1. IMAGING IN STROKE
MODERATOR- DR C P AHIRWAR (MD)
PRESENTOR- DR NEELAM SONI

2. STROKE
 Stroke is an acute central nervous system injury with
abrupt onset.
 This can occur following ischemia caused by
blockage (thrombosis, arterial embolism) or a
hemorrhage of CNS or intracranial blood-vessels.
 Approximately 80% of all strokes are due to acute
ischemia .
 It is a leading cause of morbidity and mortality in the
developed world.

3.  GOALS OF IMAGING
 To establish the diagnosis as early as possible.
 Give accurate information about intracranial
vasculature and brain perfusion for guidance in
selecting the appropriate therapy.

4. Imaging should target assessment of
4 P’s:
• Parenchyma:
• Assess early signs of acute stroke, rule out hemorrhage
• Pipes
• Assess extracranial circulation (carotid and vertebral
arteries of the neck) and intracranial circulation for
evidence of intravascular thrombus
• Perfusion
• Assess cerebral blood volume, cerebral blood flow, and
mean transit time
• Penumbra
• Assess tissue at risk of dying if ischemia continues with
out re-canalization of intravascular thrombus

5. Overview of imaging modalities
 Unenhanced CT
• Can be performed quickly.
• Can help identify early signs of stroke, and can
help rule out hemorrhage.
 CT angiography can depict intravascular
thrombi
 CT perfusion imaging can demonstrate
salvageable tissue which is indicated by a
penumbra.

6.  Acute infarcts may be seen early on
conventional MR images, but diffusion-
weighted MR imaging is more sensitive for
detection of hyperacute ischemia.
 Gradient-echo MR sequences can be helpful
for detecting a hemorrhage.

7.  MR Angiography – To evaluate the status of
neck and intracranial vessels
 DWI AND PWI - A mismatch between findings
on diffusion and perfusion MR images may be
used to predict the presence of a penumbra.

8. PENUMBRA
 TISSUE AT RISK OR
SALVAGEABLE TISSUE.
 Pathophysiology -
 Neuronal tissue is sensitive
for ischemia due to lack of
stored energy
 With complete absence of
flow neuronal viability is 2-3
minutes
 In acute stroke ischemia is
always incomplete due to rich
collateral supply

9. ACUTE STROKE
 Acute cerebral ischemia may
result in a central irreversibly
infarcted tissue core
surrounded by a peripheral
region of stunned cells that is
called as a penumbra
 This region is potentially
salvageable with early
recanalization

10. The transition from ischemia to irreversible
infarction depends on both the severity and
the duration of the diminution of blood flow
Minutes
Days and weeksTime
Hours

11. ISCHEMIC PENUMBRA
 IDENTIFIED BY
 CT - ALTERED PARAMETERS IN PERFUSION
 MR – PERFUSION DIFFUSION MISMATCH
 PRESENCE OF PENUMBRA HAS SIGNIFICANT
IMPLICATIONS IN PT MANAGEMENT

12. CT
 KEY TECHNIQUES
 NECT
 CTA
 PERFUSION CT

13. NECT
 Widely available.
 Can be done quickly.
 It not only can help identify a hemorrhage (a
contraindication to thrombolytic therapy),
but it also can help detect early-stage acute ischemia by
depicting features such as –
1. THE HYPERDENSE VESSEL SIGN.
2. THE INSULAR RIBBON SIGN.
3. OBSCURATION OF THE LENTIFORM NUCLEUS

14. HYPERDENSE VESSEL SIGN
 Acute thrombus has high attenuation value
this feature is referred to as the hyperdense
vessel sign.
 Highly specific but sensitivity is poor.
 FALSE POSITIVE
 HIGH HEMATOGRIT LEVEL
 MCA CALCIFICATION
But in such cases the hyperattenuation is usually
bilateral!!!
 Rarely, fat emboli appear hypoattenuated when compared
with attenuation in the contralateral vessel .

15. HYPERDENSE MCA

16. OBSCURATION OF LENTIFORM NUCLEUS
 Lentiform nucleus appears hypoattenuated because
of acute ischemia of the lenticulostriate territory ,
resulting in obscuration of the lentiform nucleous.
 This feature may be seen on CT images within 2
hours after the onset of a stroke .

17. OBSCURATION OF LENTIFORM NUCLEOUS

18. INSULAR RIBBON SIGN
 It is the local hypoattenuation of the insular cortex
region due to Cytotoxic edema as this region is
susceptible to early and irreversible ischemic
damage.

19. INSULAR RIBBON
Axial unenhanced CT image,
obtained
in a 73-year-old woman 21⁄2 hours
after
the onset of left hemiparesis,
shows hypoattenuation
and obscuration of the posterior
part of the
right lentiform nucleus (white
arrow) and a loss
of gray matter–white matter
definition in the lateral
margins of the right insula (black
arrows).
The latter feature is known as the
insular ribbon
sign.

20. WINDOW SETTING
 Detection of early acute ischemic stroke on unenhanced
CT images may be improved by using variable window
width and center level settings to accentuate the contrast
between normal and edematous tissue
 STANDARD WINDOW SETTING (W80 C 20) – SENSITIVITY
57% SPECIFICITY 100%
 STROKE WINDOW SETTING (W8 C 32) SENSITIVITY 71%
SPECIFICITY 100%

21. CT
ANGIOGRAPHY
CT angiography typically involves a volumetric helical acquisition
that extends from the aortic arch to the circle of Willis.
 The examination is performed by using a time-optimized
bolus of contrast material for vessel enhancement.
 CT angiographic demonstration of a significant thrombus
burden can guide appropriate therapy in the form of
intraarterial or mechanical thrombolysis.
 Identification of carotid artery disease and visualization of the
aortic arch may provide clues to the cause of the ischemic
event and guidance for the interventional neuroradiologist

22. (a) Unenhanced CT image in a 72-year-old woman with acute right hemiplegia shows
hyperattenuation in a proximal segment of the left MCA (arrows).
(b, c) Axial (b) and coronal (c) reformatted images from CT angiography show the
apparent absence of the same vessel segment (arrows).

23. CTA

24. CT Perfusion
(CTP):
Basic concept…..
 With CT and MR-diffusion we can get a good impression of
the area that is infarcted.
 But, we cannot preclude a large ischemic penumbra (tissue at
risk).
 With perfusion studies we monitor the first pass of an
iodinated contrast agent bolus through the cerebral
vasculature.
 Areas of decreased perfusion will tell us which area is at risk.

25. CT perfusion maps of cerebral blood volume (a) and cerebral
blood flow (b) show, in the left hemisphere, a region of decreased
blood volume (white oval) that corresponds
to the ischemic core and a larger region of decreased blood flow
(black oval in b) that includes the ischemic core and a peripheral
region of salvageable tissue. The difference between the two
maps (black oval white oval) is the penumbra.

26. CT PERFUSION
 PARAMETERS ASSESSED
 CBV – VOLUME OF BLOOD PER UNIT OF BRAIN TISSUE
(N 4-5ML/100GM)
 CBF – VOLUME OF BLOOD FLOW PER UNIT OF BRAIN
TISSUE PER MINUTE (N 50-60ML/100GM/MINUTE)
 MTT – TIME DIFFERENCE BETWEEN THE ARTERIAL
INFLOW AND VENOUS OUTFLOW
 TIME TO PEAK ENHANCEMENT – TIME FROM THE
BEGINNING OF CONTRAST INJECTION TO MAXIMUM
CONTRAST CONCENTRATION IN A ROI

27. CTP TECHNIQUES
 DYNAMIC CONTRAST ENHANCED CT
 BASED ON MULTI COMPARTMENT TRACER KINETIC MODEL
 PERFORMED ON MDCT
 2-4 SECTIONS ARE OBTAINED AND ONE OF THE SECTIONS
PASS THROUGH BASAL GANGLIA
 PERFUSED-BLOOD-VOLUME MAPPING- LESS
COMMONLY USED

28. Dynamic Contrast Enhanced CT
 Performed by monitoring a first
pass of contrast bolus through
the cerebral circulation
 The transient increase in
attenuation generates time-
attenuation curves for an
arterial and venous ROI
 Mathematical modeling can be
then used to calculate perfusion
parameters and generate color
coded perfusion maps
(deconvolution analysis)

30. CBF = CBV / MTT
CBF
MTT
Normal CBF is 55 cc/ 100 gm tissue / minute
CBF below this refers to penumbra or tissue at risk

31. EFFECT OF REDUCTION IN CBF
Diagram shows the evolution of events at a microscopic level with decreasing
cerebral perfusion (from right to left). Irreversible cell death generally occurs when
cerebral blood flow decreases to less than 10 mL/100 g/min.

32. INTERPRETATION OF PCT
 INFARCTED AREA
 SEVERELY DECREASED CBF (<30%) AND CBV (<40%)
 PROLONGED MTT
 PENUMBRA
 INCREASED MTT
 MODERATELY DECREASED CBF (>60%)
 INCREASED CBV (80-100% OR HIGHER)
OR
 INCREASED MTT
 MARKEDLY REDUCED CBF (>30%)
 MODERATELY REDUCED CBV (>60%)

33. CT PERFUSION PROTOCOL

34. Acute stroke in a 65-year-old man with left hemiparesis. CT perfusion
maps of cerebral blood volume (a), cerebral blood flow (b), and mean
transit time (c) show mismatched abnormalities (arrows) that imply the
presence of a penumbra. The area with decreased blood volume
represents the ischemic core, and that with normal blood volume but
decreased blood flow and increased mean transit time is the penumbra.

36. CONVENTIONAL MRI
 SPIN ECHO IMAGES MORE SENSITIVE AND
SPECIFIC THAN CT IN ACUTE CVA
 SEQUENCES
 T1
 T2
 FLAIR
 GRE

37. ACUTE CVA
 HYPER ON T2 AND FLAIR
 LOSS OF GRAY WHITE MATTER
DIFFERENTIATION
 SULCAL EFFACEMENT
 MASS EFFECT
 LOSS OF FLOW VOID IN T2WI IN VESSEL
 BLOOMING IN GRE IF HRGE
 LESS SENSITIVE THAN DWI IN FIRST FEW
HOURS

38. Acute stroke in the left medial
temporal lobe in a 44-year-old man.
(a) Axial T2-weighted and (b)fluid attenuated
inversion recovery images
show areas with increased signal intensity.
(c) Gradient-echo image shows abnormal
low signal intensity in the same areas.
These findings are suggestive of hemorrhage

39. MR ANGIOGRAPHY
 Sensitive for intravascular thrombus.
 MR angiograms in two patients with acute stroke symptoms
reveal flow gaps in the left proximal middle cerebral artery
(arrow in a) and the basilar artery (arrows in b). Both findings
were due to intravascular thrombi.

40. Diffusion-Weighted Imaging
 Brownian motion
 The normal motion of
water molecules within
living tissues is random.
 Acute stroke causes
excess intracellular water
accumulation or
“cytotoxic edema”, with
an overall decreased rate
of water molecular
diffusion within the
affected tissue. Brownian Motion

41. DWI
 AREAS OF CYTOTOXIC EDEMA WITH
RESTRICTED WATER MOLECULE DIFFUSION IN
ACUTE STROKE APPEAR BRIGHTER COMPARED
TO NORMAL TISSUE
 TAKES FEW SECS TO 2 MINUTES

42. DWI ACUTE CVA
Acute stroke–induced
cytotoxic edema in the
right cerebellar
hemisphere. Diffusion-
weighted MR image
shows areas of signal
intensity increase due to
the restricted mobility
of water molecules

43. Acute stroke of the posterior circulation in a 77-year-old man. (a)
Diffusion weighted MR image shows bilateral areas of increased
signal intensity (arrows) in the thalami and occipital lobes. (b) ADC
map shows decreased ADC values in the same areas (arrows). These
findings are indicative of acute ischemia.

44. CLINICAL APP OF DWI
 CHANGES IN DWI OCCUR WITH IN 30MIN OF ONSET
OF ISCHEMIA WITH CORRESPONDING REDUCTION IN
ADC AND SEEN UP TO 5 DAYS
 MILD HYPERINTENSE DWI WITH PSEUDONORMAL
ADC FROM 1 -4WKS
 AFTER SEVERAL WKS DWI SIGNAL VARIES (T2
EFFECT) WITH INCREASED ADC
 DWI ALONE CANNOT BE USED AND SHOULD ALWAYS
BE COMPARED WITH ADC TO ASSESS THE AGE OF
INFARCT

45. CHRONIC INFARCT
Chronic infarcts in a 71-year-old man with a remote history of
multiple strokes. (a) Diffusion weighted MR image shows areas
of decreased signal intensity in the left frontal lobe. (b) ADC
map shows increased ADC values in the white matter of the right
frontal lobe. These features are suggestive of chronic infarction.

46. ACCURACY
 CT/ CONVENTIONAL MRI
 SENSITIVITY AND SPECIFICITY < 50%
 DWI
 SENSITIVITY 88-100%
 SPECIFICITY 86-100%
 FALSE -VE DWI
 LACUNAR INFARCTS OF BRAIN STEM
 SMALL DEEP GREY MATTER INFARCTS
 FALSE +VE DWI
 ABSCESS
 CELLULAR TUMOURS LIKE LYMPHOMA

47. MR PERFUSION
 The passage of an intravascular MR contrast agent
through the brain capillaries causes a transient loss
of signal because of the T2* effects of the contrast
agent.
 The dynamic contrast-enhanced MR perfusion
imaging technique involves tracking of the tissue
signal changes caused by susceptibility (T2*) effects
to create a hemodynamic time–signal intensity
curve,as in dynamic CT perfusion imaging.
 Perfusion maps of cerebral blood volume and mean
transit time can be calculated from this curve by
using a deconvolution technique.

48. MR PERFUSION
 LESION WHICH SHOWS CHANGES BOTH IN
DWI AND PERFUSION MR – INFARCT CORE
 LESION WHICH SHOWS CHANGES ONLY IN
PERFUSION - PENUMBRA

49. (a) Diffusion-
weighted MR image
shows an area of mildly increased
signal intensity in the right parietal
lobe (arrows). The ADC values
in this region were decreased.
(b) Perfusion-weighted MR
image shows a larger area with
increased time to peak
enhancement (arrows) in the right
cerebral hemisphere.
The mismatch
between the perfusion
and diffusion images is indicative
of a large penumbra.
Acute stroke in a 67-year-old woman with acute
left hemiplegia

50. CLINICAL APPLICATION
 Unenhanced CT: rule out hemorrhage
 Not very good to detect ischemia
 T1 or T2 weighted MRI
 Good for detecting ischemia
 Cannot differentiate between acute versus
chronic ischemia
 So we have…

51. Diffusion-weighted MR
 More sensitive for detection of hyperacute
ischemia
 becomes abnormal within 30 minutes
 Distinguish b/w old and new stroke
 New stroke: bright on DWI
 Old stroke: Low SI on DWI
 It detects irreversible infarcted tissue

52. MRI
OLD –VS- NEW
ISCHEMIC INFARCT
T1 T2 DIFFUSION

53. Perfusion-Weighted imaging
 Allows the measurement of capillary
perfusion of the brain
 Uses a MR contrast agent
 The contrast bolus passage causes a nonlinear
signal decrease in proportion to the perfusion
cerebral blood volume
 Meaning, it can identify areas of
hypoperfusion, the reversible ischemia, as
well (unlike DWI)

54. Comparison of PWI and DWI
 DWI  Depicts irreversibly damaged infarct
 PWI  Reflects the complete area of
hypoperfusion
 The volume difference between these two,
the PWI/DWI mismatch would be the
PENUMBRA!
 If there is no difference in PWI and DWI, no
penumbra is present

55. Significance of PWI/DWI mismatch
 IV thrombolytic treatment is not typically
administered to patients with acute stroke
beyond 3-hrs period
 Risk of hemorrhage
 However, recent studies have shown that IV
thrombolytic therapy may benefit patients
who are carefully selected according to
PWI/DWI mismatch, beyond 3-hrs window

56. CT VS MRI

58. ACUTE CVA IMAGING PROTOCOL

59. IV-TPA-WONDERFUL THERAPY.
 FDA-USA approved Rx of Ischemic Stroke.
 Improved outcome within 3 hours in properly
selected patients.
 Results are best within 90 minutes.
 Results are better within 90 -180 minutes.
TPA reverses ischemic changes saving brain.

60. Thrombolytic Therapy - IV -t-PA
I. Inclusion Criteria
1. Within 3 hours of the stroke and patient not needing
ventilator.
2. CT Scan head Normal or < 1/3 MCA hypo density.
II. Exclusion Criteria
1. BP > 185/110 mm on admission.
2. Use of Oral Anticoagulants.
3. Major surgery preceding FOURTEEN days.
4. Head injury - LAST THREE MONTHS.
5. Prior Intracranial hemorrhage/Recent GI bleed.
6. Prolonged PT / aPTT / INR / low Platelet count.

62. Intraarterial TPA.
 IA-TPA in selected pts. In < 6 hours due to MCA
& BA occlusion
 In BA occlusion it can be given even after > 12
hours.
In future IA-TPA will be rewarding.
IV &IA(IMS Trial) showed 56% of recanalisation.

65. CONCLUSION
 Current imaging techniques can be used
to identify hyperacute stroke and guide
therapy
 Both CT and MR imaging are useful for
the comprehensive evaluation of acute
stroke

66. THE FUTURE
 Selection of patients for thrombolytic therapy
may be made more effectively by performing
appropriate imaging studies rather than relying
on the time of onset as the sole determinant of
selection.
 New emerging technique MR permeability
image used to predict microvascular
permeability and quantification of BBB – Pts
with defective BBB are more prone for bleeding
complication following thrombolytic therapy.

67. QUIZ

68. CT Signs in Early MCA Ischemia
Hyperdense MCA Insular Ribbon Lentiform Nucleus

69. MCA Infarct
MCA

70. ACA Infarct

71. PCA Infarct
PCA

72. What do you see here? What do you
expect on CTA?

74.  Q. Imaging should target assessment of 4 P’s
??????

75. MRI in Stroke Intervention
“The 4 P’s”
Pipes  Perfusion  Parenchyma
MRA Perfusion MR Diffusion MR
“Penumbra”Rowley AJNR 22(4); 599-601, 2001

76. THANK YOU