CT Perfusion in Acute Stroke

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Acute stroke protocol

A protocol for the imaging of acute stroke should address the central questions necessary to triage patients appropriately (see Box 2). The acute stroke protocol used at our institution has three components: unenhanced CT, arch-to-vertex CTA, and dynamic first-pass cine CTP. A similar CTA/CTP protocol, or its equivalent, could be applied using any commercially available multidetector-row helical CT scanner with only minor variations.

The role of unenhanced CT in stroke triage is principally to

Quantitation and resolution

Although CTP and MR-PWI both attempt to evaluate the intricacies of capillary level hemodynamics, the differences in technique create several important distinctions that should be considered (Fig. 1). Although dynamic susceptibility contrast (DSC) MR-PWI techniques rely on the indirect T2* effect induced in adjacent tissues by high concentrations of intravenous gadolinium, CTP relies on direct visualization of the contrast material. The linear relation between contrast concentration and

CT perfusion: general principles

Perfusion-weighted CT and MR imaging techniques—as opposed to those of MR angiography and CTA, which detect bulk vessel flow—are sensitive to capillary tissue level blood flow [70]. This evaluation of capillary level hemodynamics extends the traditional anatomic role of imaging to provide insight into the delivery of blood to brain parenchyma. The idea of contrast-enhanced CTP imaging emerged as early as 1976, when a computerized subtraction technique was used to measure relative cerebral blood

CT perfusion theory and modeling

Although easy to define in theory, the perfusion parameters of CBV, CBF, and MTT can be difficult to quantify in practice. The dynamic first-pass approach to CTP measurement involves the dynamic intravenous administration of an intravascular contrast agent, which is tracked with serial imaging during its first-pass circulation through the brain tissue capillary bed. Depending on the assumptions regarding the arterial inflow and the venous outflow of the tracer, the perfusion parameters of CBV,

CT perfusion postprocessing

In urgent clinical cases, perfusion changes can often be observed immediately after scanning by direct visual inspection of the axial source images at the CT scanner console. Soft copy review at a workstation using movie or cine mode can reveal relative perfusion changes over time, although advanced postprocessing is required to appreciate subtle changes and to obtain quantification. Axial source images acquired from a cine CTP study are networked to a freestanding workstation for detailed

Clinical applications of CT perfusion

Indications (and potential indications) for advanced functional imaging of stroke in the first 12 hours include the following: (1) exclusion of patients most likely to hemorrhage and inclusion of patients most likely to benefit from thrombolysis; (2) extension of the time window beyond 3 hours for intravenous and 6 hours for anterior circulation intra-arterial thrombolysis; (3) triage to other available therapies, such as hypertension or hyperoxia administration; (4) disposition decisions

CT perfusion interpretation: infarct detection

A number of groups have suggested that CTA source images, such as DWI, can sensitively detect tissue destined to infarct despite successful recanalization (Fig. 3) [29], [93], [94]. Theoretic modeling indicates that CTA-SI, assuming an approximately steady state of contrast in the brain arteries and parenchyma during image acquisition, are predominantly blood volume weighted rather than blood flow weighted, although this has yet to be validated empirically in a large series [20], [43], [44],

CT perfusion interpretation: ischemic penumbra and infarct core

An important goal of advanced stroke imaging is to provide an assessment of ischemic tissue viability that transcends an arbitrary clock-time [103], [104], [105]. The original theory of penumbra stems from experimental studies in which two thresholds were characterized [106]. One threshold identified a CBF value below which there was cessation of cortical function, without increase in extracellular potassium or reduction in pH. A second lower threshold identified a CBF value below which there

Imaging predictors of clinical outcome

Predicting outcome is perilous. The penumbra is dynamic, and several factors influence its fate, including time after ictus, residual and collateral blood flow, admission glucose, temperature, hematocrit, systolic blood pressure, and treatment (including hyperoxia) [121]. As already mentioned, CTA/CTP has the potential to serve as a surrogate marker of stroke severity, likely exceeding the NIHSS score or ASPECTS as a predictor of outcome [24], [25], [26], [27], [28], [29], [30], [31], [32].

Experimental applications of CT perfusion in stroke

The additional information about capillary level hemodynamics afforded by CTP could be particularly important in future clinical trials of acute stroke therapy, in which CTP could refine the selection of subjects to include only those patients most likely to benefit from treatment; this imaging-guided patient selection may help to demonstrate beneficial effects that would be obscured if patients without salvageable tissue were included. CTA combined with CTP could be used to identify patients

Summary

As new treatments are developed for stroke, the potential clinical applications of CTP imaging in the diagnosis, triage, and therapeutic monitoring of these diseases are certain to increase.

Technical advances in scanner hardware and software should no doubt continue to increase the speed, coverage, and resolution of CTP imaging. CTP offers the promise of efficient use of imaging resources and, potentially, of decreased morbidity. Most importantly, current CT technology already permits the

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References (135)

  • Tissue plasminogen activator for acute ischemic stroke. The National Institute of Neurological Disorders and Stroke rt-PA Stroke Study Group

    N Engl J Med

    (1995)
  • A. Furlan et al.

    Intra-arterial prourokinase for acute ischemic stroke

    JAMA

    (1999)
  • J.R. Marler et al.

    Early stroke treatment associated with better outcome: the NINDS rt-PA stroke study

    Neurology

    (2000)
  • G.J. del Zoppo et al.

    Recombinant tissue plasminogen activator in acute thrombotic and embolic stroke

    Ann Neurol

    (1992)
  • W. Hacke et al.

    Intravenous thrombolysis with recombinant tissue plasminogen activator for acute hemispheric stroke. The European Cooperative Acute Stroke Study (ECASS)

    JAMA

    (1995)
  • K.P. Madden et al.

    Accuracy of initial stroke subtype diagnosis in the TOAST study. Trial of ORG 10172 in Acute Stroke Treatment

    Neurology

    (1995)
  • M.A. Ezzeddine et al.

    CT angiography with whole brain perfused blood volume imaging: added clinical value in the assessment of acute stroke

    Stroke

    (2002)
  • N. Dubey et al.

    Early computed tomography hypodensity predicts hemorrhage after intravenous tissue plasminogen activator in acute ischemic stroke

    J Neuroimaging

    (2001)
  • M.H. Lev et al.

    Computed tomographic angiography and computed tomographic perfusion imaging of hyperacute stroke

    Top Magn Reson Imaging

    (2000)
  • J. Wardlaw et al.

    Can stroke physicians and neuroradiologists identify signs of early cerebral infarction on CT?

    J Neurol Neurosurg Psychiatry

    (1999)
  • M.H. Lev et al.

    CT angiography in the rapid triage of patients with hyperacute stroke to intraarterial thrombolysis: accuracy in the detection of large vessel thrombus

    J Comput Assist Tomogr

    (2001)
  • S. Wildermuth et al.

    Role of CT angiography in patient selection for thrombolytic therapy in acute hemispheric stroke

    Stroke

    (1998)
  • M. Knauth et al.

    Potential of CT angiography in acute ischemic stroke [see comments]

    AJNR Am J Neuroradiol

    (1997)
  • P.D. Schellinger et al.

    Imaging-based decision making in thrombolytic therapy for ischemic stroke: present status

    Stroke

    (2003)
  • S. Warach

    Tissue viability thresholds in acute stroke: the 4-factor model

    Stroke

    (2001)
  • H.C. Roberts et al.

    CT perfusion flow assessment: “up and coming” or “off and running”?

    AJNR Am J Neuroradiol

    (2001)
  • L.M. Hamberg et al.

    Quantitative high resolution measurement of cerebrovascular physiology with slip-ring CT

    AJNR Am J Neuroradiol

    (1996)
  • L.M. Hamberg et al.

    Measurement of cerebral blood volume with subtraction three-dimensional functional CT

    AJNR Am J Neuroradiol

    (1996)
  • S.H. Fox et al.

    Future directions in CT technology

    Neuroimaging Clin N Am

    (1998)
  • W.S. Smith et al.

    Safety and feasibility of a CT protocol for acute stroke: combined CT, CT angiography, and CT perfusion imaging in 53 consecutive patients

    AJNR Am J Neuroradiol

    (2003)
  • G.W. Albers

    Expanding the window for thrombolytic therapy in acute stroke. The potential role of acute MRI for patient selection

    Stroke

    (1999)
  • J.P. Broderick et al.

    Finding the most powerful measures of the effectiveness of tissue plasminogen activator in the NINDS tPA stroke trial

    Stroke

    (2000)
  • P.D. Schellinger et al.

    Monitoring intravenous recombinant tissue plasminogen activator thrombolysis for acute ischemic stroke with diffusion and perfusion MRI

    Stroke

    (2000)
  • D. Tong et al.

    Correlation of perfusion- and diffusion weighted MRI with NIHSS score in acute (<6.5 hour) ischemic stroke

    Neurology

    (1998)
  • T. Berzin et al.

    CT perfusion imaging versus MR diffusion weighted imaging: prediction of final infarct size in hyperacute stroke [abstract]

    Stroke

    (2001)
  • S. Warach

    New imaging strategies for patient selection for thrombolytic and neuroprotective therapies

    Neurology

    (2001)
  • R. von Kummer et al.

    Interobserver agreement in assessing early CT signs of middle cerebral artery infarction

    AJNR Am J Neuroradiol

    (1996)
  • J.C. Grotta et al.

    Agreement and variability in the interpretation of early CT changes in stroke patients qualifying for intravenous rtPA therapy [see comments]

    Stroke

    (1999)
  • W.J. Koroshetz et al.

    Imaging stroke in progress: magnetic resonance advances but computed tomography is poised for counterattack

    Ann Neurol

    (1999)
  • W.J. Koroshetz et al.

    Contrast computed tomography scan in acute stroke: “you can't always get what you want but you get what you need”

    Ann Neurol

    (2002)
  • M.H. Lev

    CT versus MR for acute stroke imaging: is the “obvious” choice necessarily the correct one?

    AJNR Am J Neuroradiol

    (2003)
  • M.H. Lev et al.

    CT or MRI for imaging patients with acute stroke: visualization of “tissue at risk”?

    Stroke

    (2002)
  • R. von Kummer et al.

    Acute stroke: usefulness of early CT findings before thrombolytic therapy [see comments]

    Radiology

    (1997)
  • R. von Kummer

    Early major ischemic changes on computed tomography should preclude use of tissue plasminogen activator

    Stroke

    (2003)
  • M. Fiorelli et al.

    Early ischemic changes on computed tomography in patients with acute stroke

    JAMA

    (2002)
  • M.E. Mullins et al.

    Influence of availability of clinical history on detection of early stroke using unenhanced CT and diffusion-weighted MR imaging

    AJR Am J Roentgenol

    (2002)
  • M. Lev et al.

    Acute stroke: improved nonenhanced CT detection—benefits of soft-copy interpretation by using variable window width and center level settings

    Radiology

    (1999)
  • L. Axel

    Cerebral blood flow determination by rapid-sequence computed tomography

    Radiology

    (1980)
  • G.J. Hunter et al.

    Assessment of cerebral perfusion and arterial anatomy in hyperacute stroke with three-dimensional functional CT: early clinical results

    AJNR Am J Neuroradiol

    (1998)
  • K.T. Bae et al.

    Multiphasic injection method for uniform prolonged vascular enhancement at CT angiography: pharmacokinetic analysis and experimental porcine model

    Radiology

    (2000)
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