2.
An ischaemic stroke results from a sudden
cessation of adequate amounts of blood
reaching parts of the brain.
The vascular territory affected will determine
exact symptoms and clinical behavior of the
lesion.
4. Goals of Acute Stroke Imaging
Four Ps
1.
Parenchyma: Assess early signs of acute stroke,
rule
out hemorrhage
2.
Pipes:
Assess extracranial circulation and
intracranial circulation for evidence
of
intravascular thrombus
3.
Perfusion:
Assess cerebral blood volume,
cerebral
blood flow, and
mean transit time
4.
Penumbra:
Assess tissue at risk of dying if
ischemia
continues without
recanalization of
intravascular
thrombus
5. Unenhanced CT
Role:
1. Rule out hemorrhage
2. Identification of parenchymal involvement in
acute stroke.
3. Quantification (prognostic and therapeutic
value)
Sensitivity of CT to diagnose stroke is 64%
and the specificity is 85%.
9. Early (1-3 hours) (Hyperacute
phase)
1. cortical hypodensity with associated
parenchymal swelling with resultant gyral
effacement:
due to cytotoxic edema developing as a
result of failure of the ion-pumps.
highly specific for irreversible ischemic brain
damage if it is detected within first 6 hours.
Has prognostic value.
11. Early (1-3 hours) (Hyperacute
phase)
2. Loss of grey-white matter differentiation, and
hypoattenuation of deep nuclei:
Obscuration of the lentiform nucleus:
Blurred basal ganglia sign.
changes seen as early as 1 hour after
occlusion.
13. Insular Ribbon sign:
Hypodensity and swelling of the insular cortex.
Early sign of infarction in the territory of the
middle cerebral artery.
This region is very sensitive to ischemia
because it has poor collateral supply
16. First week
With time the hypo-attenuation and swelling
become more marked resulting in significant
mass effect.
This is a major cause of secondary damage in
large infarcts.
18. Second to third week
As time goes on the swelling starts to subside and
small amounts of cortical petechial haemorrhages
results in elevation of the attenuation of the cortex.
19. CT fogging phenomenon:
Seen on non contrast CT
Represents a transient phase of the evolution
of cerebral infarct where the region of cortical
infarction regains a near normal appearance.
Imaging a stroke at this time can be
misleading as the affected cortex will appear
near normal.
A similar phenomenon is also seen on T2
weighted sequences on MRI of the brain.
20. NECT of the brain demonstrates a low density region within the
left frontal lobe involving both white matter and overlying grey
matter which is indistinct. The basal ganglia are spared. There
is only minor positive mass effect.
21. Single slice at the same level, obtained 7 days later,
demonstrates essentially normal appearing brain.
22. Months:
The residual swelling passes, and gliosis sets
in eventually appearing as a region of low
density with negative mass effect.
Cortical mineralisation can also sometimes be
seen appearing hyperdense.
26. Lacunar infarcts
are small deep infarcts in the distal distribution
of penetrating vessels
(lenticulostriate, thalamoperforating, pontine
perforating arteries).
Result from occlusion of small penetrating end
arteries at the base of the brain and are due to
fibrinoid degeneration.
27. CT:
small discrete foci of hypodensity
3 - 15 mm in diameter, most commonly 10mm
may enhance in the late acute or early
subacute stage
higher signal intensity than CSF (marginal
gliosis)
29. Quantitation of Ischemic
Involvement
1. The Alberta
Stroke Program
Early CT
Score(ASPECTS):
The MCA territory is
divided into 10 regions,
each of which
accounts for one point
in the total score.
The normal MCA
territory - 10
For each area involved
in stroke on the NECT
images, one point is
deducted from that
score.
2. One-thirdMCA
30. CT Angiography
Demonstration of a significant thrombus
burden
Identification of carotid artery disease and
visualization of the aortic arch may provide
clues to the cause of the ischemic event
Prognosis
Guidance for the interventions
31. Unenhanced CT image in a 72-year-old woman with acute right hemiplegia
shows hyperattenuation in a proximal segment of the left MCA
33. Penumbra
Acute cerebral
ischemia may result in
a central irreversibly
infarcted tissue core
surrounded by a
peripheral region of
stunned cells that is
called a Penumbra.
This region is
potentially salvageable
with early
34. CT Perfusion Imaging
CT perfusion imaging also allows quantitative
and qualitative evaluation of the cerebral blood
volume, cerebral blood flow, mean transit time
and Time to Peak.
Central
volume principle {CBF = CBV/MTT}
Cerebral
blood volume:
Cerebral blood flow:
4 –5 mL/100 g
50 – 60 mL/100 g/min
A penumbra is evidenced by a discrepancy in
perfusion parameters.
35.
There is a linear relationship between contrast
agent concentration and attenuation, with the
contrast agent causing a transient increase in
attenuation proportional to the amount of
contrast agent in a given region.
36. 1.
2.
3.
4.
Performed on a helical CT scanner after the
acquisition of unenhanced CT images.
Depending on the CT detector configuration, two
to four sections, each with a thickness of
5, 6, 8, 10, or 12 mm, may be obtained, with at
least one of the axial sections passes through
the level of the basal ganglia.
Monitoring the first pass of an iodinated contrast
agent bolus through the cerebral vasculature.
CT Perfusion Data Postprocessing
37. CT Perfusion Data
Postprocessing
1.
2.
3.
Freehand or
automated
placement of an
ROI over an input
artery
Freehand or
automated
placement of an
ROI over an input
Generation of the
arterial and venous
time-attenuation
38. CT Perfusion Data
Postprocessing
4.
Deconvolution analysis of arterial and tissue
time attenuation curves to obtain the mean
transit
time
5.
Calculation of cerebral blood volume from the
area under the curve in a parenchymal pixel
divided by the area under the curve in an
arterial
pixel
6.
Calculation of cerebral blood flow by using the
central volume principle (CBF=CBV/MTT)
39. The clinical application of CT perfusion imaging
in acute stroke is based
Penumbra
increased MTT with
moderately decreased CBF
(>60%) and normal or
increased CBV (80%-100%
or higher) secondary to
autoregulatory
mechanisms.
increased MTT with
markedly reduced CBF
(>30%) and moderately
reduced CBF (>60%)
Infarct
Infarcted tissue shows
severely decreased CBF
(<30%) and CBV (<40%)
with increased MTT
44. References:
1.
2.
3.
Non-Hemorrhagic stroke; Textbook of
Radiology and Imaging-David Sutton-volume02
Ashok Srinivasan, MD et al; State-of-the-Art
Imaging of Acute Stroke; Radiographics
Ischemic stroke; Radiopaedia
Editor's Notes
diagnosis is infarction, because of the location (vascular territory of the middle cerebral artery (MCA) and because of the involvement of gray and white matter, which is also very typical for infarction.
, because this level contains representative territories supplied by the anterior, middle, and posterior cerebral arteries
The arterial ROI is optimally selected in one unaffected vessel that is perpendicular to the acquisition plane, either one of the anterior cerebral arteries (ACAs) or the contralateral MCA.
