Origin of Image contrast Flashcards
Where is histological slice obtained from?
Post-mortem
Where is there good contrast between?
Grey matter periphery and white mater centrally
Spaces that would’ve been filled by CSF
What does MRI allow you to look at?
Structure and function
What does longitudinal plane involve?
Z axis
What is Z axis typically used to denote?
Orientation of B0
What is the Transverse plane?
x-y plane
Orthogonal to the B0 direction
What plane can you get a measurable MR signal?
Transverse plane
How is the transverse magnetisation generated?
Manipulating the equilibrium condition
What is the Bloch Equation?
A phenomenological equation that was created and developed to describe behaviour that was observed for MRI/MR signal
Magnetisation in a magnetic field
There will be some change of magnetisation with time [pattern of behaviour over time]
Related to magnetisation vector and effective field that is applied (e.g. B0 and B1)
cross product
forces that are applied orthogonal to these directions
Longitudinal component
Difference to M0 (equilibrium magnetisation) and Mz component
What is T1?
Time constant that is describing the temporal behaviour of the magnetisation that is aligned along Z
What is T2 dependent on?
How large the transverse component is
What is the decay of transverse magnetisation described by?
T2
What is the approach to equilibrium in a static field described by?
T1
What is excitation?
The generation of Transverse component
What is the Bloch Equation broken down into?
- Precession
2. Relaxation
What does the rotating frame do?
Takes away all of the rotational component and allows us to focus solely on the relaxation parts
[How the magnetisation is recovering or decaying over time]
What are the features of Longitudinal Magnetisation Time Course?
- Exponential saturation curve
- The growth depends on amount present (protons)
- The time taken is characterised by a time constant T1
After T1
we will have 99% of the magnetisation recovered T=5 T1
What does different tissues have?
Different T1 values
What is the amount of recovery that occurs dependent on?
Tissue type we are looking at