Role of CT in Acute Stroke

Dr. PG SridharSr. Consultant

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

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”

“Time is Brain”

National Institute of Neurological Diseases and Stroke trial (NINDS)

(N Engl J Med 1995;333:1581-7.)

3Hrs

European Cooperative Acute Stroke Study III (ECASS III)

(Stroke. 2009;40:2262-2263 )

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 Sign73Y/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 Up24 Hrs 1 Week

Stroke windowStd. soft

tissue window Stroke window

width centre

8020

832

Sensitivity

57% 71%

Specificity

100% 100%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.

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

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 PCA85Y/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

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 dividedby 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/MIN 25 ML/100GM/MIN

CBV 4 ML/100GM 2 ML/100GM

MTT 4 SECONDS4.8 SECONDS

Calamante et al. MRM 2000;44(3):466-77.

CT PERFUSION

Wintermark M, Stroke 2006;37:979–985.

Penumbra

CBF CBVOligemia survival

>60% of normal

>80% of normal

Oligemia infarction

30-60% of normal

60-80% of normal

infarction<30% of normal90% Sensitivity

70% specificity

<40% of normal90% Sensitivity

86% specificity1) 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 CBF CBV

2.5 hours left hemiparesisB C DA

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

Thickness

(in mm)

KV MAContrast

ml (ml/sec)Comments

Scout 5 - 80 40 - -

Noncontrast

Brain14 2.5 120 150 - Axial

CT Angio 7.5 0.625 120 500 60(4.5) helical

CT Perfusion 50 5 120 400 50(4)4cm coverage

Post contrast

Brain7.5 2.5 120 150 - Axial

Other Emerging CT Imaging Techniques In

Acute Stroke• Single Photon Emission Computed

Tomography (SPECT)

• Xenon Enhanced CT

• Positron Emission Tomography