A review of errors in multi-frequency EIT instrumentation

McEwan, Alistair; Cusick, G.; Holder, David

doi:10.1088/0967-3334/28/7/s15

Cited by 131 publications

(92 citation statements)

References 54 publications

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“…MHz [10]- [15]. In these methods, current is either injected into the body by surface electrodes (EIT), or induced in the body using external coils (MIT), and data is measured either on the surface of the body or outside the body.…”

Section: Motivationmentioning

confidence: 99%

Convection-Reaction Equation Based Magnetic Resonance Electrical Properties Tomography (cr-MREPT)

Hafalir

Oran

Gürler

et al. 2014

IEEE Trans. Med. Imaging

197

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Tomographic imaging of electrical conductivity and permittivity of tissues may be used for diagnostic purposes as well as for estimating local specific absorption rate (SAR) distributions. Magnetic Resonance Electrical Properties Tomography (MREPT) aims at noninvasively obtaining conductivity and permittivity images at RF frequencies of MRI systems. MREPT algorithms are based on measuring the B 1 field which is perturbed by the electrical properties of the imaged object. In this study, the relation between the electrical properties and the measured B + 1 field is formulated, for the first time as, the well-known convection-reaction equation. The suggested novel algorithm, called "cr-MREPT", is based on the solution of this equation, and in contrast to previously proposed algorithms, it is applicable in practice not only for regions where electrical properties are relatively constant but also for regions where they vary. The convection-reaction equation is solved using a triangular mesh based finite difference method and also finite element method (FEM).The convective field of the convection-reaction equation depends on the spatial derivatives of the B + 1 field. In the regions where the magnitude of convective field is low, a spot-like artifact is observed in the reconstructed conductivity and dielectric permittivity images. For eliminating this artifact, two different methods are developed, namely "constrained cr-MREPT" and "double-excitation cr-MREPT". In the constrained cr-MREPT method, in the region where the magnitude of convective field is low, the electrical properties are reconstructed by neglecting the convective term in the equation. The obtained solution is used as a constraint for solving electrical properties in the whole domain. In the double-excitation cr-MREPT method, two B 1 excitations, which create two convective field distributions having low magnitude of convective field in different iii iv locations, are applied separately. The electrical properties are then reconstructed simultaneously using data from these two applied B + 1 field.These methods are tested with both simulation and experimental data from phantoms. As seen from results, successful electrical property reconstructions are obtained in all regions including electrical property transition region. The performance of cr-MREPT method against noise is also investigated.

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Section: Motivationmentioning

confidence: 99%

Convection-Reaction Equation Based Magnetic Resonance Electrical Properties Tomography (cr-MREPT)

Hafalir

Oran

Gürler

et al. 2014

IEEE Trans. Med. Imaging

197

View full text Add to dashboard Cite

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“…Absolute imaging is theoretically possible, but is computationally intensive and very sensitive to errors resulting from inaccurate boundary geometry, electrode positions and other sources of systematic artefacts in measured data (McEwan et al, 2007;Seo et al, 2008). The simple frequency-difference method, which reconstructs the EIT images from relative data referred to a certain frequency using a linear method, was proven that it can work in a homogeneous and frequency invariant background (Packham et al, 2012).…”

Section: Mfeit Methodsmentioning

confidence: 99%

“…As such, MFEIT offers a potential solution, as images can be produced from data collected at a single given point in time. However, MFEIT application is more challenging due to the high sensitivity of its solution to modelling and instrumentation errors (Kolehmainen et al, 1997;McEwan et al, 2007;Malone et al, 2014b) .…”

Section: Introductionmentioning

confidence: 99%

Multifrequency electrical impedance tomography with total variation regularization

et al. 2015

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Abstract. Multifrequency Electrical Impedance Tomography (MFEIT) reconstructs the distribution of conductivity by exploiting the dependence of tissue conductivity on frequency. MFEIT can be performed on a single instance of data, making it promising for applications such as stroke and cancer imaging, where it is not possible to obtain a 'baseline' measurement of healthy tissue. A nonlinear MFEIT algorithm able to reconstruct the volume fraction distribution of tissue rather than conductivities has been developed previously. For each volume, the fraction of a certain tissue should be either 1 or 0; this implies that the sharp changes of the fractions, representing the boundaries of tissue, contain all the relevant information However, these boundaries are blurred by traditional regularisation methods employing 2 l norm. The Total Variation (TV) regularisation can overcome this problem, but it is difficult to solve due to its non-differentiability. As the fraction must be between 0 and 1, this imposes a constraint on the MFEIT method based on the fraction model. Therefore, a constrained optimisation method capable of dealing with non-differentiable problems is required. We propose a new constrained TV regularised method, to solve the fraction reconstruction problem, based on the Primal and Dual Interior Point Method (PDIPM) method. The noise performance of the new MFEIT method is analysed using simulations on a 2D cylindrical mesh. Convergence performance is also analysed, through experiments using a cylindrical tank. Finally, simulations on an anatomically realistic head-shaped mesh are demonstrated. The proposed MFEIT method with TV regularisation shows higher spatial resolution, particularly at the edges of the perturbation, and stronger noise robustness, and its image noise and shape error are 20% to 30% lower than the traditional fraction method.

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“…predictability of constant current with the noise advantages, the current source are commonly employed on EIS systems as is utilized by Kyung Hee (IIRC & Mk1); Oxford Brookes (OXBACT5); Rensselaer (ACT4); Sheffield (Mk3.5); UCL (Mk2.5&1b) and also the Leicester group (Mk3) [1][2][3][4][5][6][7] . The enhancement of the EIS system focuses on developing electrical and electronic instrumentations to improve the accuracy of the transfer impedance measurements to make them operate up to high frequency for the purpose of measuring impedivity and conductivity of different tissues types [8][9][10] . The transfer impedance measurement is the ratio between current injections and voltage measurements obtained from the subject under test or a biological tissue sample to images the distribution of impedivity.…”

Section: Introductionmentioning

confidence: 99%

Current source enhancements in Electrical Impedance Spectroscopy (EIS) to cancel unwanted capacitive effects

et al. 2017

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Electrical Impedance Spectroscopy (EIS) has emerged as a non-invasive imaging modality to detect and quantify functional or electrical properties related to the suspicious tumors in cancer screening, diagnosis and prognosis assessment. A constraint on EIS systems is that the current excitation system suffers from the effects of stray capacitance having a major impact on the hardware subsystem as the EIS is an ill-posed inverse problem which depends on the noise level in EIS measured data and regularization parameter in the reconstruction algorithm. There is high complexity in the design of stable current sources, with stray capacitance reducing the output impedance and bandwidth of the system. To confront this, we have designed an EIS current source which eliminates the effect of stray capacitance and other impacts of the capacitance via a variable inductance. In this paper, we present a combination of operational CCII based on a generalized impedance converter (OCCII-GIC) with a current source. The aim of this study is to use the EIS system as a biomedical imaging technique, which is effective in the early detection of breast cancer. This article begins with the theoretical description of the EIS structure, current source topologies and proposes a current conveyor in application of a Gyrator to eliminate the current source limitations and its development followed by simulation and experimental results. We demonstrated that the new design could achieve a high output impedance over a 3MHz frequency bandwidth when compared to other types of GIC circuits combined with an improved Howland topology.

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A review of errors in multi-frequency EIT instrumentation

Cited by 131 publications

References 54 publications

Convection-Reaction Equation Based Magnetic Resonance Electrical Properties Tomography (cr-MREPT)

Convection-Reaction Equation Based Magnetic Resonance Electrical Properties Tomography (cr-MREPT)

Multifrequency electrical impedance tomography with total variation regularization

Current source enhancements in Electrical Impedance Spectroscopy (EIS) to cancel unwanted capacitive effects

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