Role of CT in Acute Stroke

1. Dr. PG Sridhar Sr. Consultant Role of CT in Acute Stroke

2. Epidemiology • Third most common cause of death world wide • Age adjusted prevalence rate of stroke in India  250-350/100,000* • Age adjusted prevalence rate of stroke in Bangalore  262/100,000** • Estimated stroke related death 1.2 % of the total deaths* *Neurology Asia 2006; 11 : 1 – 4 **Neuroepidemiology 2004;23:261–268

3. Stroke • Infarction 85% • Cerebral atherothrombosis 30-40% • Cardiogenic embolism 20-25% • Penetrating artery disease (lacune) 20% • Other unusual causes 5% • Hemorrhage 15% • In India, ratio of cerebral infarct to hemorrhage is estimated to be 2.21* *Neurology Asia 2006; 11 : 1 – 4

4. “Time is Brain”

5. “Time is Brain”

6. Goals of Acute Stroke Imaging • Parenchyma: Assess early signs of acute stroke and rule out hemorrhage • Pipes: Assess extracranial 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 without recanalization of intravascular thrombus Rowley HA. AJNR 2001;22:599–601.

7. Non contrast CT • CT perfusion • CT angiogram • Other emerging imaging techniques

8. Unenhanced CT • R/o hemorrhage. • Insular ribbon sign • obscuration of the lentiform nucleus • Cerebral swelling • Dense vessel sign (MCA or MCA dot sign)

9. Intracranial Hemorrhage

10. obscuration of the lentiform nucleus May be seen on CT images within 2 hours after the onset of a Stroke

11. Insular Ribbon Sign 73Y/F, 2 1⁄2 hours after the onset of left hemiparesis

12. 66Y/M, Left hemiparesishistory of a visit to a chiropractitioner

13. Stroke Window

14. Follow Up 24 Hrs 1 Week

15. Stroke window Lev et al. Radiology 1999; 213: 150-155

16. Lev et al. Radiology 1999; 213: 150-155 • small attenuation difference between normal and acutely edematous brain tissue can be accentuated by using variable, nonstandard window width and center level settings.

17. Alberta Stroke Program Early CT Score(ASPECTS)

18. ASPECT SCORE • An ASPECTS score less than or equal to 7 predicts worse functional outcome at 3 months as well as symptomatic haemorrhage.

19. Dense Basilar and PCA 85Y/F, Change in mental status

21. 41Y/F, right sided weakness

22. 4 Day F/UP MRI & MRA

23. False Positive Dense vessel sign • increased hematocrit • wall calcifications • Polycythemia • arterial dolichoectasia

24. CT PERFUSION

25. CT PERFUSION • Cerebral blood volume (CBV): the volume of blood per unit of brain tissue • Cerebral blood flow (CBF): the volume of blood flow per unit of brain tissue per minute • Mean transit time (MTT): defined as the time difference between the arterial inflow and venous outflow • Time to peak (TTP): The time from the beginning of contrast material injection to the maximum concentration of contrast material within a region of interest

26. Techniques • Dynamic contrast material–enhanced perfusion imaging (First pass technique) • Perfused-blood-volume mapping .

27. Steps in CT Perfusion Data Postprocessing • Freehand or automated placement of an ROI over an input artery to obtain the arterial time-attenuation curve or arterial input function • Freehand or automated placement of an ROI over an input vein to obtain the venous time-attenuation curve • Generation of the arterial and venous time-attenuation curves

28. Perfusion Parameters • MTT- Deconvolution of arterial and tissue enhancement curve • CBV- calculated as the area under the curve in a parenchymal pixel divided by the area under the curve in an arterial pixel. • CBF- using the central volume equation: CBF= CBV/MTT • Since the input artery is usually smaller than the input vein, the venous ROI serves to correct for volume averaging in the arterial ROI.

29. NORMAL DIFFERENCES IN PERFUSION PARAMETERS BETWEEN GRAY AND WHITE MATTER Calamante et al. MRM 2000;44(3):466-77.

31. CT PERFUSION Wintermark M, Stroke 2006;37:979–985.

32. Penumbra 1) Hakim AM. J Cereb Blood Flow Metab 1989;9:523 2) Marchal G. Stroke 1996;27:5993) Schramm P. Stroke 2002;33:2426

33. 50 Y/F, fluctuating left facial droop and left arm weakness(> 3 hrs)

34. CT Perfusion MTT CBF CBV Penumbra with no infarct. No residual weakness following I/V tPA

35. B A C D 2.5 hours left hemiparesis NECT CBF CBV Day 5 NECT Large penumbra with focal infarct in the right basal ganglia

36. Matched Defect No penumbra MTT CBF CBV

37. No Treatment, Hemorrhage

38. Perfused-blood-volume mapping.(slow infusion technique) • Quantitative cerebral blood volume values are obtained by subtracting the unenhanced CT image data from the CT angiographic source image data. • Advantage: ability to depict the whole brain • Disadvantage: cannot be used to evaluate cerebral blood flow and mean transit time (hence, the penumbra)

39. CT Angiogram • to enable more accurate determination of prognosis • To guide therapy

40. CT Angiogram • Site of occlusion • R/o arterial dissection • grade collateral blood flow • characterize atherosclerotic disease. • whole-brain "perfused blood volume map

41. CT Angiogram

43. Our Stroke Protocol (64 slice)

44. Other Emerging CT Imaging Techniques In Acute Stroke • Single Photon Emission Computed Tomography (SPECT) • Xenon Enhanced CT • Positron Emission Tomography