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Showing papers in "Physiological Measurement in 2005"


Journal ArticleDOI
TL;DR: In this review, the emerging role of the wavelet transform in the interrogation of the ECG is discussed in detail, where both the continuous and the discrete transform are considered in turn.
Abstract: The wavelet transform has emerged over recent years as a powerful time-frequency analysis and signal coding tool favoured for the interrogation of complex nonstationary signals. Its application to biosignal processing has been at the forefront of these developments where it has been found particularly useful in the study of these, often problematic, signals: none more so than the ECG. In this review, the emerging role of the wavelet transform in the interrogation of the ECG is discussed in detail, where both the continuous and the discrete transform are considered in turn.

794 citations


Journal ArticleDOI
TL;DR: This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles and presents various efforts that take advantage of novel microscale flow phenomena and microFabrication techniques to build microfluidity cell analysis systems.
Abstract: This review describes recent developments in microfabricated flow cytometers and related microfluidic devices that can detect, analyze, and sort cells or particles. The high-speed analytical capabilities of flow cytometry depend on the cooperative use of microfluidics, optics and electronics. Along with the improvement of other components, replacement of conventional glass capillary-based fluidics with microfluidic sample handling systems operating in microfabricated structures enables volume- and power-efficient, inexpensive and flexible analysis of particulate samples. In this review, we present various efforts that take advantage of novel microscale flow phenomena and microfabrication techniques to build microfluidic cell analysis systems.

449 citations


Journal ArticleDOI
TL;DR: The basic assumptions that are made when applying ICA are discussed, along with their implications when applied particularly to biomedical signals, and the criterion used for establishing independence between sources is reviewed and this leads to the introduction of ICA/BSS techniques based on time, frequency and joint time-frequency decomposition of the data.
Abstract: Independent component analysis (ICA) is increasing in popularity in the field of biomedical signal processing. It is generally used when it is required to separate measured multi-channel biomedical signals into their constituent underlying components. The use of ICA has been facilitated in part by the free availability of toolboxes that implement popular flavours of the techniques. Fundamentally ICA in biomedicine involves the extraction and separation of statistically independent sources underlying multiple measurements of biomedical signals. Technical advances in algorithmic developments implementing ICA are reviewed along with new directions in the field. These advances are specifically summarized with applications to biomedical signals in mind. The basic assumptions that are made when applying ICA are discussed, along with their implications when applied particularly to biomedical signals. ICA as a specific embodiment of blind source separation (BSS) is also discussed, and as a consequence the criterion used for establishing independence between sources is reviewed and this leads to the introduction of ICA/BSS techniques based on time, frequency and joint time–frequency decomposition of the data. Finally, advanced implementations of ICA are illustrated as applied to neurophysiologic signals in the form of electro-magnetic brain signals data.

441 citations


Journal ArticleDOI
TL;DR: Retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms from the two internal carotid arteries and two vertebral arteries of 17 young, normal volunteers, suggesting that the representative waveform shapes presented here may be used to characterize normal ICA and VA flow rate dynamics.
Abstract: Knowledge of normal cerebrovascular volumetric flow rate (VFR) dynamics is of interest for establishing baselines, and for providing input data to cerebrovascular model studies. Retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms from the two internal carotid arteries (ICA) and two vertebral arteries (VA) of 17 young, normal volunteers (16M:1F) at rest in a supine posture. After normalizing each waveform to its respective cycle-averaged VFR, the timing and amplitude of feature points from the individual waveforms were averaged together to produce archetypal ICA and VA waveform shapes. Despite significant inter-individual differences in cycle-averaged VFR within the ICA compared to VA (275+/-52 versus 91+/-18 mL min-1), the respective waveform shapes were qualitatively similar overall. The VA waveform shape did, however, exhibit significantly higher amplitudes (e.g., peak:average VFR of 1.78+/-0.30 versus 1.66+/-0.16; p<0.05) and significantly higher variability both between and within subjects. A significant correlation was observed between peak and cycle-averaged VFR, suggesting that the representative waveform shapes presented here-when scaled by an individual's cycle-averaged VFR-may be used to characterize normal ICA and VA flow rate dynamics. This capability may be of particular utility for studies where cerebrovascular flow dynamics are required, but only average flow rates are available.

310 citations


Journal ArticleDOI
TL;DR: The results confirm that different choices of reference electrodes result in systematic changes in the distribution of EEG frequency power, and in order to reduce the effect of such systematic shifts on the explanation of EEG mappings, a common reference is necessary for EEG research.
Abstract: Based on EEG data recorded from 11 subjects with eyes open and the left mastoid (M) reference, three data sets were generated by re-referencing to the conventional linked mastoids (L), average (A) and the new 'infinity' (I) reference provided by the reference electrode standardization technique (REST, Yao 2001 Physiol. Meas. 22 693–711). The EEG power in the alpha frequency band with the four different references was calculated and compared with respect to the total energy and spatial amplitude weight centre (AWC) coordinates, to compare the effects of different references on power mapping in the frequency domain. Compared with the I reference, the AWCs of the EEG with the M reference show significant shifts to the right, frontal and superficial positions, the L reference significant shifts to frontal and superficial positions, and the A reference shifts the AWC significantly to a deeper position. Furthermore, the power maps of the M and L references have larger total power than the I reference, while that of the A reference has the smallest total power. These results confirm that different choices of reference electrodes result in systematic changes in the distribution of EEG frequency power, and in order to reduce the effect of such systematic shifts on the explanation of EEG mappings, a common reference is necessary for EEG research. We recommend the I reference for objective use in cross-laboratory studies and clinical practices, as it is far from all the other electrodes and can act as a neutral reference.

157 citations


Journal ArticleDOI
TL;DR: A novel feature termed the 'intra-snore-pitch-jump' (ISPJ) to diagnose OSA is proposed, and it is shown that ISPJ delivers OSA detection sensitivities of 86-100% while holding specificity at 50-80%.
Abstract: Obstructive sleep apnea (OSA) is a highly prevalent disease in which upper airways are collapsed during sleep, leading to serious consequences. The gold standard of diagnosis, called polysomnography (PSG), requires a full-night hospital stay connected to over ten channels of measurements requiring physical contact with sensors. PSG is inconvenient, expensive and unsuited for community screening. Snoring is the earliest symptom of OSA, but its potential in clinical diagnosis is not fully recognized yet. Diagnostic systems intent on using snore-related sounds (SRS) face the tough problem of how to define a snore. In this paper, we present a working definition of a snore, and propose algorithms to segment SRS into classes of pure breathing, silence and voiced/unvoiced snores. We propose a novel feature termed the 'intra-snore-pitch-jump' (ISPJ) to diagnose OSA. Working on clinical data, we show that ISPJ delivers OSA detection sensitivities of 86-100% while holding specificity at 50-80%. These numbers indicate that snore sounds and the ISPJ have the potential to be good candidates for a take-home device for OSA screening. Snore sounds have the significant advantage in that they can be conveniently acquired with low-cost non-contact equipment. The segmentation results presented in this paper have been derived using data from eight patients as the training set and another eight patients as the testing set. ISPJ-based OSA detection results have been derived using training data from 16 subjects and testing data from 29 subjects.

140 citations


Journal ArticleDOI
TL;DR: The air mattress sensor system allows the measurement of the respiration and heart beat movements without the use of a harness or sensor on the subject's body, which eliminates the difficulties these pose for long term measurements.
Abstract: The cardio-respiratory signal is a fundamental vital sign used for assessment of a patient's status. Additionally, the cardio-respiratory signal provides a great deal of information to healthcare providers wishing to monitor healthy individuals. The air mattress sensor system allows the measurement of the respiration and heart beat movements without the use of a harness or sensor on the subject's body, which eliminates the difficulties these pose for long term measurements. In order to increase the sensitivity, a differential measurement technique between two air cells was used. The concept of a balancing tube between two air cells is suggested in order to increase the robustness against postural changes during the measurements. With this balancing tube, the meaningful frequency range could be selected using a pneumatic method. A mathematical model was constructed and validation experiments were performed for step and sinusoidal input signals. This technique was applied to measurements of respiration and heart beat movements in the supine posture on the bed, which showed potential for applications in sleep analysis, unconstrained healthcare monitoring and neonate monitoring.

121 citations


Journal ArticleDOI
TL;DR: The clinical value of objective photoplethysmography pulse measurements collected simultaneously from the right and left great toes to diagnose disease in the lower limbs is investigated and the low-cost and simplicity of this optical-based technology could offer significant benefits to healthcare.
Abstract: The assessment and diagnosis of lower limb peripheral arterial occlusive disease (PAOD) is important since it can lead progressively to disabling claudication, ischaemic rest pain and gangrene. Historically, the first assessment has been palpation of the peripheral pulse since it can become damped, delayed and diminished with disease. In this study we investigated the clinical value of objective photoplethysmography (PPG) pulse measurements collected simultaneously from the right and left great toes to diagnose disease in the lower limbs. In total, 63 healthy subjects and 44 patients with suspected lower limb disease were studied. Pulse wave analysis techniques extracted timing, amplitude and shape characteristics for both toes and for right-to-left toe differences. Normative ranges of pulse characteristics were then calculated for the healthy subject group. The relative diagnostic values of the different pulse features for detecting lower limb arterial disease were determined, referenced to the established ankle-brachial pressure index (ABPI) measurement. The ranges of pulse characteristics and degree of bilateral similarity in healthy subjects were established, and the degrees of pulse delay, amplitude reduction, and damping and bilateral asymmetry were quantified for different grades of disease. When pulse timing, amplitude and shape features were ranked in order of diagnostic performance, the shape index (SI) gave substantial agreement with ABPI (>90% accuracy, kappa 0.75). SI also detected higher grade disease, for legs with an ABPI less than 0.5, with a sensitivity of 100%. The simple-to-calculate timing differences between pulse peaks produced a diagnostic accuracy of 88% for all grades of arterial disease (kappa 0.70), and 93% for higher grade disease (kappa 0.77). These contrasted with the limited discriminatory value of PPG pulse amplitude. The low-cost and simplicity of this optical-based technology could offer significant benefits to healthcare, such as in primary care where non-invasive, accurate and simple-to-use (de-skilled) diagnostic techniques are desirable.

111 citations


Journal ArticleDOI
TL;DR: An analysis of electrocardiographic pattern recognition parameters for premature ventricular contraction (PVC) and normal (N) beat classification is presented and the achieved specificity and sensitivity are comparable with, and greater than, the results reported in the literature.
Abstract: An analysis of electrocardiographic pattern recognition parameters for premature ventricular contraction (PVC) and normal (N) beat classification is presented. Twenty-six parameters were defined: 11 x 2 for the two electrocardiogram (ECG) leads, width of the complex and three parameters derived from a single-plane vectorcardiogram (VCG). Some of the parameters include amplitudes of maximal positive and maximal negative peaks, area of absolute values, area of positive values, area of negative values, number of samples with 70% higher amplitude than that of the highest peak, amplitude and angle of the QRS vector in a VCG plane. They were measured for all heartbeats annotated as N or PVC in all 48 ECG recordings of the MIT-BIH arrhythmia database. Two reference sets for the Kth nearest-neighbours rule were used-global and local. The classification indices obtained with the global reference set were 75.4% specificity and 80.9% sensitivity. Using the local reference set we increased the specificity to 96.7% and the sensitivity to 96.9%. The achieved specificity and sensitivity are comparable with, and greater than, the results reported in the literature.

108 citations


Journal ArticleDOI
TL;DR: An inverse solver based on the Gauss-Newton-one-step method for differential imaging is developed, and four different regularization schemes are implemented and tested, demonstrating the feasibility of difference imaging with MIT.
Abstract: Magnetic induction tomography (MIT) of biological tissue is used to reconstruct the changes in the complex conductivity distribution inside an object under investigation. The measurement principle is based on determining the perturbation ?B of a primary alternating magnetic field B0, which is coupled from an array of excitation coils to the object under investigation. The corresponding voltages ?V and V0 induced in a receiver coil carry the information about the passive electrical properties (i.e. conductivity, permittivity and permeability). The reconstruction of the conductivity distribution requires the solution of a 3D inverse eddy current problem. As in EIT the inverse problem is ill-posed and on this account some regularization scheme has to be applied. We developed an inverse solver based on the Gauss?Newton-one-step method for differential imaging, and we implemented and tested four different regularization schemes: the first and second approaches employ a classical smoothness criterion using the unit matrix and a differential matrix of first order as the regularization matrix. The third method is based on variance uniformization, and the fourth method is based on the truncated singular value decomposition. Reconstructions were carried out with synthetic measurement data generated with a spherical perturbation at different locations within a conducting cylinder. Data were generated on a different mesh and 1% random noise was added. The model contained 16 excitation coils and 32 receiver coils which could be combined pairwise to give 16 planar gradiometers. With 32 receiver coils all regularization methods yield fairly good 3D-images of the modelled changes of the conductivity distribution, and prove the feasibility of difference imaging with MIT. The reconstructed perturbations appear at the right location, and their size is in the expected range. With 16 planar gradiometers an additional spurious feature appears mirrored with respect to the median plane with negative sign. This demonstrates that a symmetrical arrangement with one ring of planar gradiometers cannot distinguish between a positive conductivity change at the true location and a negative conductivity change at the mirrored location.

103 citations


Journal ArticleDOI
TL;DR: The obtained results show that both methods demonstrate high agreement in relation to the number of contractions recognized as being consistent, and the appropriate way of further development of electrohysterography seems to be spectral analysis.
Abstract: Monitoring of uterine contraction activity is an important diagnostic tool used during both pregnancy and labour. The strain the pregnant uterus exerts on the maternal abdomen is measured via external tocography. However, limitation of this approach has caused the development of another technique-electrohysterography--which is based on the recording of electrical uterine activity. A computer-aided system is presented, which allows the recording of electrohysterographic signals from the maternal abdomen and their on-line analysis both in time and frequency domains. As a research material, we acquired 108 traces during a 24 h period before labour from a group of patients between 37 and 40 weeks of gestation. The comparison study between electrohysterography and tocography was carried out thanks to the possibility of simultaneous recording of mechanical and electrical uterine activities. The obtained results show that both methods demonstrate high agreement in relation to the number of contractions recognized as being consistent. However, their agreement in relation to the quantitative description of recognized patterns has appeared to be unacceptable to consider these methods as fully alternative. The appropriate way of further development of electrohysterography seems to be spectral analysis. Several spectral parameters describing electrophysiological properties of uterine muscle can be obtained by the use of electrohysterographic signals.

Journal ArticleDOI
TL;DR: In this paper a method for generating accurate FEMs of the human head is presented where MRI images are manually segmented using custom adaptation of industry standard commercial design software packages.
Abstract: The use of realistic anatomy in the model used for image reconstruction in EIT of brain function appears to confer significant improvements compared to geometric shapes such as a sphere. Accurate model geometry may be achieved by numerical models based on magnetic resonance images (MRIs) of the head, and this group has elected to use finite element meshing (FEM) as it enables detailed internal anatomy to be modelled and has the capability to incorporate information about tissue anisotropy. In this paper a method for generating accurate FEMs of the human head is presented where MRI images are manually segmented using custom adaptation of industry standard commercial design software packages. This is illustrated with example surface models and meshes from adult epilepsy patients, a neonatal baby and a phantom latex tank incorporating a real skull. Mesh quality is assessed in terms of element stretch and hence distortion.

Journal ArticleDOI
TL;DR: Noise level reductions can be achieved by optimizing MREIT pulse sequences and using signal averaging, and two different methods to estimate magnetic flux noise levels are suggested.
Abstract: In magnetic resonance electrical impedance tomography (MREIT), we measure the induced magnetic flux density inside an object subject to an externally injected current. This magnetic flux density is contaminated with noise, which ultimately limits the quality of reconstructed conductivity and current density images. By analysing and experimentally verifying the amount of noise in images gathered from two MREIT systems, we found that a carefully designed MREIT study will be able to reduce noise levels below 0.25 and 0.05 nT at main magnetic field strengths of 3 and 11 T, respectively, at a voxel size of 3 × 3 × 3 mm3. Further noise level reductions can be achieved by optimizing MREIT pulse sequences and using signal averaging. We suggest two different methods to estimate magnetic flux noise levels, and the results are compared to validate the experimental setup of an MREIT system.

Journal ArticleDOI
TL;DR: The feasibility of the MREIT technique in producing conductivity images of different biological soft tissues with a high spatial resolution and accuracy when the authors use a sufficient amount of the injection current is experimentally demonstrated.
Abstract: We present cross-sectional conductivity images of two biological tissue phantoms. Each of the cylindrical phantoms with both diameter and height of 140 mm contained chunks of biological tissues such as bovine tongue and liver, porcine muscle and chicken breast within a conductive agar gelatin as the background medium. We attached four recessed electrodes on the sides of the phantom with equal spacing among them. Injecting current pulses of 480 or 120 mA ms into the phantom along two different directions, we measured the z-component Bz of the induced magnetic flux density B = (Bx, By, Bz) with a magnetic resonance electrical impedance tomography (MREIT) system based on a 3.0 T MRI scanner. Using the harmonic Bz algorithm, we reconstructed cross-sectional conductivity images from the measured Bz data. Reconstructed images clearly distinguish different tissues in terms of both their shapes and conductivity values. In this paper, we experimentally demonstrate the feasibility of the MREIT technique in producing conductivity images of different biological soft tissues with a high spatial resolution and accuracy when we use a sufficient amount of the injection current.

Journal ArticleDOI
TL;DR: CMA71 microdialysis catheters can, therefore, be used for routine clinical monitoring of extracellular substances, as well as for their intended research role of larger molecular weight protein sampling.
Abstract: Microdialysis monitoring of cerebral metabolism is now performed in several neuro-intensive care units. Conventional microdialysis utilizes CMA70 catheters with 20 kDa molecular weight cut-off membranes enabling the measurement of small molecules such as glucose, lactate, pyruvate and glutamate. The CMA71 100 kDa molecular weight cut-off microdialysis catheter has recently been introduced to allow detection of larger molecules such as cytokines. The objective of this study was to perform in vitro and in vivo testing of the CMA71 microdialysis catheter, comparing its performance with the CMA70. In vitro comparison studies of three of each catheter using reference analyte solutions, demonstrated equivalent recovery for glucose, lactate, pyruvate and glutamate (range 94–97% for CMA70 and 88–103% for CMA71). In vivo comparison involved intracranial placement of paired CMA70 and CMA71 catheters (through the same cranial access device) in six patients with severe traumatic brain injury. Both catheters were perfused with CNS Perfusion Fluid without dextran at 0.3 µl min−1 with hourly sampling and bedside analysis on a CMA600 microdialysis analyser. The two catheters yielded equivalent results for glucose, lactate, pyruvate, glutamate and lactate/pyruvate ratio. CMA71 microdialysis catheters can, therefore, be used for routine clinical monitoring of extracellular substances, as well as for their intended research role of larger molecular weight protein sampling.

Journal ArticleDOI
TL;DR: STSM can evaluate tissue stiffness quantitatively and yield reproducible data, and was used to test elastomer samples with known mechanical properties.
Abstract: Simple but objective measurement of soft tissue consistency would be advantageous in the assessment of many neurological, lymphostatic and venous disorders. The aim of the present study was to evaluate the feasibility of using a novel hand-held computerized soft tissue stiffness meter (STSM). The STSM describes the soft tissue stiffness (STS) in the form of the instantaneous force (N) by which the tissue resists the constant deformation produced by a cylindrical intender. Firstly, the STSM was used to test elastomer samples with known mechanical properties. In the in vivo assessment, 12 healthy, nondisabled adults (age range, 24-57 years) and 16 subjects with chronic myofascial neck pain syndrome (age range, 27-55 years) were studied. To study the reproducibility (coefficient of variation (CV(%))) of the method, the measurement sites were either marked with a marker pen (marked points) or localized anatomically (unmarked points). Measurements were made from the dorsal forearm (Arm), trapezius (Tra), levator scapulae (Lev), infraspinatus (Inf) and deltoideus (Del) muscle areas. STS in the forearm was studied during different types of short-term relative isometric loading of the muscle as well as during venous occlusion. STS values of the myofascial trigger points in the Lev muscles were evaluated bilaterally. A linear, positive relationship was found between the indenter force (N) and the dynamic compressive modulus (MPa) of elastomer stiffness (r(2) = 0.90, n = 9). Intra- and interrater CVs of marked and unmarked sites varied between 4.31% and 12.06%. STS increased linearly along the relative muscle load (r(2) = 0.96) and nonlinearly during the venous occlusion (r(2) = 0.97). Statistically significant regional variation of STS was found between the different measurement sites (p < 0.05). In conclusion, STSM can evaluate tissue stiffness quantitatively and yield reproducible data.

Journal ArticleDOI
TL;DR: The main conclusion is that, thanks to the alpha parameter in the Cole equation, the bioimpedance is not only useful to monitor the intra/extra- cellular volume imbalances or the inter-cellular junctions resistance but also to detect tissue structural alterations.
Abstract: In the case of living tissues, the spectral width of the electrical bioimpedance dispersions (closely related with the α parameter in the Cole equation) evolves during the ischemic periods. This parameter is often ignored in favor of other bioimpedance parameters such as the central frequency or the resistivity at low frequencies. The object of this paper is to analyze the significance of this parameter through computer simulations (in the α and β dispersion regions) and to demonstrate its practical importance through experimental studies performed in rat kidneys during cold preservation. The simulations indicate that the dispersion width could be determined by the morphology of the extra-cellular spaces. The experimental studies show that it is a unique parameter able to detect certain conditions such as a warm ischemia period prior to cold preservation or the effect of a drug (Swinholide A) able to disrupt the cytoskeleton. The main conclusion is that, thanks to the α parameter in the Cole equation, the bioimpedance is not only useful to monitor the intra/extra-cellular volume imbalances or the inter-cellular junctions resistance but also to detect tissue structural alterations.

Journal ArticleDOI
TL;DR: The FLIP technique may be useful in accessing the role of the OGJ in diseases such as gastroesophageal reflux disease (GORD) and achalasia and their treatments with surgical and endoscopic therapies.
Abstract: No quantitative method has been implemented routinely in clinical practice to assess the oesophago-gastric junction (OGJ). Using impedance planimetry a functional lumen imaging probe (FLIP) was constructed to measure eight cross-sectional areas (CSA) at 4 mm intervals inside a saline-filled bag. To validate the FLIP technique for profiling the OGJ, polymethylmethacrylate (Perspex) cylinders with different CSAs were measured ten times by the FLIP to assess reproducibility and accuracy. A geometric sphincter phantom was constructed and its geometry was measured with a 360 degrees radial ultrasound (US) mini-probe pulled through it at a rate of 1 mm s(-1). The measurements were compared with FLIP measurements. Safety and technique reproducibility were tested on a volunteer. Reproducibility and accuracy between the ten samples were good. The probe performed well with and without a balloon mounted on it except for the smallest CSA (38.5 mm(2)) where there was a difference of 22% from the actual value at one CSA measurement point. The FLIP imaged the phantom geometry as well as the radial scanning US mini-probe. Pilot studies on a volunteer showed that the probe could be placed in the OGJ and the balloon distensions revealed the geometry of the sphincter at various levels of distension. The technique may be useful in accessing the role of the OGJ in diseases such as gastroesophageal reflux disease (GORD) and achalasia and their treatments with surgical and endoscopic therapies.

Journal ArticleDOI
TL;DR: A new type of gradiometers (zero flow gradiometer, ZFGRAD) which combines the advantages of ZFC and PGRAD is developed which shows a clear, bright feature at the correct position of the sphere and are comparable to those with P GRAD arrays.
Abstract: Magnetic induction tomography (MIT) is a low-resolution imaging modality which aims at the three-dimensional (3D) reconstruction of the electrical conductivity in objects from alternating magnetic fields. In MIT systems the magnetic field perturbations to be detected are very small when compared to the excitation field (ppm range). The voltage which is induced by the excitation field in the receiver coils must be suppressed for providing sufficient dynamic range. In the past, two very efficient strategies were proposed: adjusted planar gradiometers (PGRAD) and the orientation of a receiver coil with respect to the excitation coil such that the net magnetic flow is zero (zero flow coil, ZFC). In contrast to the PGRAD no voltage is induced in the ZFC by the main field. This is advantageous because two comparatively high voltages in the two gradiometer coils can never be subtracted perfectly, thus leaving a residual voltage which is prone to drift. However, a disadvantage of the ZFC is the higher susceptibility to interferences from far RF sources. In contrast, in the gradiometer such interferences are cancelled to a high degree. We developed a new type of gradiometer (zero flow gradiometer, ZFGRAD) which combines the advantages of ZFC and PGRAD. All three systems were compared with respect to sensitivity and perturbation to signal ratio (PSR) defined as the ratio of the signal change due to a magnetic perturbation field at the carrier frequency and the signal change due to shifting a metallic sphere between two test points. The spatial sensitivity of the three systems was found to be very similar. The PSR of the ZFGRAD was more than 12 times lower than that of the ZFC. Finally, the feasibility of image reconstruction with two arrays of eight excitation coils and eight ZFGRAD, respectively, was shown with a single-step Gauss–Newton reconstructor and simulated measurement data generated for a cylindrical tank with a spherical perturbation. The resulting images show a clear, bright feature at the correct position of the sphere and are comparable to those with PGRAD arrays.

Journal ArticleDOI
TL;DR: The results show that the reconstruction mesh and the radius of the reconstruction domain have less influence on the conditioning of the sensitivity matrix than the electrode pattern, which enabled the reconstruction of images of relatively similar quality.
Abstract: Electrical impedance endotomography (EIE) is a modality of impedance imaging where the electrodes are located on an insulating core placed at the centre of the region of interest. The absence of a physical limit to the medium surrounding the probe enables the use of remote electrodes. The present study compares the features of 2-lead measurements, where the two pairs of electrodes are located on the probe, to 1-lead measurements, where one of the two injection electrodes and one of the two sensing electrodes are located at a distance far away from the probe. The methodology was the characterization of the sensitivity matrix under the influence of electrode pattern, reconstruction radius and mesh construction. Three mesh constructions, three values of the reconstruction radius and five electrode patterns were compared. The study was carried out in 2D using calculated data. Measurement noise was simulated by an addition of 5% Gaussian white noise. The images were reconstructed using the Tikhonov method and L-curve technique. The results show that the reconstruction mesh and the radius of the reconstruction domain have less influence on the conditioning of the sensitivity matrix than the electrode pattern. Both 1-lead and 2-lead configurations enabled the reconstruction of images of relatively similar quality. Additional selection criteria are expected from hardware considerations.

Journal ArticleDOI
TL;DR: It is concluded that both surface electromyography and myotonometry parameters are indicative of intramuscular pressure, but neither of these methods can be used alone to diagnose non-invasively chronic compartment syndrome with acceptable accuracy.
Abstract: The aim of the study was to characterize the electromechanical properties of skeletal muscle during isometric loading as well as to assess the potential of estimating intramuscular pressure by electrical and mechanical methods. Simultaneous electromyography (EMG), mechanical myotonometry (MYO, frequency and decrement of decay) and intramuscular pressure (IMP) measurements were conducted at rest and during short-term and long-term isometric contractions in patients with chronic pain in the anterior leg or dorsal forearm. The EMG amplitude and MYOfreq accounted significantly (24–73%, p < 0.0001) for the variations in the IMP under short-term isometric loading. The IMP, EMG and MYOfreq increased linearly with the relative muscle load (r = 0.868–0.993, p < 0.05). Mean values of EMG amplitudes at the contraction levels of 75% and 100% maximum voluntary contraction (MVC) and MYOfreq values at all contraction levels (0–100% MVC) were higher for subjects with pathological values of IMP than for those with IMP values in the normal range. Total changes in IMP and EMG amplitude during 1 min isometric contraction were linearly interrelated (r = 0.747, p < 0.0001). We conclude that both surface electromyography and myotonometry parameters are indicative of intramuscular pressure, but neither of these methods can be used alone to diagnose non-invasively chronic compartment syndrome with acceptable accuracy.

Journal ArticleDOI
TL;DR: The present study confirms that the proposed biological signal sensing device is suitable for various implanted applications following an appropriate biocompatible packaging procedure.
Abstract: This study presents an implantable microcontroller-based bi-directional transmission system with an inductive link designed for biological signal sensing. The system comprises an external module and an implantable module. The external module incorporates a high-efficiency class-E transceiver with amplitude modulation scheme and a data recovery reader. The transceiver sends both power and commands to the implanted module, while the reader recovers the recorded biological signal data and transmits the data to a personal computer (PC) for further data processing. To reduce the effects of interference induced by the 2 MHz carrier signal, the implanted module uses two separate coils to perform the necessary two-way data transmission. The outward backward telemetry circuitry of the implanted module was based on the load-shift keying (LSK) technique. The transmitted sensed signal had a 10-bit resolution and a read-out rate of 115 kbps. The implanted module, measuring 4.5 ? 3 ? 1.2 cm3, was successfully verified in animal experiment in which the electroneurogram (ENG) signal was recorded from the sciatic nerve of New Zealand rabbits in response to nociceptive stimulation of foot. The reliable operating distance of the system was within about 3.5 cm with an efficiency of around 25%. Our present study confirms that the proposed biological signal sensing device is suitable for various implanted applications following an appropriate biocompatible packaging procedure.

Journal ArticleDOI
TL;DR: TMD measurements do not provide a reliable non-invasive measure of ICP in patients with shunted hydrocephalus, and Vm cannot be used as a surrogate for ICP.
Abstract: A non-invasive method of assessing intracranial pressure (ICP) would be of benefit to patients with abnormal cerebral pathology that could give rise to changes in ICP. In particular, it would assist the regular monitoring of hydrocephalus patients. This study evaluated a technique using tympanic membrane displacement (TMD) measurements, which has been reported to provide a reliable, non-invasive measure of ICP. A group of 135 hydrocephalus patients was studied, as well as 13 patients with benign intracranial hypertension and a control group of 77 volunteers. TMD measurements were carried out using the Marchbanks measurement system analyser and compared between the groups. In 36 patients, invasive measurements of ICP carried out at the same time were compared with the TMD values. A highly significant relationship was found between TMD and ICP but intersubject variability was high and the predictive value of the technique low. Taking the normal range of ICP to be 10–15 mmHg, the predictive limits of the regression are an order of magnitude wider than this and therefore Vm cannot be used as a surrogate for ICP. In conclusion, TMD measurements do not provide a reliable non-invasive measure of ICP in patients with shunted hydrocephalus.

Journal ArticleDOI
TL;DR: The objective of this work is to provide an efficient phonocardiogram segmentation technique, under difficult recording situations, by utilizing the underlying complexity of the dynamical system (heart) giving rise to the heart sound.
Abstract: Segmentation of the phonocardiogram into its major sound components is the first step in the automated diagnosis of cardiac abnormalities. Almost all of the existing phonocardiogram segmentation algorithms utilize absolute amplitude or frequency characteristics of heart sounds, which vary from one cardiac cycle to the other and across different patients. The objective of this work is to provide an efficient phonocardiogram segmentation technique, under difficult recording situations, by utilizing the underlying complexity of the dynamical system (heart) giving rise to the heart sound. Complexity-based segmentation is invariant to amplitude and frequency variations of the heart sound and yields better time gates for heart sounds.

Journal ArticleDOI
TL;DR: This literature review concludes by advocating specific methods of practice and that future research should focus on nonlinear and time-varying behaviors, validation of identification methods, and less understood neural regulatory mechanisms.
Abstract: Short-term, beat-to-beat cardiovascular variability reflects the dynamic interplay between ongoing perturbations to the circulation and the compensatory response of neurally mediated regulatory mechanisms. This physiologic information may be deciphered from the subtle, beat-to-beat variations by using digital signal processing techniques. While single signal analysis techniques (e.g., power spectral analysis) may be employed to quantify the variability itself, the multi-signal approach of system identification permits the dynamic characterization of the neural regulatory mechanisms responsible for coupling the variability between signals. In this review, we provide an overview of applications of system identification to beat-to-beat variability for the quantitative characterization of cardiovascular regulatory mechanisms. After briefly summarizing the history of the field and basic principles, we take a didactic approach to describe the practice of system identification in the context of probing neural cardiovascular regulation. We then review studies in the literature over the past two decades that have applied system identification for characterizing the dynamical properties of the sinoatrial node, respiratory sinus arrhythmia, and the baroreflex control of sympathetic nerve activity, heart rate and total peripheral resistance. Based on this literature review, we conclude by advocating specific methods of practice and that future research should focus on nonlinear and time-varying behaviors, validation of identification methods, and less understood neural regulatory mechanisms. Ultimately, we hope that this review stimulates such future investigations by both new and experienced system identification researchers.

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TL;DR: Convincing correlation between the bilateral differences in the local blood pressure and in the corresponding PWTT delay has been established, and the average value of leg stenosis diagnostic threshold was established to be in the range of 23 +/- 9 ms, with full reliability above 32 ms.
Abstract: A newly developed portable multi-channel photoplethysmography (PPG) device has been used for comparative studies of 20 healthy control subjects and 45 patients with diagnosed arterial stenosis in a leg. The peripheral blood pulsations were detected simultaneously at four body sites—the same fingers and toes of both arms and legs. The PPG pulses recorded at the periphery of the stenotic leg, if compared with those of the healthy leg, were much weaker, with delayed arrival as a consequence of increased pulse wave transit time (PWTT) due to higher vascular resistance. The specific PWTT delays for the occluded legs were in the range of 20–80 ms, while in the case of healthy subjects the leg PPG signals arrived without delays or with smaller time-shifts not exceeding 14 ms. The reference bilateral PPG signals detected at the fingertips did not show any notable PWTT delays in both groups. Parallel measurements of local blood pressures by means of the oscillometry method with subsequent calculation of the ankle–brachial index were performed. Convincing correlation between the bilateral differences in the local blood pressure (a routine tool for diagnostics of leg stenosis) and in the corresponding PWTT delay (Pearson's coefficient r = 0.93), as well as between the PWTT delay and the ankle–brachial index (r = −0.96) has been established. From the point of view of PWTT delay, the average value of leg stenosis diagnostic threshold was established to be in the range of 23 ± 9 ms, with full reliability above 32 ms. The obtained data may find further applications in alternative methodologies for detection and/or assessment of arterial occlusions in human extremities.

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TL;DR: This study indicates that for the analysis of EIT, data errors caused by chest expansion and tissue/organ movement need to be considered.
Abstract: One promising application of electrical impedance tomography (EIT) is the monitoring of pulmonary ventilation and edema. Using three-dimensional (3D) finite difference human models as virtual phantoms, the factors that contribute to the observed lung resistivity changes in the EIT images were investigated. The results showed that the factors included not only tissue resistivity or vessel volume changes, but also chest expansion and tissue/organ movement. The chest expansion introduced artifacts in the center of the EIT images, ranging from -2% to 31% of the image magnitude. With the increase of simulated chest expansion, the percentage contribution of chest expansion relative to lung resistivity change in the EIT image remained relatively constant. The averaged resistivity changes in the lung regions caused by chest expansion ranged from 0.65% to 18.31%. Tissue/organ movement resulted in an increased resistivity in the lung region and in the center anterior region of EIT images. The increased resistivity with inspiration observed in the heart region was caused mainly by a drop in the heart position, which reduced the heart area at the electrode level and was replaced by the lung tissue with higher resistivity. This study indicates that for the analysis of EIT, data errors caused by chest expansion and tissue/organ movement need to be considered.

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TL;DR: The results suggest that the measurements of low frequency electrical and dielectric properties may provide information on the mechanical status of trabecular bone and, possibly, may even help to diagnose bone microdamage.
Abstract: In trabecular bone, the interrelationships of electrical and dielectric properties with mechanical characteristics are poorly known. Information on these relations is crucial for evaluation of the diagnostic potential of impedance techniques. In this study, electrical and dielectric properties, i.e. permittivity, conductivity, phase angle, loss factor, specific impedance and dissipation factor of human trabecular bone samples (n = 26, harvested from the distal femur and proximal tibia) were characterized in a wide frequency range (50 Hz-5 MHz). Mechanical properties, i.e. Young's modulus, ultimate strength, yield stress, yield strain and resilience of the samples (n = 20) were determined by using destructive compressive testing. Subsequently, measurements of electrical and dielectric properties were repeated after mechanical testing. The measurements were also repeated for the control samples (n = 6) that were not mechanically tested. Electrical, dielectric or mechanical properties showed no significant differences between the intact femoral and tibial samples. The electrical and dielectric parameters as well as the linear correlations between the dielectric and electrical parameters with mechanical parameters were strongly frequency dependent. At the frequency of 1.2 MHz, the relative permittivity showed the strongest linear correlations with the Young's modulus (r = 0.71, p < 0.01, n = 20) and ultimate strength (r = 0.73, p < 0.01, n = 20). Permittivity and dissipation factor showed statistically significant changes after mechanical testing. Our results suggest that the measurements of low frequency electrical and dielectric properties may provide information on the mechanical status of trabecular bone and, possibly, may even help to diagnose bone microdamage. In the future, these measurement techniques may be further developed for use during open surgery, such as bone grafting or total hip replacement surgery.

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TL;DR: The results show that the electrical power directly applied to the esophagus is insignificant and hence theEsophageal injury is exclusively due to thermal conduction from the atrium, and both the programmed target temperature of the electrode and the duration of the ablation also have a significant effect on the lesion in the Esophagus.
Abstract: Recent studies on intraoperative radiofrequency ablation of atrial fibrillation have reported some cases of injury to the esophagus. The aim of this study was to perform computer simulations using a theoretical model in order to investigate the effect of different factors on the temperature distributions in the esophagus during ablation. A three-dimensional model was built to include an active electrode, atrial tissue, epicardial fat layer and a fragment of esophagus, aorta and lung, all linked by connective tissue. The finite-element method was used to calculate the temperature distribution during a procedure of constant-temperature ablation. The lesion geometry was assessed using a 50 degrees C isotherm. Our results show that the electrical power directly applied to the esophagus is insignificant and hence the esophageal injury is exclusively due to thermal conduction from the atrium. The esophageal lesion is mainly influenced by the thickness of connective tissue. Both the programmed target temperature of the electrode and the duration of the ablation also have a significant effect on the lesion in the esophagus. In contrast, the epicardial fat layer (0.9 mm thickness) did not show a significant influence. In conclusion, this theoretical model allows us to study the effect of different factors on the thermal injury in the esophagus during intraoperative radiofrequency ablation of atrial tissue.

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TL;DR: It is found that, with increasing pressure, the resistivity readings increase in a consistent way up to 80% and it is hypothesize that these changes may be mainly associated with the squeezing of water from the extracellular space.
Abstract: Electrical bioimpedance spectroscopy (EBIS) is a technique that uses a probe to calculate the transfer impedance from tissues. This transfer impedance can give information about the normal or pathological condition of the tissue. To take readings, pressure has to be applied to the probe in order to get a good contact between the electrodes and the tissue. We have been using EBIS to investigate the early diagnosis of dysplasia and cancer in the human cervix, oesophagus and bladder. We have found that, with increasing pressure (range used here was approximately 1 kPa to approximately 50 kPa), the resistivity readings increase in a consistent way up to 80%. In this paper, we show how this is a case in three different tissue types (oesophageal, gastric and vesical samples). These increases can be higher than those associated with the pathological changes that we are investigating (non-inflamed columnar tissue, for instance, shows values 50% higher than dysplastic columnar tissue). Finite-element modelling was also used to investigate the effect of volume reduction in the connective tissue or stroma. This simulation suggests no strong correlation between reduction of this structure and increase in resistivity. We hypothesize therefore that these changes may be mainly associated with the squeezing of water from the extracellular space. Finally, as pressure is difficult to control by hand, we raise the issue of the necessity of considering this variable when making EIS measurements.