Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Principles of CN > Lecture 4: Methods - MRI > Flashcards

Lecture 4: Methods - MRI Flashcards

(74 cards)

Start Studying
1
Q

Diagram of MRI image

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Lecture focuses on - (2)

A
  • how MRI image generated
  • How functional MRI image (different regions of brain) is active
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

There is key components in MRI scanner which is - (3)

A

Static magnetic field
Gradient coils
Radio-frequency (RF) coils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

There are 3 different gradien coils in MRI scanner , important for creating an image, which is - (3)

A

X,Y and Z

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

MRI measures the atom

A

hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

The earth has a

A

magnetic field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

M in MRI is for

A

magnetic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Magnetic field of earth created by the

A

earths rotation and iron in the inner core.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The static magnet field in MRI is generated by an

A

large electrical coil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Strength of the magnetic field is determined by the

A

amount of current following through the coil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

3 or 7 tesla magnet in MRI are

A

different strength of magnet and higher magnet gives better signal to noise

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Most MRI scanners in hospitals is

A

1.5 T

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Magnetic field of Earth is …. smaller than MRI magnet

A

50 000

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Ensure homeogenity of magnetic field in MRI which is determined by

A

the number of turns in the coil and by the ratio of length to diameter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

We need to ensure homeogenity of magnetic field in MRI as it gives

A

better MRI signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

For a homegenous coil we want a long and narrow coil but not feasible as

A

people will get claustrophobic in scanner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

The MRI is developed from the technique NMR (nucleus magnetic resonance) with N representing

A

nuclear

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

All matter is composed of

A

atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Example of matter composed of atoms

A

Brain is made of up 75% of water atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

The nucleus of each atom in matter contains

A

contains positively charged protons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Hydrogen (mostly in the form of water) is the most and its nucleus contains… - (2)

A

abundant atom in the body.

Its nucleus contains a single proton.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Because the proton in a hydrogen atom has a single electrical charge that spins, it creates a corresponing

A

magnetic field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

MRI commonly measures magnetic signals from

A

hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

The R in MRI is

A

resonance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
When (hydrogen) protons are placed in the static magnetic field of an MRI, they
resonate around the main axis of the external field
26
The precision field of H in a 7T magnet is
298 MTS
27
The frequency at which the hydrogen protons precess around main axis of external field is known as
Larmor frequency
28
The Larmor frequency depends on the .. - (2)
atom and the field strength
29
The Larmor frequency for Hydrogen is
42.58 MHz/T.
30
In a 3T magnet a hydrogen atom precesses about
127 million times per second
31
When hydrogen atoms are placed in a static magnetic field, they align to the
main axis
32
If RF at precession freq (see Larmor) apply perpendicular to z direction it can
knock hydrogen atoms to x and y direction
33
A receieve coil measure the signal we get in
x and y plane
34
When hydrogen atoms precess at 90 degrees to main magnetic field and transerve (or x,y plane) then
coil produces electrical current
35
The T2 decay is that - (2)
hydrogen atoms transerving across x and y plane together (coherent magnetic field) then spread out Causing reduction in fMRI signal you get in x and y direction
36
Equal magnetic signals that point at all directions will
cancel out
37
T2 is important for especially
fMRI
38
After T2 takes place, static magnetic field takes dominant and pulls hydrogen atoms in direction of static field which is
z axis
39
Schematic of T2 decay - (3)
* Blue - hydrogen atoms in different directions * * We still get average direction - some signal * After time, some spread out spreading into different direction - then signal is zero
40
T2 delay happens in
milliseconds - quickly
41
T1 takes ... to happen
seconds
42
Schematic of T1 recovery shows that
Magnetic field takes dominant and pulls hydrogen atoms to z direction
43
The gradient coils chages the
strength of static magnetic field in x,y and z direction
44
If the magnetic field was increased along the z axis (sometimes referred as B0) the RG to excite
top of the brain would be different to the bottkm
45
If the magnetic field was increased along the z axis (sometimes referred as B0) the RG to excite top of the brain would be different to the bottom - why?
z gradient changes magnetic field strength from top to bottom Strength at top of brain is 3.1 T and bottom of brain is 2.9 T and strength in middle is 3 What we do in order to excite sample, we apply RF which has to be matched with precession frequency of hydrogen atoms That precision frequnency determined by magnets Top is fastest as compared to bottom If we change RF we can excite different slides of brain
46
Once excited slice of brain along z axis we can also excite it on the
x and y axis
47
MR pulse sequences is sequence of
creating an MR image
48
MR Pulse sequences - (4)
* RF = Radio frequency pulse which is matched with particular z gradient * Apply Z gradient coil that selects a specific slice * Apply different levels of x and y gradient which allows spatial info along x,y, plane of that specific slice (Gx, Gy) * We then do the measurement of measuring magneitc signal as it goes through the pip * TE i(short)s time from RF pulse to measurement * TR (long) is time between succession radio frequency pulses * Can vary TE and TR to pick out different types of tissue
49
Different MRI pulse sequences leading to different
types of images
50
Different types of MRI images you can obtain - (3)
* Proton density imaging * T1 contrast * T2 contrast
51
For proton density imagining we would want in terms of TE and TR - (2)
long TR short TE
52
The T1 contrast is the most image that is commonly
used
53
The T1 contrast used for ..
anatomical images of the brain
54
We can't do proton density in T1 contrast as - (2)
* density of water same so signal would be the same * Here is interested in T1 recovery
55
T2 contrast has long and intermediate
long TR and intermedite TE
56
TE gives biggest difference between
T1 and T2
57
T2 used most clinically as picks up ... and also sued for
a lot of fluied and used in fMRI
58
Oncograph measures expansion of a
somatosensory cortex when the sciatic nerve from the leg was stimulated
59
Experiment by Roy and Sherrington in which revealed
link between blood flow and brain function
60
Experiment by Roy and Sherrington show
change in blood flow goes along the activity in region of somatosensory cortex
61
The core sources of energy we have for brain is - (2)
glucose and oxygen
62
Anaerobic respiration is when
glucose is only used for energy reserve
63
glucose not that efficient in
producing energy
64
Aerobic (oxygen + glucose) resp produces more ATP (34) than
anaerobic respiration (glucose)
65
Oxygenated haemoglobin has no
magnetic momement - dimagnetic
66
Haemglobin is a protein that can allows to
carry oxygen around body
67
Diagram of MRI signal when oxygenated vs deoxygenated
68
deoxygenated haemoglobin is paramagnetic and disrupt the
MRI signal
69
The magnetic properties of deoxyHb causes spin dephasing (loss of syncrhonisation) of
hydrogen atoms in the transverse direction.
70
The magnetic properties of deoxyHb causes spin dephasing of hydrogen atoms in the transverse direction. This results in the
T2 decay being significantly shorter in the presence of deoxyHb than oxyHB (T2* decay)
71
If there is less oxygen in Hb then less
MRI signal
72
BOLD stands for
blood oxygen level dependent
73
When region is active in brain in MRI there is a higher concentration of
oxygenated Hb than dexoygenated Hb
74

Principles of CN (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions