COXSWAIN ENGINEERING. Marine Engines -Basic Operation 4 Stroke & 2 Stroke.
Basic Stroke Imaging
Transcript of Basic Stroke Imaging
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Imaging of Acute Stroke
Joseph Ronsivalle, DO
Associated Radiologists of the Finger Lakes
May 13, 2013
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Background (cont.)Pathophysiology:
Ischemic Stroke:
O Most often caused by extracranial thromboemolism or
intracranial thrombosis
--arterial stenosis or occlusion
--atherosclerotic debris and ulceration (emboli from carotid
arteries)--emboli: usually from cardiac source (accounts for up to 15-20%
of ischemic stroke)
O Other causes include venous infarction and
hypotension/anoxia
O At the cellular level, the disruption of blood flow results in an
ischemic cascade that results in neuronal death and cerebral
infarct.
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Acute Ischemic Stroke: Radiologic Workup
Goals of Radiologic Workup:
O Make a definitive diagnosis of stroke anddetermine if there is salvageable brain
O Determine if there is nonischemic cause for thepatients presentation--intraparenchymal hemorrhage
--SAH
--tumor
O Identify any hemorrhagic component to theinfarct
--Non Contrast CT
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Computed Tomography
(CT)
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Non Contrast Computed Tomography
O Most efficient method for workup of acute stroke within thefirst 24 hours
O Early Findings:
O Normal scan
O hyperdense MCA sign (MCA accounts for approximately 60% of allstrokes) due to intraluminal high density clot (not very sensitive, but very
specific)
O Hyperdense thrombus/calcified embolus
O May also be seen in basilar artery and venous sinuses
O Early signs of cytotoxic edema:
O Within 6 hours, there may be loss of gray-white borders
1) vanishing basal ganglia sign
2) insular ribbon sign
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Loss of Insular Ribbon:
--Normal Insular Cortex (gray matter) is
more dense as compared to white
matter
--In acute ischemic stroke, this area of gray matter
becomes edematous first and hypodense
--Insular ribbon/stripe is then lost
(SOLID ARROWS ON LEFT)
--may begin to see effacement of sulci of insular
cortex due to cytotoxic edema
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Vanishing Basal Ganglia Sign:
--Loss of definition of normallyhyperdense lentiform nucleus
--highly metabolically active gray
matter
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Non Contrast Computed Tomography
O Within 12-24 hours, indistinct area of low density is apparent in
appropriate vascular distribution
O Minimal mass effect
O Sulcal asymmetry (EFFACEMENT)O Mass effect on ventricle
O Peaks at 3-5 days, then should decrease
O If mass effect persists beyond 6 weeks, think of alternative
diagnosis
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At presentation Approximately 24
hours post ictus
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CT perfusion
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Magnetic Resonance
Imaging (MRI)
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MRI
O Findings may be seen on MR within the first few hours.
O The earliest changes involve loss of normal vessel signal voids
O Swelling of the cortex is seen on T1WI and on FLAIR before
abnormal signal intensity is seen
O By 8 hours an area of hyperintensity may be seen on T2WI
O FLAIR images are even more conspicuous decreased signal
from CSF while maintaining the signal of pathologic
processes
O By 16 hours, low signal intensity is seen on T1WI
O On FLAIR, arteries with slow/no flow may be hyperintense and
show a hypointense outline of CSF
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O MRI: 67 year old male
T2WI: Subtle bright signal
intensity is seen in the right
occipital lobe
Intermediate-weighted images
make the lesion more conspicuous
by decreasing signal from CSF
http://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4a.jpeghttp://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4b.jpeghttp://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4a.jpeg -
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FLAIR images demonstrate acute ischemic
infarction with more conspicuity because
of nulling of CSF signal
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MRI: Diffusion Weighted Imaging
O
MRI technique that is sensitive to Brownian motion (randommotion of water molecules)
O Cytotoxic edema results in decreased extracellular fluid
O Decreased free water motion
O High (VERY BRIGHT) signal intensity on MRI
O Able to detect stroke in approximately 30 minutesO Allows for definitive and prompt diagnosis, and appropriate
treatment
O Apparent Diffusion Coefficient:
O Measures apparent diffusion of water molecules
O Low signal with restriction
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DWI: can assess the acuity of an infarction.
5 hrs 3 days 7 days 30 days
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Perfusion Imaging
Characterizes MICROSCOPIC FLOW at the capillary level
Brain Parenchymal Flow = Cerebral Blood Volume
Transit Time of Bld Thru brain
Techniques used to measure flow
O Gadolinium GIVING CONTRAST (dynamic contrast
susceptibility/bolus tracking)
O Spin Tagging of H20 (MAGNETICALLY TAGGING ARTERIAL
WATER)
O Requires no injection and can be repeated easily
O Limited to fewer slices than dynamic contrast susceptibility
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Perfusion Imaging
O COMMON Parameters USED TO MEASURE CEREBRAL BLOODFLOW
O Relative Cerebral Blood Flow (rCBF): Normal 100mL/min/100gm tissue
O Relative Cerebral Blood Volume (rCBV)
O Relative Mean Transit Time (rMTT): increased due to any hemodynamicproblems, best to assess asymmetry
O Time to Peak (TTP)
rCBF = rCBV/rMTT
O Regions with prolonged rMTT and decreased rCBV have a highprobability of irreversible ischemic damage
O rCBF: oligemia = 20-40 mL/min/100gm asymptomatic,
underperfused region, can recover spontaneouslyO Ischemic hypoperfused brain is symptomatic, increased risk for
permanent damage if no revascularization
O Ischemia
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Perfusion Imaging
T2WI DWI MTTP Follow up
DWI
Perfusion imaging may be able to
show salvagable tissue at risk
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Perfusion MTTDWI
Perfusion MR obtained 1 hour after infarct:
--bright signal on DWI
--blue/dark on perfusion MR
--large red area = ischemic penumbra + infarct on MTT map
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MR Angiography:
O 3 techniques can be used to generate MRA:
O Time of Flight (TOF)O Flow Related Enhancement: Moving protons retain signal
because of more transient exposure to RF pulse
O 2D (sensitive to slower flow), axial and coronal plane
(venous sinus evaluation)
O 3D (sensitive to higher flow better spatial resolution)
O Phase Contrast:
O Will produce images only based on true flow
O Less susceptible to artifact
O Can detect venous infarcts
O Contrast Enhanced Imaging (Gadolinium)
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MRA: 3D TOF
O
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Angiography
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Venous Thrombosis:
O Progresses to infarct in 50%
O Etiology of Infarct:
O decreased cerebral blood flow from venous thrombosis
O Vasogenic edema/Hemorrhage
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O
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Merci retriever Concentric Medical
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Penumbra
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Solitaire FR ev3/Covidien
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Solitaire flow restoration device versus the Merci Retriever in patients
with acute ischaemic stroke (SWIFT): a randomised, parallel-group, non-
inferiority trial
Interpretation
The Solitaire Flow Restoration Device achieved substantially better angiographic, safety, and clinical outcomes than
did the Merci Retrieval System. The Solitaire device might be a future treatment of choice for endovascular
recanalisation in acute ischaemic stroke.
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Thank You!
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