Lecture 17- Intro to neuroimaging

Question 1

What part of the neuron is a major factor in determining MR signal and contrast?

Answer 1

Myelin (unsheathes axons for faster conduction velocity). Is fatty and so has white appears leading to contrast between white and grey matter.

Question 2

What are the two types of tissue in the brain and what do they consist of?

Answer 2

• Grey matter: around outside= cell bodies

- White matter: on inside= axons + myelin

Question 3

How does an MRI compare to post-mortem way of looking at the brain?

Answer 3

MRI allows picture to taken from a living person in a non- invasive way

Question 4

What is CSF, where is it found? What can be seen in postmortem anaylsis?

Answer 4

• Is a fluid and shows up dark in a MRI
• CSF bathes the outside of the brain and spinal chord (hence name)
• Acts as shock absorber and provide nutrients + takes away waste
• In post mortem analysis all we see is holes because CSF is gone

Question 5

What are the two adjectives used to describe an MRI in the lecture?

Answer 5

• Noisy

- Variable

Question 6

What does the analysis of an MRI ultimately come back to?

Answer 6

-Statistics: there are various options and alternatives (T-test, ANOVA) so more than one ‘right’ way to do the analysis but there are also wrong ways that will lead to unreliable results that cannot be trusted

Question 7

What is an MRI essentially?

Answer 7

A giant magnet: there is a base line field and then there is also coils that can be adjusted in order to get out the desired signal

Question 8

What can be an issue seen as MRI’s are magnetic?

Answer 8

-It’s always on so need to make sure they are safe to enter i.e. don’t have pacemaker, clips +pins from operations (particularly old fashioned ones), clothing

Question 9

What do MRI’s make use of?

Answer 9

• The read the signals from the water in our brain by manipulating the hydrogen ions contained there.
• H ions have what are called a magnetic moment, when there is not external magnetic field they bounce around. On the other hand when there is a strong magnetic field the H ions line up and move in the direction of the field
• It’s these properties of Hydrogen ions that allows us to measure the properties of the brain with an MRI

Question 10

What resolution does an structural MRI typically measure at? Can this change?

Answer 10

• Typically at resolution of less than 1mm
• Can change resolution of the scan but as person has to stay very still during scan don’t want to increase too much because obtaining finer detail (increasing resolution) takes longer

Question 11

What happens for a structural MRI if you change the timing/ signals of the magnetic field?

Answer 11

• Highlight certain tissues/ flows and features

- Basically key take home is that you can adjust the MRI in many different ways to obtain useful pictures/ data

Question 12

In MRI analysis what should we formulate?

Answer 12

• A research question
• A alternative hypothesis
• A null hypothesis

Question 13

What are the initial steps of MRI anaylsis?

Answer 13

• Brain extraction (remove skull)
• Segmentation (determine differ tissue types)

MRI just gives the initial image you then need to adjust what you see to give useful information according to the research question you have decided on

Question 14

How would a T-test be used in an MRI context?

Answer 14

• Statistical constructs help us quantity the level at which we accept there is a real difference in our groups cause otherwise it would be reasonably subjective (just based on how much overlap we visually see in the curves)
• Use a T-test, is the result significant p<0.05

Question 15

How do CTs compare to MRIs?

Answer 15

• MRI is better resolution, but CT is better for bones and membranes.
• MRI not good for those with pacemaker.
• MRI can show functional CT can’t

Question 16

Other than CT what is an additional complementary technique to MRI’s?

Answer 16

Histology (staining certain parts e.g. cell bodies to see clear distinctions)