Lecture 24- Brain Systems

Question 1

What is a brain system?

Answer 1

A collection of structures in the brain that work together to perform a common function

Question 2

How is a brain system different to a network?

Answer 2

-A ‘network’ loosely refers to
the structure of circuits that connect areas of neurons together like the hardwiring

-A system on the other hand is how the structures in the brain work together.

Question 3

Do systems work together or alone? What is systems Neuroscience?

Answer 3

-Systems can work alone or in concert with other systems to bring about changes in behaviour e.g. sensory information from different areas of the brain joining together to inform movement as executed by the motor/ pre-motor cortex.
-Analysis of how different brain systems work together is called systems neuroscience

Question 4

Broadly speaking what technique is used to identify the different components of the brain?

Answer 4

Neuroimaging

Question 5

Draw the flow chart from slide 8 summarizing how different neuroimaging techniques are used to understand the brain’s structure and function…

Answer 5

Answers on the slide :)

Question 6

What does Tomography mean?

Answer 6

Imaging by creating ‘slices’ using any kind of penetrating wave

Question 7

How does X-ray radiation work on principle?

Answer 7

-x-rays absorbed to different degrees by tissues of different densities – dense tissues like bone absorb most X-rays so photographic film would be minimally exposed # ‘white’; whereas low density fat/water passes X-rays easily and exposes the film to appear dark

Question 8

What is CT?

Answer 8

-Computerized Tomography
-Rotation of a source of X-rays and a detector separated 180 deg from
the source – very thin slices: computer integrates to form an image

Question 9

What are the relative densities of different parts of the head? And what does this mean for CT scans?

Answer 9

air (‘darkest’=least dense) < fat < CSF < white matter < grey matter < blood from haemorrhage (dense globin) < bone (‘brightest’=most dense)

Question 10

What are the advantages of CT?

Answer 10

Good for showing acute bleeding or fracture of the skull, relatively quick (less than 1 minute), cheap, less scary for people: not as enclosed or noisy as MRI

Question 11

What are the disadvantages of CT?

Answer 11

Structure only, not function, not good for detail in the brain because of minimal contrast between areas, dose of radiation

Question 12

What are the principles of PET scanning i.e. how does it work?

Answer 12

Radiation emitted from a radioisotope injected intravenously is registered by external detectors. ‘Positrons’ from isotope travel short distance (2-3 mm), combine with electrons and ‘annihilation’ results in energy release picked up by detectors

Question 13

What is PET used for identification?

Answer 13

-Used to highlight areas of increased metabolism of glucose (e.g. by cancers) – commonly use F18 radiolabelled fluoro-2-
deoxyglucose (FDG) injected intravenously and enters organs where it highlights area of high glucose transport/phosphorylation

Question 14

What are some functions of PET scans?

Answer 14

-Metabolism: functional
-Molecular: gene therapy

Question 15

What are the advantages of PET scans?

Answer 15

Functional, can identify/ characterize tumors as malignant or benign

Question 16

What are the disadvantages of PET scans?

Answer 16

Poor resolution of brain tissue (can combine with CT) but also area localized is only approximate (within 5 mm), requires radiation dose

Question 17

What are the general principles/ the physics behind MRI scans?

Answer 17

-Person placed within a high-powered magnet (scanner)

-Magnetic field aligns hydrogen atoms (BOTH the parallel component = axis orientation and perpendicular
component=rotation)

-Turn radio pulse on which causes hydrogen ions to go out of the magnetic alignment/ out of synchrony

-Measure time it takes for the hydrogen atoms to recover their alignment and spin after the radiofrequency pulse is turned off.

-Hydrogen ions in different tissues take different amounts of
time to recover.

-The recovery times are mapped to form an anatomical image

Question 18

In an MRI image what are Units of the image called?

Answer 18

-Voxels (volume pixel or 3D pixel)

Question 19

Is an MRI machine dangerous even when it isn’t scanning?

Answer 19

Yes, it is always on. Also have to be very careful that don’t scan someone either wearing metal or that has metal inside of them (clips, pacemaker etc.). Components of the machine that are in the room i.e. buttons, controls also have to be careful designed so they are not metal and magnetic.

Question 20

In an MRI what is the order of how long different tissues take to recover and how does this how up in images? I.e. what type of tissue corresponds to what degree of darkness?

Answer 20

-Fat (e.g. in bone marrow)
-White Matter
-Grey Matter
-CSF

This list is in progression from the fastest recovery (lightest) to the slowest recovery (darkest).

Note: different order to CT which is based on density.

Question 21

Do the grey and white matter always stay the same degree of darkness on T1 MRI images?

Answer 21

No, Sometimes grey and white matter can appear REVERSED under T1
- look at the fat (bright) CSF (dark) not the white and grey matter as to define the difference between T1 and T2 images

Question 22

How do CTs and MRI compare on scanning time?

Answer 22

-CT’s are quicker and less scary
-MRI’s are slower (take 30 mins) and more scary (confining + noisy)

Question 23

How do CTs and MRI compare on quality?

Answer 23

-CT’s are inferior for brain detail
-MRI’s are good for detail

Question 24

How do CTs and MRI for showing bones and blood?

Answer 24

-CT’s are preferable for rapid assessment of bleeding and good for identifying skull fracture

-MRI’s are inferior for rapid assessment for bleeding and the skull is not well identified so are not much of a help for fractures

Question 25

What is a T1 weighed structural MRI? What are it’s functions?

Answer 25

-T1 = recovery time for the magnetic vector (orientation allignment) of the hydrogen atoms to return to resting alignment after the radiofrequency pulse is turned off

Functions:
-Useful to highlight fat in the brain
-T1-weighted images are used for structural (anatomical) analysis
-Volume of brain and/or specific brain regions (‘voxel based morphology’ or VBM)
- Can measure in relation to a specific characteristic/ habit of individuals e.g. to measure changes in the grey matter volume in limbic system as related to
mindfulness.

Question 26

What is a T2 weighed structural MRI? What are it’s functions?

Answer 26

-Recovery time for the
axel spin (spin alignment) of the hydrogen atoms to return to resting state after the
radiofrequency pulse - can
produce almost opposite
image effects to T1

-Used to investigate water in the brain

Question 27

How do T1 and T2 weighted MRI images compare in regards to fat?

Answer 27

-In T1 fat is bright
-In T2 fat is dark

Question 28

How do T1 and T2 weighted MRI images compare in regards water (CSF)?

Answer 28

-In T1 water is dark
-In T2 eyes and the CSF are bright

Question 29

How do T1 and T2 weighted MRI images compare in regards to flow of blood?

Answer 29

-In T1 new blood flow is bright
-In T2 blood flow is dark meaning vessels containing blood show up dark

Question 30

What are T2 weighted MRI images good for?

Answer 30

-Showing the fluid filled ventricles (Bright)
-Also lesions if these lesions are far away from the CSF (sometimes can be hard to tell difference)