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HSC3007 MRI > Week 3 > Flashcards

Week 3 Flashcards

1
Q

intrinsic / uncontrollable contrast parameters

A

T1 recovery time, T2 decay time, proton density

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2
Q

extrinsic / controllable contrast parameters

A

TR, TE, TI, ETL

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3
Q

what controls T1W

A

TR

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4
Q

what controls T2W

A

TE

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5
Q

contrast weighting of long TR

A

2000+ ms

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6
Q

contrast weighting of short TR

A

300 - 700 ms

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7
Q

contrast weighting of long TE

A

60 ms

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8
Q

contrast weighting of short TE

A

10 - 25 ms

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9
Q

characteristics of T1W

A

bright fat + dark water

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10
Q

T1W is used to demonstrate __

A

anatomy

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11
Q

characteristics of T2W

A

bright water + dark fat

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12
Q

T2W is used to demonstrate __

A

pathology as water is often associated with it

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13
Q

T1W = __ TE + TR

A

short TE + TR

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14
Q

T2W = __ TE + TR

A

long TE + TR

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15
Q

PD = __ TR + __ TE

A

long TR + TE

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16
Q

T2 relaxation is __

A

natural decay of transverse magnetization

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17
Q

T2* relaxation is faster than T2 due to

A

magnetic inhomogeneity + field distortion / susceptibility

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18
Q

number of phase & frequency encoding determines __

A

resolution

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19
Q

total MR signal due to sum of FIDs from voxels with different __

A

amplitudes, frequencies, phases

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20
Q

signal received by coil is ___ & digitized using ___

A

pre-amplified; analog digital converters

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21
Q

where is signal stored in

A

K-space which is raw data matrix for every frequency & phase combo

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22
Q

each point in K-phase has defined particular combo of ___

A

frequency & phase shifts

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23
Q

K-space does not correspond to __

A

spatially

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24
Q

central K-space provides __

A

low frequency details / contrast

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25
Q

outer K-space provides ___

A

high frequency details / edges

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26
Q

order of filling K-space is __

A

K-space trajectory

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27
Q

signal which is phase-shifted by 90 degrees to determine ___

A

direction of magnetization rotation

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28
Q

In Fourier Transform, any signal / waveform made up by adding ___

A
  • pure tones / sine waves
  • appropriate frequency
  • amplitude
  • phase
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29
Q

spatial / coil encoding is used for ___

A

parallel imaging

30
Q

time encoding is used for ___

A

multi-slice imaging

31
Q

spin-echo cancels out __

A

fixed magnetic effects of inhomogeneity & susceptibility

32
Q

spin-echo sequence characterized by __

A

90 degrees RF pulse > 180 degrees RF rephasing pulse at TE/2

33
Q

spin-echo mainly used for __

A

T1 imaging

34
Q

HASTE

A

half-former acquisition single shot turbo spin echo

35
Q

HASTE preparation, excitation, readout

A

preparation: none
excitation: spin-echo
readout: single shot TSE

36
Q

HASTE AKA

A

single shot fast spin echo

37
Q

2D TSE w/ high turbo factor

A

all lines of fourier plane in single TR

38
Q

radial TSE

A

turbo spin echo w/ motion correction

39
Q

radial TSE preparation, excitation, readout

A

preparation: none
excitation: spin-echo
readout: radial TSE

40
Q

radial TSE AKA

A

PROPELLAR

41
Q

spin-echo cancels __

A

fixed magnetic field effects of inhomogeneity & susceptibility

42
Q

gradient pulse applied to __

A

accelerate spin dephasing

43
Q

gradient echo features an RF pulse at an angle followed by __

A

bipolar reading gradient

44
Q

since gradient choes don’t have refocusing plane, it is ___

A

more sensitive to B0 magnetic field inhomogeneity

45
Q

gradient echo preparation, excitation, readout

A

preparation: none
excitation: gradient-echo
readout: spin-echo

46
Q

gradient echo AKA

A

fast low angle shot (FLASH)

spoiled gradient echo (SPGR)

47
Q

GRE T2*W preparation, excitation, readout

A

preparation: none
excitation: gradient-echo
readout: segmented echoes

48
Q

balanced steady state free-precession preparation, excitation, readout

A

preparation: none
excitation: gradient-echo
readout: steady state

49
Q

echo planar imaging preparation, excitation, readout

A

preparation: fat preparation
excitation: spin-echo (diffusion), gradient- echo (fMRI)
readout: Echo planar

50
Q

echo planar imaging is __

A

single shot ultra fast acquisition; 1 slice = 50 ms

51
Q

what is fat saturation

A

removal of fat signal for better visualization of lesions & oedemas

52
Q

different methods of fat saturation

A
  • spectral fat saturation
  • inversion recovery
  • water excitation
  • dixon
53
Q

inversion recovery is ___

A

180 degrees inversion pulse before excitation

54
Q

Pulse sequence determines __

A

number, strength, timing of RF & gradient pulses which determines image contrast & K-space trajectory

55
Q

Number of points on echo determines __

A

resolution in frequency direction

56
Q

Lines in center of K-space determines __

A

contrast

57
Q

spin-echo sequences are mainly used for

A

T1 imaging

58
Q

what is TOF

A
  • Tissues saturated with constant RF pulses
  • Vessels traversing perpendicular through are transiently affected and appear bright
  • Saturation bands can block either arterial or venous flow
59
Q

what are the disadvantages of GRE T2*W

A

Increases susceptibility artifacts

Bad for implants but good for paramagnetic substances

60
Q

what is fat saturation

A

Removes fat signal = prevents fat ghosting

Improves visualization of lesions esp post contrast & oedemas in fatty areas

61
Q

what are the preparation, excitation and readout for echo planar imaging

A

Preparation = Fat saturation, excitation = spin echo for diffusion / gradient echo for fMRI, readout = echoplanar

62
Q

DWI is highly sensitive and specific for __

A

acute stroke detection

63
Q

what does DWI assume

A

haemorrhage excluded

64
Q

what is used to localize signals

A

gradients

65
Q

High spatial frequencies in K-space are stored at __

A

periphery, defines sharp edges of an image, acquired before or after the center

66
Q

what cannot produce T2*w

A

spin echo sequences

67
Q

what is the key difference between spin & gradient echoes

A

presence of 180 degrees refocusing pulse, excitation RF pulse less than 90 degrees and gradient echo is faster

68
Q

gradient echo can be modified by __

A

RF, TE, TR

69
Q

why does early bleeding appear darker in T1w

A

higher susceptibility

70
Q

why does MRI take a long time

A

due to phase encoding

HSC3007 MRI (10 decks)

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