PERFUSION IMAGING OF STROKE

Adila IqbalR-3, NRD, SHL.

LEARNING OBJECTIVES

Brief review of vascular territories

Early CT and MR signs of infarction

How to identify patients with tissue at risk for guidance in selecting the appropriate therapy

Penumbra

Rai AT, Carpenter JS, Peykanu JA, Popovich T, Hobbs GR, Riggs JE. The role of CT perfusion imaging in acute stoke diagnosis: a large single-center experience. J Emerg Med 2008; 35:287–292

STANDARD WINDOW SETTING (W80 C 20) – SENSITIVITY 57% SPECIFICITY 100%

STROKE WINDOW SETTING (W8 C 32) SENSITIVITY 71% SPECIFICITY 100%

Alberta Stroke Program Early CT Score(ASPECTS)

Proposed in 2001 as a means of quantitatively assessing acute ischemia on CT images.

MCA territory is divided into 10 regions, each of which accounts for one point in the total score.

Silvennoinen HM, Hamberg LM, Lindsberg PJ, Valanne L, Hunter GJ. CT perfusion identifies increased salvage of tissue in patients receiving intravenous recombinant tissue plasminogen activator within 3 hours of stroke onset. Am J Neuroradiol 2008; 29:1118–1123

10 regions of the MCA distribution, each of which accounts for one point in the ASPECTS system: M1, M2, M3, M4, M5, M6, the caudate nucleus (C), the lentiform nucleus (L), the internal capsule (IC), and the insular

cortex (I). For each area involved in ischemia depicted at unenhanced CT, one point is subtracted from the total score of 10.

Silvennoinen HM, Hamberg LM, Lindsberg PJ, Valanne L, Hunter GJ. CT perfusion identifies increased salvage of tissue in patients receiving intravenous recombinant tissue plasminogen activator within 3 hours of stroke onset. Am J Neuroradiol 2008; 29:1118–1123

Normal symmetric brain perfusion. All color maps are coded red for higher values and blue for

lower values.

PERFUSION CT BRAINHealthy 53-year-old man

Unenhanced CT scan

Perfusion CT cerebral blood volume

Perfusion CT cerebral blood flow

Perfusion CT mean transit time

Perfusion CT maps cerebral blood volume

CBV:Total volume of blood within an imaging voxel including blood in the tissues and blood vessels.CBV is measured in units of milliliters of blood per 100 g of brain.

Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142–153

Perfusion CT cerebral blood flow

CBF:Total volume of blood moving through a voxel in a given unit of time and is commonly measured in units of milliliters of blood per 100 g of brain tissue per minute. After a bolus of contrast material is injected, time is required for each individual molecule of contrast material to circulate.

Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142–153

MTT: Average transit time of all the molecules of contrast medium with the bolus

through a given volume of brain measured in seconds.MTT can be approximated according to the central volume principle:

MTT = CBV / CBF.

Perfusion CT mean transit time

Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142–153

CBF maps show flow reduction in nearly the whole cortical territory of the left MCA.

Temporal (B2), severe; parietal (B1), moderate to severe.

Color code: red, blood vessels; green, normal cortex; blue, normal white matter; violet, low flow area).

61-year-old woman experienced acute right hemiplegia and global aphasia

during coronary angiography.

Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142–153

TTP concentration of contrast enhancement maps show time delay in the cortical territory of the left MCA and artifact in

areas where no peak is discernible.

Color code: blue, segmented blood vessels, normal cortex; dark green, normal white matter; light green, yellow, and

red, low flow area).

61-year-old woman experienced acute right hemiplegia and global aphasia

during coronary angiography.

Hopyan J, Ciarallo A, Dowlatshahi D, et al. Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography. Radiology 2010; 255:142–153

CT PERFUSION PROTOCOLArterial and venous regions of interest (ROIs)

and pre- and postenhancement cutoff values are selected from the perfusion CT source images to generate representative arterial input and venous outflow time-attenuation curves.

The A2 segment of the anterior cerebral artery is commonly used to obtain the arterial input function (AIF) ROI because it travels perpendicular to the axial plane.

Similarly, the superior sagittal sinus can be used to obtain the venous output function (VOF) ROI.

Murayama K, Katada K, Nakane M, et al. Whole brain perfusion CT performed with a prototype 256-detector row CT system: initial experience. Radiology 2009; 250:202–211

Figure 3b.  Perfusion CT software. (a) CT scan with superimposed labels illustrates semiautomatic selection of arterial (ACA or contralateral MCA) and venous ROIs. (b) Graph illustrates time-attenuation curves for arterial (red) and venous (blue) ROIs.

RadioGraphics, http://pubs.rsna.org/doi/abs/10.1148/rg.286085502

Published in: Enrique Marco de Lucas; Elena Sánchez; Agustín Gutiérrez; Andrés González Mandly; Eva Ruiz; Alejandro Fernández Flórez; Javier Izquierdo; Javier Arnáiz; Tatiana Piedra; Natalia Valle; Itziar Bañales; Fernando Quintana; RadioGraphics  2008, 28, 1673-1687.DOI: 10.1148/rg.286085502© RSNA, 2008

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Perfusion CT software : Graph illustrates time-attenuation curves for arterial (red) and venous (blue) ROIs.

Mathematical modeling can be then used to calculate perfusion parameters and generate color coded perfusion maps (deconvolution analysis)

CT PERFUSION INTERPRETATIONAcute Infarction

Areas of decreased CBF and CBV, and increased MTT and TTP.

Matched perfusion abnormalities on CBV and MTT maps correspond to areas of nonsalvageable brain tissue and neuronal death, also known as “core infarct”.

Mismatched areas of prolonged MTT and diminished CBF where CBV is relatively preserved correspond to areas of salvageable tissue, also called “ischemic penumbra”.

Murayama K, Katada K, Nakane M, et al. Whole brain perfusion CT performed with a prototype 256-detector row CT system: initial experience. Radiology 2009; 250:202–211

CT PERFUSION INTERPRETATIONAcute Infarction

Because of compensatory cerebrovascular mechanisms, many patients are able to preserve CBV within an area at risk for ischemic injury shortly after the initial insult.

Patients with areas of CBV-MTT mismatch that are large or that involve eloquent areas of brain may be good candidates for reperfusion therapy.

CBF may also be decreased to a lesser degree within ischemic penumbra.

Murayama K, Katada K, Nakane M, et al. Whole brain perfusion CT performed with a prototype 256-detector row CT system: initial experience. Radiology 2009; 250:202–211

Murayama K, Katada K, Nakane M, et al. Whole brain perfusion CT performed with a prototype 256-detector row CT system: initial experience. Radiology 2009; 250:202–211

Mean transit time reveals prolongation within same region (arrows)

51-year-old man who presented with right facial droop and acute aphasia.

Cerebral blood flow reveals region of decreased perfusion within left

middle cerebral artery (MCA) territory

Cerebral blood volume shows relative symmetric maintenance of

blood volume.

An example of applying the CT protocol to triage patients with acute ischemic stroke for endovascular therapy-mm clot on the coronal ultrathin noncontrasted CT (middle).

Shang T , and Yavagal D R Neurology 2012;79:S86-S94

Copyright © 2012 by AAN Enterprises, Inc.

Acute stroke–induced cytotoxic edema in posterior, anterior and middle cerebral infarction

Any abnormality???

CLINICAL APPLICATION OF DWIMore sensitive for detection of hyperacute ischemiabecomes abnormal within 30 minutesDistinguish b/w old and new strokeDWI should always be used with ADC to assess AGE OF

INFARCT

Pseudo-normalization of DWI in a 2 weeks old posterior infarction normal DWI.On T2WI there is some subtle hyperintensity in the right occipital lobe in the vascular territory of the posterior cerebral artery.The T1WI after the administration of Gadolinium shows gyral enhancement

Time course of an ischemic infarction

large area with restricted diffusion in the territory of the right MCAwith involvement of the basal ganglia.There is a perfect match with the perfusion images, so this patient should not undergo any form of thrombolytic therapy

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Acute stroke (6 hours evolution) in a 46-year-old woman with left hemiplegia

Acute stroke (2 hours evolution) in a 46-year-old man with left hemiparesis.

SUMMARYThe on-call radiologist has a key role in the management of

acute stroke.

A complete CT study (nonenhanced CT, perfusion CT, and CT angiography) may be performed and analyzed rapidly

and easily by general radiologists using a simple standardized protocol.

Hemorrhages should be ruled out at nonenhanced CT, but time should not be lost in puzzling over subtle early

ischemic signs.

Perfusion CT can delineate the salvageable brain tissue (mismatch), and CT angiography helps detect vessel

occlusion and collateral flow.

What do you see here? What do you expect on CTA?

THANK YOU! ?