Lidé

doc. Ing. Radoslav Bortel, Ph.D.

Všechny publikace

Microwave ablation of lung tumors: A probabilistic approach for simulation-based treatment planning

  • DOI: 10.1002/mp.14923
  • Odkaz: https://doi.org/10.1002/mp.14923
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Purpose Microwave ablation (MWA) is a clinically established modality for treatment of lung tumors. A challenge with existing application of MWA, however, is local tumor progression, potentially due to failure to establish an adequate treatment margin. This study presents a robust simulation-based treatment planning methodology to assist operators in comparatively assessing thermal profiles and likelihood of achieving a specified minimum margin as a function of candidate applied energy parameters. Methods We employed a biophysical simulation-based probabilistic treatment planning methodology to evaluate the likelihood of achieving a specified minimum margin for candidate treatment parameters (i.e., applied power and ablation duration for a given applicator position within a tumor). A set of simulations with varying tissue properties was evaluated for each considered combination of power and ablation duration, and for four different scenarios of contrast in tissue biophysical properties between tumor and normal lung. A treatment planning graph was then assembled, where distributions of achieved minimum ablation zone margins and collateral damage volumes can be assessed for candidate applied power and treatment duration combinations. For each chosen power and time combination, the operator can also visualize the histogram of ablation zone boundaries overlaid on the tumor and target volumes. We assembled treatment planning graphs for generic 1, 2, and 2.5 cm diameter spherically shaped tumors and also illustrated the impact of tissue heterogeneity on delivered treatment plans and resulting ablation histograms. Finally, we illustrated the treatment planning methodology on two example patient-specific cases of tumors with irregular shapes.

Bronchoscopically delivered microwave ablation in an in vivo porcine lung model

  • Autoři: Ing. Jan Šebek, Ph.D., Kramer, S., Rocha, R., Yu, K.-Ch., doc. Ing. Radoslav Bortel, Ph.D., Beard, W.-L., Biller, D.-S., Hodgson, D.-S., Ganta, C.-K., Wibowo, H., Yee, J., Myers, R., Lam, S., Prakash, P.
  • Publikace: European Respiratory Journal Open Research. 2020, 6 ISSN 2312-0541.
  • Rok: 2020
  • DOI: 10.1183/23120541.00146-2020
  • Odkaz: https://doi.org/10.1183/23120541.00146-2020
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Background: Percutaneous microwave ablation is clinically used for inoperable lung tumor treatment. Delivery of microwave ablation applicators to tumor sites within lung parenchyma under virtual bronchoscopy guidance may enable ablation with reduced risk of pneumothorax providing a minimally-invasive treatment of early-stage tumors, which are increasingly detected with CT screening. Objectives: The objective of this study was to integrate a custom microwave ablation platform, incorporating a flexible applicator, with a clinically-established virtual bronchoscopy guidance system, and assess technical feasibility for safely creating localized thermal ablations in porcine lungs in vivo. Methods: Pre-ablation CTs of normal pigs were acquired to create a virtual model of the lungs, including airways and significant blood vessels. Virtual bronchoscopy guided microwave ablation procedures were performed with 24–32 W power (at the applicator distal tip) delivered for 5–10 mins. A total of 8 ablations were performed in 3 pigs. Post-treatment CT images were acquired to assess the extent of damage and ablation zones were further evaluated with viability stains and histopathologic analysis. Results: The flexible microwave applicators were delivered to ablation sites within lung parenchyma 5–24 mm from the airway wall via a tunnel created under virtual bronchoscopy guidance. No pneumothorax or significant airway bleeding were observed. The ablation short axis observed on gross pathology ranged between 16.5–23.5 mm and 14–26 mm on CT imaging. Conclusion: We have demonstrated the technical feasibility for safely delivering microwave ablation in the lung parenchyma under virtual bronchoscopic guidance in an in vivo porcine lung model.

NIRS-based monitoring of kidney graft perfusion

  • DOI: 10.1371/journal.pone.0243154
  • Odkaz: https://doi.org/10.1371/journal.pone.0243154
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Acute early vascular complications are rare, but serious complications after kidney transplantation. They often result in graft loss. For this reason, shortening the diagnostic process is crucial. Currently, it is standard procedure to monitor renal graft perfusion using Doppler ultrasound (DU). With respect to acute vascular complications, the main disadvantage of this type of examination is its periodicity. It would be of great benefit if graft blood perfusion could be monitored continuously during the early postoperative period. It appears evident that a well-designed near infrared spectroscopy (NIRS) monitoring system could prove very useful during the early post-transplantation period. Its role in the immediate diagnosis of vascular complications could result in a significant increase in graft salvage, thus improving the patient's overall quality of life and lowering morbidity and mortality for renal graft recipients. The aim of this study was to design, construct and test such a monitoring system. We designed a rough NIRS-based system prototype and prepared a two-stage laboratory experiment based on a laboratory pig model. In the first stage, a total of 10 animals were used to verify and optimize the technical aspects and functionality of the prototype sensor by testing it on the animal kidneys in-vivo. As a result of these tests, a more specific prototype was designed. During the second stage, we prepared a unique laboratory model of a pig kidney autotransplantation and tested the system for long-term functionality on a group of 20 animals. Overall sensitivity and specificity were calculated, and a final prototype was prepared and completed with its own analytic software and chassis. We designed and constructed a NIRS-based system for kidney graft perfusion monitoring. The measurement system provided reliable performance and 100% sensitivity when detecting acute diminished blood perfusion of the transplanted kidneys in laboratory conditions.

Broadband lung dielectric properties over the ablative temperature range: Experimental measurements and parametric models

  • DOI: 10.1002/mp.13704
  • Odkaz: https://doi.org/10.1002/mp.13704
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Computational models of microwave tissue ablation are widely used to guide the development of ablation devices, and are increasingly being used for the development of treatment planning and monitoring platforms. Knowledge of temperature‐dependent dielectric properties of lung tissue is essential for accurate modeling of microwave ablation (MWA) of the lung. We employed the open‐ended coaxial probe method, coupled with a custom tissue heating apparatus, to measure dielectric properties of ex vivo porcine and bovine lung tissue at temperatures ranging between 31 and 150 urn:x-wiley:00942405:media:mp13704:mp13704-math-0007C, over the frequency range 500 MHz to 6 GHz. Furthermore, we employed numerical optimization techniques to provide parametric models for characterizing the broadband temperature‐dependent dielectric properties of tissue, and their variability across tissue samples, suitable for use in computational models of microwave tissue ablation. Rapid decreases in both relative permittivity and effective conductivity were observed in the temperature range from 94 to 108 urn:x-wiley:00942405:media:mp13704:mp13704-math-0008C. Over the measured frequency range, both relative permittivity and effective conductivity were suitably modeled by piecewise linear functions [root mean square error (RMSE) = 1.0952 for permittivity and 0.0650 S/m for conductivity]. Detailed characterization of the variability in lung tissue properties was provided to enable uncertainty quantification of models of MWA. The reported dielectric properties of lung tissue, and parametric models which also capture their distribution, will aid the development of computational models of microwave lung ablation.

Development of Low-Cost Solder Paste Hand Dispenser

  • Pracoviště: Katedra elektrotechnologie, Katedra teorie obvodů
  • Anotace:
    In prototyping and piece-production, stencil printing of the solder paste is expensive, and with the use of the stencil, it is not possible to react fast on changes in the design. Therefore, automatic or manual dispensers are used. This work aimed to develop a low-cost dispensing system based on a simple principle that uses torsion springs and its plastic construction is printable by a 3D printer. Unlike other dispensing systems, the presented dispenser allows continuous deposition of the solder paste. As the performance test showed, the deposition can be as good as with a commercial dispenser. Furthermore, the cost of the dispenser does not exceed 1€. In comparison with other commercial solutions, it is a negligible amount.

Ruční dávkovač pájecí pasty s velmi nízkými výrobními náklady

Suppression of overlearning in independent component analysis used for removal of muscular artifacts from electroencephalographic records

  • DOI: 10.1371/journal.pone.0201900
  • Odkaz: https://doi.org/10.1371/journal.pone.0201900
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper addresses the overlearning problem in the independent component analysis (ICA) used for the removal of muscular artifacts from electroencephalographic (EEG) records. We note that for short EEG records with high number of channels the ICA fails to separate artifact-free EEG and muscular artifacts, which has been previously attributed to the phenomenon called overlearning. We address this problem by projecting an EEG record into several subspaces with a lower dimension, and perform the ICA on each subspace separately. Due to a reduced dimension of the subspaces, the overlearning is suppressed, and muscular artifacts are better separated. Once the muscular artifacts are removed, the signals in the individual subspaces are combined to provide an artifact free EEG record. We show that for short signals and high number of EEG channels our approach outperforms the currently available ICA based algorithms for muscular artifact removal. The proposed technique can efficiently suppress ICA overlearning for short signal segments of high density EEG signals.

Analysis of minimally invasive directional antennas for microwave tissue ablation

  • DOI: 10.1080/02656736.2016.1195519
  • Odkaz: https://doi.org/10.1080/02656736.2016.1195519
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Purpose: Microwave ablation (MWA) applicators capable of creating directional heating patterns offer the potential of simplifying treatment of targets in proximity to critical structures and avoiding the need for piercing the tumour volume. This work reports on improved directional MWA antennas with the objectives of minimising device diameter for percutaneous use (≤ ∼13 gauge) and yielding larger ablation zones. Methods: Two directional MWA antenna designs, with a modified monopole radiating element and spherical and parabolic reflectors are proposed. A 3D-coupled electromagnetic heat transfer with temperature-dependent material properties was implemented to characterise MWA at 40 and 77 W, for 5 and 10 min. Simulations were also used to assess antenna impedance matching within liver, kidney, lung, bone and brain tissue. The two antenna designs were fabricated and experimentally evaluated with ablations in ex vivo tissue at the two power levels and treatment durations (n = 5 repetitions for each group). Results: The computed specific absorption rate (SAR) patterns for both antennas were similar, although simulations indicated slightly greater forward penetration for the parabolic antenna. Based on simulations for antennas inserted within different tissues, the proposed antenna design appears to offer good impedance matching for a variety of tissue types. Experiments in ex vivo tissue showed radial ablation depths of 19 ± 0.9 mm in the forward direction for the applicator with spherical reflector and 18.7 ± 0.7 mm for the applicator with parabolic reflector. Conclusion: These results suggest the applicator may be suitable for creating localised directional ablation zones for treating small and medium-sized targets with a percutaneous approach.

DoA Outdoor RFID Locator - System Verification Report

  • Pracoviště: Katedra teorie obvodů, Katedra telekomunikační techniky
  • Anotace:
    The paper discusses testing the RFID locator system in real traffic in a 1 km2 area of interest for localization. Digital processing of the signal, arriving to a 20-element antenna array at the individual receiving stations, is based on the direction on arrival (DoA) method. The achieved accuracy is typically within 1 m, thus the system met its creators' expectations. The paper describes the basic operating principle of the proposed system and compares the existing outdoor localization methods. There is also a description and the results of the experimental verification of the technology at two locations, including a determination of the localization error. The key idea is to use this technology in area of security application (especially critical infrastructures) and disaster management application.

RFID Lokalizátor

  • Pracoviště: Katedra elektromagnetického pole, Katedra teorie obvodů, Katedra telekomunikační techniky
  • Anotace:
    Systém RFID lokalizátor umožňuje identifikovat oběti katastrof či zraněné osoby v definované oblasti. Systém zpracovává přenášené signály a do podrobné mapy zobrazuje v reálném čase polohu tagů, kterými jsou označeny oběti katastrofy či ranění. Řešení umožní optimalizovat postup záchranných prací a zároveň minimalizovat čas potřebný k záchraně, a to i v situaci, kdy jsou standardní komunikační systémy v důsledku katastrofy mimo provoz.

Sensitivity of microwave ablation models to tissue biophysical properties: A first step toward probabilistic modeling and treatment planning.

  • DOI: 10.1118/1.4947482
  • Odkaz: https://doi.org/10.1118/1.4947482
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Computational models of microwave ablation are widely used during the design optimization of novel devices and are under consideration for patient-specific treatment planning. The objective of this study was to assess the sensitivity of computational models to tissue biophysical properties. The Morris method was employed to assess the global sensitivity of the coupled EM model, which was implemented with the finite element method (FEM). The FEM model incorporated temperature dependencies of tissue physical properties. Furthermore, the sensitivity results were statistically analyzed and absolute influence of each input parameter was quantified. A framework for systematically incorporating model uncertainties for treatment planning was suggested. Tissue dielectric parameters, specifically relative permittivity, effective conductivity, and the threshold temperature at which they transitioned to lower values, were identified as the most influential parameters for the shape of the ablation zone and antenna impedance matching. Of the thermal parameters considered in this study, the nominal blood perfusion rate and the temperature interval across which the tissue changes phase were identified as the most influential. The latent heat of tissue water vaporization and the volumetric heat capacity of the vaporized tissue were recognized as the least influential parameters. Based on the evaluation of absolute changes, the most important parameter (perfusion) had approximately 40.23 times greater influence on ablation area than the least important parameter (volumetric heat capacity of vaporized tissue). Another significant input parameter (permittivity) had 22.26 times higher influence on the deviation of ablation edge shape from a sphere than one of the less important parameters (latent heat of liver tissue vaporization).

Design of RFID Outdoor Localization System RFID Locator for Disaster Management

GNSS/RFID Active Transponder Design

  • DOI: 10.15598/aeee.v13i5.1384
  • Odkaz: https://doi.org/10.15598/aeee.v13i5.1384
  • Pracoviště: Katedra elektromagnetického pole, Katedra teorie obvodů, Katedra telekomunikační techniky
  • Anotace:
    The paper describes a design of global navigation satellite system (GNSS)/Radio frequency identification (RFID) active transponder which is primarily designed for localization of objects as a part of localization system designated for efficient handling of situations with mass casualties. The precise localization is improved by differential GNSS. The block diagram of such GNSS/RFID active transponder is described including main operation procedures of the firmware. Measurement of the localization by algorithms of RTKLIB library and by algorithms of GNSS module is compared. Dynamic tests, i.e. GNSS/RFID active transponder placed in the moving car (50~kmph), and static tests, i.e. GNSS/RFID active transponder placed in the position for 15~min, are performed.

NEW ALGORITHM FOR EEG AND EMG SEPARATION

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The paper presents newly proposed algorithm for the blind separation of EEG and EMG sources measured by high density electrode arrays. The algorithm is based on the maximization of the variance of variances of filtered principal components. Utilized high pass filter was optimized in order to extract the information which is used by the gradient algorithm to separate New Algorithm for EEG and EMG SeparationEEG and EMG components. The performance of the algorithm was evaluated by its use for the muscular artifacts removal. Present muscular artifacts were extracted from the estimated components with the use of the previously used classifier. It is compared with other similar approaches and it is shown that the suggested algorithm achieves higher quality of the processed EEG signal especially in the case of strong muscular artifacts and is therefore useful for the preprocessing of the EEG records contaminated with the muscle activity.

Outdoor Localization Technique Using Active RFID Technology Aimed for Security and Disaster Management Applications

UHF RFID Tag Design for Disaster Management

  • Pracoviště: Katedra telekomunikační techniky
  • Anotace:
    This paper deals with the Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag design as a part of RFID localization system primarily designated for mass disasters. The design of RFID tag considers many casualties in an area of hundreds square meters, human body impedance, battery lifetime, maximal output power, resistant encapsulation etc. All requirements are taken into account in the design of several versions of RFID tag and the best one is chosen. Subsequently the design is manufactured and measured. Results show the designed RFID tag prototype is suitable for application in a disaster management.

Approximation of the null distribution of the multiple coherence estimated with segment overlapping

  • DOI: 10.1016/j.sigpro.2013.10.003
  • Odkaz: https://doi.org/10.1016/j.sigpro.2013.10.003
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    In this fast communication we suggest an approximation of the null distribution of the multiple coherence (MC) estimated with segment overlapping. The approximation is based on the formulas known for the non-overlapped segmentation, but the parameter corresponding to the number of segments is altered. The suggested approximation is statistically tested through a Monte Carlo simulation, and it is shown that its precision is quite high for a considerable range of MC parameters.

Invariance of the Null Distribution of the Multiple Coherence

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    In this paper we investigate the invariance of the null distribution of the multiple coherence (MC) to the statistics of the examined signals. We show that when the MC is computed between a group of signals x_i[n], i=1,...,K and a signal y[n], the null distribution of the MC is independent of the distribution of x_i[n] and y[n] if at a given frequency the joint distribution of the spectra of the segments of x_i[n] and y[n] is rotationally symmetric with respect to the rotation of the spectra of the segments of x_i[n] or y[n]. The significance of this result lies in the improvement of the multiple coherence analysis. Hitherto, the null distribution of the MC was known only for signals with the multivariate Gaussian distribution; therefore, an MC estimate could be evaluated for its statistical significance only in this limited case. With the results presented in this paper, it will be possible to evaluate the statistical significance of MC estimates for much wider class of signals.

Potential approximation in realistic Laplacian computation

  • DOI: 10.1016/j.clinph.2012.08.020
  • Odkaz: https://doi.org/10.1016/j.clinph.2012.08.020
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Objective: This paper aims to improve the shortcomings of the extant methodologies for realistic Laplacian (RL) computation, and correct the erroneous claims published in the past. Methods: We implemented several variants of RL computation methods, using various potential approximation techniques and different regularization approaches. The individual variants of the RL computation were tested using simulations based on a realistic head model computed with the boundary element method (BEM). The results which disagreed with previously published works were further analyzed, and the reasons for the disagreement were identified. Results: We identified the best regularization techniques for the surface potential approximation, and we showed that once these techniques are used there is often little difference between various potential approximations, which is in contrast with previous claims that promoted the radial basis function (RBF) approximation. Further, our analysis shows that the RBF approximation suffers from Runge phenomenon, which cannot be mitigated simultaneously for both deep and shallow sources; therefore, its good performance is guarantied only if a priori knowledge about the source depth is available. Conclusions: The previously published methodology for RL computation was not optimal. Improvements are possible if the newly suggested approach is used. Significance: The methodology presented in our paper allows more efficient utilization of the RL, providing a useful tool for processing of high density EEG recordings. Presented techniques allow to achieve high EEG spatial resolution, and avoid unnecessary spatial blurring caused by the problems in the previously published RL methodology.

Statistical evaluation of coherence estimated from optimally beamformed signals.

  • DOI: 10.1016/j.compbiomed.2013.06.010
  • Odkaz: https://doi.org/10.1016/j.compbiomed.2013.06.010
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    In this paper we investigate a situation where we want to perform a coherence analysis of two signal sources, one of which is measured directly, and the other is measured through a sensor array affected by noise. To extract the latter signal, we suggest the use of the optimal beamforming with reference. We note, however, that this approach results in a coherence estimate that is noticeably biased, and cannot be evaluated by the known statistical tests. We therefore derive a new statistical test, that allows the evaluation of the biased coherence estimate. We illustrate the applicability of our methodology on the coherence analysis of EEG and EMG signals. We note that the suggested approach has several advantages over the surface Laplacian, which is a spatial filter commonly used in the EEG-EMG coherence analysis.

Wearable Textile Electrodes for ECG Measurement

  • Pracoviště: Katedra telekomunikační techniky
  • Anotace:
    The electrocardiogram (ECG) is one of the most important parameters for monitoring of the physiological state of a person. Currently available systems for ECG monitoring are both stationary and wearable, but the comfort of the monitored person is not at a satisfactory level because these systems are not part of standard clothing. This article is therefore devoted to the development and measurement of wearable textile electrodes for ECG measurement device with high comfort for the user. The electrode material is made of electrically conductive textile. This creates a textile composite that guarantees high comfort for the user while ensuring good quality of ECG measurements. The composite is implemented by a carrier (a T-shirt with flame retardant) and sensing electrodes embroidered with yarn based on a mixture of polyester coated with silver nanoparticles and cotton. The electrodes not only provide great comfort but are also antibacterial and antiallergic due to silver nanoparticles.

Real-Time Robust Heart Rate Estimation Based on Bayesian Framework and Grid Filters

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    In this chapter we discuss derivation, implementation and testing of a robust real-time algorithm for the estimation of heart rate (HR) from electrocardiograms recorded on subjects performing vigorous physical activity. We formulate the problem of HR estimation as a problem of inference in a Bayesian network, which utilizes prior information about the probability distribution of HR changes. From this formulation we derive an inference procedure, which can be implemented as a grid filter. The resulting algorithm can then follow even a rapidly changing HR, whilst withstanding a series of missed or false QRS detections. Also, the HR estimate is complete with confidence intervals to allow the identification of the moments, where the precision of HR estimation is lowered. Additionally, the computational complexity of this algorithm is acceptable for battery powered portable devices.

Amplifier for Biological Signal Sensing with Efficient Common Mode Rejection

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The paper describes a new method for the suppression of the common mode interference, which is commonly present in biopotential measurements. The newly suggested method uses known principle of feedback for active common mode signal rejection. Our system is at least as effective as known systems, but with simpler circuitry and thus lower cost. In addition, the proposed system reduces problems with potential instability, and introduces less overall instrumental noise.

Robust Heart Rate Estimation Based on Imperfect QRS Detection

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper presents an algorithm for the estimation of heart rate (HR) based on imperfect detection of QRS complexes.It aims to be applicable in real world HR measurement on individuals working in highly stressful and harsh environ- ments (fireman, soldiers, etc...). The described algorithm proved to be a robust method for the estimation of HR based on intensely corrupt ECG that can be recorded on individuals performing dangerous, physically demanding and stressful tasks.

Electrode Position Scalling in Realistic Laplacian Computation

  • DOI: 10.1109/TBME.2008.921168
  • Odkaz: https://doi.org/10.1109/TBME.2008.921168
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This note discusses the effects of the electrode position scaling on the realistic Laplacian (RL) computation. It is shown that when the RL is estimated with the help of Tikhonov regularization and the generalized cross-validation (GCV) criterion, improper electrode position scaling may influence the GCV criterion, which results in the decrease of RL precision. We identify what the proper scaling should be, and we provide a closer examination of how the GCV criterion is affected by the electrode position scaling.

Robust and Computationally Efficient QRS Detector for HR estimation

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper introduces a QRS detection algorithm aimed for the use in portable ECG devices carried by intensely moving subjects. The algorithm features high robustness against several types of artifacts while it keeps its computational requirements low enough to be implemented on an 8051 type microcontroller.

Approximation of statistical distribution of magnitude squared coherence estimated with segment overlapping

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper suggests an approximation to the statistical distribution of a magnitude squared coherence (MSC) function estimated with segment overlapping. So far, the statistical distribution is known for an MSC computed without segment overlapping only. However, as the overlapped segmentation provides a more accurate MSC estimate, its statistical distribution is desired to allow its evaluation. This paper provides an approximation of the cumulative density function, probability density function, confidence limit formula, confidence interval computation and a procedure for the comparison of two MSC estimates, all for an MSC accurately estimated with the segment overlapping. Additionally, the benefits of the knowledge of the approximated statistics are illustrated on EEG-EMG (i.e. cortico-muscular) MSC estimates.

Regularization Techniques in Realistic Laplacian Computation

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper explores regularization options for the ill-posed spline coefficient equations in the realistic Laplacian computation. We investigate the use of the Tikhonov regularization, truncated singular value decomposition, and the so-called lambda-correction with the regularization parameter chosen by the L-curve, generalized cross-validation, quasi-optimality, and the discrepancy principle criteria. The provided range of regularization techniques is much wider than in the previous works. The improvement of the realistic Laplacian is investigated by simulations on the three-shell spherical head model. The conclusion is that the best performance is provided by the combination of the Tikhonov regularization and the generalized cross-validation criterion-a combination that has never been suggested for this task before.

EEG Beamforming and Efficient Way to Extract Cortical Control of Muscles

  • Autoři: doc. Ing. Radoslav Bortel, Ph.D.,
  • Publikace: POSTER 2006 - 10th International Student Conference on Electrical Engineering. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2006.
  • Rok: 2006
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper suggests a new EEG spatial filtration, which is based on the beamforming techniques. The ability of the beamforming to focus an array of sensors to a desired source is utilized to acquire brain signals involved in the control of a muscular contraction. The beamforming is shown to be superior to the currently used spatial filtration, so called surface Laplacian. It is illustrated that once EEG is filtered with the beamforming, it manifests more distinct coherence with a muscular signal. Thus, the EEG beamforming provides a better tool for the investigation of the cortico-muscular relationship.

EEG-EMG Coherence Enhancement

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The paper introduces a new approach to the estimation of the EEG-EMG coherence, which is used to examine the functional connection between a human brain and muscles. A typical EEG-EMG coherence estimation, with a magnitude squared coherence (MSC) barely exceeding 0.15, is enhanced so that MSC reaches or even goes above 0.5. The proposed method is mathematically analyzed, and its properties are discussed. Additionally, the paper includes several EEG-EMG coherence analysis results, with MSC exceeding 0.5.

Zdokonalenie odhadu povrchového Laplasiánu využívajúceho aproximáciu realistického tvaru hlavy spline funkciami

Zvýšenie presnosti koherenčnej analýzy pomocou novo odvodených štatistík pre odhad koherencie s prekryvom segmentov

Confidence Limit Computation for EEG-EMG Coherence Estimated with Segment Overlapping

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper suggests a formula for the computation of a confidence limit for a magnitude squared coherence (MSC) estimated with segment overlapping. So far, the confidence limit could be computed exactly only if MSC was estimated without segment overlapping. In case of overlapped segmentation the confidence limit could be only estimated through a quantile estimation, a procedure, which is shown to be imprecise. The suggested formula allows a solid evaluation of MSC estimated with segment overlapping, which provides more precise results. The confidence limit computation is intended for the cortico-muscular coherence analysis, which investigate coupling between the electroencephalogram (EEG) and the electromyogram (EMG). The formula is shown to be valid for signals with length typically used for EEG-EMG MSC computation - in particular the signal length assuring at least 100 degrees of freedom of an MSC estimate.

EEG and EMG Pre-Processing for EEG-EMG Coherence Computation

  • Autoři: doc. Ing. Radoslav Bortel, Ph.D.,
  • Publikace: POSTER 2005. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2005.
  • Rok: 2005
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper deals with EEG and EMG pre-processing techniques used for EEG-EMG coherence computation. Techniques of EMG rectificatoin, 50Hz noise cancellation, EEG spatial filtration and artifact detection are discussed, and their benefits are illustrated.

Efects of Handedness on the oscillatory cortex - muscle coupling during isometric hand muscle contraction

  • Autoři: Rachmanová, R., Mlynář, J., doc. Ing. Radoslav Bortel, Ph.D., Stančák, A.
  • Publikace: Neuroscience 05 - Abstract Viewer/Itinerary planer. Washington, DC: Society for Neuroscience, 2005. pp. 398.13.
  • Rok: 2005

On the Use of the Constant Phase Term in the EEG-EMG Time Delay Estimation

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper discusses the treatment of the constant phase term that is used to fit the phase of a cross-spectrum in the estimation of the time delay between the record of electrical activity of a brain (EEG), and the record of electrical activity of a contracted muscle (EMG). Commonly, when the EEG-EMG time delay is estimated as a slope of the phase of an EEG-EMG cross-spectrum the phase spectrum is fitted with a line given by a slope and an additive constant phase term. We point out that if analyzed signals are short the permanent use of the constant phase term may be unwise. First, based on the analysis of EEG-EMG data sets, we show that the constant phase term is often not significantly different from zero. Second, we illustrate that the use of the constant phase term provides results with much greater variance than without it. As a consequence, we suggest to limit the use of the constant phase term only to the cases where it is showed to be significantly different from zero.

Beamforming Applied on EEG-EMG Coherence Computation

  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    We present a beamforming application on electroencephalogram (EEG) records with an aim to improve coherence between the EEG and an electromyogram (EMG) record of an iso- metrically contracted muscle. The EEG beamforming is shown to be superior to the currently used EEG spatial filtration, so called surface Laplacian. Moreover, the beamforming has demonstrated the ability to reveal EEG-EMG binding in 6-12Hz band, which has hitherto been observed rarely.

Beamforming EEG odhaluje EEG-EMG koherence v pásmu 6-12Hz

MEG-EMG Coherence Enhancements

Oscillations in Switched Current Differentiator Based Biqadratic Section

  • Autoři: doc. Ing. Radoslav Bortel, Ph.D.,
  • Publikace: Radioelektronika 2003 - Conference Proceedings. Brno: VUT v Brně, FEI, Ústav radioelektroniky, 2003. pp. 443-446. ISBN 80-214-2383-8.
  • Rok: 2003
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    This paper discusses oscillation problems, which can occur in a differentiator based biquadratic sections realized by SI techniques. First, the oscillations in a simple biquad are demonstrated, and then the solution to the problem is suggested.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk