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MRI Physics > Unit 5 > Flashcards

Unit 5 Flashcards

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1
Q

What is RF pulse?

A

a burst of radiofrequency energy

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2
Q

What is Net Magnetization relaxation?

A

the return of M to equilibrium as it releases absorbed RF (T1), and loses energy (T2)

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3
Q

What is free induction decay?

A

simple signal given off by the relaxation of M to equilibrium

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4
Q

What is spin/proton density?

A

relative number of protons in a sample

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5
Q

What is spin echo?

A

signal given off by the relaxation of M to equilibrium after a refocusing pulse

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6
Q

What is T1 relaxation relaxation/longitudinal recovery?

A

regrowth of net magnetization along the Z axis

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7
Q

What is spin-lattice relaxation?

A

process of RF being dissipated (T1 relaxation)

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8
Q

What is T2 relaxation/transverse decay?

A

decay of transverse magnetization

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9
Q

What is spin-spin relaxation?

A

process of spins interacting w/ each other => phase changes (T2 relaxation)

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10
Q

What is T2* relaxation?

A

transverse decay in presence of B0 inhomogeneities

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11
Q

What is phase?

A

degree to which spins are precessing

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12
Q

Why is T2* relaxation shorter than T2 relaxation?

A

B0 inhomogeneity increases dephasing

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13
Q

Which relaxation is most affected by B0 inhomogeneity?

A

T2*

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14
Q

At what time is true T1 relaxation measured?

A

at 63% of regrowth

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15
Q

At what time is true T2 relaxation measured?

A

at 63% of decay (37% remaining)

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16
Q

Which substance has the shorted T1 and T2 times?

A

fat

17
Q

Which substance has the longes T2 and T2 times?

A

water

18
Q

Which substance is bright on T1 weighted image?

A

fat

19
Q

Which substance is bright on T2 weighted image?

A

water

20
Q

How do water and fat nuclei experience magnetic fields?

A

Fat nuclei experience a lower magnetic field (C offers slight buffer)
Water nuclei experience a higher magnetic field (O exposes H)

21
Q

True/False: Tissues w/ long T1 times appear bright on T1 weighted image.

A

false - appear dark

22
Q

True/False: Tissues w/ long T2 times appear bright on T2 weighted image.

A

true

23
Q

Which flip angle RF pulse creates a FID?

A

90 or less

24
Q

Which flip angle RF pulse creates a spin-echo?

A

180

25
Q

Which type of relaxation (weighted image) is created by spin-spin interactions and B0 inhomogeneity?

A

T2*

26
Q

Which type of relaxation (weighted image) is created by only spin-spin interactions?

A

T2

MRI Physics (8 decks)

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