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MRI Physics 2 > Review on parameters > Flashcards

Review on parameters Flashcards

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1
Q

What are the parameters that scan time is directly affected by?

A

TR
Phase matrix
NEX
ETL

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2
Q

Rectangular FOV (created by reducing the number phase encodings) ____ scan time while maintaining spatial resolution (but ____ SNR).

a) reduces, reduces
b) reduces, increases
c) increases, reduces
d) increases, increases

A

a) reduces, reduces

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3
Q

___ FOV = ↑ SNR

A

↑ FOV = ↑ SNR

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4
Q

___ FOV = ↓ spatial resolution

A

↑ FOV = ↓ spatial resolution

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5
Q

___ matrix = ↓ SNR

A

↑ matrix = ↓ SNR

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6
Q

___ matrix = ↑ spatial resolution

A

↑ matrix = ↑ spatial resolution

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7
Q

___ slice thickness = ↓ SNR

A

↓ slice thickness = ↓ SNR

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8
Q

___ slice thickness = ↑ spatial resolution

A

↓ slice thickness = ↑ spatial resolution

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9
Q

How does changing receive bandwidth affect SNR?

A

Recall: receive bandwidth is the range of frequencies sampled during application of the readout gradient.
Decreasing bandwidth results in less noise being sampled relative to the signal.
↑receive bandwidth = ↓SNR
↓ receive bandwidth = ↑SNR
Halving bandwidth increases SNR by about 40%.
Reducing bandwidth also increases chemical shift artefact, and increases the minimum TE available.
↓ receive bandwidth = ↑chemical shift artefact

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10
Q

How does changing NEX affect SNR?

A

Recall: NEX is the number of times data is collected (i.e. number of times each line of K space is filled).
Data contains both signal and random noise – doubling NEX therefore doubles the amount of signal collected, but also the random noise.

↑NEX = ↑SNR

Doubling NEX only creates a √2 = 1.4 (or 40%) increase in SNR
2x NEX = 1.4x SNR
4x NEX = 2x SNR

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11
Q

How does changing TE affect SNR?

A

↑TE = ↓SNR

-Therefore, sequences with short TE’s (T1- and PD-weighted) have greater SNR than those with long TE’s (T2-weighted).

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12
Q

A coarse matrix has a:

i) low number of frequency encodings and/or phase encodings
ii) high number of frequency encodings and/or phase encodings
iii) No frequency encodings and/or phase encodings

A

i) low number of frequency encodings

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13
Q

A fine matrix has a:

i) low number of frequency encodings and/or phase encodings
ii) high number of frequency encodings and/or phase encodings
iii) No frequency encodings and/or phase encodings

A

ii) high number of frequency encodings and/or phase encodings

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14
Q

A range of freq. that are sampled during readout is known as___

A

receive bandwidth

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15
Q

A range of freq. transmitted in an RF excitation pulse is known as___

A

transmit bandwidth

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16
Q

The outer lines of K-space are filled with…?

A

high-resolution data

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17
Q

The central lines of K-space are filled with…?

A

signal & contrast data

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18
Q

What are the 3 factors that control contrast for an inversion recovery sequence?

A

TR
TE
TI

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19
Q

A spin echo pulse sequence preceded by a 180 RF pulse is…..

A

an inversion recovery pulse sequence

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20
Q

An inversion recovery sequence with a short TI is…

A

a STIR

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21
Q

An inversion recovery sequence with a long TI is…

A

a FLAIR

22
Q

The time between the 180° preparation pulse and the 90° excitation pulse during an inversion recovery sequence is known as…

A

TI (inversion time)

23
Q

What type of pulse sequence does a 90° RF followed by 180° RF produce?

A

spin echo

24
Q

A 90° RF followed by a train of 180° RF pulses produces what type of pulse sequence?

A

fast spin echo (FSE)

25
Q

What type of pulse sequence does a 180° RF followed by 90°RF produce?

A

inversion recovery

26
Q

What type of pulse sequence is produced by using a variable RF pulse followed by a gradient?

A

gradient echo

27
Q

Which of the following is a benefit of increasing NEX?

a. Decreases T1 weighting
b. Increases SNR
c. Decreases slices
d. Increases scan time

A

increases SNR

28
Q

What increases the image resolution at the expense of reduction of SNR?

A

thinner slices
increasing matrix size
decreasing FOV

29
Q

What is the difference between high and low bandwidths?

A

High bandwidth: reduce the time of sample = faster scans and shorter TEs, but decreases the SNR

Low bandwidth: improves the SNR but increases the min TE

30
Q

What are the consequences of decreasing Phase Matrix?

A

reduce scan time
reduce reso
high SNR
increase truncation artifact

31
Q

How do you improve low SNR?

A

increase FOV
decrease matrix
increase slice thickness
decrease bandwidth

32
Q

How do you improve poor resolution?

A

increase matrix
decrease slice thickness
decrease FOV

33
Q

How do you improve chemical shifts?

A

increase bandwidth

34
Q

How many lines of k-space are filled per echo?

A

1 line of k-space

35
Q

Where are a series of 0s and 1s series are stored in k-space?

A

all over the MRI image

36
Q

How do frequency and phase fill in k-space?

A

frequency = row
phase = column

37
Q

What are the 2 benefits of Parallel Imaging?

A

decrease scan time
lower SAR

38
Q

What are the 2 disadvantages of Parallel Imaging?

A

low SNR
reduce artifacts

39
Q

Does Frequency Matrix have any direct effect on scan time?

A

No, only Phase Matrix has

40
Q

What are the multi-coil benefits without Parallel Imaging?

A

Better SNR

41
Q

What are the advantages of FSE?

A

more NEX
more matrices
improve scan time

42
Q

What are the disadvantages of FSE?

A

image blurring
increased SAR

43
Q

In FSE, what drives longitudinal recovery?

A

driven equilibrium in shorter TR

44
Q

What makes fat brighter in a T2?

A

FAT SAT
STIR

45
Q

What happens when you increase ETL per TR?

A

less slices available per TR

46
Q

Does k-space fill in order?

A

No. It’s filled out of order

47
Q

Which technique fills all k-space in one TR?

A

single shot spin echo

48
Q

Where is Effective TE stored in FSE?

A

in the center of k-space (due to shallow gradient slope)

49
Q

What does the FLAIR sequence suppress?

A

CSF

50
Q

What does the STIR sequence suppress?

A

fat

MRI Physics 2 (3 decks)

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