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CSB063 MRI EXAM STUDY GUIDE
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CSB063 MRI EXAM STUDY GUIDE ...
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CSB063 MRI EXAMSTUDY GUIDE
10 000 Guass = - Answer 1 Tesla
earths gravitation pull in tesla - Answer 0.5. Therefore 3T magnet is 30,000 x stronger
than earths magnetic field
Shimming - Answer Shim coils used to improve the magnetic field homongeneity.
Pre-phase prior to sequence - machine sends/receives RF signal & modifies output for
sequence/patient.
RF coils - Answer close to body part to receive returned signal
gradient coils - Answer Adds magnetic field in x y z direction in addition to B0, gradient
sequences utilise these
Shielding - Answer all magnets are shielded using reverse polarity to deflect and create
a safe barrier
why is hydrogen used? - Answer abundant
free electron
net charge
large magnetic moment
aligns to B0
lamour frequency - Answer w0= precessional freq
y= gyromagnetic ratio of hydrogen 42.58
B0= magnetic field strength
lamour frequency for 1.5T / 3T - Answer 1.5T = 63.4MHz
3T = 127.7MHz
MRI Advantages - Answer - non-ionising
- great soft tissue contrast
- MPR
, - high spatial resolution
- function & anatomical
- vascular imaging w/o catheterization
- cardiac imaging
- not operator dependent
- gold for neuro/MSK
MRI Disadvantages - Answer - timely
- costly
- patient cooperation with claustrophobia and keeping still
- implants
- large people
What is the 5 guass line? - Answer Line drawn on floor of which people with implant
cannot go past
What is the protocol for ICU Patients where you cannot ask them the safety Q? - Answer
ICU Clinican has to sign off but usually the patient will have a CT or xrays to confirm
there are no metal implants and check skin surface for scars etc.
Contraindications? - Answer Pacemakers/defibrillators
cochlear implants
IOFB
ferromagnetic intra-cranial aneurysm clips
ECG lead clips on skin
surgery/tattoos past 6 weeks
first trimester pregnancy
What happens to electrical and mechanical devices in the magnetic field? - Answer
Battery life is sucked, cards with magnetic strips ie go card, credit cards will be erased
What is a Cryogen? - Answer Cold liquid substance used to cool materials to v low
temperatures -273c
What can happen to a patient if the magnet Quenches? - Answer pressure lock, rutured
eardrums, asphyxiation, frost bite
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