MRI Flashcards
What is MRI used for?
Imaging of brain, joints, breast, abdomen, cardiac & pelvis
manages patients with cancer & chronic diseases
Why is MRI more applicable for disease progression imaging?
High soft tissue contrast
Why atoms are you looking at in MRI?
Density of hydrogen atoms - most abundant ion in the body
What happens to hydrogen atoms when theyre in the presence of a magnetic field?
Align with it (low energy) or against it (high energy)
What is the ratio of anti-parallel:parallel?
100,000:100,007
What is net magnetization vector?
Those aligned parallel increase with increasing magnetic strength
What happens if protons are exposed to an external magnetic field?
higher energy align againts main magnetic field
low energy align with main magnetic field
What does the rate at which protons spin/precess depend on?
Strength of main magnetic field
What happens when protons absorb an aura pulse?
90 degree pulse will flip net magnetization 90 degrees of main magnetic field -> hydrogen protons all precess on the same pass
What happens when the RF pulse is taken away?
Protons try to revert back to original state (T1 recovery) -> give up their energy (T2) by realigning with main magnetic field & dephasing off same precessional path
Which part of the body composition has a high signal intensity in T2 images?
fluid
How does the MRI machine work?
provides external magnetic field to magnetize patient
MRI delivers RF pulse to begin MRI experiment
What does the gradient coil do?
Localizes signal within patient
What causes main magnetic field?
Superconducting coil
What does the RF coil do?
pick up valuable signal coming from patient
What are permanent magnets?
iron, cobalt nickel will retain magnetism once magnetized
runs vertically
open magnetic system (0.4T)
What is Faradays law of electromagnetic induction states?
If a current is passed through a long straight wire a magnetic field is produced arou d the wire
What do solenoid magnets use?
Loops of wire -> strength of magnetic field proportional to amount of loops & strength of current (0.2-0.3T)
What are superconducting electromagnets?
Alloy of niobium & titanium used that exhibits superconductivity at a certain temperature (14T)
What temperature is need for the SC electromagnets?
Temperature of 4K needed (-269degrees)
What 2 gases are needed to cool SC electromagnets?
Helium or nitrogen
What are 3 safety considerations for MRI?
static magnetic field - biological effects, projectile hazards
Gradient magnetic field - peripheral nerve stimulation, muscle stimulation & acoustic noise
RF magnetic fields - induced current burns & contact burns
What does the 3mT line represent?
Projectile line -> all ferromagnetic particles display a force at this line
What does the 0.5mT line represent?
Exclusion line -> many impantable devices are affected by magnetic field at this line
What are 4 examples of risk reducing solutions of static magnetic field?
Controlled zones
signage
properly screened
staff education
What is a gradient magnetic field?
Switching magnetic field to spatially localise where signal is coming from
What are 3 causes of burns?
patient is touching or too close to RF coil
if patient has conduction material on them
large calibre body loops - small areas of skin to skin contact
malfunction of active devices
What is the quench procedure?
Helium is vented from cyrostat around windings which exhibits superconductivity
What are 3 risks of quench?
Frostbite
flammable
high pressure
What are 4 advantages of MRI?
no ionising radiation
cross sectional anatomy
superior ability to image soft tissue
ability to reconstruct in any plane
What are 3 disadvantages of MRI?
long scan times
safety concerns
claustrophobic
T1 weighted images look at?
Recover - fluid is low -> harder to appreciate pathology
More signal in general -> good for looking at anatomy
What is T2 good for looking at?
Pathological processes - fluid is bright
What are 3 planes?
axial
sagittal
coronal
What is cauda equina syndrome?
Tingling or weakness in legs -> bulging disc pressing on nerve fibres
What therapy is the therapy of choice if spinal cord is compressed?
Radiotherapy
What does general principle-cytotoxic oedema cause?
Influx of swelling into brain tissue - occurs as part of stroke -> reduces Brownian motion
What are changing magnetic fields used for?
Molecular ;level to image water restriction
What does cardiac MRI provide?
High spatial & temporal resolution
What are 3 causes of sudden adulty death syndrome?
Hypertrophic cardiomyopathy - abnormal thickening of left ventricle
Dilated cardiomyopathy - heart muscle stretches & thins
arrhythmogenic RV cardiomyopathy - muscle of RV replaced by fat & fibrous tissue
What coil is used to look at haert in children?
Coil used for adult brains
What does MRI identify in cardiac imaging?
Scar tissue due to a coronary artery getting blocked
What are benefits of MRI in trauma imaging?
Image spinal cord
identify oedema, haemorrhage & cord bruising
aid in decision on operating
What is musculoskeletal imaging ideal for?
Imaging ligaments & tendons
What does MRI look for in knee imaging?
Meniscal tears
anterior & posterior cruciate tears
cartilage defects
Which contrast agent is given to MRI patients if cancer is suspected?
Gadolinium
How is cervical cancer spotted?
Gel separates vagina - cervical cancer doesn’t dilate cavity as well
