Electrode Models under Shape Deformation in Electrical Impedance - - PowerPoint PPT Presentation

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Electrode Models under Shape Deformation in Electrical Impedance - - PowerPoint PPT Presentation

Sep 21, 2022 204 likes •410 views

Electrode Models under Shape Deformation in Electrical Impedance Tomography Alistair Boyle and Andy Adler Systems and Computer Engineering, Carleton University, Ottawa, Canada Motivation Using Difference EIT, most unknowns do not affect

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Electrode Models under Shape Deformation

in Electrical Impedance Tomography

Alistair Boyle and Andy Adler

Systems and Computer Engineering, Carleton University, Ottawa, Canada

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Motivation

  • Using Difference EIT, most unknowns do not affect

image quality as long as they are not changing:

– e.g. contact impedance, – electrode area, or – electrode location [1]

  • ... but what happens when the body is deforming?

[1] Barber & Brown, Errors in reconstruction of resistivity images using a linear reconstruction technique, 1988, Clin. Phys. Physiol. Meas

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Motivation

  • Many shape deformations result in artifacts[2]
  • Why are conformal changes interesting?

– Isotropic conductivities remain isotropic and do

not introduce artifacts [3]

  • ... but is this true for all electrode models?

– We compare electrode model behaviour when the

body is deforming, in simulation

[3] WRB Lionheart, Boundary Shape and Electrical Impedance Tomography, 1998, IOP Journal Inv. Problems [2] A Adler et al, Impedance imaging of lung ventilation: do we need to account for chest expansion?, 1996, IEEE BME

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Mathematical Electrode Models

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Mathematical Electrode Models

Continuous Model

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Mathematical Electrode Models

Gap Model

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Mathematical Electrode Models

Shunt Model

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Mathematical Electrode Models

Complete Electrode Model

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Finite Element Method Electrode Models

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Finite Element Method Electrode Models

Point Electrode Model

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Finite Element Method Electrode Models

Shunt Electrode Model

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Finite Element Method Electrode Models

Complete Electrode Model

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Focus

– PEM does not introduce artifacts.

What about CEM? Complete Electrode Model Point Electrode Model

  • With respect to conformal deformations:

(PEM) (CEM)

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Conformal Deformations

Dilation Complex

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Electrode Deformation

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Electrode Deformation and Contact Impedance

ringing!

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Electrode Contact Impedance

2=∣∣

3≤≤3

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Electrode Contact Impedance

2=1 3≤≤3

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Discussion:

Electrode Models under Shape Deformation

  • Using the CEM, reconstructions of conformal

deformations can result in artifacts

  • Changes in contact impedance and electrode area

can result in similar artifacts

  • Increases in contact impedance do not result in

reconstruction artifacts

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Thank You

Questions?