control system toward neurological injury rehabilitation.

      PubDate: 2014-12-16T04:42:30Z
  • Development of a shear measurement sensor for measuring forces at
           human–machine interfaces
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12
      Author(s): Young Kuen Cho , Seong Guk Kim , Donghyun Kim , Hyung Joo Kim , Jeicheong Ryu , Dohyung Lim , Chang-Yong Ko , Han Sung Kim
      Measuring shear force is crucial for investigating the pathology and treatment of pressure ulcers. In this study, we introduced a bi-axial shear transducer based on strain gauges as a new shear sensor. The sensor consisted of aluminum and polyvinyl chloride plates placed between quadrangular aluminum plates. On the middle plate, two strain gauges were placed orthogonal to one another. The shear sensor (54mm×54mm×4.1mm), which was validated by using standard weights, displayed high accuracy and precision (measurement range, −50 to 50N; sensitivity, 0.3N; linear relationship, R 2 =0.9625; crosstalk error, 0.635%±0.031%; equipment variation, 4.183). The shear force on the interface between the human body and a stand-up wheelchair was measured during sitting or standing movements, using two mats (44.8cm×44.8cm per mat) that consisted of 24 shear sensors. Shear forces on the sacrum and ischium were almost five times higher (15.5N at last posture) than those on other sites (3.5N on average) during experiments periods. In conclusion, the proposed shear sensor may be reliable and useful for measuring the shear force on human–machine interfaces.

      PubDate: 2014-12-16T04:42:30Z
  • Editorial Board
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11

      PubDate: 2014-12-16T04:42:30Z
  • The effect of different humeral prosthesis fin designs on shoulder
           stability: A computational model
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Chia-Ming Chang , Wen-Lin Yeh , Wen-Chuan Chen , Colin J. McClean , Yi-Long Chen , Yu-Shu Lai , Cheng-Kung Cheng
      Humeral prostheses commonly use a fin structure as an attachment point for the supraspinatus muscle in total shoulder arthroplasty (TSA), but these fins may cause injury to the muscle during implantation, inadvertently influencing stability. In order to prevent supraspinatus injury, the effect of different humeral prostheses on shoulder joint stability needs to be investigated. A commercially available prosthesis and two modified humeral prostheses that substituted the fin structure for 2 (2H) or 3 holes (3H) were evaluated using computational models. Glenohumeral abduction was simulated and the superioinferior/anterioposterior stability of the shoulder joint after TSA was calculated. The results revealed that the 2H design had better superioinferior stability than the other prostheses, but was still less stable than the intact shoulder. There were no obvious differences in anterioposterior stability, but the motion patterns were clearly distinguishable from the intact shoulder model. In conclusion, the 2H design showed better superioinferior stability than the 3H design and the commercial product during glenohumeral joint abduction; the three prostheses show similar results in anterioposterior stability. However, the stability of each tested prosthesis was not comparable to the intact shoulder. Therefore, as a compromise, the 2H design should be considered for TSA because of its superior stability.

      PubDate: 2014-12-16T04:42:30Z
  • Detection of physical activities using a physical activity monitor system
           for wheelchair users
    • Abstract: Publication date: Available online 10 November 2014
      Source:Medical Engineering & Physics
      Author(s): Shivayogi V. Hiremath , Stephen S. Intille , Annmarie Kelleher , Rory A. Cooper , Dan Ding
      Availability of physical activity monitors for wheelchair users can potentially assist these individuals to track regular physical activity (PA), which in turn could lead to a healthier and more active lifestyle. Therefore, the aim of this study was to develop and validate algorithms for a physical activity monitoring system (PAMS) to detect wheelchair based activities. The PAMS consists of a gyroscope based wheel rotation monitor (G-WRM) and an accelerometer device (wocket) worn on the upper arm or on the wrist. A total of 45 persons with spinal cord injury took part in the study, which was performed in a structured university-based laboratory environment, a semi-structured environment at the National Veterans Wheelchair Games, and in the participants’ home environments. Participants performed at least ten PAs, other than resting, taken from a list of PAs. The classification performance for the best classifiers on the testing dataset for PAMS-Arm (G-WRM and wocket on upper arm) and PAMS-Wrist (G-WRM and wocket on wrist) was 89.26% and 88.47%, respectively. The outcomes of this study indicate that multi-modal information from the PAMS can help detect various types of wheelchair-based activities in structured laboratory, semi-structured organizational, and unstructured home environments.

      PubDate: 2014-12-16T04:42:30Z
  • Imaging and finite element analysis: A methodology for non-invasive
           characterization of aortic tissue
    • Abstract: Publication date: Available online 6 November 2014
      Source:Medical Engineering & Physics
      Author(s): Vittoria Flamini , Arthur P. Creane , Christian M. Kerskens , Caitríona Lally
      Characterization of the mechanical properties of arterial tissues usually involves an invasive procedure requiring tissue removal. In this work we propose a non-invasive method to perform a biomechanical analysis of cardiovascular aortic tissue. This method is based on combining medical imaging and finite element analysis (FEA). Magnetic resonance imaging (MRI) was chosen since it presents relatively low risks for human health. A finite element model was created from the MRI images and loaded with systolic physiological pressures. By means of an optimization routine, the structural material properties were changed until average strains matched those measured by MRI. The method outlined in this work produced an estimate of the in situ properties of cardiovascular tissue based on non-invasive image datasets and finite element analysis.

      PubDate: 2014-12-16T04:42:30Z
  • A novel in vivo impact device for evaluation of sudden limb loading
    • Abstract: Publication date: Available online 11 November 2014
      Source:Medical Engineering & Physics
      Author(s): Erin Boutwell , Rebecca Stine , Steven Gard
      The lower limbs are subjected to large impact forces on a daily basis during gait, and ambulators rely on various mechanisms to protect the musculoskeletal system from these potentially damaging shocks. However, it is difficult to assess the efficacy of anatomical mechanisms and potential clinical interventions on impact forces because of limitations of the testing environment. The current paper describes a new in vivo measurement device (sudden loading evaluation device, or SLED) designed to address shortcomings of previous loading protocols. To establish the repeatability and validity of this testing device, reliability and human participant data were collected while the stiffnesses of simulated and prosthetic limbs were systematically varied. The peak impact forces delivered by the SLED ranged from 706±3N to 2157±32N during reliability testing and from 784±30N to 938±18N with the human participant. The relatively low standard deviations indicate good reliability within the impacts delivered by the SLED, while the magnitude of the loads experienced by the human participant (98–117% BW) were comparable to ground reaction forces during level walking. Thus, the SLED may be valuable as a research tool for investigations of lower-limb impact loading events.

      PubDate: 2014-12-16T04:42:30Z
  • The effect of stent graft oversizing on radial forces considering nitinol
           wire behavior and vessel characteristics
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): B. Senf , S. von Sachsen , R. Neugebauer , W.-G. Drossel , H.-J. Florek , F.W. Mohr , C.D. Etz
      Stent graft fixation in the vessel affects the success of endovascular aneurysm repair. Thereby the radial forces of the stent, which are dependent on several factors, play a significant role. In the presented work, a finite element sensitivity study was performed. The radial forces are 29% lower when using the hyperelastic approach for the vessel compared with linear elastic assumptions. Without the linear elastic modeled plaque, the difference increases to 35%. Modeling plaque with linear elastic material approach results in 8% higher forces than with a hyperelastic characteristic. The significant differences resulting from the investigated simplifications of the material lead to the conclusion that it is important to apply an anisotropic nonlinear approach for the vessel. The oversizing study shows that radial forces increase by 64% (0.54N) when raising the oversize from 10 to 22%, and no further increase in force can be observed beyond these values (vessel diameter D =12mm). Starting from an oversize of 24%, the radial force steadily decreases. The findings of the investigation show that besides the oversizing the material properties, the ring design and the vessel characteristics have an influence on radial forces.

      PubDate: 2014-12-16T04:42:30Z
  • A new measure of the CoP trajectory in postural sway: Dynamics of heading
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Christopher K. Rhea , Adam W. Kiefer , F.J. Haran , Stephen M. Glass , William H. Warren
      The maintenance of upright stance requires the simultaneous control of posture in both the anterior–posterior (AP) and medial–lateral (ML) dimensions. Postural sway is typically measured by quantifying the movement of the center of pressure (CoP) in the AP and ML dimensions independently. Metrics such as path length and 95% ellipse area have been developed to take into account movement in both the AP and ML directions, but these metrics only quantify the magnitude of the CoP movement. The movement of the CoP is technically a vector quantity with both magnitude and direction characteristics. The direction of displacement, or heading, of the CoP may provide further insight into the control of posture. Accordingly, we present a novel variable that describes the rate of change in direction of CoP displacement in two dimensions, the heading change (Δϕ), which is derived from the CoP heading (ϕ). We then compared the standard deviation (SD) and the dynamic structure characterized by sample entropy (SampEn) of the heading change time series to previously examined metrics presented in the literature (SD and SampEn of the AP and ML time series, path length, SD and SampEn of the CoP resultant magnitude time series) during a 60s single-leg stance performed by healthy participants and patients with a ruptured anterior cruciate ligament (ACL) prior to surgical intervention. Patients with an ACL rupture exhibited a different dynamic structure in Δϕ compared to healthy controls, t(14)=2.44, p =0.029, whereas none of the other metrics differed between groups (all p >0.05). The novelty and utility of Δϕ is that it characterizes directional changes of the CoP, whereas previously documented postural control analyses describe only changes in magnitude.

      PubDate: 2014-12-16T04:42:30Z
  • Development of a closed-loop J–T cryoablation device with a long
           cooling area and multiple expansion parts
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Cheonkyu Lee , Seungwhan Baek , Jisung Lee , Gyuwan Hwang , Sangkwon Jeong , Sang Woo Park
      Cryoablation is a surgical procedure used to freeze defective cells by inserting a low temperature probe into a human body to destroy malignant tissues. Miniaturized Joule–Thomson (J–T) refrigerators are often used to minimize the volume of the cooling device and reduce the destruction zone of normal tissue. The cooling effects of the existing probes are not uniformly generated along the longitudinal direction of the probe, which makes their applications less effective in surgeries of incompetent great saphenous veins (GSVs), where the target cells are distributed over a broad range. Long uniform refrigeration is required across the entire area of the probe to apply the same cooling effects. In this paper, a closed-loop J–T cryoablation probe was designed and fabricated to provide uniform refrigeration over a large area, with multiple expansion parts. Using flow boiling heat transfer, uniform cooling of a 200mm-long and 0.3mm thickness piece of target tissue was possible and simulated in a gelatin solution. The developed probe produced a greater than 53Kmin−1 cooling rate and the cooling temperature was below 253K to satisfy the required cell death conditions.

      PubDate: 2014-12-16T04:42:30Z
  • Monolithic superelastic rods with variable flexural stiffness for spinal
           fusion: Modeling of the processing–properties relationship
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Yann Facchinello , Vladimir Brailovski , Yvan Petit , Jean-Marc Mac-Thiong
      The concept of a monolithic Ti–Ni spinal rod with variable flexural stiffness is proposed to reduce the risks associated with spinal fusion. The variable stiffness is conferred to the rod using the Joule-heating local annealing technique. The annealing temperature and the mechanical properties’ distributions resulted from this thermal treatment are numerically modeled and experimentally measured. To illustrate the possible applications of such a modeling approach, two case studies are presented: (a) optimization of the Joule-heating strategy to reduce annealing time, and (b) modulation of the rod's overall flexural stiffness using partial annealing. A numerical model of a human spine coupled with the model of the variable flexural stiffness spinal rod developed in this work can ultimately be used to maximize the stabilization capability of spinal instrumentation, while simultaneously decreasing the risks associated with spinal fusion.

      PubDate: 2014-12-16T04:42:30Z
  • Modified bone density-dependent orthotropic material model of human
           mandibular bone
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12
      Author(s): Franci Gačnik , Zoran Ren , Nataša Ihan Hren
      The prediction accuracy of computational simulations of various biomechanical problems of human bones depends on proper modelling of the problem geometry and boundary conditions but it is also essentially dependent on proper description of the mechanical properties of the all constitutive elements. As the human mandibular bone is a very important load-carrying element in biomechanics, the main aim of this research was to develop an innovative, not yet described in literature, spatial and bone density-dependent orthotropic material model of the human mandibular bone for use in the computational simulations. We compared it with the most used constitutive material models in the computational simulations of the human mandibular bone behaviour with inserted dental implant. The results show that the von Mises equivalent stress distribution values in the bone density-dependent orthotropic model are higher in comparison with other models but the highest are on the top of the alveolar ridge and higher in the lingual than in the buccal part of the lower jaw.

      PubDate: 2014-12-16T04:42:30Z
  • A multi-scale feedback ratio analysis of heartbeat interval series in
           healthy vs. cardiac patients
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12
      Author(s): Chengyu Huo , Xiaolin Huang , Huangjing Ni , Hongxing Liu , Chunhua Bian , Xinbao Ning
      The second-order difference plot, as a modified Poincaré plot, is one of the important approaches for assessing the dynamics of heart rate variability. However, corresponding quantitative analysis methods are relatively limited. Based on the second-order difference plot, we propose a novel method, called the multi-scale feedback ratio analysis, which can measure the feedback properties of heart rate fluctuations on different temporal scales. The index R ¯ TF [ τ 1 , τ 2 ] is then defined to quantify the average feedback ratio through a definite scale range. Analysis of Gaussian white, 1/f and Brownian noises show that the feedback ratios are indeed on different levels. The method is then applied to heartbeat interval series derived from healthy subjects, subjects with congestive heart failure and subjects with atrial fibrillation. Results show that, for all groups, the feedback ratios vary with increasing time scales, and gradually reach relatively stable states. The R ¯ TF [ 10,20 ] values of the three groups are significantly different. Thus, R ¯ TF [ 10,20 ] becomes an effective parameter for distinguishing healthy and pathologic states. In addition, R ¯ TF [ 10,20 ] for healthy, congestive failure and atrial fibrillation subjects are close to those of the 1/f, Brownian and white noises respectively, indicating different intrinsic dynamics.

      PubDate: 2014-12-16T04:42:30Z
  • Editorial Board
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12

      PubDate: 2014-12-16T04:42:30Z
  • Operational challenges of retinal prostheses
    • Abstract: Publication date: December 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 12
      Author(s): Erich W. Schmid , Wolfgang Fink , Robert Wilke
      Two computational models for research on retinal implants are presented. In the first model, the electric field produced by a multi-electrode array in a uniform retina is calculated. It is shown how cross talk of activated electrodes and the resulting bunching of field lines in monopole and dipole activation prevent high resolution imaging with retinal implants. Furthermore, it is demonstrated how sequential stimulation and multipolar stimulation may overcome this limitation. In the second model a target volume, i.e., a probe cylinder approximating a bipolar cell, in the retina is chosen, and the passive Heaviside cable equation is solved inside this target volume to calculate the depolarization of the cell membrane. The depolarization as a function of time indicates that shorter signals stimulate better as long as the current does not change sign during stimulation of the retina, i.e., mono-phasic stimulation. Both computational models are equally applicable to epiretinal, subretinal, and suprachoroidal vision implants.

      PubDate: 2014-12-16T04:42:30Z
  • Influence of clearance on the time-dependent performance of the hip
           following hemiarthroplasty: A finite element study with biphasic
           acetabular cartilage properties
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Junyan Li , Xijin Hua , Zhongmin Jin , John Fisher , Ruth K. Wilcox
      Hip hemiarthroplasty is a common treatment for femoral neck fracture. However, the acetabular cartilage may degenerate after hemiarthroplasty leading to postoperative failure and the need for revision surgery. The clearance between the acetabular cartilage and head of the prosthesis is one of the potential reasons for this failure. In this study, the influence of joint clearance on the biomechanical function of a generic hip model in hemiarthroplasty was investigated using biphasic numerical simulation. Both a prolonged loading period of 4000s and dynamic gait load of 10 cycles were considered. It was found that a larger clearance led to a higher stress level, a faster reduction in load supported by the fluid and a faster cartilage consolidation process. Additionally, the mechanical performance of the acetabular cartilage in the natural model was similar to that in the hemiarthroplasty model with no clearance but different from the hemiarthroplasty models with clearances of 0.5mm and larger. The results demonstrated that a larger clearance in hip hemiarthroplasty is more harmful to the acetabular cartilage and prosthesis heads with more available dimensions (i.e. smaller increments in diameter) could be manufactured for surgeons to achieve a lower clearance, and reduced contact stress in hemiarthroplasty surgeries.

      PubDate: 2014-12-16T04:42:30Z
  • Multi-frequency Rayleigh damped elastography: in silico studies
    • Abstract: Publication date: Available online 2 December 2014
      Source:Medical Engineering & Physics
      Author(s): Andrii Y. Petrov , Paul D. Docherty , Mathieu Sellier , J. Geoffrey Chase
      Rayleigh damping (RD) is commonly used to model energy attenuation for analyses of structures subjected to dynamic loads. In time-harmonic Magnetic Resonance Elastography (MRE), the RD model was shown to be non-identifiable at a single frequency data due to the ill-posed nature of the imaginary components describing energy dissipation arising from elastic and inertial forces. Thus, parametrisation or multi-frequency (MF) input data is required to overcome the fundamental identifiability issue of the model. While parametrisation allows improved accuracy of the identified parameters, simultaneous inversion using MF input data is a prerequisite for theoretical identifiably of the model. Furthermore, to establish good practical identifiability, frequencies should be separated over a wide range to produce different dynamic response. This research investigates the effects on practical identifiability of the RD model using MF data over different combinations of frequencies in noise-free heterogenous simulated geometry and compares the outcomes to reconstruction result based on single frequency input data. We tested eight frequencies in silico for a phantom type geometry comprises three independent material regions characterised by different mechanical properties. Combinations of two near or well separated frequencies are used to test the separation necessary to obtain accurate results, while the use of four or eight simultaneous frequencies is used to assess robustness. Results confirm expected non-identifiability of the RD model given single frequency input data. Practical identifiability of the RD parameters improved as more input frequencies were used for simultaneous inversion and when two frequencies were well separated. Best quality reconstruction results were achieved using full range data comprising eight available frequencies over a wide range. The main outcome is that high quality motion data over at least two frequencies over a wide range is required for establishing minimal practical identifiability of the model, while quality of the practical identifiability increases proportionally with more input frequencies used. Further simulation studies are required to determine acceptable signal-to-noise ratio (SNR) thresholds in motion data for accurate inversion of the RD parameters.

      PubDate: 2014-12-16T04:42:30Z
  • Effect of fixation on neovascularization during bone healing
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Feng Zhao , Zhilun Zhou , Yang Yan , Zhen Yuan , Guanzhong Yang , Hao Yu , Hao Su , Tao Zhang , Yubo Fan
      Fixation and vascularity after bone fracture are two critical factors for successful healing, and their influences on bone healing have been studied by many researchers. This research aims to obtain three-dimensional (3D) reconstruction images of neovascularization of the soft tissues surrounding the fracture with vascular perfusion and micro-computer tomography (micro-CT) imaging, and to investigate the effect of stable fixation on neovascularization and the pattern of vascularity during the process of bone healing. To accomplish this, 36 Sprague-Dawley (SD) rats underwent mid-shaft transverse osteotomy of the right tibia. Half of them received stable fixation with a newly custom-designed external fixator (FSF, the group of fracture with stable fixation), while the rest received no fixation (FNF, the group of fracture with no fixation). The results indicated that FNF samples had more transversal vascular distribution than FSF samples; FSF samples had more longitudinal vascular distribution than FNF samples; and the spatio-temporal pattern of vascularity in FSF samples was more similar to that in the control group (CON, the group without fracture) than that in FNF samples. At the time of 2 and 4 weeks postoperatively, FNF samples had significantly higher vessel volume ratio (VV/TV), larger vessel number (VN) and higher vessel surface density (VS/TV) than CON samples. At all sacrifice times, FSF samples contained significantly higher VV/TV, VN and VS/TV values compared with FNF samples. In summary, neovascularization and its pattern are obviously influenced by the mechanical fixation. Stable fixation can promote longitudinal vascularity pattern formation, which tends to be similar to the natural vascularity pattern, and this benefits the inter-fragmentary blood fluid connectivity during bone healing process.

      PubDate: 2014-12-16T04:42:30Z
  • Permeability study of cancellous bone and its idealised structures
    • Abstract: Publication date: Available online 16 December 2014
      Source:Medical Engineering & Physics
      Author(s): Ardiyansyah Syahrom , Mohammed Rafiq Abdul Kadir , Muhamad Nor Harun , Andreas Öchsner
      Artificial bone is a suitable alternative to autografts and allografts, however their use is still limited. Though there were numerous reports on their structural properties, permeability studies of artificial bones were comparably scarce. This study focused on the development of idealised, structured models of artificial cancellous bone and compared their permeability values with bone surface area and porosity. Cancellous bones from fresh bovine femur were extracted and cleaned following an established protocol. The samples were scanned using micro-computed tomography (μCT) and three-dimensional models of the cancellous bones were reconstructed for morphology study. Seven idealised and structured cancellous bone models were then developed and fabricated via rapid prototyping technique. A test-rig was developed and permeability tests were performed on the artificial and real cancellous bones. The results showed a linear correlation between the permeability and the porosity as well as the bone surface area. The plate-like idealised structure showed a similar value of permeability to the real cancellous bones.

      PubDate: 2014-12-16T04:42:30Z
  • Digital tomosynthesis (DTS) for quantitative assessment of trabecular
           microstructure in human vertebral bone
    • Abstract: Publication date: Available online 8 December 2014
      Source:Medical Engineering & Physics
      Author(s): Woong Kim , Daniel Oravec , Srikant Nekkanty , Janardhan Yerramshetty , Edward A. Sander , George W. Divine , Michael J. Flynn , Yener N. Yeni
      Digital tomosynthesis (DTS) provides slice images of an object using conventional radiographic methods with high in-plane resolution. The objective of this study was to explore the potential of DTS for describing microstructural, stiffness and stress distribution properties of vertebral cancellous bone. Forty vertebrae (T6, T8, T11, and L3) from 10 cadavers (63–90 years) were scanned using microCT and DTS. Anisotropy (μCT.DA), and the specimen-average and standard deviation of trabecular bone volume fraction (BV/TV), thickness (Tb.Th), number (Tb.N) and separation (Tb.Sp) were obtained using stereology. Apparent modulus (E FEM), and the magnitude (VMExp/σ app) and variability (VMCV) of trabecular stresses were calculated using microCT-based finite element modeling. Mean intercept length, line fraction deviation and fractal parameters were obtained from coronal DTS slices, then correlated with stereological and finite element parameters using linear regression models. Twenty-one DTS parameters (out of 27) correlated to BV/TV, Tb.Th, Tb.N, Tb.Sp and/or μCT.DA (p <0.0001–p <0.05). DTS parameters increased the explained variability in E FEM and VMCV (by 9–11% and 13–19%, respectively; p <0.0001–p <0.04) over that explained by BV/TV. In conclusion, DTS has potential for quantitative assessment of cancellous bone and may be used as a modality complementary to those measuring bone mass for assessing spinal fracture risk.

      PubDate: 2014-12-16T04:42:30Z
  • Leg general muscle moment and power patterns in able-bodied subjects
           during recumbent cycle ergometry with ankle immobilization
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): J. Szecsi , A. Straube , C. Fornusek
      Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads. Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60rpm during passive cycling and at two workloads (low 15W and high 40W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations. During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0–258°) hip extension moment and a shortened range (350–150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase. For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.

      PubDate: 2014-12-16T04:42:30Z
  • Exploiting parameter sparsity in model-based reconstruction to accelerate
           proton density and T2 mapping
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Xi Peng , Xin Liu , Hairong Zheng , Dong Liang
      T2 mapping is a powerful noninvasive technique providing quantitative biological information of the inherent tissue properties. However, its clinical usage is limited due to the relative long scanning time. This paper proposed a novel model-based method to address this problem. Typically, we directly estimated the relaxation values from undersampled k-space data by exploiting the sparse property of proton density and T2 map in a penalized maximum likelihood formulation. An alternating minimization approach was presented to estimate the relaxation maps separately. Both numerical phantom and in vivo experiment dataset were used to demonstrate the performance of the proposed method. We showed that the proposed method outperformed the state-of-the-art techniques in terms of detail preservation and artifact suppression with various reduction factors and in both moderate and heavy noise circumstances. The superior reconstruction performance validated its promising potential in fast T2 mapping applications.

      PubDate: 2014-12-16T04:42:30Z
  • Biomechanical study of expandable pedicle screw fixation in severe
           osteoporotic bone comparing with conventional and cement-augmented pedicle
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Yi-Long Chen , Wen-Chuan Chen , Chi-Wei Chou , Jou-Wen Chen , Chia-Ming Chang , Yu-Shu Lai , Cheng-Kung Cheng , Shih-Tien Wang
      Pedicle screws are widely utilized to treat the unstable thoracolumbar spine. The superior biomechanical strength of pedicle screws could increase fusion rates and provide accurate corrections of complex deformities. However, osteoporosis and revision cases of pedicle screw substantially reduce screw holding strength and cause loosening. Pedicle screw fixation becomes a challenge for spine surgeons in those scenarios. The purpose of this study was to determine if an expandable pedicle screw design could be used to improve biomechanical fixation in osteoporotic bone. Axial mechanical pull-out test was performed on the expandable, conventional and augmented pedicle screws placed in a commercial synthetic bone block which mimicked a human bone with severe osteoporosis. Results revealed that the pull-out strength and failure energy of expandable pedicle screws were similar with conventional pedicle screws augmented with bone cement by 2ml. The pull-out strength was 5-fold greater than conventional pedicle screws and the failure energy was about 2-fold greater. Besides, the pull-out strength of expandable screw was reinforced by the expandable mechanism without cement augmentation, indicated that the risks of cement leakage from vertebral body would potentially be avoided. Comparing with the biomechanical performances of conventional screw with or without cement augmentation, the expandable screws are recommended to be applied for the osteoporotic vertebrae.

      PubDate: 2014-12-16T04:42:30Z
  • Experimental investigations and finite element simulation of cutting heat
           in vibrational and conventional drilling of cortical bone
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Yu Wang , Meng Cao , Xiangrui Zhao , Gang Zhu , Colin McClean , Yuanyuan Zhao , Yubo Fan
      Heat generated during bone drilling could cause irreversible thermal damage, which can lead to bone necrosis or even osteomyelitis. In this study, vibrational drilling was applied to fresh bovine bones to investigate the cutting heat in comparison with conventional drilling through experimental investigation and finite element analysis (FEA). The influence of vibrational frequency and amplitude on cutting heat generation and conduction were studied. The experimental results showed that, compared with the conventional drilling, vibrational drilling could significantly reduce the cutting temperature in drilling of cortical bone (P <0.05): the cutting temperature tended to decrease with increasing vibrational frequency and amplitude. The FEA results also showed that the vibrational amplitude holds a significant effect on the cutting heat conduction.

      PubDate: 2014-12-16T04:42:30Z
  • Biomechanical study of tarsometatarsal joint fusion using finite element
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Yan Wang , Zengyong Li , Ming Zhang
      Complications of surgeries in foot and ankle bring patients with severe sufferings. Sufficient understanding of the internal biomechanical information such as stress distribution, contact pressure, and deformation is critical to estimate the effectiveness of surgical treatments and avoid complications. Foot and ankle is an intricate and synergetic system, and localized intervention may alter the functions to the adjacent components. The aim of this study was to estimate biomechanical effects of the TMT joint fusion using comprehensive finite element (FE) analysis. A foot and ankle model consists of 28 bones, 72 ligaments, and plantar fascia with soft tissues embracing all the segments. Kinematic information and ground reaction force during gait were obtained from motion analysis. Three gait instants namely the first peak, second peak and mid-stance were simulated in a normal foot and a foot with TMT joint fusion. It was found that contact pressure on plantar foot increased by 0.42%, 19% and 37%, respectively after TMT fusion compared with normal foot walking. Navico-cuneiform and fifth meta-cuboid joints sustained 27% and 40% increase in contact pressure at second peak, implying potential risk of joint problems such as arthritis. Von Mises stress in the second metatarsal bone increased by 22% at midstance, making it susceptible to stress fracture. This study provides biomechanical information for understanding the possible consequences of TMT joint fusion.

      PubDate: 2014-12-16T04:42:30Z
  • Quantitative analysis of liver fibrosis in rats with shearwave dispersion
           ultrasound vibrometry: Comparison with dynamic mechanical analysis
    • Abstract: Publication date: November 2014
      Source:Medical Engineering & Physics, Volume 36, Issue 11
      Author(s): Ying Zhu , Xinyu Zhang , Yi Zheng , Xin Chen , Yuanyuan Shen , Haoming Lin , Yanrong Guo , Tianfu Wang , Siping Chen
      Ultrasonic elastography, a non-invasive technique for assessing the elasticity properties of tissues, has shown promising results for disease diagnosis. However, biological soft tissues are viscoelastic in nature. Shearwave dispersion ultrasound vibrometry (SDUV) can simultaneously measure the elasticity and viscosity of tissue using shear wave propagation speeds at different frequencies. In this paper, the viscoelasticity of rat livers was measured quantitatively by SDUV for normal (stage F0) and fibrotic livers (stage F2). Meanwhile, an independent validation study was presented in which SDUV results were compared with those derived from dynamic mechanical analysis (DMA), which is the only mechanical test that simultaneously assesses the viscoelastic properties of tissue. Shear wave speeds were measured at frequencies of 100, 200, 300 and 400Hz with SDUV and the storage moduli and loss moduli were measured at the frequency range of 1–40Hz with DMA. The Voigt viscoelastic model was used in the two methods. The mean elasticity and viscosity obtained by SDUV ranged from 0.84±0.13kPa (F0) to 1.85±0.30kPa (F2) and from 1.12±0.11Pas (F0) to 1.70±0.31Pas (F2), respectively. The mean elasticity and viscosity derived from DMA ranged from 0.62±0.09kPa (F0) to 1.70±0.84kPa (F2) and from 3.38±0.32Pas (F0) to 4.63±1.30Pas (F2), respectively. Both SDUV and DMA demonstrated that the elasticity of rat livers increased from stage F0 to F2, a finding which was consistent with previous literature. However, the elasticity measurements obtained by SDUV had smaller differences than those obtained by DMA, whereas the viscosities obtained by the two methods were obviously different. We suggest that the difference could be related to factors such as tissue microstructure, the frequency range, sample size and the rheological model employed. For future work we propose some improvements in the comparative tests between SDUV and DMA, such as enlarging the harmonic frequency range of the shear wave to highlight the role of viscosity, finding an appropriate rheological model to improve the accuracy of tissue viscoelasticity estimations.

      PubDate: 2014-12-16T04:42:30Z
  • On feature extraction and classification in prostate cancer radiotherapy
           using tensor decompositions
    • Abstract: Publication date: Available online 20 November 2014
      Source:Medical Engineering & Physics
      Author(s): Auréline Fargeas , Laurent Albera , Amar Kachenoura , Gaël Dréan , Juan-David Ospina , Julie Coloigner , Caroline Lafond , Jean-Bernard Delobel , Renaud De Crevoisier , Oscar Acosta
      External beam radiotherapy is commonly prescribed for prostate cancer. Although new radiation techniques allow high doses to be delivered to the target, the surrounding healthy organs (rectum and bladder) may suffer from irradiation, which might produce undesirable side-effects. Hence, the understanding of the complex toxicity dose–volume effect relationships is crucial to adapt the treatment, thereby decreasing the risk of toxicity. In this paper, we introduce a novel method to classify patients at risk of presenting rectal bleeding based on a Deterministic Multi-way Analysis (DMA) of three-dimensional planned dose distributions across a population. After a non-rigid spatial alignment of the anatomies applied to the dose distributions, the proposed method seeks for two bases of vectors representing bleeding and non bleeding patients by using the Canonical Polyadic (CP) decomposition of two fourth order arrays of the planned doses. A patient is then classified according to its distance to the subspaces spanned by both bases. A total of 99 patients treated for prostate cancer were used to analyze and test the performance of the proposed approach, named CP-DMA, in a leave-one-out cross validation scheme. Results were compared with supervised (linear discriminant analysis, support vector machine, K-means, K-nearest neighbor) and unsupervised (recent principal component analysis-based algorithm, and multidimensional classification method) approaches based on the registered dose distribution. Moreover, CP-DMA was also compared with the Normal Tissue Complication Probability (NTCP) model. The CP-DMA method allowed rectal bleeding patients to be classified with good specificity and sensitivity values, outperforming the classical approaches.

      PubDate: 2014-12-16T04:42:30Z
  • Simultaneous pressure–volume measurements using optical sensors and
           MRI for left ventricle function assessment during animal experiment
    • Abstract: Publication date: Available online 11 December 2014
      Source:Medical Engineering & Physics
      Author(s): Dima Abi-Abdallah Rodriguez , Emmanuel Durand , Ludovic de Rochefort , Younes Boudjemline , Elie Mousseaux
      Simultaneous pressure and volume measurements enable the extraction of valuable parameters for left ventricle function assessment. Cardiac MR has proven to be the most accurate method for volume estimation. Nonetheless, measuring pressure simultaneously during MRI acquisitions remains a challenge given the magnetic nature of the widely used pressure transducers. In this study we show the feasibility of simultaneous in vivo pressure–volume acquisitions with MRI using optical pressure sensors. Pressure–volume loops were calculated while inducing three inotropic states in a sheep and functional indices were extracted, using single beat loops, to characterize systolic and diastolic performance. Functional indices evolved as expected in response to positive inotropic stimuli. The end-systolic elastance, representing the contractility index, the diastolic myocardium compliance, and the cardiac work efficiency all increased when inducing inotropic state enhancement. The association of MRI and optical pressure sensors within the left ventricle successfully enabled pressure–volume loop analysis after having respective data simultaneously recorded during the experimentation without the need to move the animal between each inotropic state.

      PubDate: 2014-12-16T04:42:30Z
  • Modelling the heart with the atrioventricular plane as a piston unit
    • Abstract: Publication date: Available online 22 November 2014
      Source:Medical Engineering & Physics
      Author(s): Elira Maksuti , Anna Bjällmark , Michael Broomé
      Medical imaging and clinical studies have proven that the heart pumps by means of minor outer volume changes and back-and-forth longitudinal movements in the atrioventricular (AV) region. The magnitude of AV-plane displacement has also shown to be a reliable index for diagnosis of heart failure. Despite this, AV-plane displacement is usually omitted from cardiovascular modelling. We present a lumped-parameter cardiac model in which the heart is described as a displacement pump with the AV plane functioning as a piston unit (AV piston). This unit is constructed of different upper and lower areas analogous with the difference in the atrial and ventricular cross-sections. The model output reproduces normal physiology, with a left ventricular pressure in the range of 8–130mmHg, an atrial pressure of approximatly 9mmHg, and an arterial pressure change between 75mmHg and 130mmHg. In addition, the model reproduces the direction of the main systolic and diastolic movements of the AV piston with realistic velocity magnitude (∼10cm/s). Moreover, changes in the simulated systolic ventricular-contraction force influence diastolic filling, emphasizing the coupling between cardiac systolic and diastolic functions. The agreement between the simulation and normal physiology highlights the importance of myocardial longitudinal movements and of atrioventricular interactions in cardiac pumping.

      PubDate: 2014-12-16T04:42:30Z
  • Design optimization of a deflectable guidewire
    • Abstract: Publication date: Available online 22 November 2014
      Source:Medical Engineering & Physics
      Author(s): H.C.M. Clogenson , A. Simonetto , J.J. van den Dobbelsteen
      Over the years, the design of the tip of available catheters and guidewires has evolved into various shapes whose geometry is mostly based on common sense and experimentation. However, while the tip shape of conventional instruments can be easily modified and tested, the length of the tip of a deflectable guidewire cannot. Hence, other approaches are necessary in order to determine the proper dimensions of original instruments. In this paper, we formulate the length of the different parts of the deflectable tip of a guidewire as an optimization problem with the objective to obtain a design that is suitable for cannulating several target bifurcations of the peripheral vasculature. A direct relationship between the design of the deflectable tip and the geometry of the target bifurcations was found and the optimal dimension of the tip of the instrument was computed. Following the length specifications defined by the optimization, a new prototype was assembled, and evaluated. The deflectable guidewire could successfully cannulate most of the pre-selected branches except those bifurcations with an angle α >70°. The latter limitation could be ascribed to the mechanical properties of the instrument.

      PubDate: 2014-12-16T04:42:30Z
  • Feature dimensionality reduction for myoelectric pattern recognition: A
           comparison study of feature selection and feature projection methods
    • Abstract: Publication date: Available online 5 October 2014
      Source:Medical Engineering & Physics
      Author(s): Jie Liu
      This study investigates the effect of the feature dimensionality reduction strategies on the classification of surface electromyography (EMG) signals toward developing a practical myoelectric control system. Two dimensionality reduction strategies, feature selection and feature projection, were tested on both EMG feature sets, respectively. A feature selection based myoelectric pattern recognition system was introduced to select the features by eliminating the redundant features of EMG recordings instead of directly choosing a subset of EMG channels. The Markov random field (MRF) method and a forward orthogonal search algorithm were employed to evaluate the contribution of each individual feature to the classification, respectively. Our results from 15 healthy subjects indicate that, with a feature selection analysis, independent of the type of feature set, across all subjects high overall accuracies can be achieved in classification of seven different forearm motions with a small number of top ranked original EMG features obtained from the forearm muscles (average overall classification accuracy >95% with 12 selected EMG features). Compared to various feature dimensionality reduction techniques in myoelectric pattern recognition, the proposed filter-based feature selection approach is independent of the type of classification algorithms and features, which can effectively reduce the redundant information not only across different channels, but also cross different features in the same channel. This may enable robust EMG feature dimensionality reduction without needing to change ongoing, practical use of classification algorithms, an important step toward clinical utility.

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

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

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

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

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

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

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

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

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

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

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

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

      PubDate: 2014-09-22T06:41:31Z
  • In vivo measurements of patellar tracking and finite helical axis using a
           static magnetic resonance based methodology
    • Abstract: Publication date: Available online 18 September 2014
      Source:Medical Engineering & Physics
      Author(s): Jie Yao , Bin Yang , Wenxin Niu , Jianwei Zhou , Yuxing Wang , He Gong , Huasong Ma , Rong Tan , Yubo Fan
      Patellofemoral (PF) maltracking is a critical factor predisposing to PF pain syndrome. Many novel techniques of measuring patellar tracking remain research tools. This study aimed to develop a method to measure the in vivo patellar tracking and finite helical axis (FHA) by using a static magnetic resonance (MR) based methodology. The geometrical models of PF joint at 0°, 45°, 60°, 90°, and 120° of knee flexion were developed from MR images. The approximate patellar tracking was derived from the discrete PF models with a spline interpolation algorithm. The patellar tracking was validated with the previous in vitro and in vivo experiments. The patellar FHA throughout knee flexion was calculated. In the present case, the FHA drew an “L-shaped” curve in the sagittal section. This methodology could advance the examination of PF kinematics in clinics, and may also provide preliminary knowledge on patellar FHA study.

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

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

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

      PubDate: 2014-09-11T05:24:38Z
  • Nonlinear properties of cardiac rhythm and respiratory signal under paced
           breathing in young and middle-aged healthy subjects
    • Abstract: Publication date: Available online 4 September 2014
      Source:Medical Engineering & Physics
      Author(s): Ana Kapidžić , Mirjana M Platiša , Tijana Bojić , Aleksandar Kalauzi
      We examined the effects of gender and age in young and middle-aged subjects on the level of cardio-respiratory interaction by analyzing properties of cardiac, respiratory and cardiac-respiratory regulatory mechanisms under paced breathing. In 56 healthy subjects, ECG (RR interval) and respiratory signal were simultaneously acquired in supine position at paced (0.1–0.45Hz, steps of 0.05Hz) and spontaneous breathing. The participants were divided into gender matched group of young adults (19–25 years old) and middle-aged adults (35–44 years old). Power spectral analysis was applied on RR interval time series and spectral components in very low frequency (VLF), low frequency (LF) and high frequency (HF) ranges were computed. We also calculated sample entropy of RR interval series (SampEnRR), respiratory series (SampEnResp), and their cross-sample entropy (cross-SampEn). Under paced breathing, reduction of all spectral powers with age (p <0.05) is not gender dependent but reduction of some entropy measures is; SampEnRR and SampEnResp were lower only in men (p <0.05). In the middle-aged subjects, effect of gender on spectral measures is significant; males had lower HF (p <0.05). Pattern of dependencies of SampEn and cross-SampEn on paced breathing frequency were significantly different in men (young vs. middle-aged, p =0.001 and p =0.037) and in middle-aged subjects (females vs. males, p =0.011 and p =0.008). In middle-aged males, lower entropy measures indicated reduced and less complex partial cardiac and respiratory control, and central cardio-respiratory control. In conclusion, in healthy middle-aged subjects changes in cardio-respiratory coupling are detectable only in males.

      PubDate: 2014-09-06T04:51:13Z
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