basic stroke imaging

7/28/2019 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
http://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4c.jpeghttp://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4c.jpeghttp://radiology.rsnajnls.org/content/vol212/issue2/images/large/r99au16g4c.jpeg


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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
http://radiology.rsnajnls.org/content/vol221/issue1/images/large/r01oc08g1x.jpeg


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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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basic stroke imaging

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