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MRI Registry > MRI All-In-One > Flashcards

MRI All-In-One Flashcards

1
Q

Heart Rate / Pulse

A

Adults: 70-80 bpm
Children: 90-100 bpm

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2
Q

Blood Pressure

A

Systolic: 110-140 mmHg
Diastolic: 60-80 mmHg

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3
Q

Respiratory Rate

A

12-20 breaths/min

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4
Q

Temperature

A

Oral: 98.6 F
Axillary: 97.6 F
Tympanic: 97.6 F
Rectal: 99.6 F

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5
Q

CPR Rate

A

80-100 compressions/min

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6
Q

CPR Depth

A

1.5-2 inches

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7
Q

CPR Ratio

A

1 Rescuer: 30/2

2 Rescuer: 30/2

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8
Q

CPR Location

A

Lower 1/3 of the sternum

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9
Q

O2 Saturation

A

95-100%

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10
Q

Gadolinium Dosage

A

0.1 mmol/kg or 0.2 ml/kg

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11
Q

Image Effects:

Gadolinium-Based Agents

A

T1 - Reduces T1 relaxation times of tissues / brightens

T2 - Reduces T2 decay times of tissues / darkens

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12
Q

Image Effects:

Iron Oxide Agents

A

T2 - Reduces T2 decay times of tissues (liver) / darkens

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13
Q

Image Effects:

Manganese Agents

A

T1 - Reduces T1 relaxation times of tissues (liver) / brightens / normal liver tissue bright, liver lesions dark

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14
Q

Image Effects:

Hyperpolarized Helium Agents

A

T1 - Reduces the T1 relaxation times of tissues (lung parenchyma) / brightens

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15
Q

Image Effects:

Oral Contrast Agents

A

T1 - Reduces T1 relaxation time of the bowel / brightens

T2 - Reduces T2 decay time of the bowel / darkens

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16
Q

Symptoms of NSF can appear:

A

Within a few days or up to six months later

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17
Q

Gd Enhancing Brain Structures

A
  • Falx cerebri
  • Choroid plexus
  • Pituitary gland
  • Pineal gland
  • infundibulum
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18
Q

Mild Reactions

A
  • Nausea
  • Vomiting
  • Coldness
  • Warmth
  • Pain
  • Headaches
  • Dizziness
  • Itching
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19
Q

Moderate Reactions

A
  • Nasal stuffiness
  • Swelling of the eyes or face
  • Tachycardia or bradycardia
  • Hypertension
  • Bronchospasms
  • Dyspnea
  • Laryngeal edema
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20
Q

Severe Reactions

A
  • Respiratory distress
  • Convulsions
  • Arrhythmias
  • Unresponsiveness
  • Cardiopulmonary arrest
  • Progressive Angioedema
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21
Q

MRI Environment Climate

A

Temp - 65-75 F

Humidity - 50-70%

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22
Q

RF Biological Effects include:

A
  • Tissue heating
  • Antennae Effects
  • Thermal injuries
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23
Q

FDA SAR LIMITS

Whole Body

A

4 W/kg / 15 min

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24
Q

FDA SAR LIMITS

Head

A

3 W/kg / 10 min

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25
Q

FDA SAR LIMITS

Torso

A

8 W/kg / 5 min

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26
Q

FDA SAR LIMITS

Extremities

A

12 W/kg / 5 min

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27
Q

Body Core

A

1 C / n/a

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28
Q

Magneto-hemodynamic Effect

Static

A

An increase in the amplitude of the T wave on an ECG due to the strength of the static magnetic field

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29
Q

Magnetophosphenes

Gradient

A

The process of “seeing stars” when sensory receptors in the retina are stimulated by the changing magnetic field

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30
Q

FDA Static Field Strength Limits

A

< 1 month - 4T

> 1 month - 8T

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31
Q

Renal function must be tested within 6 weeks for:

A

Patients with hypertension, diabetes, or over 60 years of age

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32
Q

Renal function must be tested within 24 hours for:

A

Patients with hepatocellular disease

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33
Q

Greenfield filter is aka

A

IVC clot filter

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34
Q

Pregnant patients should not be scanned during the ___ trimester

A

1st

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35
Q

In active shielding, electromagnets are located at the ends of the gantry within the:

A

Cryostat

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36
Q

Faraday’s Law aka

A

Law of electromagnetic induction

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37
Q

Faraday’s Law state that:

A

For electromagnetic induction to take place, a conductor, magnetic field, and motion (between the two) must be present

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38
Q

Lenz’s Law states that:

A

An electromagnetically induced current within a conductor creates a magnetic field opposing the magnetic field that produced the electromagnetically induced current (eddy currents)

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39
Q

3 Types of magnets

A
  • Superconductive electromagnet
  • Resistive electromagnet
  • Permanent magnet
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40
Q

Superconductive electromagnet

A
  • Constructed from niobium and titanium
  • 0.3-8T
  • Requires no additional power
  • Most expensive
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41
Q

Active temperature of liquid helium

A

2 K (below 4K is considered superconductive)

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42
Q

Resistive electromagnet

A
  • Current carrying loop of wire
  • Less than 0.3T
  • Requires constant power
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43
Q

Permanent Magnet

A
  • Composed of ALNICO
  • Less than 0.3T
  • Don’t need power or cryogen
  • Least expensive but worst magnetic field homogeneity
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44
Q

1T equals

A

10,000G or 10kG

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45
Q

Magnetic Field Strength Classifications

A

Low - less than 0.35T
Mid - 0.5-0.7T
High - 1-1.5T
Ultra-high - greater or equal to 3T

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46
Q

Diamagnetic

A
  • Have paired orbital electrons (no magnetic moment)
  • Repel external magnetic field slightly
  • Copper, oxygen, silver, mercury, lead, water, graphite
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47
Q

Paramagnetic

A
  • Have unpaired orbital electrons (small positive magnetic moment of <1)
  • Slightly attract external magnetic field and align
  • Tungsten, cesium, lithium, aluminum, magnesium, sodium, platinum, gadolinium contrast agents
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48
Q

Superparamagnetic

A
  • Intermediate magnetic moment (between paramagnetic and ferromagnetic)
  • Only display a magnetic moment in bulk, individual molecules have no magnetic moment
  • Iron oxide particles, iron oxide contrast agents (generally used as T2 or T2* contrast agents in the liver)
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49
Q

Ferromagnetic

A
  • Have half-filled electron shells (large magnetic moment of >1)
  • Attract external magnetic field with great strength
  • Retain their magnetization
  • Steel, iron, nickel, cobalt
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50
Q

RF coil aka

A

Body coil

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51
Q

Decreasing Receive Bandwidth

A
  • Increase in SNR

- Increase in chemical shift artifacts

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52
Q

Increasing Receive Bandwith

A
  • Decrease in SNR

- Decrease in chemical shift artifacts

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53
Q

Gradient Slew Rate

A
  • Time it takes for a gradient to achieve maximum gradient amplitude
  • Describes the speed and strength of the gradients
  • Measured in mT/m/s
  • Typically 70-200 mT/m/s
  • Best indicator of overall gradient performance
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54
Q

Gradient slew rate is calculated by

A

Dividing the maximum gradient amplitude by the rise time

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55
Q

Maximum Gradient Amplitude

A
  • Maximum strength or slope that is achievable by a particular gradient
  • Measured in mT/m or G/cm
  • Typically 10-40 mT/m (most commonly 33 mT/m in modern systems)
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56
Q

Gradient Rise Time

A
  • Time it takes for a gradient to switch on, achieve the required gradient strength/slope, and switch off
  • Measured in microseconds
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57
Q

Duty Cycle

A
  • Time that a gradient is capable of working at a maximum amplitude
  • Usually expressed as %
  • Nearly 100% can be achieved on modern systems
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58
Q

Name of electromagnet in the form of a current carrying wire coiled into a tightly packed helix

A

Solenoid

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59
Q

Larmor Equation

A

Mathematical equation that determines the value of the precessional frequency of nuclei in the presence of an external magnetic field

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60
Q

Gyromagnetic ratio of hydrogen

A

42.57 mHz/T

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61
Q

2 things occur with resonance:

A
  • Spins flip into the transverse plane

- Spins begin to precess in-phase (become coherent)

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62
Q

Free Induction Decay

A

Natural decay of the NMV after the RF is turned off

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63
Q

T1 Relaxation

A
  • Aka “spin-lattice relaxation” and “longitudinal relaxation”
  • Time it takes for 63% of the longitudinal magnetization (Mz) to recover in tissues
  • For SEPS, controlling factor is TR
  • For GEPS, controlling factors are TR and flip angle
  • For IRPS, the controlling factors are TR and TI
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64
Q

T1 relaxation times of fat and water:

A

Fat - 200 ms

Water - 2500 ms

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65
Q

T2 Decay

A
  • Aka “spin-spin relaxation” and “transverse decay”
  • Time it takes for 63% of transverse magnetization (Mxy) to decay
  • Controlling factor during all pulse sequences is TE
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66
Q

T2 decay times of fat and water:

A

Fat - 100 ms

Water - 2500 ms

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67
Q

T2* Decay

A
  • Aka “susceptibility decay”

- Similar to T2 decay, except that transverse decay occurs quicker due to the combination of T2 decay and T2 prime

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68
Q

T2 Prime

A

The dephasing of precessing spins due to magnetic field inhomogeneities

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69
Q

Proton Density

A
  • Aka “spin density”

- Represents the relative number of mobile hydrogen protons per unit volume

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70
Q

NMV, M0

A
  • A vector produced as a result of excess hydrogen nuclei aligning with the main magnetic field
  • Increases with increasing magnetic field strength, and results in improved signal from the patient
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71
Q

The slope in static magnetic field allows for the performance of 3 spatial encoding tasks:

A
  • Slice selection
  • Phase encoding
  • Frequency encoding
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72
Q

Slice Select Gradient

A
  • Switches on during the application of the alpha pulse and any subsequent RF rephasing pulses applied during a pulse sequence
  • The scan plan selected during slice prescription determines which of the three physical gradients performs slice selection during the transmission of an RF pulse
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73
Q

Phase-Encoding Gradient

A
  • Usually spatially encodes the signal sampled along the short axis of anatomy within a slice
  • Energizes after the application of the alpha pulse and before the application of the rephasing pulse
  • Applied slope and polarity of the phase-encoding gradient determines which line of k-space will be filled during readout
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74
Q

Frequency Encoding

A
  • Aka “readout gradient”
  • Usually spatially encodes the signal sampled along the long axis of anatomy within a slice
  • Applied during the collection of the echo to allow the system to sample data for storage in k-space
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75
Q

K-Space (raw data)

A
  • Spatial frequency domain that serves as a temporary storage space for data collected during image acquisition
  • Rectangular and has two axes; the phase axis (y-axis), and the frequency axis (x-axis)
  • Steep phase encoding gradient slope stores spatial resolution info (low signal amplitude) on the outer edges
  • Shallow phase encoding gradient slope encodes contrast info (high signal amplitude) into the center
  • Physically located in the array processor
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76
Q

Fast Fourier Transform (FFT)

A
  • Mathematical process that converts data obtained during image acquisition so that it may be stored in k-space
  • Also applied when data is removed from k-space for image formation
77
Q

Phase Mismapping (phase ghosting, motion artifact, flow artifact) compensation (P)

A
  • Swapping phase and frequency encoding axes
  • Placing pre-saturation pulses
  • Employing motion reduction techniques (increasing NSA, using Propeller sequences, increasing concatenations improving patient comfort, etc.)
78
Q

Aliasing (phase wrap, wrap-around artifact) compensation (P)

A
  • Enlarging the FOV in the phase direction
  • Placing pre-saturation pulses
  • Using no phase wrap (phase oversampling, anti-foldover)
  • Proper centering of the anatomy to the coil
  • Disengaging coils that are not needed
79
Q

Truncation (Gibbs artifact) compensation (P)

A
  • Increasing NSA (NEX)

- Increasing phase encoding matrix

80
Q

Degree of Chemical Shift depends on:

A
  • Magnetic field strength (higher)
  • Receive bandwidth (narrower)
  • Pixel size (larger)
81
Q

Chemical Shift (type 1 artifact) compensation (F)

A
  • Increasing receive bandwidth
  • Decreasing pixel size (small FOV, large matrix)
  • Scanning at lower field strengths
82
Q

Chemical Misregistration (type 2 artifact aka out-of-phase artifact) compensation (CGE)

A
  • Using SE sequences (since 180 degree RF pulses are efficient at rephasing)
  • Applying a TW interval of 4.2ms (when fat and water are in phase with each other)
83
Q

Magnetic Susceptibility compensation (CGE)

A
  • Using FSE sequence with a long ETL (since multiple 180 degree RF pulses are more efficient at rephasing)
  • Decreasing the TE (long TE allows more dephasing from inhomogeneities)
  • Removing metallic objects
84
Q

Radiofrequency Artifact (zipper artifact) compensation (F)

A

-Make sure there is no RF leaks into the scanner room

85
Q

Partial Volume Averaging compensation

A

-Decreasing voxel size by using a small FOV, large matrix, and thin slices

86
Q

Cross-Talk compensation

A
  • Careful placement of multiple stacks of slices

- Reducing slice angle when multiple stacks of slices are used

87
Q

Cross Excitation compensation

A
  • Using a gap space of at least 30% the slice thickness

- Using interleaving option instead of the sequential option

88
Q

Moire Pattern compensation (OGE) compensation

A
  • Using SE pulse sequences (to compensate for field inhomogeneities)
  • Keeping patient anatomy away from bore
  • Making sure that all the anatomy fits in the FOV (to prevent wrap)
89
Q

Parallel Imaging Artifact compensation (P)

A
  • Reducing the acceleration factor (R factor)

- Proper use of a calibration scan

90
Q

Magic Angle compensation (55 degree!)

A
  • Altering the angle of the anatomy

- Lengthening the TE applied (since T2 decay is no slower)

91
Q

Precessional frequency differences between fat and water

A

1T - 147 Hz
1.5T - 220 Hz
2T - 440 Hz

92
Q

Artifacts in Phase encoding axis

A
  • Phase Mismapping (phase ghosting, motion artifact, flow artifact)
  • Aliasing (phase wrap, wrap-around artifact)
  • Truncation (Gibbs artifact)
  • Parallel Imaging Artifact
93
Q

Artifacts in Frequency encoding axis

A
  • Chemical Shift (type 1 artifact)

- Radiofrequency Artifact (zipper artifact)

94
Q

Artifacts that commonly occur in GE sequences

A
  • Chemical Misregistration (type 2 artifact aka out-of-phase artifact)
  • Magnetic Susceptibility
95
Q

Artifacts that only occur in GE sequences

A

-Moire Pattern

96
Q

Four steps of Quality Control

A
  1. Acceptance testing
  2. Establishing baseline performance
  3. Detection and diagnosis of changes in equipment performance
  4. Correction verification
97
Q

Slice Thickness QC

A
  • Annually using AMAP

- 5.0mm +- 0.7mm with axial T1 ACR series

98
Q

Spatial Resolution QC

A
  • Weekly using AMAP
  • 1.0mm or better with axial T1 ACR series
  • All four holes in at least one row of the AP image should be recognized as separate and distinct points.
99
Q

Contrast Resolution QC

A
  • Weekly using AMAP

- Should be reported if the number of visible spokes is reduced by more than three.

100
Q

Center Frequency QC

A
  • Weekly using AMAP
  • To detect off-resonance operation in an attempt to prevent a consequential reduction in SNR
  • Should not deviate by more than 1.5ppm between weekly measurements
101
Q

Transmit Gain or Attenuation QC

A
  • Weekly using AMAP
  • To determine problems with the RF chain by acquiring several signals while varying the transmitter attenuation (or gain) so that imaging can proceed using the proper flip angle
  • Any changes in transmit gain exceeding the prescribed action limited should be reported
102
Q

Geometric Accuracy QC

A
  • Weekly using AMAP

- Should be +- 2mm of the actual values when using a 25cm FOB

103
Q

Equipment Handling and Inspection QC

A
  • At least weekly and can include:
  • Bed transport system
  • Alignment and system indicator lights
  • RF room integrity
  • Emergency cart
  • Safety lights
  • Signage
  • Monitors, coils, cables
104
Q

Contrast to Noise Ratio (CNR)

A
  • The difference in the SNR between two adjacent pixels

- Has the greatest influence on image quality and is controlled by the same factors as SNR

105
Q

Signal to Noise Ratio (SNR)

A
  • The ratio of signal amplitude to the average amplitude of the noise
  • Most greatly affected by the size of the FOV
106
Q

Spatial Resolution

A
  • The ability of the imaging system to detect two points as separate and distinguishable
  • Enhanced by square pixels but the ONLY characteristic that directly affects spatial resolution is voxel volume
107
Q

Voxel Volume formula

A

Pixel Phase Dimension x Pixel Frequency Dimension x Slice Thickness = Voxel Volume (mm^3)

108
Q

Acquisition Time

A
  • The amount of time it takes to fill k-space during data acquisition
  • Only affected by TR, NSA, Phase Matrix, Number of Slices (only in 3D), and ETL
109
Q

Acquisition Time 2D Scan Time Formula (Conventional Sequence)

A

TR x NSA x Phase Encodings

110
Q

Acquisition Time 2D Scan Time Formula (Fast Sequence)

A

(TR x NSA x Phase Encodings) / ETL

111
Q

Acquisition Time 3D Scan Time Formula (Conventional Sequence)

A

TR x NSA x Phase Encodings x # of Slices

112
Q

Intrinsic Parameters

A
  • T1 recovery
  • T2 decay
  • Proton density
  • Flow
  • Apparent diffusion coefficient
  • Perfusion
  • Diffusion
113
Q

Extrinsic Parameters

A
  • TR
  • TE
  • Flip angle
  • TI
  • ETL
  • B value
  • FOV
  • Matrix
114
Q

NSA

A
  • The number of times that data is collected per TR period
  • Square root relationship with SNR
  • Directly proportional relationship with scan time
115
Q

Double NSA

A
  • Scan time doubled

- 41% increase in SNR

116
Q

Quadruple NSA

A
  • Scan time quadrupled

- 100% increase in SNR

117
Q

FOV

A
  • Greatest impact on SNR

- Directly squared relationship with SNR

118
Q

Double FOV

A

Signal quadrupled

119
Q

Halve FOV

A

Only 1/4 of signal is acquired

120
Q

The maximum slice number achievable during a sequence is determined by the:

A

TR selected and SAR limitation

121
Q

Slice thickness is determined by the:

A

Slope of the slice select gradient and the transmitted bandwidth

122
Q

Thin slice

A

Steep slice-select gradient slope and narrow transmit bandwidth

123
Q

Thick slice

A

Shallow slice-select gradient and broad transmit bandwidth

124
Q

Echo Train Length

A
  • Number of times the echo is sampled per TR period during SE pulse sequence
  • Corresponds to the number of rephasing 180 degree RF pulse applied
125
Q

Transmit Bandwidth is automatically selected by the system upon:

A

Slice thickness selection

126
Q

Receive Bandwidth

A
  • Range of frequencies sampled during the time that the readout frequency gradient is active
  • Has a square root relation with SNR
127
Q

Double receive bandwidth

A

40% of signal is lost

128
Q

Halve receive bandwidth

A

40% of signal gained

129
Q

If the receive bandwidth is decreased, the minimum TE that is obtainable during a pulse sequence:

A

Increases

130
Q

Spatial Saturation Pulse

A
  • An additional RF pulse with a 90 deg flip angle and wide transmission bandwidth (to saturate all tissues) strategically placed over areas of unwanted anatomy both inside or outside the FOV
  • Increase tissue heating
131
Q

GMN (aka flow comp or gradient moment rephasing) requires the use of:

A

Either slice-select (axial) or frequency (coronal or sagittal) encoding gradients

132
Q

Chemical Suppression Techniques

A
  • Applies and extra 90 deg RF pulse with a narrow transmission bandwidth (at the precessional frequency of fat, water, or sometimes silicone) before the application of the alpha pulse
  • Can be improved by applying a shim over the anatomy
133
Q

Sat TR

A

Period of time bewteen the 90 deg saturation pulse and the alpha pulse

134
Q

Sat TR Calculation

A

TR / Slice #

135
Q

R to R Interval

A

Period of time bewteeen the R phases (ventricular contraction) of the cardiac cycle

136
Q

R to R Interval Calculation

A

60,000 ms / BPM

137
Q

Trigger Window take place during the:

A

Final 10% of the R to R interval

138
Q

Trigger Delay is generally bewteen:

A

5-10 ms

139
Q

As Acceleration Factor (R factor) increases:

A
  • Scan time decreases
  • Noise decreases
  • Aliasing increases
140
Q

In-phase/Out-of-phase Imaging uses:

A

GE pulse sequence with specific TE values to better demonstrate areas where fat and water interface

141
Q

Fast Spin Echo (FSE)

A
  • Uses a 90 deg alpha pulse and multiple 180 deg rephasing pulses per TR
  • Multiple lines of K-space filled per TR
142
Q

Fast Spin Echo (FSE) Disadvantages

A
  • Increase motion
  • Increase blurring
  • Decrease SNR
  • Decrease magnetic susceptibility artifacts
143
Q

Single Shot Fast Spin Echo (SS-FSE)

A
  • Combines FSE with a Partial Fourier technique to fill all lines of K-space during a single TR period
  • Reduces time but increases SAR (due to extra RF rephasing pulses used)
144
Q

Driven Equilibrium Fourier Transform (DRIVE)

A
  • Uses a reverse flip angle excitation pulse after the echo train to “drive” any residual transverse magnetization into the longitudinal plane so that it cannot be further excited at the beginning of the next TR cycle (causes T1 relaxation to occur quicker)
  • Yield hyperintense fluid signal compared to standard FSE
145
Q

Gradient Recall Echo (GRE)

A
  • Use an alpha pulse with a variable flip angle
  • Uses the frequency encoding gradient for rephasing
  • All GE images have some extent of T2* (cannot compensate for magnetic field inhomogeneities)
  • Sensitive to flow, extremely fast
146
Q

Gradient Echo pulse sequences consist of:

A
  • CGE
  • Steady State
  • FGE
  • Balanced Gradient Echo
  • Echo Planar Imaging
147
Q

Steady State

A
  • Uses two excitation pulses with variable flip angles at TR time intervals less than the T1 and T2 times of the body’s tissues in order to maintain RTM for the creation of stimulated echo (due to rephasing of the RTM by the second excitation pulse)
  • Maintain partial longitudinal and transverse magnetization at all times
148
Q

Hann Echo

A

The echo created by the application of the second excitation pulse if the steady state uses two 90 deg excitation pulses

149
Q

3 Types of Steady State Sequences

A
  • Incoherent Gradient Echo
  • Coherent Gradient Echo
  • Steady State Free Precession (SSFP)
150
Q

Incoherent (Spoiled) Gradient Echo

A
  • Only the gradient echo (FID) is sampled
  • Stimulated echo (RTM) is spoiled (dephased)
  • Typically used for T1 and sometimes PD
151
Q

Coherent Gradient Echo

A
  • Both the gradient echo (FID) and stimulated echo (RTM) are sampled
  • Rewinder gradient rephases RTM so it can contribute to image contrast
  • Typically used for T2*
152
Q

Steady State Free Precession (SSFP)

A
  • Only stimulated echo (RTM) is sampled
  • Rewinder gradient rephases RTM
  • Typically used for “truer” T2 weighted images (removes magnetic field inhomogeneities)
153
Q

Fast Gradient Echo

A
  • Coherent or incoherent
  • Uses shorter TE by only transmitting part of an RF pulse and by only reading a portion of the echo (Partial Echo Technique)
  • Acquisition of an entire volume with a single breath hold
  • Temporal resolution enhancement during post contrast dynamic imaging
154
Q

Balanced Gradient Echo

A
  • Coherent
  • Uses a balanced gradient system (to correct phase errors in flowing blood and CSF) as well as larger flip angles
  • High SNR, good CNR, and very short scan times
  • Typically used to image the heart and great vessels, spinal column (esp c-spine), and iacs
155
Q

Echo Planar Imaging (EPI)

A
  • Uses blipped, or constant oscillation of the phase-encoding gradient in order to fill all lines of K-space during single TR period
  • K-space is filled linearly, line by line, in a stair-stepped fashion
  • Used for perfusion, spectroscopy
  • Problems include distortions and chemical shift artifacts
  • Fastest form of data acquisition
156
Q

Spin Echo EPI (SE EPI)

A
  • Uses 90 deg excitation pulse, then 180 deg rephasing pulse, then a pulsing phase encoding gradient
  • Addition of the rephasing pulse helps to eliminate magnetic inhomogeneities and chemical shift
  • Longer than GE EPI but better image quality
157
Q

Gradient Echo EPI (GE EPI)

A
  • Uses a 90 deg excitation pulse, then a pulsing phase encoding gradient (no 180 deg rephasing pulse)
  • Shortest scan times but worse image quality than SE EPI
158
Q

Centric Filling

A
  • Filled linearly from the center outwards
  • Shallow first in the center as contrast data
  • Steep next in the periphery as spatial resolution data
  • Typically used during FGE to compensate for poor SNR and CNR
159
Q

Spiral Filling

A
  • Filled starting in the center and spiraling outward using both the frequency and phase encoding gradients
  • Elliptical (demonstrates arterial flow and suppresses venous flow)
  • Propeller (used for motion suppression)
160
Q

Keyhole Filling

A
  • Filled linearly with the outer lines being filled before contrast injection and inner lines filled after contrast injection
  • Dynamic angiography studies
161
Q

Fast Fourier Transformation (FFT)

A
  • A mathematical formula that converts the frequency/time domain into the frequency/amplitude domain
  • Occurs directly after readout
162
Q

T2 Shine Through Artifact

A

-Occurs when areas with a very long T2 decay time remain bright on DWI trace images

163
Q

Pathology (Restricted Diffusion Areas)

A

Bright on DWI trace and dark on ADC maps

164
Q

Normal Tissue (Free Diffusion Areas)

A

Dark on DWI trace and bright on ACD maps

165
Q

High-velocity signal loss

A

As flow velocity increases, less flowing nuclei are present within the slice for both excitation and rephasing pulse, thus TOF effects increase

166
Q

Flow-related enhancement

A

As flow velocity decreases, more flowing nuclei are present in the slice for excitation and rephasing pulse, thus TOF effects decrease

167
Q

Time of Flight Phenomenon

A
  • Stationary spins always receive both the excitation and rephasing pulse, and flowing spins present within the slice for excitation have usually traveled out of the slice before being rephased (thus returning no signal
  • Only observable during SE sequences
168
Q

Entry Slice Phenomenon

A
  • “Inflow effect”
  • How spins flowing perpendicular to a stack of slices enter the stack fresh (unsaturated) and produce more signal than stationary nuclei that receive repeated RF excitation (saturated)
169
Q

Time-of-Flight Imaging

A

-A type of MRA technique that uses an incoherent GE pulse sequence with GMN, as well as very specific imaging parameters

170
Q

2D TOF

A

Provides larger FOV (lower resolution) and is suitable for imaging areas with slow flow (carotids)

171
Q

3D TOF

A

Provides a smaller FOV (higher resolution) and is suitable for imaging areas of fast flow (COW)

172
Q

TOF Parameters

A
  • Flip angle: 45-60 deg
  • Short TR: 20-50 ms
  • TE: minimum
173
Q

Phase Contrast Imaging

A

-A type of MRA technique that uses a GE pulse sequence with a small flip angle to saturate the signal from stationary tissue, as well as to two additional bi-polar gradient pulses (VENC) to create phase changes in flowing blood

174
Q

High VENC setting should be used for:

A
  • Fast flowing bloods such as within arteries with small circumferences
  • COW, vertebral arteries
175
Q

Low VENC setting should be used for:

A
  • Slow flowing blood, such as within arteries with a large circumference
  • Aorta, femoral
176
Q

DWI - anisotropic

A
  • Diffusion gradients applied along all three axes independently to show directional differences
  • Display white matter
177
Q

DWI - isotropic

A
  • Diffusion gradients applied along all three axes simultaneously to show non-directional differences
  • Display gray matter
178
Q

B Factor (B value)

A
  • Parameter that controls the duration, strength, and amplitude of the gradient pulses on either side of the 180 deg RF pulse used in DWI and DTI
  • 500-1500 s/mm
  • Higher the B value, more DW is present
179
Q

Diffusion

A

The movement of molecules within extra-cellular spaces due to random thermal motion

180
Q

ADC

A

Net displacement of molecules within the extracellular space due to diffusion

181
Q

Perfusion Imaging

A
  • Allows the differences between tagged and untagged spins
  • Images are usually acquired before, during, and after gad injection
  • Measures quality of vascular supply to tissues
  • Information are displayed on a Time Intensity Curve and Cerebral Blood Volume Map (CBV)
182
Q

Perfusion

A

Volume of blood that flows into one gram of tissue (a measure of the regional blood flow in tissues)

183
Q

Time Intensity Curve

A
  • Signal decay curve that is obtained after all data is acquired
  • Used to determine blood volume, transient time, and the measurement of perfusion
184
Q

Cerebral Blood Volume Map (CBV)

A
  • Map obtained by the combination of multiple time-intensity curves for images acquired during and after contrast injection
  • Provided information on the overall blood volume delivered to the cerebrum
185
Q

Fast GE pulses are used during dynamic imaging because:

A
  • High temporal resolution

- Permit dynamic imaging of an enhancing lesion

186
Q

The division between the frontal lobe and the temporal lobe is known as:

A

Sylvian fissure

187
Q

Which blood vessel is located directly anterior to the pons?

A

Basilar artery

188
Q

What cranial nerves run through the IACs?

A

VII and VIII

MRI Registry (4 decks)

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