Showing papers in "Medical & Biological Engineering & Computing in 2000"

Continuous estimation of systolic blood pressure using the pulse arrival time and intermittent calibration

Abstract: A continuous noninvasive method of systolic blood pressure estimation is described. Systolic blood pressure is estimated by combining two separately obtained components: a higher frequency component obtained by extracting a specific frequency band of pulse arrival time and a lower frequency component obtained from the intermittently acquired systolic blood pressure measurements with an auscultatory or oscillometric system. The pulse arrival time was determined by the time interval from QRS apex in electrocardiogram to the onset of photoplethysmogram in a fingertip beat-by-beat via an oximetric sensor. The method was examined in 20 patients during cardiovascular surgery. The estimated values of systolic blood pressure were compared with those measured invasively using a radial arterial catheter. The results showed that the correlation coefficients between estimated values and invasively obtained systolic blood pressure reached 0.97±0.02 (mean±SD), and the error remained within ±10% in 97.8% of the monitoring period. By using a system with automatic cuff inflation and deflation to acquire intermittent systolic blood pressure values, this method can be applicable for the continuous noninvasive monitoring of systolic blood pressure.

Collagen-based biomaterials as 3D scaffold for cell cultures: applications for tissue engineering and gene therapy.

Abstract: Many substances are used in the production of biomaterials: metals (titanium), ceramics (alumina), synthetic polymers (polyurethanes, silicones, polyglycolic acid (PGA), polylactic acid (PLA), copolymers of lactic and glycolic acids (PLGA), polyanhydrides, polyorthoesters) and natural polymers (chitosan, glycosaminoglycans, collagen). With the rapid development in tissue engineering, these different biomaterials have been used as three-dimensional scaffolds and cell transplant devices. The principal biochemical and biological characteristics of the collagen-based biomaterials are presented, including their interactions with cells (fibroblasts), distinct from those of synthetic polymers, and their potential use in gene therapy through the formation of neo-organs or organoids.

3D micro-computed tomography of trabecular and cortical bone architecture with application to a rat model of immobilisation osteoporosis

Abstract: Bone mass and microarchitecture are the main determinants of bone strength. Three-dimensional micro-computed tomogrpahy has the potential to examine complete bones of small laboratory animals with very high resolution in a non-invasive way. In the presented work, the proximal part of the tibiae of hindlimb unloaded and control rats were measured with 3D MicroCT, and the secondary spongiosa of the scanned region was evaluated using direct evaluation techniques that do not require model assumptions. For determination of the complete bone status, the cortex of the tibiae was evaluated and characterised by its thickness. It is shown that with the proposed anatomically conforming volume of interest (VOI), up to an eight-fold volume increase can be evaluated compared to cubic or spherical VOIs. A pronounced trabecular bone loss of −50% is seen after 23 days of tail suspension. With the new evaluation techniques, it is shown that most of this bone loss is caused by the thinning of trabeculae, and to a lesser extent by a decrease in their number. What changes most radically is the structure type: the remaining bone is more rod-like than the control group's bone. Cortical bone decreases less than trabecular bone, with only −18% after 23 days.

Boundary modelling and shape analysis methods for classification of mammographic masses

Abstract: The problem of computer-aided classification of benign and malignant breast masses using shape features is addressed. The aim of the study is to look at the exceptions in shapes of masses such as circumscribed malignant tumours and spiculated benign masses which are difficult to classify correctly using common shape analysis methods. The proposed methods of shape analysis treat the object's boundary in terms of local details. The boundaries of masses analysed using the proposed methods were manually drawn on mammographic images by an expert radiologist (JELD). A boundary segmentation method is used to separate major portions of the boundary and to label them as concave or convex segments. To analyse the shape information localised in each segment, features are computed through an iterative procedure for polygonal modelling of the mass boundaries. Features are based on the concavity fraction of a mass boundary and the degree of narrowness of spicules as characterised by a spiculation index. Two features comprising spiculation index (SI) and fractional concavity (fcc) developed in the present study when used in combination with the global shape feature of compactness resulted in a benign/malignant classification accuracy of 82%, with an area (Az) of 0.79 under the receiver operating characteristics (ROC) curve with a database of the boundaries of 28 benign masses and 26 malignant tumours. SI alone resulted in a classification accuracy of 80% with Az of 0.82. The combination of all the three features achieved 91% accuracy of circumscribed versus spiculated classification of masses based on shape.

3D reconstruction method from biplanar radiography using non-stereocorresponding points and elastic deformable meshes

Abstract: Standard 3D reconstruction of bones using stereoradiography is limited by the number of anatomical landmarks visible in more than one projection. The proposed technique enables the 3D reconstruction of additional landmarks that can be identified in only one of the radiographs. The principle of this method is the deformation of an elastic object that respects stereocorresponding and non-stereocorresponding observations available in different projections. This technique is based on the principle that any non-stereocorresponding point belongs to a line joining the X-ray source and the projection of the point in one view. The aim is to determine the 3D position of these points on their line of projection when submitted to geometrical and topological constraints. This technique is used to obtain the 3D geometry of 18 cadaveric upper cervical vertebrae. The reconstructed geometry obtained is compared with direct measurements using a magnetic digitiser. The order of precision determined with the point-to-surface distance between the reconstruction obtained with that technique and reference measurements is about 1 mm, depending on the vertebrae studied. Comparison results indicate that the obtained reconstruction is close to the actual vertebral geometry. This method can therefore be proposed to obtain the 3D geometry of vertebrae.

Classification of breast tissue by electrical impedance spectroscopy.

Abstract: Electrical impedance spectroscopy is a minimally invasive technique that has clear advantages for living tissue characterisation owing to its low cost and ease of use. The present paper describes how this technique can be applied to breast tissue classification and breast cancer detection. Statistical analysis is used to derive a set of rules based on features extracted from the graphical representation of electrical impedance spectra. These rules are used hierarchically to discriminate several classes of breast tissue. Results of statistical classification obtained from a data set of 106 cases representing six classes of excised breast tissue show an overall classification efficiency of ∼92% with carcinoma discrimination >86%.

Modelling the effects of electric fields on nerve fibres: Influence of the myelin sheath

Abstract: The excitation and conduction properties of computer-based cable models of mammalian motor nerve fibres, incorporating three different myelin representations, are compared. The three myelin representations are a perfectly insulating single cable (model A), a finite impedance single cable (model B) and a finite impedance double cable (model C). Extracellular stimulation of the three models is used to study their strength-duration and current-distance (I-X) relationships, conduction velocity (CV) and action potential shape. All three models have a chronaxie time that is within the experimental range. Models B and C have increased threshold currents compared with model A, but each model has slope to the I-X relationship that matches experimental results. Model B has a CV that matches experimental data, whereas the CV of models A and C are above and below the experimental range, respectively. Model C is able to produce a depolarising afterpotential (DAP), whereas models A and B exhibit hyperpolarising afterpotentials. Models A and B are determined to be the preferred models when low-frequency stimulation (< approximately 25 Hz) is used, owing to their efficiency and accurate excitation and conduction properties. For high frequency stimulation (approximately 25 Hz and greater), model C, with its ability to produce a DAP, is necessary accurately to simulate excitation behaviour.

Information domain analysis of cardiovascular variability signals: evaluation of regularity, synchronisation and co-ordination.

Abstract: A unifying general approach to measure regularity, synchronisation and co-ordination is proposed. This approach is based on conditional entropy and is specifically designed to deal with a small amount of data (a few hundred samples). Quantitative and reliable indexes of regularity, synchronisation and co-ordination (ranging from 0 to 1) are derived in a domain (i.e. the information domain) different from time and frequency domains. The method is applied to evaluate regularity, synchronisation and co-ordination among cardiovascular beat-to-beat variability signals during sympathetic activation induced by head-up tilt (T), during the perturbing action produced by controlled respiration at 10, 15 and 20 breaths/min (CR10, CR15 and CR20), and after peripheral muscarinic blockade provoked by the administration of low and high doses of atropine (LD and HD). It is found that: (1) regularity of the RR interval series is around 0.209; (2) this increases during T, CR10 and HD; (3) the systolic arterial pressure (SAP) series is more regular (0.406) and its regularity is not affected by the specified experimental conditions; (4) the muscle sympathetic (MS) series is a complex signal (0.093) and its regularity is not influenced by HD and LD; (5) the RR interval and SAP series are significantly, though weakly, synchronised (0.093) and their coupling increases during T, CR10 and CR15; (6) the RR interval and respiration are coupled (0.152) and their coupling increases during CR10; (7) SAP and respiration are significantly synchronised (0.108) and synchronisation increases during CR10; (8) MS and respiration are uncoupled and become coupled (0.119) after HD; (9) the RR interval, SAP and respiration are significantly co-ordinated (0.118) and co-ordination increases during CR10 and CR15; (10) during HD the co-ordination among SAP, MS and the respiratory signal is larger than that among the RR interval, SAP, MS and the respiratory signal, thus indicating that the RR interval contributes towards reducing co-ordination.

Improvement of walking speed prediction by accelerometry and altimetry, validated by satellite positioning

Abstract: Activity monitors based on accelerometry are used to predict the speed and energy cost of walking at 0% slope, but not at other inclinations. Parallel measurements of body accelerations and altitude variation were studied to determine whether walking speed prediction could be improved. Fourteen subjects walked twice along a 1.3km circuit with substantial slope variations (−17% to +17%). The parameters recorded were body acceleration using a uni-axial accelerometer, altitude variation using differential barometry, and walking speed using satellite positioning (DGPS). Linear regressions were calculated between acceleration and walking speed, and between acceleration/altitude and walking speed. These predictive models, calculated using the data from the first circuit run, were used to predict speed during the second circuit. Finally the predicted velocity was compared with the measured one. The result was that acceleration alone failed to predict speed (meanr=0.4). Adding altitude variation improved the prediction (meanr=0.7). With regard to the altitude/acceleration-speed relationship, substantial inter-individual variation was found. It is concluded that accelerometry, combined with altitude measurement, can assess position variations of humans provided inter-individual variation is taken into account. It is also confirmed that DGPS can be used for outdoor walking speed measurements, opening up new perspectives in the field of biomechanics.

Artifact reduction in electrogastrogram based on empirical mode decomposition method.

Abstract: Severe contamination of the gastric signal in electrogastrogram (EGG) analysus by respiratory, motion, cardiac artifacts, and possible myoelectrical activity from other organs, poses a major challenge to EGG interpretation and analysis. A generally applicable method for removing a variety of artifacts from EGG recordings is proposed based on the empirical mode decomposition (EMD) method. This decomposition technique is adaptive, and appears to be uniquely suitable for nonlinear, non-stationary data analysis. The results show that this method, combined with instantaneous frequency analysis, effectively separate, identify and remove contamination from a wide variety of artifactual sources in EGG recordings.

Thermal--electrical finite element modelling for radio frequency cardiac ablation: effects of changes in myocardial properties.

Abstract: Finite element (FE) analysis has been utilised as a numerical tool to determine the temperature distribution in studies of radio frequency (RF) cardiac ablation. However, non of the previous FE analyses clarified such computational aspects as software requirements, computation time or convergence test. In addition, myocardial properties included in the previous models vary greatly. A process of FE modelling of a system that included blood, myocardium, and an ablation catheter with a thermistor embedded at the tip is described. The bio-heat equation is solved to determine the temperature distribution in myocardium using a commercial soft-ware application (ABAQUS). A Cauchy convergence test (∈=0.1°C) was performed and it is concluded that the optimal number of elements for the proposed system is 24610. The effects of changes in myocardial properties (±50% electric conductivity, +100%/−50% thermal conductivity, and +100%/−50% specific heat capacity) in both power-controlled (PCRFA) and temperature-controlled RF ablation (TCRFA) were studied. Changes in myocardial properties affect the results of the FE analyses of PCRFA more than those of TCRFA, and the maximum changes in lesion volumes were −58.6% (−50% electric conductivity), −60.7% (+100% thermal conductivity), and +43.2% (−50% specific heat).

Measurement of femoral neck anteversion in 3D. Part 1: 3D imaging method.

Abstract: Femoral neck anteversion is the torsion of the femoral head with reference to the distal femur. Conventional methods that use cross-sectional computed tomography (CT), magnetic resonance or ultrasound images to estimate femoral anteversion have met with several problems owing to the complex, three-dimensional (3D) structure of the femur. These problems include not only the difficulty of defining the direction of the femoral neck axis and condylar line but also the dependency upon patient positioning. In particular, the femoral neck axis, the direction of the femoral head, known as the major source of error, is difficult to determine from either a single or several two-dimensional (2D) cross-sectional images. A new method has been devised for the measurement of femoral anteversion using the 3D imaging technique. 3D reconstructed CT images from the femoral head and trochanter to the distal femur are used to measure the anteversion. It is necessary to remove the soft tissue from the CT images and extract just the bone part. Then, the femoral anteversion is measured from a computer-rendered femur image. The 3D imaging method is compared with both the conventional 2D method and the physical method using 20 dried femurs. For the physical method, which is used as a reference value, a special apparatus is devised. The average difference between the results of the physical method and those of the 2D CT method is 5.33°. The average difference between the results of the physical method and those of the 3D imaging method is 0.45°. Seventy-four patients, who suffer from toe-in-gait disease, are tested to compare the 3D imaging method with the conventional 2D CT method. The average difference between the 2D and 3D methods is 8.6°, and the standard is 7.43°. This method provides a very accurate and reliable measurement of femoral anteversion, as it is virtually equivalent to the direct measurement of bisected dried femur in vitro.

Real-time brain-computer interfacing: a preliminary study using Bayesian learning.

Abstract: Preliminary results from real-time 'brain-computer interface' experiments are presented. The analysis is based on autoregressive modelling of a single EEG channel coupled with classification and temporal smoothing under a Bayesian paradigm. It is shown that uncertainty in decisions is taken into account under such a formalism and that this may be used to reject uncertain samples, thus dramatically improving system performance. Using the strictest rejection method, a classification performance of 86.5 +/- 6.9% is achieved over a set of seven subjects in two-way cursor movement experiments.

Computerised acoustical respiratory phase detection without airflow measurement.

Abstract: A simple, non-invasive acoustical method is developed to detect respiratory phases in relationship to swallows without the direct measurement of airflow. In 21 healthy subjects (4-51 years) breath sounds are recorded at the trachea and at five different recording locations at the chest wall, with simultaneous recording of airflow by a pneumotachograph. The chest signal with the greatest inspiratory-expiratory power difference ('best location') is either in the mid-clavicular line in the second interspace on the left or third interspace on the right. Using the 'best location' on the chest wall and the tracheal signal, a phase detection algorithm is developed and achieves 100% accuracy in the estimation of respiratory phases without using the measured airflow signal. Thus, acoustically monitoring breaths and swallows holds promise as a non-invasive and reliable assessment tool in the study of swallowing dysfunction.

High-resolution electro-encephalogram: source estimates of Laplacian-transformed somatosensory-evoked potentials using a realistic subject head model constructed from magnetic resonance images

Abstract: A novel high-resolution electro-encephalographic (EEG) procedure is proposed, including high spatial sampling (128 channels), a realistic magnetic resonance-constructed subject head model, a multi-dipole cortical source model and regularised weighted minimum-norm linear inverse source estimation (WMN). As an innovation, EEG potentials (two healthy subjects; median-nerve, short-latency somatosensory-evoked potentials (SEPs)) are preliminarily Laplacian-transformed (LT) to remove brain electrical activity generated by subcortical sources (i.e. not represented in the source model). LT-WMN estimates are mathematically evaluated by figures of merit (WMN estimates as a reference). Results show higher dipole identifiability (0.69; 0.088), lower dipole localisation error (0.6 mm; 7.8 mm) and lower spatial dispersion (8.6 mm; 24 mm) in LT-WMN than in WMN estimates (Bonferroni corrected p < 0.001). These estimates are presented on the subject modelled cortical surface to highlight the increased spatial information content in LT-WMN compared with WMN estimates. The proposed high-resolution EEG technique is useful for the study of somatosensory functions in basic research and clinical applications.

Analysis of postural sway using entropy measures of signal complexity.

Abstract: A stochastic complexity analysis is applied to centre-of-pressure (COP) time series, by using different complexity features, namely the spectral entropy, the approximate entropy, and the singular value decomposition spectrum entropy. A principal component analysis allows an estimate of the overall signal complexity in terms of the ensemble complexity score; the difference in values between open-eyes (OE) and closed-eyes (CE) trials is used for clustering purposes. In experiments on healthy young adults, the complexity of the mediolateral component is shown not to depend on the manipulation of vision. Conversely, the increase of the anteroposterior complexity in OE conditions can be statistically significant, leading to a functional division of the subjects into two groups: the Romberg ratios (RRs), namely the ratios of the CE measure to the OE measure, are: RR=1.19±0.15 (group 1 subjects), and RR=1.05±0.14 (group 2 subjects). Multivariate statistical techniques are applied to the complexity features and the parameters of a postural sway model recently proposed; the results suggest that the complexity change is the sign of information-generating behaviours of postural fluctuations, in the presence of a control strategy which aims at loosening long-range correlation and decreasing stochastic activity when visual feedback is allowed.

Dipole location errors in electroencephalogram source analysis due to volume conductor model errors.

Abstract: An examination is made of dipole location errors in electroencephalogram (EEG) source analysis, due to not incorporating the ventricular system (VS), omitting a hole in the skull and underestimating skull conductivity. The simulations are performed for a large number of test dipoles in 3D using the finite difference method. The maximum dipole location error encountered, utilising 27 and 53 electrodes is 7.6 mm and 6.1 mm, respectively when omitting the VS, 5.6 mm and 5.2 mm, respectively when neglecting the hole in the skull, and 33.4 mm and 28.0 mm, respectively when underestimating skull conductivity. The largest location errors due to neglecting the VS can be found in the vicinity of the VS. The largest location erros due to omitting a hole can be found in the vicinity of the hole. At these positions the fitted dipoles are found close to the hole. When skull conductivity is underestimated, the dipole is fitted close to the skull-brain border in a radial direction for all test dipoles. It was found that the location errors due to underestimating skull conductivity are typically higher than those found due to neglecting the VS or neglecting a hole in the skull.

Anisotropy of Young's modulus of human tibial cortical bone.

Abstract: The anisotropy of Young's modulus in human cortical bone was determined for all spatial directions by performing coordinate rotations of a 6 by 6 elastic stiffness matrix. The elastic stiffness coefficients were determined experimentally from ultrasonic velocity measurements on 96 samples of normal cortical bone removed from the right tibia of eight human cadavers. The following measured values were used for our analysis: c11 = 19.5 GPa, c22 = 20.1 GPa, c33 = 30.9 GPa, c44 = 5.72 GPa, c55 = 5.17 GPa, c66 = 4.05 GPa, c23 = 12.5 GPa. The remaining coefficients were determined by assuming that the specimens possessed at least an orthorhombic elastic symmetry, and further assuming that c13 = c23 c12 = c11 - 2c66. Our analysis revealed a substantial anisotropy in Young's modulus in the plane containing the long axis of the tibia, with maxima of 20.9 GPa parallel to the long axis, and minima of 11.8 GPa perpendicular to this axis. A less pronounced anisotropy was observed in the plane perpendicular to the long axis of the tibia. To display our results for the full three-dimensional anisotropy of cortical bone, a closed surface was used to represent Young's modulus in all spatial directions.

Preparation of a pure autologous biodegradable fibrin matrix for tissue engineering

Abstract: Parallel to the growing role of tissue engineering, the need for cell embedding materials, which allow cells to stabilise in a three-dimensional distribution, has increased. Although several substances have been tested, fibrin is thus far the only one that permits the clinical application of cultured tissue. To date, can cause severe immunological side effects. The objective of this study was to explore the practicability of obtaining autologous thrombin from a single patient in an adequate concentration and amount. Fibrinogen was cryoprecipitated from 200 ml of freshly-frozen plasma. Thrombin was isolated from the supernatant through ionexchange chromatography. The thrombin was first bound to Sephadex A-50 and then eluated using 2ml of a salt buffer (2.0M NaCl in 0.015M trisodiumcitrate, pH 7.0). The activity of the thrombin (51 NIH ml−1 to 414 NIH ml−1) reached levels comparable to those in commercially available fibrin glues (4–500 NIH ml−1). The study has shown that it is possible to obtain a sufficient amount of autologous thrombin from a single donor to create a fibrin matrix of high efficiency without the risk of immunological and infectious side effects.

Integrated pressure-force-kinematics measuring system for the characterisation of plantar foot loading during locomotion.

Abstract: Plantar pressure, ground reaction force and body-segment kinematics measurements are largely used in gait analysis to characterise normal and abnormal function of the human foot The combination of all these data together provides a more exhaustive, detailed and accurate view of foot loading during activities than traditional measurement systems alone do A prototype system is presented that integrates a pressure platform, a force platform and a 3D anatomical tracking system to acquire combined information about foot function and loading A stereophotogrammetric system and an anatomically based protocol for foot segment kinematics is included in a previously devised piezo-dynamometric system that combines pressure and force measurements Experimental validation tests are carried out to check for both spatial and time synchronisation Misalignment of the three systems is found to be within 60, 50 and 15mm for the stereophotogrammetric system, force platform and pressure platform, respectively The combination of position and pressure data allows for a more accurate selection of plantar foot subareas on the footprint Measurements are also taken on five healthy volunteers during level walking to verify the feasibility of the overall experimental protocol Four main subareas are defined and identified, and the relevant vertical and shear force data are computed The integrated system is effective when there is a need for loading measurements in specific plantar foot subareas This is attractive both in clinical assessment and in biomechanics research

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers.

Abstract: A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4μm by 4μm to 50μm by 50μm are fabricated on shanks (cantilever beams) 6μm thick and which taper to an area approximately 100μm wide and 200μm long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.

Comparative analysis of different collagen-based biomaterials as scaffolds for long-term culture of human fibroblasts.

Abstract: Biodegradable scaffolds, along with cells, are important components of most tissue-engineered consructs. In the study, there is a comparison of the behaviour of human fibroblasts cultured for up to six weeks in four diffeeent collagen-based three-dimensional matrices, in the form of sponges composed of pure native type I collagen (control), of collagen-GAG-chitosan (CGC) and of collagen cross-linked by two concentrations of diphenylphosphorylazide (DPPA-2 and DPPA-3). Variations in size and weight of the sponges, as well as fibroblast growth and migration, and total protein and collagen synthesis, are determined with time in culture. Owing to their low thermal stability, the partial denaturation and dissolution of the control sponges after incubation at 37°C lead to considerable contraction and low cell proliferation. CGC sponges, stabilised by ionic interactions between the different components, show, after six weeks, limited contraction (20%) and weight increase (10% when seeded) and high growth (threefold increase). Similar results are obtained with weakly, cross-linked (DPPA-2) collagen sponges. Highly crosslinked (DPPA-3) sponges do not contract, whereas weight gain and cell proliferation are no different from those found with CGC and DPPA-2 sponges. Similar levels of total protein and collagen synthesis shown for fibroblasts seeded in different matrices, with a slight general decrease (twofold) after three weeks, a much lower value than that observed with fibroblasts in culture within a contracted collagen gel (sixfold). Furthermore, the fraction of neo-synthesised collagen deposited in the sponges after six weeks represents more than 60% of the total, compared with only 10% obtained with fibroblasts in monolayer culture or 30% within a collagen gel. These results indicate that the matrices, particularly the CGC and DPPA-2 sponges, provide excellent supports for fibroblast growth and the formation of dermal and skin equivalents.

Spreading and motility of human glioblastoma cells on sheets of silicone rubber depend on substratum compliance.

Abstract: Although there is a substantial quantity of experimental data examining the effects of adhesion on the morphology and migration of tissue cells, little attention has been focused on how changes in substratum mechanical properties affect these cellular behaviours. To determine whether the ability of a substratum mechanically to support traction influences cell morphology and motility, measurements are taken of the spreading, the fraction of a population with pseudopodia, the number of pseudopodia and the translocation of human SNB-19 glioblastoma cells cultured on films of poly(methylphenyl)siloxane possessing a range of mechanical compliances. Cells cultured on these films generate deformations (i.e. ‘wrinkles’) that are used as a basis to estimate effective substratum compliances. The average projected cell area decreases by over 60%, with a two-orders-of-magnitude increase in compliance. Time-lapse videomicroscopy reveals that cell migration also decreases with increasing compliance: the average cell speed decreases from approximately 8 μmh−1 on the most rigid substrata to 1.2 μmh−1 on the most compliant substrata examined. Changes in compliance do not alter mean directional persistence time. These results are interpreted in terms of the predictions of mathematical models for the effects of substratum compliance on motility.

A spot check for estimating stereophotogrammetric errors.

Abstract: Good practice rules in the management of a movement analysis laboratory recommend that photogrammetric measurement errors are assessed, prior to every experimental session, using an ad hoc experiment referred to as a spot check. The paper proposes an inexpensive and easy to make spot check. The test uses a rigid rod carrying two markers and a target point taken on the line joining them and coinciding with the rod tip. The latter point is placed in a fixed and measured position in the laboratory frame and the markers are tracked while the rod is kept stationary and while it is manually made to rotate about the target point. Several target points are used within the measurement volume. The instantaneous errors with which the laboratory co-ordinates of the latter points are reconstructed are determined and submitted to statistical analysis. A normalisation procedure is illustrated that aims at making the test results independent from the geometry of the test object. The experimental and analytical methods underlying the proposed spot check were validated experimentally in two movement analysis laboratories using repeated tests. A rod, 1.5 m long, carrying four markers was used. In this way, several test-object geometries were tested. Results confirmed that the photogrammetric error could be divided into a zero-mean random and a systematic component. It was shown that the normalisation procedure was effective for the standard deviation of both error components when the two markers were located at a distance between them 1.5 times larger than the distance of their centroid from the tip of the rod. The systematic component bias could not be normalised, however a conservative value of it could be estimated. The two above-mentioned normalised standard deviations and the bias value can be taken as descriptors of the photogrammetric error of the specific measuring system tested. These parameters may also be used to assess the precision and the accuracy with which the laboratory position of a target point, defined relative to any specified marker cluster, may be reconstructed during movement analysis.

A portable instrument for non-invasive monitoring of beat-by-beat cardiovascular haemodynamic parameters based on the volume-compensation and electrical-admittance method.

Abstract: A new, portable instrument has been developed for simultaneous monitoring of blood pressure, cardiac output and other cardiovascular haemodynamic variables. The measurements are based on the volume-compensation method and the transthoracic electrical admittance method. The instrument is small and light and can be carried by the subject. The portable unit controls the measurement procedures, performs the blood pressure and cardiac output measurement, processes signals and stores almost 32 000 beats of time-series data in a fully automated manner. A conventional personal computer is used to initialise the measurement system, and to reproduce and evaluate the measurement data. The measurement system provides a means to evaluate in detail, without restriction, the subject's cardiovascular haemodynamic responses to daily physical activities as well as to various psycho-physiological stresses. The paper describes a new, portable, cardiovascular haemodynamic instrument and in-the-field test results. Twelve subjects are monitored for trials, 60–210 min, and fewer than 3% of the data in each trial are artifactuel. Artefacts are due mainly to body movements.

Assessment of neck tissue fibrosis using an ultrasound palpation system: A feasibility study

Abstract: Fibrotic change in the soft tissue of the neck is a common side-effect after radiotherapy treatment for cancers of the head and neck region. The development of a quantitative approach for the assessment of neck tissue stiffness using an ultrasound palpation system (UPS) is reported. A testing protocol was established with the participation of eight normal subjects and four patients who had neck fibrosis after previous radiotherapy to the neck. Six reference sites were assessed on each side of the neck in each subject. Site-dependence, inter-observer variability, and intra-observer variability were further evaluated by measurement of sites 1cm anterior, posterior, superior and inferior to two of the reference sites on each side of the neck, and by repeating measurements using a second observer on the same occasion and using the same observer one week afterwards. The mean tissue Young's modulus for normal subjects was 12.8±3.9 kPa, and that of the radiotherapy-treated patients ranged from 46.4 to 108.3 kPa. The modulus shows limited variation among anatomical sub-sites within the neck. For a confidence level of 95%, there was a variation of ±14.2% for site-dependence, ±15.2% for inter-observer, and ±7.2% for intra-observer tests for the group of normal subjects. The variation in the patients was ±13.6% for site-dependence, and ±13.1% for the inter-observer test.

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation

Abstract: Measurement noise in the electro-encephalogram (EEG) and inaccurate formation about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm−1 cm and 0.27 cm−1 cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.

Increase in pulse transit time to the foot after epidural anaesthesia treatment.

Abstract: Epidurally induced anaesthetic treatment is a routine treatment for pain relief during surgical procedure, based on blocking the sensory and sympathetic fibres that mediate pain. The epidural sympathetic block results in relaxation of the muscle walls in the lower limbs, which can be assessed by the resultant haemodynamic changes. In the current study, the difference tt,f in the transit time of the blood pressure pulses between the toe and the finger is measured by photoplethysmography (PPG). Fifteen patients are administered 10 ml 0.25% of bupivacaine, ten patients are administered 10 ml 0.5%, and 17 patients are administered 40 ml 0.0625%. tt,f decreases as a function of the patient's age and blood pressure, both before and after the sympathetic block, owing to the decrease in arterial compliance with age and blood pressure. The time delay tt,f increases after the epidural treatment by 10.1±7.0 and by 16.8±10.8 ms for the 0.25% and the 0.5% concentrations, respectively. The time delay increase for the lowest concentration is not statistically significant. The toe-finger time delay change is found to reflect the haemodynamic changes induced by the sympathetic block with higher reliability than the routine methods of skin temperature or arterial blood pressure.

Phase determination during normal running using kinematic data

Abstract: Algorithms to predict heelstrike and toe-off times during normal running at subject-selected speeds, using only kinematic data, are presented. To assess the accuracy of these algorithms, results are compared with synchronised force platform recordings from ten subjects performing ten trials each. Using a single 180Hz camera, positioned in the sagittal plane, the average RMS error in predicting heelstrike times is 4.5 ms, whereas the average RMS error in predicting toe-off times is 6.9ms. Average true errors (negative for an early prediction) are +2.4 ms for heelstrike and +2.8ms for toe-off, indicating that systematic errors have not occured. The average RMS error in predicting contact time is 7.5ms, and the average true error in predicting contact time is 0.5ms. Estimations of event times using these simple algorithms compare favourably with other techniques requiring specialised equipment. It is concluded that the proposed algorithms provide an easy and reliable method of determining event times during normal running at a subject selected pace using only kinematic data and can be implemented with any kinematic data-collection system.

Modelling of chronic wound healing dynamics

Abstract: Following chronic wound area over time can give a general overview of wound healing dynamics. Decrease or increase in wound area over time has been modelled using either exponential or linear models, which are two-parameter mathematical models. In many cases of chronic wound healing, a delay of healing process was noticed. Such dynamics cannot be described solely with two parameters. The reported study deals with two-, three-, and four-parameter models. Assessment of the models was based on weekly measurements of 226 chronic wounds of various aetiologies. Several quantitative fitting criteria, i.e. goodness of fit, handling missing data and prediction capability, and qualitative criteria, i.e. number of parameters and their biophysical meaning were considered. The median of goodness of fit of three- and four-parameter models was between 0.937 and 0.958, and the median of two-parameter moels was 0.821 to 0.883. Two-parameter models fitted wound area over time significantly (p=0.001) worse than three- and four-parameter models. The criterion handling missing data provided similar results, with no significant difference between three- and four-parameter models. Median prediction error of two-parameter models was between 111 and 746; three-parameter models resulted in an error of 64 to 128, and finally four-parameter models resulted in the highest prediction error of 407 and 238. Based on the values of quantitative fitting criteria obtained, three parameters were chosen as the most appropriate. Based on qualitative criteria, the delayed exponential model was selected as the most general three-parameter model. It was found to have good prediction capability and in this capacity it could be used to help physicians choose the most appropriate treatment for patients with chronic wounds after an initial three-week observation period, when the median error increase of fitting is 74%.