Showing papers in "Physiological Measurement in 1997"
TL;DR: Simulation is demonstrated by simulation the effects of different error components that are included in the reconstruction of static EIT images by carrying out simulations with the so-called complete electrode model.
Abstract: In electrical impedance tomography (EIT), difference imaging is often preferred over static imaging. This is because of the many unknowns in the forward modelling which make it difficult to obtain reliable absolute resistivity estimates. However, static imaging and absolute resistivity values are needed in some potential applications of EIT. In this paper we demonstrate by simulation the effects of different error components that are included in the reconstruction of static EIT images. All simulations are carried out in two dimensions with the so-called complete electrode model. Errors that are considered are the modelling error in the boundary shape of an object, errors in the electrode sizes and localizations and errors in the contact impedances under the electrodes. Results using both adjacent and trigonometric current patterns are given.
160 citations
TL;DR: The methods and devices which are currently available for providing FES are reviewed, as are the sorts of result and benefit that may be expected from them.
Abstract: In the health-care professions, electrical stimulation is used for three purposes: to aid diagnosis; as a therapeutic tool; and to restore lost or damaged functions. Functional electrical stimulation (FES) and functional neurostimulation (FNS) are terms which are more or less interchangeable, and which encompass the third of these purposes. FES itself can also be conveniently divided into three classes, according to purpose: the restoration of sensor functions; the restoration of skeleto-motor functions; and the restoration of autonomic functions. Potentially, a fourth class would comprise devices restoring cognitive or psychological functions, but no such devices are clinically available as yet. The methods and devices which are currently available for providing FES are reviewed, as are the sorts of result and benefit that may be expected from them. The structure and emphasis of the review is on the clinical applications and the relevant anatomical and neurophysiological considerations and this approach is chosen for two main reasons. Firstly, the clinical, anatomical, and physiological considerations are independent of technological change and development, so they will not become quickly out of date. Secondly, the author is a clinician by profession, and an engineer only by inclination. The functional aims of FES methods will continue to develop as a result of experience gained following the introduction and use of successful devices, and these evolutionary improvements will come from within the FES programme; but the engineering embodiment of those devices may be revolutionized at any time by technological advances coming from elsewhere.
83 citations
TL;DR: This is a multi-author book that avoids many of the pitfalls of this genre and is a major resource for anyone involved in nitric oxide research and deserves a place on their laboratory and library bookshelves.
Abstract: In their preface the editors of this book say they wished to produce a comprehensive text on the methods used in nitric oxide research. There is absolutely no doubt they have succeeded. The book is divided into nine sections. The first is an overview of nitric oxide (NO) chemistry which provides the background to the subsequent sections. The remaining sections cover the preparation of NO containing species, enzymology of NO synthases, methods to detect and localize NO synthase activity, measurement of substrate and cofactors, measurement of nitrogen oxides, measurement of NO adducts, bioassay techniques and clinical techniques. The 46 chapters are all written by well known experts from around the world. Each chapter is divided into a section on background information and a section on practical details. The editors have taken the unusual step of nearly always using two or more authors from different centres, and in many cases different countries, to write each chapter in order to get a consensus view rather than an individual's or research group's view. The editors have obviously worked hard to keep an overall consistency within the chapters. The result is a multi-author book that avoids many of the pitfalls of this genre. The style is similar throughout most of the book, as is the level detail within chapters. The background information is detailed and well referenced, and the descriptions of practical techniques are well written and laced with small details that make it apparent that the authors are very familiar with the techniques they are describing. Although the book covers many fields, from inorganic chemistry to clinical research, it is easy to read as excessive jargon is avoided. The cross referencing between chapters is good, and there is virtually no duplication. Anyone planning a multi-author text should use this one as an example! This book is a major resource for anyone involved in nitric oxide research and deserves a place on their laboratory and library bookshelves. It can be read throughout to provide a very comprehensive background on nitric oxide research, or used as a reference source. The book arrived for reviewing just as we were setting up a new nitric oxide assay, and so its quality as a reference book was tested `in the field'. It passed the test with flying colours.
64 citations
TL;DR: It is concluded that the D-max appears to be a reliable method for defining the individual physiological responses to exercise tests, with the advantage of objectivity, but there is no evidence to support the theory that the exercise intensity defined by theD-max method is superior to that defined by other methods to prescribe training intensity or predict aerobic performance for athletes.
Abstract: The purpose of this study was to examine the reliability of using a mathematical method, D-max, to define blood lactate kinetics in response to an incremental exercise test, and to compare the physiological responses corresponding to the workload at D-max with those at the traditional 4 mmol l-1 lactate threshold and ventilatory thresholds. Ten male endurance trained athletes, with an average (+/- SD) age of 25.6 +/- 8.2 years and maximal oxygen consumption of 64.0 +/- 1.7 ml kg-1 min-1, performed an incremental cycling test on two occasions separated by four weeks. The expired gas was analysed on-line and plasma lactate concentration was analysed for each workload and at exhaustion. The lactate response to exercise was represented by a third-order polynomial regression curve. The D-max was defined as the point on the regression curve that yields the maximal distance to the straight line formed by the two end points of the curve. The results demonstrated a high test-retest reliability (intraclass correlation coefficients 0.77-0.93, p < 0.01) in oxygen consumption, heart rate and exercise intensity at both D-max point and exhaustion. No significant differences were found in the mean values of the variables between the two tests. It is concluded that the D-max appears to be a reliable method for defining the individual physiological responses to exercise tests, with the advantage of objectivity. However, there is no evidence to support the theory that the exercise intensity defined by the D-max method is superior to that defined by other methods to prescribe training intensity or predict aerobic performance for athletes. Further investigations are warranted to examine the validity of using this method in exercise prescription.
50 citations
TL;DR: The results demonstrate that the computer model of the human ventricular myocardium is well suited for complementing a database of QRS-integral maps obtained during clinical pace mapping and can help enhance the efficacy of the ablative treatment of ventricular arrhythmias.
Abstract: Body surface potential maps recorded during catheter pace mapping can facilitate the localization of the site of origin of ventricular tachycardia. In this study, we investigated the value of a realistic computer model of the human ventricular myocardium in generating body surface potential maps as templates for identifying sites of ectopic activation. Our model features an anatomically accurate geometry and an anisotropy due to transmural fibre rotation, that were reconstructed with a spatial resolution of 0.5 mm. It simulates the electrotonic interactions of cardiac cells by solving a nonlinear parabolic partial differential equation, but it behaves as a cellular automaton when the transmembrane potential exceeds the threshold value. We successfully validated our model by comparing the simulated activation sequences - described by isochronal maps, epicardial potential maps and body surface potential maps - with the measured sequences of epicardial and body surface maps reported in the literature. By systematically pacing the left ventricular and right ventricular endocardial surfaces in our ventricular model, we generated a database of 155 QRS-integral maps, which provides a high-resolution reference frame for localizing distinct endocardial pacing sites. This database promises to be a useful tool in improving the performance of catheter pace mapping used in combination with body surface potential mapping. Overall, the results demonstrate that our computer model of the human ventricular myocardium is well suited for complementing a database of QRS-integral maps obtained during clinical pace mapping and can help enhance the efficacy of the ablative treatment of ventricular arrhythmias. Keywords: computer model, anisotropic ventricular myocardium, ectopic activation, body surface potential mapping, QRS-integral maps
36 citations
TL;DR: The development of a portable monitor of ambulation is described, based on a system of position sensors and an accelerometer which is sampled when the subject is standing, and the relationship of activity to disability in rheumatoid arthritis explored.
Abstract: The measurement of patient activity over prolonged periods has been attempted with accelerometer-based devices, but these summate total acceleration and deceleration over time periods, are difficult to relate to recognizable activities and are influenced by passive movement. We describe the development of a portable monitor of ambulation. This logs posture (sitting, standing and lying) and number and vigour of steps in real time over prolonged periods, usually 24 h. This is based on a system of position sensors and an accelerometer which is sampled when the subject is standing. Data are processed through an interface and stored on a Psion Series 3 `palm top' computer. The system has been validated against observation, and the relationship of activity to disability in rheumatoid arthritis explored. Keywords: monitoring, activity, disability
36 citations
TL;DR: Addition of EIC measurements during standard clinical exercise testing might be of benefit in occupational medicine, cardiology and pulmonary medicine, and in the latter setting no validation studies have been performed, major methodological problems are not expected.
Abstract: Over the past three decades, the technique of electrical impedance cardiography (EIC) has developed into a valid and reliable instrument for the assessment of stroke volume. Recent developments have made EIC suitable for routine use during exercise testing, too. However, standardization of electrode positioning, stroke volume calculation, and data processing is lacking. In our opinion the most reliable options are, respectively, a modified semicircular electrode array, the Kubicek equation including a haematocrit-based resistivity value, and computerized signal averaging. Although EIC derived stroke volume calculation is based on several debated assumptions, numerous validation studies have shown good accuracy and reproducibility, also during exercise. Addition of EIC measurements during standard clinical exercise testing might be of benefit in occupational medicine, cardiology and pulmonary medicine. Although in the latter setting no validation studies have been performed, major methodological problems are not expected.
32 citations
TL;DR: The purpose of the laboratory tests presented here was to assess the effect of varying ambient temperature and varying simulated patient temperature on the performance of the three infrared tympanic thermometers.
Abstract: This article provides an experimental assessment of three commercially available clinical thermometers, using different thermal infrared sensors. This kind of thermometer measures body temperature by detecting infrared radiation from the tympanic membrane. These thermometers are growing in popularity thanks to their simplicity of use, rapid response and minimal distress to the patient. The purpose of the laboratory tests presented here was to assess the effect of varying ambient temperature and varying simulated patient temperature on the performance of the three infrared tympanic thermometers.
30 citations
TL;DR: It is concluded that the adaptive logic network technique offers a slightly higher accuracy and shows several potential advantages for automated detection of ischaemia in resting electrocardiograms.
Abstract: The aim of this study was to introduce an adaptive logic network computing method for detecting patients who were likely to show transient ischaemic episodes during ambulatory Holter monitoring, using parameters from a previously recorded standard twelve-lead resting electrocardiogram (ECG). In the present study, the adaptive logic network computing method is compared with other commonly used classification methods, such as backpropagation network and discriminant analysis techniques. Of 1367 study subjects aged 65 and above, 733 were women and 634 were men. Ambulatory Holter recordings were made to detect episodic ischaemia in study patients. Those subjects showing ischaemic episodes were classified as 'ischaemic' patients, and the remaining subjects were 'non-ischaemic'. Accuracy was 67% using the adaptive logic network computing method, 56% using the backpropagation network computing method, and 65% using statistical discriminant analysis. We concluded that the adaptive logic network technique offers a slightly higher accuracy and shows several potential advantages for automated detection of ischaemia in resting electrocardiograms.
24 citations
TL;DR: It is concluded that EIC is a reliable and valid method for measurements of SV and CO in COPD during exercise and was closely correlated to oxygen uptake using the CO2-rebreathing as well as the EIC method.
Abstract: In exercise testing of patients with chronic obstructive pulmonary disease (COPD), non-invasive assessment of stroke volume (SV) and cardiac output (CO) would be valuable. Electrical impedance cardiography (EIC) has proved to be a valid and reliable instrument in healthy subjects. In this study it is investigated whether this also applies to patients with COPD. In 19 COPD patients simultaneous SV measurements were performed during steady-state exercise using the CO2-rebreathing method and EIC (using a fixed blood resistivity value (rho = 135 or 150 omega cm: EIC-135 and EIC-150) or a haematocrit based rho (EIC-ht)). Although close correlations were found (overall correlation between CO2-rebreathing and EIC-ht: R = 0.92 for CO, R = 0.79 for SV), SV and CO measured by means of EIC were significantly higher at low-intensity exercise and lower at high-intensity exercise. The mean differences between the CO2-rebreathing method and EIC-ht were 0.55 ml for SV and 0.01 l min-1 for CO (overall exercise data). The limits of agreement (2SD of the mean difference) were 24.7 ml for SV and 2.56 l min-1 for CO. These figures are comparable to what is found when healthy subjects are studied. CO was closely correlated to oxygen uptake using the CO2-rebreathing as well as the EIC method; the slope of the regression line was closer to what has been reported in the literature with EIC. Results were better with the EIC-ht than with the EIC-135 and EIC-150 methods. It is concluded that EIC is a reliable and valid method for measurements of SV and CO in COPD during exercise.
19 citations
TL;DR: In order to increase the success rates in patients with ventricular tachycardias caused by coronary artery disease, mapping systems that can identify arrhythmogenic pathways more accurately and more efficiently and ablation devices capable of generating larger lesions are needed.
Abstract: Since its first use in the early 1980s, radiofrequency catheter ablation has gained acceptance as primary therapy for many cardiac rhythm disorders. This article reviews fundamentals of cardiac mapping and radiofrequency ablation and their clinical use for treatment of ventricular tachycardia. The review concludes that the use of radiofrequency ablation to cure ventricular tachycardia has consistently increased over the years, as better mapping and ablation tools have been made available to the medical community. Presently, high success and low complication rates are achieved only in patients with bundle branch, idiopathic, or monomorphic and stable ventricular tachycardias. The reviewed studies and reports suggest that, in order to increase the success rates in patients with ventricular tachycardias caused by coronary artery disease, mapping systems that can identify arrhythmogenic pathways more accurately and more efficiently and ablation devices capable of generating larger lesions are needed. Keywords: ventricular tachycardia, catheter, ablation, mapping
TL;DR: The results show that it is possible to determine local metabolic activity under in vivo conditions and this method was used in early chick embryos to determine the metabolic activity of the area vasculosa during the first 6 d of normoxic incubation.
Abstract: The Erlangen micro-lightguide spectrophotometer (EMPHO) was used to determine local mitochondrial activity. The measurement was based on a commercially available test (WST1, Boehringer Mannheim, Germany). A tetrazolium salt is cleaved to formazan by the `succinate - tetrazolium reductase' system which belongs to the respiratory chain of the mitochondria and is active only in viable cells. of the reagent is placed in a recess at the tip of the lightguide. The tip of the lightguide is then placed at the tissue surface. The reagent diffuses into the cells and is cleaved to formazan. The absorption change is measured and analysed. This method was used in early chick embryos to determine the metabolic activity of the area vasculosa during the first 6 d of normoxic incubation. During this period of time the absorption change measured after 30 min increased from 0.001 units on day 2 to 0.262 units on day 6. This indicates an increase in local metabolic activity which may be due to an increase in metabolic activity of individual cells and/or an increase in the number of cells in the area under investigation. The results show that it is possible to determine local metabolic activity under in vivo conditions. Keywords: micro lightguide spectrophotometer, tetrazolium salt, formazan, mitochondrial activity, local metabolism
TL;DR: Blood content and RBV were found to be dependent on age and gender at most sites with higher readings being observed in males and younger volunteers, and heavy prior sun exposure and skin thickness could not be demonstrated to impact on either RFS or LD readings independently of the effects of anatomical site, gender or age.
Abstract: This study was designed to determine normal variations in cutaneous blood content, red blood cell content and skin thickness in healthy human volunteers. The blood content (BC) of human skin and the velocity of red blood cells (RBV) has been comprehensively mapped over 30 anatomical sites in 28 volunteers between the age of 7 and 77 years using reflectance spectrophotometry (RFS) and laser Doppler (LD) techniques respectively. Total skin thickness, which may have a relationship with blood content, has been mapped at the same anatomical sites in six of the volunteers using two-dimensional array, 12 MHz ultrasound equipment. The major determinant of BC and RBV was found to be anatomical site. Regardless of age, gender or prior sun exposure, anatomical sites above the waist produced higher readings than below. BC and RBV were found to be dependent on age and gender at most sites with higher readings being observed in males and younger volunteers. The largest difference was seen in males under 55 years whose RFS readings above the waist were significantly higher than in older males or females of any age. Heavy prior sun exposure and skin thickness could not be demonstrated to impact on either RFS or LD readings independently of the effects of anatomical site, gender or age. In general, RFS and LD readings paralleled one another and correlated linearly at most anatomical sites. While RFS readings tended to decrease in the cranio-caudal direction, LD readings were relatively uniform across the body except for the head and groin where they were higher, and the abdomen where they were lower. The site-to-site variations in RFS readings observed in this study correspond well to capillary density variations noted in previous studies. Keywords: human skin, blood content, blood flow, skin thickness, reflectance spectrophotometry, laser doppler, ultrasound, effects of sun exposure, age and gender variations
TL;DR: In this work a semi-automatic method for measuring coagulation time is evaluated and it is shown that all the three methods can be used interchangeably for clinical purposes.
Abstract: Clinical assessment of the blood clotting mechanism is usually made by measuring the time necessary for a sample of plasma to clot. In this work a semi-automatic method for measuring coagulation time is evaluated. It employs ultrasound, at 2.7 MHz, for monitoring variations of the viscosity in a plasma sample undergoing coagulation. The evaluation is performed by comparing measurements obtained by two well-known methods, the manual tilt tube and the fibrometer, with those obtained using the ultrasonic method. A total of 330 plasma samples from individuals with normal and altered homeostatic process were analysed. The experimental protocol follows two standard tests: the prothrombin time (141 samples) and the activated partial thromboplastin time (189 samples). The agreement between the three different methods is estimated statistically and it is shown that all the three can be used interchangeably for clinical purposes.
TL;DR: Low-frequency ultrasound can be used to directly predict the mechanical properties of trabecular bone specimens in vitro and raises questions about the validity of applying the bar wave equation in the context of higher-frequency velocity measurements in the intact calcaneus in vivo.
Abstract: Ultrasonic velocities were measured in three orthogonal directions for 17 cubes ( approximately) of defatted calcaneal trabecular bone using a novel pulse transmission method with 37 kHz transducers. Since the wavelength was greater than the cross-sectional dimensions of the specimens, it was assumed that bar wave propagation was occurring and this allowed Young's modulus to be derived from velocity and apparent density. Velocity varied from in axis 1 (proximo-distal) to in axis 3 (medio-lateral). Thus, the velocities measured in axis 3 were considerably lower than those typically seen in clinical measurements of the calcaneus. The derived Young's moduli ranged from (axis 1) to (axis 3), and were comparable in magnitude to some previously published data from mechanical testing. The results suggest that velocities measured with this technique do indeed correspond to bar velocities, and consequently that low-frequency ultrasound can be used to directly predict the mechanical properties of trabecular bone specimens in vitro. On the other hand, given the marked differences in geometry, wavelengths used and the presence of fat, it raises questions about the validity of applying the bar wave equation in the context of higher-frequency velocity measurements in the intact calcaneus in vivo, despite the fact that this has been found to be useful by a number of previous workers. This may require a review of the clinical implications of high-frequency ultrasound data. Keywords: ultrasound, low frequency, trabecular bone, calcaneus, mechanical properties
TL;DR: The use of non-invasive and unshielded magnetocardiographic measurements to evaluate the DC injury currents associated with ST shifts during coronary artery occlusions in the isolated rabbit heart shows that the ST shift starts earlier when inducing ischaemia in hearts previously subjected to ischaemic episodes than in hearts where the ischaia was produced for the first time.
Abstract: The study of injury potentials associated with DC currents that generate the primary or secondary ST shifts during cardiac ischaemia is possible only through the invasive technique of the DC electrogram. Clinical surface ECG recordings are AC coupled and cannot be used. This paper reports the use of non-invasive and unshielded magnetocardiographic measurements to evaluate the DC injury currents associated with ST shifts during coronary artery occlusions in the isolated rabbit heart. The effect on the magnetic ST shift is studied under different ischaemic conditions including regional ischaemia, global ischaemia, global ischaemia following long periods of regional ischaemia, regional ischaemia after repeated episodes of reversible global ischaemia, and bilateral regional ischaemia. Recording of DC magnetic fields allows the characterization of primary and secondary ST displacement for each induced ischaemic condition. Our measurements show that the ST shift starts earlier when inducing ischaemia in hearts previously subjected to ischaemic episodes than in hearts where the ischaemia was produced for the first time.
TL;DR: Voluntary cardiorespiratory synchronization was used to investigate heart rate change (HRC) in 16 subjects as a function of age, body position, and respiratory tidal volumes, showing the importance of respiratory rate in measuring HRC.
Abstract: Voluntary cardiorespiratory synchronization (VCRS), where inspiration and expiration follows a fixed number of heart beats, was used to investigate heart rate change (HRC) in 16 subjects (grouped as 20 - 30 and 46 - 57 years of age) as a function of age, body position, and respiratory tidal volumes of 500 and 1000 ml. In phase I, the subjects, following a tone, inspired for two heart beats and expired for three beats. In phase II, the older group's breathing pattern was 2/2, 2/3, 3/3, 4/4, 5/5, and 6/6 inspiratory and expiratory heart beats, respectively, per respiratory cycle. Comparing the younger and older groups, we found a statistically significant (p<0.05) decrease in HRC for beat 1, 2, and 4 of the respiratory cycle in the supine position, and also for beat 2 in the sitting position, but no significant change with tidal volume. The ratio of the younger to older group's beat 2 HRC was 2.54 sitting and 3.54 supine. Increasing the number of beats per respiratory cycle from four to 12 resulted in the HRC growing from 1.8 to 7.5 beats over the respiratory cycle, showing the importance of respiratory rate in measuring HRC. VCRS can easily observe the influence of each phase of the respiratory cycle on the HRC and show the unique phase dependent changes that occur. Keywords: heart rate variability, respiration, VCRS, body position
TL;DR: It was noted that the infra-red interactance instrument yielded a very narrow range of body fats in females in comparison with the other techniques, and it is essential that these differences are reconciled beforeinfra- red interactance takes a significant role in body composition analysis.
Abstract: Infra-red interactance has been evaluated as a technique for measuring total body fat in comparison with a range of alternative methods. The alternative techniques employed were neutron activation analysis, tritiated water dilution, whole-body potassium-40 counting, skinfold anthropometry, bioelectrical impedance analysis and the body mass index. The study group consisted of 43 healthy adults (16 males and 27 females). For 11 women, measurements were obtained before and after 11 weeks on a very low-calorie diet, giving a total of 54 sets of data. Correlation coefficients between infra-red interactance and the other techniques varied between 0.58 (p<0.0002) and 0.80 (p<0.0001) for females, and between 0.64 (p<0.009) and 0.94 (p<0.0001) for males. The average fat for the study group was underestimated by 15% using infra-red interactance in comparison with the average fat obtained from the other techniques. It was also noted that the infra-red interactance instrument yielded a very narrow range of body fats in females in comparison with the other techniques. It is essential that these differences are reconciled before infra-red interactance takes a significant role in body composition analysis. Keywords: infra-red interactance, in vivo body composition analysis, total body fat
TL;DR: Spectral HRV indices demonstrate a diagnostic value in discriminating between hypotension-resistant and hypotension prone patients and are evaluated estimating the misclassification probability of a Bayesian quadratic classifier.
Abstract: The usefulness of spectral indices extracted from the heart rate variability (HRV) in discriminating between hypotension-prone and hypotension-resistant haemodialysis patients was investigated. In 30 patients, classified as hypotension resistant (stable group) or hypotension prone (unstable group), beat-to-beat heart period was measured during haemodialysis sessions terminated without collapses. HRV was analysed in the frequency domain combining classic autoregressive spectral estimation with two eigen decomposition-based techniques: the reduced rank approximation (RRA) of the autocorrelation matrix and the Pisarenko harmonic decomposition (PHD). Five spectral indices were obtained: the ratio between the powers in the LF and HF bands (LF/HF), the same ratio calculated after application of RRA , the frequency of the main oscillatory component of HRV estimated through PHD with a decomposition order equal to 1 and equal to 2 and the difference between the frequencies of the two oscillatory components resolved in the latter case . The performances of these indices in discriminating between the two groups of patients were evaluated estimating the misclassification probability of a Bayesian quadratic classifier. The HRV spectral pattern was markedly different: in the stable patients power was mainly in the low-frequency band, whereas in the unstable group it was mainly in the high-frequency band. The frequency of the main oscillatory component was significantly greater in the unstable group than in the stable one. Spectral indices displayed good discrimination power, increasing with the length of the dialysis interval. Best performances were achieved by both over short dialysis periods ( over 20 min intervals) and over longer periods ( over 160 min); similar results were obtained with over short periods and LF/HF over long periods. Spectral HRV indices demonstrate, therefore, a diagnostic value in discriminating between hypotension-resistant and hypotension-prone patients. Keywords: heart rate variability, hypotension, haemodialysis, spectral analysis, Pisarenko harmonic decomposition
TL;DR: There was little difference between the results for the different scan techniques or volume estimation alogorithms, although, perhaps as expected, the ellipsoid results were the least precise.
Abstract: A new system is described for estimating volume from a series of multiplanar 2D ultrasound images. Ultrasound images are captured using a personal computer video digitizing card and an electromagnetic localization system is used to record the pose of the ultrasound images. The accuracy of the system was assessed by scanning four groups of ten cadaveric kidneys on four different ultrasound machines. Scan image planes were oriented either radially, in parallel or slanted at 30 degrees to the vertical. The cross-sectional images of the kidneys were traced using a mouse and the outline points transformed to 3D space using the Fastrak position and orientation data. Points on adjacent region of interest outlines were connected to form a triangle mesh and the volume of the kidneys estimated using the ellipsoid, planimetry, tetrahedral and ray tracing methods. There was little difference between the results for the different scan techniques or volume estimation alogorithms, although, perhaps as expected, the ellipsoid results were the least precise. For radial scanning and ray tracing, the mean and standard deviation of the percentage errors for the four different machines were as follows: Hitachi EUB-240, -3.0 +/- 2.7%; Tosbee RM3, -0.1 +/- 2.3%; Hitachi EUB-415, 0.2 +/- 2.3%; Acuson, 2.7 +/- 2.3%.
TL;DR: This note proposes and validates a novel parameter for precision, the standard deviation of the Z-score (ZSD), and shows that the precision of ultrasound velocity, even when expressed as ZSD, is superior to BUA by a factor of approximately two in the calcaneus.
Abstract: There are now several commercial systems available for the ultrasonic assessment of osteoporosis, differing in anatomical location (calcaneus, tibia and phalanges), measurement parameters (broadband ultrasonic attenuation, BUA, and velocity) and their respective calculation algorithms. Comparison of system performance to date has centred upon precision (reproducibility) defined as coefficient of variation (CV%). It has been shown by both theoretical and in vivo studies that the computational algorithm implemented in the calculation of BUA of the calcaneus may have a significant effect upon CV%. The CV% for BUA is inherently inferior to the CV% for velocity by a factor of approximately seven since no allowance is made for population dynamic range. This note proposes and validates a novel parameter for precision, the standard deviation of the Z-score (ZSD). The precision of ultrasound velocity, even when expressed as ZSD, is superior to BUA by a factor of approximately two in the calcaneus. Since precision defined as ZSD is automatically scaled for both mean value and population dynamic range, and is dimensionless, it may be applied to all densitometric technologies. There is a broad range of precision values within the population and future work should investigate the causes of the variability. Keywords: ultrasound, bone, densitometry, precision
TL;DR: The system permits measurement of the change in airway pressure produced by a stimulated diaphragm contraction, without disconnection from the ventilator, and other important respiratory measurements such as twitch mouth pressure, simulated cough and P0.1 can also be performed on non-ventilated patients in a repeatable and systematic manner.
Abstract: In this paper we describe a system that allows an indicator of diaphragmatic strength to be determined non-invasively in mechanically ventilated patients. The system is comprised of an occlusion device that can be incorporated into the ventilator tubing and an occlusion control unit to operate the occlusion. The system electronically coordinates the timing of airway occlusion at the mouthpiece, application of a magnetic phrenic nerve stimulus and rapid removal of the occlusion once the measurement has been made. The system therefore permits measurement of the change in airway pressure produced by a stimulated diaphragm contraction, without disconnection from the ventilator. Other important respiratory measurements such as twitch mouth pressure, simulated cough and P0.1 can also be performed on non-ventilated patients in a repeatable and systematic manner.
TL;DR: The phantom demonstrates limitations in the potential accuracy of BMD determination at low densities using the Small Animal Software on the Lunar DPX-L, and improved recognition of low-density regions was obtained with the Lunar EXPERT.
Abstract: Dual-energy x-ray absorptiometry (DXA) is a precise, widely used method for measuring bone mineral density (BMD), usually of the lumbar spine and femoral neck. Recent developments, such as a lower x-ray tube current and pixel by pixel analysis, enable smaller bones and thinner tissue volumes, as in the hand, to be measured. Measurements of hand bone mineral content (BMC) and BMD could be useful in assessing disease severity in early rheumatoid arthritis and in monitoring disease progression and response to therapeutic intervention. A phantom is required for evaluating the software, measuring long-term precision and comparing with other DXA methods. This note describes the design and evaluation of a hand phantom for use on a Lunar DPX-L dual-energy x-ray absorptiometer. The phantom consists of three sections representing the metacarpals, and proximal and distal phalanges, using aluminium and Perspex as the bone and lean tissue equivalents respectively. The BMD of the three sections is approximately 1.0, 0.6 and . The phantom demonstrates limitations in the potential accuracy of BMD determination at low densities using the Small Animal Software on the Lunar DPX-L. Improved recognition of low-density regions was obtained with the Lunar EXPERT with precision values of 0.9, 1.1 and 2.0% for the three sections of the phantom respectively. Keywords: hand, phantom, bone densitometry, DXA
TL;DR: The results show that the physical and mathematical principles involved in VES-Sch are applicable to animal structures such as that composed of skin and fat and that it could be possible, for instance, to determine the thickness of the subcutaneous fat.
Abstract: Tetrapolar linear arrays are commonly used in geophysics to explore the vertical distribution of resistivity values in a geological section of a specific point on the earth. This technique, known as vertical electric sounding (VES), uses different electrode configurations. For our experiments, we utilized its more popular variation, called the Schlumberger arrangement (VES - Sch), to make measurements on a system composed of pig backfat placed on a conductive paste that simulates the longitudinal resistivity of muscle. The results show that the physical and mathematical principles involved in VES-Sch are applicable to animal structures such as that composed of skin and fat and that it could be possible, for instance, to determine the thickness of the subcutaneous fat. This might be useful in studies of body composition and to evaluate nutritional status. In the future, an electrical impedance tomograph (EIT) of low frequency could be used to obtain static images using this approach. Keywords: Electrical bio-impedance, electrical resistivity, electrical impedance tomography (EIT), fat thickness, biomedical-engineering methods
TL;DR: A new system for the synchronous recording and review of a combined oesophageal manometry and video fluoroscopic barium swallow examination provides for a deeper understanding and improved clinical assessment of complex motility disorders over those obtained when these two modalities are applied separately.
Abstract: We present the technical details of a new system for the synchronous recording and review of a combined oesophageal manometry and video fluoroscopic barium swallow examination. The system developed uses a portable manometry recorder and personal computer (PC) with an integrated digital video acquisition system. These are controlled using software to enable the real time capture of digital video and manometric data throughout the combined examination. The recorded pressure waveforms can then be synchronously displayed on a screen with the recorded digital video of the fluoroscopic barium swallow. This new tool enables both comparative measurement and detailed analysis of the relationship between visualized bolus transport and pressure measurements. It provides for a deeper understanding and improved clinical assessment of complex motility disorders over those obtained when these two modalities are applied separately. The system is easily incorporated into a clinical radiology suite and it is both user and patient friendly. It uses readily available computer hardware together with multimedia software and is a comparatively economical addition to the radiology suite with the manometry analysis available fulfilling the criteria laid down by the Clinical Associates Group of the British Society of Gastroenterology. Keywords: clinical environment, JPEG, oesophageal manometry, multimedia, real time system, synchronization
TL;DR: The technique allows small changes in lumen volume and wall compliance to be differentiated using a standard angioplasty catheter and balloon, and it is concluded that it can be differentiated with greater than 95% confidence.
Abstract: We have developed a device and technique for measuring the pressure - volume characteristics of an arterial segment from a standard angioplasty balloon, enabling us in this laboratory study to investigate the ability of the technique to measure changes in lumen volume and wall compliance. Percutaneous transluminal coronary angioplasty (PTCA) is a valuable clinical procedure for alleviating arterial stenosis, but the long-term success of the technique is less than ideal. The ability to monitor the effect of the balloon on the artery during inflations could lead to improvements in the technique. In this study, 10 different lumen diameters (1.6 to 3.4 mm) were produced in a Perspex block, and six different wall compliances produced with silicone tubes of constant inner diameter (2.0 mm) but different outer diameters (3.5 to 6.0 mm). A standard PTCA balloon was inflated under automatic control at a constant rate of to 800 kPa (8 bar). Pressure and volume data were recorded to computer continuously throughout the procedure. Differences in lumen volume of and wall compliance of could be differentiated with greater than 95% confidence. We conclude that our technique allows small changes in lumen volume and wall compliance to be differentiated using a standard angioplasty catheter and balloon. Keywords: angioplasty, arterial compliance, balloon catheter, coronary artery, PTCA
TL;DR: The densitometric technique presented can be incorporated into routine angiography and could become a strong alternative to the geometric approach that is presently dominating this field.
Abstract: In vitro studies have demonstrated that densitometric quantification of coronary artery stenoses is superior to geometric methods to assess non-circular lumens. However, in patients, several authors have reported significant discrepancies between area reduction percentages obtained densitometrically from two different imaging projections. Some of the factors causing the discrepancies can be reduced by simple precautions taken during image acquisition. Some others may be compensated for during analysis. Nevertheless, two factors remain problematic. The first is the inadequate spatial orientation of the vessel axes at the stenotic and reference cross sections with respect to the x-rays. The second is the difficulty in identifying the same vessel cross section in both planes at the time of analysis. We have designed a new densitometric technique that eliminates the error contributions of these two factors. The technique requires simultaneously acquired biplane coronary angiograms and biplane images of a translucent cube bearing steel markers acquired in exactly the same biplane geometry. Using the two projection matrices calculated from the images of the cube, the centrelines and the edges of the coronary arteries can be reconstructed in space from the biplane angiograms. The angles between the vessel axes and the x-ray beams can be determined and the densitometric cross sections can be corrected accordingly. Moreover, the 3D reconstruction allows the identification of the same cross section in the two planes for the determination of the area reduction percentages. Validation measurements were performed on a Perspex phantom and in patients, before and after angioplasty. In both types of measurement, the interplane discrepancies could be roughly halved. The densitometric technique presented can be incorporated into routine angiography and could become a strong alternative to the geometric approach that is presently dominating this field. Keywords: coronary angiography, coronary stenosis, densitometry, QCA
TL;DR: This work shows that the angle of rotation associated with the reactive component of the reference data set may be determined using a priori knowledge of the distribution of frequencies of the Cole- Cole plot, and the true Cole-Cole plot can be obtained from the impedance spectrum extracted from the MFEIT image data set.
Abstract: Computer modelling has shown that electrical characteristics of individual pixels may be extracted from within multiple-frequency electrical impedance tomography (MFEIT) images formed using a reference data set obtained from a purely resistive, homogeneous medium. In some applications it is desirable to extract the electrical characteristics of individual pixels from images where a purely resistive, homogeneous reference data set is not available. One such application of the technique of MFEIT is to allow the acquisition of in vivo images using reference data sets obtained from a non-homogeneous medium with a reactive component. However, the reactive component of the reference data set introduces difficulties with the extraction of the true electrical characteristics from the image pixels. This study was a preliminary investigation of a technique to extract electrical parameters from multifrequency images when the reference data set has a reactive component. Unlike the situation in which a homogenous, resistive data set is available, it is not possible to obtain the impedance and phase information directly from the image pixel values of the MFEIT images data set, as the phase of the reactive reference is not known. The method reported here to extract the electrical characteristics (the Cole-Cole plot) initially assumes that this phase angle is zero. With this assumption, an impedance spectrum can be directly extracted from the image set. To obtain the true Cole-Cole plot a correction must be applied to account for the inherent rotation of the extracted impedance spectrum about the origin, which is a result of the assumption. This work shows that the angle of rotation associated with the reactive component of the reference data set may be determined using a priori knowledge of the distribution of frequencies of the Cole-Cole plot. Using this angle of rotation, the true Cole-Cole plot can be obtained from the impedance spectrum extracted from the MFEIT image data set. The method was investigated using simulated data, both with and without noise, and also for image data obtained in vitro. The in vitro studies involved 32 logarithmically spaced frequencies from 4 kHz up to 1 MHz and demonstrated that differences between the true characteristics and those of the impedance spectrum were reduced significantly after application of the correction technique. The differences between the extracted parameters and the true values prior to correction were in the range from 16% to 70%. Following application of the correction technique the differences were reduced to less than 5%. The parameters obtained from the Cole-Cole plot may be useful as a characterization of the nature and health of the imaged tissues.
TL;DR: In this article, the authors used three different scan techniques (radial, parallel and slanted) and four volume estimation algorithms (ellipsoid, planimetry, tetrahedral and ray tracing) to estimate the volume of foetal livers.
Abstract: Sixteen formalin-fixed foetal livers were scanned in vitro using a new system for estimating volume from a sequence of multiplanar 2D ultrasound images. Three different scan techniques were used (radial, parallel and slanted) and four volume estimation algorithms (ellipsoid, planimetry, tetrahedral and ray tracing). Actual liver volumes were measured by water displacement. Twelve of the sixteen livers also received x-ray computed tomography (CT) and magnetic resonance (MR) scans and the volumes were calculated using voxel counting and planimetry. The percentage accuracy (mean +/- SD) was 5.3 +/- 4.7%, -3.1 +/- 9.6% and -0.03 +/- 9.7% for ultrasound (radial scans, ray volumes), MR and CT (voxel counting) respectively. The new system may be useful for accurately estimating foetal liver volume in utero.
TL;DR: Techniques for determining ventricular clearance rate and ejection fraction are compared and validated here for polyurethane and silicone rubber ventricles operated in a mock circulatory loop at various stroke volumes and pulse rates.
Abstract: Characterization of flow properties for an artificial ventricle may aid development of designs to minimize thrombosis. Techniques for determining two such flow properties, viz. ventricular clearance rate and ejection fraction, are compared and validated here for polyurethane and silicone rubber ventricles operated in a mock circulatory loop at various stroke volumes and pulse rates. Ventricular clearance rates were measured both by clinical radionuclide tracer techniques and by an optical tracer method. Ejection fractions were measured by radionuclide imaging and validated by direct measurements of flow rate and ventricular volume. Results from the two methods for ventricular clearance are in close agreement. The optical tracer method is superior in spatial resolution, convenience and economy, but the radionuclide tracer method for ejection fraction gives excellent agreement with the absolute measurements. Keywords: flow visualization, fluid tracer, ventricular assist device, artificial ventricle