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Model Based Enhancement of Bioimpedance Spectroscopy Analysis: Towards Textile Enabled Applications
KTH, School of Technology and Health (STH), Medical sensors, signals and systems (MSSS). (Measurements Signals Sensors and Systems)
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Several signal processing approaches have been developed to overcome the effect of stray capacitances in Electrical Bioimpedance Spectroscopy (EBIS) measurements. EBIS measurements obtained with textile-enabled instrumentation are more vulnerable to stray capacitances. Currently, the most widespread approach for correcting the effect of stray capacitances in EBIS is the time delay (

Td) compensation method, which also has several drawbacks. In this study, the Td method is revisited and its limitations and its lack of a scientific basis are demonstrated. To determine better ways to overcome the effect of stray capacitances, a simplified measurement model is proposed that is based on previous models of artefacts in EBIS measurements described in the literature. The model consists of a current divider with a parasitic capacitance (Cpar) in parallel with the load. Cpar creates a pathway for the measurement current to leak away from the load, provoking a capacitive leakage effect. In this thesis, three approaches with different limitations are proposed to overcome the capacitive leakage effect. The first approach estimates Cpar and subtracts it from the measurements, thus finding the load. Cpar can be estimated because the susceptance of biological tissue is null at infinite frequency. Therefore, at high frequencies, the susceptance of the tissue can be neglected, and the slope of the susceptance of the measurement is Cpar. The accuracy of Cpar depends on the maximum frequency measured and the value of Cpar. Therefore, it may not be possible to accurately estimate small values of Cpar in the typical frequency ranges used in EBIS. The second and third approaches use the Cole fitting process to estimate the Cole parameters, which form the basis for most EBIS applications. Because the conductance of the measurement is free from the effect of Cpar, performing Cole fitting on the conductance avoids the effect of Cpar in the fitting process. With a poor skin-electrode contact, this approach may not be sufficiently accurate. The third approach would be to perform the Cole fitting on the modulus with a reduced upper frequency limit because the modulus and the low-medium frequencies are very robust against the effect of artefacts. In this approach, a slight capacitive leakage effect is unavoidable. Since it is common to find tainted measurements, especially among those obtained with textile-enabled instrumentation, it is important to find viable methods to avoid their effect. The three methods studied showed that they could reduce the effect of tainted measurements.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. , xviii, 42 p.
Series
Trita-STH : report, ISSN 1653-3836 ; 2011:6
Keyword [en]
Physiological measurements, Bioimpedance, modelling, textiles
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-90884ISBN: 978-91-7501-230-8 (print)OAI: oai:DiVA.org:kth-90884DiVA: diva2:507141
Presentation
2012-02-28, 4X, Alfred Nobels Allé 8, Huddinge, 11:33 (English)
Opponent
Supervisors
Note
QC 20120313Available from: 2012-03-13 Created: 2012-03-02 Last updated: 2012-03-15Bibliographically approved
List of papers
1. Experimental validation of a method for removing the capacitive leakage artifact from electrical bioimpedance spectroscopy measurements
Open this publication in new window or tab >>Experimental validation of a method for removing the capacitive leakage artifact from electrical bioimpedance spectroscopy measurements
2010 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 21, no 11Article in journal (Refereed) Published
Abstract [en]

Often when performing electrical bioimpedance (EBI) spectroscopy measurements, the obtained EBI data present a hook-like deviation, which is most noticeable at high frequencies in the impedance plane. The deviation is due to a capacitive leakage effect caused by the presence of stray capacitances. In addition to the data deviation being remarkably noticeable at high frequencies in the phase and the reactance spectra, the measured EBI is also altered in the resistance and the modulus. If this EBI data deviation is not properly removed, it interferes with subsequent data analysis processes, especially with Cole model-based analyses. In other words, to perform any accurate analysis of the EBI spectroscopy data, the hook deviation must be properly removed. Td compensation is a method used to compensate the hook deviation present in EBI data; it consists of multiplying the obtained spectrum, Z meas (ω), by a complex exponential in the form of exp(–jωTd). Although the method is well known and accepted, Td compensation cannot entirely correct the hook-like deviation; moreover, it lacks solid scientific grounds. In this work, the Td compensation method is revisited, and it is shown that it should not be used to correct the effect of a capacitive leakage; furthermore, a more developed approach for correcting the hook deviation caused by the capacitive leakage is proposed. The method includes a novel correcting expression and a process for selecting the proper values of expressions that are complex and frequency dependent. The correctness of the novel method is validated with the experimental data obtained from measurements from three different EBI applications. The obtained results confirm the sufficiency and feasibility of the correcting method.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2010
Keyword
electrical bioimpedance spectroscopy; capacitive leakage; artifact removal
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-73065 (URN)10.1088/0957-0233/21/11/115802 (DOI)000285262000026 ()
Note
QC 20120209Available from: 2012-02-09 Created: 2012-02-01 Last updated: 2017-12-08Bibliographically approved
2. Cole parameter estimation from electrical bioconductance spectroscopy measurements
Open this publication in new window or tab >>Cole parameter estimation from electrical bioconductance spectroscopy measurements
2010 (English)In: 2010 ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY (EMBC), IEEE Press, 2010, Vol. 2010, 3495-3498 p.Conference paper, Published paper (Refereed)
Abstract [en]

Several applications of Electrical Bioimpedance (EBI) make use of Cole parameters as base of their analysis, therefore Cole parameters estimation has become a very common practice within Multifrequency- and EBI spectroscopy. EBI measurements are very often contaminated with the influence of parasitic capacitances, which contributes to cause a hook-alike measurement artifact at high frequencies in the EBI obtained data. Such measurement artifacts might cause wrong estimations of the Cole parameters, contaminating the whole analysis process and leading to wrong conclusions. In this work, a new approach to estimate the Cole parameters from the real part of the admittance, i.e. the conductance, is presented and its performance is compared with the results produced with the traditional fitting of complex impedance to a depressed semi-circle. The obtained results prove that is feasible to obtain the full Cole equation from only the conductance data and also that the estimation process is safe from the influence capacitive leakage.

Place, publisher, year, edition, pages
IEEE Press, 2010
Series
IEEE Engineering in Medicine and Biology Society Conference Proceedings, ISSN 1557-170X
Keyword
BODY, BIOIMPEDANCE, IMPEDANCE
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-73051 (URN)10.1109/IEMBS.2010.5627790 (DOI)000287964003223 ()21097029 (PubMedID)978-1-4244-4124-2 (ISBN)
Conference
32nd Annual International Conference of the IEEE Engineering-in-Medicine-and-Biology-Society (EMBC 10), Buenos Aires, ARGENTINA, AUG 30-SEP 04, 2010
Note
© 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20120209Available from: 2012-02-09 Created: 2012-02-01 Last updated: 2013-09-17Bibliographically approved
3. Hook Effect correction & resistance-based Cole fitting prior Cole model-based analysis: Experimental validation
Open this publication in new window or tab >>Hook Effect correction & resistance-based Cole fitting prior Cole model-based analysis: Experimental validation
Show others...
2010 (English)In: Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2010, IEEE Engineering in Medicine and Biology , 2010, 6563-6566 p.Conference paper, Published paper (Refereed)
Abstract [en]

The analysis of measurements of Electrical Bioimpedance (EBI) is on the increase for performing non-invasive assessment of health status and monitoring of pathophysiological mechanisms. EBI measurements might contain measurements artefacts that must be carefully removed prior to any further analysis. Cole model-based analysis is often selected when analysing EBI data and might lead to miss-conclusion if it is applied on data contaminated with measurement artefacts. The recently proposed Correction Function to eliminate the influence of the Hook Effect from EBI data and the fitting to the real part of the Cole model to extract the Cole parameters have been validated on experimental measurements. The obtained results confirm the feasible experimental use of these promising pre-processing tools that might improve the outcome of EBI applications using Cole model-based analysis.

Place, publisher, year, edition, pages
IEEE Engineering in Medicine and Biology, 2010
Series
IEEE Engineering in Medicine and Biology Society Conference Proceedings, ISSN 1557-170X
Keyword
bioelectric phenomena, electric impedance measurement, medical signal processing, patient diagnosis, patient monitoring, Cole model-based analysis, EBI data, Hook effect correction, electrical bioimpedance, health status, noninvasive assessment, pathophysiological mechanisms, resistance-based Cole fitting
National Category
Medical Laboratory and Measurements Technologies Signal Processing
Identifiers
urn:nbn:se:kth:diva-74129 (URN)10.1109/IEMBS.2010.5627109 (DOI)000287964006240 ()
Conference
Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)
Note
QC 20120215Available from: 2012-02-09 Created: 2012-02-02 Last updated: 2013-09-17Bibliographically approved
4. Cole parameter estimation from total right side electrical bioimpedance spectroscopy measurements: Influence of the number of frequencies and the upper limit
Open this publication in new window or tab >>Cole parameter estimation from total right side electrical bioimpedance spectroscopy measurements: Influence of the number of frequencies and the upper limit
2011 (English)In: 2011 ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY (EMBC), 2011, 1843-1846 p.Conference paper, Published paper (Refereed)
Abstract [en]

Applications based on measurements of Electrical Bioimpedance Spectroscopy (EBIS) analysis are proliferating. The most spread and known application of EBIS is the non-invasive assessment of body composition. Fitting to the Cole function to obtain the Cole parameters, R<sub>0</sub> and R<sub>&#x221E;</sub>, is the core of the EBIS analysis to obtain the body fluid distribution. An accurate estimation of the Cole parameters is essential for the Body Composition Assessment (BCA) and the estimation process depends on several factors. One of them is the upper frequency limit used for the estimation and the other is the number of measured frequencies in the measurement frequency range. Both of them impose requirements on the measurement hardware, influencing largely in the complexity of the bioimpedance spectrometer. In this work an analysis of the error obtained when estimating the Cole parameters with several frequency ranges and different number of frequencies has been performed. The study has been done on synthetic EBIS data obtained from experimental Total Right Side (TRS) measurements. The results suggest that accurate estimations of R<sub>0</sub> and R<sub>&#x221E;</sub> for BCA measurements can be achieved using much narrower frequency ranges and quite fewer frequencies than electrical bioimpedance spectrometers commercially available nowadays do.

Keyword
biomedical equipment, electric impedance measurement, electrochemical impedance spectroscopy, frequency estimation, measurement errors, Cole parameter estimation, bioimpedance spectrometer, body composition assessment, body fluid distribution, error analysis, measurement hardware, total right side electrical bioimpedance spectroscopy measurements
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-74134 (URN)10.1109/IEMBS.2011.6090524 (DOI)000298810001243 ()2-s2.0-84055193230 (Scopus ID)978-1-4244-4121-1 (ISBN)
Conference
33rd Annual International Conference of the IEEE Engineering-in-Medicine-and-Biology-Society (EMBS). Boston, MA. AUG 30-SEP 03, 2011
Note
QC 20120329Available from: 2012-02-02 Created: 2012-02-02 Last updated: 2013-09-17Bibliographically approved
5. Cole Parameter Estimation from the Modulus of the Electrical Bioimpeadance for Assessment of Body Composition: A Full Spectroscopy Approach
Open this publication in new window or tab >>Cole Parameter Estimation from the Modulus of the Electrical Bioimpeadance for Assessment of Body Composition: A Full Spectroscopy Approach
2011 (English)In: Journal of Electrical Bioimpedance, ISSN 1891-5469, E-ISSN 1891-5469, Vol. 2, 72-78 p.Article in journal (Refereed) Published
Abstract [en]

Activities around applications of Electrical Bioimpedance Spectroscopy (EBIS) have proliferated in the past decade significantly. Most of these activities have been focused in the analysis of the EBIS measurements, which eventually might enable novel applications. In Body Composition Assessment (BCA) the most common analysis approach currently used in EBIS is based on the Cole function, which most often requires curve fitting. One of the most implemented approaches for obtaining the Cole parameters is performed in the impedance plane through the geometrical properties that the Cole function exhibit in such domain as depressed semi-circle. To fit the measured impedance data to a semi-circle in the impedance plane, obtaining the Cole parameters in an indirect and sequential manner has several drawbacks. Applying a Non-Linear Least Square (NLLS) iterative fitting on the spectroscopy measurement, obtains the Cole parameters considering the frequency information contained in the measurement. In this work, from experimental total right side EBIS measurements, the BCA parameters have been obtained to assess the amount and distribution of whole body fluids. The values for the BCA parameters have been obtained using values for the Cole parameters estimated with both approaches: circular fitting on the impedance plane and NLLS impedance-only fitting. The comparison of the values obtained for the BCA parameters with both methods confirms that the NLLS impedance-only is an effective alternative as Cole parameter estimation method in BCA from EBIS measurements. Using the modulus of the Cole function as the model for the fitting would eliminate the need for performing a phase detection in the acquisition process, simplifying the hardware specifications of the measurement instrumentation when implementing a bioimpedance spectrometer.

Place, publisher, year, edition, pages
Oslo: University of Oslo, 2011
Keyword
Bioimpedance, spectroscopy measurements, Cole Analysis, Body Composition
National Category
Medical Laboratory and Measurements Technologies Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-73199 (URN)10.5617/jeb.197 (DOI)
Note
QC 20120214Available from: 2012-02-14 Created: 2012-02-01 Last updated: 2017-12-08Bibliographically approved

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Citation style
  • apa
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  • nn-NO
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  • Other locale
More languages
Output format
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  • asciidoc
  • rtf