Lecture 12 - MRI Flashcards Preview

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Flashcards in Lecture 12 - MRI Deck (13)
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1
Q

What magnet does MRI use

A

3-7 tesla

2
Q

What does mri measure

A

the alignment of water molecules within a magnetic field, and how long it takes to get back

3
Q

How does MRI work

A

no external field -> external magnetic field applied, water molecules align with the magnet (T1 IMAGE) –> external radio frequency pulse applied –> some molecules flip to antiparallel spins –> pulse stops –> protons align parallel again and give off radio frequency energy –> energy is detected by the reception coil and forms T2 image

4
Q

What are the two features we adjust on MRI?

A

TE - ECHO TIME

TR - REPETITION TIME

5
Q

What is T1

A

t1 relaxation, uses short TE (echo time) and short TR (repeition)

  • longitudinal or spin lattice relaxation
  • fat looks bright
  • water looks dark
6
Q

What are the properties of tissue that we are measuring on MRI

A
  • proton density

- proton relaxation time (T1 and T2)

7
Q

What is T2

A

T2 relaxation - uses long TR and TE

DIFFERENTIATES BETWEEN WHITE AND GREY MATTER BETTER THAN T1

  • transverse, spin spin relaxation
  • fat is dark and water is bright
8
Q

What is FLAIR

A

it is a T2 image, but water is dark, providing better contrast

9
Q

What is proton density

A

PD

uses short TE and long TR, reflection hydrogen concentration

10
Q

What is VBM

A

Voxel based morphometry

  • statstically compares voxels of the brain to examine its shape, volume and integrity
  • you can look at one structure, compare it to other structures and other groups of people (within person or between groups)
11
Q

What colour is water in a T1 and T2 scan?

A

T1 - dark

T2 - bright

12
Q

What is fMRI?

A

BOLD - Blood oxygenation level dependent

  • brain regions become oxygen rich after activity
  • Hbr (deoxyhaemoglobin) acts as the contrast
13
Q

What is DTI

A

Diffusion-tensor imaging

measures random motion of water molecules.

CSF in ventricles – molecules are unconstrained, so high velocity diffusion

BRAIN TISSUE - less diffusion as CSF constrained