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MRI > Parameters > Flashcards

Parameters Flashcards

1
Q

Contrast parameters that affect SNR

A

TR, TE, TI, flip angle

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2
Q

As NSA is increased by 2, the SNR increases by…

A

By the square root of the change. Square root of 2 = 1.41, 40%

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3
Q

Scan time formula for conventional 2d acquisition

A

Tr x Ny (phase encodings) x NSA

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4
Q

Scan time formula for 3d acquisition

A

TR X Ny X NSA X # slices (partitions)

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5
Q

Scan time formula for 2d FSE Acquisition

A

TR X Ny X NSA/ETL

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6
Q

Scan time formula for EPI

A

TR X NSA X #shots (# shots is matrix / ETL)

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7
Q

Increasing TR has what affect on SNR?

A

Increasing

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8
Q

What effect does increasing TR have on artifacts?

A

None apparent

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9
Q

What effect does increasing TE have on SNR?

A

Reduces

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10
Q

What affect does increasing TE have on artifacts?

A

Increases susceptibility artifacts and can change chemical shift

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11
Q

What sequences are useful in pediatric brain exams?

A

Inversion sequences for heavy T1 weighting. Relatively short TR with short TE and TI to null CSF

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12
Q

Reducing the flip angle has the same effect on contrast as…

A

Increasing the TR, less T1 weighted

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13
Q

Increasing flip angle has what effect on SNR?

A

Increase up to the Ernst angle

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14
Q

Increasing NSA had what effect on artifacts?

A

Reduce some forms of motion artifacts

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15
Q

What affect did increasing FOV have on SNR?

A

Increase SNR by the square

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16
Q

What affect does increasing as FOV Have son artifacts?

A

Increased susceptibility artifact
Increased chemical shift artifact
Decreases aliasing when FIV is larger than the anatomy
Increases partial volume averaging

17
Q

What effect does increasing matrix have on SNR?

A

Overall reduction
Increase by the square root in sampling
Decrease directly by voxel size

18
Q

What effect does increasing matrix have on artifacts?

A

Decreases Gibbs or truncation artifact

And partial volume averaging

19
Q

What effect does increasing slice thickness have on artifacts?

A

Increased susceptibility artifact

Increase partial volume averaging

20
Q

What effect does increased ETL have on scan time?

A

Decreases scan time

21
Q

What effect does increasing ETL have on resolution?

A

Decreased resolution thru increased blurring

22
Q

What effect does increasing the number of slices in a 3d acquisition have on SNR and Resolution?

A

Increased SNR with # of slices (more sampling),

increased resolution with decrease in thickness

23
Q

What effect does narrowing receiver bandwidth have on TE?

A

Increase,

More t2 weighting, less slices

24
Q

What effect does narrowing receiver bandwidth have on artifact?

A

Increased chemical shift

25
Q

When imaging vascular structures using TOF, what order should slices be acquired in to maximize signal?

A

Against the flow

MRI (8 decks)

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