Neuroimaging in Stroke: What and when

Neuroimaging in Stroke: What and When? Harsh Mahajan, M.D. Mahajan Imaging Centres, New Delhi

Motivations For Stroke Imaging
Early diagnosis of ischemic stroke critical to success of therapeutic interventions like thrombolysis and anticoagulation
Diagnosis within 3 hours post ictus provides opportunity for i/v or i/a thrombolysis and intra-arterial clot mechanical treatment
Diagnosis between 3 and 6 hours provides opportunity for i/a thrombolysis and mechanical treatment

Motivations For Stroke Imaging
Diagnosis in 1 st 12 hours provides opportunity for administration of neuro-protective agents which may improve outcome
In posterior circulation, esp. the basilar artery treated by some physicians regardless of time of onset or up until 12-24 hours by others due to potentially high mortality and morbidity associated with basilar artery thrombosis

Goals for Stroke Imaging
Immediate access to high quality equipment : MR and CT scanners close to each other preferably near the emergency dept.
Ability to perform specialized examinations: MDCTs for NCCT, CTA and CT perfusion and MR imaging including DWI, PWI and MRA
Accurate and timely diagnosis: 24 hour coverage for interpretation and quick answer to four primary diagnostic questions:
Is there an infarct?
Is there intra-cranial hemorrhage? Usually stroke treatment not altered based on petechial hemorrhage
Can stroke mimics, like encephalitis or tumor be excluded?
What part of brain is completely infarcted and what part is salvageable or at risk of infarction?

Goals for Stroke Imaging
Vascular imaging: MRA/CTA of the neck arteries and intra-cranial vessels. CTA preferred
Radiation control : As low as reasonably allowable (ALARA)
Cost: Though difficult to prove it is believed that an accurate imaging diagnosis likely decreases overall cost to the system

Radiology Triage of the Stroke Patient
Good history leads to correct diagnosis
If stroke possible, expedite neuroimaging
Call neurologist/stroke team immediately
Neuroimaging directly impacts further management; whether discharged, admitted to regular floor or to neurosciences ICU
Neuroimaging guides treatment options

FIRST SCAN
Usually NCCT in most centres
To demonstrate lack of I/C hemorrhage and lack of large territorial infarct (usually MCA distribution)
An excellent modality even in remote rural areas where a CT is usually accessible

Scenario Classification
Hyperacute: Symptoms lasting fewer than 3 to 6 up until 12 hours
Acute: Few hours to several days but usually <24 hours
Subacute: Several days to weeks
Chronic: Months to years, typically >3 months
Literature on terminology is variable and it is best to descriptive, specific and consistent

Hyperacute – Acute Stroke
Initial NCCT esp. to exclude I/C hemorrhage
MR susceptibility imaging (SWAN) clearly superior to CT in indentifying hemosiderin blood products that may increase risk of I/C hemorrhage during stroke treatment
MRI with DWI & PWI can demonstrate best hyperacute and acute infarcts and also demonstrate penumbra
NCCT may be followed immediately by CTA & CTP which rapidly assess arterial clot and stenosis, large evolved infarcts, infarct size and location. MRI primarily adds DWI which best shows the infarcts

Hyperacute – Acute Stroke
Increased detail in vessel imaging in CTA is frequently more helpful than MRA
Repeating MRA after CTA usually not indicated except for problem solving
T1 fat-sat sequences for diagnosing potential arterial dissection

Subacute Stroke
NCCT head followed by CTA of head and neck without perfusion
MR imaging including DWI and susceptibility imaging
CT or MR perfusion generally not performed because most available treatments in this clinical scenario do not require perfusion data inputs (Eg. Carotid endarterectomy)

Chronic Stroke
Conventional MR with DWI and susceptibility
MRA of head and neck
Neck MRA with gadolinium based contrast
Intracranial MRA without contrast by using 3D-TOF
2D-TOF MRA of neck may complement 3D contrast enhanced MRA in some patients

NCCT
Hemorrhage identified in about 5% (Mullens et al)
Primarily represents hemorrhagic transformation of ischemic infarct
In young patients underlying vascular lesions may be considered
If in non arterial distribution, consider venous infarct
Delayed hemorrhagic conversion most likely related to late increased arterial flow or collaterals to damage brain (i.e. reperfusion injury) or coagulopathy

Stroke Follow-Up Imaging
NCCT provides answers to most questions
Has there been extension of previous infarct?
Is there an new location of infarct?
Is there hemorrhagic transformation?
If there was previous hemorrhage, has it increased?
Has there been bleeding away from infarct?
Is there hydrocephalus?
Is there cerebral edema?
Is there brain herniation?

What Imaging Exam is Really the Best?
Detection of Blood Products:
NCCT has overall sensitivity of about 91-92%. Decrease in accuracy with time is likely caused by evolution of blood density
FLAIR may be positive as early as 23 minutes and has sensitivity of 92-100% and specificity of 100% in small groups (Russell et al)
T1 sequence useful for identifying methemoglobin
Susceptibility and GRE sequences best for identifying hemosiderin but also useful for acute blood products

Detection of Infarct:
MR with DWI superior to NCCT and conventional MR without DWI
NCCT becomes better about 12 hours following ictus
CTA and perfusion imaging provide improvement over NCCT
CTA placed somewhere between NCCT and MRI with DWI in terms of statistical values

Access and Time of Examinations:
Limited availability of MRI is a limitation to widespread use of conventional MR imaging and DWI for diagnosis of acute stroke
CT scanners have better penetration in the community and are accessed more easily and faster
NCCT followed by CTA takes nearly similar time as MR with DWI
Inclusion of MRA nearly doubles time for MR imaging
An NCCT must always be done before a CTA to exclude I/C hemorrhage which might otherwise be overlooked because of contrast enhancement

Carotid Evaluation Scan Technique: 64 x 0.625 mm 338 mm in 4.2 seconds Mahajan Imaging Centre

RT F M R I

Spectroscopy

Propeller

Hyperacute infarction 35 minutes

CBV / NEI ICA occlusion

Mean transit time / MTE ICA occlusion

ICA occlusion

* SUSCEPTIBILITY WEIGHTED ANGIOGRAPHY(SWAN)

Microbleed

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Neuroimaging in Stroke: What and when

by Mahajan Imaging Centre on Jun 06, 2010

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Neuroimaging in Stroke: What and when — Presentation Transcript