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Z MRI Physics > MRI in practice chapter 2 > Flashcards

MRI in practice chapter 2 Flashcards

(75 cards)

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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
TR pulse length in T1 weighting
short so neither has time to fully return to B(o)
26
\_\_\_\_\_\_controls the amount of decay of T2 taht is allowed to occur before the signal is received
TE
27
TE length in T2 weighting
long enough to give both fat and water time to decar
28
effects of T1 and T2 contrast must be diminished so that ___________ can dominate
proton density
29
TR must be ________ and TE must be ___________ for a PD weighted image
long short
30
when the RF excitation pulse is removed the relaxation and decay process start immediately
T2\*
31
is the decay of the FID following RF pulse removal
T2\*
32
comination of two effects T2 decay dephasing due to magnetic field inhomgeneities
T2\* faster than T2
33
NMV pushed beyond 90°
parially saturated
34
NMV pushed to full 180°
fully saturated
35
partial saturation of fat and water
T1 weighting occurs
36
saturation of fat and water does NOT occur
PD weighting occurs
37
predominant factor in T2\* decay
inhomogeneities in magnetic field
38
has significant effect on saturation effects
flip angle
39
amount that RF pulse moves NMV via resonance
flip angle
40
sequences that use a 180° pulse to regeneratesignal
spin echo pulse
41
sequences that use a gradient
gradient echo pulse
42
uses a 90° pulse to flip the NMV then a 180° pulse when that one is removed
spin echo pulse sequence
43
occurs after a 180° pulse when the magnetic moments rephase and align
spin echo
44
contains T1 and T2 information reduces T2\* dephasing
spin echo signal
45
Time to rephase after the application of a 180° pulse equals the time to dephase after the 90° pulse was removed
TAU
46
twice the TAU
TE
47
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
spin echo with one echo
48
used to produce both PD and T2 weghting
spin echo with 2 echoes
49
first spin echo short TE minimizing T2 decay second echo long TE (significant T2 decay) Long TR so T1 differences are minimized
spin echo using 2 echoes
50
controls T1 weighting
TR
51
maximizes T1 weighting
short TR
52
maximizes PD weighting
long TR
53
controls T2 weighting
TE
54
miminizes T2 weighting
short TE
55
maximizes T2 weighting
long TE
56
rephase the magnetic moments so that a signal is received by the coil which contains T1 and T2 information
gradient echo
57
generated by coils of wire situated with the bore of the magnet
magnetic field gradients
58
middle axis of magnetic field strength
magnetic isocenter
59
gradient filed adds or subtracts from main mag field depending on direction of current flow through gradient coils
polarity
60
increase when mag field strength increase decreases when mag field strength decrease
precessional freq
61
precessional freq slow down
less gradient
62
precessional freq increase
more gradient
63
gradients taht dephase
spoilers
64
gradients that rephase
rewinders
65
associated with shorter scan times than spin echo pulses sequences
gradient echo pulse sequence
66
TR decreased (less than 90° flip angles) low flip angles means less full recovery time
advantage of gradient echo pulse sequence
67
no compensation for mag field inhomogeneities very susceptible to mag field inhomogeneities contain mag susceptibility artefact
disadvantages of gradient echo pulse sequences
68
control T1 relaxation in gradient echo pulse sequence
TR and clip angle
69
short TR high flip angle short TE
T1 weighting in gradient echo
70
long TE long TR small flip angle
T2\* weighting in gradient echo
71
short TE long TR small flip angle
PR weighting in gradient echo
72
gradient echo pulse uses a \_\_\_\_\_\_\_to rephase the magnetic moments
gradient
73
variable \_\_\_\_\_\_\_\_\_are used
flip angles
74
can be shorter than in spin echo imaging
TE
75
do not eliminate effects from mag filed inhomogeneities
gradients

Z MRI Physics (12 decks)

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