Lecture 32; Preterm injury 3 Flashcards
What does MRI measure using its gradients?
resonance frequency of a nuclie is directly proportional to the strength of applied magnetic field
Hz is dependant on location in inhomogenous magnetic field. = 3D picutre
What is T1 good for?
Anatomy
Grey vs white matter
What is T2 good for?
Pathology big bright white tumors
How can we see focal cystic lesions?
T1 hyperintensive MRI
How can we see diffuse WMI?
T2 weight, less defined white matter grey matter boundries
What does each voxel in dMRI represent?
Each image voxel has intensity that reflects rate of water diffusion in single direction
What does a voxel contain?
Each voxel contains preferred direc&on and magnitude (rate) of water diffusion; sensi1ve to pathology
What is Diffusion tensor imaging?
Using dMRI in several directions
What does isotropic and anisotropic reflect?
Uniform and constrained brownian motion
What is a primary and secondary eigenvector?
in 3D diffusion tensor imaging
–Longest axis parallel to direc1on of greatest diffusion (primary eigenvector; λ1) I.e along axon
–Perpendicular eigenvectors (λ2 & λ3) i.e side to side in axon
What does DTI give you?
– Mean diffusivity
– Degree of anisotropy
– Main direc1on of diffusivity
In ADC imaging (mean diffusitivity) what do the colours represent?
- High mean diffusivity – white
- Low mean diffusivity – dark
- Mean diffusivity of WM decreases with age –increasing cellular structure impedes water diffusion
- Useful for assessing WM matura1on `
How do we create a 3D fibre map tracking?
- Uses direc1on of primary eigenvector for each voxel to reconstruct fiber connec1vity in 3D
- Cerebral white matter (axon) tracts and connectivity over development and in disease
What can we use water diffusion for?
To measure diffuse myelination failure
In the normal brain what plays a role in FA?
Axonal membranes play primary role in anisotropy
Microtubules/neurofilaments do not play significant role in anisotropic water diffusion
Myelin can also modulate anisotropy
