Conductivity Tensor Imaging of the Human Brain Using Water Mapping Techniques.

Area of Science:

• Medical Imaging
• Biophysics
• Neuroscience

Background:

• Conductivity tensor imaging (CTI) maps brain conductivity using MRI, but conventional methods (MR-EPT) yield low signal-to-noise ratio (SNR) and limited resolution.
• Artifacts at tissue boundaries and poor spatial resolution hinder the diagnostic potential of current CTI techniques.

Purpose of the Study:

• To develop an improved CTI methodology independent of MR-Electric Properties Tomography (MR-EPT).
• To enhance spatial resolution, reduce artifacts, and improve SNR in CTI brain mapping.
• To establish a novel framework for accurate conductivity tensor mapping in vivo.

Main Methods:

• A novel CTI approach was developed, combining high-frequency conductivity from water maps with multi b-value diffusion tensor imaging (DTI) data.
• A specialized pipeline was implemented for optimizing diffusion data pre-processing and fitting a multi-compartment diffusivity model.
• The methodology relies on the assumption that water concentration uniquely determines electrical conductivity.

Main Results:

• The optimized pre-processing and fitting procedures significantly improved the quality of conductivity maps.
• Reproducible conductivity measurements were achieved across healthy participants, with specific values reported for gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF).
• An in-plane isotropic spatial resolution close to 1 mm was attained, reducing partial volume effects and improving discrimination between GM and WM.

Conclusions:

• The proposed CTI framework offers superior spatial resolution and tissue discrimination compared to conventional MR-EPT methods.
• This technique provides reproducible conductivity values in the healthy brain, potentially serving as a biomarker for neurological conditions.
• The improved CTI may enhance head tissue compartment definition for electroencephalography/magnetoencephalography (EEG/MEG) source imaging and aid in diagnosing conditions like stroke and tumors.