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C2 Modules CLINICAL > MRI of intracerebral Haemorrhage and Stroke > Flashcards

MRI of intracerebral Haemorrhage and Stroke Flashcards

1
Q

What are the appearances of haematomas on MRI principally down to?

A

Signal generated by the haemoglobin

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2
Q

What happens clot first forms?

A

Contained within intact red cell membrane and is bound to haemoglobin

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3
Q

What happens within 3 days of haemoglobin?

A

metabollic processes within RBC and enzyme cascade starts to deteriorate - the haemoglobin becomes oxidised to Met

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4
Q

Where does the advanced blood products occur?

A

Around periphery of the clot

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5
Q

What is found at the centre of the clot?

A

Blood products closest to oxygenated haemoglobin

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6
Q

What is the clot?

A
  1. Highly proteinous

2. Proteins is very effective at stopping X-rays

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7
Q

What are the signal of T2-w and T1-w for Oxy-Hb?

A
  1. T2-w: hyper

2. T1-w: Iso (hyper cf, H2)

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8
Q

What are the signal of T2-w and T1-w for Deoxy-Hb?

A
  1. T2-w: Hypo

2. T1-w: Iso

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9
Q

What are the signal of T2-w and T1-w for Met-Hb?

A
  1. T2-w: Hypo

2. T1-w: Hyper

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10
Q

What are the signal of T2-w and T1-w for Met-Hb (extracellular)?

A
  1. T2-w: Hyper

2. T1-w: Hyper

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11
Q

What are the signal of T2-w and T1-w for Haemoglobin?

A
  1. T2-w: Hypo

2. T1-w: Hypo

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12
Q

What happens as proteins get degraded?

A

clot shrinks and the attenuation values drop and so the clot becomes progressively less bright

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13
Q

Why does Tw-1 appear hyperintense to water and iso-intense to brain parenchyma?

A

Protein content within brain

Causes T1 shortening effects

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14
Q

What does Met-hb have?

A

Lots of free electrons and porphyrin ring which contains iron

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15
Q

What happens when there is signal loss?

A

images look hyperintense

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16
Q

What is the characteristic of T2*?

A

Centre of the clot is high but the periphery of clot is very low

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17
Q

When does T2* sequence become very dark?

A

Anything that can cause a susceptible artefact

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18
Q

What is FLAIR at its heart?

A

Its for parenchymal tissue contrast
T2-weighted
It’s a T2 but the bulk fluid has been suppressed

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19
Q

Why does T2* appear very dark?

A

Susceptibility signal loss has been amplified on the gradient echo

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20
Q

What is the first blood-sensitive sequence?

A

Gradient echo

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21
Q

What doesnt have a refocusing pulse?

A

T2w gradient echo

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22
Q

What is the most useful for acute syndrome?

A

CT

23
Q

What is susceptibility weighted imaging?

A

MRI sequence that is particularly sensitive to compounds which distort the local magnetic field and as such make it useful in detecting blood products, calcium

24
Q

What are the characteristics of SWI?

A
  • Enhances not only the presence of susceptibility weighted signal loss but also phase changes caused by these little field in homogeneities
  • Gradient echo amplified
  • Much more sensitive presence of hemisydrin
25
Q

MRI in Ischaemic Stroke

A 
•	Hyperacute
•	Acute
–	Stroke workup
–	Defining final infarct
•	Longer term
–	Monitoring eg. Sickle cell, moya moya
–	Treatment planning eg. Revascularisation, endovascular R
26
Q

Hyperacute stroke

A 
•	Conventional structural MR
–	Changes of ischaemia
–	Identifying haemorrhage
•	Diffusion
–	Core infarct
–	Discrimination of new lesions from old
•	Perfusion
–	Ischaemic penumbra
•	MRA and vascular sequences
–	Vascular stenoses, occlusions and dissections
27
Q

What are the strucutal sequences?

A

• T2-weighted
- Using longer TE and TR times
- The contrast and brightness are predominantly determined by T2 properties of tissue
• T1-weighted
- Short TE and TR times
- The contrast and brightness are predominantly determined by T1 properties of tissue
• Flair (fluid-attenuated inversion recovery)
• Gradient echo (T2*)

28
Q

What are the standard T2 and T1 weighted images sequences depend on?

A

shifts in water content in order to create a contrast between normal parenchyma and infarcted tissue

29
Q

T2 weighted

A

most sensitive and tends to start to become abnormal 4 and ½ hours after onset of ischaemic

30
Q

4 and 1/2 hours

A

onset of vasogenic edema and BBB breaks down – infarct, water goes into the infarcted tissue

31
Q

At 4 and 1/2 hours

A

about 50% of infarct are visible on T2 FLAIR images

• About 24 hours vast majority are visible

32
Q

What is Diffusion-weighted imaging?

A
  1. Highly cellular tissues or those with cellular swelling exhibit lower diffusion coefficients
  2. Measure of diffusivity of water through tissue
  3. T2 weighted sequence
33
Q

What does DWI determine?

A

How far the water molecules within the voxel has moved between 2 diffusion gradients

if moved a long way: the voxel will lose a lot of potential signal

34
Q

What is the amount of signal that the voxel is losing proportional to?

A

Distance that the water molecules are diffusing

35
Q

What loses signal?

A

Tissue with mobile H20

36
Q

What is restricted diffusion?

A

Bright • No diffusion  no signal loss  Bright
• Some diffusion  some signal loss  Intermediate
• Diffusion  signal loss  dark

37
Q

What do normal tissues have?

A

Natural barriers to diffusion: cell membrane, white matter tracts

38
Q

What happens within normal tissue?

A

There is moderate restriction to diffusion

39
Q

What will normal tissue on DWI image look like?

A

Grey

40
Q

What happens if water molecules dont move anymore?

A

Retain all of that signal

41
Q

Cytotoxic edema

A
  • Oxygen dependent processes fail, and membrane pump fails, and the cells swells
  • The interstitial spaces around them are phased
  • Water molecules and tissues like to diffuse between cells
  • As swelling occurs, the water molecules diffusivity becomes restricted – sits where there are
42
Q

Pitfall for T2 shine through

A

• Final signal on DWI trace dependent on:
- Diffusivity of water
- T2 character of tissue
• High T2  persistent high signal  ‘shine through’
• Most pathology has high T2- problem
• Apparent Diffusion Coefficient – ADC map
- an MRI image that more specifically shows diffusion than conventional DWI, by eliminating the T2 weighting that is otherwise inherent to conventional DW
- Measure of diffusivity only
- Restricted diffusion dark
• Bright DWI + Dark ADC = Restricted diffusion
• Bright DWI + Normal/bright ADC = T2 shine through

43
Q

What is the B value?

A

Looks at the rate of fall of signal between diffusion gradients

A measure of strong the diffusion gradients are

44
Q

B value

A
  • B0 – the first image we acquire which is effectively a low resolution T2 map – there is no diffusion gradient applied
  • B1000 – the standard image that is produced when 2 diffusion gradients have been applied
45
Q

What is the slope which is depicted with the ADC map?

A
  • Decline in signal between 2 diffusion gradients creates a slope
  • LOW ADC map – dark
  • High ADC map – steep diffusion gradient – bright
46
Q

What is restricted diffusion?

A

Bright DWI + Dark ADC

47
Q

What is T2 shine through?

A

Bright DWI + Normal/bright ADC

48
Q

What is MR perfusion a measure of?

A

– MTT- mean transit time
– rCBV- relative cerebral blood volume
– rCBF- relative cerebral blood flow

49
Q

MRA

A 
•	Stroke workup
–	Intracranial occlusion/ stenosis
–	Extracranial circulation
•	Carotid bifurcation stenosis
•	Vertebral origin stenosis
–	Dissection- fat sat axial sequences
50
Q

Impact on MR signal

A
  1. Susceptibility
  2. Proton-electron dipole-dipole interaction
  3. Protein
51
Q

Susceptibility

A 
•	Para-/ superparamagnetic molecules
•	Compartmentalised
–	Local field inhomogeneities
–	Spin dephasing ® signal loss
•	Principally ¯T2	(¯signal T2-w)
•	++ on gradient echo sequences
52
Q

Proton-electron dipole-dipole

A

• H2O protons close to Fe2+/ Fe3+
– Spin down ® spin up (¯T1) [spin-lattice relaxation]
• Principally ¯T1 (¬signal T1-w)
• Only in Hb where Fe accessible (in plane)

53
Q

Proteins

A
  • Large macromolecules
  • Precess close to lamor Hz of H2O protons
  • Spin down ® spin up (¯T1)
  • Principally ¯T1 (¬signal T1-w)

C2 Modules CLINICAL (26 decks)

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