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Z MRI Physics > MRI in practice chapter 2 > Flashcards

MRI in practice chapter 2 Flashcards

1
Q

parameters that cannot be changed because they are inherent to the body’s tissues

A

intrinsic contrast parameters

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2
Q

parameters that can be changed

A

extrinsic contrast parameters

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3
Q

T1 recovery

T2 decay

proton density

flow

apparent diffusion coefficient

A

intrinisc contrast parameters

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4
Q

TR

TE

flip angle

TI

turbo factor/echo train lenght

b value

A

extrinisc contrast factors

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5
Q

molecular lattice is more able to absorb energy from hydrogen nuclei

A

in herent energy of tissue is low

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6
Q

molecular lattice does not absorb energy from hydrogen nuclei as easily

A

inherent tissue energy is high

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7
Q

good energy match between bydrogen nuclei and molecular lattice is efficient

A

good match in Larmor frequency

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8
Q

good interaction between magnetic fields of neighboring hydrogen nuclei

A

good interaction important in T2 decay

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9
Q

time for 63% of total magnetization to be regained in longitudinal plane

A

T1 relaxation

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10
Q

63% of total magnetization lost in transverse plane

A

T2 decay

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11
Q

T1 time in fat

A

short

bright contrast

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12
Q

T1 recovery time in water

A

Long

dark contrast

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13
Q

T2 time of fat

A

short

dark contrast

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14
Q

T2 time of water

A

long

bright contrast

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15
Q

difference in signal intensity between tissues that are a consequence of their relative number of mobile protons per unit volume

A

proton density contrast

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16
Q

tissues with high proton density

large transverse component

A

bright contrast on PD weighted image

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17
Q

tissues with low proton density

small transverse component

A

dark on PD weighted images

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18
Q

large component of coherent magnetization in transverse plane

A

produce high signal

bright contrast

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19
Q

small component of coherent magnetization in transverse plane

A

low signal

dark contrast

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20
Q

characterized by

bright fat

dark water

A

T1 images

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21
Q

characterized by

bright water

dark fat

A

T2 images

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22
Q

although inherent to tissue are dependent on magnet field strength

A

T1 and T2 relaxation times

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23
Q

tissues take longer to recover

A

as field strength increases

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24
Q

_______controls how far each vector recovers before slice is excited by next RF pulse

A

TR

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25
Q

TR pulse length in T1 weighting

A

short

so neither has time to fully return to B(o)

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26
Q

______controls the amount of decay of T2 taht is allowed to occur before the signal is received

A

TE

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27
Q

TE length in T2 weighting

A

long

enough to give both fat and water time to decar

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28
Q

effects of T1 and T2 contrast must be diminished so that ___________ can dominate

A

proton density

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29
Q

TR must be ________ and TE must be ___________ for a PD weighted image

A

long

short

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30
Q

when the RF excitation pulse is removed the relaxation and decay process start immediately

A

T2*

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31
Q

is the decay of the FID following RF pulse removal

A

T2*

32
Q

comination of two effects

T2 decay

dephasing due to magnetic field inhomgeneities

A

T2* faster than T2

33
Q

NMV pushed beyond 90°

A

parially saturated

34
Q

NMV pushed to full 180°

A

fully saturated

35
Q

partial saturation of fat and water

A

T1 weighting occurs

36
Q

saturation of fat and water does NOT occur

A

PD weighting occurs

37
Q

predominant factor in T2* decay

A

inhomogeneities in magnetic field

38
Q

has significant effect on saturation effects

A

flip angle

39
Q

amount that RF pulse moves NMV via resonance

A

flip angle

40
Q

sequences that use a 180° pulse to regeneratesignal

A

spin echo pulse

41
Q

sequences that use a gradient

A

gradient echo pulse

42
Q

uses a 90° pulse to flip the NMV

then a 180° pulse when that one is removed

A

spin echo pulse sequence

43
Q

occurs after a 180° pulse when the magnetic moments rephase and align

A

spin echo

44
Q

contains T1 and T2 information

reduces T2* dephasing

A

spin echo signal

45
Q

Time to rephase after the application of a 180° pulse equals the time to dephase after the 90° pulse was removed

A

TAU

46
Q

twice the TAU

A

TE

47
Q

short TE ensures the 180° pulse and echo occur early (little T2 decay)

differnce in T2 times of tissues do not dominate the echo and contrast

short TR ensures fat and water do not fully recover so their T1 times dominate the echo and contrast

A

spin echo with one echo

48
Q

used to produce both PD and T2 weghting

A

spin echo with 2 echoes

49
Q

first spin echo short TE minimizing T2 decay

second echo long TE (significant T2 decay)

Long TR so T1 differences are minimized

A

spin echo using 2 echoes

50
Q

controls T1 weighting

A

TR

51
Q

maximizes T1 weighting

A

short TR

52
Q

maximizes PD weighting

A

long TR

53
Q

controls T2 weighting

A

TE

54
Q

miminizes T2 weighting

A

short TE

55
Q

maximizes T2 weighting

A

long TE

56
Q

rephase the magnetic moments so that a signal is received by the coil which contains T1 and T2 information

A

gradient echo

57
Q

generated by coils of wire situated with the bore of the magnet

A

magnetic field gradients

58
Q

middle axis of magnetic field strength

A

magnetic isocenter

59
Q

gradient filed adds or subtracts from main mag field depending on direction of current flow through gradient coils

A

polarity

60
Q

increase when mag field strength increase

decreases when mag field strength decrease

A

precessional freq

61
Q

precessional freq slow down

A

less gradient

62
Q

precessional freq increase

A

more gradient

63
Q

gradients taht dephase

A

spoilers

64
Q

gradients that rephase

A

rewinders

65
Q

associated with shorter scan times than spin echo pulses sequences

A

gradient echo pulse sequence

66
Q

TR decreased (less than 90° flip angles)

low flip angles means less full recovery time

A

advantage of gradient echo pulse sequence

67
Q

no compensation for mag field inhomogeneities

very susceptible to mag field inhomogeneities

contain mag susceptibility artefact

A

disadvantages of gradient echo pulse sequences

68
Q

control T1 relaxation in gradient echo pulse sequence

A

TR and clip angle

69
Q

short TR

high flip angle

short TE

A

T1 weighting in gradient echo

70
Q

long TE

long TR

small flip angle

A

T2* weighting in gradient echo

71
Q

short TE

long TR

small flip angle

A

PR weighting in gradient echo

72
Q

gradient echo pulse uses a _______to rephase the magnetic moments

A

gradient

73
Q

variable _________are used

A

flip angles

74
Q

can be shorter than in spin echo imaging

A

TE

75
Q

do not eliminate effects from mag filed inhomogeneities

A

gradients

Z MRI Physics (12 decks)

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