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ANAT242 > Neuroimaging techniques > Flashcards

Neuroimaging techniques Flashcards

1
Q

brain system

A

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

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2
Q

brain network

A

the structure of circuits that connect areas of neurons together

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3
Q

systems neuroscience

A

an analysis of how systems bring about change in behaviour

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4
Q

what neuroimaging method uses X-ray radiation

A

CT

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5
Q

what neuroimaging method uses radio waves?

A

MRI

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6
Q

what neuroimaging method uses radiolabelling?

A

PET

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7
Q

Computed tomography (CT)

A

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

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8
Q

x-rays

A

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.

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9
Q

CT machinery

A

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

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10
Q

CT hierarchy

A

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

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11
Q

advantages of CT

A

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

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12
Q

disadvantages of CT

A

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

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13
Q

Positron Emission Tomography (PET) method

A

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.

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14
Q

what can PET be used for?

A

to highlight areas of increased metabolism of glucose

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15
Q

advantages of PET

A

functional

can identify and characterise tumors and benign/melignant

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16
Q

disadvantages of PET

A

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

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17
Q

four general principles of MRI

A
  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.
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18
Q

what is the idea behind MRI?

A

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

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19
Q

MRI tissue hierarchy

A

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

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20
Q

units of MRI images

A

voxel - volume pixel

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21
Q

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

A

CT - quick and less scary

MRI - takes much longer, confining/noisy

22
Q

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

A

CT - inferior for brain detail

MRI - superior for brain detail

23
Q

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

A

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

24
Q

T1 MRI

A

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

25
Q

what is T1 useful for?

A

highlighting fat in the brain

26
Q

T2 MRI

A

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

27
Q

what is T2 useful for?

A

investigate water in the brain

28
Q

T2-flair

A

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

29
Q

what does flair stand for?

A

fluid attenuation inversion recovery

30
Q

what is T2-flair used for?

A

distinguish between CSF and edema fluid

31
Q

Water is bright in what type of scan?

A

T2 MRI

32
Q

diffusion MRI

A

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

33
Q

anisotropy

A

the degree to which hydrogen ions travel along white fibre bundles

34
Q

cohesiveness or integrity are used to measure…

A

white fibre bundles

35
Q

isotropic

A

when hydrogen atoms are not constrained, anisotropy = 0

36
Q

anisotropic

A

when hydrogen atoms are constrained, anisotropy = 1

37
Q

fractional anisotropy

A

has a range between 0 and 1.

it is the practical assessment of the degree of white matter integrity

38
Q

diffusion tractography

A

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

39
Q

what is diffusion tractography useful for?

A

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

40
Q

Functional MRI

A

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.

41
Q

BOLD

A

blood oxygen level-dependent

42
Q

task-functional MRI

A

when participants perform a task while in the scanner

43
Q

resting-functional MRI

A

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

44
Q

diffusion tensor imaging

A

maps the functional anisotropy of a fibre bundle.

45
Q

when during the lifetime does FA increase?

A

during adolescence

46
Q

the smaller the FA…

A

the less organized the white matter

47
Q

advantages of MRI

A

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

48
Q

Advantages of MRI compared with CT

A

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

49
Q

Advantages of MRI compared with PET

A

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

50
Q

Disadvantages of MRI

A

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

51
Q

Disadvantages of MRI compared with CT

A

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

52
Q

Disadvantages of MRI compared with PET

A

much more difficult to accurately quantify metabolic or molecular processes

ANAT242 (17 decks)

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