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Fundamentals of MRI > Module 6 > Flashcards

Module 6 Flashcards

Learn material from module 6

1
Q

What are the two purposes of a RF pulse ?

A
  1. Rephasing in spin echo sequences

2. Excitation purposes

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2
Q

What are the main types of pulse sequences ?

A
  1. Spin Echo

2. Gradient Echo

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3
Q

What is the main difference between spin echo and gradient echo?

A

The spin echo is rephased with a 180 rephasing pulse and gradient echo rephases with a gradient

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4
Q

How would T1 contrast be generated with conventional spin echo with one echo?

A
  • one echo
  • short TR
  • short TE
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5
Q

What types of contrast are generated with two echos?

A

T2 or Proton Density

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6
Q

True or False - T1 images are the best images for showing pathology.

A

False - T1 images are best for showing anatomy

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7
Q

Which type of contrast has higher SNR?

A

T1 has higher SNR but lower CNR

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8
Q

In fast or turbo spin echo what does the number of pulses performed per TR correspond to ?

A
  • number of echos produced

- number of lines of k space filled

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9
Q

True or False : if the echo train is too long the pulses will get smaller and eventually run out of signal

A

True

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10
Q

What is the effective TE?

A

This is what is used to weight the image even though the data has different weightings. Phase encoding slopes will be applied to the data to achieve this weighting

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11
Q

If there is a steep phase encoding gradient how does that affect the amplitude of the resulting echo?

A

They reduce the amplitude of the resulting echo

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12
Q

How are shallow and steep slopes placed ?

A 
Shallow slopes (max signal) - centre over effective TE
Steep slopes - Away from effective TE
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13
Q

What is the result of placing steep slopes away from the effective TE?

A

They fill the outer lines of k-space so they have more effect on resolution less effect on contrast

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14
Q

Why does FSE have limited use in the chest and abdomen?

A

Breathing artefacts are worse

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15
Q

Why is fat bright on T2 weighted FSE images ?

A

The extra RF pulses causes fat spin spin interaction effects to be reduced

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16
Q

True or False : The repeated 180 degree pulses causes magnetization transfer effects to increase and muscle to appear lighter

A

False it cause muscles to appear darker

17
Q

How can blurring be reduced at the edges of tissues with different T2 values?

A

Reducing the echo train length

18
Q

Which of the following is not an advantage of FSE:

a. Excellent image quality
b. Reduced artefacts
c. Increased T2 information
d. Can use multiple NEX and high resolution matrix

A

b. is not an advantage there is actually more flow and motion artefacts in FSE

19
Q

How are the lines of k-space filled in Single Shot Fast Spin Echo ?

A

They are filled all at once

20
Q

Why is there a possibility of not getting enough coverage in single shot fast spin echo?

A

High SAR because of the amount of 180 degree pulses which can cause heat to generate which can be dangerous

21
Q

What does a reverse flip angle excitation pulse do? Why?

A

Moves remaining transverse magnetization into longitudinal plane
this allows it to be available for next TR

22
Q

What is unique about the resultant image of Driven Equilibrium Fourier transform?

A

Signal intensity of water is increased

23
Q

What is the correct sequence for inversion recovery?

A

180 degree inversion pulse —> inversion time —–>90 degree excitation pulse —-> FID is rephased by 180 degree pulse to produce a spin echo

24
Q

What is the main factor for image contrast with inversion recovery ?

A

Inversion time

25
Q

How is a T1 weighted image acquired ?

A

90 degree pulse applied after NMV has relaxed through transverse plane

26
Q

Why does the 180 degree inverting pulse cause large differences in contrast ?

A

They recover from full saturation rather than from transverse plane
More time for differences in T1 weighting to show up

27
Q

What is done for pathology weighting?

A

Longer TE is used so that long T2 tissues are bright therefore pathology appears bright

28
Q

What is a disadvantage of inversion recovery ?

A

Long scan times is a disadvantage

29
Q

What are the two types of fast inversion recovery?

A

STIR and FLAIR

30
Q

How is the TI chosen for a STIR sequence ?

A

It is chosen so it matches fat is fully recovered to the transverse plane this nulls the signal from fat

31
Q

Why is STIR sequence used for musculoskeletal imaging ?

A

It nulls signal from the fat in bones so that bone bruising and tumors are easier to see

Fundamentals of MRI (6 decks)

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