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The estimation of muscle tension and velocity of shortening from the myoelectric signal have been considered in numerous papers. These papers consider the estimates of each variable separately, with the other appearing in the estimation as a constant parameter. The work described in this paper develops a model for the relationship between a muscle's mechanical outputs and the myoelectric signal. The model suggests that the myoelectric signal is related directly to the muscle mechanical power via a nonlinear differential equation in velocity of shortening. The model is general in that it includes as special cases the isometric and anisometric constant-velocity work of other authors and agrees with their experimental results. In this work anisometric experiments are performed on the biceps brachii muscle to verify the model. Estimates of muscle velocity of shortening and mechanical power are obtained from the myoelectric signal during anisometric contractions and the results agree well with the actual velocity and power. The model points out that the myoelectric signal is a direct measure of muscle tension only under isometric conditions. [ABSTRACT FROM AUTHOR]

This paper presents a new, simple model to evaluate the instrumental random errors in kinematic analysis of human movements using stereophotogrammetry. By means of equations analogous to that relate linear or angular momentum with linear or angular velocities, a direct measurement of instantaneous motion can be made without previous finite displacement analysis. Single explicit expressions can be obtained to evaluate the influence of instrumental random errors in the accuracy of the kinematic variables. From these expressions, some conclusions about the effect of marker cluster design on the experimental errors are obtained. An experiment has been carried out in order to validate the proposed technique and to assess the experimental errors in linear and angular velocity measurement and its influence in instantaneous helical axis determination. [ABSTRACT FROM AUTHOR]

The primary objective of conservative care for the diabetic foot is to protect the foot from excessive pressures. Pressure reduction and redistribution may be achieved by designing and fabricating orthotic devices based on foot structure, tissue mechanics, and external loads on the diabetic foot. The purpose of this paper is to describe the process used for the development of patient-specific mathematical models of the second and third rays of the foot, their solution by the finite element method, and their sensitivity to model parameters and assumptions. We hypothesized that the least complex model to capture the pressure distribution in the region of the metatarsal heads would include the bony structure segmented as toe, metatarsal and support, with cartilage between the bones, plantar fascia and soft tissue. To check the hypothesis, several models were constructed with different levels of details. The process of numerical simulation is comprised of three constituent parts: model definition, numerical solution and prediction. In this paper the main considerations relating model selection and computation of approximate solutions by the finite element method are considered. The fit of forefoot plantar pressures estimated using the FEA models and those explicitly tested were good as evidenced by high Pearson correlations (r=0.70-0.98) and small bias and dispersion. We concluded that incorporating bone support, metatarsal and toes with linear material properties, tendon and fascia with linear material properties, soft tissue with nonlinear material properties, is sufficient for the determination of the pressure distribution in the metatarsal head region in the push-off position, both barefoot and with shoe and total contact insert. Patient-specific examples are presented. [ABSTRACT FROM AUTHOR]

The paper describes a spherical harmonic-based finite element scheme for solving Poisson-type equations throughout volumes characterised by irregularly shaped inner and outer surfaces. The inner and outer surfaces are defined by spherical harmonics, and the volume in between these surfaces is divided into nested shells that are weighted averages of the inner and outer surfaces. The resulting mesh comprises hexahedral elements, wherein each hexahedral element is defined by inner and outer shells in the radial direction and divisions in the polar and azimuthal directions. The spacing between shells can be set to any desired value. Similarly, the size of the polar and azimuthal divisions can be specified. A test of the scheme on an anisotropic sphere, meshed with 720 nodes, yielded a relative error of 0.78% on the sphere's surface. As a comparison, a previously published combined finite element/boundary element scheme with a 946-node mesh produced a corresponding error of 3.57%. [ABSTRACT FROM AUTHOR]

In the functional electrical stimulation of nerve an expression defined as the 'activating function' has been introduced to evaluate the propensity for a particular fibre to excite. This approach to determine resulting activation is only an approximation as it neglects the presence of the fibres on the applied field, in contrast to activity determined from a rigorous solution to the core conductor/excitable membrane equations. An alternative approach to determining relative excitability based on the induced transmembrane potential is presented, thereby allowing for current redistribution via the space constant of the target fibre. The paper critically examines the approximations made with activating functions, and concludes that as currently formulated the activating function has limitations in predicting relative excitability under a number of important conditions. In contrast, it is the induced (passive) transmembrane potential that provides a quantitatively reliable estimate of the tendency for fibres to excite. [ABSTRACT FROM AUTHOR]

If a defibrillating stimulus current is applied to a one-dimensional fibre, and if the fibre has junction resistances joining the individual cells, what pattern of transmembrane voltages is induced by the stimulus, and what are the curretns that flow to produce the transmembrane voltages? These questions were considered in an earlier report; in this paper, two additional solution procedures are provided, one exact and one approximate, the latter relatively simple. Earlier work used a resistive model of the cells and junctions, together with a computer solution of 330 simultaneous equations for a 30-cell fibre. The present methods exploit the known solutions for the continuous (zero junctional resistance) fibre together with an analytic treatment of the junctions. With the present methods solution for currents and transmembrane potentials in the same 30-cell fibre requires a solution of only 29 equations (exact method) or the solution of none at all (the approximate method). The results show that, compared with previous results, the exact method provides almost identical transmembrane values; the approximate method gives values within 2 per cent. [ABSTRACT FROM AUTHOR]

The efficiency and accuracy of prosthetic alignment may be greatly improved with the help of a model which establishes the relationship between alignment settings and physical parameters which are closely related to amputee comfort and performance. The paper presents a mathematical model, based on equations of motion of the shank and foot, relating above-knee amputees' stump loading to alignment adjustments. Included is a numerical example, which demonstrates the use of a computer simulation, to predict the alignment setting for minimal thigh axial torque (t.a.t.). It is suggested that the use of such a simulation should precede actual change of alignment in clinical practice. [ABSTRACT FROM AUTHOR]

This paper considers the magnetic field arising from action currents associated with the propagation of an action potential along a cylindrical fibre. The equivalent current sources of the magnetic field are precisely the difference in axial current density on each side of the membrane. Fibre bundles are considered by superposition. The total magnetic field varies as 0(1/R) hence it is quadrupolar. The equivalent source is more strongly related to the discontinuity in conductivity between the membrane andsurrounding media than directly to the ionic (primary) currents. [ABSTRACT FROM AUTHOR]

Localization of active neural source (ANS) from measurements on head surface is vital in magnetoencephalography. As neuron-generated magnetic fields are extremely weak, significant uncertainties caused by stochastic measurement interference complicate its localization. This paper presents a novel computational method based on reconstructed magnetic field from sparse noisy measurements for enhanced ANS localization by suppressing effects of unrelated noise. In this approach, the magnetic flux density (MFD) in the nearby current-free space outside the head is reconstructed from measurements through formulating the infinite series solution of the Laplace's equation, where boundary condition (BC) integrals over the entire measurements provide "smooth" reconstructed MFD with the decrease in unrelated noise. Using a gradient-based method, reconstructed MFDs with good fidelity are selected for enhanced ANS localization. The reconstruction model, spatial interpolation of BC, parametric equivalent current dipole-based inverse estimation algorithm using reconstruction, and gradient-based selection are detailed and validated. The influences of various source depths and measurement signal-to-noise ratio levels on the estimated ANS location are analyzed numerically and compared with a traditional method (where measurements are directly used), and it was demonstrated that gradient-selected high-fidelity reconstructed data can effectively improve the accuracy of ANS localization. [ABSTRACT FROM AUTHOR]

This paper explores methods that make use of visual cues aimed at generating actual haptic sensation to the user, namely pseudo-haptics. We propose a new pseudo-haptic feedback-based method capable of conveying 3D haptic information and combining visual haptics with force feedback to enhance the user's haptic experience. We focused on an application related to tumor identification during palpation and evaluated the proposed method in an experimental study where users interacted with a haptic device and graphical interface while exploring a virtual model of soft tissue, which represented stiffness distribution of a silicone phantom tissue with embedded hard inclusions. The performance of hard inclusion detection using force feedback only, pseudo-haptic feedback only, and the combination of the two feedbacks was compared with the direct hand touch. The combination method and direct hand touch had no significant difference in the detection results. Compared with the force feedback alone, our method increased the sensitivity by 5%, the positive predictive value by 4%, and decreased detection time by 48.7%. The proposed methodology has great potential for robot-assisted minimally invasive surgery and in all applications where remote haptic feedback is needed. [ABSTRACT FROM AUTHOR]

Neural source localization using electroencephalographic data is usually performed using either dipolar models or minimum norm based techniques. While the former demands a priori information about the number of active sources and is particularly suitable for generators, which occupy small pieces of cortical tissue, the major drawbacks of the second approach are its dependence on the uncorrelated noise, and its tendency to localize the sources at the surface. In this paper, a simple mathematical procedure, based on the behavior of the dispersion of the minimum norm solutions, is introduced, in order to estimate the depth of the sources. The correct position of the active generators is obtained using successively deeper surfaces instead of the application of a regularization matrix, as is commonly described in the bibliography. The evaluation of this technique is performed using single and double dipolar simulated generators and two different models for the head: spherical and realistic. The results yield a mean accuracy of about 10 mm for the most disadvantageous situations studied and thus, this method seems to be very promising to handle the depth of the neural generators. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional (3D) reconstruction system of the human spine for the routine evaluation of musculoskeletal pathologies like idiopathic scoliosis. The main objective of this 3D reconstruction system is to offer a versatile and robust tool for the 3D analysis of spines in any healthcare centre with standard clinical setup using standard uncalibrated radiographic images. The novel system uses a self-calibration algorithm and a weak-perspective method to reconstruct the 3D coordinates of anatomical landmarks from bi-planar radiographic images of a patient's trunk. Additionally, a small planar object of known dimensions is proposed to warrant an accurately scaled model of the spine. In order to assess the validity of the 3D reconstructions yielded by the proposed system, a clinical study using 60 pairs of digitized X-rays of adolescents was conducted. The subject cohort in the study group was composed of 51 scoliotic and 9 non-scoliotic patients, with an average Cobb angle on the frontal plane of 25 degrees. For each case, a 3D reconstruction of the spine and pelvis was obtained with the previous system used at our hospital (which requires a positioning apparatus and a calibration jacket), and with the proposed method. Results show that 3D reconstructions obtained with the new system using uncalibrated X-ray images yield geometrically accurate models with insignificant differences for 2D and 3D clinical indexes commonly used in the evaluation of spinal deformities. This demonstrates the system to be a viable and accurate tool for clinical studies and biomechanical analysis purposes, with the added advantage of versatility to any clinical setup for routine follow-ups and surgical planning. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical model of the ankle joint, i.e. tibio-talar articulation, which shows how the articular surfaces and the ligaments, acting together as a mechanism, can control the passive kinematics of the joint. The authors had previously shown that, in virtually unloaded conditions, the ankle behaves as a single degree-of-freedom system, and that two ligament fibres remain nearly isometric throughout the flexion arc. Two different equivalent spatial parallel mechanisms together with corresponding kinematic models were formulated. These assumed isometricity of fibres within the calcaneal-fibular and tibio-calcaneal ligaments and rigidity of the articulating surfaces, taken as three sphere-plane contacts in one model, and as a single spherical pair in the other. Geometry parameters for the models were obtained from three specimens. Motion predictions compare quite well with the measured motion of the specimens. The differences are accounted for by the simplifications adopted to represent the complex anatomical structures, and might be reduced by future more realistic representations of the natural articular surfaces. [ABSTRACT FROM AUTHOR]

This paper presents an inertial based sensing system for real-time three-dimensional measurement of human spinal motion, in a portable and non-invasive manner. Applications of the proposed system range from diagnosis of spine injury to postural monitoring, on-field as well as in the lab setting. The system is comprised of three inertial measurement sensors, respectively attached and calibrated to the head, torso and hips, based on the subject's anatomical planes. Sensor output is transformed into meaningful clinical parameters of rotation (twist), flexion-extension and lateral bending of each body segment, with respect to calibrated global reference space. Modeling the spine as a compound flexible pole model allows dynamic measurement of three-dimensional spine motion, which can be animated and monitored in real-time using our interactive GUI. The accuracy of the proposed sensing system has been verified with subject trials using a VICON optical motion measurement system. Experimental results indicate an error of less than 3.1 degrees in segment orientation tracking. [ABSTRACT FROM AUTHOR]

In this paper, we describe a computational model dedicated to building an apnoea monitoring system for newborn babies. The proposed model is based on whole body plethysmography, which involves non-invasive measurement of lung ventilation indirectly from the pressure deflections generated when a subject breathes inside a chamber of fixed volume (Bert in C R Soc Biol Paris 20:22-23, 1868). The computational model simulates thermal and environmental flow conditions occurring in the neonate chamber, especially steady state flow with heat transfer and carbon dioxide (CO2) transport during the exhalation phase. This permits the variance of all critical parameters and the analysis of their effects on the distributions of interest. The main objective is to study thermal and air quality comfort conditions under which infants can be monitored for long-term periods. The method deploys computational fluid dynamics techniques and parametric modelling which, by allowing input parameters to be modulated, represent a more efficient and flexible analytical tool than previous experimental techniques. Simulation data reveal that the largest flow rates occur in areas near the openings with slight formation of air recirculation zones; temperature distribution shows signs of stratification, with higher temperatures than the supplied air, CO2 distribution presents acceptable air quality level and predicted mean vote index affords a relatively acceptable thermal comfort level. This analytical approach can be considered as innovative, and can find a new application in clinical infant apnoea monitoring in a way that allows determination of the optimal location for placing a sensor to detect respiration activity without any contact with the infant's body, and without any risk, in contrast to available whole body plethysmography techniques previously tested in infants (Fleming et al. in J Appl Physiol 55:1924-1931, 1983). [ABSTRACT FROM AUTHOR]

Very few finite element models on the lumbosacral spine have been reported because of its unique biomechanical characteristics. In addition, most of these lumbosacral spine models have been only validated with rotation at single moment values, ignoring the inherent nonlinear nature of the moment-rotation response of the spine. Because a majority of lumbar spine surgeries are performed between L4 and S1 levels, and the confidence in the stress analysis output depends on the model validation, the objective of the present study was to develop a unique finite element model of the lumbosacral junction. The clinically applicable model was validated throughout the entire nonlinear range. It was developed using computed tomography scans, subjected to flexion and extension, and left and right lateral bending loads, and quantitatively validated with cumulative variance analyses. Validation results for each loading mode and for each motion segment (L4-L5, L5-S1) and bisegment (L4-S1) are presented in the paper. [ABSTRACT FROM AUTHOR]

The paper presents a new approach for simultaneous estimation of muscle fibre conduction velocity (MFCV) and muscle fibre orientation (MFO) for motor units (MUs) in two-dimensional (2D) multichannel surface electromyography recordings. This is an important tool for detecting changes and abnormalities in muscle function and structure. In addition, simultaneous estimation of MFO and MFCV avoids the necessity of manual electrode alignment. The proposed method detected propagating MU action potentials (MUAPs) in a running time window as moving components in amplitude maps. Thereafter, estimations were obtained by fitting a three-dimensional function to these maps. The performance was evaluated using synthetic MU signals at 10 dB SNR and authentic biceps brachii measurements. Results demonstrated MFCV and MFO estimates with standard deviations of less than 0.05 m s(-1) and 1 degrees for simulated signals, and less than 0.2 m s(-1) and 4 degrees for experimental data. However, standard deviations as low as 0.12 m s(-1) and 1.6 degrees from real signals were demonstrated. It was concluded that the method performs as well as, or better than, linear array multichannel methods when individual propagating MUAPs can be identified, even if electrodes are not aligned with fibre direction. [ABSTRACT FROM AUTHOR]

Hyperthermia plays an important role in oncological therapies, most often being used in combination with radiotherapy, chemotherapy and immunotherapy. The success of this therapy is strongly dependent on the precision and control of thermal deposition. Hyperthermia based on induction heating, with thermally self-regulating thermoseeds inserted into the tumorous mass, is used for interstitial treatment. The technique was the subject of the numerical study presented in the paper. The analysis was carried out using coupled electromagnetic heating and thermo-fluid dynamic FEM simulations. During thermal deposition by induction heating of inserted seeds, the simulations estimated the thermal field inside and outside the tumour, as well as the sensitivity of the thermal field to variations regarding seed temperature, configuration and proximity to vessels. The method, for which accurate anatomical patient's information is essential, is suitable for providing useful qualitative and quantitative information about thermal transients and power density distribution for hyperthermic treatment. Several grid steps were analysed and compared. A 1 cm seed grid was resulted in good homogeneity and effectiveness of the thermal deposition. The cold spot effect caused by large vessels was demonstrated and quantified. Simulations of the heating of a tumorous mass in the liver showed that an indcutor generator operating at 200 kHz frequency and 500 A current, producing a pulsating magnetic field of H = 60 A cm(-1), was adequate for the treatment. The seeds that perform best among those tested (Nicu (28% Cu), PdNi (27.2% Ni), PdCo (6.15% Co) and ferrite core) were the PdNi (1 mm radius, 10 mm length), as they have a low Curie temperature (52 degrees C), which is the closest to the desired treatment temperature and thus reduces the risk of hot spots. [ABSTRACT FROM AUTHOR]

Uniaxial stress-strain data were obtained from in vitro experiments on 20 porcine livers for compressions, elongations and cycles of compression and then elongation. There were about 70 cylindrical samples, with diameter 7mm and varying height (4-11 mm). The combined compression and elongation test provide a unified framework for both compression and elongation for applications such as computer-aided surgical simulation. It enable the zero stress state of the experimental liver sample to be precisely determined. A new equation that combined both logarithmic and polynomial strain energy forms was proposed in modelling these experimental data. The assumption of incompressibility was justified from a preliminary Poisson's ratio for elongation and compression at 0.43+/-0.16 and 0.47+/-0.15, respectively. This equation provided a good fit for the observed mechanical properties of liver during compression-elongation cycles and for separate compressions or elongations. The root mean square errors were 91.92+/-17.43 Pa, 57.55+/-13.23 Pa and 29.78+/-17.67 Pa, respectively. In comparison with existing strain energy functions, this combined model was the better constitutive equation. Application of this theoretical model to small liver samples and other tissues demonstrated its suitability as the material model of choice for soft tissue. [ABSTRACT FROM AUTHOR]

The paper presents a technique for the segmentation of the fibro-glandular disc in mammograms based upon a statistical model of breast density. The density function of the model was represented by a mixture of up to four weighted Gaussians, each one corresponding to a specific density class in the breast. The parameters of the model and the number of tissue classes in the breast were determined using the expectation-maximisation algorithm and the minimum description length method. Grey-level statistics of the pectoral muscle were used to determine the tissue categories that are likely to represent the fibro-glandular disc. The method was applied to 84 medio-lateral oblique mammograms from the Mini-MIAS database. The results of the segmented fibro-glandular disc were assessed by a radiologist using the original and the segmented images, with reference to a ranking table categorising the results of segmentation as: 1: excellent; 2: good; 3: average; 4: poor; and 5: complete failure. Of the 84 cases analysed, 64.3% were rated as excellent, 16.7% were rated as good, 10.7% were rated as average, and 4.7% were rated as poor; only 3.6% of the cases were rated as a complete failure with regard to segmentation of the fibro-glandular disc. [ABSTRACT FROM AUTHOR]

The flexibility of the scoliotic spine is an important biomechanical parameter to take into account in the planning of surgical instrumentation. The objective of the paper was to develop a method to characterise in vivo the mechanical properties of the scoliotic spine using a flexible multi-body model. Vertebrae were represented as rigid bodies, and intervertebral elements were defined at every level using a spherical joint and three torsion springs. The initial mechanical properties of motion segments were defined from in vitro experimental data reported in the literature. They were adjusted using an optimisation algorithm to reduce the discrepancy between the simulated and the measured Ferguson angles in lateral bending of three spine segments (major or compensatory left thoracic, right thoracic and left lumbar scoliosis curves). The flexural rigidity of the spine segments was defined in three categories (flexible, nominal, rigid) according to the estimated mechanical factors (alpha). This approach was applied with ten scoliotic patients undergoing spinal correction. Personalisation of the model resulted in an increase of the initial flexural rigidity for seven of the ten lumbar segments (1.38 < or = alpha < or = 10.0) and four of the ten right thoracic segments (1.74 < or = alpha < or = 5.18). The adjustment of the mechanical parameters based on the lateral bending tests improved the model's ability to predict the spine shape change described by the Ferguson angles by up to 50%. The largest differences after personalisation were for the left lumbar segments in left bending (4 degrees +/- 3 degrees). The in vivo identification of the mechanical properties of the scoliotic spine will improve the ability of biomechanical models adequately to predict the surgical correction, which should help clinicians in the planning of surgical instrumentation manoeuvres. [ABSTRACT FROM AUTHOR]

It is still unclear what fundamental criteria influence the ability of alternating current (AC) to induce ventricular fibrillation (VF) in vivo. As the VF threshold has a bowl-shaped relationship with frequency (showing a minimum threshold at some frequency), similar to the nervous system, one proposed model has assumed that the mechanisms underlying AC stimulation of nerves are at work for VF induction. More recent work has suggested a second approach, whereby a simple RC-like model is sufficient to understand the cardiac AC stimulation threshold's frequency dependence, suggesting that some unarticulated mechanism is at work for VF. The paper directly tests these two models. In 12 intact dogs and 20 intact guinea pigs, DC pulses were used to stimulate AC square and AC sine waves at 10, 20, 40, 80 and 160 Hz. All electrodes were endocardial, with the return electrode being on a paw or thorax. It was found that, for square and sine wave stimulation in both dogs and guinea pigs, the stimulation threshold increased monotonically with frequency from 10Hz up to 160Hz (p < 0.01 for dogs and guinea pigs). Between 80 and 160Hz, the AC stimulation threshold doubled, exactly as predicted by an RC model. It was concluded that the AC stimulation threshold is not bowl-shaped and is best understood with an RC model. As the VF threshold does exhibit a bowl-shape with frequency, as opposed to the stimulation threshold which does not, the VF induction frequency dependence must have different origins. [ABSTRACT FROM AUTHOR]

This paper describes a portable heart simulator for the study of electromagnetic interference with active implantable devices. The simulator consists of plexiglas box divided into three chambers simulating the left atrium and the ventricles, plus a lateral compartment for the implantable device. The box is linked to a laptop computer by an analogue-to-digital convertor board, and the three chambers are monitored and driven by dedicated hardware and software interfaces. Synthetic endocardial atrial and ventricle signals for 13 cardiac rhythms are stored in the computer. They are applied to the cardiac chambers by AgCl plates. Sensing electrodes are in the form of AgCl needles inserted in saline. The simulator was able to demonstrate the behaviour of three pacemakers tested in the absence and presence of electromagnetic interference, generated by mobile phones (European GSM 900 and 1800 MHz) that emitted up to 2W (1 W at 1800 MHz). Pacemakers can be programmed with sensitivity from 0.1 mV to 5 mV, pulse width from 0.1 ms to 1.5 ms and pulse amplitude from 0.5 V to 5 V. The structural separation in three cardiac chambers (plus the one for the device) allowed a fast analysis procedure for dual- and tri-chamber implantable devices. [ABSTRACT FROM AUTHOR]

Radiofrequency (RF) ablation has become an important means of treatment of non-resectable primary and metastatic liver tumours. Recurrence of treated tumours is associated with cancer cell survival next to blood vessels. The paper examines the performance of classical monopolar, and two configurations of bipolar, RF ablation using a LeVeen ten-prong catheter. Finite element method models of monopolar and bipolar configurations were created at 5 mm distance from a vessel of the size of a typical portal vein (10 mm diameter). In one bipolar configuration, the probes were oriented in the same axial direction (asymmetric configuration); in the second bipolar configuration, the two probes were facing each other (symmetric configuration). The distribution of temperature and current density was analysed for three different flow conditions: normal flow, reduced flow due to portal hypertension and high flow. For normal flow, the distance between the formed coagulation zone and the blood vessel was 1.8 mm for monopolar, 1 mm for asymmetric bipolar, and 0.2 mm for symmetric bipolar, configurations. Symmetric bipolar RF ablation creates coagulation zones significantly closer to blood vessels compared with monopolar RF ablation. This may reduce tumour cell survival next to blood vessels and reduce recurrence rates. [ABSTRACT FROM AUTHOR]

The problem of maximising the performance of ST-T segment automatic recognition for ischaemia detection is a difficult pattern classification problem. The paper proposes the network self-organising map (NetSOM) model as an enhancement to the Kohonen self-organised map (SOM) model. This model is capable of effectively decomposing complex large-scale pattern classification problems into a number of partitions, each of which is more manageable with a local classification device. The NetSOM attempts to generalize the regularization and ordering potential of the basic SOM from the space of vectors to the space of approximating functions. It becomes a device for the ordering of local experts (i.e. independent neural networks) over its lattice of neurons and for their selection and co-ordination. Each local expert is an independent neural network that is trained and activated under the control of the NetSOM. This method is evaluated with examples from the European ST-T database. The first results obtained after the application of NetSOM to ST-T segment change recognition show a significant improvement in the performance compared with that obtained with monolithic approaches, i.e. with single network types. The basic SOM model has attained an average ischaemic beat sensitivity of 73.6% and an average ischaemic beat predictivity of 68.3%. The work reports and discusses the improvements that have been obtained from the implementation of a NetSOM classification system with both multilayer perceptrons and radial basis function (RBF) networks as local experts for the ST-T segment change problem. Specifically, the NetSOM with multilayer perceptrons (radial basis functions) as local experts has improved the results over the basic SOM to an average ischaemic beat sensitivity of 75.9% (77.7%) and an average ischaemic beat predictivity of 72.5% (74.1%). [ABSTRACT FROM AUTHOR]

The results are presented of a study performed to determine the measurement frequencies that provide optimal extraction of tissue impedance model parameters from in vivo measured electrical impedance spectra. Measurement frequency sets that are logarithmic and quasi-linear, and frequency sets that produce angularly equidistant points on the Nyquist loci are used to test the parametric fitting algorithm that calculates R0, R infinity, alpha and tau tissue parameters from complex impedance spectra. Simulated data, calculated in the presence of < or = 5% measurement noise, and in vivo experiments indicate that the quality of the fitted parameters depends upon the selection of measurement frequencies. The results show that, if measurements are performed with a system that has a realistic measurement bandwidth, then, for the best estimation of: R0, the measurement frequencies should include the decade from 100 Hz-1 kHz; R infinity, the algorithm should not include frequencies under 1 kHz; alpha and tau, the measurement frequencies should be equidistantly spaced on the Nyquist locus. [ABSTRACT FROM AUTHOR]

The paper documents a new concept in prosthetic foot design. It is based on the capacity of a flexible keel to allow a greater medio-lateral function than previously available. The heel has a complex curvature consisting of a medially concave shape that joins the mid-foot. There a hump acting as a leaf-spring ends at the metatarsal break, with an inwardly curved toe extremity. These curvatures contribute to increased medio-lateral control at heel-strike and propulsion for weight transfer and push-off. Results from finite-element modelling indicate that the asymmetrically shaped keel is at least twice as active in storing energy compared with a completely symmetrical one. A preliminary gait study is carried out for a 24-year-old below-knee amputee fitted with the new design, the SPACE foot and a dynamic elastic response foot with a symmetrical keel. With the SPACE foot, there is a 14% increase in walking speed combined with a reduction in the phasic asymmetries. The absolute difference between the initial and terminal double support is 1.4% for the asymmetrical keel design compared with 4.4% for the symmetrical keel foot prosthesis. The peak ankle power generation burst indicates that the SPACE foot behaves as a dynamic elastic response foot. [ABSTRACT FROM AUTHOR]

The paper outlines a biomechanical approach to quantifying anticipatory postural adjustments in the elderly. The measurement problems that occur in applying the biomechanical approach to elderly subjects are described and the 'signal-to-noise' properties of three candidate measures are compared, using data from volitional unilateral arm-raise tests performed on 100 elderly subjects. The results suggest that changes in vertical ground reaction force provide the greatest potential for accurate measurement of anticipatory adjustments, in comparison with changes in horizontal force or centre-of-pressure displacement. By normalising the anticipatory change in vertical ground reaction force with respect to the vertical perturbation force induced by the arm motion, a measure of relative anticipatory response is derived. The use of this measure, as well as its limitations, are demonstrated by analysing its relationship to actual falling risk, monitored prospectively in the elderly subject population. The findings showed evidence of larger relative anticipatory adjustments in the subjects who experienced recurrent falls, and it is suggested that these responses may be indicative of disordered motor programming. However, to detect these differences, it was necessary to average responses over multiple trials and to exclude trials with very small arm acceleration or very large baseline 'noise' (associated with ongoing postural sway). The need to screen and exclude data would seem to limit the practical utility of this approach in testing elderly populations. [ABSTRACT FROM AUTHOR]

The paper reports the results of investigations comparing the relative in vitro responses of different signal processing algorithms commonly employed in laser Doppler flowmetry (LDF). A versatile laser Doppler system is described which enabled complex signal processing to be implemented relatively simply using digital analysis. The flexibility of the system allowed a variety of processing algorithms to be studied by simply characterising the algorithm of interest under software control using a personal computer. An in vitro physical model is also presented which was used to maintain reproducible fluid flows. Flows of particles were studied in a physical model using both a near-infra-red (NIR) diode and an He/Ne laser source. The results show that frequency-weighted algorithms are responsive to both particle velocity and concentration, whereas non-weighted algorithms respond to concentration only. The linearity of the velocity response is critically dependent on both the dimensions of the in vitro model and the frequency bandwidth of the signal-processing algorithm. [ABSTRACT FROM AUTHOR]

Since its discovery some 50 years ago, the electro-encephalogram (EEG) has formed the basis for classification of sleep into several stages, either laboriously performed by visual examination of the EEG and related signals or, more recently, by automated techniques. Both visual scoring and most automated analyses are highly subjective and rely on application of a predefined set of rules. A method of analysing the EEG which requires no such application of rules and aims to give some indication of the dynamics of sleep in humans is proposed in the paper. [ABSTRACT FROM AUTHOR]

The cardiokymograph or displacement cardiograph (DCG) is a noncontacting device which senses movement of the heart throughout the cardiac cycle by the interaction of a radiofrequency (10-20 MHz) electromagnetic field, generated by a sensing coil, with the thorax. In the paper three different techniques of detecting this movement will be discussed: monitoring the changes in sensing resonant frequency (FM modulation), monitoring the changes in impedance of the coil at resonant frequency (AM modulation) and a new technique which monitors the changes in coil impedance at fixed frequency. The sensitivities of these three techniques will be compared. A simplified theory of the mode of coupling between the coil and the thorax will be studied in terms of a transformer model. Preliminary clinical measurements of anterior left and right ventricular motion will be given. The presence of higher-frequency features related to atrial motion and the opening and closing of the aortic and pulmonary values will also be described. [ABSTRACT FROM AUTHOR]

An important measure of the performance of a myoelectric control channel for powered artificial limbs is the myoelectric signal processor output signal-to-noise ratio (SNR). The signal and noise in this context are, respectively, the mean and variance of the estimate of some signal parameter to be used for control purposes. These quantities are determined by the signal processor, motor unit recruitment and motor unit firing statistics. The paper investigates, through analytical, simulation and experimental work, the role and significance of recruitment and firing statistics in channel performance. Equations are derived which express, for the single and multi-unit cases, channel SNR as a function of the number of active units, firing rates, action potential amplitude variation and action potential moments. A computer-simulated myoelectric signal is generated in which these variables can be controlled and SNR measured. The simulation results are compared with the theoretical and found to agree very well. Limited experiments with wire intramuscular electrodes and surface electrodes are performed to measure in vivo SNR from the biceps brachii muscle. The results of the experiments agree well with those of the simulation and theoretical work. The significance of this work is that it provides insight into the roles of important physiological parameters in myoelectric channel performance. It will also provide data necessary for the development of SNR enhancement techniques. [ABSTRACT FROM AUTHOR]

The paper describes the effect of the extracellular volume conductor on the electrophysiological behaviour of an adjoining multifibred cardiac muscle preparation, where the fibres are parallel to the interface and to each other. It is shown how, at any given depth from the interface, an approximating linear-core conductor model can be formulated, where the interstitial resistance per unit length depends on the depth. At the surface the interstitial resistance is zero whereas at the greatest depth it approaches the value that results when the preparation is in oil. Because of this varying total axial resistance with depth, and because of the effect of the total axial resistance on velocity, action potential foot, and maximum rising-phase slope, the wavefront and waveform will also vary with depth. Furthermore these qualities will be anisotropic, since the tissue conductivities are anisotropic. Numerical examples are presented to show that the hypotheses are consistent with experimental results. [ABSTRACT FROM AUTHOR]

Arterial pressure and flow measurements can be analysed using a mathematical model of the circulation. A comparison of four models of the circulation used in this way is presented. The results indicate some criteria for evaluating circulation model performance in general. [ABSTRACT FROM AUTHOR]

This paper develops a model of 2-dimensional anisotropic cardiac tissue which permits the examination of the electrical sources arising from excitation at a point. The specific results depend on the anisotropy parameters and two cases are considered in detail. For assumed equal anisotropicity ratios in the interstitial and intracellular space the isochrones are (asymptotically) confocal ellipses and the total double layer source is (asymptotically) uniform. Surface fields are calculated and plotted for this condition. (For nonequal anisotropy ratios the total double layer source is necessarily nonuniform). When the preparation is very thin so that all fibres are essentially in contact with the extracellular medium the isochrones are (asymptotically) confocal ellipses but the total double-layer sources are now nonuniform. The sources for this case are determined and the fields at the surface of the cardiac tissue evaluated and plotted. The aforementioned 'thin' and 'thick' tissue preparations are contrasted with each other and the effects of anisotropicity in cardiac tissue discussed. [ABSTRACT FROM AUTHOR]

Various electrical-impedance methods have been proposed for the measurement of haemodynamic parameters noninvasively. For example, an impedance method is proposed for the measurement of cardiac output from the skin surface and is called impedance cardiography. However, there are many problems in the application of the impedance technique for the noninvasive measurement of haemodynamic parameters. One of them is the complicated structure of organs in the body. Another is the anomalous electrical properties of tissues. For these reasons, it is very difficult to obtain exact information about haemodynamics from the waveforms measured by the impedance cardiograph, in spite of the fact that the waveforms include much useful information. We can get useful information, if the relationships between the waveforms and the biomedical events in the subject are understood. In this paper, the relationships between the waveforms and the circulation of the blood are discussed theoretically and experimentally. The effects of the complicated structure of the organs and the anomalous electrical properties of tissues upon the waveforms are also discussed both theoretically and experimentally. For the analysis of the waveforms, it is very important to discuss (a) equipotential lines and potential distribution on the thorax, (b) the impedance or admittance between a pair of electrodes, (c) impedance or admittance changes due to blood circulation, (d) waveforms due to the pulsatile blood flow and (e) the effects of the complicated structure of organs upon the waveforms. From our results, it is concluded that: [ABSTRACT FROM AUTHOR]

Electrocardiographic inverse solutions frequently assume multiple-dipole equivalent generators with locations fixed throught the QRS complex. This paper describes investigations which extend the solution to optimise the dipole locations at any instant of time. The combined results lead to a moving multiple-dipole inverse solution which is more accurate than the conventional solutions at each instant and also contains information related to the dynamic movement of the physiological generators. Tests so far have been limited to a 3-dipole solution in a highly simplified torso model. The generators in this study were dipoles displaced varying amounts from a standard central location; the inverse solution starts by using the standard location and then is led to an improved solution by a guided search. Moderate displacements, as compared to the size of the heart model, were shown to yield root mean square errors in the inverse-solution source strengths as high as 40% when the latter were found via a least-mean-square procedure. The method of steepest descent was utilised in the second step to improve the locations and strengths of the initially assumed equivalent-dipole generators and thus improve the accuracy of the inverse solution. The percentage root-mean-square source-strength errors were reduced from as high as 40% to under 10% in most cases. The initial position error of up to 10% for the source dipoles typically was reduced to less than 5% throught the use of the search routine. The ability of the solution dipoles to track the original locations was demonstrated. [ABSTRACT FROM AUTHOR]

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The pathophysiology underlying neurocognitive dysfunction following mild traumatic brain injury (TBI), or concussion, is poorly understood. In order to shed light on the effects of TBI at the functional network or modular level, our research groups are engaged in the acquisition and analysis of functional magnetic resonance imaging data from subjects post-TBI. Complementary to this effort, in this paper we use mathematical and computational techniques to determine how modular structure changes in response to specific mechanisms of injury. In particular, we examine in detail the potential effects of focal contusions, diffuse axonal degeneration and diffuse microlesions, illustrating the extent to which functional modules are preserved or degenerated by each type of injury. One striking prediction of our study is that the left and right hemispheres show a tendency to become functionally separated post-injury, but only in response to diffuse microlesions. We highlight other key differences among the effects of the three modelled injuries and discuss their clinical implications. These results may help delineate the functional mechanisms underlying several of the cognitive sequelae associated with TBI. [ABSTRACT FROM AUTHOR]

The fetal electrocardiogram (fECG) contains important information regarding the health of the fetus. However, the fECG obtained noninvasively from the abdominal surface electrical recordings of a pregnant woman are dominated by strong interference from the maternal electrocardiogram (mECG). In this paper, based on the H(infinity) principle, two adaptive algorithms are proposed for the extraction of fECG from the trans-abdominal recordings of pregnant women. The motivation behind the application of H(infinity) techniques is the fact that they are robust with respect to model uncertainties and lack of statistical information regarding noise. The proposed algorithms are applied to simulated as well as real multichannel ECG recordings and their performances are compared to that of the well-known least-mean-square (LMS) adaptive algorithm. It is found that the proposed H(infinity) based algorithms perform superior to the LMS algorithm in extracting the fECG signal. [ABSTRACT FROM AUTHOR]

Surface-recorded somatosensory-evoked potentials (SEPs) are neural signals elicited by an external stimulus. In the case of electrically induced SEPs, the artifact generated by the stimulation process can severely distort the signal. In some cases, the artifact tail often lasts well into the initiation of the SEP making the determination of absolute latency very difficult. In this work, a new approach was taken to identify factors that affect the tail of the artifact. The methodology adopted was the development of a lumped electrical circuit model of the artifact generation process. While the modeling of the instrumentation hardware is relatively simple, this is not the case with tissue and electrode/skin interface effects. Consequently, this paper describes a novel tissue modeling approach that uses an autoregressive moving average (ARMA) parametric technique and an artificial neural network (ANN) to estimate tissue parameters from experimental data. This coupled with an estimation of the stimulation electrode-skin impedance completes the lumped circuit model. Simulink (The Mathworks Inc.) was used to evaluate the model under several different conditions. These results show that both the stimulation electrode-skin interface impedance and nature of the body tissue directly under the recording electrodes have a profound effect on the appearance of the stimulus artifact tail. This was verified by experimentally recorded data obtained from the median nerve using surface electrodes. Conclusions drawn from this work include that stimulation electrodes with low series capacitance should be used whenever possible to minimize the duration of the artifact tail. [ABSTRACT FROM AUTHOR]

In the medical field, there is a need for small ambulatory sensor systems for measuring the kinematics of body segments. Current methods for ambulatory measurement of body orientation have limited accuracy when the body moves. The aim of the paper was to develop and validate a method for accurate measurement of the orientation of human body segments using an inertial measurement unit (IMU). An IMU containing three single-axis accelerometers and three single-axis micromachined gyroscopes was assembled in a rectangular box, sized 20 x 20 x 30 mm. The presented orientation estimation algorithm continuously corrected orientation estimates obtained by mathematical integration of the 3D angular velocity measured using the gyroscopes. The correction was performed using an inclination estimate continuously obtained using the signal of the 3D accelerometer. This reduces the integration drift that originates from errors in the angular velocity signal. In addition, the gyroscope offset was continuously recalibrated. The method was realised using a Kalman filter that took into account the spectra of the signals involved as well as a fluctuating gyroscope offset. The method was tested for movements of the pelvis, trunk and forearm. Although the problem of integration drift around the global vertical continuously increased in the order of 0.50 degrees s(-1), the inclination estimate was accurate within 3 degrees RMS. It was shown that the gyroscope offset could be estimated continuously during a trial. Using an initial offset error of 1 rad s(-1), after 2 min the off-set error was roughly 5% of the original offset error. Using the Kalman filter described, an accurate and robust system for ambulatory motion recording can be realised. [ABSTRACT FROM AUTHOR]

The electrogastrogram (EGG), a cutaneous measurement of gastric electrical activity, is a mixture of gastric slow waves and noise. To detect the propagation of gastric slow waves, it is desired to obtain gastric slow waves in each of multichannel EGGs. Recently, independent component analysis (ICA) has shown its efficiency in separating the gastric slow wave from noisy multichannel EGGs. However, this method is not able to recover gastric slow waves in each of the multichannel EGGs. In this paper, a two-stage combined method was proposed for extracting gastric slow waves. First, ICA was performed to separate the gastric slow wave component from noisy multichannel EGGs. Second, adaptive signal enhancement with a reference input derived by the ICA in the first stage was employed to extract gastric slow waves in each channel. Quantitative analysis showed that, with the proposed method, the maximum root-mean-square error between the estimated time lag and its theoretical value in the simulations was only 0.65. The results from real EGG data demonstrated that the combined method was able to extract gastric slow waves from individual channels of EGGs which are important to identify the slow wave propagation. Therefore, the proposed method can be used to detect propagation of gastric slow waves from multichannel EGGs. [ABSTRACT FROM AUTHOR]

Abnormal intra-QRS potentials (AIOPs) in signal-averaged electrocardiograms have been proposed as a risk evaluation index for ventricular arrhythmias. The purpose of the paper was to develop an automatic algorithm for selecting the optimum parametric model order in the analysis of AIOPs to make the modelling approach clinically more feasible. A total of 130 normal Taiwanese subjects and 87 patients with ventricular premature contractions and 23 with sustained ventricular tachycardia were recruited. The unpredictable AIQP signal was estimated from the modelling residual. The cross-correlation coefficient between the original signal and the ORS estimate was employed to evaluate the accuracy of the estimate. A pre-selected threshold cross-correlation coefficient of 0.9999 was used to determine the optimum order. The mean AIQP in lead Y for ventricular tachycardia patients was 3.9 microV, which was significantly smaller than 4.9 microV for ventricular premature contraction patients (p < 0.01) and 6.3 microV for normal subjects (p < 0.001). The linear combination of AIQP in lead Y and the time-domain parameter RMS40 provided the best global performance (the area under the receiver operating characteristic curve was 89.1%). A higher risk of ventricular arrhythmias was associated with lower AIQP in lead Y, and the automatic modelling algorithm improved the clinical feasibility of AIQP analysis. [ABSTRACT FROM AUTHOR]

The paper studies a surface electromyogram (SEMG) decomposition technique suitable for identification of complete motor unit (MU) firing patterns and their motor unit action potentials (MUAPs) during low-level isometric voluntary muscle contractions. The algorithm was based on a correlation matrix of measurements, assumed unsynchronised (uncorrelated) MU firings, exhibited a very low computational complexity and resolved the superimposition of MUAPs. A separation index was defined that identified the time instants of an MU's activation and was eventually used for reconstruction of a complete MU innervation pulse train. In contrast with other decomposition techniques, the proposed approach worked well also when the number of active MUs was slightly underestimated, if the MU firing patterns partly overlapped and if the measurements were noisy. The results on synthetic SEMG show 100% accuracy in the detection of innervation pulses down to a signal-to-noise ratio (SNR) of 10 dB, and 93+/-4.6% (mean+/-standard deviation) accuracy with 0 dB additive noise. In the case of real SEMG, recorded with an array of 61 electrodes from biceps brachii of five subjects at 10% maximum voluntary contraction, seven active MUs with a mean firing rate of 14.1 Hz were identified on average. [ABSTRACT FROM AUTHOR]

A numerical model able to investigate the influence of biomechanical factors on the long-term secondary stability of implants would be extremely useful for the design of new cementless prosthetic devices. A purely biomechanical model of osseo-integration has been developed, formulated as a rule-based adaptation scheme. Due to its complexity, the problem was divided into three steps: preliminary implementation of the model (proof of concept); implementation of the complete model and investigation of the model solution; and model validation. The paper describes the first of these three steps. The model was implemented as a discrete-states machine, and the few parameters required were derived from the literature. It was then applied to a real clinical case. The study was conducted using the frictional contact finite element model of a human femur implanted with a cementless anatomical stem. A stable solution was achieved after between three and 15 iterations for all initial positions considered. Similar initial conditions yielded similar final configurations. The model predicted all initial configurations, with the exception of a partial osseo-integration, ranging between 62% (distal fit) and 78% (proximal fit) of the viable interface. This is in good agreement with the values reported in the literature that never exceed 75%, even in the best conditions, and report better clinical results for proximal fit. For the varus configuration, which lacks cortical support, the algorithm predicted a completed loosening. [ABSTRACT FROM AUTHOR]

The fundamental goal of ultrasound thermal therapy is to provide proper thermal lesion formations for effective tumour treatment. The quality of the therapy depends mostly on its positional precision. To date, most ultrasound thermal therapy treatments have focused on the formation of power or temperature patterns. The non-linear and time-delay effects of thermal dose formation prohibit direct control of the thermal dose distribution. In the paper, the control of thermal lesions by regulation of the temperature of a pilot point is proposed. This scheme utilises the high correlation between temperature elevation and thermal dose at the forward boundary of thermal lesions. To verify the feasibility, a 2D ultrasound phased array system was used to generate thermal lesions of various sizes, and the temperature elevation required to generate a thermal dose threshold was investigated. Results showed that the required temperature elevation was found to be a reasonably constant value of 52.5 degrees C under differing conditions when the focal area was small. When the focal area under consideration was large, the required temperature elevation became a monotonic function of blood perfusion rate, ranging from 49.2 to 52.5 degrees C. When the reference temperature of the pilot point was set at a conservative value (52.5 degrees C), the thermal lesions were controlled precisely under a wide range of blood perfusion and power pattern changes, tested by using a more realistic model that takes into account thermal-induced attenuation and blood perfusion changes. This changed the complex thermal dose control problem into a simple temperature regulation problem, which makes implementation of thermal lesion control easier, giving the scheme a high potential for application to current ultrasound thermal therapy systems. [ABSTRACT FROM AUTHOR]

In biomedical visualisation, the isosurface is usually used to represent (approximate) the boundary surface of the structure within biomedical volumetric images. However, in many confocal microscopy volumetric images of neurons, the grey values of the object and/or background are usually uneven. Therefore a fixed isosurface is not suitable for use in approximating the boundary surface of the neuron. A method is proposed to construct the adaptively approximating surface of the boundary surface of the neuron. In this method, the boundary surface of the neuron could be locally and adaptively approximated with different surface patches in different local regions. Consequently, the approximation accuracy has been considerably improved. [ABSTRACT FROM AUTHOR]

In clinical cardiology, stenosis in a coronary artery is measured on the basis of visual assessment. The reading of coronary arteriograms leads, however, to large inter- and intra-observer variability. Image analysis and computer assistance result in a more consistent assessment, but this approach is mainly based upon static geometric parameters, such as diameter reduction of a segment of the stenosed artery. A more functional, physiological measurement is thus desirable. This can be realised by measuring the difference between the normal coronary blood flow and the increased flow under hyperaemic conditions, yielding the so-called coronary flow reserve (CFR). In clinical practice, however, this method is difficult and time-consuming. A less demanding approach is reported, in which relative flow distributions are determined densitometrically from digital angiograms acquired under basal and hyperaemic conditions. The proposition is that, if the relative flow distribution in hyperaemic state differs from that during rest, the functional severity of a stenosis downstream from the bifurcation can be indicated. The new approach is validated by comparing the results of a theoretical model for steady flow with a flow phantom experiment for steady and pulsatile flow. The obtained flow ratios correlate very well, both in steady and pulsatile flow, with correlation coefficients exceeding 0.95. [ABSTRACT FROM AUTHOR]

A new method is proposed, based on the pole phase angle (PPA) of a second-order autoregressive (AR) model, to track spectral alteration during localised muscle fatigue when analysing surface myo-electric (ME) signals. Both stationary and non-stationary, simulated and real ME signals are used to investigate different methods to track spectral changes. The real ME signals are obtained from three muscles (the right vastus lateralis, rectus femoris and vastus medialis) of six healthy male volunteers, and the simulated signals are generated by passing Gaussian white-noise sequences through digital filters with spectral properties that mimic the real ME signals. The PPA method is compared, not only with spectra-based methods, such as Fourier and AR, but also with zero crossings (ZCs) and the first AR coefficient that have been proposed in the literature as computer efficient methods. By comparing the deviation (dev), in percent, between the linear regression of the theoretical and estimated mean frequencies of the power spectra for simulated stationary (s) and non-stationary (ns) signals, in general, it is found that the PPA method (devs = 4.29; devns = 1.94) gives a superior performance to ZCs (dvs = 8.25) and the first AR coefficient (4.18 < devs < 21.8; 0.98 < devns < 4.36) but performs slightly worse than spectra-based methods (0.33 < devs < 0.79; 0.41 < devns < 1.07). However, the PPA method has the advantage that it estimates spectral alteration without calculating the spectra and therefore allows very efficient computation. [ABSTRACT FROM AUTHOR]