Tissue electrical properties: principles and their relation to magnetization
Rosalind Sadleir1
1Arizona State University, United States

Synopsis

Keywords: Contrast mechanisms: Non-proton, Transferable skills: Metrology of MRI, Physics & Engineering: Multimodal

MRI is increasingly used to provide quantitative measurements and images of electromagnetic property contrasts. Effects of tissue susceptibility and electrical conductivity properties become more apparent as main magnetic fields increase. Electrical properties contain rich information about the microscopic tissue environment and membrane structure in addition to ionic composition. We will describe the spectral properties and contrasts of tissues; explain how MR sequences can be adapted to isolate them, and how they can be analyzed; and show how these properties can potentially enhance understanding of normal and pathological processes.

Introduction

  • As MRI systems move to higher fields, effects of both magnetic and electrical inhomogeneities become more apparent. These may be regarded as artifacts, but can also be harnessed to provide a deeper understanding of tissue structure.

Tissue Electrical Properties and Maxwell's Equations

  • An overview of tissue electrical conductivity and permittivity and spectra shows that there is a wide range (at least a thousandfold) of tissue contrasts. Interaction of these properties with Maxwell's equations will be demonstrated.

Potential Applications and Synergies

  • Differences in electrical properties occur because of pathology, and these can be exploited to improve or complement existing diagnoses. There are also opportunities to measure treatment effects as they are applied within a scanner.

Electrical Conductivity Imaging Techniques

  1. Measurements Using Currents
  • Current Density Imaging
  • Electric Properties Tomography - Properties at the Larmor frequency
  • MR Electrical Impedance Tomography (MREIT) - Properties at low frequencies
  • Diffusion Tensor MREIT
2. Confluence of Diffusion and Electrical Properties
3. Measurement without Currents
  • Conductivity Tensor Imaging

Practical Measurement of Electrical Conductivity

  1. Measurements using externally applied currents
  2. Measurements using B1 mapping
  3. Measurements derived from diffusion or water mapping.

Current work in MR-based electrical conductivity measurement

  • Future directions for electromagnetic mapping.

Acknowledgements

Kyung Hee University

NIH/NIBIB 1R21EB030858

NIH/NIMH 1RF1MH114290

NIH/NINDS 1R21NS081646

NIH/NINDS R01NS07704

References

SADLEIR, R. J. & MINHAS, A. 2022. Electrical Properties of Tissues: Quantitative Magnetic Resonance Mapping, Springer. Advances in Experimental Medicine and Biology, 1380
Proc. Intl. Soc. Mag. Reson. Med. 31 (2023)