stroke imaging

Question 1

cerebral blood flow

Answer 1

rate of delivery of blood and nutrient to the tissue capillary bed, is the main parameter to measure cerebral perfusion

Question 2

cardiac stroke volume

Answer 2

70ml

Question 3

average heart frequency

Answer 3

70/min

Question 4

cardiac output

Answer 4

5L/min

Question 5

flow in the brain is expressed as

Answer 5

mL/min/100g

Question 6

normal cerebral blood flow

Answer 6

50mL/min/100g

Question 7

gray matter blood flow

Answer 7

60-100 mL/min/100g

Question 8

white matter blood flow

Answer 8

30-45 mL/min/100g

Question 9

cerebral perfusion prressure

Answer 9

the difference between the mean arterial pressure (MAP) and the intracranial pressure (ICP)
MAP-ICP = CPP

Question 10

normal CPP

Answer 10

50-150 mm Hg

Question 11

if CPP is too low

Answer 11

the brain becomes ischaemic

Question 12

if CPP is too high

Answer 12

the brain becomes hypereamic

Question 13

autoregulation

Answer 13

maintains blood flow to the brain

unlike other organs, the cerebral blood low in independant of arterial pressure (in normal range)

Question 14

what happens in an embolic infarct

Answer 14

the territoory perfused by this artery and areas with little or no collateral flow are subjected too extreme hypoxia and nectrotic cell death
in the penumbra, where there is some degree of collateral blood flow, a gradient of tissue perfusion establishes a threshold among nectrotic cell death (infarct core), apoptotic cell death (ischaemic penumbra), and tissue survival

Question 15

when oxydative phoosphorylation stops

Answer 15

membrane pump failure 
influx of Na and Ca
cytotxic oedema 
damage to endothelium 
vasogenic oedema (inundation of water - seen on CT, takes a few hours)

Question 16

4 goals of multimodal imaging in stoke

Answer 16

parenchyma - rule out haemorrhage
pipes (vessels) - assess extracranlial (carotid and vertebral) and intracranial circulation for evidence of intravascular thrombus
perfusion - assess cerebral blood volume, cerebral blood flow, mean transit time and capillary permeability
penumbra - assess tissue at risk of dying brain tissue if ischaemia continues without recanalisation of intravascular thrombus

Question 17

how to rule out intracranial heamorrhage

Answer 17

CT remains the gold standard to rule out intracranial haemorrhage
intracerebral or subarachnoid

spontaneous (non-traumatic) intracranial haemorrhage accounts for 15-20% of all acute stroke syndromes

Question 18

early signs of acute stroke

Answer 18

non-contrast CT is not very good in showing early signs of infarction
traditional CT signs or early infarction in the distribution territory of the middle cerebral artery
- hyperdense MCA sign - a hyperdense left middle cerebral artery
- obscuration of the lentiform nucleus
- insular ribbon sign - asssymetry between the grey matter

Question 19

limitations of CT in acute stroke

Answer 19

in most cases CT is normal within the first hours after onset of symptoms
therefore, in acute stroke, noncontrast CT is not reliable

Question 20

what about MRI in acute stroke

Answer 20

preferred techniquue, not available in western australia

Question 21

why dies diffusion restriction signal aucte stroke

Answer 21

in normal brain tissue there is free brownian motioon of water molecules
in cytootoxic oedema, swelling of cells with restricted movement of H2O molecules

Question 22

‘mismatch’ concept

Answer 22

relied on perfusion imaging to show the difference between infarct core and penumbra
predicts how the stroke will evolve

Question 23

CT perfusion test

Answer 23

IV bolus 40mL iodinated contrast

sequential time=points show contrast transversing the capillary bed at a fixed level

Question 24

can CT be used for easrly detection of ischaemic brain

Answer 24

no

Question 25

contrast agent used for CT

Answer 25

iodine

Question 26

contrast agent used for MR

Answer 26

gadolinium

Question 27

does CT involve radiation

Answer 27

yes

Question 28

does MR involve radiation

Answer 28

no

Question 29

to detect heamorrhage

Answer 29

NCCT remains frontline, MRI may be more sensitive

Question 30

to show vesssel ollcusion

Answer 30

CTA is the best method

Question 31

for identification of infarct core

Answer 31

diffusion MRI is the preferref technique

Question 32

for identification of the penumbra

Answer 32

perfussion imaging holds intellectual appeal, but the evidence remains insufficient