Medical Engineering & Physics - Articles in Press

Usability and performance of a wearable tele-echography robot for focused assessment of trauma using sonography - Corrected Proof

Keiichiro Ito, Shigeki Sugano, Ryohei Takeuchi, Kyota Nakamura, Hiroyasu Iwata — 2012-05-22

Abstract: Focused Assessment with Sonography for Trauma (FAST) is widely used as a first lifesaving step for patients suffering from internal bleeding. Because it may take a long time to transport such patients to a hospital, a wearable and portable tele-echography robot that a paramedic can attach to the patient has been developed. In the current study, experiments were conducted to evaluate the usability and performance of attached FAST.The proposed robot must be attached to 4 areas to perform FAST. The time required for attachment and the positions of attachment completed by 9 non-medical staff members, as well as the time it took for the FAST to reach a medical doctor, were measured. The echo images obtained when the patient's body was in motion were evaluated by a medical doctor.The robot could be attached to all 4 areas within approximately 5min, and the maximum gap was 4.8cm. This indicates that a paramedic who has received training in emergency medical care should be able to attach the robot to a patient quickly and accurately. Additionally, it was confirmed that the robot could be used to complete FAST under a doctor's control within 9min and that the extracted echo images were suitable for FAST.A comparison of the results with current ambulance transportation time confirmed that FAST could be completed approximately 14min before the patient reached the hospital. The results of the current study indicate that the robot is worth using, is suitable for FAST, and will be effective in emergency medical care.

Development and application of a portable manual non-contact-type goniometric instrument for measuring human anatomical angular parameters - Corrected Proof

Shin-ichi Susato — 2012-05-21

Abstract: Several manual contact-type goniometric instruments have previously been developed to measure joint range of motion (ROM) during physical-therapy evaluation. These include the universal goniometer and the gravity-dependent goniometer, or inclinometer, which are used to measure the ROM angle of a subject in a fully erect posture. Here, we developed a manual non-contact-type portable goniometric instrument for the measurement of anatomical angular parameters based on the principle of spot irradiation by using laser markers. The accuracy of the developed instrument was tested and its performance was compared with that of a contact-type instrument by using a skeletal model (14 static angle assessments), a free posture manikin (18 static angle assessments), and healthy human bodies (5 males and 5 females; 11 dynamic angle assessments). Measurement errors were examined also. When taking the measurements, a visual landmark-detection method was used in place of the conventional palpation method, which is inappropriate for a non-contact measuring system. The instrument developed here is applicable for practical non-contact goniometry and ROM measurements.

Theoretical study of the flow rate toward the right heart territory in case of total occlusion of the right coronary artery - Corrected Proof

2012-05-14

Abstract: In this work, patients with severe coronary disease and chronic occlusion of the right coronary artery (RCA) are studied. In this clinical situation, the collateral circulation is an important factor in the preservation of the myocardium until reperfusion of the area at risk. An accurate estimation of collateral flow is crucial in surgical bypass planning as it can influence the outcome of a given treatment for a given patient. The evaluation of collateral flow is frequently achieved using an index (CFI, Collateral Flow Index) based on pressure measurements.Using a model of the coronary circulation based on hydraulic/electric analogy, we demonstrate, through theoretical simulations, that a wide range of fractional collateral flow values can be obtained for any given distal pressure difference depending on the values of the capillary and collateral resistances.

Influence of unit distance and conduction velocity on the spectra of extracellular action potentials recorded with intrafascicular electrodes - Corrected Proof

Shaoyu Qiao, Ken Yoshida — 2012-05-14

Abstract: The use of highly selective penetrating electrodes yields multi-unit extracellular action potential (EAP) recordings of the nerve fibers in the vicinity of the electrode. Accessing the information carried within the neural data stream further requires discrimination and separation of the multi-unit recording into their constituent multiple single unit spike trains. Shape differences in the single fiber action potentials (SFAPs) are typically used as the criteria for unit separation. The present paper explores the origins of the shape differences through analysis of the EAP in the frequency domain. We present the derivation and computational model predictions of a method to quantitatively analyse changes in the spectral components of SFAPs with an axially located intrafascicular electrode with non-radially symmetrical sensitivity function. A spatial tissue filter relationship was derived using reciprocity equations in the spatial frequency domain and transformed to time frequency. A three dimensional bioelectrical volume conductor finite element model of a recording electrode residing in a nerve fascicle was developed to explore the potential distribution in the nerve fascicle and further derive the electrode–fiber coupling function in the time-frequency domain. It was found that the spectral distribution of the SFAP was multimodal in nature, similar to empirical reported earlier, and could be predicted by taking the single fiber action currents (SFACs) filtered by the electrode–fiber coupling function. This function manifested itself as a low-pass filter of the SFAC, dependent upon the fiber's location relative to the electrode and conduction velocity. Analysis of the spectral distribution revealed that changes in the landmarks of the distribution could be related to the fiber location and conduction velocity. Moreover, a consistent relationship was found when exploring the distribution of fibers located off the one axis of symmetry.

Automated setup of functional electrical stimulation for drop foot using a novel 64 channel prototype stimulator and electrode array: Results from a gait-lab based study - Corrected Proof

2012-05-07

Abstract: Functional electrical stimulation is commonly used to correct drop foot following stroke or multiple sclerosis. This technique is successful for many patients, but previous studies have shown that a significant minority have difficulty identifying correct sites to place the electrodes in order to produce acceptable foot movement. Recently there has been some interest in the use of ‘virtual electrodes’, the process of stimulating a subset of electrodes chosen from an array, thus allowing the site of stimulation to be moved electronically rather than physically. We have developed an algorithm for automatically determining the best site of stimulation and tested it on a computer linked to a small, battery-powered prototype stimulator with 64 individual output channels. Stimulation was delivered via an 8×8 array adhered to the leg by high-resistivity self-adhesive hydrogel. Ten participants with stroke (ages 53–71 years) and 11 with MS (ages 40–80 years) were recruited onto the study and performed two walks of 10m for each of the following conditions: own setup (PS), clinician setup (CS), automated setup (AS) and no stimulation (NS). The PS and CS conditions used the participant's own stimulator with two conventional electrodes; the AS condition used the new stimulator and algorithm. Outcome measures were walking speed, foot angle at initial contact and the Borg Rating of Perceived Exertion.Mean walking speed with no stimulation was 0.61m/s; all FES setups significantly increased speed relative to this (AS p<0.05, PS p<0.01, CS p<0.01). Speed for PS (0.72m/s) was faster than both AS (0.65m/s, p<0.01) and CS (0.68m/s, p<0.05). Frontal plane foot orientation at heel-strike was more neutral for AS (0.3° everted) than in the NS (11.2° inverted, p<0.01), PS (4.5° inverted, p<0.05) and CS (3.1° inverted, p<0.05) conditions. Dorsiflexion angles for AS (4.2°) were larger than NS (−3.0°, p<0.01), not different to PS (4.3°, p>0.05) and less dorsiflexed than CS (6.0°, p<0.05).This proof of principle study has demonstrated that automated setup of an array stimulator produces results broadly comparable to clinician setup. Slower walking speed for automated and clinician setups compared to the participants’ own setup may be due to the participants’ lack of familiarity with responses different to their usual setups. Automated setup using the method described here seems sufficiently reliable for future longer-term investigation outside the laboratory and may lead to FES becoming more viable for patients who, at present, have difficulty setting up conventional stimulators.

Optimised in vitro applicable loads for the simulation of lateral bending in the lumbar spine - Corrected Proof

Marcel Dreischarf, Antonius Rohlmann, Georg Bergmann, Thomas Zander — 2012-05-07

Abstract: In in vitro studies of the lumbar spine simplified loading modes (compressive follower force, pure moment) are usually employed to simulate the standard load cases flexion-extension, axial rotation and lateral bending of the upper body. However, the magnitudes of these loads vary widely in the literature. Thus the results of current studies may lead to unrealistic values and are hardly comparable. It is still unknown which load magnitudes lead to a realistic simulation of maximum lateral bending.A validated finite element model of the lumbar spine was used in an optimisation study to determine which magnitudes of the compressive follower force and bending moment deliver results that fit best with averaged in vivo data.The best agreement with averaged in vivo measured data was found for a compressive follower force of 700N and a lateral bending moment of 7.8Nm.These results show that loading modes that differ strongly from the optimised one may not realistically simulate maximum lateral bending. The simplified but in vitro applicable loading cannot perfectly mimic the in vivo situation. However, the optimised magnitudes are those which agree best with averaged in vivo measured data. Its consequent application would lead to a better comparability of different investigations.

A computer-aided diagnosis approach for emphysema recognition in chest radiography - Corrected Proof

2012-04-23

Abstract: The purpose of this work is twofold: (i) to develop a CAD system for the assessment of emphysema by digital chest radiography and (ii) to test it against CT imaging. The system is based on the analysis of the shape of lung silhouette as imaged in standard chest examination. Postero-anterior and lateral views are processed to extract the contours of the lung fields automatically. Subsequently, the shape of lung silhouettes is described by polyline approximation and the computed feature-set processed by a neural network to estimate the probability of emphysema.Images of radiographic studies from 225 patients were collected and properly annotated to build an experimental dataset named EMPH. Each patient had undergone a standard two-views chest radiography and CT for diagnostic purposes. In addition, the images (247) from JSRT dataset were used to evaluate lung segmentation in postero-anterior view.System performances were assessed by: (i) analyzing the quality of the automatic segmentation of the lung silhouette against manual tracing and (ii) measuring the capabilities of emphysema recognition. As to step i, on JSRT dataset, we obtained overlap percentage (Ω) 92.7±3.3%, Dice Similarity Coefficient (DSC) 95.5±3.7% and average contour distance (ACD) 1.73±0.87mm. On EMPH dataset we had Ω=93.1±2.9%, DSC=96.1±3.5% and ACD=1.62±0.92mm, for the postero-anterior view, while we had Ω=94.5±4.6%, DSC=91.0±6.3% and ACD=2.22±0.86mm, for the lateral view. As to step ii, accuracy of emphysema recognition was 95.4%, with sensitivity and specificity 94.5% and 96.1% respectively. According to experimental results our system allows reliable and inexpensive recognition of emphysema on digital chest radiography.

Novel set of vectorcardiographic parameters for the identification of ischemic patients - Corrected Proof

Raúl Correa, Pedro D. Arini, Max E. Valentinuzzi, Eric Laciar — 2012-04-19

Abstract: New signal processing techniques have enabled the use of the vectorcardiogram (VCG) for the detection of cardiac ischemia. Thus, we studied this signal during ventricular depolarization in 80 ischemic patients, before undergoing angioplasty, and 52 healthy subjects with the objective of evaluating the vectorcardiographic difference between both groups so leading to their subsequent classification. For that matter, seven QRS-loop parameters were analyzed, i.e.: (a) Maximum Vector Magnitude; (b) Volume; (c) Planar Area; (d) Maximum Distance between Centroid and Loop; (e) Angle between XY and Optimum Plane; (f) Perimeter and, (g) Area-Perimeter Ratio. For comparison, the conventional ST-Vector Magnitude (STVM) was also calculated. Results indicate that several vectorcardiographic parameters show significant differences between healthy and ischemic subjects. The identification of ischemic patients via discriminant analysis using STVM produced 73.2% Sensitivity (Sens) and 73.9% Specificity (Spec). In our study, the QRS-loop parameter with the best global performance was Volume, which achieved Sens=64.5% and Spec=74.6%. However, when all QRS-loop parameters and STVM were combined, we obtained Sens=88.5% and Spec=92.1%. In conclusion, QRS loop parameters can be accepted as a complement to conventional STVM analysis in the identification of ischemic patients.

Noninvasive induction implant heating: An approach for contactless altering of mechanical properties of shape memory implants - Corrected Proof

2012-04-16

Abstract: This article shows an approach to change the properties of an orthopaedic shape memory implant within biological tissue, using contactless induction heating. Due to inducing the one way-memory effect, triggered by the rise of temperature within the implant, the geometry and hence the mechanical properties of the implant itself, are altered. The power uptake of the implant, depending on the induction parameters as well as on its position within the induction coil, is shown. Thermographic measurements are carried out in order to determine the surface temperature distribution of the implant. In order to simulate biological tissue, the implant was embedded in agarose gel. Suitable heating parameters, in terms of a short heating process in combination with a reduced heat impact on the surrounding environment, were determined.

The important roles of tissue anisotropy and tissue-to-tissue contact on the dynamical behavior of a symmetric tri-leaflet valve during multiple cardiac pressure cycles - Corrected Proof

A.F. Saleeb, A. Kumar, V.S. Thomas — 2012-04-09

Abstract: Restricting our scope to the dynamical motion of the leaflets, we present a computational model for a symmetric, tri-leaflet, bioprosthetic heart valve (BHV) at the end of five complete cardiac pressure cycles, reaching the steady state of deformation during both closing and opening phases. To this end, we utilized a highly anisotropic material model for the large deformation behavior of the tissue material, for which an experimental validation was provided. The important findings are: (1) material anisotropy has significant effect on the valve opening/closing; (2) the asymmetric deformations, especially in the fully closed configuration, justify the use of cyclic symmetry; (3) adopting the fully-open position as an initial/reference configuration has the advantage of completely bypassing any complications arising from the need to assume the size and shape of the contact area in the coaptation regions of the leaflets that is necessary when the alternative, commonly-used, approach of selecting the fully-closed position is used as a reference; and (4) with proper treatments for both material anisotropy and tissue-to-tissue contact, the overall BHV model provide realistic results in conformity with the ex vivo/in vitro experiments.

A multi-tissue mass-spring model for computer assisted breast surgery - Corrected Proof

2012-04-09

Abstract: The aim of this work was to develop and validate a 3D female breast deformation model for computer assisted breast surgery. Magnetic resonance (MR) image data of a patient undergoing breast biopsy, were acquired using two different protocols with the patient in prone position: (i) uncompressed breast and (ii) compressed breast, with lateral single breast compression, realized with a movable slab. The acquired images were then segmented using a semi-automatic procedure and from the extracted volumes of interest tetrahedral meshes representing skin, fat and mammary glands were generated. Tissue deformation was ruled by a mass-spring model: first, an iterative approximation algorithm was implemented to estimate the spring's rest length and stiffness, accounting for gravity force; then the resulting parameters were used to deform the uncompressed breast model in order to reach the real compressed one (ground truth). Results showed that gravity force applied to the mesh was properly compensated by the internal elastic forces, leading to a distance between the deformed mesh and the reference data of 0.036±0.092mm (median±inter quartile range). The point to mesh residual distance between the deformed mesh and the ground truth was 1.224±2.202mm (median±inter quartile range). Further investigation on a larger patient dataset is required for a more robust confirmation of model accuracy in predicting breast deformations.

An experimental investigation on thermal exposure during bone drilling - Corrected Proof

JuEun Lee, O. Burak Ozdoganlar, Yoed Rabin — 2012-04-06

Abstract: This study presents an experimental investigation of the effects of spindle speed, feed rate, and depth of drilling on the temperature distribution during drilling of the cortical section of the bovine femur. In an effort to reduce measurement uncertainties, a new approach for temperature measurements during bone drilling is presented in this study. The new approach is based on a setup for precise positioning of multiple thermocouples, automated data logging system, and a computer numerically controlled (CNC) machining system. A battery of experiments that has been performed to assess the uncertainty and repeatability of the new approach displayed adequate results. Subsequently, a parametric study was conducted to determine the effects of spindle speed, feed rate, hole depth, and thermocouple location on the measured bone temperature. This study suggests that the exposure time during bone drilling far exceeds the commonly accepted threshold for thermal injury, which may prevail at significant distances from the drilled hole. Results of this study suggest that the correlation of the thermal exposure threshold for bone injury and viability should be further explored.

The potential of multi-slice computed tomography based quantification of the structural anisotropy of vertebral trabecular bone - Corrected Proof

Zbisław Tabor, Rafał Petryniak, Zbigniew Latała, Tomasz Konopka — 2012-04-05

Abstract: In the present paper we addressed the problem of whether the information about the structural anisotropy of trabecular bone can be retrieved from low-quality data, captured with clinical multi-raw spiral CT scanners. Two measures of quantifying structural anisotropy were tested – the current standard mean intercept length (MIL) and the gray-level structure tensor (GST). Thirty two vertebral bodies were μCT and CT scanned. The reference values of structural anisotropy were measured in μCT images and compared with the measures of structural anisotropy determined from low-quality CT data. MIL-based measures of structural anisotropy cannot be reliably determined from CT data. The assessment of the GST is significantly better than that of MIL, but the accuracy is not, in general, satisfactory. Based on the results of experiments with artificial data and the analysis of the real images, it can be concluded that a possible reason of the poor performance is anisotropic resolution of clinical CT scanners.

Improving comfort of shoe sole through experiments based on CAD-FEM modeling - Corrected Proof

Pasquale Franciosa, Salvatore Gerbino, Antonio Lanzotti, Luca Silvestri — 2012-04-04

Abstract: It was reported that next to style, comfort is the second key aspect in purchasing footwear. One of the most important components of footwear is the shoe sole, whose design is based on many factors such as foot shape/size, perceived comfort and materials. The present paper focuses on the parametric analysis of a shoe sole to improve the perceived comfort. The sensitivity of geometric and material design factors on comfort degree was investigated by combining real experimental tests and CAD-FEM simulations. The correlation between perceived comfort and physical responses, such as plantar pressures, was estimated by conducting real tests. Four different conditions were analyzed: subjects wearing three commercially available shoes and in a barefoot condition. For each condition, subjects expressed their perceived comfort score. By adopting plantar sensors, the plantar pressures were also monitored. Once given such a correlation, a parametric FEM model of the footwear was developed. In order to better simulate contact at the plantar surface, a detailed FEM model of the foot was also generated from CT scan images. Lastly, a fractional factorial design array was applied to study the sensitivity of different sets of design factors on comfort degree. The findings of this research showed that the sole thickness and its material highly influence perceived comfort. In particular, softer materials and thicker soles contribute to increasing the degree of comfort.

Model-oriented review and multi-body simulation of the ossicular chain of the human middle ear - Corrected Proof

G. Volandri, F. Di Puccio, P. Forte, S. Manetti — 2012-04-03

Abstract: The ossicular chain of the human middle ear has a key role in sound conduction since it transfers vibrations from the tympanic membrane to the cochlea, connecting the outer and the inner part of the hearing organ.This study reports firstly a description of the main anatomical features of the middle ear to introduce a detailed survey of its biomechanics, focused on model development, with a collection of geometric, inertial and mechanical/material parameters. The joint issues are particularly discussed from the perspective of developing a model of the middle ear both explanatory and predictive. Such a survey underlines the remarkable dispersion of data, due also to the lack of a standardization of the experimental techniques and conditions.Subsequently, a 3D multi-body model of the ossicular chain and other structures of the middle ear is described. Such an approach is justified as the ossicles were proven to behave as rigid bodies in the human hearing range and was preferred to the more widely used finite element one as it simplifies the model development and improves joint modeling. The displacement of the umbo (a reference point of the tympanic membrane) in the 0.3–6kHz frequency range was defined as input of the model, while the stapes footplate displacement as output. A parameter identification procedure was used to find parameter values for reproducing experimental and numerical reference curves taken from the literature. This simple model might represent a valid alternative to more complex models and might provide a useful tool to simulate pathological/post-surgical/post-traumatic conditions and evaluate ossicular replacement prostheses.

A mechanical jig for measuring ankle supination and pronation torque in vitro and in vivo - Corrected Proof

Daniel Tik-Pui Fong, Mandy Man-Ling Chung, Yue-Yan Chan, Kai-Ming Chan — 2012-04-03

Abstract: This study presents the design of a mechanical jig for evaluating the ankle joint torque on both cadaver and human ankles. Previous study showed that ankle sprain motion was a combination of plantarflexion and inversion. The device allows measurement of ankle supination and pronation torque with one simple axis in a single step motion. More importantly, the ankle orientation allows rotation starting from an anatomical position. Six cadaveric specimens and six human subjects were tested with simulated and voluntary rotation respectively. The presented mechanical jig makes possible the determination of supination torque for studying ankle sprain injury and the estimation of pronation torque for examining peroneal muscle response.

A numerical parametric study of the mechanical action of pulsatile blood flow onto axisymmetric stenosed arteries - Corrected Proof

Tristan Belzacq, Stéphane Avril, Emmanuel Leriche, Alexandre Delache — 2012-04-02

Abstract: In the present paper, a fluid–structure interaction model is developed, questioning how the mechanical action of the blood onto an atheromatous plaque is affected by the length and the severity of the stenosis. An axisymmetric model is considered. The fluid is assumed Newtonian. The plaque is modelled as a heterogeneous hyperelastic anisotropic solid composed of the arterial wall, the lipid core and the fibrous cap. Transient velocity and pressure conditions of actual pulsatile blood flow are prescribed. The simulation is achieved using the Arbitrary Lagrangian Eulerian scheme in the COMSOL commercial Finite Element package. The results reveal different types of behavior in function of the length (denoted L) and severity (denoted S) of the stenosis. Whereas large plaques (L>10mm) are mostly deformed under the action of the blood pressure, it appears that shorter plaques (L<10mm) are significantly affected by the shear stresses. The shear stresses tend to deform the plaque by pinching it. This effect is called: “the pinching effect”. It has an essential influence on the mechanical response of the plaque. For two plaques having the same radius severity S=45%, the maximum stress in the fibrous cap is 50% larger for the short plaque (L=5mm) than for a larger plaque (L=10mm), and the maximum wall shear stress is increased by 100%. Provided that they are confirmed by experimental investigations, these results may offer some new perspectives for understanding the vulnerability of short plaques.

A new approach to detect congestive heart failure using sequential spectrum of electrocardiogram signals - Corrected Proof

Chandrakar Kamath — 2012-03-29

Abstract: The aim of this study is to evaluate the discriminative power of sequential spectrum analysis of the short-term electrocardiogram (ECG) time series in separating normal and congestive heart failure (CHF) subjects. The raw ECG time series is transformed into a series of discretized binary symbols and the distribution of mono-sequences (i.e., tuples containing only one type of symbol ‘0’ or ‘1’) is computed. The relative distribution of mono-sequences containing only one type of symbol constitutes binary occupancy for that symbol in the sequential spectrum. The quantified approximate entropies of the binary occupancies in the sequential spectra are found to have potential in discriminating normal and CHF subjects and thus can significantly add to the prognostic value of traditional cardiac analysis. The statistical analyses and the receiver operating characteristic curve (ROC) analysis confirm the robustness of this new approach, which exhibits an average accuracy, average sensitivity, average positive predictivity, and average specificity, all 100.0%.

The stress state of the fraenal notch region in complete upper dentures - Corrected Proof

2012-03-26

Abstract: The present study determines the stress field in the region of the labial flange of the complete upper denture (CUD).Using commercial edentulous molds and standardized procedures eight identical CUDs were fabricated with an initial fraenal notch of 5mm. Three addition notch conditions were produced by deepening the notch two times giving a total depth of the notch of 7 and 9mm respectively. Finally an incisal diastema of 7mm was created in every CUD.Three elements rosette strain gauge was cemented onto the midline of each denture specimen near the fraenal notch, for calculating the two principal stresses and the maximum shear stress.It is less possible that a failure crack in a CUD will be initiated from the region of the fraenal notch, due to the compressive nature of the principal stresses (they are varied significantly among the four notch conditions with P=0.035 for σ1 and P=0.007 for σ2) and the low value of the maximum shear stress. The creation of an incisal diastema significantly decreased the values of the principal stresses σ1 (P=0.012) and σ2 (P=0.025). Further investigation is needed to detect the region of the CUD where a failure crack may be initiated.

Biomechanical stress maps of an artificial femur obtained using a new infrared thermography technique validated by strain gages - Corrected Proof

Suraj Shah, Habiba Bougherara, Emil H. Schemitsch, Rad Zdero — 2012-03-20

Abstract: Femurs are the heaviest, longest, and strongest long bones in the human body and are routinely subjected to cyclic forces. Strain gages are commonly employed to experimentally validate finite element models of the femur in order to generate 3D stresses, yet there is little information on a relatively new infrared (IR) thermography technique now available for biomechanics applications. In this study, IR thermography validated with strain gages was used to measure the principal stresses in the artificial femur model from Sawbones (Vashon, WA, USA) increasingly being used for biomechanical research. The femur was instrumented with rosette strain gages and mechanically tested using average axial cyclic forces of 1500N, 1800N, and 2100N, representing 3 times body weight for a 50kg, 60kg, and 70kg person. The femur was oriented at 7° of adduction to simulate the single-legged stance phase of walking. Stress maps were also obtained using an IR thermography camera. Results showed good agreement of IR thermography vs. strain gage data with a correlation of R2=0.99 and a slope=1.08 for the straight line of best fit. IR thermography detected the highest principal stresses on the superior–posterior side of the neck, which yielded compressive values of −91.2MPa (at 1500N), −96.0MPa (at 1800N), and −103.5MPa (at 2100N). There was excellent correlation between IR thermography principal stress vs. axial cyclic force at 6 locations on the femur on the lateral (R2=0.89–0.99), anterior (R2=0.87–0.99), and posterior (R2=0.81–0.99) sides. This study shows IR thermography's potential for future biomechanical applications.

Construction, in vitro and in vivo evaluation of an in-house conductance meter for measurement of skin hydration - Corrected Proof

2012-03-19

Abstract: Different probes are used in dermato-cosmetic research to measure the electrical properties of the skin. The principle governing the choice of the geometry and material of the measuring probe is not well defined in the literature and some device's measuring principles are not accessible for the scientific community. The purpose of this work was to develop a simple inexpensive conductance meter for the objective in vivo evaluation of skin hydration.The conductance meter probe was designed using the basic equation governing wave propagation along Transverse Electromagnetic transmission lines. It consisted of two concentric copper circular electrodes printed on FR4 dielectric material.The performance of the probe was validated by evaluating its measurement depth, its ability to monitor in vitro water sorption–desorption and in vivo skin hydration effect in comparison to that of the Corneometer CM 825. The measurement depth of the probe, 15μm, was comparable to that of CM 825. The in vitro readings of the probe correlated strongly with the amount of water adsorbed on filter paper. Skin hydration after application of a moisturizer was monitored effectively by the new probe with good correlation to the results of CM 825.In conclusion, a simple probe for evaluating skin hydration was made from off-the-shelf materials and its performance was validated in comparison to a commercially available probe.

An intrinsically compliant robotic orthosis for treadmill training - Corrected Proof

Shahid Hussain, Sheng Quan Xie, Prashant K. Jamwal, John Parsons — 2012-03-15

Abstract: A new intrinsically compliant robotic orthosis powered by pneumatic muscle actuators (PMA) was developed for treadmill training of neurologically impaired subjects. The robotic orthosis has hip and knee sagittal plane rotations actuated by antagonistic configuration of PMA. The orthosis has passive mechanisms to allow vertical and lateral translations of the trunk and a passive hip abduction/adduction joint. A foot lifter having a passive spring mechanism was used to ensure sufficient foot clearance during swing phase. A trajectory tracking controller was implemented to evaluate the performance of the robotic orthosis on a healthy subject. The results show that the robotic orthosis is able to perform the treadmill training task by providing sufficient torques to achieve physiological gait patterns and a realistic stepping experience. The orthosis is a new addition to the rapidly advancing field of robotic orthoses for treadmill training.

Technical variability of the GT3X accelerometer - Corrected Proof

2012-03-14

Abstract: To analyze the intra- and inter-instrument reliability of the ActiGraph GT3X accelerometer using a vibration table on each orthogonal axis and at five frequencies of motion. Ten GT3X units were subjected to a specific vibration using a motorized vibration table along the vertical, horizontal right–left and horizontal front–back axis, and at 1.1, 2.1, 3.1, 4.1 and 10.2Hz. The 5min data for each frequency were analyzed separately for frequency, axis effects, and inter- and intra-instrument variability. We found overall high intra-and inter-instrument reliability for the GT3X accelerometer at frequencies between 2.1 and 4.1Hz. For frequencies ranging between 2.1 and 4.1Hz, the intra-instrument coefficient of variation was ≤2.5%. The inter-instrument coefficient of variation ranged widely along axes and frequencies, with the lowest values (≤9%) corresponding to 2.1–4.1Hz. The intra-class correlation coefficient for activity counts across frequencies and for all axes was 0.97. Overall, our findings support the use of the GT3X accelerometer as an accurate tool to estimate free-living physical activity, at least within those frequencies that are common to most types of human daily activities.

Hemodynamics of small aneurysm pairs at the internal carotid artery - Corrected Proof

Liang-Der Jou, Hesham Morsi, Hashem M. Shaltoni, Michel E. Mawad — 2012-03-14

Abstract: Cerebral aneurysms carry significant risks because rupture-related subarachnoid hemorrhage leads to serious and often fatal consequences. The rupture risk increases considerably for multiple aneurysms. Multiple aneurysms can grow from the same location of an artery, and the interaction between these aneurysms raises the rupture risk even higher. Four aneurysm pair cases at the internal carotid artery are investigated for their hemodynamic behaviors using patient-specific modeling. For each case, aneurysms are separated from the parent artery and three models are reconstructed, one with two aneurysms and the other two models with only one of the two aneurysms. Results show that the relative anatomic location of one aneurysm to the other may determine the hemodynamic environment of an aneurysm. The presence of a proximal aneurysm reduces the intra-aneurysmal flow into the distal aneurysm; the proximal aneurysm and larger aneurysm have a greater area under low wall shear stress. The average intra-aneurysmal inflow ratio ranges from 16% to 41%, and reduction of the inflow ratio by an aneurysm pair varies from 6% to 15%. The maximum wall shear stress increases for serial aneurysms, but decreases for parallel aneurysms. Interaction between parallel aneurysms is not significant; however, the proximal aneurysm in serial aneurysms may be subject to a greater rupture risk.

3D simulation of the aqueous flow in the human eye - Corrected Proof

2012-03-14

Abstract: Glaucoma results in an increase in the resistance of the aqueous humor outflow, which in turn leads to an increase of the intraocular pressure (IOP). Several treatments are proposed to reduce and stabilize the IOP that include medications, filtering surgery and glaucoma drainage devices (GDD). So far computational fluid dynamics (CFD) modeling of the eye drainage system has not yet been well studied. Therefore our goal was to provide a 3D CFD model of the eye based on the anatomy of a real human eye. Such a tool would serve for future evaluation of new glaucoma surgical techniques involving, for example, GDD. The model was based on stacks of microphotographs from human eye slides from which digital processing of the images of the eye structure and 3D reconstruction of the model were performed. Simulations of the distribution of pressure and flow velocity in the model of a healthy eye gave results comparable to physiology references. Mimicking glaucoma conditions led to an increase of the IOP from normal range, which went down to lower values after a filtering procedure. Further refinements in the boundary conditions for the filtering procedure shall improve the accuracy of this innovative tool for modeling glaucoma surgery.

Intracranial hypertension prediction using extremely randomized decision trees - Corrected Proof

Fabien Scalzo, Robert Hamilton, Shadnaz Asgari, Sunghan Kim, Xiao Hu — 2012-03-09

Abstract: Intracranial pressure (ICP) elevation (intracranial hypertension, IH) in neurocritical care is typically treated in a reactive fashion; it is only delivered after bedside clinicians notice prolonged ICP elevation. A proactive solution is desirable to improve the treatment of intracranial hypertension. Several studies have shown that the waveform morphology of the intracranial pressure pulse holds predictors about future intracranial hypertension and could therefore be used to alert the bedside clinician of a likely occurrence of the elevation in the immediate future. In this paper, a computational framework is proposed to predict prolonged intracranial hypertension based on morphological waveform features computed from the ICP. A key contribution of this work is to exploit an ensemble classifier method based on extremely randomized decision trees (Extra-Trees). Experiments on a representative set of 30 patients admitted for various intracranial pressure related conditions demonstrate the effectiveness of the predicting framework on ICP pulses acquired under clinical conditions and the superior results of the proposed approach in comparison to linear and AdaBoost classifiers.

Accuracy of algorithms for detection of atrial fibrillation from short duration beat interval recordings - Corrected Proof

2012-03-09

Abstract: Atrial fibrillation (AF) is characterised by highly variable beat intervals. The aims of the study were to assess the accuracy of AF detection algorithms from short analysis durations and to validate prospectively the accuracy on a large community-based cohort of elderly subjects. Three algorithms for AF detection were evaluated: coefficient of variation (CV), mean successive difference (Δ) and coefficient of sample entropy (COSEn), using two databases of beat interval recordings: 167 recordings of 300s duration for a range of rhythms acquired in a hospital setting and 2130 recordings of 10s duration acquired in the community. Using the longer recordings receiver operating characteristic (ROC) analysis was used to identify optimal algorithm thresholds and to evaluate analysis durations ranging from 5s to 60s. An ROC area of 93% was obtained at recording duration of 60s but remained above 90% for durations as low as 5s. Prospective analysis on the 2130 recordings gave AF detector sensitivities from 90.5% (CV and Δ) to 95.2% (COSEn), specificities from 89.3% (Δ) to 93.4% (COSEn) and accuracy from 89.3% (Δ) to 93.4% (COSEn), not significantly different to those obtained on the initial database. AF detection algorithms are effective for short analysis durations, offering the prospect of a simple and rapid diagnostic test based on beat intervals alone.

A new approach to scaffold fixation by magnetic forces: Application to large osteochondral defects - Corrected Proof

2012-03-01

Abstract: Scaffold fixation represents one of the most serious challenges in osteochondral defect surgery. Indeed, the fixation should firmly hold the scaffold in the implanted position as well as it should guaranty stable bone/scaffold interface for efficient tissue regeneration. Nonetheless successful results have been achieved for small defect repair, the fixation remains really problematic for large defects, i.e. defects with areas exceeding 2cm2. This paper advances an innovative magnetic fixation approach based on application of magnetic scaffolds. Finite element modeling was exploited to investigate the fixation efficiency. We considered three magnetic configurations: (1) external permanent magnet ring placed around the leg near the joint; (2) four small permanent magnet pins implanted in the bone underlying the scaffold; (3) four similarly implanted stainless steel pins which magnetization was induced by the external magnet. It was found that for most appropriate magnetic materials and optimized magnet-scaffold positioning all the considered configurations provide a sufficient scaffold fixation. In addition to fixation, we analyzed the pressure induced by magnetic forces at the bone/scaffold interface. Such pressure is known to influence significantly the bone regeneration and could be used for magneto-mechanical stimulation.

MRI/SPECT-based diagnosis and CT-guided high-intensity focused-ultrasound treatment system in MPTP mouse model of Parkinson's disease - Corrected Proof

2012-03-01

Abstract: Single-photon emission computed tomography (SPECT) of dopamine transporters with 99mTc-TRODAT-1 has recently been proposed to offer valuable information for the diagnosis of Parkinson's disease (PD). Furthermore, High-intensity focused ultrasound (HIFU) is a newly developed technique in which the energy of ultrasound wave is directed to a focused spot for the purpose treatment of PD. This study presents a diagnosis and image-guided system using HIFU to treat the mouse with PD under a designed stereotactic frame. The system comprises two key components: an automatic atlas-based SPECT/MRI image registration module for diagnosis and a stereotactic CT-guided module for HIFU treatment. The SPECT/MR image registration here is important in the non-invasive examination of the dopamine concentration in vivo. From the experimental results, the image registration module proves to have comparable performance to that derived from manual drawing by experts. In addition, the stereotactic CT-guided module achieved a positioning accuracy to within 2mm on the average, which is acceptable for the purpose of HIFU treatment.

Computational analysis on the mechanical interaction between a thrombus and red blood cells: Possible causes of membrane damage of red blood cells at microvessels - Corrected Proof

2012-02-22

Abstract: Previous studies investigating thrombus formation have not focused on the physical interaction between red blood cells (RBCs) and thrombus, although they have been speculated that some pathological conditions such as microangiopathic hemolytic anemia (MAHA) stem from interactions between RBCs and thrombi. In this study, we investigated the mechanical influence of RBCs on primary thrombi during hemostasis. We also explored the mechanics and aggravating factors of intravascular hemolysis. Computer simulations of primary thrombogenesis in the presence and the absence of RBCs demonstrated that RBCs are unlikely to affect the thrombus height and coverage, although their presence may change microvessel hemodynamics and platelet transportation to the injured wall. Our results suggest that intravascular hemolysis owing to RBC membrane damage would be promoted by three hemodynamic factors: (1) dispersibility of platelet thrombi, because more frequent spatial thrombus formation decreases the time available for an RBC to recover its shape and enforces more severe deformation; (2) platelet thrombus stiffness, because a stiffer thrombus increases the degree of RBC deformation upon collision; and (3) vessel size and hemocyte density, because a smaller vessel diameter and higher hemocyte density decrease the room for RBCs to escape as they come closer to a thrombus, thereby enhancing thrombus–RBC interactions.

Stratification of risk in thin cap fibroatheromas using peak plaque stress estimates from idealized finite element models - Corrected Proof

William Jacob S. Dolla, John A. House, Steven P. Marso — 2012-02-20

Abstract: Thin cap fibroatheroma (TCFA) in coronary arteries is believed to be associated with plaque rupture leading to cardiovascular death and non-fatal myocardial infarction. Catheter-based imaging platforms can identify TCFAs but detection algorithms lack specificity. Here we report results of an exploratory study of the variability in TCFA plaque attributes and effects on peak von Mises stress of TCFA using idealized finite element models. A total of 1272 idealized TCFA finite element models were developed by strategically varying attribute dimensions – external elastic membrane diameter, lumen diameter, necrotic core thickness, fibrous cap thickness, and necrotic core angle – obtained from a global registry of subjects undergoing percutaneous coronary intervention with Virtual Histology intravascular ultrasound. Peak stress exhibited parabolic or higher order proportionality with lumen diameter, sigmoidal proportionality with necrotic core thickness, inverse hyperbolic proportionality with fibrous cap thickness, and skewed sinusoidal proportionality with necrotic core angle. Each of these relationships was governed by highly sensitive, complex, and interdependent influences of various attributes on plaque stress. An over 7-fold increase in peak stress from 101 to 788kPa was observed in models of coronary dimensions commonly encountered in clinical practice. Peak stress of intramural TCFA within this common coronary artery subset did not exceed 300kPa for fibrous cap thickness greater than 100μm and necrotic core angle outside 90–120° range, indicating low risk of rupture. This exploratory study demonstrated the complex and interdependent influence of plaque attributes on the peak stress of TCFA.

The effect of tendon surface treatment on cell attachment for potential enhancement of tendon graft healing: An ex vivo model - Corrected Proof

Takahiro Hashimoto, Yu-Long Sun, Kai-Nan An, Peter C. Amadio, Chunfeng Zhao — 2012-02-20

Abstract: For both tendon allografts and autografts, the surface, initially optimized for gliding, may not be ideal to facilitate tissue integration for graft healing to host tendon or bone. As a prelude to studying tendon–bone integration, we investigated the effect of surface treatments with trypsin or mechanical abrasion on cell attachment to the tendon surface in a canine ex vivo intrasynovial tendon tissue culture model. Intrasynovial tendon allograft surfaces were seeded with cells after the following treatments: (1) no treatment, (2) mechanical abrasion, (3) trypsin, and (4) abrasion and trypsin. The area covered by cells was determined using confocal laser microscopy at one and two weeks. Results were compared to untreated extrasynovial tendon. Additional tendons were characterized with scanning electron microscopy. Tendons with trypsin treatment had significantly more surface coverage with cells than the other groups, after both one and two weeks of culture. In terms of the cellular shape and size, cells on tendons with trypsin treatment spread more and were more polygonal in shape, whereas tendons with mechanical abrasion with/without trypsin treatment contained smaller, more spindle-like cells. Surface roughening can affect cell behavior with topographical stimulation. Trypsin surface digestion exposes a mesh-like structure on the tendon surface, which could enhance cell adherence and, possibly, tendon/bone healing.

The quality of bone surfaces may govern the use of model based fluoroscopy in the determination of joint laxity - Corrected Proof

P. Moewis, N. Wolterbeek, G. Diederichs, E. Valstar, M.O. Heller, W.R. Taylor — 2012-02-20

Abstract: The assessment of knee joint laxity is clinically important but its quantification remains elusive. Calibrated, low dosage fluoroscopy, combined with registered surfaces and controlled external loading may offer possible solutions for quantifying relative tibio-femoral motion without soft tissue artefact, even in native joints. The aim of this study was to determine the accuracy of registration using CT and MRI derived 3D bone models, as well as metallic implants, to 2D single-plane fluoroscopic datasets, to assess their suitability for examining knee joint laxity.Four cadaveric knees and one knee implant were positioned using a micromanipulator. After fluoroscopy, the accuracy of registering each surface to the 2D fluoroscopic images was determined by comparison against known translations from the micromanipulator measurements. Dynamic measurements were also performed to assess the relative tibio-femoral error. For CT and MRI derived 3D femur and tibia models during static testing, the in-plane error was 0.4mm and 0.9mm, and out-of-plane error 2.6mm and 9.3mm respectively. For metallic implants, the in-plane error was 0.2mm and out-of-plane error 1.5mm. The relative tibio-femoral error during dynamic measurements was 0.9mm, 1.2mm and 0.7mm in-plane, and 3.9mm, 10.4mm and 2.5mm out-of-plane for CT and MRI based models and metallic implants respectively. The rotational errors ranged from 0.5° to 1.9° for CT, 0.5–4.3° for MRI and 0.1–0.8° for metallic implants.The results of this study indicate that single-plane fluoroscopic analysis can provide accurate information in the investigation of knee joint laxity, but should be limited to static or quasi-static evaluations when assessing native bones, where possible. With this knowledge of registration accuracy, targeted approaches for the determination of tibio-femoral laxity could now determine objective in vivo measures for the identification of ligament reconstruction candidates as well as improve our understanding of the consequences of knee joint instability in TKA.

Robust femur condyle disambiguation on biplanar X-rays - Corrected Proof

Antoine Serrurier, Sergio Quijano, Remy Nizard, Wafa Skalli — 2012-02-20

Abstract: Three-dimensional (3D) reconstruction of the skeleton from biplanar X-rays relies on scarce information digitalised by an operator on both frontal and lateral radiographs. In clinical routine, difficulties occur for non-skilled operators to discriminate the medial from the lateral femur condyle on the lateral view. Our study proposes an algorithm able to detect automatically a possible inversion of the two condyles by the operator at an early stage of the reconstruction process. It relies on the computation of two 3D femur surfaces, one directly from the operator digitalisation and the other from the same digitalisation with medial and lateral condyles automatically swapped. Pairs of virtual biplanar X-rays are computed for both reconstructions and the closest pair to the original X-rays is selected on the basis of similarity measures, pointing the correct 3D surface. The algorithm shows a success rate higher than 85% for both asymptomatic and pathological femurs whatever the initial condyle digitalisation of the operator, bringing automatically non-skilled operators acting in clinical routine to the level of skilled operators. This study validates moreover the proof-of-concept of automatic shape adjustments of a 3D surface on the basis of similarity measures in the process of 3D reconstruction from biplanar X-rays.

Classification of frontal cortex haemodynamic responses during cognitive tasks using wavelet transforms and machine learning algorithms - Corrected Proof

Berdakh Abibullaev, Jinung An — 2012-02-10

Abstract: Recent advances in neuroimaging demonstrate the potential of functional near-infrared spectroscopy (fNIRS) for use in brain–computer interfaces (BCIs). fNIRS uses light in the near-infrared range to measure brain surface haemoglobin concentrations and thus determine human neural activity. Our primary goal in this study is to analyse brain haemodynamic responses for application in a BCI. Specifically, we develop an efficient signal processing algorithm to extract important mental-task-relevant neural features and obtain the best possible classification performance. We recorded brain haemodynamic responses due to frontal cortex brain activity from nine subjects using a 19-channel fNIRS system. Our algorithm is based on continuous wavelet transforms (CWTs) for multi-scale decomposition and a soft thresholding algorithm for de-noising. We adopted three machine learning algorithms and compared their performance. Good performance can be achieved by using the de-noised wavelet coefficients as input features for the classifier. Moreover, the classifier performance varied depending on the type of mother wavelet used for wavelet decomposition. Our quantitative results showed that CWTs can be used efficiently to extract important brain haemodynamic features at multiple frequencies if an appropriate mother wavelet function is chosen. The best classification results were obtained by a specific combination of input feature type and classifier.

External work is deficient in both limbs of patients with unilateral PAD - Corrected Proof

2012-02-10

Abstract: External work was utilized to measure differences between the unaffected and the affected limb in patients with unilateral peripheral arterial disease compared to healthy controls. Patients with unilateral peripheral arterial disease have shown deficits in peak joint powers during walking in the unaffected and affected legs. However, no research has detailed the amount of work that is being performed by each leg compared to healthy controls even though such an analysis would provide valuable information on the energy output from the affected and the unaffected legs. Two hypotheses were tested: (a) the unaffected and affected leg would perform less work than healthy controls in a pain-free state, and (b) the onset of symptomatic claudication pain would result in further changes in the external work. Results showed that during a pain-free state, both the unaffected and affected legs perform less work than the healthy controls. After onset of claudication pain, the work output by the affected limb becomes further decreased while the unaffected limb experiences changes in negative external work. These findings combined with recent evidence of decreased peak powers in both legs in unilateral peripheral arterial disease patients reflects altered pathomechanics in both limbs compared to healthy controls.

Nonlinear analysis of actigraphic signals for the assessment of the attention-deficit/hyperactivity disorder (ADHD) - Corrected Proof

2012-02-02

Abstract: Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral disorder in children and adolescents; however, its etiology is still unknown, which hinders the existence of reliable, fast and inexpensive standard diagnostic methods. In this paper, we propose a novel methodology for automatic diagnosis of the combined type of ADHD based on nonlinear signal processing of 24h-long actigraphic registries. Since it relies on actigraphy measurements, it constitutes an inexpensive and non-invasive objective diagnostic method. Our results on real data reach 96.77% sensitivity and 84.38% specificity by means of multidimensional classifiers driven by combined features from different time intervals. Our analysis also reveals that, if features from a single time interval are used, the whole 24-h interval is the only one that yields classification figures with practical diagnostic capabilities. Overall, our figures overcome those obtained by actigraphy-based methods reported and are comparable with others based on more expensive (and not so convenient) adquisition methods.

Deformation behavior of the iliotibial tract under different states of fixation - Corrected Proof

2012-02-01

Abstract: Background and objective: The iliotibial tract (tract) is an important structure for the biomechanics of both the hip and knee joint. While a detailed characterization of its mechanical properties might help to better understand its specific role in the load transfer from the pelvis to femur and tibia, determination of those properties is complicated by its particular structure of thin fibers in the fresh state. Moreover, although the tracts mechanical properties are often derived from cadaveric material chemically fixed with either ethanol or formaldehyde, the influence of such fixation methods remains to be elucidated. Aim of this study was to determine Young's modulus (tensile modulus, YM) of the tract. We hypothesized that either ethanol or formaldehyde fixation would significantly increase the YM compared to the tracts condition in a fresh state.Material and methods: 13 specimens of tract were gained from donators. The ends of the probes were plastinated with resin creating a sharp interface between the clamp and the probe to prevent material slippage. The specimens were measured in their fresh state, under ethanol- and formaldehyde-fixed conditions and re-measured after rinsing with tap water.Results: The YM of the fresh probes averaged 397.3N/mm2 with a standard deviation (SD) of 151.5N/mm2. The YM of the ethanol-fixed specimens was significantly higher (673.2N/mm2, SD 328.5N/mm2, p<0.05). After rinsing with tap water, the YM decreased to 95% of the fresh condition value (377.4N/mm2, SD 144.5N/mm2, non-significant change from fresh). After formaldehyde fixation, the YM reached 490.3N/mm2 (SD 143.0N/mm2, p<0.05). When the formaldehyde-fixed specimens were rinsed, the YM was 114% of the value of the fresh condition (452.6N/mm2, SD 115.1N/mm2, non-significant change from fresh).Conclusions: This study found a significant influence of the chemical fixation method on the YM of the IT tract. If such fixation is required, our results suggest using a treatment with ethanol and subsequent rinsing that results in minimal changes to the tracts YM. Furthermore, plastination of the ends of the specimens could be crucial to allow in vitro determination of valid YM of ligaments data that can then be integrated with confidence in further finite element analyses.

The accuracy and repeatability of an automatic 2D–3D fluoroscopic image-model registration technique for determining shoulder joint kinematics - Corrected Proof

Zhonglin Zhu, Daniel F. Massimini, Guangzhi Wang, Jon J.P. Warner, Guoan Li — 2012-01-30

Abstract: Fluoroscopic imaging, using single plane or dual plane images, has grown in popularity to measure dynamic in vivo human shoulder joint kinematics. However, no study has quantified the difference in spatial positional accuracy between single and dual plane image-model registration applied to the shoulder joint. In this paper, an automatic 2D–3D image-model registration technique was validated for accuracy and repeatability with single and dual plane fluoroscopic images. Accuracy was assessed in a cadaver model, kinematics found using the automatic registration technique were compared to those found using radiostereometric analysis. The in vivo repeatability of the automatic registration technique was assessed during the dynamic abduction motion of four human subjects. The in vitro data indicated that the error in spatial positional accuracy of the humerus and the scapula was less than 0.30mm in translation and less than 0.58° in rotation using dual plane images. Single plane accuracy was satisfactory for in-plane motion variables, but out-of-plane motion variables on average were approximately 8 times less accurate. The in vivo test indicated that the repeatability of the automatic 2D–3D image-model registration was 0.50mm in translation and 1.04° in rotation using dual images. For a single plane technique, the repeatability was 3.31mm in translation and 2.46° in rotation for measuring shoulder joint kinematics. The data demonstrate that accurate and repeatable shoulder joint kinematics can be obtained using dual plane fluoroscopic images with an automatic 2D–3D image-model registration technique; and that out-of-plane motion variables are less accurate than in-plane motion variables using a single plane technique.

Shear force measurements on low- and high-stiffness posterior fusion devices - Corrected Proof

2012-01-27

Abstract: Low-stiffness posterior fusion devices for the lumbar spine have been developed to treat degenerative spinal conditions. However, the demands on an implant vary between a stable motion segment and one which exhibits a significant degree of sagittal plane instability. Shear motion in the antero-posterior direction is a relevant mode of instability for clinical conditions such as degenerative lumbar spondylolisthesis. Shear load-sharing between the implant and spine in conditions of antero-posterior instability has not been studied, nor have there been comparisons between traditional rigid implants and novel low-stiffness implants. The objective of this study was to develop a method to measure in vitro shear forces on three clinically relevant fusion implants when they are applied to an unstable model of degenerative spondylolisthesis in a human cadaver spine. Uniaxial strain gauges were affixed to the surface of the implants and a spine-segment-specific calibration method was used to calibrate the strain output to an applied shear force. The accuracy of the force measurements was within 3.4N for all implant types and the repeatability was within 5.4N. The force measurement technique was sufficiently accurate and reliable to conclude that it is suitable for use in in vitro experiments to measure implant shear force.

Mechanical and functional assessment of the wrist affected by rheumatoid arthritis: A finite element analysis - Corrected Proof

M.N. Bajuri, Mohammed Rafiq Abdul Kadir, Murali Malliga Raman, T. Kamarul — 2012-01-25

Abstract: Understanding the pathomechanics involved in rheumatoid arthritis (RA) of the wrist provides valuable information, which will invariably allow various therapeutic possibilities to be explored. The computational modelling of this disease permits the appropriate simulation to be conducted seamlessly. A study that underpins the fundamental concept that produces the biomechanical changes in a rheumatoid wrist was thus conducted through the use of finite element method. The RA model was constructed from computed tomography datasets, taking into account three major characteristics: synovial proliferation, cartilage destruction and ligamentous laxity. As control, a healthy wrist joint model was developed in parallel and compared. Cartilage was modelled based on the shape of the articulation while the ligaments were modelled with linear spring elements. A load-controlled analysis was performed simulating physiological hand grip loading conditions. The results demonstrated that the diseased model produced abnormal wrist extension and stress distribution as compared to the healthy wrist model. Due to the weakening of the ligaments, destruction of the cartilage and lower bone density, the altered biomechanical stresses were particularly evident at the radioscaphoid and capitolunate articulations which correlate to clinical findings. These results demonstrate the robust finding of the developed RA wrist model, which accurately predicted the pathological process.

Correlation of the experimental and numerical results for the holding power of dental, traumatic, and spinal screws - Corrected Proof

Chia-Ching Lee, Shang-Chih Lin, Shu-Wei Wu, Yu-Ching Li, Ping-Yuen Fu — 2012-01-24

Abstract: The holding power of the bone–screw interfaces is one of the key factors in the clinical performance of screw design. The value of the holding power can be experimentally measured by pullout tests. Historically, some researchers have used the finite-element method to simulate the holding power of the different screws. Among them, however, the assumed displacement of the screw withdrawal is unreasonably small (about 0.005–1.0mm). In addition, the chosen numerical indices are quite different, including maximum stress, strain energy, and reaction force. This study systematically uses dental, traumatic, and spinal screws to experimentally measure and numerically simulate their bone-purchasing ability within the synthetic bone. The testing results (pullout displacement and holding power) and numerical indices (maximum stress, total strain energy, and reaction forces) are chosen to calculate their correlation coefficients. The pullout displacement is divided into five regions from initial to final withdrawal. The experimental results demonstrate that the pullout displacement consistently occurs at the final region (0.6–1.6mm) and is significantly higher than the assumed value of the literature studies. For all screw groups, the measured holding power within the initial region is not highly or even negatively correlated with the experimental and numerical results within the final region. The observation from the simulative results shows the maximum stress only reflects the loads concentrated at some local site(s) and is the least correlated to the measured holding power. Comparatively, both energy and force are more global indices to correlate with the gross failure at the bone–screw interfaces. However, the energy index is not suitable for the screw groups with rather tiny threads compared with the other specifications. In conclusion, the underestimated displacement leads to erroneous results in the screw–pullout simulation. Among three numerical indices the reaction-force is the optimal index for the screw–pullout problem.

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results - Corrected Proof

2012-01-24

Abstract: The aims of the present work were to build a 3D subject-specific heel pad model based on the anatomy revealed by MR imaging of a subject's heel pad, and to compare the load–displacement responses obtained from this model with those obtained from a compression device used on the subject's heel pad. A 30 year-old European healthy female (mass=54kg, height=165cm) was enrolled in this study. Her left foot underwent both MRI and compression tests. A numerical model of the heel region was developed based on a 3D CAD solid model obtained by MR images. The calcaneal fat pad tissue was described with a visco-hyperelastic model, while a fiber-reinforced hyperelastic model was formulated for the skin. Numerical analyses were performed to interpret the mechanical response of heel tissues. Different loading conditions were assumed according to experimental tests. The heel tissues showed a non-linear visco-elastic behavior and the load–displacement curves followed a characteristic hysteresis form. The energy dissipation ratios measured by experimental tests (0.25±0.02 at low strain rate and 0.26±0.03 at high strain rate) were comparable with those evaluated by finite element analyses (0.23±0.01 at low strain rate and 0.25±0.01 at high strain rate). The validity and efficacy of the investigation performed was confirmed by the interpretation of the mechanical response of the heel tissues under different strain rates. The mean absolute percentage error between experimental data and model results was 0.39% at low strain rate and 0.28% at high strain rate.

Design and validation of transducers to measure interface force distribution in a spinal orthosis - Corrected Proof

Andrew Chan, Edmond Lou, Doug Hill, Gary Faulkner — 2012-01-20

Abstract: Scoliosis is a spinal deformity that affects millions of adolescents in the United States. Bracing is the most common non-surgical treatment method for scoliosis, but the biomechanics of such treatment is unclear. The objective of this study is to develop and validate a force logging system that can record forces at multiple locations inside a brace, as well as brace strap tension, and correlate these forces with different body positions. The force logging system can be used to investigate the biomechanics function of a brace to treat scoliosis during the treatment period.Two phases were completed in this study: design phase, involving custom development and calibration of strap tension transducers and modifications of in-brace force transducers; and validation phase, including preliminary testing on a subject with different postures.In-brace force load cell and tension transducer were tested and validated. Their sensitivities were 193.5±4.9mV/N and 35.5±0.2mV/N, respectively, with both linear correlation coefficients were 0.99, reflecting high repeatability and linearity. Qualitative validation was also completed, allowing general relationships to be found between subject posture and force distribution. This study shows an excellent functionality and utility of the developed system.

An optimized method for tremor detection and temporal tracking through repeated second order moment calculations on the surface EMG signal - Corrected Proof

Cristiano De Marchis, Maurizio Schmid, Silvia Conforto — 2012-01-18

Abstract: In this study, the problem of detecting and tracking tremor from the surface myoelectric signal is addressed. A method based on the calculation of a Second Order Moment Function (SOMF) inside a window W sliding over the sEMG signal is here presented. An analytical formulation of the detector allows the extraction of the optimal parameters characterizing the algorithm. Performance of the optimized method is assessed on a set of synthetic tremor sEMG signals in terms of sensitivity, precision and accuracy through the use of a properly defined cost function able to explain the overall detector performance. The obtained results are compared to those emerging from the application of optimized versions of traditional detection techniques. Once tested on a database of synthetic tremor sEMG data, a quantitative assessment of the SOMF algorithm performance is carried out on experimental tremor sEMG signals recorded from two patients affected by Essential Tremor and from two patients affected by Parkinson's Disease. The SOMF algorithm outperforms the traditional techniques both in detecting (sensitivity and positive predictive value >99% for SNR higher than 3dB) and in estimating timings of muscular tremor bursts (bias and standard deviation on the estimation of the onset and offset time instants lower than 8ms). Its independence from the SNR level and its low computational cost make it suitable for real-time implementation and clinical use.

Needle-free jet injection using real-time controlled linear Lorentz-force actuators - Corrected Proof

Andrew Taberner, N. Catherine Hogan, Ian W. Hunter — 2012-01-16

Abstract: Needle-free drug delivery by jet injection is achieved by ejecting a liquid drug through a narrow orifice at high pressure, thereby creating a fine high-speed fluid jet that can readily penetrate skin and tissue. Until very recently, all jet injectors utilized force- and pressure-generating principles that progress injection in an uncontrolled manner with limited ability to regulate delivery volume and injection depth. In order to address these shortcomings, we have developed a controllable jet injection device, based on a custom high-stroke linear Lorentz-force motor that is feed-back controlled during the time-course of an injection.Using this device, we are able to monitor and modulate continuously the speed of the drug jet, and regulate precisely the volume of drug delivered during the injection process. We demonstrate our ability to control injection depth (up to 16mm) and repeatably and precisely inject volumes of up to 250μL into transparent gels and post-mortem animal tissue.

A new method for the evaluation of dental implant stability using an inductive sensor - Corrected Proof

2012-01-12

Abstract: We developed a new method for the measurement of dental implant stability by analyzing the impulse response of the implant. The movement of the implant was measured by an inductive sensor with a dedicated adaptor. The large inductance of the adapter amplified the small displacement signal of the implant. The Periotest (Siemens, Bensheim, Germany) was used as a source of excitation force to acquire the impact response of the implant. Power spectrum analysis was applied to the impact response of the implant. The peak frequency of the spectrum was used as a measure of the implant stability. The performance of the system was tested and verified through simulation of the implant–bone interface in an in vitro model. Various implant–bone interfacial conditions were assessed. Holes of varying depth and diameter were drilled into a dental implantation model. Two types of impression materials (EXAMIXFINE, Regisil Rigid) with different degrees of hardness were used to fix the implant into the hole. The implant stability was also measured using the ISQ (implant stability quotient) by resonance frequency analysis on the Osstell Mentor (Integration Diagnostics AB, Goteborgsvagen, Sweden) for comparison. Linear regression analysis of the peak frequency as a stability parameter showed a linear relationship with both the depth and the diameter of the hole (p<0.05). When EXAMIXFINE was used, the peak frequency was linearly associated with the depth (R2=0.443) and diameter (R2=0.396) of the hole. When Regisil Rigid was used, the peak frequency also showed a linear relationship with the depth (R2=0.555) and diameter (R2=0.350) of the hole. The peak frequency also increased as the hardness of the impression material increased. Differentiability of the system was evaluated by an ANOVA test. A statistically significant difference (p<0.01) was found between all implantation conditions, except in one case using the Regisil Rigid material. In contrast, the ISQ value did not consistently differentiate under several implantation conditions. The developed method could differentiate the stability changes in simulated implantation conditions with a wider dynamic range and with higher resolution than the ISQ value.

Movement quantification in epileptic seizures: A feasibility study for a new 3D approach - Corrected Proof

2012-01-09

Abstract: Movement quantification of the human body is presently used for analyzing deficits resulting from Central Nervous System (CNS) pathologies or exploring the insights of the human motor system behaviour. Following our previous work on 2D movement quantification of epileptic seizures, we now present a feasibility study for a newly developed 3D technique. In order to validate this new 3D approach we made a comparison with the previous method. Both techniques were tested in two different datasets: a simple motor execution performed by a volunteer and a complex motor motion induced by a real epileptic seizure. The results obtained showed, as expected, the superior robustness and precision of the 3D approach but also confirmed the validity of the 2D method, given certain constraints. We conclude that the newly developed 3D system will highly improve our capacity of pursuing the clinical research on quantitative characterization of seizure semiology to support epilepsy diagnosis.

Influences of supra-physiological temperatures on microstructure and mechanical properties of skin tissue - Corrected Proof

Min Lin, Xiao Zhai, Shuqi Wang, Zhengjin Wang, Feng Xu, Tian Jian Lu — 2012-01-09

Abstract: Thermal therapies under supra-physiological temperatures are increasingly used to treat skin diseases (e.g., superficial melanoma, removal of port-wine stains pigmented and cutaneous lesions). The efficacy of these therapies depends on the thermal and mechanical loadings that skin experiences during the treatment process. Therefore, it is of great significance to better understand the role of thermally induced changes in skin mechanical behavior and microstructure. In this study, rabbit belly skin was thermally damaged by immersing skin samples into saline solutions with controlled temperatures. We investigated the effect of thermal damage on skin mechanical behavior. We quantified the changes in skin microstructure (i.e., fiber, fibril) using histological staining and transmission electron microscopy (TEM). The results indicate that (i) the elastic modulus of skin, obtained by the uniaxial tensile test, decreased with increasing heating temperature; (ii) the skin tensile behavior was correlated with its microstructure changes induced by thermal denaturation of collagen fibers under supra-physiological temperatures; (iii) skin thermal damage predicted using the Arrhenius burn integration quantitatively agrees well with the evolution of the microstructure (i.e., percentage of the collagen area in Hematoxylin and Eosin (H&E) staining results). This study provides a better understanding of the coupled bio-thermo-mechanical behavior of skin tissue that could help to improve clinical thermal therapies.

Evaluation of migration forces of a retrievable filter: Experimental setup and finite element study - Corrected Proof

2012-01-09

Abstract: The aim of this paper is to provide a computational study of migration forces of a retrievable filter (Günther Tulip inferior vena cava filter). Using an experimental setup and finite element simulation, the migration forces and stress at the end of the anchored hooks in the struts were estimated. After that, the estimation value of migration stress (τrup) was used to analyze the effect of different mechanical factors (strut thickness, vena cava diameter) in the migration of the IVC filter.Our results show that the migration stress is τrup=4.37N/mm2. Using this value we obtain that the filter with higher strut diameter (ϕstrut=0.45mm) shows the maximal migration forces in every cava diameter. On the other hand, the value of the migration force decreases when the cava diameter increases. In addition, the finite element simulations also show that there are contact between the struts of the filter and the vein in regions close to the anchors.