Synopsis

This course will present methods of imaging and mapping tissue electrical properties (Electric Properties Mapping, EPM) using MRI. An overview of the characteristics underlying tissue electrical properties will be given followed by a brief summary of methods that have been used to measure them. Finally, the diverse approaches, present applications and emerging areas within EPM using MRI will be presented and described.

Target Audience

The target audience of this presentation is those who are interested in testing methods for Acquiring and Reconstructing Electrical Property Images. It would be appropriate for graduate students beginning in this area or researchers curious to understand this alternative contrast.

Objectives and Outcomes

The objective of the presentation is to describe imaging and reconstruction processes for EPM, and to illustrate applications of EPM methods in neuroscience and other relevant fields.
After participating in the course, attendees should have a good overview of different approaches used to image EPM and of the potential of EPM to extend existing MRI contrasts.
Additionally, attendees may find the books listed in the reference list useful sources of information about methods of imaging electrical properties.

Significance and Purpose

The electrical properties of the human body are sensitive indicators of many important determinants of physiological state, including ionic concentrations, ionic mobility, cell density, cell type, and the presence of absence of disease. EPM therefore provides a new and distinct contrast that can be used to characterize tissues using MRI.
EPM methods are increasingly being used in neuroimaging to non-invasively determine conductivities at frequencies similar to those experienced by endogenous brain activity. These conductivity maps have application in numerous areas, including to the improvement of EEG-based source localization methods and better targeting of neuromodulation strategies such as transcranial AC or DC stimulation. EPM methods can also be used to image properties at higher frequencies and at the Larmor frequency. Each technique provides a unique view of tissue properties that can be used in diagnosis or modeling.

Topics Covered

The course will start by describing the origin and characteristics of tissue electrical properties. The different methods to measure electrical properties in the laboratory will be described, followed by an overview of electrical impedance tomography, a technique used to image properties using electrode networks only. Finally, a detailed examination of the different EPM approaches used in MRI will be presented. The topics to be presented are:

• Electrical Properties of Tissues
  

- Conductivities of aqueous solutions and their dependence on ionic concentration, mobility and temperature.
- Relationship between conductivity and diffusion properties
- Membrane properties
- Tissue properties as a function of frequency

• Laboratory Measurement of Tissue Electrical Properties

- Low and high frequency conductivity measurement methods and compensation
- Overview of tissue properties and characteristics.

• Electrical Impedance Tomography

- Approaches and Applications
- Reconstruction methods and Results
- Advantages of MRI measurement

• EPM Methods using MRI

- Current Density Imaging
§ Basic principles
§ Results
§ Noise characteristics of CTI
- Magnetic Resonance Electrical Impedance Tomography
§ Single component measurement strategy
§ SNR optimization
§ J-substitution algorithm
§ Harmonic B_z algorithm
§ Projected current density
§ Diffusion Tensor MREIT
§ Emerging Methods in MREIT
- Electric Properties Tomography (EPT)
§ Principles of EPT
§ Conductivity Measurement with EPT
§ Permittivity Measurement with EPT
§ Applications of EPT in medicine
§ Emerging methods in EPT
- Conductivity Tensor Imaging (CTI)
§ Principles of CTI
§ Applications of CTI

• Conclusions

Acknowledgements

This work was supported by the National Institute of Neurological Disorders and Stroke and the National Institute of Mental Health of the National Institutes of Health under awards R21 NS081646, R01 NS0077004 and RF1 MH114290 to RJS.