Dti in epilepsy

1. Evaluation of epilepsy using
Diffusion tensor imaging

2. Within the central nervous system, water diffusion is more anisotropic in
white matter and isotropic in gray matter and CSF
This property can be exploited to highlight white matter changes in various
pathological processes
DTI is a powerful tool for assessment of microstructural integrity of the
white matter qualitatively as well as quantitatively

3. • DTI enables the measurement of the restricted diffusion of water in tissues in order to
produce neural tract images.
• It generates multiple parameters like apparent diffusion coefficient (ADC) and fractional
anisotropy (FA), which can be used to study the pathological as well as the normal
appearing areas of the brain.
• In focal epilepsy widespread DTI abnormalities have been reported. In mesial
temporal lobe sclerosis(MTLS) patients, although conventional MRI unilateral
involvement of the hippocampal sclerosis, DTI was found to be useful in
demonstrating the spread of epileptiform activity to other regions of brain as well.

4. Principle of DTI
Water molecules in biological tissues are in constant movement,
governed by two major principles:
a. Fick`s Law: Random diffusion due to
concentration differences
b. Temperature and ion-ion interactions
Diffusion of water molecules can be restricted in various
pathological conditions

5. Random Brownian
movement
Free diffusion Restricted diffusion

6. Diffusion imaging
Detects the molecular motion of water and allows for quantitative
assessement of the freedom of diffusion
The addition of 2 strong, symmetric gradients to a echoplanar
sequence helps in differentiation of stationary from mobile water
molecules
If there is net movement of spins (i.e. if diffusion occurs) between the
2 gradients, signal attenuation occurs

7. ANISOTROPIC – Diffusion preferentially
increased in some directions
ISOTROPIC- Equal diffusion in
all directions
Diffusion Tensor imaging

8. Tensor is a mathematical model of directional anisotropy of diffusion
Acquisition in at least 6 directions is required, but clinically
up to 30 directions are used
 From the tensor, we can calculate:
a. Direction of greatest diffusion
b. Degree of anisotropy
c. Diffusion constant in any direction

9. • Index of diffusion – mean diffusivity.
• Index of anisotropic diffusion – Functional anisotropy -
• Calculated FA value ranges from 0 – 1 :
FA= 0 → Diffusion is spherical (i.e. isotropic)
FA= 1 → Diffusion is tubular (i.e. anisotropic)

10. Diffusion Kurtosis imaging
Mean Diffusivity (MD) = (λ1+λ2+λ3)/3
Axial Diffusivity (Da) = λ1
Radial Diffusivity (Dr) = (λ2+λ3)/2
λ1
λ2
λ3
λ1
λ2
λ3
ISOTROPIC
ANISOTROPIC
Diffusion Kurtosis imaging
Diffusion Kurtosis imaging
DTI Metrics and Tensor

11. Use of DTI in epilepsy
Increased MD, ADC and lower FA values are seen in hippocampi of
patients with mesial temporal sclerosis
In patients with malformations of cortical development, increased
MD and lower FA values are seen in abnormal areas.
Increased MD and low FA can be used to localize lesions in MR
negative cases of epilepsy

12. • We will compare the mean diffusivity, ADC and fractional anisotropy (FA) from
symmetrical voxels by sampling the following areas namely middle cerebellar
peduncle, corpus callosum ,uncinate fasciculus, inferior fronto occipital fasciculus ,
inferior temporo-occipital fasciculus, parahippocampal white matter, fimbria and
fornix ,hippocampus cingulated gyrus ,thalamus, internal capsule, caudate and
lentiform nucleus.
• We will compare these measurements with the high-resolution MR imaging, and
clinical information.