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

Epidemiology Third most common cause of death world wide Age adjusted prevalence rate of stroke in India  /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

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

“Time is Brain”

National Institute of Neurological Diseases and Stroke trial (NINDS) (N Engl J Med 1995;333: ) 3Hrs European Cooperative Acute Stroke Study III (ECASS III) (Stroke. 2009;40: ) 4.5 Hrs

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.

Non contrast CT CT perfusion CT angiogram Other emerging imaging techniques

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

Intracranial Hemorrhage

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

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

66Y/M, Left hemiparesis history of a visit to a chiropractitioner

Stroke Window

Follow Up 24 Hrs 1 Week

Stroke window Std. soft tissue window Stroke window width centre Sensitivi ty 57%71% Specifici ty 100% Lev et al. Radiology 1999; 213:

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

Alberta Stroke Program Early CT Score (ASPECTS)

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

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

41Y/F, right sided weakness

4 Day F/UP MRI & MRA

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

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

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

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

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.

NORMAL DIFFERENCES IN PERFUSION PARAMETERS BETWEEN GRAY AND WHITE MATTER GRAY MATTER WHITE MATTER CBF 60 ML/100GM/MIN25 ML/100GM/MIN CBV 4 ML/100GM2 ML/100GM MTT 4 SECONDS 4.8 SECONDS Calamante et al. MRM 2000;44(3):

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

Penumbra CBFCBV Oligemia survival >60% of normal >80% of normal Oligemia infarction 30-60% of normal 60-80% of normal infarction <30% of normal 90% Sensitivity 70% specificity <40% of normal 90% Sensitivity 86% specificity 1) Hakim AM. J Cereb Blood Flow Metab 1989;9:523 2) Marchal G. Stroke 1996;27:599 3) Schramm P. Stroke 2002;33:2426

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

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

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

CBF MTT CBV Matched Defect No penumbra

No Treatment, Hemorrhage

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)

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

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

CT Angiogram

Our Stroke Protocol (64 slice) Time (in sec) Slice Thicknes s (in mm) KVMA Contrast ml (ml/sec) Comment s Scout Noncontrast Brain Axial CT Angio (4.5)helical CT Perfusion (4) 4cm coverag e Post contrast Brain Axial

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