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Cole Parameter Estimation from the Modulus of the Electrical Bioimpeadance for Assessment of Body Composition: A Full Spectroscopy Approach
KTH, School of Technology and Health (STH), Medical sensors, signals and systems (MSSS).
Department of Theory of the Signal and Communications. (Applied Signal Processing)
KTH, School of Technology and Health (STH), Medical sensors, signals and systems (MSSS).ORCID iD: 0000-0002-6995-967X
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. Vol. 2, 72-78 p.
Keyword [en]
Bioimpedance, spectroscopy measurements, Cole Analysis, Body Composition
National Category
Medical Laboratory and Measurements Technologies Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-73199DOI: 10.5617/jeb.197OAI: oai:DiVA.org:kth-73199DiVA: diva2:488632
Note
QC 20120214Available from: 2012-02-14 Created: 2012-02-01 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Model Based Enhancement of Bioimpedance Spectroscopy Analysis: Towards Textile Enabled Applications
Open this publication in new window or tab >>Model Based Enhancement of Bioimpedance Spectroscopy Analysis: Towards Textile Enabled Applications
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
Physiological measurements, Bioimpedance, modelling, textiles
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-90884 (URN)978-91-7501-230-8 (ISBN)
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
2. Improvements in Bioimpedance SpectroscopyData Analysis: Artefact Correction, ColeParameters, and Body Fluid Estimation
Open this publication in new window or tab >>Improvements in Bioimpedance SpectroscopyData Analysis: Artefact Correction, ColeParameters, and Body Fluid Estimation
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The estimation of body fluids is a useful and common practice in the status assessment of diseasemechanisms and treatments. Electrical bioimpedance spectroscopy (EBIS) methods are non-invasive,inexpensive, and efficient alternatives for the estimation of body fluids. However, these methods areindirect, and their robustness and validity are unclear.Regarding the recording of measurements, a controversy developed regarding a spectrum deviationin the impedance plane, which is caused by capacitive leakage. This deviation is frequentlycompensated for by the extended Cole model, which lacks a theoretical basis; however, there is nomethod published to estimate the parameters. In this thesis, a simplified model to correct thedeviation was proposed and tested. The model consists of an equivalent capacitance in parallel withthe load.Subsequently, two other measurement artefacts were considered. Both artefacts were frequentlydisregarded with regard to total body and segmental EBIS measurements as their influence isinsignificant with suitable skin-electrode contact. However, this case is not always valid, particularlyfrom a textile-enabled measurement system perspective. In the estimation of body fluids, EBIS dataare fitted to a model to obtain resistances at low and high frequencies. These resistances can berelated to body fluid volumes. In order to minimise the influence of all three artefacts on theestimation of body fluids and improve the robustness and suitability of the model fitting the differentdomains of immittance were used and tested. The conductance in a reduced frequency spectrum wasproposed as the most robust domain against the artefacts considered.The robustness and accuracy of the method did not increase, even though resistances at low and highfrequencies can be robustly estimated against measurement artefacts. Thus, there is likely error in therelation between the resistances and volumes. Based on a theoretical analysis, state of the artmethods were reviewed and their limitations were identified. New methods were also proposed. Allmethods were tested using a clinical database of patients involved in growth hormone replacementtherapy. The results indicated EBIS are accurate methods to estimate body fluids, however they haverobustness limits. It is hypothesized that those limits in extra-cellular fluid are primarily due toanisotropy, in total body fluid they are primarily due to the uncertainty ρi, and errors in intra-cellularfluid are primarily due to the addition of errors in extracellular and total body fluid. Currently, theseerrors cannot be prevented or minimised. Thus, the limitations for robustness must be predicted priorto applying EBIS to estimate body fluids.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 83 p.
Series
Trita-STH : report, ISSN 1653-3836 ; 2013:7
Keyword
Bioimpedance, Cole, Body Fluid
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-128529 (URN)978-91-7501-874-4 (ISBN)
Public defence
2013-10-04, Sal 3-264, Alfred Nobels allé 10, Fremingsberg, 13:00 (English)
Opponent
Supervisors
Note

QC 20130917

Available from: 2013-09-17 Created: 2013-09-12 Last updated: 2013-09-17Bibliographically approved

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