| 1. |
- Hult, Peter, 1964-, et al.
(författare)
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A bioacoustic method for timing of the different phases of the breathing cycle and monitoring of breathing frequency
- 2000
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Ingår i: Medical Engineering and Physics. - 1350-4533 .- 1873-4030. ; 22:6, s. 425-433
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the flow of air through the trachea during respiration causes vibrations in the tissue near the trachea, which propagate to the surface of the body and can be picked up by a microphone placed on the throat over the trachea. Since the vibrations are a direct result of the airflow, accurate timing of inspiration and expiration is possible. This paper presents a signal analysis solution for automated monitoring of breathing and calculation of the breathing frequency. The signal analysis approach uses tracheal sound variables in the time and frequency domains, as well as the characteristics of the disturbances that can be used to discriminate tracheal sound from noise. One problem associated with the bioacoustic method is its sensitivity for acoustic disturbances, because the microphone tends to pick up all vibrations, independent of their origin. A signal processing method was developed that makes the bioacoustic method clinically useful in a broad variety of situations, for example in intensive care and during certain heart examinations, where information about both the precise timing and the phases of breathing is crucial.
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| 2. |
- Stasiunas, Antanas, et al.
(författare)
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A non-linear circuit for simulating OHC of the cochlea
- 2003
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Ingår i: Medical Engineering and Physics. - London : Elsevier. - 1350-4533 .- 1873-4030. ; 25:7, s. 591-601
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, referring to known characteristics of the outer hair cells functioning in the cochlea of the inner ear, a functional model of the outer hair cells is constructed. It consists of a linear feed-forward circuit and a non-linear positive feedback circuit. The feed-forward circuit reflects the contribution of local basilar and tectorial membrane areas and passive outer hair cells’ physical parameters to the forming of low-selectivity resonance characteristics. The non-linear positive feedback circuit reflects the non-linear outer hair cell signal transduction processes and the active role of efferents from the medial superior olive in altering circuit sensitivity and selectivity.Referring to an analytical description of the circuit model and computer simulation results, an explanation is given over the biological meaning of the outer hair cells’ non-linearities in signal transduction processes and the role of the non-linearities in achieving the following: signal compression, the dependency of circuit sensitivity and frequency selectivity upon the input signal amplitude, the compatibility of high-frequency selectivity and short transient response of the biological filtering circuits.
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| 3. |
- Sierpowska, Joanna, et al.
(författare)
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Effect of human trabecular bone composition on its electrical properties.
- 2007
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 29:8, s. 845-852
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties of bone are determined not only by bone mineral density (BMD), but also by tissue trabecular structure and organic composition. Impedance spectroscopy has shown potential to diagnose trabecular bone BMD and strength, however, the relationships between organic composition and electrical and dielectric properties have not been systematically investigated. To investigate these issues organic composition of 26 human trabecular bone samples harvested from the distal femur and proximal tibia was determined and compared with relative permittivity, loss factor, conductivity, phase angle, specific impedance and dissipation factor measured at wide range (50 Hz to 5 MHz) of frequencies. A strong linear correlation was found between the relative permittivity at 1.2 MHz and trabecular bone fat content (r = -0.85, p<0.01, n=26). On the other hand, relative permittivity measured at 200 Hz served as a good predictor of water content (r = 0.83). Phase angle, specific impedance and especially conductivity were strongly related to the trabecular bone dry density and water content (|r| > or = 0.69). Variation in bone tissue collagen content was strongly related to the relative permittivity measured at 1.2 MHz (r = 0.64), but only moderately to other parameters. Glycosaminoglycan content showed no significant relations with any investigated electrical parameters. The present study indicates that if the trabecular bone composition is known, the relationships presented in this study could facilitate calculation of current field distribution, e.g. during electrical stimulation of osteogenesis. On the other hand, our results suggest that permittivity measured at low (<1 kHz) or high (>100 kHz) frequencies could be used, e.g. during implant surgery, for prediction of trabecular bone water or fat contents, respectively.
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| 4. |
- Ahmed, Kirstin, 1974, et al.
(författare)
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Mechanical load applied by Intraosseous Transcutaneous Amputation Prosthesis (ITAP) during walking on level and sloped treadmill: A case study
- 2023
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Ingår i: Medical Engineering and Physics. - 1350-4533 .- 1873-4030.
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Tidskriftsartikel (refereegranskat)abstract
- This proof of concept study presents a method to collect and analyse kinetic data from one participant with a transfemoral amputation fitted with a percutaneous osseointegrated implant walking on a level and sloped treadmill. We describe the construction of and results from a bespoke wireless six axis load cell built into one participant’s prosthetic assembly. The load cell does not clinically compromise the participant in any way and is an initial milestone in the development of a light-weight wireless load cell for use with percutaneous osseointegrated implants. In this case, it is the first time that kinetic data from a participant fitted with an Intraosseous Transcutaneous Amputation Prosthesis has been published. We propose that the data can be used to model the load transfer to the host bone, with several clinically significant applications. The raw dynamic data are made available and quasi-static load cases for each functional phase of gait are presented. Peak forces obtained in the medio-lateral (X), cranio-caudal (Y) and antero-posterior (Z) axes over level ground respectively were -243.8 N (0.24 BW), 1321.5 N (1.31 BW) and -421.8 N (0.42 BW); uphill were -141.0 N (0.14 BW), 1604.2 N (1.59 BW), -498.1 (0.49 BW); downhill were -206.0 N (0.20 BW), 1103.9 N (1.09 BW), -547.2 N (0.54 BW). The kinetics broadly followed non-amputated gait patterns with some gait strategies consistent in participants with other implant designs or prosthetic socket connections, for example offloading the artificial limb downhill.
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| 5. |
- Alegre-Martínez, C., et al.
(författare)
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On the axial distribution of plaque stress : Influence of stenosis severity, lipid core stiffness, lipid core length and fibrous cap stiffness
- 2019
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 68, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations of blood flow through a partially-blocked axisymmetric artery are performed to investigate the stress distributions in the plaque. We show that the combined effect of stenosis severity and the stiffness of the lipid core can drastically change the axial stress distribution, strongly affecting the potential sites of plaque rupture. The core stiffness is also an important factor when assessing plaque vulnerability, where a mild stenosis with a lipid-filled core presents higher stress levels than a severe stenosis with a calcified plaque. A shorter lipid core gives rise to an increase in the stress levels. However, the fibrous cap stiffness does not influence the stress distributions for the range of values considered in this work. Based on these mechanical analyses, we identify potential sites of rupture in the axial direction for each case: the midpoints of the upstream and downstream regions of the stenosis (for severe, lipid-filled plaques), the ends of the lipid core (for short cores), and the middle of the stenosis (for mild stenoses with positive remodelling of the arterial wall).
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| 6. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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Mechanical characterization of human skin—A non-invasive digital twin approach using vibration-response integrated with numerical methods
- 2023
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Ingår i: Medical Engineering and Physics. - 1350-4533 .- 1873-4030. ; 121
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes an innovative approach to identify elastic material properties and mass density of soft tissues based on interpreting their mechanical vibration response, externally excited by a mechanical indenter or acoustic waves. A vibration test is performed on soft sheets to measure their response to a continuous range of excitation frequencies. The frequency responses are collected with a pair of high-speed cameras in conjunction with 3-D digital image correlation (DIC). Two cases are considered, including suspended/fully-free rectangular neoprene sheets as artificial tissue cutout samples and continuous layered human skin vibrations. An efficient theoretical model is developed to analytically simulate the free vibrations of the neoprene artificial sheet samples as well as the continuous layered human skins. The high accuracy and validity of the presented analytical simulations are demonstrated through comparison with the DIC measurements and the conducted frequency tests, as well as a number of finite element (FE) modeling. The developed analytical approach is implemented into a numerical algorithm to perform an inverse calculation of the soft sheets' elastic properties using the imported experimental vibration results and the predicted system's mass via the system equivalent reduction/expansion process (SEREP) method. It is shown that the proposed frequency-dependent inverse approach is capable of rapidly predicting the material properties of the tested samples with high accuracy.
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| 7. |
- Brånemark, Rickard, 1960, et al.
(författare)
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An in-vivo method for biomechanical characterization of bone-anchored implants.
- 1998
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Ingår i: Medical engineering & physics. - 1350-4533. ; 20:3, s. 216-9
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Tidskriftsartikel (refereegranskat)abstract
- Experimental equipment for in-vivo registrations of pull-out load vs displacement, applied torque vs angle of rotation, and lateral load vs lateral displacement has been developed. The set-up is designed for testing three implants inserted in a row and osseointegrated in, for instance, the proximal tibia of the beagle dog. The details of the set-up are described and considerations of the stress distributions are reported.
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| 8. |
- Buendia, Ruben, 1983-, et al.
(författare)
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Influence of electrode mismatch on Cole parameter estimation from Total Right Side Electrical Bioimpedance Spectroscopy measurements
- 2012
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 34:7, s. 1024-1028
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Tidskriftsartikel (refereegranskat)abstract
- Applications based on measurements of Electrical Bioimpedance (EBI) spectroscopy analysis, like assessment of body composition, have proliferated in the past years. Currently Body Composition Assessment (BCA) based in Bioimpedance Spectroscopy (BIS) analysis relays on an accurate estimation of the Cole parameters R-0 and R-infinity. A recent study by Bogonez-Franco et al. has proposed electrode mismatch as source of remarkable artefacts in BIS measurements. Using Total Right Side BIS measurements from the aforementioned study, this work has focused on the influence of electrode mismatch on the estimation of R-0 and R-infinity using the Non-Linear Least Square curve fitting technique on the modulus of the impedance. The results show that electrode mismatch on the voltage sensing electrodes produces an overestimation of the impedance spectrum leading to a wrong estimation of the parameters R-0 and R-infinity, and consequently obtaining values around 4% larger that the values obtained from BIS without electrode mismatch. The specific key factors behind electrode mismatch or its influence on the analysis of single and spectroscopy measurements have not been investigated yet, no compensation or correction technique is available to overcome the deviation produced on the EBI measurement. Since textile-enabled EBI applications using dry textrodes, i.e. textile electrodes with dry skin-electrode interfaces and potentially large values of electrode polarization impedance are more prone to produce electrode mismatch, the lack of a correction or compensation technique might hinder the proliferation of textile-enabled EBI applications for personalized healthcare monitoring.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Carnaz, Leticia, et al.
(författare)
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A comparison between flexible electrogoniometers, inclinometers and three-dimensional video analysis system for recording neck movement
- 2013
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 35:11, s. 1629-1637
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Tidskriftsartikel (refereegranskat)abstract
- This study compared neck range of movement recording using three different methods goniometers (EGM), inclinometers (INC) and a three-dimensional video analysis system (IMG) in simultaneous and synchronized data collection. Twelve females performed neck flexion-extension, lateral flexion, rotation and circumduction. The differences between EGM, INC, and IMG were calculated sample by sample. For flexion-extension movement, IMG underestimated the amplitude by 13%; moreover, EGM showed a crosstalk of about 20% for lateral flexion and rotation axes. In lateral flexion movement, all systems showed similar amplitude and the inter-system differences were moderate (4-7%). For rotation movement, EGM showed a high crosstalk (13%) for flexion-extension axis. During the circumduction movement, IMG underestimated the amplitude of flexion-extension movements by about 11%, and the inter-system differences were high (about 17%) except for INC-IMG regarding lateral flexion (7%) and EGM-INC regarding flexion-extension (10%). For application in workplace, INC presents good results compared to IMG and EGM though INC cannot record rotation. EGM should be improved in order to reduce its crosstalk errors and allow recording of the full neck range of movement. Due to non-optimal positioning of the cameras for recording flexion-extension, IMG underestimated the amplitude of these movements. (C) 2013 IPEM. Published by Elsevier Ltd. All rights reserved.
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| 13. |
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| 14. |
- Evegren, Philip, et al.
(författare)
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Wall shear stress variations in a 90-degree bifurcation in 3D pulsating flows
- 2010
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 32:2, s. 189-202
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Tidskriftsartikel (refereegranskat)abstract
- The exact role of fluid mechanics in the patho-physiological process of atherosclerosis has been a research topic over many years, yet without clear conclusive result. One has observed that morphological manifestations of the disease are found at some well-defined locations: certain vessel bifurcations and in curvatures. The flow in these regions is characterized by unsteadiness and often separation. Currently there are no complete theories that can explain the process since the different components in the process are not fully understood. Here we carry out detailed computations of the unsteady flow in an arterial segment typical to location of early appearance of arterial lesions. We study the wall shear stress (WSS) field variations near a junction with the purpose of identifying fluid-mechanical parameters that can be related to sites of atheroslcerosis. The results show that regions associated with atherosclerosis experience highly elevated temporal- and spatial-derivatives of the WSS, also at less commonly known locations. Thus, large derivatives in time and space do not seem unique for the most common areas of atherosclerosis. Differences in WSS character between these locations are identified as differences in the time period of back flow as well as differences in the magnitude of the WSS derivatives. The data is presented in a way that facilitates understanding of the variations in WSS.
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| 15. |
- Gharehbaghi, Arash, et al.
(författare)
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A novel method for discrimination between innocent and pathological heart murmurs
- 2015
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 37:7, s. 674-682
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel method for discrimination between innocent and pathological murmurs using the growing time support vector machine (GTSVM). The proposed method is tailored for characterizing innocent murmurs (IM) by putting more emphasis on the early parts of the signal as IMs are often heard in early systolic phase. Individuals with mild to severe aortic stenosis (AS) and IM are the two groups subjected to analysis, taking the normal individuals with no murmur (NM) as the control group. The AS is selected due to the similarity of its murmur to IM, particularly in mild cases. To investigate the effect of the growing time windows, the performance of the GTSVM is compared to that of a conventional support vector machine (SVM), using repeated random sub-sampling method. The mean value of the classification rate/sensitivity is found to be 88%/86% for the GTSVM and 84%/83% for the SVM. The statistical evaluations show that the GTSVM significantly improves performance of the classification as compared to the SVM.
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| 16. |
- Gharehbaghi, Arash, et al.
(författare)
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Detection of systolic ejection click using time growing neural network
- 2014
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 36:4, s. 477-483
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a novel neural network for classification of short-duration heart sounds: the time growing neural network (TGNN). The input to the network is the spectral power in adjacent frequency bands as computed in time windows of growing length. Children with heart systolic ejection click (SEC) and normal children are the two groups subjected to analysis. The performance of the TGNN is compared to that of a time delay neural network (TDNN) and a multi-layer perceptron (MLP), using training and test datasets of similar sizes with a total of 614 normal and abnormal cardiac cycles. From the test dataset, the classification rate/sensitivity is found to be 97.0%/98.1% for the TGNN, 85.1%/76.4% for the TDNN, and 92.7%/85.7% for the MLP. The results show that the TGNN performs better than do TDNN and MLP when frequency band power is used as classifier input. The performance of TGNN is also found to exhibit better immunity to noise.
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| 17. |
- Hernando, D, et al.
(författare)
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Identification of patients prone to hypotension during hemodialysis based on the analysis of cardiovascular signals.
- 2015
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 37:12, s. 1156-1161
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Tidskriftsartikel (refereegranskat)abstract
- Intradialytic hypotension (IDH) is a major complication during hemodialysis treatment, and therefore it is highly desirable to identify, at an early stage during treatment, whether the patient is prone to IDH. Heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) were analyzed during the first 30 min of treatment to assess information on the autonomic nervous system. Using the sequential floating forward selection method and linear classification, the set of features with the best discriminative power was selected, resulting in an accuracy of 92.1%. Using a classifier based on the HRV features only, thereby avoiding that continuous blood pressure has to be recorded, accuracy decreased to 90.2%. The results suggest that an HRV-based classifier is useful for determining whether a patient is prone to IDH at the beginning of the treatment.
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| 18. |
- Holmer, Mattias, et al.
(författare)
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Detection of ventricular premature beats based on the pressure signals of a hemodialysis machine
- 2018
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533. ; 51, s. 49-55
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Tidskriftsartikel (refereegranskat)abstract
- Monitoring of ventricular premature beats (VPBs), being abundant in hemodialysis patients, can provide information on cardiovascular instability and electrolyte imbalance. In this paper, we describe a method for VPB detection which explores the signals acquired from the arterial and the venous pressure sensors, located in the extracorporeal blood circuit of a hemodialysis machine. The pressure signals are mainly composed of a pump component and a cardiac component. The cardiac component, severely overshadowed by the pump component, is estimated from the pressure signals using an earlier described iterative method. A set of simple features is extracted, and linear discriminant analysis is performed to classify beats as either normal or ventricular premature. Performance is evaluated on signals from nine hemodialysis treatments, using leave-one-out crossvalidation. The simultaneously recorded and annotated photoplethysmographic signal serves as the reference signal, with a total of 149,686 normal beats and 3574 VPBs. The results show that VPBs can be reliably detected, quantified by a Youden's J statistic of 0.9, for average cardiac pulse pressures exceeding 1 mmHg; for lower pressures, the J statistic drops to 0.55. It is concluded that the cardiac pressure signal is suitable for VPB detection, provided that the average cardiac pulse pressure exceeds 1 mmHg.
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| 19. |
- Hu, Jingwen, et al.
(författare)
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Development and validation of a modified hybrid-III six-year-old dummy model for simulating submarining in motor-vehicle crashes
- 2012
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 34:5, s. 541-551
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Tidskriftsartikel (refereegranskat)abstract
- In motor-vehicle crashes, young school-aged children restrained by vehicle seat belt systems often suffer from abdominal injuries due to submarining. However, the current anthropomorphic test device, so-called “crash dummy”, is not adequate for proper simulation of submarining. In this study, a modified Hybrid-III six-year-old dummy model capable of simulating and predicting submarining was developed using MADYMO (TNO Automotive Safety Solutions). The model incorporated improved pelvis and abdomen geometry and properties previously tested in a modified physical dummy. The model was calibrated and validated against four sled tests under two test conditions with and without submarining using a multi-objective optimization method. A sensitivity analysis using this validated child dummy model showed that dummy knee excursion, torso rotation angle, and the difference between head and knee excursions were good predictors for submarining status. It was also shown that restraint system design variables, such as lap belt angle, D-ring height, and seat coefficient of friction (COF), may have opposite effects on head and abdomen injury risks; therefore child dummies and dummy models capable of simulating submarining are crucial for future restraint system design optimization for young school-aged children
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| 20. |
- Huo, Jinxing, et al.
(författare)
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Failure location predictoin by finite element analysis for an additive manufactured mandible implant
- 2015
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 37:9, s. 862-869
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 21. |
- Höglund, Gustav, et al.
(författare)
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The importance of inertial measurement unit placement in assessing upper limb motion
- 2021
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 92, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Motion analysis using inertial measurement units (IMU) has emerged as an alternative to optical motion capture. However, the validity and reliability of upper limb measurements varies significantly between studies. The objective of this study was to determine how sensor placement affects kinematic output in the assessment of motion of the arm, shoulder, and scapula. IMUs were placed proximally/distally on arms, and medially/laterally on the scapula, in a group of eleven healthy participants, while performing nine different motion tasks. Linear regressions and mixed models analysed how these different sensor placements affected the estimated joint motion by establishing the linear relationship between sensors placed on the same body segment. The placement of sensors affected the measured kinematic output considerably, most prominent affect was seen for sensor placement on scapula during flexion and abduction, and on forearm during pronation/supination. The slope of the linear regression lines was 2.5 during flexion, 2.7 during abduction, and 1.8 for forearm pronation/supination. The results of this study suggest that the forearm sensor should be placed on the dorsal side of the forearm, at the distal end; the upper arm sensor should be placed laterally, on the distal part of the arm; and the sensor on the scapula should be placed cranially, along the spine of scapula.
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| 22. |
- Januario, Leticia, 1990-, et al.
(författare)
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Serratus anterior sEMG – sensor placement and test position for normalization purposes during maximal and submaximal exertions
- 2022
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 101
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Tidskriftsartikel (refereegranskat)abstract
- There is great variability regarding serratus anterior sEMG sensor placement and test positions during normalization procedures. We investigated between-trials reliability of serratus anterior sEMG, acquired at two sensor placements and four test positions, during maximal and submaximal isometric contractions. Twenty young healthy women participated. sEMG was captured at the 7th intercostal space and at the xiphoid process level, in the mid-axillary line, during maximal and submaximal isometric contractions, in four test positions. Intraclass Correlation Coefficient (ICC2,1), coefficient of variation and standard error of measurement were calculated. Interactions between sensor placements and test positions were investigated using a two-way repeated-measures ANOVA. All test conditions presented ICC2,1 > 0.8. There was no interaction between sensor placement and test position. Signal obtained from the sensor at 7th intercostal space was more stable between-trials and showed higher amplitude, during maximal and submaximal contractions, at seated positions with shoulder protracted at both 90° or 125° of flexion. We suggest to acquire serratus anterior sEMG at the 7th intercostal space and perform maximal or submaximal isometric contractions for signal normalization with shoulder protracted and flexed, at seated position.
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| 23. |
- Jönsson, Bo-Anders
(författare)
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A case study of successful e-learning: A web-based distance course in medical physics held for school teachers of the upper secondary level
- 2005
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:7, s. 571-581
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Tidskriftsartikel (refereegranskat)abstract
- Learning activities and course design in the new context of e-learning, such as in web-based courses involves a change both for teachers and students. The paper discusses factors important for e-learning to be successful. The development of an online course in medical physics and technology for high school teachers of physics, details of the course, and experience gained in connection with it are described. The course syllabus includes basics of radiation physics, imaging techniques using ionizing or non-ionizing radiation, and external and internal radiation therapy. The course has a highly didactic approach. The final task is for participants to design a course of their own centered on some topic of medical physics on the basis of the knowledge they have acquired. The aim of the course is I to help the teachers integrate medical physics into their own teaching. This is seen as enhancing the interest of high school students in later studying physics, medical physics or some other branch of science at the university level, and as increasing the knowledge that they and people generally have of science. It is suggested that the basic approach taken can also have applicability to the training of medical, nursing or engineering students, and be used for continuing professional development in various areas. (c) 2005 IPEM. Published by Elsevier Ltd. All rights reserved.
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| 24. |
- Kang, Byung-Soo, et al.
(författare)
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Metal plasma immersion ion implantation and deposition (MePIIID) on screw-shaped titanium implant: The effects of ion source, ion dose and acceleration voltage on surface chemistry and morphology.
- 2011
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 0951-8320 .- 1350-4533. ; 33:6, s. 730-738
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the effect of metal plasma immersion ion implantation and deposition (MePIIID) process parameters, i.e., plasma sources of magnesium and calcium, ion dose, and acceleration voltage on the surface chemistry and morphology of screw-type titanium implants that have been most widely used for osseointegrated implants. It is found that irrespective of plasma ion source, surface topography and roughness showed no differences at the nanometer level; that atom concentrations increased with ion dose but decreased with acceleration voltage. Data obtained from X-ray photoelectron spectroscopy and auger electron spectroscopy suggested that MePIIID process produces ‘intermixed’ layer of cathodic arc deposition and plasma immersion ion implantation. The MePIIID process may create desired bioactive surface chemistry of dental and orthopaedic implants by tailoring ion and plasma sources and thus enable investigations of the effect of the surface chemistry on bone response.
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| 25. |
- Karimi, Mohammad Taghi, et al.
(författare)
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Evaluation of the hip joint contact force in subjects with Perthes based on OpenSIM
- 2019
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 67, s. 44-48
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Tidskriftsartikel (refereegranskat)abstract
- The head of femoral bone is deformed in the subjects with Leg Calve Perthes disease (LCPD). This may be due to the excessive loads applied on it. There are no studies that report the hip joint contact force in subjects with LCPD. Therefore, the aim of this study was to evaluate the hip joint contact force in subjects with Perthes disease. Ten typically-developing (TD) children and 10 children with LCPD were recruited in this study. The kinematics and kinetics of the subjects were evaluated in 3D motion analysis. The hip joint contact force was approximated using OpenSIM software. Differences were determined with an independent t-test. There was a significant difference between walking speed of TD and Perthes subjects (63.8 (±8.1) and 57.4 (±7.0) m/min, respectively). The first peak of hip joint contact force was 4.8 (±1.7) N/BW in Perthes subjects, compared to 7.6 (±2.5) N/BW in TD subjects (p = 0.004). The peak hip joint contact force in mediolateral and anteroposterior directions was significantly lower in Perthes subjects (p < 0.05). The hip joint excursion was 40.0 (±5.6) and 46.4 (±8.5) degrees in Perthes and normal subjects, respectively (p = 0.03). The hip joint contact forces were lower in the subjects with Perthes disease. Therefore, it can be concluded that the strategies used by LCPD subjects were successful to decrease hip joint contact force.
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| 26. |
- Kok, Joeri, et al.
(författare)
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Augmenting a dynamic hip screw with a calcium sulfate/hydroxyapatite biomaterial
- 2021
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533. ; 92, s. 102-109
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Tidskriftsartikel (refereegranskat)abstract
- Internal fixation failure in hip fractures can lead to reoperation. Calcium sulfate/hydroxyapatite (CaS/HA) is a biomaterial that can be used for augmenting fracture fixation. We aimed to determine whether an injection of 2 ml CaS/HA increases the fixation of a dynamic hip screw inserted in synthetic and human trabecular bone. The study consists of two parts: 1) synthetic bone blocks (n = 74), with three subgroups: empty (cannulated screw, no injection), cannulated, and fenestrated; and 2) osteoporotic human femoral heads (n = 29), with the same subgroups. The heads were imaged using µCT. Bone volume fraction, insertion angle, and head diameter were measured. Pullout tests were performed and peak force, stiffness, and work were measured. The fenestrated group showed increases in pullout strength compared to no injection in the synthetic blocks. The cannulated group showed a higher pullout strength in low-density blocks. In the femoral heads, the variation was larger and there were no significant differences between groups. The bone volume fraction correlated with the peak force and work, and the insertion angle correlated with the stiffness. CaS/HA can improve the fixation of a dynamic hip screw. For clinical use, spreading of the material around the threads of the screw must be ensured.
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| 27. |
- Kulmala, Katariina, et al.
(författare)
-
Diffusion of ionic and non-ionic contrast agents in articular cartilage with increased cross-linking : contribution of steric and electrostatic effects
- 2013
-
Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 35:10, s. 1415-20
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To investigate the effect of threose-induced collagen cross-linking on diffusion of ionic and non-ionic contrast agents in articular cartilage.DESIGN: Osteochondral plugs (Ø=6mm) were prepared from bovine patellae and divided into two groups according to the contrast agent to be used in contrast enhanced computed tomography (CECT) imaging: (I) anionic ioxaglate and (II) non-ionic iodixanol. The groups I and II contained 7 and 6 sample pairs, respectively. One of the paired samples served as a reference while the other was treated with threose to induce collagen cross-linking. The equilibrium partitioning of the contrast agents was imaged after 24h of immersion. Fixed charge density (FCD), water content, contents of proteoglycans, total collagen, hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP) and pentosidine (Pent) cross-links were determined as a reference.RESULTS: The equilibrium partitioning of ioxaglate (group I) was significantly (p=0.018) lower (-23.4%) in threose-treated than control samples while the equilibrium partitioning of iodixanol (group II) was unaffected by the threose-treatment. FCD in the middle and deep zones of the cartilage (p<0.05) and contents of Pent and LP (p=0.001) increased significantly due to the treatment. However, the proteoglycan concentration was not systematically altered after the treatment. Water content was significantly (-3.5%, p=0.007) lower after the treatment.CONCLUSIONS: Since non-ionic iodixanol showed no changes in partition after cross-linking, in contrast to anionic ioxaglate, we conclude that the cross-linking induced changes in charge distribution have greater effect on diffusion compared to the cross-linking induced changes in steric hindrance.
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| 28. |
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| 29. |
- Lantz, Jonas, et al.
(författare)
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Is aortic wall shear stress affected by aging? An image-based numerical study with two age groups
- 2015
-
Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 37:3, s. 265-271
-
Tidskriftsartikel (refereegranskat)abstract
- The size of the larger arteries increases during the entire life, but not much is known about how the change in size affects the blood flow. This study compares the flow field in a group of young males (N = 10, age = 23.5 +/- 1.4), with a group of older males (N = 8, age = 58.0 +/- 2.8). Aortic geometries were obtained by magnetic resonance imaging, and the aortic blood flow field was computed using computational fluid dynamics. The aortic wall shear stress was obtained from the computations, and it was concluded that time-averaged wall shear stress decreased with increased age, probably as a consequence of increased aortic diameter and decreased stroke volume, which in turn reduces the shear rates in the aorta. However, the oscillatory shear index, which is a measure of the oscillatory nature of the wall shear stress vector, seemed to be unaffected by aging.
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| 30. |
- Lantz, Jonas, et al.
(författare)
-
Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
- 2012
-
Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 34:8, s. 1139-1148
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons.
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| 31. |
- Macdonald, Warren, 1954, et al.
(författare)
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A novel liner locking mechanism enhances retention stability.
- 2003
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Ingår i: Medical engineering & physics. - 1350-4533. ; 25:9, s. 747-54
-
Forskningsöversikt (refereegranskat)abstract
- Acetabular liner retention of a novel design of liner locking was evaluated in static and cyclic endurance modes. The locking mechanism combines geometric form and accurate machining to give high conformity to the acetabular shell and minimise relative motion against the metal shell, minimising debris generation and escape or ingress. Using amended test liners with integral coupling, mean static pullout strength was determined to be 399+/-53 N and lever-out strength 28.03+/-2.8 N m. Cyclic loading of 5 N m for up to 10 million cycles caused no significant reduction in strength, no detectable fretting wear, and the sealing mechanism prevented particle access between the cup interior and the "effective joint space". The stability measured ensures secure and reliable in vivo retention of the liner, comparable with extant component designs using other liner locking mechanisms.
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| 32. |
- Macdonald, Warren, 1954, et al.
(författare)
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Improved tibial cutting accuracy in knee arthroplasty.
- 2004
-
Ingår i: Medical engineering & physics. - : Elsevier BV. - 1350-4533. ; 26:9, s. 807-12
-
Tidskriftsartikel (refereegranskat)abstract
- Initial stability and development of long-term fixation for cementless tibial components at the knee both depend on the accuracy of fit between implanted components and prepared bone surfaces. Tibial surfaces prepared for total knee replacement with conventional saw-blades and guides were shown by Toksvig-Larsen to vary by over 2 mm, from a flat surface at the point of maximum variation, and all points varied with a standard deviation of up to 0.4 mm. Surface cutting errors are caused by flexion of the saw-blade and blade angulation from the ideal alignment, due to poor guidance or control by the saw-block or guide. Most conventional knee instrumentation relies on flat surface or slotted cutting blocks, constraining the moving saw-blade against one or two guide surfaces. Improved cutting action was achieved by constraining the saw from the pivot point of the blade, and controlling motion of this constraint with parallel action slides. Using this saw-guide and an improved saw-blade, tibial cuts were made in mock arthroplasty procedures on twenty four cadaveric tibiae in mortuo. Analysis of Variance and Tukey's HSD test showed that the improved saw technique yielded significantly better flatness (p < 0.03) and greatly improved roughness (p < 0.0005).
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| 33. |
- Maksuti, Elira, et al.
(författare)
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Modelling the heart with the atrioventricular plane as a piston unit
- 2015
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 37:1, s. 87-92
-
Tidskriftsartikel (refereegranskat)abstract
- 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 8-130 mmHg, an atrial pressure of approximatly 9 mmHg, and an arterial pressure change between 75 mmHg and 130 mmHg. In addition, the model reproduces the direction of the main systolic and diastolic movements of the AV piston with realistic velocity magnitude (similar to 10 cm/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.
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| 34. |
- Man, V., et al.
(författare)
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Impact of isotropic constitutive descriptions on the predicted peak wall stress in abdominal aortic aneurysms
- 2018
-
Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 53, s. 49-57
-
Tidskriftsartikel (refereegranskat)abstract
- Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-ofthe-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for achieving acceptable stress predictions in it. Influence of five different isotropic constitutive descriptions of AAA wall is tested; models reflect realistic non-linear, artificially stiff non-linear, or artificially stiff pseudo-linear constitutive descriptions of AAA wall. Influence of the AAA wall model is tested on idealized (n = 4) and patient-specific (n = 16) AAA geometries. Wall stress computations consider a (hypothetical) load-free configuration and include residual stresses homogenizing the stresses across the wall. Wall stress differences amongst the different descriptions were statistically analyzed. When the qualitatively similar non-linear response of the AAA wall with low initial stiffness and subsequent strain stiffening was taken into consideration, wall stress (and PWS) predictions did not change significantly. Keeping this non-linear feature when using an artificially stiff wall can save up to 30% of the computational time, without significant change in PWS. In contrast, a stiff pseudo-linear elastic model may underestimate the PWS and is not reliable for AAA wall stress computations.
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| 35. |
- Michaud, B., et al.
(författare)
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Determining in vivo sternoclavicular, acromioclavicular and glenohumeral joint centre locations from skin markers, CT-scans and intracortical pins : A comparison study
- 2016
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 38:3, s. 290-296
-
Tidskriftsartikel (refereegranskat)abstract
- CoR were located using anatomical, predictive, functional and imaging-based methods.Gold-standard locations were obtained using intracortical pins.Sternoclavicular joint: our findings are in agreement with ISB (Wu, 2005).Acromioclavicular joint: anatomical method of by van der Helm (1996) is suggested.Glenohumeral joint: the regression equation of Rab (2002) is suggested. To describe shoulder motion the sternoclavicular, acromioclavicular and glenohumeral joint centres must be accurately located. Within the literature various methods to estimate joint centres of rotation location are proposed, with no agreement of the method best suited to the shoulder. The objective of this study was to determine the most reliable non-invasive method for locating joint centre locations of the shoulder complex. Functional methods using pin mounted markers were compared to anatomical methods, functional methods using skin mounted markers, imaging-based methods using CT-scan data, and regression equations. Three participants took part in the study, that involved insertion of intracortical pins into the clavicle, scapula and humerus, a CT-scan of the shoulder, and finally data collection using a motion analysis system. The various methods to estimate joint centre location did not all agree, however suggestions about the most reliable non-invasive methods could be made. For the sternoclavicular joint, the authors suggest the anatomical method using the most ventral landmark on the sternoclavicular joint, as recommended by the International Society of Biomechanics. For the acromioclavicular joint, the authors suggest the anatomical method using the landmark defined as the most dorsal point on the acromioclavicular joint, as proposed by van der Helm. For the glenohumeral joint, the simple regression equation of Rab is recommended.
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| 36. |
- Panarese, Alessandro, et al.
(författare)
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A modified low-cost haptic interface as a tool for complex tactile stimulation
- 2011
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 33:3, s. 386-390
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the development and evaluation of a platform for the investigation of the human tactile ability. Specifically, it enables precise and reproducible application of time-varying 3D force stimuli to the skin of an immobilized human limb. We proceeded in the following steps: (1) programming a low-cost haptic interface to apply time-varying 3D force stimuli to a fixed rigid target, (2) implementing a combined feed-forward/feedback controller to improve the platform's precision and reliability in force stimulation, (3) determining the optimal tuning of the control loop parameters and (4) evaluating the system's performances when applying time-varying 3D force stimuli to an immobilized human finger pad. The system's performances were evaluated in terms of the accuracy and repeatability when delivering standard 3D force stimuli, i.e., stimuli with specified force components in the normal and skin tangential directions. Within the range of forces tested (5N in various directions), the maximum difference between the actual force and the desired value during static phases was <30mN (accuracy) and the root-mean-square of the standard deviation (repeatability) was 15mN during static phases and <75mN during dynamic phases.
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| 37. |
- Parker, Louis P., et al.
(författare)
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In silico parametric analysis of femoro-jugular venovenous ECMO and return cannula dynamics : In silico analysis of femoro-jugular VV ECMO
- 2024
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 125
-
Tidskriftsartikel (refereegranskat)abstract
- Background: : Increasingly, computational fluid dynamics (CFD) is helping explore the impact of variables like: cannula design/size/position/flow rate and patient physiology on venovenous (VV) extracorporeal membrane oxygenation (ECMO). Here we use a CFD model to determine what role cardiac output (CO) plays and to analyse return cannula dynamics. Methods: : Using a patient-averaged model of the right atrium and venae cava, we virtually inserted a 19Fr return cannula and a 25Fr drainage cannula. Running large eddy simulations, we assessed cardiac output at: 3.5–6.5 L/min and ECMO flow rate at: 2–6 L/min. We analysed recirculation fraction (Rf), time-averaged wall shear stress (TAWSS), pressure, velocity, and turbulent kinetic energy (TKE) and extracorporeal flow fraction (EFF = ECMO flow rate/CO). Results: : Increased ECMO flow rate and decreased CO (high EFF) led to increased Rf (R = 0.98, log fit). Negative pressures developed in the venae cavae at low CO and high ECMO flow (high CR). Mean return cannula TAWSS was >10 Pa for all ECMO flow rates, with majority of the flow exiting the tip (94.0–95.8 %). Conclusions: : Our results underpin the strong impact of CO on VV ECMO. A simple metric like EFF, once supported by clinical data, might help predict Rf for a patient at a given ECMO flow rate. The return cannula imparts high shear stresses on the blood, largely a result of the internal diameter.
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| 38. |
- Peacock, John, et al.
(författare)
-
Measurement of the vibration of the middle ear ossicles with removed eardrum : a method for quantification of ossicular fixation.
- 2013
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 35:12, s. 1786-92
-
Tidskriftsartikel (refereegranskat)abstract
- Chronic inflammation of the middle ear is a common disease in which the mobility of the middle ear ossicles may be reduced; resulting in hearing impairment. Knowledge of the degree of ossicular mobility is useful in helping a surgeon determine how to proceed with treatment. In advanced cases, mobility can be assessed by manually pressing on the ossicles, but in less advanced cases manual assessment can provide limited useful information. Ossicular vibration can be measured with a laser vibrometer, but only the manubrium of the malleus is optically visible without removing the eardrum. Since the eardrum is the means by which acoustic energy is translated into the mechanical motion of the ossicles, removing it renders any subsequent measurements of ossicular motion meaningless. We therefore devised a technique in which the ossicles are vibrated magnetically. After measuring the response of the umbo to acoustic stimulation, we removed the eardrum and attached a small magnet to the manubrium. An electromagnetic excitation coil was then used to vibrate the magnet, and the signal to the coil was adjusted until the vibration of the ossicles matches that achieved acoustically. In this paper we explain the method and describe some test measurements on a vinyl membrane, and some preliminary results obtained on a fresh-frozen human temporal bone before and after artificial fixation of the ossicles.
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| 39. |
- Polzer, S., et al.
(författare)
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Importance of material model in wall stress prediction in abdominal aortic aneurysms
- 2013
-
Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 35:9, s. 1282-1289
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Results of biomechanical simulation of the abdominal aortic aneurysm (AAA) depend on the constitutive description of the wall. Based on in vitro and in vivo experimental data several constitutive models for the AAA wall have been proposed in the literature. Those models differ strongly from each other and their impact on the computed stress in biomechanical simulation is not clearly understood. Methods: Finite element (FE) models of AAAs from 7 patients who underwent elective surgical repair were used to compute wall stresses. AAA geometry was reconstructed from CT angiography (CT-A) data and patient-specific (PS) constitutive descriptions of the wall were derived from planar biaxial testing of anterior wall tissue samples. In total 28 FE models were used, where the wall was described by either patient-specific or previously reported study-average properties. This data was derived from either uniaxial or biaxial in vitro testing. Computed wall stress fields were compared on node-by-node basis. Results: Different constitutive models for the AAA wall cause significantly different predictions of wall stress. While study-average data from biaxial testing gives globally the same stress field as the patient-specific wall properties, the material model based on uniaxial test data overestimates the wall stress on average by 30. kPa or about 67% of the mean stress. A quasi-linear description based on the in vivo measured distensibility of the AAA wall leads to a completely altered stress field and overestimates the wall stress by about 75. kPa or about 167% of the mean stress. Conclusion: The present study demonstrated that the constitutive description of the wall is crucial for AAA wall stress prediction. Consequently, results obtained using different models should not be mutually compared unless different stress gradients across the wall are not taken into account. Highly nonlinear material models should be preferred when the response of AAA to increased blood pressure is investigated, while the quasi-linear model with high initial stiffness produces negligible stress gradients across the wall and thus, it is more appropriate when response to mean blood pressure is calculated.
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| 40. |
- Sandberg, Frida, et al.
(författare)
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Predicting spontaneous termination of atrial fibrillation using the surface ECG
- 2006
-
Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 28:8, s. 802-808
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Tidskriftsartikel (refereegranskat)abstract
- By recognizing and characterizing conditions under which atrial fibrillation (AF) is likely to terminate spontaneously or be sustained, improved treatment of sustained AF may result and unnecessary treatment of self-terminating AF avoided. Time-frequency measures that characterize AF, such as fibrillatory frequency, amplitude, and waveform shape (exponential decay), are extracted from the residual ECG following QRST cancellation. Three complexity measures are also studied, characterizing the degree of organization of atrial activity. All measures are analysed using a training set, consisting of 20 recordings of AF with known termination properties, and a test set of 30 recordings. Spontaneous termination was best predicted by a low and stable fibrillatory frequency and a low exponential decay. Using these predictors, 90% of the test set was correctly classified into terminating and sustained AF. Neither fibrillation amplitude nor the complexity measures differed significantly between the two sets. (c) 2005 IPEM. Published by Elsevier Ltd. All rights reserved.
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| 41. |
- Sandsten, Maria, et al.
(författare)
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Estimation of HRV spectrogram using multiple window methods focussing on the high frequency power
- 2006
-
Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 28:8, s. 749-761
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the results of different multiple window spectrum analysis methods are compared in the estimation of heart rate variability (HRV) power spectra, in the high frequency band (HF), around 0.25 Hz, related to respiratory sinus arrhythmia (RSA). The evaluation is performed by simulating different spectrum shapes and peak frequency locations and calculating the mean squared error of a frequency range close around the strongest spectral peak. The results show that it is preferable to use the Peak Matched Multiple Windows in most situations, but the Welch method and the Sinusoid Multiple Windows can be as reliable in certain aspects.
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| 42. |
- Sandsten, Maria
(författare)
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Evaluation of the optimal lengths and number of multiple windows for spectrogram estimation of SSVEP
- 2010
-
Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 32:4, s. 372-383
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to present the optimal number of windows and window lengths using multiple window spectrogram for estimation of non-stationary processes with shorter or longer duration. Such processes could start in the EEG as a result of a stimuli, e.g. steady-state visual evoked potentials (SSVEP). In many applications the Welch method is used with standard set-ups for window lengths and number of averaged spectra/spectrograms. This paper optimizes the window lengths and number of windows of the Welch method and compare the calculated mean squared error for this method with the optimal parameter choices of other more recent, socalled, multiple window or multitaper methods. The results could be useful in the choice of more optimal window functions for spectrogram estimation in certain applications. Some examples of spectrogram estimation of SSVEP are shown.
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| 43. |
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| 44. |
- Sebelius, Fredrik, et al.
(författare)
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Classification of motor commands using a modified self-organising feature map.
- 2005
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:5, s. 403-413
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a control system for an advanced prosthesis is proposed and has been investigated in two different biological systems: (1) the spinal withdrawal reflex system of a rat and (2) voluntary movements in two human males: one normal subject and one subject with a traumatic hand amputation. The small-animal system was used as a model system to test different processing methods for the prosthetic control system. The best methods were then validated in the human set-up. The recorded EMGs were classified using different ANN algorithms, and it was found that a modified self-organising feature map (SOFM) composed of a combination of a Kohonen network and the conscience mechanism algorithm (KNC) was superior in performance to the reference networks (e.g. multi-layer perceptrons) as regards training time, low memory consumption, and simplicity in finding optimal training parameters and architecture. The KNC network classified both experimental set-ups with high accuracy, including five movements for the animal set-up and seven for the human set-up.
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| 45. |
- Smoljkić, M., et al.
(författare)
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Comparison of in vivo vs. ex situ obtained material properties of sheep common carotid artery
- 2018
-
Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 55, s. 16-24
-
Tidskriftsartikel (refereegranskat)abstract
- Patient-specific biomechanical modelling can improve preoperative surgical planning. This requires patient-specific geometry as well as patient-specific material properties as input. The latter are, however, still quite challenging to estimate in vivo. This study focuses on the estimation of the mechanical properties of the arterial wall. Firstly, in vivo pressure, diameter and thickness of the arterial wall were acquired for sheep common carotid arteries. Next, the animals were sacrificed and the tissue was stored for mechanical testing. Planar biaxial tests were performed to obtain experimental stress-stretch curves. Finally, parameters for the hyperelastic Mooney–Rivlin and Gasser–Ogden–Holzapfel (GOH) material model were estimated based on the in vivo obtained pressure-diameter data as well as on the ex situ experimental stress-stretch curves. Both material models were able to capture the in vivo behaviour of the tissue. However, in the ex situ case only the GOH model provided satisfactory results. When comparing different fitting approaches, in vivo vs. ex situ, each of them showed its own advantages and disadvantages. The in vivo approach estimates the properties of the tissue in its physiological state while the ex situ approach allows to apply different loadings to properly capture the anisotropy of the tissue. Both of them could be further enhanced by improving the estimation of the stress-free state, i.e. by adding residual circumferential stresses in vivo and by accounting for the flattening effect of the tested samples ex vivo.
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| 46. |
- Stasiunas, Antanas, et al.
(författare)
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An adaptive panoramic filter bank as a qualitative model of the filtering system of the cochlea : The peculiarities in linear and nonlinear mode
- 2012
-
Ingår i: Medical Engineering and Physics. - Oxford : Elsevier. - 1350-4533 .- 1873-4030. ; 34:2, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- Outer hair cells in the cochlea of the ear, together with the local structures of the basilar membrane, reticular lamina and tectorial membrane constitute the adaptive primary filters (PF) of the second order. We used them for designing a serial-parallel signal filtering system. We determined a rational number of the PF included in Gaussian channels of the system, summation weights of the output signals, and distribution of the PF along the basilar membrane. A Gaussian panoramic filter bank each channel of which consists of five PF is presented as an example. The properties of the PF, the channel and the filter bank operating in the linear and nonlinear modes are determined during adaptation and under efferent control. The results suggest that application of biological filtering principles can be useful for designing cochlear implants with new speech encoding strategies. © 2011 IPEM.
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| 47. |
- Stasiunas, Antanas, et al.
(författare)
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Compression, adaptation and efferent control in a revised outer hair cell functional model
- 2005
-
Ingår i: Medical Engineering and Physics. - Amsterdam : Elsevier. - 1350-4533 .- 1873-4030. ; 27:9, s. 780-789
-
Tidskriftsartikel (refereegranskat)abstract
- In the cochlea of the inner ear, outer hair cells (OHC) together with the local passive structures of the tectorial and basilar membranes comprise non-linear resonance circuits with the local and central (afferent–efferent) feedback. The characteristics of these circuits and their control possibilities depend on the mechanomotility of the OHC. The main element of our functional model of the OHC is the mechanomotility circuit with the general transfer characteristic y = k tanh(x − a). The parameter k of this characteristic reflects the axial stiffness of the OHC, and the parameter a working position of the hair bundle. The efferent synaptic signals act on the parameter k directly and on the parameter a indirectly through changes in the membrane potential. The dependences of the sensitivity and selectivity on changes in the parameters a and k are obtained by the computer simulation. Functioning of the model at low-level input signals is linear. Due to the non-linearity of the transfer characteristic of the mechanomotility circuit the high-level signals are compressed. For the adaptation and efferent control, however, the transfer characteristic with respect to the initial operating point should be asymmetrical (a > 0). The asymmetry relies on the deflection of the hair bundle from the axis of the OHC.
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| 48. |
- Stasiunas, Antanas, et al.
(författare)
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Physiologically inspired signal preprocessing for auditory prostheses : Insights from the electro-motility of the OHC
- 2008
-
Ingår i: Medical Engineering and Physics. - Oxford, England : Elsevier. - 1350-4533 .- 1873-4030. ; 30:2, s. 171-181
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Tidskriftsartikel (refereegranskat)abstract
- We designed a non-linear functional model of the outer hair cell (OHC) functioning in the filtering system of the cochlea and then isolated from it two second-order structures, one employing the mechanism of the somatic motility and the other the hair bundle motion of the OHC. The investigation of these circuits showed that the main mechanism increasing the sensitivity and frequency selectivity of the filtering system is the somatic motility. The mechanism of the active hair bundle motion appeared less suitable for realization of the band-pass filtering structures due to the dependence of the sensitivity, natural frequency and selectivity on the signal intensity. We combined three second-order filtering structures employing the mechanism of the somatic motility and the lateral inhibition to form a parallel-type filtering channel of the sixth order with the frequency characteristics of the Butterworth-type and Gaussian-type. The investigation of these channels showed that the Gaussian-type channel has the advantage over the Butterworth-type channel. It is more suitable for realization of a filter bank with common lateral circuits and has less distorted frequency characteristic in the nonlinear mode.
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| 49. |
- Sul, Young-Taeg, 1960, et al.
(författare)
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The electrochemical oxide growth behaviour on titanium in acid and alkaline electrolytes.
- 2001
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Ingår i: Medical Engineering & Physics. - 1350-4533. ; 23:5, s. 329-46
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Tidskriftsartikel (refereegranskat)abstract
- Titanium implants have a thin oxide surface layer. The properties of this oxide layer may explain the good biocompatibility of titanium implants. Anodic oxidation results in a thickening of the oxide film, with possible improved biocompatability of anodized implants. The aim of the present study was twofold: (1) firstly, to characterize the growth behaviour of galvanostatically prepared anodic oxide films on commercially pure (c.p.) titanium and (2) secondly, to establish a better understanding of the electroche0mical growth behaviour of anodic oxide on commercially pure titanium (ASTM grade 1) after changes of the electrochemical parameters in acetic acid, phosphoric acid, calcium hydroxide, and sodium hydroxide under galvanostatic anodizing mode. The oxide thickness was measured by Ar sputter etching in Auger Electron spectroscopy (AES) and the colours were estimated by an L*a*b* system (lightness, hue and saturation) using a spectrophotometer. In the first part of our study, it was demonstrated that the interference colours were useful to identify the thickness of titanium oxide. It was also found that the anodic forming voltages with slope (dV/dt) in acid electrolytes were higher than in alkaline electrolytes. Each of the used electrolytes demonstrates an intrinsically specific growth constant (nm/V) in the range of 1.4--2.78 nm/V. In the second part of our study we found, as a general trend, that an increase of electrolyte concentration and electrolyte temperature respectively decreases the anodic forming voltage, the anodic forming rate (nm/s) and the current efficiency (nm.cm(2)/C), while an increase of the current density and the surface area ratio of the anode to cathode increase the anodic forming voltage, the anodic forming rate and the current efficiency. The effects of electrolyte concentration, electrolyte temperature, and agitation speed were explained on the basis of the model of the electrical double layer.
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- Tabakov, S, et al.
(författare)
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Development of educational image databases and e-books for medical physics training
- 2005
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:7, s. 591-598
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Tidskriftsartikel (refereegranskat)abstract
- Medical physics education and training requires the use of extensive imaging material and specific explanations. These requirements provide an excellent background for application of e-Learning. The EU projects Consortia EMERALD and EMIT developed five volumes of such materials, now used in 65 countries. EMERALD developed e-Learning materials in three areas of medical physics (X-ray diagnostic radiology, nuclear medicine and radiotherapy). EMIT developed e-Learning materials in two further areas: ultrasound and magnetic resonance imaging. This paper describes the development of these e-Learning materials (consisting of e-books and educational image databases). The e-books include tasks helping studying of various equipment and methods. The text of these PDF e-books is hyperlinked with respective images. The e-books are used through the readers' own Internet browser. Each Image Database (IDB) includes a browser, which displays hundreds of images of equipment, block diagrams and graphs, image quality examples, artefacts, etc. Both the e-books and IDB are engraved on five separate CD-ROMs. Demo of these materials can be taken from www.emerald2.net.
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