Diffusion Tensor Imaging : Applications

Diffusion Tensor Imaging (DTI).

Diffusion image measures the random motion of water (and other liquids with hydrogen). DTI is an important tool because it is sensitive to acute brain injury. With DTI we could see some strokes that could not be seen in using the MRI. DTI is correlated with the white matter integrity.


In the flow of water, the diffusion is max when the liquid is in line, and the value of signal captured is minimal because there is not any block of the water. At the position where the diffusion is minimal, the molecule of the water is blocked and the signal captured is maximal.

In order to describe the diffusion of water at each point, we consider three values of threes dimensions (directions). In DTI, we use the term tensor to represent the diffusion at each point. Each tensor is a matrix. We could divise into three directions with the representation of three eigen vectors. But which eigen vector corresponds which direction. We use the value of eigen to know the direction of fiber.

If we collect more directions, the value of tensor is more accurate. The increasing of directions does not cause the increasing of the time of acquistion, and the patient could moves their heads at each time of collection.

Coloring the DTI

We choose the largest eigen value.
The principal eigen is colored by the code map
The blue is used for the superior - inferior. The green is for anterior - posterior. The red is for the left and right.

Mesurement

We use some term to mesure the DTI.
Apparent diffusion coefficient (ADC).
FA (fractional anisotropy). The portion of the diffusion tensor on the anisotropy. FA is sensitive with the low value of diffusion anisotropy.
RA (Relative anisotropy). The portion of the anisotropic vs iostropic.
VR (volume radio). The diffusion ellipsoid volume vs the sphere (radius). VR is sensitive with the high value of diffusion anisotropy.
When FA = 0 and RA = 0, the tensor is medium. When FA goes to 1 and RA goes to sqrt(2), the tensor goes to higher symmetric anisotropy.
VR varies from 1 (diffusion) to 0. They use 1-VR is more often.

Applications
We use DTI for the diagnostic neuroradiology.

• Cerebral ischemia
• Brain maturation
• Traumatic brain injury
• Epilepsy
• Multiple sclerosis
• Alzheimer 's disease
• Brain tumors
• Metabolic disorders
• Leukoaraiosis and wallerium degeneration

References:

1.http://www.cabiatl.com/CABI/resources/dti-analysis/
2.Diffusion tensor imaging of the brain: review of clinical applications.P C Sundgren, Q Dong, D Gómez-Hassan, S K Mukherji, P Maly, R Welsh Neuroradiology. 2004 May; 46(5): 339–350. Published online 2004 April 21. doi: 10.1007/s00234-003-1114-x