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Z MRI Physics > exam 2 > Flashcards

exam 2 Flashcards

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1
Q

Phase is measured in____________

A

Radians or Degrees

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2
Q

The 90 degree RF pulse is also called the ______________

A

flip angle

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3
Q

Using a long TE enhances T2 and T2* contrast.

true/false

A

true

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4
Q

A long TE gives spins more time to dephase therefor increasing T2 contrast

true/false

A

true

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5
Q

The definition of weighting is the parameters are selected to make one contrast mechanism dominate or the others.

true/false

A

true

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6
Q

What is meant by the tumbling rate?

A

The rate at which a molecule moves. This has a direct effect on T1 and T2 relaxation times of tissues.

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7
Q

Fat has a fast tumbling rate motion due to Lipids tightly packed together.

true/false

A

false

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8
Q

The T1 time of fat is short

true/false

A

true

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9
Q

T1 time of water is long

true/false

A

true

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10
Q

Select all the Extrinsic factors.

A

TR

TE

Flip Angle

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11
Q

Select all that apply to Intrinsic factors

A

T2 recovery

T1 recovery

Proton Density

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12
Q

This parameter determines the—Time between the excitation pulse and the middle of the Spin Echo,Measures in ms and determines amount of Transverse or T2 decay

A

TE

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13
Q

Time between Excitation Pulses determines the amount of Longitudinal or T1Recovery is…..

A

TR

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14
Q

Select all that apply to T1 weighting.

A

Bright Fat, Dark Water

Short TR and TE times

TR must be short so that fat and water have time to recover to Bo

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15
Q

Gradients serve many functions in MRI. Select all that apply to them.

A

Clice selectoin

phase encoding

frequency encoding

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16
Q

The two points along a gradient contain a range of frequencies. This band of frequencies are called?

A

bandwidth

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17
Q

The range of frequencies the RF pulse sends in to match the band of frequencies along our slope is termed?

A

transmit bandwidth

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18
Q

When increasing your slice thickness from 3mm to 10mm select the two items needed to achieve this.

A

Shallow slope of the gradient.

broad transmit bandwidth

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19
Q

Which gradient is turned on during the echo (signal)?

A

frequency encoding

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20
Q

Frequency encoding typically is along the long axis of the anatomy.

true/false

A

true

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21
Q

The frequency encoding gradient is also called the?

A

readout gradient

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22
Q

The steepness of the slope of the read out gradient will determine the Frequency Field of View

true/false

A

true

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23
Q

A steep phase encoding gradient results in large phase shifts

true/false

A

true

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24
Q

The amount of time the read out gradient is left on is known as the acquisition window.

true/false

A

true

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25
Q

The sampling frequency is determined by the Nyquist theorem.

true/false

A

true

26
Q

Receive Bandwidth = ________ x Nyquist frequency

A

2

27
Q

In FFT if a high amplitude is located within a pixel will this be assigned a Dark or Bright signal?

A

bright

28
Q

——Advantages of this pulse sequence is it rephases faster requiring a shorter TE as well as a shorter TR

—Disadvantages- susceptible to magnetic field inhomogeneities. What pulse sequence are these characteristics describing.

A

gradient echo

29
Q

Rephase gradients are called__________ ?

A

rewinders

30
Q

—This parameter is the time between Excitation Pulses. —Determines the amount of Longitudinal or T1Recovery

A

TR

31
Q

—T1 time of water is long.

true/false

A

true

32
Q

What type of energy is involved in making MR images

A

Radio frequency

33
Q

f = γB0 represents _____________ equation?

A

larmor

34
Q

If you had a 1.5 Tesla MRI unit what would the processional frequency of a hydrogen be approximately?

A

63.86

35
Q

The time from the initial 90 degree RF pulse to the next RF pulse is termed?

A

Repetition Time

36
Q

—T1 recovery(spin lattice relaxation) is the relaxation time for 63% of the Net magnetization of the tissue to recover.

true/false

A

true

37
Q

—The T2 relaxation time is the time it takes for tissue to decay in the transverse plane to 37% (or 63% to be lost)

true/false

A

true

38
Q

——Advantages of this pulse sequence is it rephases faster requiring a shorter TE as well as a shorter TR

—Disadvantages- susceptible to magnetic field inhomogeneities. What pulse sequence are these characteristics describing.

A

gradient echo

39
Q

—The T2 time of water is long.

true/false

A

true

40
Q

—The T2 time of fat is short

true/false

A

true

41
Q

What best describes Temporal resolution?

A

Ability to distinguish structural differences over time

42
Q

If you increase the receive bandwidth what affect will this have on SNR?

A

decrease

43
Q

To determine voxel volume you need the pixel dimensions and the slice thickness to determine volume.

true/false

A

true

44
Q

One 90 degree Excitation Pulse and one 180 degree refocusing pulse describes what pulse sequence?

A

spin echo

45
Q

What is the TI of CSF in a T2 weighted image?

A

1700-2200ms

46
Q

This modified TSE/FSE parameter pushes any transverse magnetization into the longitudinal plane, making it available for the beginning of the next TR period.

A

DRIVE

47
Q

This type of K space filling will fill the outer lines first and then fill the central lines after contrast injection

A

key hole

48
Q

What pulse sequence would be best to show pathology that may be next to CSF?

A

FLAIR

49
Q

When gradients are used to dephase and rephase the residual magnetization this is called?

A

gradient spoiling

50
Q

RF is transmitted at a certain frequency to exite a slice at a specific phase.

A

RF spoiling

51
Q

What type of energy is involved in making MR images

A

Radio frequency

52
Q

Hydrogen Nuclei start to Recover back to Bo or the Longitudinal Plane, they are now Out of Phase

true/false

A

true

53
Q

________mechanics deals with large objects

A

classical

54
Q

Precession Frequency depends on what two factors?

A

Type of nucleus

Strength of Bo

55
Q

The F.I.D. can be defined as

A

Signal after the R.F. pulse is removed

Primary signal

Dephasing Hydrogen ProtonsCorre

All of these

56
Q

Magnetic susceptability can be defined as

A

The ease by which an object can become magnetized

57
Q

When a patient is subjected to a strong magnetic field the patient becomes polarized and has

A

net magnetization

58
Q

FerroMagnetism refers to ojects that are

A

easily infuenced by BO

59
Q

Hydrogen contains its own large magnetic moment due to the odd number of Protons in the Nucleus

true/false

A

true

60
Q

In order for resonance to occur the RF Pulse needs to match the exact precessional Frequency of Hydrogen Atoms

true/false

A

true

61
Q

Once a Magnetic Moment is exposed to an external Magnetic Field it will line up with or against the external field.

true/false

A

true

Z MRI Physics (12 decks)

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