Modern methods in neuroscience I

Question 1

What is magnetic resonance imaging used for?

Answer 1

To produce high resolution images of under the skin

Question 2

Why is MRI safer than X-rays and CT scans?

Answer 2

Doesn’t use ionising radiation

Question 3

What does MRI scanning use to get an image of under the skin?

How?

Answer 3

Powerful magnets

Elicit a signal from the protons contained in the water molecules of the body

Question 4

What type of particle emits electromagnetic waves?

What does this produce?

Answer 4

An ACCELERATING, CHARGED particle

Produces electromagnetic radiation which can be detected

Question 5

What is acceleration?

Answer 5

The rate of CHANGE of velocity

Question 6

What does velocity comprise of?

Answer 6

Magnitude(size) AND direction

How FAST something moves in a particular DIRECTION

Question 7

If a particle is accelerating, what has changed?

Answer 7

The magnitude or direction of a CHARGED particle

Question 8

What type of particle is CONSTANTLY accelerating?

What does this particle release?

Answer 8

A spinning CHARGED particle - A PROTON

Constantly releases electromagnetic radiation

Question 9

What does any spinning particle have?

Answer 9

A magnetic dipole (North and South)

Question 10

How are the protons arranged in a given body tissue?

What does this cause?

Answer 10

All the north poles are orientated in DIFFERENT directions

Cancel each other out
Causes NO NET magnetic effect
NO electromagnetic radiation can be detected (it is 0)

Question 11

What happens when a powerful VERTICAL, STATIC external magnetic field is applied?

What does this produce?

Answer 11

Protons line up with the magnetic field (vertically) - no longer cancel each other out

Forms a weak electromagnetic field in the tissue
All the spins of the protons add together - produces electromagnetic radiation

Question 12

What happens when a powerful HORIZONTAL, PULSING external magnetic field is applied? (after the vertical one)

What does this produce? Why?

Answer 12

Pushes the protons over, causing them to wobble on their axis

Produces a VARYING, DETECTABLE magnetic field
As change in direction - acceleration in the the change in velocity (magnitude/direction)

Question 13

What is radio frequency?

When is this used?

Answer 13

Magnetic field that is rapidly pulsed on and off

Used as a horizontal magnetic field to push the protons over on their axis

Question 14

What does precess mean?

When is this achieved?

Answer 14

When the protons wobble on their axis

Occurs when there is a vertical static magnetic field and a horizontal radio frequency

Question 15

What component of the magnetic field of the protons is easier to detect? Why?

Answer 15

The horizontal component - gets bigger and smaller as the protons are knocked over

Changes the magnetic field

Easier to measure change

Question 16

In a MRI machine, what causes the vertical magnetic field?

Answer 16

Super-cooled, super-conducting coil

Question 17

In a MRI machine, what causes the horizontal magnetic field?

What is this magnetic field also called?

Answer 17

The head coil

RF - radio frequeny

Question 18

Which magnetic field is static?

Answer 18

Vertical

Question 19

What happens to the protons when the RF is turned off?

Answer 19

Protons move out of phase - Dephase

Question 20

How does dephasing occur?

Answer 20

Quickly

Question 21

What does dephasing lead to?

Answer 21

A loss of horiztonal magnetisation and a weakened signal in the horizontal field - The ‘dephasing signal’

Question 22

What is T2?

Answer 22

The time constant of the weakening horizontal field

Question 23

What is a T2 weighted image based upon?

Answer 23

The dephasing part of the cycle

Question 24

What happens to the protons if the horizontal radio frequency pulse remains off?

What does this result in?

Answer 24

Protons realign themselves with the strong VERTICAL magnetic field

Resulting in the restoration of the vertical magnetisation
Increase in the vertical signal

Question 25

Does the realignment happen faster or slower than the dephasing phase?

Answer 25

Much slower

Question 26

How is the return to the original alignment of the protons measured?

Answer 26

Indirectly

Question 27

What is T1?

Answer 27

The time constant of the recovery of the longitudinal magnetisation

Question 28

What is a T1 weighted image based upon?

Answer 28

When all the protons are aligned in the vertical plane (no horizontal magnetic field)

Question 29

When is the signal in T2 strongest? When does this signal reduce?

Answer 29

When the protons are in phase Reduces when the protons dephase

Question 30

When is the signal in T1 weakest? When does this signal increase?

Answer 30

When the protons are horizontal Increases when the protons stand up and realign with the vertical field

Question 31

What is useful in getting information about the tissue the protons are in?

Answer 31

Changes | Especially in the RATE OF CHANGE of the signal strength

Question 32

What do the values of T1 (realignment) and T2(dephasing) of the protons depend upon?

Answer 32

The surrounding matter

Question 33

How quick do protons dephase and realign in DENSE tissue? (eg. bone) Why?

Answer 33

Quicker than if in a less dense tissue Because the protons are closer together

Question 34

What is used to construct an MRI image?

Answer 34

A computer system attached to the scanner, which assigns a particular brightness value to the various T1 and T2s measured

Question 35

In T2, what colour do dense substances appear?

Answer 35

Bright

Question 36

In T1, what colour do dense substances appear?

Answer 36

Black

Question 37

What is the point in having T1 and T2 images?

Answer 37

Can easily see different structures Which one is used depends upon what the researcher wants to visualise

Question 38

What information does MRI give?

Answer 38

Structural information

Question 39

What can be used to determine what parts of the brain is functioning in different tasks?

Answer 39

fMRI | functional magnetic resonance imaging

Question 40

What is fMRI and what is it used for?

Answer 40

Functional MRI Used to determine what parts of the brain are functional during different tasks

Question 41

What did James Williams do? What did this show?

Answer 41

Placed a subject on a balanced table that could tip downwards at the head or foot, if the weight at either end was increased - Showed that if emotional/intellectual activity began in the subject - the head end went down - As a result of blood rush

Question 42

What happens to the blood in the brain?

Answer 42

Blood flow SLOWLY increases to metabolically active areas of the brain

Question 43

What do some people suggest about the blood flow to metabolically active parts of the brain?

Answer 43

Suggest it is to supply area working hard with nutrients and oxygen And to flush away the metabolic byproducts

Question 44

What does oxygenated blood do in the brain? What happens after this

Answer 44

Enters the capillary bed supplying an area of metabolically active brain Tissue then extracts the O2 from the blood Deoxygenated blood leaves the capillary bed

Question 45

Is oxygenated or deoxygenated blood paramagentic (has magnetic properties?? What does this allow?

Answer 45

Deoxygenated blood Magnetic field of the deoxygenated blood can be detected in an MRI scanner Can see the difference between oxygenated and deoxygented blood on the MRI image

Question 46

What is a 'BOLD' signal?

Answer 46

Blood Dependant Oxygenation Level Dependant signal

Question 47

If there is more deoxygenated blood present, what happens to the signal?

Answer 47

It is brighter

Question 48

If there is more deoxygenated blood coming out of a specific brain area, what is the assumption?

Answer 48

That more oxygenated blood has travelled to that area of the brain So, that part of the brain is more active

Question 49

What do computer programmes such as 'Statistical Parametric Mapping' and 'FSL' do? How do they do this? What does this 'map out'

Answer 49

Calculate the probability that a small chunk of brain has a DIFFERENT BOLD signal to the one next to it (Probability of increased blood flow to that tiny area) - Compare the voxel of one brain area to the voxel of the neighbouring area using a t-test - Assign a colour to each probability - Overlay the colours on the ANATOMICAL MRI image Maps out activation of the brain

Question 50

What is a VOXEL?

Answer 50

A 3D pixel (volumetric pixel) | Cube shaped pixel of the brain

Question 51

Why is the nature of the BOLD signal controversial? Why?

Answer 51

Some think it is may be a non-specific 'cooling system' of the brain Because the increased blood flow to the brain area FAR EXCEEDS the requirements of the active neurons

Question 52

Why is the usefulness of fMRI in question?

Answer 52

- Patterns of activation can be DIFFERENT in different patients performing the SAME task

Question 53

How can you make comparisons between the fMRI of different people? What are the disadvantages of this?

Answer 53

Apply non-linear registration to a STANDARD template Disadvantages: - Produces an average picture of the brain which distorts the original image and makes it appear fuzzy - As each brain is different

Question 54

What is fMRI good and bad for?

Answer 54

Good at telling you WHERE the brain is activated (good spatial resolution) Bad at telling you WHEN the brain is activated (bad temporal resolution)

Question 55

Why does fMRI have poor temporal resolution?

Answer 55

It takes several seconds for the arterioles to dilate and allow increased blood flow (detected in fMRI) BOLD signal takes several seconds to build up

Question 56

What is fMRI not idea for? Example?

Answer 56

Experiments in which timing is important Eg. investigating rapid cognitive tasks

Question 57

If investigating tasks where timing is important, what must fMRI be coupled with? How is this technique different to fMRI?

Answer 57

ELECTROENCEPHALOGRAPHY: - High TEMPORAL resolution - Low SPATIAL resolution