Showing papers in "Medical & Biological Engineering & Computing in 2008"
TL;DR: The framework takes advantage of the integration of image processing, geometric analysis and mesh generation techniques, with an accent on full automation and high-level interaction, to be performed in the context of large-scale studies.
Abstract: We present a modeling framework designed for patient-specific computational hemodynamics to be performed in the context of large-scale studies. The framework takes advantage of the integration of image processing, geometric analysis and mesh generation techniques, with an accent on full automation and high-level interaction. Image segmentation is performed using implicit deformable models taking advantage of a novel approach for selective initialization of vascular branches, as well as of a strategy for the segmentation of small vessels. A robust definition of centerlines provides objective geometric criteria for the automation of surface editing and mesh generation. The framework is available as part of an open-source effort, the Vascular Modeling Toolkit, a first step towards the sharing of tools and data which will be necessary for computational hemodynamics to play a role in evidence-based medicine.
686 citations
TL;DR: It appears that the protocol in combination with the MT9B is valid for, and theMT9B in combinationWith the protocol is accurate when, measuring shoulder and elbow kinematics, during the tasks tested, in ambulatory settings.
Abstract: Inertial and magnetic measurement systems (IMMSs) are a new generation of motion analysis systems which may diffuse the measurement of upper-limb kinematics to ambulatory settings. Based on the MT9B IMMS (Xsens Technologies, NL), we therefore developed a protocol that measures the scapulothoracic, humerothoracic and elbow 3D kinematics. To preliminarily evaluate the protocol, a 23-year-old subject performed six tasks involving shoulder and elbow single-joint-angle movements. Criteria for protocol validity were limited cross-talk with the other joint-angles during each task; scapulohumeral-rhythm close to literature results; and constant carrying-angle. To assess the accuracy of the MT9B when measuring the upper-limb kinematics through the protocol, we compared the MT9B estimations during the six tasks, plus other four, with the estimations of an optoelectronic system (the gold standard), in terms of RMS error, correlation coefficient (r), and the amplitude ratio (m). Results indicate that the criteria for protocol validity were met for all tasks. For the joint angles mainly involved in each movement, the MT9B estimations presented RMS errors 0.99 and 0.9 < m < 1.09. It appears therefore that (1) the protocol in combination with the MT9B is valid for, and (2) the MT9B in combination with the protocol is accurate when, measuring shoulder and elbow kinematics, during the tasks tested, in ambulatory settings.
285 citations
TL;DR: In this paper, the authors provide analysis algorithms for quantitative assessment of microvasculatory video sequences that provide vessel thickness, vessel length and blood velocity per vessel segment, and further provide a method of for calculating the functional microvascular density and blood velocities as distributed over vessels with different thickness in the field of view.
Abstract: The invention provides analysis algorithms for quantitative assessment of microvasculatory video sequences that provide vessel thickness, vessel length and blood velocity per vessel segment. It further provides a method of for calculating the functional microvasculatory density and blood velocity as distributed over vessels with different thickness, in the field of view.
226 citations
TL;DR: Various linear and non-linear signal-processing techniques were applied to three-channel uterine EMG records to separate term and pre-term deliveries, showing noticeable differences between term delivery records recorded before and after the 26th week.
Abstract: Various linear and non-linear signal-processing techniques were applied to three-channel uterine EMG records to separate term and pre-term deliveries. The linear techniques were root mean square value, peak and median frequency of the signal power spectrum and autocorrelation zero crossing; while the selected non-linear techniques were estimation of the maximal Lyapunov exponent, correlation dimension and calculating sample entropy. In total, 300 records were grouped into four groups according to the time of recording (before or after the 26th week of gestation) and according to the total length of gestation (term delivery records--pregnancy duration >or=37 weeks and pre-term delivery records--pregnancy duration <37 weeks). The following preprocessing band-pass Butterworth filters were tested: 0.08-4, 0.3-4, and 0.3-3 Hz. With the 0.3-3 Hz filter, the median frequency indicated a statistical difference between those term and pre-term delivery records recorded before the 26th week (p = 0.03), and between all term and all pre-term delivery records (p = 0.012). With the same filter, the sample entropy indicated statistical differences between those term and pre-term delivery records recorded before the 26th week (p = 0.035), and between all term and all pre-term delivery records (p = 0.011). Both techniques also showed noticeable differences between term delivery records recorded before and after the 26th week (p
211 citations
TL;DR: The assessment of WSS in the arterial system in vivo is discussed and the results obtained in large arteries and arterioles are presented, implying that in in vitro studies no average shear stress value can be taken to study effects on endothelial cells derived from different vascular areas or from the same artery across species.
Abstract: Based upon theory, wall shear stress (WSS), an important determinant of endothelial function and gene expression, has been assumed to be constant along the arterial tree and the same in a particular artery across species In vivo measurements of WSS, however, have shown that these assumptions are far from valid In this survey we will discuss the assessment of WSS in the arterial system in vivo and present the results obtained in large arteries and arterioles In vivo WSS can be estimated from wall shear rate, as derived from non-invasively recorded velocity profiles, and whole blood viscosity in large arteries and plasma viscosity in arterioles, avoiding theoretical assumptions In large arteries velocity profiles can be recorded by means of a specially designed ultrasound system and in arterioles via optical techniques using fluorescent flow velocity tracers It is shown that in humans mean WSS is substantially higher in the carotid artery (11–13 Pa) than in the brachial (04–05 Pa) and femoral (03–05 Pa) arteries Also in animals mean WSS varies substantially along the arterial tree Mean WSS in arterioles varies between about 10 and 50 Pa in the various studies and is dependent on the site of measurement in these vessels Across species mean WSS in a particular artery decreases linearly with body mass, eg, in the infra-renal aorta from 88 Pa in mice to 05 Pa in humans The observation that mean WSS is far from constant along the arterial tree implies that Murray’s cube law on flow-diameter relations cannot be applied to the whole arterial system Because blood flow velocity is not constant along the arterial tree either, a square law also does not hold The exponent in the power law likely varies along the arterial system, probably from 2 in large arteries near the heart to 3 in arterioles The in vivo findings also imply that in in vitro studies no average shear stress value can be taken to study effects on endothelial cells derived from different vascular areas or from the same artery in different species The cells have to be studied under the shear stress conditions they are exposed to in real life
156 citations
TL;DR: A publicly available benchmark suite of biological image datasets that can be used by machine vision experts for developing and evaluating biological image analysis methods and represents a set of practical real-life imaging problems in biology.
Abstract: New technology for automated biological image acquisition has introduced the need for effective biological image analysis methods. These algorithms are constantly being developed by pattern recognition and machine vision experts, who tailor general computer vision techniques to the specific needs of biological imaging. However, computer scientists do not always have access to biological image datasets that can be used for computer vision research, and biologist collaborators who can assist in defining the biological questions are not always available. Here we propose a publicly available benchmark suite of biological image datasets that can be used by machine vision experts for developing and evaluating biological image analysis methods. The suite represents a set of practical real-life imaging problems in biology, and offers examples of organelles, cells and tissues, imaged at different magnifications and different contrast techniques. All datasets are available for free download at http://ome.grc.nia.nih.gov/iicbu2008.
145 citations
TL;DR: It is suggested that nonlinear EEG analysis may contribute to increase the insight into brain dysfunction in AD, especially when different time scales are inspected, as is the case with AMI.
Abstract: We analysed the electroencephalogram (EEG) from Alzheimer’s disease (AD) patients with two nonlinear methods: approximate entropy (ApEn) and auto mutual information (AMI). ApEn quantifies regularity in data, while AMI detects linear and nonlinear dependencies in time series. EEGs from 11 AD patients and 11 age-matched controls were analysed. ApEn was significantly lower in AD patients at electrodes O1, O2, P3 and P4 (p < 0.01). The EEG AMI decreased more slowly with time delays in patients than in controls, with significant differences at electrodes T5, T6, O1, O2, P3 and P4 (p < 0.01). The strong correlation between results from both methods shows that the AMI rate of decrease can be used to estimate the regularity in time series. Our work suggests that nonlinear EEG analysis may contribute to increase the insight into brain dysfunction in AD, especially when different time scales are inspected, as is the case with AMI.
115 citations
TL;DR: The first version of an anatomy editing/surgical planning tool (SURGEM) targeting anatomical complexity and patient-specific computational fluid dynamics (CFD) analysis is presented and Hemodynamic performance of the systematically modified anatomies is compared with the original anatomy using CFD.
Abstract: The first version of an anatomy editing/surgical planning tool (SURGEM) targeting anatomical complexity and patient-specific computational fluid dynamics (CFD) analysis is presented. Novel three-dimensional (3D) shape editing concepts and human–shape interaction technologies have been integrated to facilitate interactive surgical morphology alterations, grid generation and CFD analysis. In order to implement “manual hemodynamic optimization” at the surgery planning phase for patients with congenital heart defects, these tools are applied to design and evaluate possible modifications of patient-specific anatomies. In this context, anatomies involve complex geometric topologies and tortuous 3D blood flow pathways with multiple inlets and outlets. These tools make it possible to freely deform the lumen surface and to bend and position baffles through real-time, direct manipulation of the 3D models with both hands, thus eliminating the tedious and time-consuming phase of entering the desired geometry using traditional computer-aided design (CAD) systems. The 3D models of the modified anatomies are seamlessly exported and meshed for patient-specific CFD analysis. Free-formed anatomical modifications are quantified using an in-house skeletization based cross-sectional geometry analysis tool. Hemodynamic performance of the systematically modified anatomies is compared with the original anatomy using CFD. CFD results showed the relative importance of the various surgically created features such as pouch size, vena cave to pulmonary artery (PA) flare and PA stenosis. An interactive surgical-patch size estimator is also introduced. The combined design/analysis cycle time is used for comparing and optimizing surgical plans and improvements are tabulated. The reduced cost of patient-specific shape design and analysis process, made it possible to envision large clinical studies to assess the validity of predictive patient-specific CFD simulations. In this paper, model anatomical design studies are performed on a total of eight different complex patient specific anatomies. Using SURGEM, more than 30 new anatomical designs (or candidate configurations) are created, and the corresponding user times presented. CFD performances for eight of these candidate configurations are also presented.
108 citations
TL;DR: This work proposes the use of statistical parameters of VAG signals, including the form factor involving the variance of the signal and its derivatives, skewness, kurtosis, and entropy, to classify V AG signals as normal or abnormal.
Abstract: Externally detected vibroarthrographic (VAG) signals bear diagnostic information related to the roughness, softening, breakdown, or the state of lubrication of the articular cartilage surfaces of the knee joint. Analysis of VAG signals could provide quantitative indices for noninvasive diagnosis of articular cartilage breakdown and staging of osteoarthritis. We propose the use of statistical parameters of VAG signals, including the form factor involving the variance of the signal and its derivatives, skewness, kurtosis, and entropy, to classify VAG signals as normal or abnormal. With a database of 89 VAG signals, screening efficiency of up to 0.82 was achieved, in terms of the area under the receiver operating characteristics curve, using a neural network classifier based on radial basis functions.
102 citations
TL;DR: A small sensor unit comprising an accelerometer and a gyroscope is developed in order to detect shank and foot segment motion and orientation during different walking conditions to have a higher performance in classification than other machine learning methods.
Abstract: A portable gait analysis and activity-monitoring system for the evaluation of activities of daily life could facilitate clinical and research studies. This current study developed a small sensor unit comprising an accelerometer and a gyroscope in order to detect shank and foot segment motion and orientation during different walking conditions. The kinematic data obtained in the pre-swing phase were used to classify five walking conditions: stair ascent, stair descent, level ground, upslope and downslope. The kinematic data consisted of anterior–posterior acceleration and angular velocity measured from the shank and foot segments. A machine learning technique known as support vector machine (SVM) was applied to classify the walking conditions. SVM was also compared with other machine learning methods such as artificial neural network (ANN), radial basis function network (RBF) and Bayesian belief network (BBN). The SVM technique was shown to have a higher performance in classification than the other three methods. The results using SVM showed that stair ascent and stair descent could be distinguished from each other and from the other walking conditions with 100% accuracy by using a single sensor unit attached to the shank segment. For classification results in the five walking conditions, performance improved from 78% using the kinematic signals from the shank sensor unit to 84% by adding signals from the foot sensor unit. The SVM technique with the portable kinematic sensor unit could automatically recognize the walking condition for quantitative analysis of the activity pattern.
98 citations
TL;DR: Low-intensity pulsed ultrasound (LIPUS) might provide a feasible tool for cartilage tissue repair in osteoarthritic patients, since it stimulates chondrocyte proliferation and matrix production.
Abstract: We investigated whether low-intensity pulsed ultrasound (LIPUS) stimulates chondrocyte proliferation and matrix production in explants of human articular cartilage obtained from donors suffering from unicompartimental osteoarthritis of the knee, as well as in isolated human chondrocytes in vitro. Chondrocytes and explants were exposed to LIPUS (30 mW/cm2; 20 min/day, 6 days). Stimulation of [35S]-sulphate incorporation into proteoglycans by LIPUS was 1.3-fold higher in degenerative than in collateral monolayers as assessed biochemically and 1.9-fold higher in explants as assessed by autoradiography. LIPUS decreased the number of cell nests containing 1–3 chondrocytes by 1.5 fold in collateral and by 1.6 fold in degenerative explants. LIPUS increased the number of nests containing 4–6 chondrocytes by 4.8 fold in collateral and by 3.9 fold in degenerative explants. This suggests that LIPUS stimulates chondrocyte proliferation and matrix production in chondrocytes of human articular cartilage in vitro. LIPUS might provide a feasible tool for cartilage tissue repair in osteoarthritic patients, since it stimulates chondrocyte proliferation and matrix production.
TL;DR: For classification of the imaginary movements, the results suggest that the type of movement and frequency band play an important role and the delta band was found to carry significant class-related information.
Abstract: The aim of this study was to classify different movements about the right wrist. Four different movements were performed: extension, flexion, pronation and supination. Two-class single trial classification was performed on six possible combinations of two movements (extension-flexion, extension-supination, extension-pronation, flexion-supination, flexion-pronation, pronation-supination). Both real and imaginary movements were analysed. The analysis was done in the joint time-frequency domain using the Gabor transform. Feature selection was based on the Davis-Bouldin Index (DBI) and feature classification was based on Elman's recurrent neural networks (ENN). The best classification results, near 80% true positive rate, for imaginary movements were achieved for discrimination between extension and any other type of movement. The experiments were run with 10 able-bodied subjects. For some subjects, real movement classification rates higher than 80% were achieved for any combination of movements, though not simultaneously for all six combinations of movements. For classification of the imaginary movements, the results suggest that the type of movement and frequency band play an important role. Unexpectedly, the delta band was found to carry significant class-related information.
TL;DR: There was a gradual decrease in nasal resistance in the posterior ethmoid sinus region following FESS, highlighting the potential of this technique as a powerful preoperative assessment tool to aid clinical decision-making.
Abstract: In this study we utilized computational fluid dynamic (CFD) techniques to construct a numerical simulation of nasal cavity airflow pre and post virtual functional endoscopic surgery (FESS). A healthy subject was selected, and CFD techniques were then applied to construct an anatomically and proportionally accurate three-dimensional nasal model based on nasal CT scans. A virtual FESS intervention was performed numerically on the normal nasal model using Fluent software. Navier-Stokes and continuity equations were used to calculate and compare airflow, velocity, distribution and pressure in both the pre and post FESS models. In the post-FESS model, there was an increase in airflow distribution in the maxillary, ethmoid and sphenoid sinuses, and a 13% increase through the area connecting the middle meatus and the surgically opened ethmoid. There was a gradual decrease in nasal resistance in the posterior ethmoid sinus region following FESS. These findings highlight the potential of this technique as a powerful preoperative assessment tool to aid clinical decision-making.
TL;DR: An improved algorithm for the extraction of respiration signal from the ECG-derived respiration (EDR) signal acquisition using conductive textile electrodes located in bed, and an optimal EDR signal among the three EDR signals derived from each lead is selected.
Abstract: In this paper, an improved algorithm for the extraction of respiration signal from the electrocardiogram (ECG) in home healthcare is proposed. The whole system consists of two-lead electrocardiogram acquisition using conductive textile electrodes located in bed, baseline fluctuation elimination, R-wave detection, adjustment of sudden change in R-wave area using moving average, and optimal lead selection. In order to solve the problems of previous algorithms for the ECG-derived respiration (EDR) signal acquisition, we are proposing a method for the optimal lead selection. An optimal EDR signal among the three EDR signals derived from each lead (and arctangent of their ratio) is selected by estimating the instantaneous frequency using the Hilbert transform, and then choosing the signal with minimum variation of the instantaneous frequency. The proposed algorithm was tested on 15 male subjects, and we obtained satisfactory respiration signals that showed high correlation (r
2 > 0.8) with the signal acquired from the chest-belt respiration sensor.
TL;DR: This study applies independent component analysis (ICA) to isolate motion artifacts in ECG signals and shows that both convolutive and constrained ICA implementations perform better than standard ICA, thus opening up a new field of application for these two methods.
Abstract: Electrocardiographic (ECG) signals are affected by several kinds of artifacts that may hide vital signs of interest. In this study we apply independent component analysis (ICA) to isolate motion artifacts. Standard or instantaneous ICA, which is currently the most addressed ICA model within the context of artifact removal, is compared to two other ICA techniques. The first technique is a frequency domain approach to convolutive mixture separation. The second is based on temporally constrained ICA, which enables the estimation of only one component close to a particular reference signal. Performance indexes evaluate ECG complex enhancement and relevant heart rate errors. Our results show that both convolutive and constrained ICA implementations perform better than standard ICA, thus opening up a new field of application for these two methods. Moreover, statistical analysis reveals that constrained ICA and convolutive ICA do not significantly differ concerning heart rate estimation, even though the latter overcomes the former in ECG morphology recovery.
TL;DR: The obtained discrimination between patients and controls was promising and seven patients with severe motor dysfunctions were distinguished in one of the patient clusters.
Abstract: We present an advanced method for feature extraction and cluster analysis of surface electromyograms (EMG) and acceleration signals in Parkinson's disease (PD). In the method, 12 different EMG and acceleration signal features are extracted and used to form high-dimensional feature vectors. The dimensionality of these vectors is then reduced by using the principal component approach. Finally, the cluster analysis of feature vectors is performed in a low-dimensional eigenspace. The method was tested with EMG and acceleration data of 42 patients with PD and 59 healthy controls. The obtained discrimination between patients and controls was promising. According to clustering results, one cluster contained 90% of the healthy controls and two other clusters 76% of the patients. Seven patients with severe motor dysfunctions were distinguished in one of the patient clusters. In the future, the clinical value of the method should be further evaluated.
TL;DR: The performance of the algorithm for synchronization of electroporation pulse delivery with electrocardiogram is evaluated and it is demonstrated that a transient RR interval decrease after application ofelectroporation pulses is demonstrated.
Abstract: Electrochemotherapy is an effective antitumor treatment currently applied to cutaneous and subcutaneous tumors. Electrochemotherapy of tumors located close to the heart could lead to adverse effects, especially if electroporation pulses were delivered within the vulnerable period of the heart or if they coincided with arrhythmias of some types. We examined the influence of electroporation pulses on functioning of the heart of human patients by analyzing the electrocardiogram. We found no pathological morphological changes in the electrocardiogram; however, we demonstrated a transient RR interval decrease after application of electroporation pulses. Although no adverse effects due to electroporation have been reported so far, the probability for complications could increase in treatment of internal tumors, in tumor ablation by irreversible electroporation, and when using pulses of longer durations. We evaluated the performance of our algorithm for synchronization of electroporation pulse delivery with electrocardiogram. The application of this algorithm in clinical electroporation would increase the level of safety for the patient and suitability of electroporation for use in anatomical locations presently not accessible to existing electroporation devices and electrodes.
TL;DR: A novel algorithm for analysing simultaneously measured ear and finger photoplethysmography (PPG) signals that separates the systolic wave and the diastolic wave of the VP and fits each of them with the sum of two Gaussian functions.
Abstract: Analysis of the contour of the blood volume pulse (VP) has become important because it contains much information about cardiovascular activity. Traditionally, pulse contour analysis requires first or higher derivatives to be calculated. This paper describes a novel algorithm for analysing simultaneously measured ear and finger photoplethysmography (PPG) signals. The algorithm separates the systolic wave and the diastolic wave of the VP and fits each of them with the sum of two Gaussian functions. The VP was obtained from PPG signals taken from 40 healthy subjects at each heartbeat cycle. From the evaluated VP, time values of the direct wave and three reflected waves were calculated, as well as the augmentation index (AI) and the reflection index (RI). The evaluated parameters were compared with those that were obtained by the derivative method, and it was demonstrated that the new method can be used to analyze VP waveforms.
TL;DR: A magnetic resonance imaging (MRI)-based, high-resolution, numerical model of the head of a healthy human subject is presented, using T1-weighted MRI to study individual thin anatomical structures of clinical relevance not visible by the standard model currently adopted in computational bioelectromagnetics.
Abstract: In this study, we present a magnetic resonance imaging (MRI)-based, high-resolution, numerical model of the head of a healthy human subject. In order to formulate the model, we performed quantitative volumetric segmentation on the human head, using T1-weighted MRI. The high spatial resolution used (1 × 1 × 1 mm3), allowed for the precise computation and visualization of a higher number of anatomical structures than provided by previous models. Furthermore, the high spatial resolution allowed us to study individual thin anatomical structures of clinical relevance not visible by the standard model currently adopted in computational bioelectromagnetics. When we computed the electromagnetic field and specific absorption rate (SAR) at 7 Tesla MRI using this high-resolution model, we were able to obtain a detailed visualization of such fine anatomical structures as the epidermis/dermis, bone structures, bone-marrow, white matter and nasal and eye structures.
TL;DR: Customized inserts with softer plugs distributed throughout the regions of high plantar pressure reduced the PPP over that of the TCI alone, which supports the outcome as predicted by the numerical model, and provides a greater degree of flexibility for customizing orthotic devices than current practice allows.
Abstract: There is evidence that appropriate footwear is an important factor in the prevention of foot pain in otherwise healthy people or foot ulcers in people with diabetes and peripheral neuropathy. A standard care for reducing forefoot plantar pressure is the utilization of orthotic devices such as total contact inserts (TCI) with therapeutic footwear. Most neuropathic ulcers occur under the metatarsal heads, and foot deformity combined with high localized plantar pressure, appear to be the most significant factors contributing to these ulcers. In this study, patient-specific finite element models of the second ray of the foot were developed to study the influence of TCI design on peak plantar pressure (PPP) under the metatarsal heads. A typical full contact insert was modified based on the results of finite element analyses, by inserting 4 mm diameter cylindrical plugs of softer material in the regions of high pressure. Validation of the numerical model was addressed by comparing the numerical results obtained by the finite element method with measured pressure distribution in the region of the metatarsal heads for a shoe and TCI condition. Two subjects, one with a history of forefoot pain and one with diabetes and peripheral neuropathy, were tested in the laboratory while wearing therapeutic shoes and customized inserts. The study showed that customized inserts with softer plugs distributed throughout the regions of high plantar pressure reduced the PPP over that of the TCI alone. This supports the outcome as predicted by the numerical model, without causing edge effects as reported by other investigators using different plug designs, and provides a greater degree of flexibility for customizing orthotic devices than current practice allows.
TL;DR: The role of cytoskeletal proteins in endothelial responses to flow has been studied in resistance arteries using pharmacological tools and transgenic models suggesting that these elements oppose the process.
Abstract: Cytoskeletal proteins determine cell shape and integrity and membrane-bound structures connected to extracellular components allow tissue integrity. These structural elements have an active role in the interaction of blood vessels with their environment. Shear stress due to blood flow is the most important force stimulating the endothelium. The role of cytoskeletal proteins in endothelial responses to flow has been studied in resistance arteries using pharmacological tools and transgenic models. Shear stress activates extracellular “flow sensing” elements associated with a thick glycocalyx communicating the signal to membrane-bound complexes (integrins and/or dystrophin-dystroglycans) and to eNOS through a pathway involving the intermediate filament vimentin, the microtubule network and actin. When blood flow increases chronically the endothelium triggers diameter enlargement and medial hypertrophy. This is facilitated by the genetic absence of the intermediate filaments, vimentin and desmin suggesting that these elements oppose the process.
TL;DR: This work presents a method, which allows automatic detection of epileptiform events and discrimination of them from eye blinks, and is based on features derived using a novel application of independent component analysis, and offers a flexible tool intended to be generalized to the simultaneous classification of many waveforms in the EEG.
Abstract: Diagnosis of several neurological disorders is based on the detection of typical pathological patterns in the electroencephalogram (EEG). This is a time-consuming task requiring significant training and experience. Automatic detection of these EEG patterns would greatly assist in quantitative analysis and interpretation. We present a method, which allows automatic detection of epileptiform events and discrimination of them from eye blinks, and is based on features derived using a novel application of independent component analysis. The algorithm was trained and cross validated using seven EEGs with epileptiform activity. For epileptiform events with compensation for eyeblinks, the sensitivity was 65 ± 22% at a specificity of 86 ± 7% (mean ± SD). With feature extraction by PCA or classification of raw data, specificity reduced to 76 and 74%, respectively, for the same sensitivity. On exactly the same data, the commercially available software Reveal had a maximum sensitivity of 30% and concurrent specificity of 77%. Our algorithm performed well at detecting epileptiform events in this preliminary test and offers a flexible tool that is intended to be generalized to the simultaneous classification of many waveforms in the EEG.
TL;DR: A mechano-regulation model is utilized to assess bone regeneration within the callus of an osteotomized mandible and predicts that the mastication loading generates such asymmetries, but their effects on the spatial distribution of callus mechanical properties are insignificant for typical latency periods used clinically.
Abstract: Mandibular symphyseal distraction osteogenesis is a common clinical procedure to modify the geometrical shape of the mandible for correcting problems of dental overcrowding and arch shrinkage. In spite of consolidated clinical use, questions remain concerning the optimal latency period and the influence of mastication loading on osteogenesis within the callus prior to the first distraction of the mandible. This work utilized a mechano-regulation model to assess bone regeneration within the callus of an osteotomized mandible. A 3D model of the mandible was reconstructed from CT scan data and meshed using poroelastic finite elements (FE). The stimulus regulating tissue differentiation within the callus was hypothesized to be a function of the strain and fluid flow computed by the FE model. This model was then used to analyse tissue differentiation during a 15-day latency period, defined as the time between the day of the osteotomy and the day when the first distraction is given to the device. The following predictions are made: (1) the mastication forces generated during the latency period support osteogenesis in certain regions of the callus, and that during the latency period the percentage of progenitor cells differentiating into osteoblasts increases; (2) reducing the mastication load by 70% during the latency period increases the number of progenitor cells differentiating into osteoblasts; (3) the stiffness of new tissue increases at a slower rate on the side of bone callus next to the occlusion of the mandibular ramus which could cause asymmetries in the bone tissue formation with respect to the middle sagittal plane. Although the model predicts that the mastication loading generates such asymmetries, their effects on the spatial distribution of callus mechanical properties are insignificant for typical latency periods used clinically. It is also predicted that a latency period of longer than a week will increase the risk of premature bone union across the callus.
TL;DR: There is reasonably strong evidence that a treatment which reduces peripheral resistance in the individual patient will, apart from reducing blood pressure, also improve the abnormal structure.
Abstract: Essential hypertension is treated primarily with a view to reducing blood pressure, and not with regard to normalizing the main pathological changes: the peripheral resistance and the cardiovascular structure. The aim of this review is to discuss whether normalization of the latter parameters, in particular resistance vessel structure, may also be a target for therapy. The review presents first the evidence for altered structure of the resistance vasculature, an increase in the media:lumen ratio of the vessels due to inward eutrophic remodelling. Secondly the degree to which it may be possible to rectify the abnormal structure is discussed, where it is shown that there is strong evidence that this requires a therapy which causes vasodilatation in the patient concerned. Thirdly evidence is presented that altered small artery structure appears to have prognostic consequences. Fourthly, the cellular mechanisms which may be involved are discussed, where there is evidence that vasoconstriction in itself can cause inward remodelling, and that this can be prevented by vasodilators. Finally, the consequences of these findings are considered as regards clues for strategies that may be able to improve the outcome of antihypertensive therapy. The review concludes that there is reasonably strong evidence that a treatment which reduces peripheral resistance in the individual patient will, apart from reducing blood pressure, also improve the abnormal structure.
TL;DR: The results indicate that accelerometry can provide valid data on the sit-to-stand (STS) movement duration, furthermore during its use additional information on the STS movement, such as balance control, can be recorded.
Abstract: Accelerometry is frequently used in movement analysis to assess body postures and motions. Here, we assessed the validity of ambulatory accelerometric measurement of the sit-to-stand (STS) movement duration. We compared accelerometric and opto-electronic assessment of the STS movement duration under four conditions (comfortable, slow, fast movement and exaggerated trunk flexion) with six healthy subjects and six subjects with stroke who performed movements six times under each condition. Accelerometric and opto-electronic data of STS movement duration were strongly related (r = 0.98). Accelerometry showed a fixed bias of 0.07 s (95% CI 0.008, 0.141) in healthy subjects and 0.32 s (95% CI 0.223, 0.422) in stroke subjects. In healthy subjects, a significant negative proportional bias of 0.1 was detected (95% CI -0.160, -0.032). Accelerometry showed discriminative validity in comparing stroke subjects to healthy subjects, and in comparing speed conditions. Our results indicate that accelerometry can provide valid data on the STS movement duration, furthermore during its use additional information on the STS movement, such as balance control, can be recorded.
TL;DR: The results suggest that cytoskeletal elements are a critical component of the signaling mechanism linking endothelial shear stress and mitochondrial release of ROS in the human coronary microcirculation.
Abstract: Mitochondrial H2O2 contributes to flow-mediated dilation (FMD) in human coronary arterioles (HCA). We examined the hypothesis that the endothelial cytoskeleton plays a critical role in transducing endothelial wall shear stress into a stimulus for releasing mitochondrial ROS. Phallacidin together with α-, β-tubulin antibodies and Mito-Tracker Red showed the proximity of F-actin, microtubules and mitochondria in endothelial cells. Cytochalasin D (CytoD) and nocodazole (Noc) disrupted endothelial F-actin and microtubules in HCA, respectively, concurrent with a reduction in the generation of cytosolic O2
•− and H2O2 (hydroethidine and dichlorodihydrofluorescein fluorescence) and mitochondrial superoxide (mitoSox) during flow (control: 3.5 ± 1.6, Cyto D: 0.51 ± 0.2, Noc: 0.81 ± 0.6). FMD, but not the dilation to bradykinin or papaverine, was reduced by Cyto D (26 ± 10% vs. 56 ± 3%) or Noc (26 ± 11% vs. 58 ± 7%). These results suggest that cytoskeletal elements are a critical component of the signaling mechanism linking endothelial shear stress and mitochondrial release of ROS in the human coronary microcirculation.
TL;DR: This article will review ongoing work in “patient specific diagnostics” in the areas of carotid, coronary and aneurismal disease and suggest how this approach may be applicable to management of aortic dissection.
Abstract: Current diagnostic testing for cardiovascular pathology usually rests on either physiological or anatomic measurement. Multiple tests must then be combined to arrive at a conclusion regarding treatment of a specific pathology. Much of the diagnostic decisions currently made are based on rough estimates of outcomes, often derived from gross anatomic observations or extrapolation of physical laws. Thus, intervention for carotid and coronary disease is based on estimates of diameter stenosis, despite data to suggest that plaque character and lesion anatomy are important determinants of outcome. Similarly, abdominal aortic aneurysm (AAA) intervention is based on maximal aneurysm diameter without regard for arterial wall composition or individual aneurysm geometry. In other words, our current diagnostic tests do not reflect the sophistication of our current knowledge of vascular disease. Using a multimodal approach, computer modeling has the potential to predict clinical outcomes based on a variety of factors including arterial wall composition, surface anatomy and hemodynamic forces. We term this more sophisticated approach “patient specific diagnostics”, in which the computer models are reconstructed from patient specific clinical visualizing modalities, and material properties are extracted from experimental measurements of specimens and incorporated into the modeling using advanced material models (including nonlinear anisotropic models) and performed as dynamic simulations using the FSI (fluid structure interaction) approach. Such an approach is sorely needed to improve the effectiveness of interventions. This article will review ongoing work in “patient specific diagnostics” in the areas of carotid, coronary and aneurismal disease. We will also suggest how this approach may be applicable to management of aortic dissection. New diagnostic methods should allow better patient selection, targeted intervention and modeling of the results of different therapies.
TL;DR: An optimization-based global property reconstruction algorithm was developed, and used for testing Rayleigh damping parameter reconstructions with gaussian noise added to the simulated motion input data, and achieved significantly better accuracy than would be predicted by examining the motion differences for differing CSM/CD damping combinations.
Abstract: A Rayleigh damping model applied to magnetic resonance elastography incorporates attenuation behavior proportionally related to both elastic and inertial forces, and allows two damping parameters to be extracted from an MRI motion dataset. Under time-harmonic conditions, the model can be implemented by the use of complex shear modulus and density, whereas viscoelastic damping models commonly used in elastography consist of only a complex shear modulus, and model only a single damping effect. Simulation studies reveal that the differences between damped elastic behavior resulting from a purely complex shear modulus (CSM damping) and from a purely complex density (CD damping) become larger as the overall level of damping present (indicated by the damping ratio) increases. A plot of results generated from the finite element (FE) model indicate the relative motion differences estimated for a range of damping ratios and CSM/CD damping combinations increase with damping ratio, and can be up to 15% at a damping ratio of 50% and therefore using the correct model for a Rayleigh damped material becomes increasingly important as damping levels increase. Resonance-related effects cause values from this plot to vary by as much as 3% as parameters such as wave speed, frequency, and problem size are altered. These motion differences can be compared to expected noise levels to estimate the parameter resolution achievable by a reconstruction algorithm. An optimization-based global property reconstruction algorithm was developed, and used for testing Rayleigh damping parameter reconstructions with gaussian noise added to the simulated motion input data. The coherent motion errors resulting from altering the combination of the two damping parameters are large enough to allow accurate determination of both of the Rayleigh damping parameters with incoherent noise levels comparable to MR measurements. The accuracy achieved by the global reconstructions was significantly better than would be predicted by examining the motion differences for differing CSM/CD damping combinations, which is likely to be due to the low ratio between number of reconstructed parameters and number of noisy measurements.
TL;DR: Three factors affecting the deployed stent-graft are considered, namely, the internal diameter of the vessel, the starting position of the graft and the diameter of curvature of the aortic arch, which may have important implications for the choice and design of stents in the future.
Abstract: Endovascular aortic stent-graft is a new, minimally invasive procedure for treating thoracic aortic diseases, and has quickly evolved to be one of the standard treatments subject to anatomic constraints. This procedure involves the placement of a self-expanding stent-graft system in a high-flow thoracic aorta. Stent-graft deployment in the thoracic aorta, especially close to the aortic arch, normally experiences a significant drag force which might lead to the risk of stent-graft failure. A comprehensive investigation on the biomechanical factors affecting the drag force on a stent-graft in the thoracic aorta is thus in order, and the goal is to perform an in-depth study on the contributing biomechanical factors. Three factors affecting the deployed stent-graft are considered, namely, the internal diameter of the vessel, the starting position of the graft and the diameter of curvature of the aortic arch. Computational fluid dynamic techniques are applied to model the blood flow. The inlet velocity and outlet pressure are assumed to be pulsatile. The three-dimensional continuity equation and the time-dependent Navier-Stokes equations for an incompressible fluid were solved numerically. The drag force due to the change of momentum within the stent-graft and the shear stress were calculated and analyzed. The drag force on a stent-graft will depend critically on the internal diameter and the starting position of stent-graft deployment. Larger internal diameter leads to larger drag force and the stent-graft deployed at the more distal position may be associated with significantly diminished drag force. Smaller diameter of curvature of the aortic arch probably results in a decline of the drag force on the stent-graft, even though this factor merely causes only a modest difference. These findings may have important implications for the choice and design of stent-grafts in the future.
TL;DR: A novel method for non-contact monitoring of stress-induced autonomic activation through the back of a chair, using a compact 24 GHz microwave radar, is developed, without large-scale equipment and placing a heavy burden on the monitored individual.
Abstract: We developed a novel method for non-contact monitoring of stress-induced autonomic activation through the back of a chair, using a compact 24 GHz microwave radar (8 × 5 × 3 cm), without large-scale equipment and placing a heavy burden on the monitored individual. Following a silent period of 120 s, audio stimuli using a composite tone of 2,120 and 2,130 Hz sine-waves at 95 dB were conducted for 120 s. From dorsal, LF/HF of HRV reflecting sympatho-vagal balance was determined by microwave radar with the maximum entropy method using eight volunteers (mean age 23 ± 1 years). Mean LF/HF measured by non-contact and contact (using electrocardiography for reference) methods during audio stimuli increased 34 and 37%, respectively, as compared with those of the silent period. Maximum cross-correlations between contact and non-contact measurements averaged 0.73 ± 0.10. Our method appears to be promising for future monitoring of stress-induced autonomic activation of operators and may reduce stress-induced accidents.