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Z MRI Physics > exam 2 > Flashcards

exam 2 Flashcards

(61 cards)

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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
The sampling frequency is determined by the Nyquist theorem. true/false
true
26
Receive Bandwidth = ________ x Nyquist frequency
2
27
In FFT if a high amplitude is located within a pixel will this be assigned a Dark or Bright signal?
bright
28
——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.
gradient echo
29
Rephase gradients are called\_\_\_\_\_\_\_\_\_\_ ?
rewinders
30
—This parameter is the time between Excitation Pulses. —Determines the amount of Longitudinal or T1Recovery
TR
31
—T1 time of water is long. true/false
true
32
What type of energy is involved in making MR images
Radio frequency
33
f = γB0 represents _____________ equation?
larmor
34
If you had a 1.5 Tesla MRI unit what would the processional frequency of a hydrogen be approximately?
63.86
35
The time from the initial 90 degree RF pulse to the next RF pulse is termed?
Repetition Time
36
—T1 recovery(spin lattice relaxation) is the relaxation time for 63% of the Net magnetization of the tissue to recover. true/false
true
37
—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
true
38
——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.
gradient echo
39
—The T2 time of water is long. true/false
true
40
—The T2 time of fat is short true/false
true
41
What best describes Temporal resolution?
Ability to distinguish structural differences over time
42
If you increase the receive bandwidth what affect will this have on SNR?
decrease
43
To determine voxel volume you need the pixel dimensions and the slice thickness to determine volume. true/false
true
44
One 90 degree Excitation Pulse and one 180 degree refocusing pulse describes what pulse sequence?
spin echo
45
What is the TI of CSF in a T2 weighted image?
1700-2200ms
46
This modified TSE/FSE parameter pushes any transverse magnetization into the longitudinal plane, making it available for the beginning of the next TR period.
DRIVE
47
This type of K space filling will fill the outer lines first and then fill the central lines after contrast injection
key hole
48
What pulse sequence would be best to show pathology that may be next to CSF?
FLAIR
49
When gradients are used to dephase and rephase the residual magnetization this is called?
gradient spoiling
50
RF is transmitted at a certain frequency to exite a slice at a specific phase.
RF spoiling
51
What type of energy is involved in making MR images
Radio frequency
52
Hydrogen Nuclei start to Recover back to Bo or the Longitudinal Plane, they are now Out of Phase true/false
true
53
\_\_\_\_\_\_\_\_mechanics deals with large objects
classical
54
Precession Frequency depends on what two factors?
Type of nucleus Strength of Bo
55
The F.I.D. can be defined as
Signal after the R.F. pulse is removed Primary signal Dephasing Hydrogen ProtonsCorre All of these
56
Magnetic susceptability can be defined as
The ease by which an object can become magnetized
57
When a patient is subjected to a strong magnetic field the patient becomes polarized and has
net magnetization
58
FerroMagnetism refers to ojects that are
easily infuenced by BO
59
Hydrogen contains its own large magnetic moment due to the odd number of Protons in the Nucleus true/false
true
60
In order for resonance to occur the RF Pulse needs to match the exact precessional Frequency of Hydrogen Atoms true/false
true
61
Once a Magnetic Moment is exposed to an external Magnetic Field it will line up with or against the external field. true/false
true

Z MRI Physics (12 decks)

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