Parameters and Tradeoffs Flashcards

(42 cards)

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?

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
Slice thickness increased
increases SNR increase coverage of anatomy increase partial voluming decrease spatial resolution
26
Slice thickness decreased
increase spatial resolution decrease partial voluming decrease SNR decrease coverage
27
FOV increased
increase SNR increase coverage of anatomy decrease potential of aliasing decrease spatial resolution
28
Matrix increased
increase spatial resolution increase scan time decrease SNR if pixel small
29
Matrix decreased
decrease scan time decrease spatial resolution increase SNR if pixel large
30
Receive bandwidth increased
decrease in chemical shift decrease in min TE decrease SNR
31
Receive bandwidth decreased
increase in SNR increase in chemical shift increase in min TE
32
Find best spatial resolution?
smaller voxel size smallest FOV
33
Find best SNR
increase voxel volume increase slice thickness increase NEX increase FOV increase TR decrease TE decrease coils decrease bandwidth decrease matrix
34
What happens when B0 increases,
SNR increases
35
How to change an image from low resolution to better resolution?
decrease FOV decrease slice thickness decrease matrix increase NEX
36
Increased multi slice leads to:
increase scan time decrease T1 weighting
37
Factors affecting SNR
TR TE flip Angle bandwidth proton Density voxel volume
38
Find new SNR
original SNR x square root of new factor of increase
39
Benefits of GRE
scan time
40
Under sampling Benefits
decrease scan time decrease SNR aliasing
41
If an image looks too fuzzy/blurry,
increase matrix decrease slice thickness decrease FOV
42
Get better T1 contrast,
decrease TR