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Neuro > Structural and Functional Neuroimaging > Flashcards

Structural and Functional Neuroimaging Flashcards

1
Q

How do x rays work?

A

You have X rays shot at person and then a plate that absorbs them on the other side
Image depends on X ray absorbance (bone absorbs well, air doesn’t)

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2
Q

pros of x rays?

A

Finding skull fractures

Shows you obvious things

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3
Q

cons of x rays?

A

Hard to interpret for non radiologists

No details

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4
Q

How does CT work?

A

Similar to X ray but this time you have multiple X ray sources (cover 180 degrees) and detectors on the other side
Computer puts this data into meaningful form

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5
Q

What are the units for x rays/CT?

A

Hounsfield units

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6
Q

How many hounsfield units in water?

A

0

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7
Q

What does an acute haemorrhage look like on CT?

A

Bright

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8
Q

how does bone look on CT and how many hounsfield units is it?

A

White - +1000

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9
Q

How does air look in CT scans and how many hounsfield units is it?

A

black - -1000

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10
Q

name different tissues in order of black to white on CT

A

Air –> Fat –> CSF –> White matter –> grey matter –> acute haemorrhage –> bone

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11
Q

what is IV contrast used for in CT?

A

to manipulate absorbance in vascular tissues (shows up as white)

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12
Q

what colour is white matter on CT?

A

Dark!

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13
Q

name the planes you can use in brain imaging

A

axial
coronal
saggital

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14
Q

how can CT be used to diagnose brain tumours?

A

if you inject contrast it will leak through the BBB at the site of the tumour and make that bit white

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15
Q

How can CT be used to diagnose ischaemic stroke?

A

subacute: not as visible

more mature infarct: darker than surrounding tissue

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16
Q

How can CT be used to diagnose haemmorhage in the brain?

A

Over time the blood loses ability to absorb X rays so it gets darker (at first a bit white –> not visible –> dark)
might also see brain distortion due to pressure from the blood

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17
Q

why is it important to know if a stroke is ischaemic or haemorrhagic?

A

It would be very bad to give a patient with haemorrhagic stroke a usual blood thinner given to the ischaemic type - that’s why we give CT scans before treating

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18
Q

what is an aneurysm?

A

one blood vessel gets thin and bursts

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19
Q

how do subarachnoid haemorrhages look in CT scans and how do they present?

A

Can see bright white usually in sylvian fissure

present with:
sudden onset
excruciating pain
may be after head trauma

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20
Q

what is important in a subarachnoid haemorrhage?

A

find where bleeding is from and stop that

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21
Q

What do we use to localise a brain aneurysm?

A

CT angiography w. contrast

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22
Q

how do you treat an aneurysm?

A

put in titanium coils to fix it before it bursts

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23
Q

what percentage of body mass does hydrogen account for?

A

9.5%

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24
Q

what aspect of hydrogen do MRIs use to crease images?

A

Much of hydrogen is in its ionic state (H+ )
Protons have not only positive charge but magnetic spin
MRI uses this magnetic spin to create images

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25
Q

how does an MRI work?

A
  1. MRI is a big magnet and aligns all the protons in one direction with a magnetic field
  2. Puts a radio frequency pulse to align them in a different direction
  3. The radio frequency pulse is stopped
  4. The time taken for the protons to realign to the magnetic field is seen
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26
Q

what are the different types of MRI sequences and how do they differ?

A

T1:
bright: subacute blood, fat
Dark: solid mass, cyst
grey: acute, chornic blood

T2:

bright: fluid, solid mass, cyst, subacute bood
dark: white matter, fat, acute/chronic blood

FLAIR: similar to T2 but spinal fluid and cysts are dark and fat is bright

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27
Q

what are different uses of the different MRI sequences?

A

T1: good for structural scan, for e.g. dementia
T2: very good for white matter disease (MS, strokes)
FLAIR helps differentiate (bright if tumour, dark if cyst)

28
Q

What is the MRI contrast agent and how does it work?

A

Gadolinium is an MR contrast agent that causes protons to relax more quickly providing better tissue contrast for vascular tissues.

29
Q

compare CT to MRI clinically - give examples

A

MRI has much more detail:

when looking at tumours you can see details and oedema

CT scans are bad at looking at posterior fossa strokes bc lots of bones are there

MS: previously undiagnosed patients are diagnosed

Dementia: can differentiate between AD (medial temporal lobes/hippocampus) and sematic dementia (left temporal lobe)

30
Q

compare CT and MRI generally

A

Brain: MRI has better resolution

Bone: CT is more detailed

Effects on body: CT causes irradiation and MRI only has issues with some metallic and plastic implants

cost: MRI is slightly more expensive (468 vs 372 pounds) - probably due to time taken

Time taken: MRI lasts 20-30 min while CT is 5 min

31
Q

why is it a benefit to use CT in emergencies?

A

You don’t want something to be really slow (MRI) if you are checking for e.g. a brain bleed so that’s when you use CT despite loss of detail

32
Q

define functional imaging

A

An imaging technique detecting changes in metabolism, blood flow, regional chemical composition and absorption

33
Q

list functional imaging techniques

A

Positron emission tomography (PET)
Functional magnetic resonance imaging (fMRI)
Multichannel electroencephalography (EEG)
Single-photon emission computed tomography (SPECT)
Magnetoencephalography (MEG)
Near infrared spectroscopic imaging

34
Q

when can most neurological diseases definitively be diagnosed?

A

post-mortem

35
Q

what can be problems with neurological diagnosis in practice?

A

Clinical overlap between diseases
Early disease may be hard: Do they have dementia or just bad memory cuz they are old?
If side effects of treatment are not insignificant

36
Q

what are the most common neurodegenerative diseases (in order of prevalence)?

A

AD and PD

37
Q

what percentage of those over 60 are affected by PD?

A

1-2% of those older than 60

38
Q

what are the hallmarks of PD?

A

Tremor
Rigidity
Akinesia
Postural instability

39
Q

what is the pathology of PD?

A

Dopaminergic SN neurons are gone

Find lewy bodies

40
Q

what does SPECT stand for?

A

single-photon emission computed tomography

41
Q

how does SPECT work?

A

Delivery of a gamma emitting radioisotope (usually intravenous administration)
Binds to a ligand forming a radioligand
Gamma camera acquires multiple 2-D images
Tomographic reconstruction by computer

42
Q

Give an example of SPECT use

A

Ioflupane:

DaTSCAN binds selectively to striatal dopamine transporters (biomarkers)

43
Q

what can ioflupane be used to diagnose?

A

PD and lewy body dementia both show reduced DAT recording intensity

44
Q

what is the prevalence of AD in those over 60 and 80?

A

1% aged 60

20% aged 80

45
Q

what is typical of AD?

A

Early episodic memory impairment followed by global cognitive decline

46
Q

explain what goes wrong with amyloid precursor protein in AD

A

normally alpha secretase cuts it through the transmembrane portion.

But in AD ppl have beta and gamma secretase which cleave non transmembrane bits, making peptides and oligomers –> aggregate

47
Q

what is the life course of someone with AD?

A

AD brain changes show decades before symptoms

before 60 start with small memory problems (also found in normal aging)

After 60 start worse memory decline

after 70 cognitive decline accelerates after diagnosis

48
Q

What is PET imaging?

A

Positron emission tomography
Similar to SPECT
Uses positron emitting radioisotope

49
Q

how is PET compared to SPECT?

A

Better contrast and spatial resolution

50
Q

Give an example of PET tracer

A

Amyloid PET tracer: a quantitative in vivo measure of insoluble cortical amyloid beta load (neuritic plaques, diffuse plaques, amyloid angiopathy)

51
Q

what are the different types of amyloid PET tracers and how do they differ?

A

Pittsburgh compound B (11C-PiB - half life 20mins)

18F-labelled tracers (half life – 110mins)

52
Q

name some 18F-labelled tracers

A

Florbetapir
florbetapen
flutemetamol

53
Q

give examples of amyloid PET tracer use

A

Florbetapir study: patients with memory problems that remained normal had Aß negative scans)

Study on people with AD gene mutation (with familial AD, the date of onset is about the same). There is a sense that up to 20 yrs before onset you can see amyloid build up in the brain (future screening?)

54
Q

what is the third leading cause of death in western countries?

A

Acute stroke

55
Q

what percentage of stroke is ischaemic?

A

80%

56
Q

what is hyperacute ischaemic stroke?

A

Arterial occlusion leads to a core of brain tissue death

57
Q

what do you want to do in stroke treatment

A

Surrounding this is hypoperfused, viable, potentially salvageable brain tissue – the penumbra (you have to try to save this by allowing blood throught the vessels again)

58
Q

how do you fix the perfusion problem in ischaemic stroke?

A

intravenous tissue plasminogen activator (tPA) to aid clot dissolution

recanalisation of vessels

59
Q

what is useful in imaging acute ischaemic stroke and why?

A

Diffusion weighted MRI because it detects ischaemic changes of stroke in minutes

or apparent diffusion coefficient imaging (a kind of diffusion weighted imaging)

60
Q

how does diffusion weighted MRI work?

A

Healthy neuronal cells allow water to move between cells
Cytotoxic intracellular injury causes intracellular accumulation of water - ‘restricted diffusion’

MR diffusion assesses the difference in water content and diffusion between injured and healthy cells (amount of water moving in direction we would expected to vs accumulation)

61
Q

what is apparent diffusion coefficient (ADC) imaging?

A

Over time ischemic area in ADC goes from black to white (in patients who had previous strokes, you see a few bright white spots so you wanna make sure you are looking at fresh strokes)

In normal diffusion-weighted imaging, all the stroke spots look white (not just the old ones)

62
Q

what is diffusion tensor imaging?

A

MRI useful when structure allows water to diffuse more easily in a particular plane – e.g axons

63
Q

how does diffusion tensor imaging compare to diffusion weighted imaging?

A

DWI provides an ‘average diffusivity’

DTI is a more extended technique to determine the ‘diffusion tensor’. From the diffusion tensor we can make inferences in white matter connectivity

64
Q

give an example of a case study with diffusion tensor imaging

A

Tractography: Tried to look for the visual pathways in an epilepsy patient - initially showed that although the seizures develop away from vision but DTI showed it spreads into visual area

patient was asked if she wanted a less extensive or more brain surgery, including area of visual pathway

Patient decided to go for more extensive surgery to improve chances of curing epilepsy

This patient had left hemianopia ( but no further seizures) - couldn’t see anything on left side with either eye after surgery

65
Q

how does fMRI work?

A

Increased neuronal activity leads to increased blood flow

Haemoglobin is diamagnetic when oxygenated and paramagnetic when deoxygenated

This difference results in small detectable changes in the MR signal of blood

Blood oxygenation level dependent (BOLD) imaging is the basis of fMRI

When you do a task, blood flow to that part of the brain increases

66
Q

give an example of when you might use fMRI

A

patient has left hippocampal sclerosis after seizures

we don’t want to damage the language centres (especially if they are adults with low plasticity)

fMRI scans show if you do surgery what the chances are that you would damage language

Neuro (23 decks)

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