Some practical biological phantoms for calibrating multifrequency electrical impedance tomography

Area of Science:

• Biomedical Engineering
• Electrical Engineering
• Materials Science

Background:

• Multifrequency electrical impedance tomography (EIT) systems require reliable calibration materials.
• Ideal calibration materials should be easy to use, stable, and possess complex impedance similar to biological tissues.

Purpose of the Study:

• To assess the suitability of inorganic and biological materials for calibrating multifrequency EIT systems.
• To identify stable materials with complex impedance characteristics comparable to biological tissues.

Main Methods:

• Materials were assessed using a Hewlett-Packard 4284A impedance analyzer and a Sheffield Mark 1 EIT system.
• Three groups of materials were tested: inorganic suspensions (barium titanate, polystyrene, fumed silica), cucumber in KCl solution, and polyurethane sponge in packed red blood cells.

Main Results:

• Inorganic materials exhibited phase angles below 1 degree, rendering them unsuitable.
• Cucumber cortex showed a phase angle of 40 degrees at 50 kHz, with contrast adjustable via KCl concentration.
• Packed red blood cells had a phase angle of approximately 25 degrees at 1 MHz. Polyurethane sponge in red cells demonstrated suitable resistivity and permittivity.

Conclusions:

• Biological materials, specifically cucumber and polyurethane sponge in red blood cells, are suitable for multifrequency EIT calibration.
• The red blood cell system offers superior stability and incorporates capacitance in both the medium and test object.
• For accuracy exceeding +/- 15%, direct impedance analysis is recommended before imaging.