MRI Flashcards
(195 cards)
1
Q
What is MRI?
A
Magnetic resonance imaging. It is an imaging modality that positions the human body within a strong magnetic field then transmits/receives radiofrequencies to/from hydrogen nuclei in the body. The RF waves are then transformed into an image computationally.
2
Q
What are the advantages of MRI?
A
+ Absence of ionising radiation
+ Excellent soft tissue contrast
+ Ability to obtain dynamic images in the axial, saggital, coronal, or oblique planes
3
Q
State the 9 types of MRI system
A
- Permanent magnet
- Resistive magnet
- Open MRI
- Superconducting magnet (clinical)
- Superconducting magnet (research)
- Portable
- Small bore (extremity or head only)
- PET/MR
- MR linac
4
Q
What are the 6 component of an MRI scanner?
A
1) Magnet: produces the static field
2) Gradient coils: spatial localisation
3) RF transmitter: induces transitions
4) RF receiver: detects signals
5) Image processor: processes raw data
6) Host computer: sequence control and image display/archiving
5
Q
What is the static magnet of an MRI scanner made of?
A
A superconducting wire submerged in liquid helium (at 2.4K) wound around a hollow bore.
6
Q
What is the typical magnetic field strength of an open/portable MRI scanner?
A
0.2-1 T
7
Q
What is the typical magnetic field strength of a clinical MRI scanner?
A
1.5-3 T
8
Q
What is the typical magnetic field strength of an animal/research scanner?
A
4.7-18 T
9
Q
What are gradient coils?
A
Coils designed to manipulate/alter the static magnetic field. They are wound around a removable more inside the static magnet bore and are active in all 3 axes (x,y,z).
10
Q
What are RF coils?
A
Coils used to get energy into tissues and detect resultant signals. The signals come from flux linkage changes in the coils. The best images are taken with RF coils that lie close to the sample.
11
Q
What are the 3 types of RF coil?
A
1) Volume coils
2) Surface coils
3) Array coils
12
Q
What is a volume coil?
A
An RF coil that transmits/receives RF signals over a 3D volume of tissue. It surrounds the region of interest and provides uniform signal coverage and deep imaging within that volume.
13
Q
Give 3 examples of volume coils
A
1) Body coil (built into scanner)
2) Head/neck coil
3) Knee coil
14
Q
What is a surface coil?
A
A type of RF coil that is placed directly on or near the body part being imaged. Surface coils only cover a limited area and are used solely for receiving MRI signals (not transmitting).
15
Q
What is an array coil?
A
A type of RF receive coil made up of multiple small surface coil elements that work together to cover a larger area and increase the signal-to-noise ratio (SNR).
16
Q
What types of scans can be completed using an MRI scanner?
A
- Anatomical
- Diffusion
- Perfusion
- Metabolic concentrations (MRS)
- Exchange rates
- Brain function (fMRI)
17
Q
Which patients may be restricted from getting MRI scans?
A
- Patients with pacemakers
- Patients with metallic implants
- Claustrophobic patients
- Patients with involuntary movements
- Patients on life-support systems
- Pregnant patients in the 1st trimester
18
Q
What are the disadvantages of MRI?
A
- Many contraindications (pacemakers, implants, etc.)
- Can be claustrophobic
- Possibility of projectiles
- Long scan times (patient discomfort + potential for movement)
- Long waiting lists
- Expensive
19
Q
What are the 4 major categories in MR safety?
A
1) Major MRI hazards
2) Biological effects of magnetic fields
3) Projectile and pacemaker safety
4) Cryogens and quench safety
20
Q
Which magnetic fields are MRI patients exposed to?
A
- The fringe field
- The static magnetic field
- The gradient time-varying fields
- The RF time-varying fields
21
Q
Which magnetic fields are MRI staff exposed to?
A
The fringe field
22
Q
Give the equation for the translational force of an MRI static magnetic field
A
F = translational force
χ = magnetic susceptibility
V = volume of material
B = magnetic field strength
r = distance
23
Q
The translational force of an MRI scanner is caused by the ______ _____ gradient.
A
Fringe field
24
Q
What is the MR fringe field?
A
The three dimensional volume of space surrounding the MR magnet that contains both the Faraday shielded volume and the 0.5mT field contour (5 Gauss line).
25
State 4 common biological effects of static magnetic fields (at 3T and above)
1) Nausea
2) Headaches
3) Taste sensations
4) Vertigo
26
Biological effects caused by high magnetic fields are associated with ____ movement.
Head
27
What is magnetic torque?
The rotational force exerted on an object with a magnetic moment by an external magnetic field, causing it to twist.
28
Give the equation for magnetic torque
T = torque
χ = magnetic susceptibility
V = volume of material
B = magnetic field strength
29
Why can magnetic torque cause a hazard?
Ferromagnetic implanted objects (e.g. hip/knee replacements) may try to twist in the magnetic field.
30
Which type of metal is MR safe?
Non-ferromagnetic metal
31
Give 3 examples of MR safe (non-ferromagnetic) metals
Titanium
Stainless steel (austentitic)
Brass
Copper
Aluminium
Silver
Gold
32
Which type of metal is MR unsafe?
Ferromagnetic metal
33
Give 3 examples of MR unsafe (ferromagnetic) metals
Iron
Stainless steel (martensitic)
Nickel
Cobalt
Alloys of the above
34
All metals can cause image ________.
Artefacts
35
What are the hazards of time varying gradients?
- Electrically conducting tissues
- Peripheral nerve stimulation (which can cause vertigo)
- Acoustic noise
36
How is PNS limited during an MRI scan?
Thresholds apply to prevent it
37
How are the hazards of acoustic noice limited during an MRI scan?
Ear protection is provided
38
What is the hazard of RF exposure?
Tissue heating from the applied RF field
39
Define specific absorption rate (SAR)
The rate at which radiofrequency (RF) energy is absorbed by tissues.
40
Give the equation for SAR
41
Which 4 theoretical factors influence SAR?
SAR increases with:
- The square of the Larmor frequency (proportional to the static field)
- The square of the applied RF field
- Patient size
- The numner of RF pulses in a given time
42
Which 5 clinical factors influence SAR?
- Type of pulse sequence
- Number of slices and resolution required
- Number of contrast types and orientations required
- Speed of the acquisition(s)
- Paitent implants or external devices
43
What is the normal clinical SAR limit?
2 W/kg
44
What is an MRI quench?
A catastrophic loss of superconductivity, leading to the loss of field and loss ('boil off') of liquid helium as gas. This can either be spontaneous or initiated by pressing the quench button.
45
When should the quench button be pressed?
In a life-threatening projectile incident or fire.
46
Why does MRI revolve around the hydrogen atom?
There is lots of hydrogen in the body and it has a strong magnetic moment.
47
What are the 3 basic properties of a proton?
- Mass
- Positive charge
- Spin
48
The nucleus of hydrogen is a _______.
Proton
49
Define magnetic moment (µ)
A measure of an object's tendency to align with a magnetic field.
50
Why doesn't the human body have a net magnetic field?
Because the magnetic moments are randomly aligned, meaning that they cancel out.
51
What happens to the magnetic moments in the human body when it is in an external field?
They allign with the static field in one of two spin states: spin up or spin down. There are slightly more spin ups as it is the lower of the two energy states, giving the body a net magnetic field measurement.
52
What are the two possible orientations for a proton in an external magnetic field?
Parallel = spin up = low energy state
Anti-parallel = spin down = high energy state = less favourable
53
What is a scalar component?
Quantities with only magnitude (e.g. temperature, mass, speed).
54
What is a vector component?
Quantities with magnitude and direction (e.g. force, velocity, acceleration).
55
Is magnetic moment a scalar or vector quantity?
Vector
56
In MRI, the _ direction is defined by the direction of the static field. This is known as the ___________ ______.
z
Longitudinal plane
57
In MRI, there is no different between _ and _ as they are both perpendicular to the static field. This is known as the _________ _____.
x
y
Transverse plane
58
Why do protons not exactly align with the static magnetic field?
Because protons precess around the static field, meaning that (according the the uncertainty principle) there is uncertainty in the exact position of the spin in the transverse plane.
59
What is phase?
The position of the vector tip of the spin precession circle at one particular time.
60
What is phase coherence?
The extent to which multiple spins maintain a synchronized state, meaning their phases are aligned and stable over time.
If the tips of the vectors at the same position then the nuclei are IN PHASE and if they aren't then the nuclei are OUT OF PHASE.
61
At equilibrium, the transverse components of spins in a static magnetic field are ___ __ ____.
Out of phase
62
Why is there a net magnetisation of spins at equilibrium in a static magnetic field?
There is a small excess of spins in the lower energy state (parallel). This means that the sum of the z components is not 0. The transverse component has no net magnetisation, meaning that the net magnetisation is in the direction of the magnetic field.
63
What is the Larmor frequency?
The frequency of precession of spins. This depends on the external magnetic field strength and the nucleus.
64
What is the Larmor frequency of hydrogen at 1T?
42.57 MHz
65
State the Larmor Equation
ω0 = Larmor frequency
γ = gyro-magnetic ratio
B0 = magnetic field strength
66
What EM frequency range is the Larmor frequency in?
The radio-frequency range of the EM spectrum
67
RF radiation has the same frequency as the Larmor frequency, causing _______.
Resonance
68
How can protons shift from one energy level (spin state) to another?
Low to high: by giving a proton exactly the right about of energy
High to low: by prompting the proton to give up an equal amount of energy (stimulated emission)
69
What plane is magnetisation measured in?
The transverse plane
70
Why can't magnetisation be measured at equilibrium?
Because it is measured in the transverse plane and magnetisation is very small in this plane compared to the static field at equilibrium.
71
Describe the motion of net magnetisation due to an RF pulse (spin excitation) in a laboratory plane
72
Describe spin excitation in the rotating frame
Net magnetisation rotates away from the z-axis and down towards the transverse plane due to an RF pulse. This requires a 90º flip angle.
73
What is a flip angle?
The angle that the RF pulse flips the net magnetisation through, from the z-direction into another direction (or another plane).
74
What happens if a 90º flip angle is applied?
A pulse of RF radiation moves the net magnetisation exactly into the transverse plane.
75
What happens if a 180º flip angle is applied?
A pulse of RF radiation moves the net magnetisation into the negative z-direction.
76
What are the 2 ways to increase flip angle from 90º to 180º?
- Double the RF pulse strength
- Double the duration of the RF pulse
77
How does a signal receiver coil detect magnetisation in the transverse plane following an RF pulse?
The receiver coil is fixed in the laboratory place, so it detects a changing magnetic field as the magnetisation rotates, which generates a current in the coil and procesed an MR signal.
78
What is Free Induction Decay (FID)?
The change in MR signal after a 90º pulse. The signal oscillates at the Larmor frequency and decays exponentially to zero.
Yellow = laboratory plane
Blue = rotating plane
79
What causes signal destruction via free induction decay?
T2* dephasing
80
What is T1 relaxation?
The recovery of longitudinal magnetisation (M_z).
81
What is T2 relaxation?
The decay of transverse magnetisation (M_xy), shown by a loss of signal.
82
After an RF pulse, all protons precessing slower or faster than the ______ _______ will dephase.
Larmor frequency
83
What is spin-spin relaxation?
The rate at which transverse magnetisation decays to zero (i.e. the rate at which protons lose their initial phase coherence due to local interactions). This is T2 relaxation.
84
Give the equation for spin-spin relaxation
M_xy = transverse magnetisation
M_0 = net magnetisation
t = time
T2 = transverse relaxation time
85
What does spin-spin relaxation depend on?
Tissue composition and how easily protons can move within their lattice. More solid tissues have a shorter T2. It also depends on dipole-dipole interactions and magnetic field inhomogeneities.
86
What is T2* relaxation?
A relaxation time with the same mechanism as T2, but where dephasing is also influenced (increased) by inhomogeneities in the static (main) field. The variations in the magnetic field have a greater impact on dephasing than proton tissue properties.
87
True or false: spin-spin relaxation doesn't lose any energy.
True
88
Which relaxation method causes protons to lose energy?
T1 relaxation: spin-lattice relaxation
89
What is spin-lattice relaxation?
The process where nuclear spins return to their equilibrium state in a magnetic field after being excited by an RF pulse. This is the recovery of longitudinal magnetisation.
90
Give the equation for spin-lattive relaxation
M_z = longitudinal magnetisation
M_0 = net magnetisation
t = time
T1 = longitudinal relaxation time
91
T1 relaxation times are ______ than T2 relaxation times.
Longer
92
Describe a graph showing T2 decay and T1 recovery
T1 recovery takes longer than T2 decay.
93
Are longitudinal magnetisation and transverse magnetisation dependent on one another?
NO. Longitudinal magnetisation is controlled by T1 and transverse magnetisation is controlled by T2.
94
What are the 2 fundamental MRI pulse sequences?
- Gradient echo (GE, GRE, FE)
- Spin echo (SE, TSE, FSE)
95
What is a pulse sequence?
A set of RF and gradient pulses. The strength, duration and timing of all pulses is critical to the selection of the image contrast.
96
What 5 characteristics do all pulse sequences have?
1) RF excitation pulse
2) Slice selection gradients
3) Phase encoding gradients
4) Frequency encode gradients
5) Signal/data collection
97
Describe the gradient echo (GE) sequence and each of its components
RF = radio frequency (a sinc pulse)
G_ss = slice select gradient
G_pe = phase encode gradient
G_fe = frequency encode gradient (second pulse is double the area of the first)
98
Why is it important to use gradients?
When all spins experience the same static and RF field, it is impossible to differentiate the position of spins. Hence, in imaging, it is important that each 'voxel' of spins experiences a unique magnetic field. This can be achieved using gradients.
99
What is an MRI gradient?
A linear variation of magnetic field strength in one axial direction, measured in mT/m.
100
Give the 3 gradient equations for each axial direction
101
What are gradients used for in 2D imaging?
- Slice selection
- Spatial encoding within the slice (frequency and phase encoding)
102
Give the equation for the total magnetic field at a given point in the x direction
B_z = total B-field
B_0 = static field
x = position
G_x = gradient in the x-direction
103
Give the equation for the resonant frequency at a given point in the x direction
f = frequency
γ = Larmor frequency
B_0 = static field
x = position
G_x = gradient in the x-direction
104
Give the equation for phase change in the rotating frame after a gradient is applied
φ = phase change
γ = Larmor frequency
x = position
G_x = gradient in the x-direction
t = time
105
Describe the plot of GE gradient dephasing
The gradient pulse causes immediate, fast dephasing
106
Describe the plot of GE gradient rephasing
A rephasing gradient pulse causes a gradient echo (GE), which is detected at the echo time (TE).
107
Describe the shape of a Fourier transformed Free Induction Decay (FID)
108
What domain is information in after Fourier transforming physical space (distance, x)?
Reciprocal space/k-space (spatial frequency, k = 1/x)
109
State the Fourier transform that converts an image from k-space to physical space
110
State the inverse Fourier transform that converts and image from physical space to k-space
111
Define spatial frequency
The inverse of the periodicity with which image intensity values change.
Image features that change in intensity over long image distances correspond to low spatial frequencies and image features that change in intensity over short image distances correspond to high spatial frequencies.
112
Are edges and details high or low spatial frequencies?
High
113
Is contrast (colour) high or low spatial frequency?
Low
114
When is the GE slice select gradient switched on?
ONLY during the excitation pulse.
115
True or fale: for MRI scans, the RF pulses contain just the Larmor frequency.
FALSE: they contain a range of frequencies.
116
How does the slice select gradient work?
The slice select gradient ensures that spins in a given axial direction precess with linearly increasing frequencies (with tissue at the isocentre precessing at the Larmor frequency). The RF pulse, which is switched on at the same time as the slice select gradient, has a finite frequency spread (a bandwidth RF). Only spins that precess within these frequencies are excited by the pulse, allowing a specific slice to be chosen.
117
What is the frequency encoding gradient?
A gradient that is applied during data acquisition in order to encode position in terms of frequency.
118
Give the equation for the frequency encoded field of view
FOV = field of view
γ = Larmor frequency
G_FE = frequency encoding gradient
t = time
119
A larger frequency encoding gradient gives a _______ field of view.
Smaller
120
A longer data acquisition gives a _______ field of view.
Smaller
121
What is the phase encoding gradient?
A gradient that temporarily applies a magnetic field gradient along one spatial direction (perpendicular to the frequency encoding gradient) before data acquisition begins. This causes protons at different positions along this axis to accumulate different phase shifts in their precession, allowing them to be distinguished from one another.
122
What are the 3 types of phase encoding gradient?
123
Phase encoding ________ with distance from the centre of the phase encoding axis.
Increases
124
True or false: each voxel in k-space represents information about the whole real space image.
True
125
Describe the difference between a low k-space image and a high k-space image.
126
MRI images are formed from ________ pixels.
K-space
127
How can the resolution of an MRI image be improved?
By increasing the gradient strength
128
How can the field of view of an MRI image be decreased?
By increasing the gradient strength
129
What is a T1-weighted scan?
A scan that minimises the effects of all mechanisms except the T1 relaxation.
130
Is a T1-weighted scan longer than a T2-weighted scan?
Not necessarily (even though T1 > T2 for tissues)
131
Describe the appearance of a T1-weighted scan
Tissues with relatively short T1 values appear bright (e.g. fat)
132
Describe the appearance of a T2-weighted scan
Tissues with relatively long T2 values appear bright (e.g. cerebrospinal fluid/CSF)
133
For medical images, is it optimal to have high or low contrast?
High
134
What 4 factors influence the intensity of an MR signal?
1) Proton density
2) T1 relaxation time (recovery)
3) T2 relaxation time (decay)
4) Chemical shift, diffusion, motion, etc.
The contribution of each mechanism depends on the sequence and sequence parameters
135
What are the 3 rules of MR image contrast?
1) The nucleus must have 'spin'
2) MR signal depends on net transverse signal
3) There has to be some longitudinal magnetisation available to be turned into transverse signal
136
Define echo time (TE)
The time between the application of the radiofrequency excitation pulse and the peak of the signal induced in the coil.
137
Define repetition time (TR)
The amount of time between successive pulse sequences applied to the same slice.
138
Describe echo time (TE) and repeatition time (TR) in terms of a gradient echo sequence
139
Which parameter controls T2 contrast?
Echo time (TE)
140
For T2 contrast, a short echo time means ____ transverse magnetisation dephasing. A very long echo time means that all transverse magnetisation has ________.
Less
Dephased
141
Why is finding the right echo time important in achieving optimum T2 contrast?
Different tissues decay at different rates, so there will be a specific echo time where there is maximum difference between signal intensities (i.e. maximum contrast).
142
Which parameter controls T1 contrast?
Repetition time (TR)
143
For T1 contrast, a short repetition time means ____ longitudinal magnetisation recovery. A long repetition time means that most of the longitudinal magnetisation has _________.
Less
Recovered
144
Why is finding the right repetition time important in achieving optimum T1 contrast?
Different tissues recover at different rates, so there will be a specific repetition time where there is maximum difference between signal intensities (i.e. maximum contrast).
145
What is a PD-weighted sequence?
A technique where images are created based on the concentration of hydrogen protons in tissues. The tissues with a higher concentration or density of protons generate the strongest signals and appear the brightest in the image.
146
State the typical TE of a T1-weighted sequence
Short
147
State the typical TE of a T2-weighted sequence
Long
148
State the typical TE of a PD-weighted sequence
Short
149
State the typical TR of a T1-weighted sequence
Short
150
State the typical TR of a T2-weighted sequence
Long
151
State the typical TR of a PD-weighted sequence
Long
152
State the typical TE of a T1-weighted GE sequence
1 - 15 ms
153
State the typical TE of a T2-weighted GE sequence
30 - 80 ms
154
State the typical TE of a PD-weighted GE sequence
1 - 15 ms
155
State the typical flip angle of a T1-weighted GE sequence
50 - 80º
156
State the typical flip angle of a T2-weighted GE sequence
10 - 40º
157
State the typical flip angle of a PD-weighted GE sequence
10 - 40º
158
What is a contrast agent?
A substance injected into the body to enhance the visibility of specific tissues or organs during a scan by changing their T1 or T2 response.
159
Which contrast agents are typically used in T1 weighted images?
Gadolinium-based agents because they reduce the T1 of nearby photons
160
In gradient echo sequences, how do you control which contrast is dominant?
By changing the flip angle and TE
161
What is a spin echo sequence?
A sequence that consists of a 90º RF pulse, a time delay of TE/2, then an additional 180º RF pulse, all repeated after TR. The 180º pulse generates a spin echo at time TE.
162
Describe the spin echo (SE) sequence and each of its components
RF = radio frequency (a sinc pulse: 90º then 180º)
G_ss = slice select gradient
G_pe = phase encode gradient
G_fe = frequency encode gradient (second pulse is double the area of the first)
163
How is a spin echo produced?
1) A 90º RF pulse flips all protons along the y-axis and causes phase coherence
2) Protons dephase (via T2 relaxation and main field inhomogeneity) for time TE/2, producing a 'fan' of spin vectors
3) A 180º RF pulse is then applied on the x-axis, which flips all proton spin vectors over
4) The protons continue to dephase in the same direction. Their frequency differences have not changed, only their phase angles (so everything that was moving slowly is now closer, so all spins rephase at the same time)
5) After a further TE/2, all protons are realigned along the y-axis, forming a 'spin echo'
164
State the typical TE of a T1-weighted SE sequence
~ 20ms
165
State the typical TE of a T2-weighted SE sequence
80 - 120 ms
166
State the typical TE of a PD-weighted SE sequence
~ 20 ms
167
State the typical TR of a T1-weighted SE sequence
300 - 600 ms
168
State the typical TR of a T2-weighted SE sequence
1800 ms+
169
State the typical TR of a PD-weighted SE sequence
1800 ms+
170
Describe the plot of SE gradient dephasing and rephrasing
171
What is Inverstion Recovery?
Inversion recovery (IR) is an MRI pulse sequence designed to enhance contrast or suppress certain tissues based on T1 relaxation times. It uses a 180° inversion pulse, followed by an inversion time (TI) before the standard imaging sequence.
IR = pre-pulse + SE or GE
172
State 3 main uses of inversion recovery
1) Heavily T1-weighted images
2) Fat suppression
3) CSF suppression
173
What is the main drawback of inversion recovery?
Very long scan times due to a long TR
174
How is an inversion pulse produced?
1) Initially, the net magnetisation is aligned along the z-axis
2) A 180º pulse rotates the net magnetisation so that it is aligned in the negative z direction
3) Magnetisation begins to recover along the z-axis (T1 recovery) until it eventually reaches z = 0 for the desired tissue
4) At this point, a 90º pulse is applied and turns longitudinal magnetisation into the transverse plane
5) Finally, a spin echo is formed as normal
175
True or false: there is never any transverse component between the 180º inversion pulse and the 90º pulse of an IR sequence.
True
176
For inversion recovery, what does signal intensity depend on?
- Inversion time (TI)
- T1 of the tissues
Any tissue can be suppressed by choosing the appropriate TI
177
Describe an inversion pulse that suppresses fat
178
State the typical TI of a T1-weighted IR sequence
Medium (400 ms)
179
State the typical TE of a T1-weighted IR sequence
Short (for minimum T2 contrast)
180
State the typical TR of a T1-weighted IR sequence
Long (> 3 x T1 to allow complete relaxation between measurements)
181
What does STIR stand for?
Short TI Inversion Recovery
182
What is the purpose of a STIR sequence?
To suppress fat (it gives a T1-weighting with black fat)
183
What is the TI, TE, and TR of a STIR sequence?
TI: short
TE: short
TR: long
184
What does FLAIR stand for?
FLuid Attenuated IR
185
What is the purpose of a FLAIR sequence?
To suppress fluid (it gives a T2-weighting with black CSF)
186
What is the TI, TE, and TR of a FLAIR sequence?
TI: long
TE: long
TR: very long
187
Describe the inversion recovery T1 relaxation curve
188
State 5 advanced MRI methods
1) Echo Planar Imaging (EPI)
2) Diffusion Weighted Imaging (DWI)
3) Diffusion Tensor Imaging (DTI)
4) Functional MRI (fMRI)
5) Spectroscopy (MRS)
189
What is echo planar imaging (EPI)?
A fast MRI technique that can acquire images by filling k-space in a single echo.
190
What is diffusion weighted imaging (DWI)?
An MRI technique that uses the random movement of water molecules to create contrast in images. Areas with normal diffusion show low signal and areas with restricted diffusion show the highest signal, meaning that injuries can be identified.
191
What is diffusion tensor imaging (DTI)?
A specialised type of MRI that uses the motion of water molecules to map the structure of brain tissue, particularly white matter. Tractography can then be carried out post-scan to show which regions of the brain connect to a ROI.
192
What is function MRI (fMRI)?
An MRI technique based on repeated T2* weighted EPI that depends on the BOLD effect to detect small increases in blood flow by intermittent stimulation of brain regions.
193
What is the BOLD effect?
Blood Oxygenation Level Dependent dephasing, which causes signals in a given region of the brain.
194
What is MR spectroscopy (MRS)?
An MRI technique that allows tissue to be interrogated for the presence and concentration of various metabolites.
195
What are the 4 key peaks analysed in MRS?
- NAA
- Creatine
- Choline
- Inositol
