MRI I and II Flashcards
What are some negatives of MRI
Long acquisition time ~10s of minutes high equipment and personnel costs patient claustrophobia image artifacts scan complexity
When did we start seeing MRIs used in clinic?
1970’s
What is the strength of the main magnets used?
usually 1.5T, sometimes 0.5T or 3T
What temperatues do the magnets need to be at and how is this accomplished?
4K and liquid Helium
What kinds of coils are in an MRI machine?
There are the main coils which create a uniform magnetic field.
There are also gradient coils, one positive and one negative, which add together to form a nice linear gradient along the length of the scanner.
There are also active and passive shim coils which even everything out.
How large of a change does the gradient coils introduce?
around 5mT
What is magnetic susceptibility?
The extent to which a material becomes magnetized in a magnetic field.
What do Diamagnetic, Paramagnetic, and Ferromagnetic materials do in a magnetic field?
Diamagnetic: has paired electron spins and they align to oppose B
Paramagnetic and Ferromagnetic: unpaired electron spins (net spin can be non-zero) and align to B
What is often used as a contrast in MRI? is is Para or Diamagnetic?
Gadillidium, Paramagnetic
How many nuclei does it take to produce a measurable signal?
10^15
What makes a nuclei medically useful?
- spin quantum number is non-interger
- abundant in body (or can be injected as contrast)
- should have a high magnetic moment
What is a typical MRI voxel size?
1mm x 1mm x 1mm
Are there more spins in the parallel or antiparallel state? How many more? Is this state higher or lower energy?
3p/million more are in the parallel state because this is lower energy
How many protons are in a typical voxel?
10^21
What is the gryomagnetic ratio of hydrogen?
42.58 MHz/T