Neuroimaging in Stroke: What and when

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  • An example of that, then, is this carotid study. This was a 90 year old patient, who had a failed Doppler TIA, and if you look at the study, you will see that they covered 338mm in 4.2 seconds. So a 90 year old patient, it was a comfortable breath hold, 4.2 seconds as opposed to what would have been probably about a 16 second scan on a 16 slice scanner. Clearly, you can see the area of infarc on the right carotid as depicted also in the rotating movie for the clinician. So they’re starting to interrogate this data much differently, getting it more in a pure arterial phase with very little venous contamination, something that they’ve been wanting to do for quite some time, and the LightSpeed VCT is now able to deliver that capability.
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  • Neuroimaging in Stroke: What and when

    1. 1. Neuroimaging in Stroke: What and When? Harsh Mahajan, M.D. Mahajan Imaging Centres, New Delhi
    2. 2. Motivations For Stroke Imaging <ul><li>Early diagnosis of ischemic stroke critical to success of therapeutic interventions like thrombolysis and anticoagulation </li></ul><ul><li>Diagnosis within 3 hours post ictus provides opportunity for i/v or i/a thrombolysis and intra-arterial clot mechanical treatment </li></ul><ul><li>Diagnosis between 3 and 6 hours provides opportunity for i/a thrombolysis and mechanical treatment </li></ul>
    3. 3. Motivations For Stroke Imaging <ul><li>Diagnosis in 1 st 12 hours provides opportunity for administration of neuro-protective agents which may improve outcome </li></ul><ul><li>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 </li></ul>
    4. 4. Goals for Stroke Imaging <ul><li>Immediate access to high quality equipment : MR and CT scanners close to each other preferably near the emergency dept. </li></ul><ul><li>Ability to perform specialized examinations: MDCTs for NCCT, CTA and CT perfusion and MR imaging including DWI, PWI and MRA </li></ul><ul><li>Accurate and timely diagnosis: 24 hour coverage for interpretation and quick answer to four primary diagnostic questions: </li></ul><ul><ul><li>Is there an infarct? </li></ul></ul><ul><ul><li>Is there intra-cranial hemorrhage? Usually stroke treatment not altered based on petechial hemorrhage </li></ul></ul><ul><ul><li>Can stroke mimics, like encephalitis or tumor be excluded? </li></ul></ul><ul><ul><li>What part of brain is completely infarcted and what part is salvageable or at risk of infarction? </li></ul></ul>
    5. 5. Goals for Stroke Imaging <ul><li>Vascular imaging: MRA/CTA of the neck arteries and intra-cranial vessels. CTA preferred </li></ul><ul><li>Radiation control : As low as reasonably allowable (ALARA) </li></ul><ul><li>Cost: Though difficult to prove it is believed that an accurate imaging diagnosis likely decreases overall cost to the system </li></ul>
    6. 6. Radiology Triage of the Stroke Patient <ul><li>Good history leads to correct diagnosis </li></ul><ul><li>If stroke possible, expedite neuroimaging </li></ul><ul><li>Call neurologist/stroke team immediately </li></ul><ul><li>Neuroimaging directly impacts further management; whether discharged, admitted to regular floor or to neurosciences ICU </li></ul><ul><li>Neuroimaging guides treatment options </li></ul>
    7. 7. FIRST SCAN <ul><li>Usually NCCT in most centres </li></ul><ul><li>To demonstrate lack of I/C hemorrhage and lack of large territorial infarct (usually MCA distribution) </li></ul><ul><li>An excellent modality even in remote rural areas where a CT is usually accessible </li></ul>
    8. 8. Scenario Classification <ul><li>Hyperacute: Symptoms lasting fewer than 3 to 6 up until 12 hours </li></ul><ul><li>Acute: Few hours to several days but usually <24 hours </li></ul><ul><li>Subacute: Several days to weeks </li></ul><ul><li>Chronic: Months to years, typically >3 months </li></ul><ul><li>Literature on terminology is variable and it is best to descriptive, specific and consistent </li></ul>
    9. 9. Hyperacute – Acute Stroke <ul><li>Initial NCCT esp. to exclude I/C hemorrhage </li></ul><ul><li>MR susceptibility imaging (SWAN) clearly superior to CT in indentifying hemosiderin blood products that may increase risk of I/C hemorrhage during stroke treatment </li></ul><ul><li>MRI with DWI & PWI can demonstrate best hyperacute and acute infarcts and also demonstrate penumbra </li></ul><ul><li>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 </li></ul>
    10. 10. Hyperacute – Acute Stroke <ul><li>Increased detail in vessel imaging in CTA is frequently more helpful than MRA </li></ul><ul><li>Repeating MRA after CTA usually not indicated except for problem solving </li></ul><ul><li>T1 fat-sat sequences for diagnosing potential arterial dissection </li></ul>
    11. 11. Subacute Stroke <ul><li>NCCT head followed by CTA of head and neck without perfusion </li></ul><ul><li>MR imaging including DWI and susceptibility imaging </li></ul><ul><li>CT or MR perfusion generally not performed because most available treatments in this clinical scenario do not require perfusion data inputs (Eg. Carotid endarterectomy) </li></ul>
    12. 12. Chronic Stroke <ul><li>Conventional MR with DWI and susceptibility </li></ul><ul><li>MRA of head and neck </li></ul><ul><li>Neck MRA with gadolinium based contrast </li></ul><ul><li>Intracranial MRA without contrast by using 3D-TOF </li></ul><ul><li>2D-TOF MRA of neck may complement 3D contrast enhanced MRA in some patients </li></ul>
    13. 13. NCCT <ul><li>Hemorrhage identified in about 5% (Mullens et al) </li></ul><ul><li>Primarily represents hemorrhagic transformation of ischemic infarct </li></ul><ul><li>In young patients underlying vascular lesions may be considered </li></ul><ul><li>If in non arterial distribution, consider venous infarct </li></ul><ul><li>Delayed hemorrhagic conversion most likely related to late increased arterial flow or collaterals to damage brain (i.e. reperfusion injury) or coagulopathy </li></ul>
    14. 14. Stroke Follow-Up Imaging <ul><li>NCCT provides answers to most questions </li></ul><ul><ul><ul><li>Has there been extension of previous infarct? </li></ul></ul></ul><ul><ul><ul><li>Is there an new location of infarct? </li></ul></ul></ul><ul><ul><ul><li>Is there hemorrhagic transformation? </li></ul></ul></ul><ul><ul><ul><li>If there was previous hemorrhage, has it increased? </li></ul></ul></ul><ul><ul><ul><li>Has there been bleeding away from infarct? </li></ul></ul></ul><ul><ul><ul><li>Is there hydrocephalus? </li></ul></ul></ul><ul><ul><ul><li>Is there cerebral edema? </li></ul></ul></ul><ul><ul><ul><li>Is there brain herniation? </li></ul></ul></ul>
    15. 15. What Imaging Exam is Really the Best? <ul><li>Detection of Blood Products: </li></ul><ul><ul><ul><li>NCCT has overall sensitivity of about 91-92%. Decrease in accuracy with time is likely caused by evolution of blood density </li></ul></ul></ul><ul><ul><ul><li>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) </li></ul></ul></ul><ul><ul><ul><li>T1 sequence useful for identifying methemoglobin </li></ul></ul></ul><ul><ul><ul><li>Susceptibility and GRE sequences best for identifying hemosiderin but also useful for acute blood products </li></ul></ul></ul>
    16. 16. What Imaging Exam is Really the Best? <ul><li>Detection of Infarct: </li></ul><ul><ul><ul><li>MR with DWI superior to NCCT and conventional MR without DWI </li></ul></ul></ul><ul><ul><ul><li>NCCT becomes better about 12 hours following ictus </li></ul></ul></ul><ul><ul><ul><li>CTA and perfusion imaging provide improvement over NCCT </li></ul></ul></ul><ul><ul><ul><li>CTA placed somewhere between NCCT and MRI with DWI in terms of statistical values </li></ul></ul></ul>
    17. 17. What Imaging Exam is Really the Best? <ul><li>Access and Time of Examinations: </li></ul><ul><ul><ul><li>Limited availability of MRI is a limitation to widespread use of conventional MR imaging and DWI for diagnosis of acute stroke </li></ul></ul></ul><ul><ul><ul><li>CT scanners have better penetration in the community and are accessed more easily and faster </li></ul></ul></ul><ul><ul><ul><li>NCCT followed by CTA takes nearly similar time as MR with DWI </li></ul></ul></ul><ul><ul><ul><li>Inclusion of MRA nearly doubles time for MR imaging </li></ul></ul></ul><ul><ul><ul><li>An NCCT must always be done before a CTA to exclude I/C hemorrhage which might otherwise be overlooked because of contrast enhancement </li></ul></ul></ul>
    18. 18. Carotid Evaluation Scan Technique: 64 x 0.625 mm 338 mm in 4.2 seconds Mahajan Imaging Centre
    19. 20. RT F M R I
    20. 21. RT F M R I
    21. 22. Spectroscopy
    22. 23. Spectroscopy
    23. 24. SAH
    24. 27. Propeller
    25. 28. Hyperacute infarction 35 minutes
    26. 29. Hyperacute infarction 35 minutes
    27. 31. CBV / NEI ICA occlusion
    28. 32. Mean transit time / MTE ICA occlusion
    29. 33. ICA occlusion
    30. 37. * SUSCEPTIBILITY WEIGHTED ANGIOGRAPHY(SWAN)
    31. 38. Microbleed

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