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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
outer K-space provides ___
high frequency details / edges
26
order of filling K-space is __
K-space trajectory
27
signal which is phase-shifted by 90 degrees to determine ___
direction of magnetization rotation
28
In Fourier Transform, any signal / waveform made up by adding ___
- pure tones / sine waves - appropriate frequency - amplitude - phase
29
spatial / coil encoding is used for ___
parallel imaging
30
time encoding is used for ___
multi-slice imaging
31
spin-echo cancels out __
fixed magnetic effects of inhomogeneity & susceptibility
32
spin-echo sequence characterized by __
90 degrees RF pulse > 180 degrees RF rephasing pulse at TE/2
33
spin-echo mainly used for __
T1 imaging
34
HASTE
half-former acquisition single shot turbo spin echo
35
HASTE preparation, excitation, readout
preparation: none excitation: spin-echo readout: single shot TSE
36
HASTE AKA
single shot fast spin echo
37
2D TSE w/ high turbo factor
all lines of fourier plane in single TR
38
radial TSE
turbo spin echo w/ motion correction
39
radial TSE preparation, excitation, readout
preparation: none excitation: spin-echo readout: radial TSE
40
radial TSE AKA
PROPELLAR
41
spin-echo cancels __
fixed magnetic field effects of inhomogeneity & susceptibility
42
gradient pulse applied to __
accelerate spin dephasing
43
gradient echo features an RF pulse at an angle followed by __
bipolar reading gradient
44
since gradient choes don't have refocusing plane, it is ___
more sensitive to B0 magnetic field inhomogeneity
45
gradient echo preparation, excitation, readout
preparation: none excitation: gradient-echo readout: spin-echo
46
gradient echo AKA
fast low angle shot (FLASH) spoiled gradient echo (SPGR)
47
GRE T2*W preparation, excitation, readout
preparation: none excitation: gradient-echo readout: segmented echoes
48
balanced steady state free-precession preparation, excitation, readout
preparation: none excitation: gradient-echo readout: steady state
49
echo planar imaging preparation, excitation, readout
preparation: fat preparation excitation: spin-echo (diffusion), gradient- echo (fMRI) readout: Echo planar
50
echo planar imaging is __
single shot ultra fast acquisition; 1 slice = 50 ms
51
what is fat saturation
removal of fat signal for better visualization of lesions & oedemas
52
different methods of fat saturation
- spectral fat saturation - inversion recovery - water excitation - dixon
53
inversion recovery is ___
180 degrees inversion pulse before excitation
54
Pulse sequence determines __
number, strength, timing of RF & gradient pulses which determines image contrast & K-space trajectory
55
Number of points on echo determines __
resolution in frequency direction
56
Lines in center of K-space determines __
contrast
57
spin-echo sequences are mainly used for
T1 imaging
58
what is TOF
- 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
what are the disadvantages of GRE T2*W
Increases susceptibility artifacts Bad for implants but good for paramagnetic substances
60
what is fat saturation
Removes fat signal = prevents fat ghosting Improves visualization of lesions esp post contrast & oedemas in fatty areas
61
what are the preparation, excitation and readout for echo planar imaging
Preparation = Fat saturation, excitation = spin echo for diffusion / gradient echo for fMRI, readout = echoplanar
62
DWI is highly sensitive and specific for __
acute stroke detection
63
what does DWI assume
haemorrhage excluded
64
what is used to localize signals
gradients
65
High spatial frequencies in K-space are stored at __
periphery, defines sharp edges of an image, acquired before or after the center
66
what cannot produce T2*w
spin echo sequences
67
what is the key difference between spin & gradient echoes
presence of 180 degrees refocusing pulse, excitation RF pulse less than 90 degrees and gradient echo is faster
68
gradient echo can be modified by __
RF, TE, TR
69
why does early bleeding appear darker in T1w
higher susceptibility
70
why does MRI take a long time
due to phase encoding

HSC3007 MRI (10 decks)

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