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MRI Physics > Parameters and Tradeoffs > Flashcards

Parameters and Tradeoffs Flashcards

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1
Q

SNR

A

signal to noise ratio

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2
Q

The amount of voltage induced in the coil at the time the echo is collected

A

signal

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3
Q

The frequencies of RF energy that exist randomly in time and space

A

noise

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4
Q

Describe low SNR

A

grainy
noisy

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5
Q

Coil position for maximum signal

A

transverse plane, perpendicular to B0

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6
Q

The parameter controls the number of echos stored per line of k-space

A

number of signal averages (NSA or NEX)

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7
Q

A range of frequencies

A

bandwidth

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8
Q

The smallest unite of a digital image

A

pixel

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9
Q

3D unit of volume

A

voxel

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10
Q

Find voxel volume

A

pixel area x slice thickness

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11
Q

Find pixel area

A

FOV/Matrix

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12
Q

Name the 2 dimensions of the pixel

A

phase matrix
frequency matrix

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13
Q

Which matrix will always be the smaller number?

A

phase matrix

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14
Q

Scan Time equation

A

TR x Phase Matrix x NEX

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15
Q

What’s known as under sampling and over sampling?

A

Rectangular FOV

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16
Q

Does Rec FOV affect voxel size?

A

no, doesn’t change resolution

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17
Q

What increases number of echoes but doesn’t add any dimension to the image?

A

oversampling

18
Q

Oversampling Benefits

A

avoid aliasing
increase SNR
increase scan time
no change to resolution

19
Q

TR increased

A

increase SNR
increase number of slices
increase scan time
decreases T1 weighting

20
Q

TR decreased

A

decrease scan time
decrease SNR
decrease number of slices
increase T1 weighting

21
Q

TE increased

A

decrease SNR
increase T2 weighting

22
Q

TE decreased

A

increase SNR
decrease T2-weighting

23
Q

NEX increased

A

increase SNR
increase in scan time
increase signal averaging

24
Q

NEX decreased

A

decrease SNR
decrease signal averaging
decrease in scan time

25
Q

Slice thickness increased

A

increases SNR
increase coverage of anatomy
increase partial voluming
decrease spatial resolution

26
Q

Slice thickness decreased

A

increase spatial resolution
decrease partial voluming
decrease SNR
decrease coverage

27
Q

FOV increased

A

increase SNR
increase coverage of anatomy
decrease potential of aliasing
decrease spatial resolution

28
Q

Matrix increased

A

increase spatial resolution
increase scan time
decrease SNR if pixel small

29
Q

Matrix decreased

A

decrease scan time
decrease spatial resolution
increase SNR if pixel large

30
Q

Receive bandwidth increased

A

decrease in chemical shift
decrease in min TE
decrease SNR

31
Q

Receive bandwidth decreased

A

increase in SNR
increase in chemical shift
increase in min TE

32
Q

Find best spatial resolution?

A

smaller voxel size
smallest FOV

33
Q

Find best SNR

A

increase voxel volume
increase slice thickness
increase NEX
increase FOV
increase TR
decrease TE
decrease coils
decrease bandwidth
decrease matrix

34
Q

What happens when B0 increases,

A

SNR increases

35
Q

How to change an image from low resolution to better resolution?

A

decrease FOV
decrease slice thickness
decrease matrix
increase NEX

36
Q

Increased multi slice leads to:

A

increase scan time
decrease T1 weighting

37
Q

Factors affecting SNR

A

TR
TE
flip Angle
bandwidth
proton Density
voxel volume

38
Q

Find new SNR

A

original SNR x square root of new factor of increase

39
Q

Benefits of GRE

A

scan time

40
Q

Under sampling Benefits

A

decrease scan time
decrease SNR
aliasing

41
Q

If an image looks too fuzzy/blurry,

A

increase matrix
decrease slice thickness
decrease FOV

42
Q

Get better T1 contrast,

A

decrease TR

MRI Physics (8 decks)

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