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MRI Physics > Final > Flashcards

Final Flashcards

1
Q

The most abundant atom in the body is

A

Hydrogen

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2
Q

Protons

A

Positive

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3
Q

Neutrons

A

No Charge

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4
Q

Electrons

A

Negative

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5
Q

The principles of MRI rely on

A

The ‘Spinning Motion’ of specific nuclei present in biological tissues

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6
Q

The laws of electromagnetic induction refer to three individual forces

A

Motion
Charge
Magnetism

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7
Q

At 1.0T the precessional frequency of hydrogen is

A

42.57 MHz

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8
Q

The ___ is the time from the application of the pulse to peak of the signal induced in the coil

A

TE - Echo Time

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9
Q

What is the purpose of image weighting in MRI

A

Highlight Specific Tissues

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10
Q

Which type of weighting is characterized by bright signals for tissues with short T1 relaxation times

A

T1 Weighting

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11
Q

What parameter is primary adjusted to control T1 weighting

A

TR - Repetition Time

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12
Q

T2 weighted images are commonly used to visualize

A

Edema and Pathology

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13
Q

What factor is crucial for achieving optimal contrast in MRI

A

Pulse Sequence Parameters

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14
Q

Increasing the TE Echo Time in an MRI sequence primarily affects

A

T2 Weighting

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15
Q

What is T1 Recovery Time in MRI

A

Time taken for Longitudinal Magnetization to Reach 63%

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16
Q

Increasing the TR Repetition Time in an MRI sequence primarily affects

A

T1 Recovery Time

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17
Q

What is T2 Decay Time in MRI

A

Time taken for Transverse Magnetization to Decrease to 37%

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18
Q

What is the primary purpose of a 180 degree pulse in a Spin Echo Sequence

A

Refocus Magnetization

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19
Q

In a typical Spin Echo Sequence, the Echo is formed by

A

180 Degree Pulse

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20
Q

The time between the initial 90 degree pulse and the center of the echo is known as

A

TE - Echo Time

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21
Q

What parameter is adjusted to control the T2 weighting in a Spin Echo sequence

A

TE - Echo Time

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22
Q

The formation of multiple echoes in a Spin Echo sequence is known as

A

Fast Spin Echo

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23
Q

Fat remains bright on T2 weighted images due to the multiple RF pulses which reduce the effects of spin spin interactions in fat and known as

A

J Coupling

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24
Q

Pulse sequences enable us to control the way in which the system applies pulses and gradients. In this way, image ___ and ___ are determined.

A

Weighting and Quality

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25
Q

Another modification to Single Shot Fast Spin Echo is a reverse flip angle excitation pulse which is applied at the end of the Echo Train

A

Drive

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26
Q

____ is an extremely important sequence in musculoskeletal imaging

A

STIR

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27
Q

___ is used in brain and spine imaging to see Periventricular nd Cord Lesions more clearly

A

FLAIR

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28
Q

What is the primary advantage of Gradient Echo Sequences over Spin Echo Sequences

A

Shorter Scan TImes

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29
Q

The Flip Angle in a Gradient Echo sequence is typically called a

A

Variable

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30
Q

Gradients can be used to dephase and rephase the residual magnetization.___ is the opposite of rewinding

A

Gradient Spoiling

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31
Q

This Gradient Echo was initially developed for imaging of the Heart and Great Vessels but is now used for Spinal Imaging

A

Balanced

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32
Q

In Gradient Echo sequences what is the role of the dephasing gradient.

A

Accelerate Signal Decay

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33
Q

What is the primary limitation of Gradient Echo sequences in terms of susceptibility artifacts

A

The are highly susceptible

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34
Q

There are three types of motion present within an atom

A

Electrons Spinning
Electrons Orbiting
Nucleus itself Spinning

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35
Q

The ___ of hydrogen produces a significant vector that is used in clinical MRI

A

NMV - Net Magnetic Vector

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36
Q

At 1.5T the precessional frequency of hydrogen is

A

63.86 MHz

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37
Q

The Hydrogen Atom is utilized in MRI because

A

Abundant in the human body

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38
Q

The ___ is the time from the application of one RF pulse to the application of the next pulse for each slice and is measured in milliseconds

A

TR - Repetition Time

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39
Q

The decay of Transverse Magnetization

A

T2 Decay

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40
Q

The Recovery of 63% of Longitudinal Magnetization in the tissue

A

T1 Relaxation Time

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41
Q

The ___ is produced when coherent (in phase) magnetization cuts across the coil

A

MRI Signal / Echo

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42
Q

The ___ is the time from the application of the pulse to peak of the signal induced in the coil and is also measured in milliseconds (ms)

A

TE - Echo Time

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43
Q

The influence of Bo produces an additional spin or wobble of the magnetic moments of hydrogen around Bo. This Secondary Spin is called

A

Precession

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44
Q

The Larmor Frequency of a ___ is proportional to the magnetic field strength it experiences

A

Hydrogen Nucleus

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45
Q

In a T2 Weighted Image

A

TE - Echo Time - Controls the amount of T2 weighting so the TE must be long

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46
Q

The factors that affect Image Contrast in diagnostic imaging are usually divided into two categories

A

Intrinsic and Extrinsic contrast parameters

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47
Q

Sequences that use a 180 degree pulse to regenerate a signal

A

Spin Echo pulse sequence

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48
Q

___ are generated by coils of wire situated within the bore of the magnet

A

Magnetic Field Gradient

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49
Q

The time from the 90 degree excitation pulse to the 180 equals the time from the 180 to the signals

A

TAU

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50
Q

Whether a gradient field adds or subtracts from the main magnetic field depends on the direction of the current passing through the gradient coils

A

Polarity

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51
Q

Gradients that dephase are called ___
Gradients that rephase are called ___

A

Spoilers /
Rewinders

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52
Q

The middle of the axis of the gradients remains at field strength of the main magnetic field

A

Magnetic Isocenter

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53
Q

TE at which the operator wishes to weight the resultant image

A

Effective TE

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54
Q

What is the purpose of Spatial Encoding in MRI

A

To assign Spatial Locations to image signals

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55
Q

In MRI what is the function of the magnetic field Gradients during Spatial Encoding

A

To vary the Resonant Frequency of spins along different directions

56
Q

Which gradient is responsible for dividing the object into slices along the z axis

A

Slice Select Gradient

57
Q

The process of assigning spatial locations to the signals in the phase encode direction

A

Phase Encoding

58
Q

What is the role of the readout gradient in spatial encoding

A

Encodes spatial information in the frequency direction

59
Q

In MRI the matrix size refers to the number of pixels in

A

Two-dimensional space

60
Q

In MRI the readout gradient is applied during which part of the imaging sequence

A

When signal is received

61
Q

Once the slice is selected the signal is Located or ___ along both axes of the image

A

Encoded

62
Q

The position of a nucleus along a gradient can be identified according to its

A

Precessional Frequency

63
Q

X Gradient

A

Sagittal Slices

64
Q

Y Gradient

A

Coronal slices

65
Q

Z Gradient

A

Axial Slices

66
Q

To give each slice thickness a ___ of nuclei must be excited by the excitation pulse

A

Band

67
Q

The Frequency encoding gradient is switched on when the signal is received

A

Readout Gradient

68
Q

Enough frequencies must occur during readout to achieve sufficient data points. This is determined by the

A

Receive Bandwidth

69
Q

These data points are Stored in

A

K- Space

70
Q

The ___ of K space is horizontal and is centered in the middle of several horizontal line.
The ____ of k space is vertical and is centered in the middle of k space perpendicular to the frequency axis

A

Frequency Axis
Phase Axis

71
Q

The central region of k-space corresponds to

A

Low Spatial Resolution

72
Q

In k-space acquisition which part corresponds to the low frequency (low resolution) information in the image

A

Central Part of K- Space

73
Q

What is the term for the process of Filling k-space with acquired dat in MRI

A

K-space Filling

74
Q

In MRI what effect does Increasing the number of phase encoding steps have on k space

A

Increases Spatial Resolution

75
Q

The Outer Portion of K- space contains data that have High Signal Amplitude and Low Resolution
(TRUE or FALSE)

A

False

76
Q

What is the primary goal of protocol optimization in MRI

A

Enhancing Image Quality

77
Q

Spin Echo pulse sequences generally have ___ that Gradient Echo sequences, as all the longitudinal magnetization is converted into transverse magnetization by the Flip Angle

A

More Signal

78
Q

The ___ controls the amount of transverse magnetization that is allowed to Decay before an echo is collected

A

TE- Echo Time

79
Q

This is the amount of times data are collected with the same amplitude of phase encoding slope

A

NEX

80
Q

The ___ controls the amount of Transverse Magnetization that is created which induces a Signal in the Coil

A

Flip Angle

81
Q

____ is a Random as it is in a different position each time data are stored

A

Noise

82
Q

In large voxels individual signal intensities are averaged together and are not represented as distinct within the voxel. This results in

A

Partial Voluming

83
Q

____ always provide better spatial resolution than ____ as the image is equally resolved along both the frequency and phase axis

A

Square Pixels
Rectangular Pixels

84
Q

The dimensions of the FOV in the phase direction is reduced compared to that in the frequency direction and so should be used when

A

Imaging anatomy that fits into a rectangle

85
Q

Large Voxels result in ___ as small structures are not resolved so well

A

Low Spatial Resolution

86
Q

Of the three main factors that affect Scan Time which one does not fit
TR
TE
NEX
Phase Matrix

A

TE

87
Q

With respect to voxel size it is directly affected by all but one
FOV
Flip Angle
Slice Thickness
Number of Pixels or Matrix

A

Flip Angle

88
Q

_____ appears as a Dense Line on the image at a specific point which is caused by extraneous RF entering the room interfering with the signal coming from the patient

A

Zipper Artifact

89
Q

Anti- Aliasing along the phase axis

A

Anti- Foldover

90
Q

An artifact that produces a Banding Artifact at the interfaces of High / Low signal

A

Truncation

91
Q

In gradient echo pulse sequences a Moire Pattern, a Black and White banding that encompasses the edge of the FOV, is is caused by a combination of

A

Wrap and Field Inhomogenity

92
Q

The use of foam pads or water bags between the coil and the patient will usually take care of what artifact

A

Shading

93
Q

The 180 rephasing pulse used in Spin Echo Sequences is very effective at compensating for phase differences between fat and water in magnetic susceptibility, while ___ are very poor at this

A

Gradient Echo Sequences

94
Q

When fat and water signals are out of phase their signals cancel each other out
(TRUE or FALSE)

A

TRUE

95
Q

The number one problem to look for when you see zipper artifact on your images and before you call for service is burned out light bulbs
(TRUE or FALSE)

A

TRUE

96
Q

Chemical shift can be limited by scanning at lower field strengths and by keeping the FOV to a minimum
(TRUE or FALSE)

A

TRUE

97
Q

At what temperature does an alloy of niobium and titanium become superconductive

A

4 Kelvin

98
Q

Permanent Magnets

A

Magnets that retain their magnetism

99
Q

Passive Shimming

A

Uses metal discs/ plates at installation to adjust for large changes in field homogeneity

100
Q

Superconductive Electromagnets

A

Solenoid electromagnet that uses super cooled coils of wire so that there is no inherent resistance in the system through which the current flows and therefore the magnetism is generated without a driving voltage

101
Q

Duty Cycle

A

Is a percentage of time during the TR period that the gradient is permitted to be at maximum amplitude or ‘Work’ during n imaging sequence

102
Q

Passive Shielding

A

Shielding accomplished by surrounding the magnet with steel plates

103
Q

Shimming

A

Process whereby the evenness of magnetic field is optimized

104
Q

Gradient Amplifier

A

Supplies power to the gradient coils

105
Q

Active Shimming

A

Additional solenoid magnets to adjust field homogeneity

106
Q

Para magnetism

A

Substance with a small but positive magnetic susceptibility

107
Q

Active Shielding

A

Uses additional superconducting coils located at each end of the main magnet inside the cryostat to shield the system

108
Q

Patient and ____ is the most effective way to avoid potential safety hazards to patients

A

Safety Education

109
Q

Although ___does not seem to be a safety issue it is a condition that commonly affects patients and MR operators should appreciate

A

Claustrophobia

110
Q

What is the primary safety concern related to ferromagnetic objects in the MRI environment

A

Projectile Effect

111
Q

The four zones concept in MRI safety refers to

A

Different areas in the hospital or imaging center

112
Q

IN MRI safety ‘Acoustic Noise’ refers to

A

The noise produced by the gradient coils

113
Q

To minimize the risk of burns during an MRI scan it is essential to

A

Limit the scan time and power deposition

114
Q

The MR Conditional designation for medical devices means that they are

A

Safe under certain conditions specified by the manufacturer

115
Q

In MRI safety the static field in the MRI suite is measured in

A

T- Tesla

116
Q

Cryogen Venting in MRI safety refers to the controlled release of

A

Cryogenic Gases

117
Q

What safety precaution is essential when using contrast agents containing gadolinium

A

Monitor the patient for nephrotoxic effects

118
Q

what is the primary concern regarding metallic implants or devices in the MRI environment

A

Induction of electric currents/ Heating

119
Q

The 5 Gauss Line is a safety guideline related to

A

Magnetic field strength

120
Q

In MRI safety, Quenching refers to

A

The release of cryogenic gases in case of an emergency

121
Q

In MRI safety what does SAR stand for

A

Specific Absorption Rate

122
Q

What is the purpose of an MRI compatible patient monitoring system during scanning

A

To monitor vital signs and patient conditions

123
Q

The technologist can leave a patient who is getting out of a wheelchair
(TRUE or FALSE)

A

FALSE

124
Q

A patient explains to the technologist what type of pain is being experienced

A

Subjective Data

125
Q

When transporting a patient back to the hospital room, some safety measures to be used are

A

Place the side rails up, the bed in the low position, and call bell at hand
Inform the nursing staff that the patient has been returned to the room

126
Q

Patient transfers from gurney to imaging table and back to gurney should be performed

A

By two or more technologist to ensure patient and technologist safety

127
Q

Pain control is not within the technologists scope of practice and should not be a concern
(TRUE or FALSE)

A

FALSE

128
Q

The leasing cause of work related injuries in the field of health care is

A

Abuse of the spine when moving and lifting patients

129
Q

The most effective means of reducing friction when moving a patient is by

A

Placing the patients arm across the chest and using a pull sheet

130
Q

The ___ controls the amount of transverse magnetization that is created which induces a signal in the coil

A

Flip Angle

131
Q

The ___ is the ratio of amplitude of the signal received to the average amplitude of the noise

A

SNR

132
Q

This is the number of times data are collected with the same amplitude of phase encoding slope

A

NEX

133
Q

The ___ controls the amount of transverse magnetization that is allowed to decay before an echo is collected

A

TE - Echo Time

134
Q

The ___ determines the number of data points we must collect during readout

A

Frequency Matrix

135
Q

Enough frequencies must occur during readout to achieve sufficient data points. This is determined by the

A

Receive Bandwidth

136
Q

The position of a nucleus along a gradient can be identified according to its

A

Precessional Frequency

137
Q

What is the role of the readout gradient in spatial encoding

A

Encodes spatial information in the frequency direction

MRI Physics (1 decks)

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