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Medical Imaging > MRI > Flashcards

MRI Flashcards

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USMLE® Step 1 flashcards
1
Q

What is MRI used for?

A

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

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2
Q

Why is MRI more applicable for disease progression imaging?

A

High soft tissue contrast

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3
Q

Why atoms are you looking at in MRI?

A

Density of hydrogen atoms - most abundant ion in the body

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4
Q

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

A

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

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5
Q

What is the ratio of anti-parallel:parallel?

A

100,000:100,007

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6
Q

What is net magnetization vector?

A

Those aligned parallel increase with increasing magnetic strength

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7
Q

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

A

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

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8
Q

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

A

Strength of main magnetic field

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9
Q

What happens when protons absorb an aura pulse?

A

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

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10
Q

What happens when the RF pulse is taken away?

A

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

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11
Q

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

A

fluid

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12
Q

How does the MRI machine work?

A

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

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13
Q

What does the gradient coil do?

A

Localizes signal within patient

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14
Q

What causes main magnetic field?

A

Superconducting coil

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15
Q

What does the RF coil do?

A

pick up valuable signal coming from patient

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16
Q

What are permanent magnets?

A

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

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17
Q

What is Faradays law of electromagnetic induction states?

A

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

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18
Q

What do solenoid magnets use?

A

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

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19
Q

What are superconducting electromagnets?

A

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

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20
Q

What temperature is need for the SC electromagnets?

A

Temperature of 4K needed (-269degrees)

21
Q

What 2 gases are needed to cool SC electromagnets?

A

Helium or nitrogen

22
Q

What are 3 safety considerations for MRI?

A

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

23
Q

What does the 3mT line represent?

A

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

24
Q

What does the 0.5mT line represent?

A

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

25
Q

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

A

Controlled zones
signage
properly screened
staff education

26
Q

What is a gradient magnetic field?

A

Switching magnetic field to spatially localise where signal is coming from

27
Q

What are 3 causes of burns?

A

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

28
Q

What is the quench procedure?

A

Helium is vented from cyrostat around windings which exhibits superconductivity

29
Q

What are 3 risks of quench?

A

Frostbite
flammable
high pressure

30
Q

What are 4 advantages of MRI?

A

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

31
Q

What are 3 disadvantages of MRI?

A

long scan times
safety concerns
claustrophobic

32
Q

T1 weighted images look at?

A

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

33
Q

What is T2 good for looking at?

A

Pathological processes - fluid is bright

34
Q

What are 3 planes?

A

axial
sagittal
coronal

35
Q

What is cauda equina syndrome?

A

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

36
Q

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

A

Radiotherapy

37
Q

What does general principle-cytotoxic oedema cause?

A

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

38
Q

What are changing magnetic fields used for?

A

Molecular ;level to image water restriction

39
Q

What does cardiac MRI provide?

A

High spatial & temporal resolution

40
Q

What are 3 causes of sudden adulty death syndrome?

A

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

41
Q

What coil is used to look at haert in children?

A

Coil used for adult brains

42
Q

What does MRI identify in cardiac imaging?

A

Scar tissue due to a coronary artery getting blocked

43
Q

What are benefits of MRI in trauma imaging?

A

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

44
Q

What is musculoskeletal imaging ideal for?

A

Imaging ligaments & tendons

45
Q

What does MRI look for in knee imaging?

A

Meniscal tears
anterior & posterior cruciate tears
cartilage defects

46
Q

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

A

Gadolinium

47
Q

How is cervical cancer spotted?

A

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

48
Q
A

Medical Imaging (10 decks)

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