Biological tissue characterization by magnetic induction spectroscopy (MIS): requirements and limitations

Area of Science:

• Biophysics
• Medical Physics
• Biomedical Engineering

Background:

• Magnetic induction spectroscopy (MIS) measures passive electrical properties (PEP) like conductivity (sigma), permittivity (epsilon), and permeability (mu) contactless.
• Previous research often focused on either conductive or magnetic properties separately.
• A unified approach is needed to leverage MIS for comprehensive tissue analysis.

Purpose of the Study:

• To synthesize conductive and magnetic aspects of MIS for biological tissue analysis.
• To demonstrate the application of a single MIS system for monitoring brain edema and estimating hepatic iron stores.
• To analyze system requirements and error sources for MIS using a planar gradiometer (PGRAD).

Main Methods:

• Developed equations to determine MIS sensitivity based on biological object PEP.
• Utilized a planar gradiometer (PGRAD) as the detector in the MIS system.
• Investigated four key error sources: moving conductors, thermal drifts, lateral displacements, and receiver phase drifts.

Main Results:

• All analyzed error sources minimally affected the imaginary part of the measured field (related to conductivity).
• Errors had a significantly lesser impact on the imaginary part compared to the real part (related to permittivity and permeability).
• The technique shows promise for resolving physiological changes in electrical conductivity with appropriate hardware and signal processing.

Conclusions:

• MIS can effectively resolve changes in electrical conductivity of biological tissues.
• Measuring magnetic permeability and permittivity changes requires advanced techniques like chopping.
• The presented MIS approach offers a versatile tool for non-invasive biomedical diagnostics.