NEURO MRI PHYSICS Flashcards

Question 1

Q

What is SWI?

Answer

A

Susceptibility weighted imaging
particularly sensitive to compounds which distort the local magnetic field
- blood products
- calcium, etc.
3D high-spatial-resolution
fully velocity corrected
gradient-echo MRI sequence
Compounds that have
- paramagnetic,
  - deoxyhemoglobin
  - ferritin
  - haemosiderin
- diamagnetic
  - bone minerals
  - Dystrophic calcification
- ferromagnetic properties
all interact with the local magnetic field distorting it
thus altering the phase of local tissue
which, in turn, results in a change of signal 2.

USE:

identification of small amounts of hx/blood products or calcium in the brain
Can also see veins as dexoygaemoglobin as DEOXYHAEMOGLOBIN results in both a loss in magnitiud and a shift in phase
Distinguishing between calcification (made up primarily of calcium phosphate, but also containing very small amounts of copper (Cu), manganese (Mn), zinc (Zn), magnesium (Mg), and iron (Fe)) 3 and blood products is not possible on the post-processed SWI images as both demonstrate signal drop out and blooming.
The filtered phase images are, however, able to (in most cases) distinguish between the two as diamagnetic and paramagnetic compounds will affect phase differently (i.e. veins/haemorrhage and calcification will appear of opposite signal intensity) 3.

Question 2

Q

What sets of Data are taken in SWI?

Answer

A

Magnitude image
phase image (passed through a high pass filter to remove artefacts)
SWI susceptibility weighted image
mIP minim intensity projection

https://www.youtube.com/watch?v=QaMkM7hNXTg

Question 3

Q

How is a Magnitude SWI image made?

Answer

A

https://www.youtube.com/watch?v=QaMkM7hNXTg

Question 4

Q

What are 3 PARAMAGNETIC COMPOUNDS?

Answer

A

Ferritin
Deoxyhaemoglobin
Hemosiderin

Question 5

Q

What determines if something is PARAMAGNETIC?

Answer

A

The images explain pretty much tells you everything there is to know!

Paramagnetic compounds (and atoms) are attracted to magnetic fields while diamagnetic compounds (and atoms) are repelled from magnetic fields.

Paramagnetic compounds have unpaired electrons while in diamagnetic compounds the electrons all have paired spins.

Very few individual atoms are paramagnetic since this requires having a half-filled MO. In contrast, nearly all molecules are diamagnetic (O2 is a notable exception). That is, they essentially have all paired electrons in MOs.

Key points:

Any time two electrons share the same orbital, their spin quantum numbers have to be different. Whenever two electrons are paired together in an orbital, or their total spin is 0, they are diamagnetic electrons. Atoms with all diamagnetic electrons are called diamagnetic atoms.

A paramagnetic electron is an unpaired electron. An atom is considered paramagnetic if even one orbital has a net spin. An atom could have ten diamagnetic electrons, but as long as it also has one paramagnetic electron, it is still considered a paramagnetic atom.

Diamagnetic atoms repel magnetic fields. The unpaired electrons of paramagnetic atoms realign in response to external magnetic fields and are therefore attracted. Paramagnets do not retain magnetization in the absence of a magnetic field, because thermal energy randomizes electron spin orientations.

Summary:

The magnetic properties of a substance can be determined by examining its electron configuration: If it has unpaired electrons, then the substance is paramagnetic and if all electrons are paired, the substance is then diamagnetic