| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Kulmala, Katariina, et al.
(författare)
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Diffusion of ionic and non-ionic contrast agents in articular cartilage with increased cross-linking : contribution of steric and electrostatic effects
- 2013
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 35:10, s. 1415-20
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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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| 7. |
- Lantz, Jonas, et al.
(författare)
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Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
- 2012
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 34:8, s. 1139-1148
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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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| 8. |
- Panarese, Alessandro, et al.
(författare)
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A modified low-cost haptic interface as a tool for complex tactile stimulation
- 2011
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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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| 9. |
- Peacock, John, et al.
(författare)
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Measurement of the vibration of the middle ear ossicles with removed eardrum : a method for quantification of ossicular fixation.
- 2013
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 35:12, s. 1786-92
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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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| 10. |
- Polzer, S., et al.
(författare)
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Importance of material model in wall stress prediction in abdominal aortic aneurysms
- 2013
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Ingår i: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 35:9, s. 1282-1289
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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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