MRI of intracerebral Haemorrhage and Stroke Flashcards

Question

MRI in Ischaemic Stroke

Answer 1

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

Answer 2

``` • 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 ```

Answer 3

• 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*)

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

about 50% of infarct are visible on T2 FLAIR images | • About 24 hours vast majority are visible

Answer 8

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

Answer 9

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

Answer 10

Distance that the water molecules are diffusing

Answer 11

Tissue with mobile H20

Answer 12

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

Answer 13

Natural barriers to diffusion: cell membrane, white matter tracts

Answer 14

There is moderate restriction to diffusion

Answer 15

Retain all of that signal

Answer 16

* 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

Answer 17

• 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

Answer 18

Looks at the rate of fall of signal between diffusion gradients A measure of strong the diffusion gradients are

Answer 19

* 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

Answer 20

* Decline in signal between 2 diffusion gradients creates a slope * LOW ADC map – dark * High ADC map – steep diffusion gradient – bright

Answer 21

Bright DWI + Dark ADC

Answer 22

Bright DWI + Normal/bright ADC

Answer 23

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

Answer 24

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

Answer 25

1. Susceptibility 2. Proton-electron dipole-dipole interaction 3. Protein

Answer 26

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

Answer 27

• 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)

Answer 28

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