Anisotropy measure from three diffusion-encoding gradient directions.

Area of Science:

• Neuroimaging
• Diffusion MRI
• Medical Physics

Background:

• Diffusion MRI (DMRI) is crucial for mapping brain white matter architecture.
• Current DMRI methods often require numerous gradient directions, increasing acquisition time.
• Estimating diffusion anisotropy and orientation efficiently remains a key challenge.

Purpose of the Study:

• To propose and validate a novel method for assessing diffusion anisotropy and orientation in the brain.
• To demonstrate the feasibility of obtaining this information using a minimal number of diffusion-encoding directions (3 orthogonal gradients).
• To introduce Diffusion Anisotropy (DiA) as a metric for this purpose.

Main Methods:

• The study utilizes the Diffusion Anisotropy (DiA) metric, which quantifies the deviation of a diffusion signal from its isotropic equivalent.
• The method is based on a Spherical Harmonics formulation, enabling estimation with only 3 orthogonal directions.
• Acquisitions from a public database were used for validation, alongside proposed simplifications and color-coding representations.

Main Results:

• The DiA method successfully provided anisotropy information from white matter using only 3 diffusion-encoding directions.
• While reduced acquisition led to increased data variability and underestimation for misaligned tracts, the core calculation of anisotropy was feasible.
• The method is compatible with existing DMRI protocols and offers complementary orientation information.

Conclusions:

• Diffusion anisotropy and orientation can be reliably estimated from DMRI using as few as 3 gradient directions with the DiA method.
• This approach significantly reduces acquisition time and complexity compared to traditional methods.
• DiA holds promise for faster, more accessible brain diffusion imaging, especially in applications requiring rapid acquisitions.