MR tractography

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MR Tractography (also called DTI Tractography is an advanced MRI technique that reconstructs and visualizes white matter fiber tracts in vivo, based on anisotropic diffusion of water molecules.

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Provides 3D maps of white matter pathways → useful in research, neurosurgical planning, and neuro-oncology.

Principle

In white matter, water diffuses preferentially along axonal fibers (anisotropic diffusion).
Diffusion Tensor Imaging (DTI) models diffusion in multiple directions, creating a tensor at each voxel.
From these tensors:
- Fractional Anisotropy (FA): Degree of directional diffusion (0 = isotropic, 1 = completely anisotropic).
- Mean Diffusivity (MD): Average diffusion regardless of direction.
By connecting voxels with similar diffusion orientation, tractography algorithms reconstruct fiber bundles.

Techniques

Techniques	Key features
Deterministic Tractography	• Follows the principal diffusion direction from voxel to voxel.
• Produces clear tracts but may miss crossing/kissing fibers.
Probabilistic Tractography	• Incorporates uncertainty in fiber orientation.
• Better for complex regions (crossing fibers, lesions).
Advanced Models
(beyond DTI)	• HARDI (High Angular Resolution Diffusion Imaging).
• Q-ball imaging.
• Diffusion Spectrum Imaging (DSI).
• Constrained Spherical Deconvolution (CSD).

Clinical Applications

1. Pre-surgical Planning

Brain tumor resection (e.g., gliomas near eloquent tracts).
Epilepsy surgery.
AVM or cavernoma resections near white matter tracts.
Ensures preservation of motor, speech, and visual pathways.

2. Stroke & Demyelination

Identifies white matter tract disruption.