2. Definition
A NEUROLOGICAL DEFICIT OF
ī§ Sudden onset
ī§ With focal rather than global dysfunction
ī§ In which, after adequate investigations,
symptoms are presumed to be of non-
traumatic vascular origin
ī§ and lasts for >24 hours
3. Functional loss of cell
Reduced blood flow
Autoregulation
CYTOTOXIC EDEMA,
CELL DEATH
Increased water content
VASOGENIC EDEMA
MASS EFFECT
GLIOSIS
MINUTES
12-24 hrs
24hrs-2wks
PATHOPHYSIOLOGY
4. Role of imaging in ischemic stroke
ī§ To rule out mimics esp hemorrhage
ī§ To suggest the therapeutic role
ī§ To establish the etiology
11. NCCT in acute stroke
ī§ OTHER EARLY SIGNS
Loss of grey white matter differentiation
Early mass effect-
Narrowing of sylvian fissure
Loss of cortical sulci
12. Hyperdense MCA sign
ī§ MCA occluded by fresh thrombus
ī§ -specificity- 100%, sensitivity -30%
ī§ Hyperdense MCA can also be seen
ONLY REVERSIBLE EARLY SIGN
īhigh hematocrit
level
ī calcification
in such cases â
usually bilateral
14. NCCT
ī§ Importance of window settings
Normal settings- w80 HU, C- 20HU
W- 8HU- C-32 HU SENSITIVITY
INCREASED
15. NCCT
ī§ Advantages
very useful to exclude hemorrhage
widely accessible
convenient
short imaging time
ī§ Disadvantages
findings are subtle
not useful for ischemic penumbra
Not useful for posterior fossa infarcts
16. Conventional MRI
ī§ Can image only vasogenic edema, necrosis
ī§ T1, T2 , FLAIR, GRE/susceptibility weighted
ī§ FLAIR- detection of infarctions in
periventricular and cortical regions,
brainstem
ī§ GRE/susceptibility weighted- for detection of
hemorrhage( IN INFARCTION)
17. Conventional MRI in acute
stroke
ī§ Hyperacute phase-
loss of grey white matter
differentiation,
loss of flow voids
sulcal effacement
mass effect
ī§ Acute infarct
lesion in arterial
distribution(Hypo-T1, Hyper â
T2)
18. Conventional MRI in stroke
ī§ Chronic â secondary signs-
Wallerian degeneration
Cortical atrophy
Negative mass effect
T1 T2 FLAIR
Sub acute Iso or
Chronic
19. Post contrast techniques
ī§ Immediate
Stagnation of contrast in vessels
ī§ Acute- Meningeal enhancement adjacent to
infarct
ī§ Subacute -Gyriform enhancement
ī§ Intravascular, Meningeal enhancement
decrease by 1 wk
21. DW- principles
ī§ Use of STRONG GRADIENT PULSES
SENSITIVE TO MOLECULAR MOTION in long
TR( T2 weighted)
ī§ Tissues with higher diffusion show greater
signal loss
ī§ To reduce motion artifacts scan time is reduced
by EPI in place of conventional SE
( EPI is fast imaging technique)
ī§ Less diffusion- bright â
diffusion restriction
22. DWI-b value
ī§ DWI quality-
ī§ B valueÎą Diffusion weighting
ī§ B value range from 0- 1500
ī§ Optimum b value is 1000
T2 Vs diffusion properties
25. DWI- ADC value
ī§ Quantitative measurement of diffusion
property
ī§ Varies with time
Nadir 4-5 days
Pseudonormalization-1-4wks
26. DWI- stroke
persistent brightness â T2
shine through
DWI ADC
Subacute Moderately bright Towards normal
Chronic Mildly bright increased
27. DWI importance
ī§ DWI- 100% sensitivity within minutes
ī§ Most sensitive technique of all for hyperacute
stroke
ī§ Essential part of MR evaluation of penumbra
ī§ Useful in detecting new hyperacute , acute
lesions among the chronic lesions â
therapeutic significance
28. False positive Diffusion
ī§ Causes of diffusion brightness
Cerebral abscess
Tumor
ī§ DWI+ conventional MRI useful
False negative
small lacunar brainstem infarction
deep gray nuclei infarction
41. Lacunar infarcts
ī§ Upto 1.5 cm in size
ī§ Occlusion of perforating arteries
ī§ Deep grey matter , deep white
matter,brainstem
ī§ Multiple
ī§ MR is useful to differentiate from VRS,focal
areas of gliosis
43. Lacunar infarct Virchow Robin
Spaces
Location Ant. To ant. comm
Size 1.5 cm 2 mm
DWI bright dark
FLAIR Peripheral
hyperintense
suppressed
44. Watershed infarcts
ī§ Junction of large arterial territories
ī§ Chronic large vessel stenosis precipitated by
hypotension
ī§ DWI , PW helpful in etiology
MORE COMMONLY HEMORRHAGIC
EARLIER ENHANCEMENT
51. Venous infarction
ī§ Parenchymal findings
Edematous infarcts
Hemorrhagic infarcts
Site-
Grey white matter junction,
White matter,
No typical territorial distribution
52.
53.
54. Transcranial doppler USG
ī§ TCD
2 MHz ,pulsed range gated device
Low band width, large less defined volume
ī§ TCCS
B mode+Frequency based color coding
1.8to 3.6 MHz
Rapid reliable vessel identification
Can also image parenchyma
55. Transcranial doppler USG-
M1 and M2 of MCA
C1 of ICA
A1 of ACA
P1 and P2 of PCA
Vertebral arteries
Basilar artery
Temporal approach Suboccipital approach
56.
57. Transcranial doppler USG
ī§ Indications
Intracranial stenosis or occlusion
Secondary effects of extra cranial occlusion
Monitoring of vessel recanalization in stroke
Detection of microemboli
ī§ Accuracy and pitfalls
sensitive and specific if stenosis > 50%
Accurate in detecting M1 lesions
Poor window in 10% - 20% of patients
58. Conventional angiography-
Indications
ī§ DSA IS USUALLY PERFORMED ONLYDSA IS USUALLY PERFORMED ONLY
WHEN ENDOVASCULAR THERAPY ISWHEN ENDOVASCULAR THERAPY IS
BEING CONSIDEREDBEING CONSIDERED
evaluation of carotidsevaluation of carotids
ī§ To determine degree of stenosis
ī§ To look for tandem lesions( carotid siphon,
horizontal MCA)
ī§ Evaluate collateral circulation
62. CTA
ī§ Fast, thin section,volumetric spiral CT
examination performed with a time-
optimized bolus of contrast material for the
opacification of vessels.
63. CTA- data aquisition
Coverage Aortic arch to circle of Willis
Scanning parameters 120 kV, 260 mAs
Scanning delay Dependent on ROI placed
(empiric delay of 25 sec)
Contrast medium dose 100â120 mL 3â4 mL/sec
Section thickness 2.5 mm
Section reconstruction 1.25 mm
64. CTA- Source images
ī§ Occlusion ,stenosis or
significant calcification
of an Extracranial
internal carotid artery
ī§ Detection of hyperacute
infarct
ī§ Substraction perfusion
65.
66. CTA- post processing
techniques
ī§ MIP
ī§ single layer of the
brightest voxels in a
given plane
ī§ Attenuation
information preserved,
ī§ Depth information is
completely lost
ī§ SSD
ī§ first layer of voxels
within defined
thresholds
ī§ Depth information is
preserved
ī§ Attenuation information
is lost.
ī§ Arteries vary in caliber
depending on the
thresholds selected
67. CTA- adv
ī§ Volume rendering.
ī§ Groups of voxels within defined attenuation
thresholds are selected,and a color as well as
an âopacityâ is assigned
71. MRA - techniques
ī§ TOF techniques
use of gradient pulses with TRshorter than
background tissueâ Flow related
enhancement of inflowing nuclei
ī§ 2D technique- individual slices
useful in slow flow states
ī§ 3D techniques-A volume of slab
useful in high flow states
Better spacial resolution
72. PROTOCOL 3D TOF
ī§ TR 39ms
ī§ TE 7ms
ī§ FLIP ANGLE 25
ī§ FOV 200mm
ī§ SLAB THICKNESS 32mm
ī§ MATRIX 512
ī§ NO OF ACQ 1
ī§ ORIENTATION TRANSVERSE
ADVANTAGESADVANTAGES
ī§ BETTER SPATIAL RESOLUTION AND VESSEL CONTRAST
ī§ QUICKER ACQUISITION
73. CE MRA
RAPID 3D GRADIENT ECHO (GRE) SEQUENCE FIRST PASS MRA USING A
SELECTIVELY LARGE BOLUS OF GADOLINIUM BASED CONTRAST.
ADVANTAGESADVANTAGES ::
ī§ NOT SUSCEPTIBLE TO SIGNAL LOSS FROM TURBULENCE OR SLOW FLOW
COMPARED WITH TOF OR PC TECHNIQUE
ī§ ALLOWS BETTER VESSEL TO BACKGROUND CONTRAST COMPARED WITH
TOF /PC
ī§ SHORTER IMAGING TIME
ī§ LESS SUSCEPTIBLE TO MOTION ARTIFACTS
ī§ ALLOWS IDENTIFICATION OF SLOW FLOW IN NEARLY OCCLUDED VESSEL
ī§ ALLOWS MORE ACCURATE ASSESSMENT OF STENOSIS & VISUALIZATION
OF ULCERATED PLAGUE
79. CT- perfusion parameters
ī§ CEREBRAL BLOOD VOLUME the volume of blood
per unit of brain tissue
ī§ CEREBRAL BLOOD FLOW the volume of blood
flow per unitof brain tissue per minute
ī§ MEAN TRANSIT TIME, the time difference
between the arterial inflow and venous
outflow
ī§ TIME TO PEAK ENHANCEMENT the time from the
beginning of contrast material injection to
peak enhancement
80. CT perfusion - principles
ī§ Early cerebral ischemia
ī§ Later, CBV and CBF both decrease
Central volume principle
CBF= CBV/ MTT
81. CT perfusion â Data aquisition
ī§ Coverage-- Four sections( of 5 mm thickness) chosen by the radiologist
( Depending on clinical presentation)
ī§ LEVEL OF BASAL GANGLIA IS CHOSEN- ALL ARTERIAL TERRITORIES
REPRESENTED
Scanning
parameters
80 kV, 105 mAs
Section thickness
5 mm
Scanning delay
5 sec
Scanning duration
50sec
Contrast medium
Dose
50 mL rate of4â5
mL/sec
82. CT- perfusion âpost
processing
ī§ A total of 200 images are taken for post
processing( 50x 4)
ī§ Two algorithms â Deconvolution technique
maximum slope method
ī§ Time attenuation curves obtained from an
individual voxel and compared with
Artery( one of the ACA or MCA)
Vein (SSS)
83. ī§ CBF calculated by central volume principle
ROI over artery ROI over vein
MTT is calculated
CBV calculated
ROI over parenchyma
85. CT perfusion - Interpretation
M TT CBF CBV
Arterial stenosis normal normal
Oligaemia
(>60%)
near normal
Penumbra
(>30%) (<80%)
Infarct
(<30%) (<40%)
86. ACCORDING TO A STUDY AT PGI
CBF CBV MTT
Infarct o.19 0.49 3.15
Noninfarct
ischemic
0.58 1.18 2.5
Thresholds for salvagable tissue- CBF>0.37,CBV>0.83
93. MR perfusion âprinciples
First pass study
Change in SI in every voxel
is studied
The passage of an intravascular
MR contrast agent
transient loss of signal
( T2* effects)
97. ASL method
ī§ Alternative and emerging noninvasive method
ī§ Water molecules in arterial blood -magnetically labelled
ī§ Pair-wise comparison -Repeated measurements of
interleaved label and control acquisitions -
Control Labelled
98. ASL method
ī§ Absolute CBF can be quantified
ī§ No contrast agent
Disadvantages
ī§ Relatively small labeling effect (<1% raw
signal). Low signal to noise ratio
ī§ Very sensitive to transit effects
99. Ischemic penumbra - comparison
CT MR
Availability Good Fair
Examination time 5 min 15 min
Imaging volume 2-4 cms Entire brain
Contrast Iodine Gadolinium
Radiation present No
Parameter Mismatch- CBF,
CBV
DW- perfusion
mismatching
100. Comparison
ī§ MODALITY SENSITIVITYMODALITY SENSITIVITY
SPECIFICITYSPECIFICITY
ī§ CT PERFUSIONCT PERFUSION 88-95 98-100
(AJNR 2000)(AJNR 2000)
ī§ MR PERFUSIONMR PERFUSION 74-84 96-
100
ī§ Different studies have concluded that CT
perfusion and DWI-PWI MR are equivalentequivalent in
identification of penumbra and prediction of
infarct size.
(STROKE 2002) ( JCAT(STROKE 2002) ( JCAT
2003)2003)
101. Functional loss of cell
Reduced blood flow
Autoregulation
CYTOTOXIC EDEMA,
CELL DEATH
Increased water content
VASOGENIC EDEMA
MASS EFFECT
GLIOSIS
Perfusion
imaging
DWI
Conventional MRI
CT
102.
103. Causes
ī§ One of top ten causes of childhood death
ī§ Presenting signs and symptoms variable
ī§ Depends on age
106. Peripheral Focal
FLAIR may not detect acute lesions
DWI, ADC values may be normal intially
Initial DWI , may not correspond to the final infarct volume
DELAYED CELL DEATH MECHANISMS
107. Imaging modality
Ultrasound- illdefined hyperechogenecity-
cystic degeneration
Conventional MR imaging
Neonate
Acute-isointense infarcted cortex
( missing cortex sign)
May not seen on FLAIR
Subacute stage-T1 hperintense, T2
hypointense
108. Imaging modality
ī§ CEMR and CECT- Gyriform enhancement
from 5 days onwards
ī§ Diffusion imaging
ī§ Perfusion imaging- Moya-Moya disease for
surgical planning
117. Dissection
ī§ Blood dissects through intimal defect- false
channel between intima and muscularis-
ī§ Complications-
ī§
īObstruction of main lumen
īIntramural thrombus
ī Embolization- stroke
ī Pseudoaneurysm
118. Dissection
ī§ Imaging technique of choice
ī§ MRA -2D TOF ,DSA-
Gradual irregular tapering,stenosis, Distal
emboli, psedoaneurysms
Non contrast fat supressed T1 sequence at base of skull and neck-
crescentic hyperintensity in vessel mura
121. NECT
HEMORRHAGE
CT PERFUSION
CTP- EVALUATION
COLOR MAPS OF TTP,CBF,CBV
CT ANGIOGRAPHY
VERTEBRAL BODY C5 TO VERTEX
END OF EXAMINATION
YES NO
CTA EVALUATION
EVALUATION & INTERPRETATION EARLY SIGNS OFISCHEMIC STROKE ?
REDUCED PERFUSION ?
STENOSIS OR OCCLUSION OF
MAJOR ARTERIES ?
122. ACUTE FOCAL NEUROLOGICAL DEFICIT WITHIN 6 HR
T2*GRE MRI ( OR CT)
NO ACUTE
HAEMORRHAGE
ACUTE HAEMORRHAGE
DWI/PWI/MRA
PWI >DWI
MCA BRANCH OCCLUSION DISTAL ICA OR
PROXIMAL MCA OCCLUSION
PWI <DWI
IV THROMBOLYSIS
IV/IA THROMBOLYSIS
123. CONCLUSION
ī§ Stroke â No longer tragic medical event
But a medical emergency
ī§ CT-initial investigation of choice
ī§ Radiologist is the integral part of hyperacute
stroke management team,in evaluating the
ischemic penumbra and probable endovascular
therapy
ī§ CTP, DW-PWI useful in evaluating penumbra
Comparable in sensitivity.Used according to the
availability
126. I.A. thrombolysis
ī§ Selective chemical thrombolysis at the site of
thrombus
Advantages
Higher conc. at site
Systemic exposure
Precise imaging
Monitoring of recanalization
Adj. mechanical thrombolysis
Disadvantages
īŧInjury to vessels
īŧHeparin use
īŧDelay in thrombolysis
īŧLogistic limitation
131. I.A. thrombolysis
contraindications
ī§ > 6 hours from onset
ī§ Baseline NIHS score <10
ī§ Rapidly improving neurological status
ī§ Intracranial hemorrhage,
ī§ Parenchymal hypodensity in >1/3 of vascular
territory
ī§ Stroke within previous 6 weeks
ī§ Head trauma within 90 days
ī§ INR > 1.7,aPTT >1.5,platelet counts< 100,000/l
ī§ Uncontrolled hypertension
132. Combined thrombolysis
ī§ Synergy of advantages
i.v. rt-PA (fast and easy to use)
ī§ Improves the speed and frequency of recanalization
ī§ t-PA dose-- 0.6mg/kg +20mg I.A
ī§ Increased risk of hemorrhage
+IAT
ī§ Titrated dose
ī§Mechanical aids o recanalization
ī§ Higher rates of recanalization