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MRI Terms Flashcards

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1
Q

A matrix with a low number of frequency encodings and/or phase encodings and results in a low number of pixels in the FOV.

A

Course Matrix

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2
Q

Flow in the same direction as slice excitation.

A

Co-Current flow

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3
Q

in phase

A

Coherent

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4
Q

The symmetry of data in K space.

A

Conjugate Symmetry

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5
Q

Flow in the opposite direction to slice excitation.

A

Counter current flow

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6
Q

energy given to nuclei in adjacent slices by the RF pulse.

A

Cross excitation

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7
Q

energy given to nuclei in adjacent slices due to spin lattice relaxation.

A

Cross talk

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8
Q

area around the coils of wire in which cryogens are placed

A

Cryogen Bath

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9
Q

Point in K space that contains digitized information from encoding.

A

Data point

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10
Q

loss of transverse magnetization

A

Decay

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11
Q

the movement of molecules due to random thermal motion.

A

Diffusion

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12
Q

Sequence in which two 180 degree pulses are used to saturate blood in black blood imaging.

A

Double IR prep

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13
Q

driven equilibrium - a pulse sequence that achieves a very high signal intensity from water even when using short TR’s.

A

DRIVE

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14
Q

digital subtraction MR angiography - contrast is selectively produced for moving spins during two acquisitions. These are then subtracted to remove the signal from the stationary spins, leaving behind an image of only the moving spins.

A

DS-MRA

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15
Q

time in milliseconds from the application of the RF pulse to the peak of the signal induced in the coil - TE determines how much decay of transverse magnetization is allowed to occur.

A

Echo time (TE)

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16
Q

series of 180 degree rephasing pulse and echoes in a fast spin echo pulse sequence.

A

Echo train

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17
Q

the time between the echo and the RF pulse that intiated it in SSFP - also the TE used in FSE

A

Effective TE

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18
Q

particles that spin around the nucleus

A

Electrons

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19
Q

once a slice is selected, the signal is located or encoded along both axes of the image.

A

Encoding

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20
Q

contrast difference of flowing nuclei relative to the stationary nuclei because they are fresh

A

Entry slice phenomena

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21
Q

technique that uses two echoes to reduce flow artefact.

A

Even echo rephasing

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22
Q

those parameters that can be changed at the operator console.

A

Extrinsic contrast parameters

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23
Q

causes an increase in the T2 decay time of fat when multiple RF pulses are applied as in fast spin echo

A

J Coupling

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24
Q

an area in the array processor where data on spatial frequencies are stored.

A

K space

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25
Q

precessional frequency

A

Larmor frequency

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26
Q

the axis parallel to Bo

A

Longitudinal plane

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27
Q

coil that transmits and receives signal over a large volume of the patient.

A

Volume Coil

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28
Q

Volume of tissue in the patient.

A

Voxel volume

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29
Q

technique that nulls signal from water by applying an RF pulse at the frequency of water to the imaging volume before slice excitation.

A

Water saturation

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30
Q

settings that control brightness and contrast in MR images

A

Window levels and settings

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31
Q

sudden loss of the superconductivity of the magnet coils so that the magnet becomes resistive.

A

Quenching

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32
Q

Echoes formed when any two 90 degree RF pulses are used in steady state sequences.

A

Hahn echoes

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33
Q

partial averaging

A

Half Fourier

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34
Q

increase in time of flight due to an increase in the velocity of flow.

A

High velocity signal loss

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35
Q

evenness of the magnetic field.

A

Homogeneity

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36
Q

combination of fast spin echo and EPI sequences where a series of gradient echoes are interspersed with spin echoes - in this way susceptibility artefacts are reduced.

A

Hybrid sequences

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37
Q

the most abundant atom in the body

A

Hydrogen

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38
Q

out of phase

A

Incoherent

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39
Q

another term for entry slice phenomenon.

A

Inflow effect

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40
Q

magnetic moments that are in the same place on the precessional path around Bo at any given time.

A

In phase

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41
Q

A method of acquiring data from alternate slices and dividing the sequence into two acquisitions - no slice gap is required.

A

Interleaving

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42
Q

phase difference between flow and stationary nuclei in a voxel.

A

Intra-voxel dephasing

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43
Q

those parameters that cannot be changed because they are inherent to the body’s tissues.

A

Intrinsic contrast parameters

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44
Q

atoms with an excess or deficit of electrons

A

Ions

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45
Q

atoms with an odd mass number.

A

Isotopes

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46
Q

voxels that have the samedimensions in all three planes.

A

Isotropic

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47
Q

technique that nulls signal from fat by applying an RF pulse at the frequency of fat to the imaging volume before slice excitation.

A

Fat saturation

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48
Q

gradient moment nulling

A

First order motion compensation

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49
Q

axes along which bipolar gradients act in order to sensitize flow along the axis of the gradient used in phase contrast MRA

A

Flow encoding axes

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50
Q

artefacts produced by flowing nuclei

A

Flow phenomena

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51
Q

decrease in time of flight due to a decrease in velocity of flow

A

Flow related enhancement

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52
Q

partial averaging

A

Fractional averaging

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53
Q

partial echo

A

Fractional echo

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54
Q

loss of signal due to relaxation

A

Free induction decay (FID)

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55
Q

Aliasing along the frequency encoding axis

A

Frequency wrap

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56
Q

nuclei that have not been beaten down by repeated RF pulses

A

Fresh spins

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57
Q

When the NMV is pushed to a full 180 degrees

A

Fully saturated

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58
Q

these allow MRI to be used to assess fuction and physiology

A

Functional imaging technique

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59
Q

basic law of electricity - voltage= current x resistance

A

Ohms law

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60
Q

area of K space filled with the steepest phase encoding gradient slopes

A

Outer lines

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61
Q

when magnetic moments are not in the same place on the precessional path

A

Out of phase

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62
Q

motion artefact in the phase axis

A

Ghosting

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63
Q

line of low signal in the cervical cord image due to truncation

A

Gibbs artefact

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64
Q

supplies power to the gradient coils

A

Gradient amplifier

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65
Q

gradient echo sequence with EPI readout

A

Gradient echo - EPI

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66
Q

a system of gradients that compensates for intra-voxel dephasing

A

Gradient moment nulling (rephasing)

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67
Q

coils of wire that alter the magnetic field strength in a linear fashion when a current is passed through them

A

Gradients

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68
Q

the use of gradients to dephase magnetic moments - the opposite of rewinding

A

Gradient spoiling

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69
Q

Gradient echo and spin echo

A

GRASE

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70
Q

the precessional frequency of an element at 1.0 T

A

Gyro-magnetic ratio

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71
Q

field created by passing current through a gradient coil

A

Magnetic Field Gradients

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72
Q

effect that causes elevation of the T-wave of the ECG of the patient when placed in a magnetic field- this is due to the conductivity of blood

A

Magneto-hemodynamic effect

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73
Q

the center of the bore of the magnet in all planes

A

Magnetic isocentre

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74
Q

denotes the direction of the north/south axis of the magnet and the amplitude of the magnetic field

A

Magnetic moment

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75
Q

ability of a substance to become magnetized

A

Magnetic susceptability

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76
Q

technique used to suppress background tissue and increase CNR

A

Magnetization transfer contrast/coherence (MTC)

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77
Q

a property of all matter that depends on the magnetic susceptability of the atom

A

Magnetism

78
Q

un-subtracted image combination of flow sensitized data

A

Magnitude image

79
Q

sum of neutrons and protons in the nucleus

A

Mass number

80
Q

where two or more atoms are arranged together

A

Molecules

81
Q

nuclei that possess an odd mass number

A

MR active nuclei

82
Q

nuclei by producing a contrast between them and the stationary nuclei

A

MR angiography (MRA)

83
Q

the voltage induced in the receiver coil

A

MR signal

84
Q

method combining a number of high resolution 3D acquisitions to produce an image that has good resolution and a large area of coverage

A

Multiple overlapping thin section angiography (MOTSA)

85
Q

where K space is divided into segments and one segment is acquired per TR

A

Multi-shot

86
Q

Technique that acquires multiple voxels by encoding in K space in MR signal

A

Multi-voxel

87
Q

the magnetic vector produced as a result of the alignment of excess hydrogen nuclei with Bo

A

Net magnetization vector (NMV)

88
Q

neutrally charged element in an atomic nucleus

A

Neutron

89
Q

number of excitations (also known as number of signals averages or acquisitions depending on manufacturers) the number of times an echo is encoded with the same slope of phase encoding gradient

A

NEX

90
Q

Frequencies that exist randomly in time and space

A

Noise

91
Q

particles in the nucleus

A

Nucleons

92
Q

the point at which there is no longitudinal magnetization in a tissue in an inversion recovery sequence

A

Null point

93
Q

states that a frequency must be sampled at least twice in order to reproduce it reliably.

A

Nyquist theorem

94
Q

a technique that uses multiple coils to fill segments of K space

A

Parallel imaging

95
Q

filling only a proportion of K space with data and putting zeros in the remainder

A

Partial averaging

96
Q

sampling only part of the echo and extrapolating the remainder in K space

A

Partial echo imaging

97
Q

occurs when the NMV is flipped beyond 90 degrees (91-179)

A

Partially saturated

98
Q

loss of spatial resolution when large voxels are used

A

Partial voluming

99
Q

acheived in IR pulse sequence with a long TE-pathology appears bright even though the image is T1 weighted

A

Pathology weighting

100
Q

the position of a magnetic moment on its precessional path at any given time

A

Phase

101
Q

technique that degenerates vascular contrast using the phase difference between stationary and flowing spins

A

Phase contrast angiography (PCMRA)

102
Q

subtracted image comination of flow sensitized data

A

Phase image

103
Q

aliasing along the phase encoding axis

A

Phase wrap

104
Q

the direction of a gradient, ie which end is greater than Bo and which end is lower than Bo. Depends on the direction of the current through the gradient coil

A

Polarity

105
Q

single voxel technique in MRS

A

Point resolved spectroscopy spin echo(PRESS)

106
Q

the speed of precession

A

Precessional (larmor) frequency

107
Q

the circular pathway of magnetic moments as they precess around Bo

A

Precessional path

108
Q

positively charged element of an atomic nucleus

A

Proton

109
Q

number of protons per unit volume of that tissue

A

Proton density

110
Q

image that demonstrates the differences in the proton densities of the tissue

A

Proton densty (PD) weighting

111
Q

frequency that is indirectly derived from a change of phase

A

Pseudo-frequency

112
Q

co-ordinates switching on and off the gradient and RF transmitter coils at appropiate times during the pulse sequence

A

Pulse control unit

113
Q

emission of energy caused by adeficit in the number of electrons compared with protons

A

Radioactivity

114
Q

low energy, low frequency electromagnetic radiation. Used to excite hydrogen nuclei in MRI

A

Radio frequency (RF)

115
Q

where sampling data points are collected when the gradient rise time is almost complete- sampling occurs while the gradient is still reaching maximum amplitude, while the gradient is at maximum amplitude and as it begins to decline

A

Ramp sampling

116
Q

the frequency encoding gradient

A

Readout gradient

117
Q

range of frequencies that are sampled during readout

A

Receive bandwidth

118
Q

growth of longitudinal magnetization

A

Recovery

119
Q

also known as asymmetric FOV - uses a FOV in the phase direction that is different to that in the frequency direction of the image

A

Rectangular FOV

120
Q

the factor by which the scan time is reduced using parallel imaging. Equals the number of coils used

A

Reduction factor

121
Q

process by which the NMV loses energy

A

Relaxation

122
Q

the effect of a substance on relaxation rate

A

Relaxivity

123
Q

time between each excitation pulses

A

Repitition time (TR)

124
Q

transverse magnetization left over from previous RF pulses in steady state conditions

A

Residual transverse magnetization

125
Q

another term for solenoid magnet

A

Resistive magnet

126
Q

uses mechanical motion of air in bellows to order K space filling and reduce respiratory motion artefacts

A

Respiratory compensation

127
Q

gates the sequences to chest wall movements to reduce respiratory motion artefacts

A

Respiratory gating/triggering

128
Q

gradients that rephase

A

Rewinders

129
Q

Supplies power to the RF transmitter coil

A

RF amplifier

130
Q

short burst of RF energy that excites nuclei into a high-energy stage

A

RF pulse

131
Q

the use of digitized RF to transmit and receive at a certain phase

A

RF spoiling

132
Q

coil that transmits RF at the resonant frequency of hydrogen to excite nuclei and move them into a high-energy state

A

RF transmitter coil

133
Q

the time it takes a gradient to switch on, acheive the required gradient slope, and switch off again

A

Rise time

134
Q

time between each R wave in gated studies

A

R to R interval

135
Q

rate at which samples are taken during readout

A

Sampling rate or frequency

136
Q

the time that the readout gradient is switched on for

A

Sampling time

137
Q

standardized absorption rate - a way of measuring the USA Food and Drug Administration limit for RF exposure

A

SAR

138
Q

time between each pre-saturation pulse

A

SAT TR

139
Q

acquisition where all the data from each slice is acquired before going on to the next

A

Sequential acquisition

140
Q

parallel imaging

A

Sensitivity encoding

141
Q

extra coils used to make the magnetic field as homogeneous as possible

A

Shim coil

142
Q

voltage induced in the receiver coil

A

Signal

143
Q

ratio of signal relative to noise

A

Signal to noise ratio (SNR)

144
Q

a fast spin echo sequence where all the lines of K space are acquired during a single TR period

A

Single shot FSE (SS-FSE)

145
Q

technique that uses three intersecting slices to locate a single voxel in MRS.

A

Single voxel

146
Q

the strength of the gradient over distance

A

Slew rate

147
Q

the seperation of individual slice locations by phase in volume acquisitions

A

Slice encoding

148
Q

selecting a slice using a gradient

A

Slice selection

149
Q

magnet that uses current passed through coils of wire to generate a magnetic field

A

Solenoid electromagnet

150
Q

encoding or locating signal in spatial three dimensions of the imaging volume

A

Spatial encoding

151
Q

creates a saturation effect which produces a cross hatching of stripes on the image. these can be compared with moving anatomy to determine its function

A

Spatial modulation of magnetization (SPAMM)

152
Q

the ability to distinguish two points as seperate

A

Spatial resolution

153
Q

the population of high energy hydrogen nuclei that align their magnetic moments anti-parallel to Bo

A

Spin-down

154
Q

echo produced as a result of a 180 degree rephasing pulse

A

Spin echo

155
Q

Spin echo sequence with EPI readout

A

Spin echo-EPI (SE-EPI)

156
Q

one that uses a 180 degree rephasing pulse to generate an echo

A

Spin echo pulse sequence

157
Q

process by which energy is given up to the surrounding lattice

A

Spin lattice relaxation

158
Q

process by which interactions between the magnetic fields of adjacent nuclei causes dephasing

A

Spin-spin relaxation

159
Q

the population of low energy hydrogen nuclei that align their magnetic moments parallel to Bo

A

Spin-up

160
Q

gradients that dephase

A

Spoilers

161
Q

condition where the TR is less than T1 and T2 relaxation times of the tissue

A

Steady state

162
Q

echoes formed when any two RF pulses are used in steady state sequences

A

Stimulated echoes

163
Q

single voxel technique in MRS

A

Stimulated echoes acquisition mode (STEAM)

164
Q

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 driving voltage

A

Superconducting magnet

165
Q

a contrast agent that shortens T1 relaxation in tissue that take up the agent

A

T1 enhancement agent

166
Q

growth of longitudinal magnetization as a result of spin lattice relaxation

A

T1 recovery

167
Q

time taken for 63% of the longitudinal magnetization to recover

A

T1 relaxation time

168
Q

image that demonstrates the differences in the T1 times of the tissues

A

T1 weighted image

169
Q

dephasing due to magnetic field inhomogeneities

A

T2*

170
Q

agents that shorten T2 relaxation times in tissue that take up the agent

A

T2 enhancement agents

171
Q

loss of transverse magnetization as a result of spin-spin relaxation

A

T2 decay

172
Q

time taken for 63% of the transverse magnetization to decay

A

T2 relaxation time

173
Q

when lesions remain bright on a trace image in DWI

A

T2 shine through

174
Q

image that demonstrates the differences in the T2 times of the tissues

A

T2 weighted image

175
Q

acquisition where the whole imaging volume is excited so that the images can be viewed in any plane

A

3D volumetric acquisition

176
Q

the time between the excitation pulse and the 180 degree rephasing pulse and the time between this and the echo. Sometimes used in STIR sequences as an alternative to the TI

A

TAU

177
Q

assumes patient temperature is constant and therefore does not influence the thermal energy of hydrogen during the MR experiment

A

Thermal equalibrium

178
Q

curve produced in perfusion imaging to show perfusion kinetics of a tissue

A

Time intensity curve

179
Q

rate of flow in a given time - causes some flowing nuclei to receive one RF pulse only and therefore produce a signal void

A

Time of flight

180
Q

technique that generates vascular contrast by using the inflow effect

A

Time of flight MR angiography (TOF-MRA)

181
Q

echo time

A

Time to echo

182
Q

time from 180 degree inverting pulse to 90 degree excitation pulse in inversion recovery pulse sequences

A

Time from inversion (TI)

183
Q

repetition time

A

TR

184
Q

image in DWI where abnormal tissue is brighter than normal tissue

A

Trace image

185
Q

coil that both transmits RF and receives the MR signal

A

Transceiver

186
Q

range of frequencies transmitted in an RF pulse

A

Transmit bandwidth

187
Q

the axis perpendicular to Bo

A

Transverse plane

188
Q

waiting period after each R wave - the time between the R wave and the beginning of data acquisition

A

trigger delay

189
Q

waiting period before each R wave in gated studies

A

Trigger window

190
Q

artefact caused by under-sampling so that edges of high and low signal are not properly mapped into the image

A

Truncation artefact

191
Q

echo train length

A

Turbo factor

192
Q

acquisition where a small amount of data is acquired from each slice before repeating the TR

A

2D volumetric acquisition

Z MRI Physics (12 decks)

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