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Imaging in stroke

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Imaging in stroke

  1. 1. IMAGING IN STROKE MODERATOR- DR C P AHIRWAR (MD) PRESENTOR- DR NEELAM SONI
  2. 2. STROKE  Stroke is an acute central nervous system injury with abrupt onset.  This can occur following ischemia caused by blockage (thrombosis, arterial embolism) or a hemorrhage of CNS or intracranial blood-vessels.  Approximately 80% of all strokes are due to acute ischemia .  It is a leading cause of morbidity and mortality in the developed world.
  3. 3.  GOALS OF IMAGING  To establish the diagnosis as early as possible.  Give accurate information about intracranial vasculature and brain perfusion for guidance in selecting the appropriate therapy.
  4. 4. Imaging should target assessment of 4 P’s: • Parenchyma: • Assess early signs of acute stroke, rule out hemorrhage • Pipes • Assess extracranial circulation (carotid and vertebral arteries of the neck) and intracranial circulation for evidence of intravascular thrombus • Perfusion • Assess cerebral blood volume, cerebral blood flow, and mean transit time • Penumbra • Assess tissue at risk of dying if ischemia continues with out re-canalization of intravascular thrombus
  5. 5. Overview of imaging modalities  Unenhanced CT • Can be performed quickly. • Can help identify early signs of stroke, and can help rule out hemorrhage.  CT angiography can depict intravascular thrombi  CT perfusion imaging can demonstrate salvageable tissue which is indicated by a penumbra.
  6. 6.  Acute infarcts may be seen early on conventional MR images, but diffusion- weighted MR imaging is more sensitive for detection of hyperacute ischemia.  Gradient-echo MR sequences can be helpful for detecting a hemorrhage.
  7. 7.  MR Angiography – To evaluate the status of neck and intracranial vessels  DWI AND PWI - A mismatch between findings on diffusion and perfusion MR images may be used to predict the presence of a penumbra.
  8. 8. PENUMBRA  TISSUE AT RISK OR SALVAGEABLE TISSUE.  Pathophysiology -  Neuronal tissue is sensitive for ischemia due to lack of stored energy  With complete absence of flow neuronal viability is 2-3 minutes  In acute stroke ischemia is always incomplete due to rich collateral supply
  9. 9. ACUTE STROKE  Acute cerebral ischemia may result in a central irreversibly infarcted tissue core surrounded by a peripheral region of stunned cells that is called as a penumbra  This region is potentially salvageable with early recanalization
  10. 10. The transition from ischemia to irreversible infarction depends on both the severity and the duration of the diminution of blood flow Minutes Days and weeksTime Hours
  11. 11. ISCHEMIC PENUMBRA  IDENTIFIED BY  CT - ALTERED PARAMETERS IN PERFUSION  MR – PERFUSION DIFFUSION MISMATCH  PRESENCE OF PENUMBRA HAS SIGNIFICANT IMPLICATIONS IN PT MANAGEMENT
  12. 12. CT  KEY TECHNIQUES  NECT  CTA  PERFUSION CT
  13. 13. NECT  Widely available.  Can be done quickly.  It not only can help identify a hemorrhage (a contraindication to thrombolytic therapy), but it also can help detect early-stage acute ischemia by depicting features such as – 1. THE HYPERDENSE VESSEL SIGN. 2. THE INSULAR RIBBON SIGN. 3. OBSCURATION OF THE LENTIFORM NUCLEUS
  14. 14. HYPERDENSE VESSEL SIGN  Acute thrombus has high attenuation value this feature is referred to as the hyperdense vessel sign.  Highly specific but sensitivity is poor.  FALSE POSITIVE  HIGH HEMATOGRIT LEVEL  MCA CALCIFICATION But in such cases the hyperattenuation is usually bilateral!!!  Rarely, fat emboli appear hypoattenuated when compared with attenuation in the contralateral vessel .
  15. 15. HYPERDENSE MCA
  16. 16. OBSCURATION OF LENTIFORM NUCLEUS  Lentiform nucleus appears hypoattenuated because of acute ischemia of the lenticulostriate territory , resulting in obscuration of the lentiform nucleous.  This feature may be seen on CT images within 2 hours after the onset of a stroke .
  17. 17. OBSCURATION OF LENTIFORM NUCLEOUS
  18. 18. INSULAR RIBBON SIGN  It is the local hypoattenuation of the insular cortex region due to Cytotoxic edema as this region is susceptible to early and irreversible ischemic damage.
  19. 19. INSULAR RIBBON Axial unenhanced CT image, obtained in a 73-year-old woman 21⁄2 hours after the onset of left hemiparesis, shows hypoattenuation and obscuration of the posterior part of the right lentiform nucleus (white arrow) and a loss of gray matter–white matter definition in the lateral margins of the right insula (black arrows). The latter feature is known as the insular ribbon sign.
  20. 20. WINDOW SETTING  Detection of early acute ischemic stroke on unenhanced CT images may be improved by using variable window width and center level settings to accentuate the contrast between normal and edematous tissue  STANDARD WINDOW SETTING (W80 C 20) – SENSITIVITY 57% SPECIFICITY 100%  STROKE WINDOW SETTING (W8 C 32) SENSITIVITY 71% SPECIFICITY 100%
  21. 21. CT ANGIOGRAPHY CT angiography typically involves a volumetric helical acquisition that extends from the aortic arch to the circle of Willis.  The examination is performed by using a time-optimized bolus of contrast material for vessel enhancement.  CT angiographic demonstration of a significant thrombus burden can guide appropriate therapy in the form of intraarterial or mechanical thrombolysis.  Identification of carotid artery disease and visualization of the aortic arch may provide clues to the cause of the ischemic event and guidance for the interventional neuroradiologist
  22. 22. (a) Unenhanced CT image in a 72-year-old woman with acute right hemiplegia shows hyperattenuation in a proximal segment of the left MCA (arrows). (b, c) Axial (b) and coronal (c) reformatted images from CT angiography show the apparent absence of the same vessel segment (arrows).
  23. 23. CTA
  24. 24. CT Perfusion (CTP): Basic concept…..  With CT and MR-diffusion we can get a good impression of the area that is infarcted.  But, we cannot preclude a large ischemic penumbra (tissue at risk).  With perfusion studies we monitor the first pass of an iodinated contrast agent bolus through the cerebral vasculature.  Areas of decreased perfusion will tell us which area is at risk.
  25. 25. CT perfusion maps of cerebral blood volume (a) and cerebral blood flow (b) show, in the left hemisphere, a region of decreased blood volume (white oval) that corresponds to the ischemic core and a larger region of decreased blood flow (black oval in b) that includes the ischemic core and a peripheral region of salvageable tissue. The difference between the two maps (black oval white oval) is the penumbra.
  26. 26. CT PERFUSION  PARAMETERS ASSESSED  CBV – VOLUME OF BLOOD PER UNIT OF BRAIN TISSUE (N 4-5ML/100GM)  CBF – VOLUME OF BLOOD FLOW PER UNIT OF BRAIN TISSUE PER MINUTE (N 50-60ML/100GM/MINUTE)  MTT – TIME DIFFERENCE BETWEEN THE ARTERIAL INFLOW AND VENOUS OUTFLOW  TIME TO PEAK ENHANCEMENT – TIME FROM THE BEGINNING OF CONTRAST INJECTION TO MAXIMUM CONTRAST CONCENTRATION IN A ROI
  27. 27. CTP TECHNIQUES  DYNAMIC CONTRAST ENHANCED CT  BASED ON MULTI COMPARTMENT TRACER KINETIC MODEL  PERFORMED ON MDCT  2-4 SECTIONS ARE OBTAINED AND ONE OF THE SECTIONS PASS THROUGH BASAL GANGLIA  PERFUSED-BLOOD-VOLUME MAPPING- LESS COMMONLY USED
  28. 28. Dynamic Contrast Enhanced CT  Performed by monitoring a first pass of contrast bolus through the cerebral circulation  The transient increase in attenuation generates time- attenuation curves for an arterial and venous ROI  Mathematical modeling can be then used to calculate perfusion parameters and generate color coded perfusion maps (deconvolution analysis)
  29. 29. CBF = CBV / MTT CBF MTT Normal CBF is 55 cc/ 100 gm tissue / minute CBF below this refers to penumbra or tissue at risk
  30. 30. EFFECT OF REDUCTION IN CBF Diagram shows the evolution of events at a microscopic level with decreasing cerebral perfusion (from right to left). Irreversible cell death generally occurs when cerebral blood flow decreases to less than 10 mL/100 g/min.
  31. 31. INTERPRETATION OF PCT  INFARCTED AREA  SEVERELY DECREASED CBF (<30%) AND CBV (<40%)  PROLONGED MTT  PENUMBRA  INCREASED MTT  MODERATELY DECREASED CBF (>60%)  INCREASED CBV (80-100% OR HIGHER) OR  INCREASED MTT  MARKEDLY REDUCED CBF (>30%)  MODERATELY REDUCED CBV (>60%)
  32. 32. CT PERFUSION PROTOCOL
  33. 33. Acute stroke in a 65-year-old man with left hemiparesis. CT perfusion maps of cerebral blood volume (a), cerebral blood flow (b), and mean transit time (c) show mismatched abnormalities (arrows) that imply the presence of a penumbra. The area with decreased blood volume represents the ischemic core, and that with normal blood volume but decreased blood flow and increased mean transit time is the penumbra.
  34. 34. CONVENTIONAL MRI  SPIN ECHO IMAGES MORE SENSITIVE AND SPECIFIC THAN CT IN ACUTE CVA  SEQUENCES  T1  T2  FLAIR  GRE
  35. 35. ACUTE CVA  HYPER ON T2 AND FLAIR  LOSS OF GRAY WHITE MATTER DIFFERENTIATION  SULCAL EFFACEMENT  MASS EFFECT  LOSS OF FLOW VOID IN T2WI IN VESSEL  BLOOMING IN GRE IF HRGE  LESS SENSITIVE THAN DWI IN FIRST FEW HOURS
  36. 36. Acute stroke in the left medial temporal lobe in a 44-year-old man. (a) Axial T2-weighted and (b)fluid attenuated inversion recovery images show areas with increased signal intensity. (c) Gradient-echo image shows abnormal low signal intensity in the same areas. These findings are suggestive of hemorrhage
  37. 37. MR ANGIOGRAPHY  Sensitive for intravascular thrombus.  MR angiograms in two patients with acute stroke symptoms reveal flow gaps in the left proximal middle cerebral artery (arrow in a) and the basilar artery (arrows in b). Both findings were due to intravascular thrombi.
  38. 38. Diffusion-Weighted Imaging  Brownian motion  The normal motion of water molecules within living tissues is random.  Acute stroke causes excess intracellular water accumulation or “cytotoxic edema”, with an overall decreased rate of water molecular diffusion within the affected tissue. Brownian Motion
  39. 39. DWI  AREAS OF CYTOTOXIC EDEMA WITH RESTRICTED WATER MOLECULE DIFFUSION IN ACUTE STROKE APPEAR BRIGHTER COMPARED TO NORMAL TISSUE  TAKES FEW SECS TO 2 MINUTES
  40. 40. DWI ACUTE CVA Acute stroke–induced cytotoxic edema in the right cerebellar hemisphere. Diffusion- weighted MR image shows areas of signal intensity increase due to the restricted mobility of water molecules
  41. 41. Acute stroke of the posterior circulation in a 77-year-old man. (a) Diffusion weighted MR image shows bilateral areas of increased signal intensity (arrows) in the thalami and occipital lobes. (b) ADC map shows decreased ADC values in the same areas (arrows). These findings are indicative of acute ischemia.
  42. 42. CLINICAL APP OF DWI  CHANGES IN DWI OCCUR WITH IN 30MIN OF ONSET OF ISCHEMIA WITH CORRESPONDING REDUCTION IN ADC AND SEEN UP TO 5 DAYS  MILD HYPERINTENSE DWI WITH PSEUDONORMAL ADC FROM 1 -4WKS  AFTER SEVERAL WKS DWI SIGNAL VARIES (T2 EFFECT) WITH INCREASED ADC  DWI ALONE CANNOT BE USED AND SHOULD ALWAYS BE COMPARED WITH ADC TO ASSESS THE AGE OF INFARCT
  43. 43. CHRONIC INFARCT Chronic infarcts in a 71-year-old man with a remote history of multiple strokes. (a) Diffusion weighted MR image shows areas of decreased signal intensity in the left frontal lobe. (b) ADC map shows increased ADC values in the white matter of the right frontal lobe. These features are suggestive of chronic infarction.
  44. 44. ACCURACY  CT/ CONVENTIONAL MRI  SENSITIVITY AND SPECIFICITY < 50%  DWI  SENSITIVITY 88-100%  SPECIFICITY 86-100%  FALSE -VE DWI  LACUNAR INFARCTS OF BRAIN STEM  SMALL DEEP GREY MATTER INFARCTS  FALSE +VE DWI  ABSCESS  CELLULAR TUMOURS LIKE LYMPHOMA
  45. 45. MR PERFUSION  The passage of an intravascular MR contrast agent through the brain capillaries causes a transient loss of signal because of the T2* effects of the contrast agent.  The dynamic contrast-enhanced MR perfusion imaging technique involves tracking of the tissue signal changes caused by susceptibility (T2*) effects to create a hemodynamic time–signal intensity curve,as in dynamic CT perfusion imaging.  Perfusion maps of cerebral blood volume and mean transit time can be calculated from this curve by using a deconvolution technique.
  46. 46. MR PERFUSION  LESION WHICH SHOWS CHANGES BOTH IN DWI AND PERFUSION MR – INFARCT CORE  LESION WHICH SHOWS CHANGES ONLY IN PERFUSION - PENUMBRA
  47. 47. (a) Diffusion- weighted MR image shows an area of mildly increased signal intensity in the right parietal lobe (arrows). The ADC values in this region were decreased. (b) Perfusion-weighted MR image shows a larger area with increased time to peak enhancement (arrows) in the right cerebral hemisphere. The mismatch between the perfusion and diffusion images is indicative of a large penumbra. Acute stroke in a 67-year-old woman with acute left hemiplegia
  48. 48. CLINICAL APPLICATION  Unenhanced CT: rule out hemorrhage  Not very good to detect ischemia  T1 or T2 weighted MRI  Good for detecting ischemia  Cannot differentiate between acute versus chronic ischemia  So we have…
  49. 49. Diffusion-weighted MR  More sensitive for detection of hyperacute ischemia  becomes abnormal within 30 minutes  Distinguish b/w old and new stroke  New stroke: bright on DWI  Old stroke: Low SI on DWI  It detects irreversible infarcted tissue
  50. 50. MRI OLD –VS- NEW ISCHEMIC INFARCT T1 T2 DIFFUSION
  51. 51. Perfusion-Weighted imaging  Allows the measurement of capillary perfusion of the brain  Uses a MR contrast agent  The contrast bolus passage causes a nonlinear signal decrease in proportion to the perfusion cerebral blood volume  Meaning, it can identify areas of hypoperfusion, the reversible ischemia, as well (unlike DWI)
  52. 52. Comparison of PWI and DWI  DWI  Depicts irreversibly damaged infarct  PWI  Reflects the complete area of hypoperfusion  The volume difference between these two, the PWI/DWI mismatch would be the PENUMBRA!  If there is no difference in PWI and DWI, no penumbra is present
  53. 53. Significance of PWI/DWI mismatch  IV thrombolytic treatment is not typically administered to patients with acute stroke beyond 3-hrs period  Risk of hemorrhage  However, recent studies have shown that IV thrombolytic therapy may benefit patients who are carefully selected according to PWI/DWI mismatch, beyond 3-hrs window
  54. 54. CT VS MRI
  55. 55. ACUTE CVA IMAGING PROTOCOL
  56. 56. IV-TPA-WONDERFUL THERAPY.  FDA-USA approved Rx of Ischemic Stroke.  Improved outcome within 3 hours in properly selected patients.  Results are best within 90 minutes.  Results are better within 90 -180 minutes. TPA reverses ischemic changes saving brain.
  57. 57. Thrombolytic Therapy - IV -t-PA I. Inclusion Criteria 1. Within 3 hours of the stroke and patient not needing ventilator. 2. CT Scan head Normal or < 1/3 MCA hypo density. II. Exclusion Criteria 1. BP > 185/110 mm on admission. 2. Use of Oral Anticoagulants. 3. Major surgery preceding FOURTEEN days. 4. Head injury - LAST THREE MONTHS. 5. Prior Intracranial hemorrhage/Recent GI bleed. 6. Prolonged PT / aPTT / INR / low Platelet count.
  58. 58. Intraarterial TPA.  IA-TPA in selected pts. In < 6 hours due to MCA & BA occlusion  In BA occlusion it can be given even after > 12 hours. In future IA-TPA will be rewarding. IV &IA(IMS Trial) showed 56% of recanalisation.
  59. 59. CONCLUSION  Current imaging techniques can be used to identify hyperacute stroke and guide therapy  Both CT and MR imaging are useful for the comprehensive evaluation of acute stroke
  60. 60. THE FUTURE  Selection of patients for thrombolytic therapy may be made more effectively by performing appropriate imaging studies rather than relying on the time of onset as the sole determinant of selection.  New emerging technique MR permeability image used to predict microvascular permeability and quantification of BBB – Pts with defective BBB are more prone for bleeding complication following thrombolytic therapy.
  61. 61. QUIZ
  62. 62. CT Signs in Early MCA Ischemia Hyperdense MCA Insular Ribbon Lentiform Nucleus
  63. 63. MCA Infarct MCA
  64. 64. ACA Infarct
  65. 65. PCA Infarct PCA
  66. 66. What do you see here? What do you expect on CTA?
  67. 67.  Q. Imaging should target assessment of 4 P’s ??????
  68. 68. MRI in Stroke Intervention “The 4 P’s” Pipes  Perfusion  Parenchyma MRA Perfusion MR Diffusion MR “Penumbra”Rowley AJNR 22(4); 599-601, 2001
  69. 69. THANK YOU

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