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Fundamentals of MRI > Module 5 > Flashcards

Module 5 Flashcards

Learn the material from module 5 so we can be MRI geniuses

1
Q

What is signal to noise ratio (SNR)?

A

amplitude of signal vs amplitude of noise

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2
Q

What factors cause variations in noise ?

A

different patient’s height, weight, anatomy being scanned and inherent noise of the system

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3
Q

which of the following does not affect SNR?

a. Voxel volume
b. Sending bandwidth
c. Coil type
d. Flip angle

A

B. Sending bandwidth does not affect SNR it is receiving bandwidth

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4
Q

Why does higher magnetic field strength cause higher SNR?

A

Higher energy results in more of a gap between high and low energy nuclei which allows for more magnetization to be available

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5
Q

True or false: high proton density results in high SNR

A

True

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6
Q

What parameters make up voxel volume?

A
  1. Slice thickness
  2. phase
  3. frequency
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7
Q

What is the difference between a coarse matrix and a fine matrix?

A

Coarse matrix has a low number of frequency encodings and a fine matrix has a large number of frequency encodings?

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8
Q

Which has smaller pixels a fine or coarse matrix?

A

Fine matrix has smaller pixels

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9
Q

Complete the following statement :

Large pixels have more (1)___________ resulting in a (2)_________ SNR

A
  1. protons

2. higher

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10
Q

If you decrease flip angle what will happen to SNR?

A

SNR will decrease if you decrease the flip angle

However scan time will also decrease !

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11
Q

Why does increasing TR increase SNR?

A

Increased TR allows for more time for recovery so more is available to be flipped.

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12
Q

If TE is long more decay occurs how does this affect the signal?

A

Less signal which means less SNR

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13
Q

Why is increasing Nex not the best method of increasing SNR?

A

It is not the best method of increasing SNR because it increases the scan time significantly without enough of an increase in SNR to make it worth it.

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14
Q

What is Nex?

A

Nex is the number of times data is collected

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15
Q

Halving bandwidth increases SNR by:

a. 20%
b. 60%
c. 50%
d. 40%

A

d. 40%

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16
Q

Why do small pixels have better spatial resolution than large pixels?

A

Small structure can be differentiated easier when the pixels are smaller.

17
Q

What is it called when the increase in pixel size causes areas of light and dark to be averaged together resulting in a gray area?

A

Partial voluming

18
Q

What happens to spatial resolution and SNR when slice thickness is decreased?

A

SNR decreases but spatial resolution increases

19
Q

Increasing FOV results in ____(1)____ pixels and ____(2)___ spatial resolution.

A

(1) larger

(2) decreased

20
Q

How does increasing matrix size effect SNR? What happens to resolution ?

A

Results in lower SNR but improves resolution

21
Q

How does an operator of a MRI machine alter pixel geometry ?

A

Selecting FOV dimensions, slice thickness and image matrix.

22
Q

Which pixel shape is better for spatial resolution : square or rectangle?

A

Square

23
Q

What situation would a rectangular FOV be beneficial? Why?

A

If the anatomy being scanned is smaller in the phase axis than in the frequency axis?
It reduces scan time but also maintains spatial resolution

24
Q

When TR, matrix size and NEX are increased what happens to scan time ?

A

Scan time is increased.

25
Q

True or false : SNR is the most important factor in image quality.

A

True

26
Q

What adjustments can be made when scanning an anatomical area of low signal?

A

More NEX and larger voxel size

27
Q

What 2 variables increase when receive bandwidth is decreased ?

A

SNR and chemical shift artefact

28
Q

Which type of coil increases SNR more: Quadrature or Phased array?

A

Phased array

29
Q

What is the optimal coil position?

A

Transverse plane perpendicular to B0

30
Q

What is contrast to noise ratio

A

The difference in SNR between 2 adjacent points

31
Q

What makes pathology easier to see on a T2 weighted scan?

A

Greater water content in pathology therefore better signal

32
Q

What happens in magnetization transfer contrast?

A

Selectively saturate bound protons over free protons so less intensity from free protons

33
Q

What does the saturation band do in Magnetization transfer contrast ?

A

Selectively destroys transverse magnetization of of bound protons

34
Q

What are some problems with increasing slice thickness ?

A

Decreases resolution and increases partial voluming

35
Q

If you decrease FOV what happens to resolution ?

A

Increases resolution

36
Q

If you increase FOV what are the benefits ?

A

SNR increases coverage area increases and aliasing decreases

Fundamentals of MRI (6 decks)

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