Neuroimaging techniques

Question 1

brain system

Answer 1

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

Question 2

brain network

Answer 2

the structure of circuits that connect areas of neurons together

Question 3

systems neuroscience

Answer 3

an analysis of how systems bring about change in behaviour

Question 4

what neuroimaging method uses X-ray radiation

Answer 4

CT

Question 5

what neuroimaging method uses radio waves?

Answer 5

MRI

Question 6

what neuroimaging method uses radiolabelling?

Answer 6

PET

Question 7

Computed tomography (CT)

Answer 7

tomography is imaging by creating slices using any kind of penetrating wave. this forms a 3D picture.

Question 8

x-rays

Answer 8

are absorbed to different degrees by tissues of different densities - dense tissues absorb the most x-rays so the photographic film would be minimally exposed.

Question 9

CT machinery

Answer 9

CT is composed of radiation of a source of x-rays, and a detector separated 180 degrees from the sources. X-ray images of very thin slices are integrated with a computer to form an image

Question 10

CT hierarchy

Answer 10

Air (darkest=least dense) < fat < CSF < white matter < grey matter < blood from haemorrhage < bone (brightest=most dense).

Question 11

advantages of CT

Answer 11

good for showing acute bleeding or fracture of the skull
relatively quick
cheap
less intimidating for people

Question 12

disadvantages of CT

Answer 12

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

Question 13

Positron Emission Tomography (PET) method

Answer 13

radiation is emitted from a radioisotope injected intravenously is registered by external detectors. positrons from isotopes travel short distances, combine with electrons, and annihilation results in energy release picked up by the detector.

Question 14

what can PET be used for?

Answer 14

to highlight areas of increased metabolism of glucose

Question 15

advantages of PET

Answer 15

functional

can identify and characterise tumors and benign/melignant

Question 16

disadvantages of PET

Answer 16

poor resolution of brain tissue
area localized is only approximate
requires radiation dose

Question 17

four general principles of MRI

Answer 17

1. magnetic field aligns hydrogen atoms
2. radiofrequency pulse is applied and moves the hydrogen atoms out of alignment
3. measure the time it takes for the hydrogen atoms to recover their alignment and spin after the pulse is turned off
4. the recovery times are mapped to form an anatomical image.

Question 18

what is the idea behind MRI?

Answer 18

hydrogen atoms in different tissues take different amounts of time to recover

Question 19

MRI tissue hierarchy

Answer 19

Fat (fastest recovery=brightest) → white matter → grey matter → CSF (slowest recovery=darkest)

Question 20

units of MRI images

Answer 20

voxel - volume pixel

Question 21

how do CT and MRI compare when it comes to scanning method?

Answer 21

CT - quick and less scary

MRI - takes much longer, confining/noisy

Question 22

how do CT and MRI compare when it comes to quality?

Answer 22

CT - inferior for brain detail

MRI - superior for brain detail

Question 23

how do CT and MRI compare when it comes to bone and blood?

Answer 23

CT - preferable for rapid assessment if bleeding; good for identifying skull fractures
MRI - inferior

Question 24

T1 MRI

Answer 24

recovery time for the magnetic vector of the hydrogen atoms to return to resting alignment after the radiofrequency pulse

Question 25

what is T1 useful for?

Answer 25

highlighting fat in the brain

Question 26

T2 MRI

Answer 26

recovery time for the axial spin of the hydrogen atoms to return to the resting state after the radiofrequency pulse - can produce almost opposite effects to T1

Question 27

what is T2 useful for?

Answer 27

investigate water in the brain

Question 28

T2-flair

Answer 28

free-flowing fluid (CSF) is dark while non-free-flowing fluid is bright

Question 29

what does flair stand for?

Answer 29

fluid attenuation inversion recovery

Question 30

what is T2-flair used for?

Answer 30

distinguish between CSF and edema fluid

Question 31

Water is bright in what type of scan?

Answer 31

T2 MRI

Question 32

diffusion MRI

Answer 32

local magnetic fields applied to the head at different angles. high vision atoms move in different directions, visualizing the movement of water along tracts

Question 33

anisotropy

Answer 33

the degree to which hydrogen ions travel along white fibre bundles

Question 34

cohesiveness or integrity are used to measure...

Answer 34

white fibre bundles

Question 35

isotropic

Answer 35

when hydrogen atoms are not constrained, anisotropy = 0

Question 36

anisotropic

Answer 36

when hydrogen atoms are constrained, anisotropy = 1

Question 37

fractional anisotropy

Answer 37

has a range between 0 and 1. | it is the practical assessment of the degree of white matter integrity

Question 38

diffusion tractography

Answer 38

the 3D representation of fractional anisotropy: build and identify white matter tracts based on the different directionality FA.

Question 39

what is diffusion tractography useful for?

Answer 39

visualizing the difference between long and short projection fibers, as well as long and short association fibers

Question 40

Functional MRI

Answer 40

T2*-weighted scan. the adjusted scan parameters are sensitive to deoxygenated hemoglobin. rapidly repeated scans measure BOLD signals. regions where there is increased blood flow and reduced conc of dHb are the active regions.

Question 41

BOLD

Answer 41

blood oxygen level-dependent

Question 42

task-functional MRI

Answer 42

when participants perform a task while in the scanner

Question 43

resting-functional MRI

Answer 43

when participants rest in the scanner without thinking about anything for 10 mins

Question 44

diffusion tensor imaging

Answer 44

maps the functional anisotropy of a fibre bundle.

Question 45

when during the lifetime does FA increase?

Answer 45

during adolescence

Question 46

the smaller the FA...

Answer 46

the less organized the white matter

Question 47

advantages of MRI

Answer 47

Detailed anatomical structure Detect pathology with anatomical precision Measure white matter integrity Ability to assess brain function and functional connectivity at rest and during tasks Does Not involve radiation, is relatively safe and individuals can be repeatedly scanned

Question 48

Advantages of MRI compared with CT

Answer 48

CT is anatomically poor contrast, cannot measure white matter integrity, cannot give a functional measure

Question 49

Advantages of MRI compared with PET

Answer 49

PET is anatomically poor, less available; MRI does not need a radioactive tracer injected

Question 50

Disadvantages of MRI

Answer 50

Susceptibility to magnetic interference - can result in poor signal quality and can be a patient safety issue Requires significant technical expertise due to the physics, computation and statistical processing Diffusion and functional imaging are approximate, but are not a direct measure of white matter/ functional brain activity

Question 51

Disadvantages of MRI compared with CT

Answer 51

cannot visualise bone or acute tissue bleeding; relatively expensive, longer procedure, can be frightening due to confinement

Question 52

Disadvantages of MRI compared with PET

Answer 52

much more difficult to accurately quantify metabolic or molecular processes