Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

HSC3007 MRI > Week 5 > Flashcards

Week 5 Flashcards

1
Q

image quality is controlled by __

A

resolution, scan time, SNR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are constraints of image quality

A

tissue contrast, specific absorption rate, and stimulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is SNR

A

MR echo amplitude received by receiver coils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

noises that can affect SNR are __

A

thermal motion, system electronics, patient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what parameters must increase signal to increase?

A
  • higher B0
  • larger voxels
  • higher averages
  • narrower receiver bandwidths
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

drawbacks of higher B0

A

more expensive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

drawbacks of using larger voxels

A

lower resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

drawbacks of using higher averages

A

longer scan time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

drawbacks of narrower receiver bandwidth

A

artifacts present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

slice resolution is increased by __

A

increasing slice thickness which raises SNR but causes more blurring & partial volume effects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what does FOV determine

A

total scan coverage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is matrix

A

number of phases & frequency encoding steps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

FOV formula

A

voxel size x matrix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what does smaller voxel size cause

A

higher spatial resolution but lower SNR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

scan time is dependent on __

A

patient comfort, tolerance and co-operation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

3 types of MRI artifacts

A

hardware, patient, radiographer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

types of hardware MRI artifacts are __

A
  • field in-homogeneity
  • gradient non-linearity
  • RF interference artifact
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what causes field in-homogeneity

A

Large FOV with large frequency differences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how does field in-homogeneity affect image quality

A

degrades from iso-center to max FOV, leading to failed fat saturation & banding artifacts

20
Q

solution to field in-homogeneity artifacts

A
  • smaller FOV
  • pulse sequences not sensitive to frequency differences
21
Q

what causes Gradient non-linearity

A

large FOV

22
Q

how does Gradient non-linearity affect image quality

A

Gradient pulses encode spatial info by applying linear field but at edge of field, linearity decreases causing shift in spatial info

23
Q

solution to Gradient non-linearity artifacts

A
  • smaller FOV
  • filter to correct distortion within gradient specifications
24
Q

what causes RF interference artifact

A

Randomly occurs along phase direction

25
Q

how does RF interference affect image quality

A

RF emission comes from external or internal source

26
Q

solution to RF interference artifacts

A

identify & remove source of interference

27
Q

types of patient MRI artifacts are __

A

motion & metal artifacts

28
Q

how does motion artifact affect image quality

A

Each TR repeated multiple times with incrementing phase encoding but with movement, data encoding in different spatial location = different K-space

29
Q

solution to motion artifacts

A

stop motion by force if needed, immobilizations, sequences less sensitive to motion

30
Q

what causes metal artifact

A

Severity of artifact dependent on metal type, size & orientation

31
Q

how does metal artifact affect image quality

A

Susceptibility causes signal voids, distortions, failure to fat saturate

32
Q

solution to metal artifacts

A

use Spin-Echo (instead of gradient echo), high bandwidth RF pulses, view angle tilted, multifrequency acquisitions, different fat saturation methods

33
Q

types of radiographer MRI artifacts are __

A
  • aliasing / phase-wrap
  • cross talk
  • chemical shift artifact
  • signal intensity variations
34
Q

what causes aliasing / phase-wrap

A

FOV in phase encoding direction smaller than object to be measured

35
Q

how does aliasing / phase-wrap artifact affect image quality

A

Ambiguous phase info since outside range of encoding

36
Q

solution to aliasing / phase-wrap

A

larger FOV in phase encoding direction, oversampling, radial encoding

37
Q

what causes cross talk

A

Slices too closely spaced or non-ideal slice profiles used

38
Q

how does cross talk artifact affect image quality

A

Excitation RF pulses do not excite perfect rectangle causing slices to interfere with each other & saturate spins in-between

39
Q

solution to cross talk artifact

A
  • Scan with gaps between slices
  • scan in multiple concatenations
  • change acquisition order
  • 3D sequences
40
Q

what causes chemical shift artifact

A

Black / white bands at structural edges containing fat & water

41
Q

how does chemical shift artifact affect image quality

A

Since system frequency tuned to water, fat protons mis-mapped to different location in frequency direction

42
Q

solution to chemical shift artifact

A
  • change frequency encoding direction
  • increase pixel bandwidth
  • saturate fat
43
Q

what causes signal intensity variation artifact

A

When using surface coils, anatomy nearest to coils have brighter signals than other parts

44
Q

how does signal intensity artifact affect image quality

A

Receiver coil sensitivity decreases with distance and hence, tissues appear less bright

45
Q

solution to signal intensity variation artifact

A
  • different coil design used
  • apply filter to normalize signal intensity

HSC3007 MRI (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions