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Ing. Jan Šebek, Ph.D.

Všechny publikace

Broadband Dielectric Properties of Ex Vivo Bovine Liver Tissue Characterized at Ablative Temperatures

  • Autoři: Fallahi, H., Ing. Jan Šebek, Ph.D., Prakash, P.
  • Publikace: IEEE Transactions on Biomedical Engineering. 2021, 68(1), 90-98. ISSN 0018-9294.
  • Rok: 2021
  • DOI: 10.1109/TBME.2020.2996825
  • Odkaz: https://doi.org/10.1109/TBME.2020.2996825
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Objective: To investigate the thermal and frequency dependence of dielectric properties of ex vivo liver tissue — relative permittivity and effective conductivity — over the frequency range of 500 MHz to 6 GHz and temperatures ranging from 20 to 130 °C. Methods: We measured the dielectric properties of fresh ex vivo bovine liver tissue using the open-ended coaxial probe method (n =15 samples). Numerical optimization techniques were utilized to obtain parametric models for characterizing changes in broadband dielectric properties as a function of temperature and thermal isoeffective dose. The effect of heating tissue at rates over the range 6.4—16.9 °C/min was studied. The measured dielectric properties were used in simulations of microwave ablation to assess changes in simulated antenna return loss compared to experimental measurements. Results: Across all frequencies, both relative permittivity and effective conductivity dropped sharply over the temperature range 89 — 107 °C. Below 91 °C, the slope of the effective conductivity changes from positive values at lower frequencies (0.5—1.64 GHz) to negative values at higher frequencies (1.64—6 GHz). The maximum achieved correlation values between transient reflection coefficients from measurements and simulations ranged between 0.83 — 0.89 and 0.68 — 0.91, respectively, when using temperature-dependent and thermal-dose dependent dielectric property parameterizations. Conclusion: We have presented experimental measurements and parametric models for characterizing changes in dielectric properties of bovine liver tissue at ablative temperatures. Significance: The presented dielectric property models will contribute to the development of ablation systems operating at frequencies other than 2.45 GHz, as well as broadband techniques for monitoring growth of microwave ablation zones.

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.

Temperature-dependent dielectric properties of human uterine fibroids over microwave frequencies

  • Autoři: Zia, G., Ing. Jan Šebek, Ph.D., Prakash, P.
  • Publikace: Biomedical Physics & Engineering Express. 2021, 7(6), ISSN 2057-1976.
  • Rok: 2021
  • DOI: 10.1088/2057-1976/ac27c2
  • Odkaz: https://doi.org/10.1088/2057-1976/ac27c2
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Microwave ablation is under investigation as a minimally-invasive treatment for uterine fibroids. Computational models play a vital role in the development, evaluation and characterization of candidate ablation devices. The temperature-dependent dielectric properties of fibroid tissue are essential for accurate computational modeling. Objective: To measure the broadband temperaturedependent dielectric properties of uterine fibroids excised during hysterectomy procedures. Methods: The open-ended coaxial probe method was employed for measuring the broadband dielectric properties of freshly excised human uterine fibroid samples (n=6) obtained from an IRB-approved tissue bank. The dielectric properties (relative permittivity, εr, and effective electrical conductivity,σeff) were evaluated at temperatures ranging from 23 °C–150 °C, over the frequency range of 0.5–6 GHz. Linear piecewise parametrization with respect to temperature and quadratic parametrization with respect to frequency was applied to characterize broadband temperature-dependent dielectric properties of fibroid tissue. Results: The baseline room temperature values of εr vary from 57.5±5.29 to 44.5±5.77 units and σeff changes from 0.91±0.19 to 6.02±0.7 Sm−1 over the frequency range of 0.5–6 GHz. At temperatures close to the water vaporization point, εr, drops considerably i.e. to 12%–14% of its baseline value for all measured frequencies. σeff values initially rise till 98 °C and then fall to 11%–13% of their baseline values at 125 °C for frequencies„2.45 GHz. The σeff follows a decreasing trend for frequencies>2.45 GHz and drops to∼6%of their baseline room temperature values. Conclusion: The temperature dependent dielectric properties of uterine fibroid tissues over microwave frequency range are reported for the first time in this study. Parametric models of uterine fibroid dielectric properties are also presented for incorporation within computational models of microwave ablation of fibroids.

Transcervical microwave ablation in type 2 uterine fibroids via a hysteroscopic approach: analysis of ablation profiles

  • Autoři: Zia, G., Ing. Jan Šebek, Ph.D., Schenck, J., Prakash, P.
  • Publikace: Biomedical Physics & Engineering Express. 2021, 7 ISSN 2057-1976.
  • Rok: 2021
  • DOI: 10.1088/2057-1976/abffe4
  • Odkaz: https://doi.org/10.1088/2057-1976/abffe4
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Type 2 uterine fibroids are challenging to resect surgically as ≥ 50% volume of myoma lies within the myometrium. A hysteroscopic approach for ablating fibroids is minimally-invasive, but places a considerable burden on the operator to accurately place the ablation applicator within the target. We investigated the sensitivity of transcervical microwave ablation outcome with respect to position of the ablation applicator within 1 – 3 cm type 2 fibroids. Methods: A finite element computer model was developed to simulate 5.8 GHz microwave ablation of fibroids and validated with experiments in ex vivo tissue. The ablation outcome was evaluated with respect to applicator insertion angles (30°, 45°, 60°) , depth and offset from the fibroid center (±2 mm for 3 cm fibroid and ±1 mm for 1 cm fibroid) with 35 W and 15 W applied power for 3 cm and 1 cm fibroids, respectively. Power deposition was stopped when thermal dose of 40 cumulative equivalent minutes at 43 °C (CEM43) was accrued in adjacent myometrium. Results: Within the range of all evaluated insertion angles, depths and offsets, the ablation coverage was less sensitive to variation in angle as compared to depth and offset, and ranged from 34.9 – 83.6% for 3 cm fibroid in 140 – 400 s and 34.1 – 67.9% for 1 cm fibroid in 30 – 50 s of heating duration. Maximum achievable ablation coverage in both fibroid cases reach ~ 90% if thermal dose is allowed to exceed 40 CEM43 in myometrium. Conclusion: The study demonstrates the technical feasibility of transcervical microwave ablation for fibroid treatment and the relationship between applicator position within the fibroid and fraction of fibroid that can be ablated while limiting thermal dose in adjacent myometrium.

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.

Directional microwave ablation: Experimental evaluation of a 2.45 GHz applicator in ex vivo and in vivo liver

  • Autoři: Pfannenstiel, A., Ing. Jan Šebek, Ph.D., Fallahi, H., Beard, W.L., Ganta, C.-K., Dupuy, D.E., Prakash, P.
  • Publikace: Journal of Vascular and Interventional Radiology. 2020, 31(7), 1170-1177. ISSN 1535-7732.
  • Rok: 2020
  • DOI: 10.1016/j.jvir.2020.01.016
  • Odkaz: https://doi.org/10.1016/j.jvir.2020.01.016
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Purpose To experimentally characterize a microwave (MW) ablation applicator designed to produce directional ablation zones. Materials and Methods Using a 14-gauge, 2.45-GHz side-firing MW ablation applicator, 36 ex vivo bovine liver ablations were performed. Ablations were performed at 60 W, 80 W, and 100 W for 3, 5, and 10 minutes (n = 4 per combination). Ablation zone forward and backward depth and width were measured and directivity was calculated as the ratio of forward to backward depth. Thirteen in vivo ablations were performed in 2 domestic swine with the applicator either inserted into the liver (80 W, 5 min, n = 3; 100 W, 5 min, n = 3; 100 W, 10 min, n = 2) or placed on the surface of the liver with a nontarget tissue placed on the back side of the applicator (80 W, 5 min, n = 5). The animals were immediately euthanized after the procedure; the livers were harvested and sectioned perpendicular to the axis of the applicator. In vivo ablation zones were measured following viability staining and assessed on histopathology. Results Mean ex vivo ablation forward depth was 8.3–15.5 mm. No backward heating was observed at 60 W, 3–5 minutes; directivity was 4.7–11.0 for the other power and time combinations. In vivo ablation forward depth was 10.3–11.5 mm, and directivity was 11.5–16.1. No visible or microscopic thermal damage to nontarget tissues in direct contact with the back side of the applicator was observed. Conclusions The side-firing MW ablation applicator can create directional ablation zones in ex vivo and in vivo tissues.

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 dielectric properties of porcine lung as a function of temperature

  • Autoři: Ing. Jan Šebek, Ph.D., Prakash, P.
  • Publikace: 2019 13TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2019. ISSN 2164-3342. ISBN 9788890701887.
  • Rok: 2019
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Computer modeling plays an important role in many aspects of microwave ablation technology development, including applicator design and ablation zone prediction for treatment planning. In order to increase the precision of models or to be able to assess the uncertainty of model predicted therapy outcome, the values of tissue dielectric parameters and dependency on temperature are required. While some data have previously been reported on temperature dependent dielectric properties of liver tissue properties, there is limited amount of information for other tissues, such as the lung. We report on the experimental measurement of broadband (500 MHz - 6 GHz) lung dielectric properties and their thermal dependency. Moreover, the dielectric properties of bovine muscle were measured as a control and validation of our measurement technique. Both relative permittivity and effective conductivity tend to decrease with rising temperature and their decay can be modelled by a linear function within the temperature range from 27°C to 94°C.

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.

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.

Computational modeling of 915 MHz microwave ablation: comparative assessment of temperature-dependent tissue dielectric models

  • Autoři: Deshazer, G., Hagmann, M., Merck, D., Ing. Jan Šebek, Ph.D., Moore, K.-B., Prakash, P.
  • Publikace: Medical Physics. 2017, 44(9), 4859-4868. ISSN 0094-2405.
  • Rok: 2017
  • DOI: 10.1002/mp.12359
  • Odkaz: https://doi.org/10.1002/mp.12359
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The objective of this study is to develop a computational model for simulating 915 MHz microwave ablation (MWA), and verify the simulation predictions of transient temperature profiles against experimental measurements. Due to the limited experimental data characterizing temperature-dependent changes of tissue dielectric properties at 915 MHz, we comparatively assess two temperature-dependent approaches of modeling of dielectric properties: model A- piecewise linear temperature dependencies based on existing, but limited, experimental data, and model B- similar to model A, but augmented with linear decrease in electrical conductivity above 95 °C, as guided by our experimental measurements.

Feasibility Assessment of Microwave Ablation for Treating Esophageal Varices

  • Autoři: Ing. Jan Šebek, Ph.D., Curto, S., Eaton-Evans, J., Bouchier-Hayes, J., Ruvio, G., Ganta, Ch., Beard, W., Buttar, N., Song, L.-W.-K., Prakash, P.
  • Publikace: Journal of Medical Devices. 2017, 11(3), ISSN 1932-6181.
  • Rok: 2017
  • DOI: 10.1115/1.4037187
  • Odkaz: https://doi.org/10.1115/1.4037187
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Esophageal varices are a significant complication of portal hypertension. Endoscopic variceal ligation (EVL) is one of the clinical standards for treating these varices and preventing their hemorrhage. Limitations of EVL include the risk of stricture formation and postband ulcer bleeding due to the damage caused to the esophageal mucosa, as well as the need for multiple endoscopic treatment sessions to eradicate the varices. The goal of this study is to develop a device and evaluate the technical feasibility of microwave ablation to seal esophageal varices, while preventing thermal damage to the surface mucosal tissue. A microwave applicator with a directional radiation pattern was developed for endoscopic ablation of esophageal varices. Electromagnetic and bioheat transfer computational models were employed to optimize the design of the microwave applicator and evaluate energy delivery strategies for this application. Experiments in ex vivo and in vivo tissue were employed to verify simulation results. Simulations predicted enhanced heating performance of the antenna using an angled monopole radiating element. Further, simulations indicate that while the endoscopic cap attenuated electric fields in tissue, it also enhanced surface cooling of tissue, increasing the likelihood of preserving mucosal tissue. Experiments in ex vivo tissue indicated the feasibility of sealing veins with 77 W microwave power delivered for 30 s. In vivo experiments demonstrated the ability to seal veins, while preserving surface tissue. This study demonstrated the technical feasibility of microwave thermal ablation for treating esophageal varices using a 2.45 GHz water-cooled directional microwave applicator.

Global microwave endometrial ablation for menorrhagia treatment

  • Autoři: Fallahi, H., Ing. Jan Šebek, Ph.D., Frattura, E., Schenck, J., Prakash, P.
  • Publikace: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Bellingham: SPIE-INT SOC OPTICAL ENGINEERING, 2017. Proceedings of SPIE. vol. 10066. ISSN 0277-786X. ISBN 978-1-5106-0573-2.
  • Rok: 2017
  • DOI: 10.1117/12.2254097
  • Odkaz: https://doi.org/10.1117/12.2254097
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Thermal ablation is a dominant therapeutic option for minimally invasive treatment of menorrhagia. Compared to other energy modalities for ablation, microwaves offer the advantages of conformal energy delivery to tissue within short times. The objective of endometrial ablation is to destroy the endometrial lining of the uterine cavity, with the clinical goal of achieving reduction in bleeding. Previous efforts have demonstrated clinical use of microwaves for endometrial ablation. A considerable shortcoming of most systems is that they achieve ablation of the target by translating the applicator in a point-to-point fashion. Consequently, treatment outcome may be highly dependent on physician skill. Global endometrial ablation (GEA) not only eliminates this operator dependence and simplifies the procedure but also facilitates shorter and more reliable treatments. The objective of our study was to investigate antenna structures and microwave energy delivery parameters to achieve GEA. Another objective was to investigate a method for automatic and reliable determination of treatment end-point. A 3D-coupled FEM electromagnetic and heat transfer model with temperature and frequency dependent material properties was implemented to characterize microwave GEA. The unique triangular geometry of the uterus where lateral narrow walls extend from the cervix to the fundus forming a wide base and access afforded through an endocervical approach limit the overall diameter of the final device. We investigated microwave antenna designs in a deployed state inside the uterus. The impact of ablation duration on treatment outcome was investigated. Prototype applicators were fabricated and experimentally evaluated in ex vivo tissue to verify the simulation results and demonstrate proof-of-concept.

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).

New algorithm for EEG and EMG Separation

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: Poster 2015. Praha: České vysoké učení technické v Praze, 2015. ISBN 978-80-01-05728-5.
  • Rok: 2015
  • 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 EEG 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.

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.

New algorithm for EEG and EMG Separation

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: Proceedings of the 19th International Scientific Student Conferenece POSTER 2015. Praha: Czech Technical University in Prague, 2015, pp. 1-5. ISBN 978-80-01-05499-4. Available from: http://radio.feld.cvut.cz/conf/poster2015/
  • Rok: 2015
  • 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 EEG 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.

Metody odstraňování svalových artefaktů ze záznamů EEG

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: IV. Letní doktorandské dny 2014. Praha: ČVUT FEL, Katedra teorie obvodů, 2014, pp. 17-20. ISBN 978-80-01-05506-9.
  • Rok: 2014
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    V příspěvku jsou popsány dva nově vyvinuté algoritmy pro odstraňování svalových artefaktů ze záznamů EEG s využitím algoritmu FastICA. U obou prezentovaných algoritmů je algoritmus FastICA použit ke zpracování několika vybraných signálů z celkového počtu měřených EEG signálů. Ke kontrole nezávislých komponent odhadnutých pomocí algoritmu FastICA je využito techniky pro kontrolu kvality separace založené na poměru výkonů nezávislých a hlavních komponent. Navržené algoritmy se od sebe liší průměrováním a využitím inverzní separační matice k rekonstrukci signálů v případě prvního algoritmu a použitím regresní techniky a odčítání odhadnutých artefaktů přímo od měřených signálů v případě druhého algoritmu. V závěru příspěvku jsou navržené algoritmy porovnány a je ukázáno, že kvalita rekonstrukce zpracovaného EEG signálu je v obou případech vyšší než u dříve publikovaných metod.

Removal of Muscular Artifacts from EEG Records

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: POSTER 2014 - 18th International Student Conference on Electrical Engineering. Prague: Czech Technical University, 2014, ISBN 978-80-01-05499-4. Available from: http://radio.feld.cvut.cz/conf/poster2014/
  • Rok: 2014
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The paper presents the algorithm for the removal of muscular artifacts from EEG signals recorded with the high density EEG electrode array. The proposed approach combines the blind source separation algorithm based on the canonical correlation analysis (CCA), the classifier based on three independent Bayesian classifiers and the regression method. In order to estimate the present muscular artifacts, the CCA is applied on electrodes located on the edge of the measuring array. Present muscular artifacts are then extracted from the estimated separated components with the use of the classifier. The last step of the algorithm involves the scaling of each muscular artifact and their subtraction from each EEG signal, so that they are no longer correlated with each other. The performance of the algorithm is evaluated for two cases. In the first case, the CCA is used as the BSS method, in the second case the Second Order Blind Identification (SOBI) method is used for comparison purposes. It is shown that the suggested algorithm achieves a high quality of the processed EEG signal even in the case of strong muscular artifacts and is therefore useful for the preprocessing of the EEG records contaminated with the muscle activity.

Classification of the EEG and EMG Sources estimated by ICA

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: POSTER 2013 - 17th International Student Conference on Electrical Engineering. Prague: Czech Technical University, 2013. ISBN 978-80-01-05242-6.
  • Rok: 2013
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    The aim of this paper is to present the proposed classifier, which is used for the classification of the independent components (ICs) estimated from a set of the measured Electroencephalograph (EEG) signals by a chosen blind source separation (BSS) algorithm, for example FastICA or SOBI. These estimated ICs are either generated by the sources located in the brain, or by the sources situated outside the brain, for example muscles on the face or neck. It is shown that the classifier is an important part of an algorithm for the removal of muscular artifacts (EMG) from EEG measurements, because it decides which estimated source signals (ICs) are useful for the reconstruction of a clean EEG signal, and which source signals are artifactual and will be suppressed. The performance of the classifier is evaluated by a classification rate of the ICs of measured EEG signals from several people. The reached classification rates for each person and the overall averaged classification rate show promising results that suggest the usefulness of this algorithm for the classification of the artifactual ICs.

Možná řešení problému přeučení algoritmu FastICA při zpracování EEG

  • Autoři: Ing. Jan Šebek, Ph.D.,
  • Publikace: III. LETNÍ DOKTORANDSKÉ DNY 2013. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2013. p. 46-53. ISBN 978-80-01-05251-8.
  • Rok: 2013
  • Pracoviště: Katedra teorie obvodů
  • Anotace:
    Cílem tohoto článku je upozornit na problém přeučení algoritmu FastICA při jeho použití na zpracování elektroencefalografického signálu (EEG) s relativně vysokým počtem kanálů vůči ne dostatečném u počtu nezávislých vzorků ve zpracovávaném časovém úseku, shrnout dříve publikované metody řešení tohoto problému a zároveň popsat nově navržený přístup k řešení problému přeučení. Byla navržena metoda, která efektivně potlačuje efekt přeučení i při zdánlivě nepříznivých poměrech počtu kanálů EEG signálu k počtu vzájemně nezávislých vzorků signálu ve zpracovávaném časovém segmentu. Jedná se o okénkovou metodu upravující činnost algoritmu FastICA. V závěru článku je tato metoda porovnána s metodami, které byly již dříve na toto téma publikovány, a zároveň je zde ukázáno, že poskytuje lepší výsledky než ostatní metody.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk