Abstract

This thesis is about investigating a potential imaging modality, magneto-acousto-electrical tomography (MAET), to provide high-spatial-resolution images of lead field current density and electrical impedance of biological tissues. A lead field current density distribution is the one obtained when a current/voltage source is applied to a sample via a pair of electrodes. The lead field current density distribution can potentially be used to obtain electrical impedance distribution which is helpful in differentiating normal and cancerous tissues. To image lead filed current density, instead of directly applying a current/voltage source to the sample, the sample is placed in a static magnetic field and an ultrasound is focused on it to simulate a point like current dipole source in the focal zone. Electrodes are used to detect the voltage/current generated by the ultrasound in the sample, which according to the reciprocity theorem is proportional to a component of the lead field current density.

Highlights

  • 1.1 Electrical properties of a biological tissueThe biological tissue consists of cells and extra-cellular fluid

  • Magnetic resonance electrical impedance tomography [18] is based on the measurements of current density distribution inside a subject body using magnetic resonance imaging (MRI)

  • magneto-acousto-electrical tomography (MAET) signals are only observed when the ultrasound pulse crosses the interfaces [22-24]. This is a fundamental limitation of MAET which needs to be solved in order to reconstruct the electrical impedance from current density at every point of the sample

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Summary

Electrical properties of a biological tissue

The biological tissue consists of cells and extra-cellular fluid. The constituents of a tissue determine its electrical properties. The cells occupy roughly 80% of the tissue volume and contain intra-cellular fluid inside a lipid membrane. The extra-cellular fluid is the · medium surrounding the cells. It contains proteins, electrolytes, plasma and the interstitial fluid. The cell contains the protoplasm that contains the cytosol, the organelles and the nucleus of the cell as shown in figure 1.1 [1]

Charge carriers in a tissue
Cellular plasma membrane
Tissue dielectricity and conductivity
Frequency dependence of impedance
Equivalent circuit model of a biological cell
Electrical properties of a cancerous tissue
Electrical impedance imaging
Hypothesis
Previous studies similar to MAET
Chapter 2
Discrete model
Experimental setup and methods
Field _profile of the transducers
Field profile of 1 MHz transducer
Verification of MAET signals
MAET signal from a single point
MAET images
Cancellation of MAET signals in the interior of the sample
Imaging current density in a thin gel phantom sample with MAET
Improvement of SNR by CHIRP
MAET images of biological tissues
Findings
Challenges and Conclusions

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