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HSC3007 MRI > Week 1 > Flashcards

Week 1 Flashcards

1
Q

MRI scanner types

A
  • permanent
  • resistive electro
  • superconducting
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2
Q

1 Tesla = ___ Gauss

A

10,000

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3
Q

Ultra-Low Field Tesla Strength

A

0.02 - 0.1 T

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4
Q

Low Field Tesla Strength

A

0.2 - 0.6 T

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5
Q

Mid Field Tesla Strength

A

1 - 1.5 T

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6
Q

High Field Tesla Strength

A

2 - 4 T

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7
Q

Ultra-High Field Tesla Strength

A

> 7 T

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8
Q

why do MRI need strong coolants

A

as temp decrease, metal resistance falls. when it drops to zero, electricity is conducted without energy loss as heat due to resistance

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9
Q

superconducting MR magnets typically use ___ wires

A

Nobium-Titanium, Tc = 9.4K

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10
Q

what is commonly used as a coolant / cryogen to lower temperature

A

liquid helium (4K)

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11
Q

HTS

A

high temperature superconductive

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12
Q

types of magnetic properties of materials

A

diamagnetic, paramagnetic, ferromagnetic

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13
Q

diamagnetic material properties

A

no intrinsic atomic magnetic moment but weakly repels magnetic field = small negative magnetic susceptibility

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14
Q

paramagnetic material properties

A

ions have unpaired electrons, resulting in a positive magnetic susceptibility less than ferromagnetic materials

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15
Q

MR Safe

A

item poses no hazard from exposure to MR environment

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16
Q

MR conditional

A

item with demonstrated safety in MR environment within defined conditions

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17
Q

MR unsafe

A

item poses unacceptable risks to patients within MR environment

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18
Q

how many preventive procedural zones

A

4

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19
Q

Zone I

A

freely accessible to general public

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20
Q

Zone II

A

screening & interviewing patients but patients may not be able to move freely throughout

21
Q

Zone III

A

controlled area - access entirely under supervision of MR personnel

22
Q

Zone IV

A

MR scanner room - highly restricted; non-MR personnel must be under immediate visual supervision of qualified MR personnel

23
Q

MRI preventive procedures

A
  • ferromagnetic detectors
  • screening questionnaire
24
Q

clinical MRI involves imaging of ___

A

hydrogen nuclei (protons)

25
Q

NMV

A

net magnetization vector

26
Q

resonance

A

tendency of system to absorb more energy when frequency of oscillations matches system’s natural frequency of vibration

27
Q

excitation

A

when RF wave is applied at resonant frequency, protons will absorb energy & tip over

28
Q

relaxation

A

when RF stops, they lose energy to surroundings and re-align to B0

29
Q

at 1.5 T, resonant frequency of 1 H is at ___ MHz

A

63.87

30
Q

T1 - longitudinal component Mz

A

time taken to lose energy to surroundings & realign to B0 (200ms - 2000ms)

31
Q

T2 - transverse component Mxy

A

time taken to lose energy to other spins (10 - 100ms)

32
Q

Unlike CT, MRI signal intensities are __

A

relative

33
Q

T1 & T2 can be used to differentiate __

A

chemical compounds, tissue structures, healthy & diseased tissues

34
Q

why are gadolinium based agents most commonly used

A

7 unpaired e- in 4f orbital = strong paramagnetic effect

35
Q

gadolinium based agents affect ___ times

A

relaxation; mainly T1

36
Q

larmor equation

A

f0 = y x B0

37
Q

other mechanisms of contrast

A

PD, diffusion, BOLD, velocity

38
Q

PD

A

proton density

39
Q

T2 timing are shorter than T1 timing about __

A

10x

40
Q

T1W contrast

A
  • bright fat
  • dark csf
  • WM brighter than GM
41
Q

PD contrast

A
  • less bright Fat & CSF
  • WM darker than GM
42
Q

T2W contrast

A
  • bright fat
  • very bright CSF
  • WM darker than GM
43
Q

effect of fat & water on T2

A

fat = low T2
water = high T2

44
Q

who is responsible for MRI safety

A

radiographer

45
Q

why does MRI have excellent soft tissue contrast

A

due to tissues having different chemical structures

46
Q

what contributes to nuclear moments in MRI

A

protons & neutrons

47
Q

what does NMV represent

A

sum of nuclear magnetic moments aligned parallel to B0

48
Q

MRI signal can be increased by __

A

increasing field strength, temperature and proton density

49
Q

the magnitude of NMV tipped is dependent on __

A

frequency, duration & amplitude of RF pulse

HSC3007 MRI (10 decks)

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