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Shiraz, A., Khodadad, D., Nordebo, S., Yerworth, R., Frerichs, I., van Kaam, A., . . . Demosthenous, A. (2019). Compressive sensing in electrical impedance tomography for breathing monitoring. Physiological Measurement, 40(3), 1-9, Article ID 034010.
Open this publication in new window or tab >>Compressive sensing in electrical impedance tomography for breathing monitoring
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2019 (English)In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 40, no 3, p. 1-9, article id 034010Article in journal (Refereed) Published
Abstract [en]

Objective: Electrical impedance tomography (EIT) is a functional imaging technique in which cross-sectional images of structures are reconstructed based on boundary trans-impedance measurements. Continuous functional thorax monitoring using EIT has been extensively researched. Increasing the number of electrodes, number of planes and frame rate may improve clinical decision making. Thus, a limiting factor in high temporal resolution, 3D and fast EIT is the handling of the volume of raw impedance data produced for transmission and its subsequent storage. Owing to the periodicity (i.e. sparsity in frequency domain) of breathing and other physiological variations that may be reflected in EIT boundary measurements, data dimensionality may be reduced efficiently at the time of sampling using compressed sensing techniques. This way, a fewer number of samples may be taken. Approach: Measurements using a 32-electrode, 48-frames-per-second EIT system from 30 neonates were post-processed to simulate random demodulation acquisition method on 2000 frames (each consisting of 544 measurements) for compression ratios (CRs) ranging from 2 to 100. Sparse reconstruction was performed by solving the basis pursuit problem using SPGL1 package. The global impedance data (i.e. sum of all 544 measurements in each frame) was used in the subsequent studies. The signal to noise ratio (SNR) for the entire frequency band (0 Hz-24 Hz) and three local frequency bands were analysed. A breath detection algorithm was applied to traces and the subsequent errorrates were calculated while considering the outcome of the algorithm applied to a down-sampled and linearly interpolated version of the traces as the baseline. Main results: SNR degradation was generally proportional with CR. The mean degradation for 0 Hz-8 Hz (of interest for the target physiological variations) was below similar to 15 dB for all CRs. The error-rates in the outcome of the breath detection algorithm in the case of decompressed traces were lower than those associated with the corresponding down-sampled traces for CR >= 25, corresponding to sub-Nyquist rate for breathing frequency. For instance, the mean error-rate associated with CR = 50 was similar to 60% lower than that of the corresponding down-sampled traces. Significance: To the best of our knowledge, no other study has evaluated the applicability of compressive sensing techniques on raw boundary impedance data in EIT. While further research should be directed at optimising the acquisition and decompression techniques for this application, this contribution serves as the baseline for future efforts.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Keywords
breath detection, compressive sensing, electrical impedance tomography
National Category
Computer and Information Sciences Other Medical Sciences not elsewhere specified
Research subject
Computer and Information Sciences Computer Science, Computer Science
Identifiers
urn:nbn:se:lnu:diva-82046 (URN)10.1088/1361-6579/ab0daa (DOI)000463392300006 ()30844770 (PubMedID)2-s2.0-85064239164 (Scopus ID)
Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-08-29Bibliographically approved
Nordebo, S., Mirmoosa, M. & Tretyakov, S. (2019). On the quasistatic optimal plasmonic resonances in lossy media. Journal of Applied Physics, 125(10), 1-11, Article ID 103105.
Open this publication in new window or tab >>On the quasistatic optimal plasmonic resonances in lossy media
2019 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 125, no 10, p. 1-11, article id 103105Article in journal (Refereed) Published
Abstract [en]

This paper discusses and analyzes the quasistatic optimal plasmonic dipole resonance of a small dielectric particle embedded in a lossy surrounding medium. The optimal resonance at any given frequency is defined by the complex valued dielectric constant that maximizes the absorption of the particle under the quasistatic approximation and a passivity constraint. In particular, for an ellipsoid aligned along the exciting field, the optimal material property is given by the complex conjugate of the pole position associated with the polarizability of the particle. In this paper, we employ the classical Mie theory to analyze this approximation for spherical particles in a lossy surrounding medium. It turns out that the quasistatic optimal plasmonic resonance is valid, provided that the electrical size of the particle is sufficiently small at the same time as the external losses are sufficiently large. Hence, it is important to note that this approximation cannot be used for a lossless medium, and which is also obvious, since the quasistatic optimal dipole absorption becomes unbounded for this case. Moreover, it turns out that the optimal normalized absorption cross sectional area of the small dielectric sphere has a very subtle limiting behavior and is, in fact, unbounded even in full dynamics when both the electrical size and the exterior losses tend to zero at the same time. A detailed analysis is carried out to assess the validity of the quasistatic estimation of the optimal resonance, and numerical examples are included to illustrate the asymptotic results.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-81700 (URN)10.1063/1.5085721 (DOI)000461370200005 ()2-s2.0-85062904957 (Scopus ID)
Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-08-29Bibliographically approved
Nordebo, S., Kristensson, G., Mirmoosa, M. & Tretyakov, S. (2019). Optimal plasmonic multipole resonances of a sphere in lossy media. Physical Review B, 99(5), Article ID 054301.
Open this publication in new window or tab >>Optimal plasmonic multipole resonances of a sphere in lossy media
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 5, article id 054301Article in journal (Refereed) Published
Abstract [en]

Fundamental upper bounds are given for the plasmonic multipole absorption and scattering of a rotationally invariant dielectric sphere embedded in a lossy surrounding medium. A specialized Mie theory is developed for this purpose and when combined with the corresponding generalized optical theorem, an optimization problem is obtained which is explicitly solved by straightforward analysis. In particular, the absorption cross section is a concave quadratic form in the related Mie (scattering) parameters and the convex scattering cross section can be maximized by using a Lagrange multiplier constraining the absorption to be non-negative. For the homogeneous sphere, the Weierstrass preparation theorem is used to establish the existence and the uniqueness of the plasmonic singularities and explicit asymptotic expressions are given for the dipole and the quadrupole. It is shown that the optimal passive material for multipole absorption and scattering of a small homogeneous dielectric sphere embedded in a dispersive medium is given approximately as the complex conjugate and the real part of the corresponding pole positions, respectively. Numerical examples are given to illustrate the theory, including a comparison with the plasmonic dipole and quadrupole resonances obtained in gold, silver, and aluminum nanospheres based on some specific Brendel-Bormann (BB) dielectric models for these metals. Based on these BB models, it is interesting to note that the metal spheres can be tuned to optimal absorption at a particular size at a particular frequency.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-80776 (URN)10.1103/PhysRevB.99.054301 (DOI)000457729700001 ()2-s2.0-85061347599 (Scopus ID)
Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-08-29Bibliographically approved
Ivanenko, Y., Custafsson, M., Jonsson, B. L., Luger, A., Nilsson, B., Nordebo, S. & Toft, J. (2019). Passive Approximation and Optimization Using B-Splines. SIAM Journal on Applied Mathematics, 79(1), 436-458
Open this publication in new window or tab >>Passive Approximation and Optimization Using B-Splines
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2019 (English)In: SIAM Journal on Applied Mathematics, ISSN 0036-1399, E-ISSN 1095-712X, Vol. 79, no 1, p. 436-458Article in journal (Refereed) Published
Abstract [en]

A passive approximation problem is formulated where the target function is an arbitrary complex-valued continuous function defined on an approximation domain consisting of a finite union of closed and bounded intervals on the real axis. The norm used is a weighted L-p-norm where 1 <= p <= infinity. The approximating functions are Herglotz functions generated by a measure with Holder continuous density in an arbitrary neighborhood of the approximation domain. Hence, the imaginary and the real parts of the approximating functions are Holder continuous functions given by the density of the measure and its Hilbert transform, respectively. In practice, it is useful to employ finite B-spline expansions to represent the generating measure. The corresponding approximation problem can then be posed as a finite-dimensional convex optimization problem which is amenable for numerical solution. A constructive proof is given here showing that the convex cone of approximating functions generated by finite uniform B-spline expansions of fixed arbitrary order (linear, quadratic, cubic, etc.) is dense in the convex cone of Herglotz functions which are locally Holder continuous in a neighborhood of the approximation domain, as mentioned above. As an illustration, typical physical application examples are included regarding the passive approximation and optimization of a linear system having metamaterial characteristics, as well as passive realization of optimal absorption of a dielectric small sphere over a finite bandwidth.

Keywords
approximation, Herglotz functions, B-splines, passive systems, convex optimization, sum rules
National Category
Mathematics
Research subject
Mathematics, Applied Mathematics
Identifiers
urn:nbn:se:lnu:diva-81228 (URN)10.1137/17M1161026 (DOI)000460127100021 ()2-s2.0-85063407473 (Scopus ID)
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-08-29Bibliographically approved
Ivanenko, Y. & Nordebo, S. (2019). Passive Approximation with High-Order B-Splines. In: Karl‐Olof Lindahl, Torsten Lindström, Luigi G. Rodino, Joachim Toft, Patrik Wahlberg (Ed.), Analysis, Probability, Applications, and Computation: . Paper presented at 11th ISAAC Congress, Växjö (Sweden) 2017 (pp. 83-94). Birkhäuser Verlag
Open this publication in new window or tab >>Passive Approximation with High-Order B-Splines
2019 (English)In: Analysis, Probability, Applications, and Computation / [ed] Karl‐Olof Lindahl, Torsten Lindström, Luigi G. Rodino, Joachim Toft, Patrik Wahlberg, Birkhäuser Verlag, 2019, p. 83-94Conference paper, Published paper (Refereed)
Abstract [en]

Convex optimization has emerged as a well-suited tool for passive approximation. Here, it is desired to approximate some pre-defined non-trivial system response over a given finite frequency band by using a passive system. This paper summarizes some explicit results concerning the Hilbert transform of general B-splines of arbitrary order and arbitrary partitions that can be useful with the convex optimization formulation. A numerical example in power engineering is included concerning the identification of some model parameters based on measurements on high-voltage insulation materials.

Place, publisher, year, edition, pages
Birkhäuser Verlag, 2019
Series
Trends in Mathematics, ISSN 2297-0215, E-ISSN 2297-024X
National Category
Mathematical Analysis
Research subject
Mathematics, Mathematics
Identifiers
urn:nbn:se:lnu:diva-82770 (URN)10.1007/978-3-030-04459-6_8 (DOI)2-s2.0-85065446429 (Scopus ID)978-3-030-04458-9 (ISBN)978-3-030-04459-6 (ISBN)
Conference
11th ISAAC Congress, Växjö (Sweden) 2017
Available from: 2019-05-27 Created: 2019-05-27 Last updated: 2019-08-29Bibliographically approved
Nordebo, S., Dalarsson, M., Khodadad, D., Müller, B., Waldermann, A. D., Becher, T., . . . Bayford, R. (2018). A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing. Journal of Physics D: Applied Physics, 51(20), Article ID 205401.
Open this publication in new window or tab >>A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing
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2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 20, article id 205401Article in journal (Refereed) Published
Abstract [en]

Classical homogenization theory based on the Hashin–Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples based on realistic parameter values and frequency ranges used with electrical impedance tomography (EIT). The theory may be potentially useful for imaging and clinical evaluations in connection with lung EIT for respiratory management and control.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
National Category
Medical Image Processing
Research subject
Natural Science, Medicine
Identifiers
urn:nbn:se:lnu:diva-74401 (URN)10.1088/1361-6463/aabc04 (DOI)
Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2019-07-09Bibliographically approved
Nordebo, S., Gustafsson, M., Ivanenko, Y., Nilsson, B. & Sjöberg, D. (2018). Cylindrical multipole expansion for periodic sources with applications for three-phase power cables. Mathematical methods in the applied sciences, 41(3), 959-965
Open this publication in new window or tab >>Cylindrical multipole expansion for periodic sources with applications for three-phase power cables
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2018 (English)In: Mathematical methods in the applied sciences, ISSN 0170-4214, E-ISSN 1099-1476, Vol. 41, no 3, p. 959-965Article in journal (Refereed) Published
Abstract [en]

This paper presents a c ylindrical multipole expansion for periodic sources with applications for three-phase power cables.It is the aim of the contribution to provide some analytical solutions and techniques that can be useful in the calculation ofcable losses. Explicit analytical results are given for the fields generated by a three-phase helical current distribution andwhich can be computed efficiently as an input to other numerical methods such as, for example , the Method of Moments.It is shown that the field computations are numerically stable at low frequencies (such as 50 Hz) as well as in the quasi-magnetostatic limit provided that sources are divergence-free. The cylindrical multipole expansion is fur thermore usedto derive an efficient analytical model of a measurement coil to measure and estimate the complex valued permeability ofmagnetic steel armour in the presence of a strong skin-effect.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-59497 (URN)10.1002/mma.3992 (DOI)000425834700011 ()2-s2.0-85040728924 (Scopus ID)
Available from: 2016-12-23 Created: 2016-12-23 Last updated: 2019-08-29Bibliographically approved
Nordebo, S., Dalarsson, M., Gustafsson, M. & Sjöberg, D. (2018). On the optimal plasmonic resonances in lossy media. In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials): . Paper presented at 12th International Congress on Artificial Materials for Novel Wave Phenomena-Metamaterials, 27 Aug.-1 Sept. 2018, Espoo, Finland (pp. 296-298). IEEE
Open this publication in new window or tab >>On the optimal plasmonic resonances in lossy media
2018 (English)In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), IEEE, 2018, p. 296-298Conference paper, Published paper (Refereed)
Abstract [en]

An optimal plasmonic resonance is derived for small homogeneous and isotropic inclusions in a lossy surrounding medium. The optimal resonance is given in terms of any particular eigenmode (electrostatic resonance) associated with the double-layer potential for a smooth, but otherwise arbitrary surface.

Place, publisher, year, edition, pages
IEEE, 2018
National Category
Other Physics Topics
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-82118 (URN)10.1109/MetaMaterials.2018.8534081 (DOI)2-s2.0-85058557520 (Scopus ID)978-1-5386-4703-5 (ISBN)978-1-5386-4702-8 (ISBN)978-1-5386-4701-1 (ISBN)
Conference
12th International Congress on Artificial Materials for Novel Wave Phenomena-Metamaterials, 27 Aug.-1 Sept. 2018, Espoo, Finland
Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2019-08-29Bibliographically approved
Ivanenko, Y., Dalarsson, M., Nordebo, S. & Bayford, R. (2018). On the plasmonic resonances in a layered waveguide structure. In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials): . Paper presented at 12th International Congress on Artificial Materials for Novel Wave Phenomena-Metamaterials, 27 Aug.-1 Sept. 2018, Espoo, Finland (pp. 188-190). IEEE
Open this publication in new window or tab >>On the plasmonic resonances in a layered waveguide structure
2018 (English)In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), IEEE, 2018, p. 188-190Conference paper, Published paper (Refereed)
Abstract [en]

An optimal plasmonic resonance and the associated Fröhlich resonance frequency are derived for a thin layer in a straight waveguide in TM mode. The layer consists of an arbitrary composite material with a Drude type of dispersion. The reflection and transmission coefficients of the layer are analyzed in detail. To gain insight into the behavior of a thin plasmonic layer, an asymptotic expansion to the first order is derived with respect to the layer permittivity.

Place, publisher, year, edition, pages
IEEE, 2018
National Category
Other Physics Topics
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-82120 (URN)10.1109/MetaMaterials.2018.8534151 (DOI)2-s2.0-85058549846 (Scopus ID)978-1-5386-4703-5 (ISBN)978-1-5386-4702-8 (ISBN)978-1-5386-4701-1 (ISBN)
Conference
12th International Congress on Artificial Materials for Novel Wave Phenomena-Metamaterials, 27 Aug.-1 Sept. 2018, Espoo, Finland
Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2019-08-29Bibliographically approved
Khodadad, D., Nordebo, S., Mueller, B., Waldmann, A. D., Yerworth, R., Becher, T., . . . Bayford, R. H. (2018). Optimized breath detection algorithm in electrical impedance tomography. Physiological Measurement, 39(9), Article ID 094001.
Open this publication in new window or tab >>Optimized breath detection algorithm in electrical impedance tomography
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2018 (English)In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 39, no 9, article id 094001Article in journal (Refereed) Published
Abstract [en]

Objective: This paper defines a method for optimizing the breath delineation algorithms used in Electrical Impedance Tomography (EIT). In lung EIT the identification of the breath phases is central for generating tidal impedance variation images, subsequent data analysis and clinical evaluation. The optimisation of these algorithms is particularly important in neonatal care since the existing breath detectors developed for adults may give insufficient reliability in neonates due to their very irregular breathing pattern. Approach: Our approach is generic in the sense that it relies on the definition of a gold standard and the associated definition of detector sensitivity and specificity, an optimisation criterion and a set of detector parameters to be investigated. The gold standard has been defined by 11 clinicians with previous experience with EIT and the performance of our approach is described and validated using a neonatal EIT dataset acquired within the EU-funded CRADL project. Main results: Three different algorithms are proposed that are improving the breath detector performance by adding conditions on 1) maximum tidal breath rate obtained from zero-crossings of the EIT breathing signal, 2) minimum tidal impedance amplitude and 3) minimum tidal breath rate obtained from Time-Frequency (TF) analysis. As a baseline the zero crossing algorithm has been used with some default parameters based on the Swisstom EIT device. Significance: Based on the gold standard, the most crucial parameters of the proposed algorithms are optimised by using a simple exhaustive search and a weighted metric defined in connection with the Receiver Operating Characterics (ROC). This provides a practical way to achieve any desirable trade-off between the sensitivity and the specificity of the detectors.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
National Category
Medical Engineering Medical Equipment Engineering
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-77552 (URN)10.1088/1361-6579/aad7e6 (DOI)000444050400001 ()30074906 (PubMedID)2-s2.0-85054669051 (Scopus ID)
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2019-08-29Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7018-6248

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