MRI

Question 1

What is MRI used for?

Answer 1

Imaging of brain, joints, breast, abdomen, cardiac & pelvis
manages patients with cancer & chronic diseases

Question 2

Why is MRI more applicable for disease progression imaging?

Answer 2

High soft tissue contrast

Question 3

Why atoms are you looking at in MRI?

Answer 3

Density of hydrogen atoms - most abundant ion in the body

Question 4

What happens to hydrogen atoms when theyre in the presence of a magnetic field?

Answer 4

Align with it (low energy) or against it (high energy)

Question 5

What is the ratio of anti-parallel:parallel?

Answer 5

100,000:100,007

Question 6

What is net magnetization vector?

Answer 6

Those aligned parallel increase with increasing magnetic strength

Question 7

What happens if protons are exposed to an external magnetic field?

Answer 7

higher energy align againts main magnetic field
low energy align with main magnetic field

Question 8

What does the rate at which protons spin/precess depend on?

Answer 8

Strength of main magnetic field

Question 9

What happens when protons absorb an aura pulse?

Answer 9

90 degree pulse will flip net magnetization 90 degrees of main magnetic field -> hydrogen protons all precess on the same pass

Question 10

What happens when the RF pulse is taken away?

Answer 10

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

Question 11

Which part of the body composition has a high signal intensity in T2 images?

Answer 11

fluid

Question 12

How does the MRI machine work?

Answer 12

provides external magnetic field to magnetize patient
MRI delivers RF pulse to begin MRI experiment

Question 13

What does the gradient coil do?

Answer 13

Localizes signal within patient

Question 14

What causes main magnetic field?

Answer 14

Superconducting coil

Question 15

What does the RF coil do?

Answer 15

pick up valuable signal coming from patient

Question 16

What are permanent magnets?

Answer 16

iron, cobalt nickel will retain magnetism once magnetized
runs vertically
open magnetic system (0.4T)

Question 17

What is Faradays law of electromagnetic induction states?

Answer 17

If a current is passed through a long straight wire a magnetic field is produced arou d the wire

Question 18

What do solenoid magnets use?

Answer 18

Loops of wire -> strength of magnetic field proportional to amount of loops & strength of current (0.2-0.3T)

Question 19

What are superconducting electromagnets?

Answer 19

Alloy of niobium & titanium used that exhibits superconductivity at a certain temperature (14T)

Question 20

What temperature is need for the SC electromagnets?

Answer 20

Temperature of 4K needed (-269degrees)

Question 21

What 2 gases are needed to cool SC electromagnets?

Answer 21

Helium or nitrogen

Question 22

What are 3 safety considerations for MRI?

Answer 22

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

Question 23

What does the 3mT line represent?

Answer 23

Projectile line -> all ferromagnetic particles display a force at this line

Question 24

What does the 0.5mT line represent?

Answer 24

Exclusion line -> many impantable devices are affected by magnetic field at this line

Question 25

What are 4 examples of risk reducing solutions of static magnetic field?

Answer 25

Controlled zones signage properly screened staff education

Question 26

What is a gradient magnetic field?

Answer 26

Switching magnetic field to spatially localise where signal is coming from

Question 27

What are 3 causes of burns?

Answer 27

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

Question 28

What is the quench procedure?

Answer 28

Helium is vented from cyrostat around windings which exhibits superconductivity

Question 29

What are 3 risks of quench?

Answer 29

Frostbite flammable high pressure

Question 30

What are 4 advantages of MRI?

Answer 30

no ionising radiation cross sectional anatomy superior ability to image soft tissue ability to reconstruct in any plane

Question 31

What are 3 disadvantages of MRI?

Answer 31

long scan times safety concerns claustrophobic

Question 32

T1 weighted images look at?

Answer 32

Recover - fluid is low -> harder to appreciate pathology More signal in general -> good for looking at anatomy

Question 33

What is T2 good for looking at?

Answer 33

Pathological processes - fluid is bright

Question 34

What are 3 planes?

Answer 34

axial sagittal coronal

Question 35

What is cauda equina syndrome?

Answer 35

Tingling or weakness in legs -> bulging disc pressing on nerve fibres

Question 36

What therapy is the therapy of choice if spinal cord is compressed?

Answer 36

Radiotherapy

Question 37

What does general principle-cytotoxic oedema cause?

Answer 37

Influx of swelling into brain tissue - occurs as part of stroke -> reduces Brownian motion

Question 38

What are changing magnetic fields used for?

Answer 38

Molecular ;level to image water restriction

Question 39

What does cardiac MRI provide?

Answer 39

High spatial & temporal resolution

Question 40

What are 3 causes of sudden adulty death syndrome?

Answer 40

Hypertrophic cardiomyopathy - abnormal thickening of left ventricle Dilated cardiomyopathy - heart muscle stretches & thins arrhythmogenic RV cardiomyopathy - muscle of RV replaced by fat & fibrous tissue

Question 41

What coil is used to look at haert in children?

Answer 41

Coil used for adult brains

Question 42

What does MRI identify in cardiac imaging?

Answer 42

Scar tissue due to a coronary artery getting blocked

Question 43

What are benefits of MRI in trauma imaging?

Answer 43

Image spinal cord identify oedema, haemorrhage & cord bruising aid in decision on operating

Question 44

What is musculoskeletal imaging ideal for?

Answer 44

Imaging ligaments & tendons

Question 45

What does MRI look for in knee imaging?

Answer 45

Meniscal tears anterior & posterior cruciate tears cartilage defects

Question 46

Which contrast agent is given to MRI patients if cancer is suspected?

Answer 46

Gadolinium

Question 47

How is cervical cancer spotted?

Answer 47

Gel separates vagina - cervical cancer doesn't dilate cavity as well