CT perfusion allows various aspects of cerebral perfusion to be determined. Its primary role in acute stroke is in determining whether brain tissue is hypoperfused and therefore at risk of infarction, or whether it is already irreversibly damaged. It can also make major contributions to diagnosis.
What is the role of CT perfusion in stroke?
CT perfusion in ischemic stroke has become established in most centers with stroke services as an important adjunct, along with CT angiography (CTA), to conventional unenhanced CT brain imaging. It enables differentiation of salvageable ischemic brain tissue (the penumbra) from irrevocably damaged infarcted brain...
Can CT perfusion replace MRI in the hyperacute stroke protocol?
Utilizing CT perfusion in lieu of MRI in the hyperacute stroke protocol may expedite intra-arterial intervention. Keywords: stroke, endovascular revascularization, magnetic resonance imaging, computed tomography perfusion, mechanical thrombectomy
What is a typical CT perfusion protocol for the brain?
Most CT perfusion protocols are centered upon the basal ganglia and supra-ganglionic level. This excludes a large volume of the brain, e.g. the posterior fossa and superior cerebral hemispheres.
What is perfusion CT used to diagnose?
Perfusion CT can also be useful in stroke differential diagnosis by helping distinguish wedge-shaped perfusion deficits caused by arterial occlusive emboli from other flow derangements, such as those caused by seizure, hypoglycemia, or hyperglycemia ( 49 ). CT evaluation of acute ischemic stroke is robust, rapid, and widely available.
Does CT perfusion rule out stroke?
CT perfusion allows various aspects of cerebral perfusion to be determined. Its primary role in acute stroke is in determining whether brain tissue is hypoperfused and therefore at risk of infarction, or whether it is already irreversibly damaged. It can also make major contributions to diagnosis.
What is the purpose of a CT perfusion?
Computed tomography (CT) perfusion imaging shows which areas of the brain are adequately supplied or perfused with blood and provides detailed information on delivery of blood or blood flow to the brain. CT perfusion scanning is a noninvasive medical test that helps physicians diagnose and treat medical conditions.
How is perfusion related to stroke?
Perfusion imaging uses an intravascular tracer and serial imaging to quantify blood flow through the brain parenchyma. In acute ischemic stroke, perfusion imaging may increase diagnostic accuracy, aid treatment target identification, and provide prognostic information about functional outcome.
Why is CT used for stroke?
If it's suspected you're experiencing a stroke, a CT scan is usually able to show whether you have had an ischaemic stroke or a haemorrhagic stroke. It's generally quicker than an MRI scan and can mean you're able to receive appropriate treatment sooner.
What is a CT stroke study?
A CT stroke protocol is obtained in the emergency setting to rapidly diagnose and quantify patients presenting with probable ischemic strokes and to enable appropriate urgent management (e.g. endovascular clot retrieval or intravenous thrombolysis).
What are the clinical indications of brain perfusion imaging?
Commonly accepted clinical indications for brain SPECT include: Dementia (early diagnosis, differentiation from normal ageing, and differential diagnosis of Alzheimer's disease from other neurodegenerative diseases), epilepsy (localization of epileptic focus by ictal and interictal studies), movement disorders, ...
When is CT perfusion indicated?
CT perfusion can be useful in the work-up of patients with acute stroke. The value of the additional diagnostic information gained should, however, be weighed against treatment delays and the added contrast and radiation exposure that are incurred by obtaining a CTP study.
What is the goal in performing perfusion studies for patients with acute stroke?
ADVANCED STROKE IMAGING USING ANGIOGRAPHY AND PERFUSION Angiography in acute stroke aims to provide the location and extent of any potentially treatable thrombus or embolus causing acute arterial occlusion whether this affects intra- or extracranial vessels.
What is contrast used for CT perfusion?
The contrast agent used is the conventional iodinated CT contrast agent; it is preferable to use a contrast agent with a high concentration of iodine (370–400 mg/l), because it gives greater tissue enhancement and can be beneficial in quantifying perfusion[35,41].
Which imaging modality is best for suspected stroke?
Currently in the United States, noncontrast computed tomography (CT) remains the primary imaging modality for the initial evaluation of patients with suspected stroke (Figure 1).
How accurate is CT scan for stroke?
In one large study, among others, that was reviewed for the guideline, stroke was accurately detected 83 percent of the time by MRI versus 26 percent of the time by CT. “Specific types of MRI scans can help reveal how severe some types of stroke are. These scans also may help find lesions early,” Schellinger said.
Why do we use non contrast CT for stroke?
Nonenhanced, or noncontrast, CT is the preferred modality because of its accessibility, speed, and patient tolerance, thereby permitting the rapid triage of patients suspected of having experienced a stroke.
Why are small infarcts poorly visualized on perfusion maps?
Small infarcts (e.g. lacunar infarcts) are poorly visualized on perfusion maps due to their low resolution. In cases of seizures, the ictal region shows hyperperfusion, which may lead to an interpretation of hypoperfusion in the contralateral hemisphere mimicking infarct.
Is MRI more sensitive to stroke?
Although MRI is more sensitive to the early parenchymal changes of infarction (see DWI in acute stroke) its clinical application has been limited by difficulties in accessing MRI in a timely fashion in many institutions; this is especially important in this clinical setting as rapid imaging and treatment are crucial to successful intervention.
Can poor cardiac output cause inaccurate perfusion maps?
In patients with poor cardiac output, atrial fibrillation, severe proximal arterial stenosis or poor placement of arterial and venous density regions of interest, the decreased blood flow can lead to inaccurate perfusion maps and specifically to overestimated MTT (i.e. erroneous diagnosis of extensive ischemia or global hypoperfusion) and underestimated CBF.
What is a CT scan of the head for stroke?
In the National Institute of Neurologic Disorders and Stroke (NINDS) trial [10], patients presenting with acute ischemic stroke underwent a noncontrast computed tomographic (CT) scan of the head to exclude intracranial hemorrhage and evaluate for completed infarctions prior to the administration of IV tPA. Due to its rapidity and widespread availability, this technique has remained the mainstay of the radiographic evaluation of acute ischemic stroke patients. Although very sensitive for the detection of hemorrhage, a noncontrast head CT scan lacks the sensitivity for early detection of ischemic stroke (i.e., within the first 3–4 h after a stroke has occurred).
What is CTP in neurointervention?
CTP is another valuable imaging tool in the growing toolbox of neurointerventionists, providing information on cerebrovascular physiology. By permitting identification and differentiation of penumbra from areas of ischemic core, CTP may be better able to select patients most suitable for endovascular intervention. Our experience with CTP combined with the clinical examination has led to an efficient, effective, and algorithmic model for identifying patients amenable for intervention. Lastly, we have demonstrated its utility in identifying patients at risk for reperfusion hemorrhage, as well as patients likely to achieve favorable outcome.
How long after stroke can you use CT perfusion?
Increasing evidence suggests CT perfusion may help us identify which patients may benefit from intravenous thrombolysis and thrombectomy, even up to 24 hours after stroke onset. In positive trials of mechanical therapy for anterior circulation stroke with large vessel occlusion, there were better outcomes where perfusion imaging was included in the patient selection criteria (SWIFT-PRIME and EXTEND-IA, which used CT perfusion) compared with non-contrast CT alone (REVASCAT and ESCAPE, which used NCCT-ASPECTS). 13 Perhaps the biggest impact will be in patients presenting beyond the conventional time windows. Both the DAWN and DEFUSE-III trials showed that the treatment time window can be extended up to 24 hours in certain patients selected for on the basis of perfusion imaging. Both trials were terminated early and showed improved functional outcomes that amounted to the biggest treatment effects seen among acute stroketherapy trials. These two studies show the advantages of stratifying acute stroke patients in terms of their tissue physiology rather than setting hard time constraints.
What is CT perfusion?
CT perfusion allows various aspects of cerebral perfusion to be determined. Its primary role in acute stroke is in determining whether brain tissue is hypoperfused and therefore at risk of infarction, or whether it is already irreversibly damaged. It can also make major contributions to diagnosis.
What is CT perfusion deficit?
CT perfusion deficits reflect clinical assessments of severity. The volume of severely hypoperfused tissue on CT perfusion closely correlates with the baseline National Institutes of Health Stroke Scale (NIHSS) score 11; the rescue of penumbral tissue (defined by CT perfusion) also correlates highly with improvements in NIHSS. 11 Both larger core and penumbral lesions are associated with poorer long-term outcomes and patients who present with a large established core have higher risks of complications from reperfusion therapy. The progression to infarction in at-risk areas on CT perfusion is strongly associated with worse outcomes and salvage with clinical recovery. 12
What is the purpose of perfusion imaging?
The aim of performing perfusion imaging in the context of cerebral ischaemia is to distinguish likely infarcted and unsalvageable areas of brain (the ischaemic core) from areas of potentially salvageable (penumbral) tissue. It is this viable penumbra that is the target for reperfusion therapy.
How long does CT perfusion last?
Recent clinical trials have shown that CT perfusion can identify those patients who may benefit from reperfusion up to 24 hours, and this is likely to lead to it being used much more widely. Familiarity with the technique is therefore important for a neurologist or stroke physician involved in acute stroke care.
Why is CT perfusion important?
CT perfusion imaging can be performed rapidly at the time of initial imaging and improves diagnostic confidence and accuracy in the patient with hyperacute stroke. It can identify potentially salvageable areas of brain in order to select patients better for reperfusion therapies.
What is non contrast CT?
Traditionally non-contrast CT alone is used in the initial assessment of patients presenting with a clinical diagnosis of acute ischaemic stroke, primarily to exclude haemorrhage and alternative pathology such as tumours.
How to assess accuracy of perfusion imaging?
One way to assess the accuracy of an imaging study such as perfusion imaging is to gauge its ability to predict outcome, with or without subsequent treatment. This outcome may not be actual patient outcome but may be an outcome related to the tissue in question, such as the development of infarction.
What is the role of perfusion imaging in vasospasm?
Perfusion imaging helps to establish the diagnosis of ischemia and differentiate it from other complications that produce neurological deficits , such as recurrent hemorrhage or metabolic disorders. The initial treatment of vasospasm is by medical means, including systemic hypertension, hemodilution, and hypervolemia (“triple-H therapy”). If not successful, endovascular methods may be employed, including intracranial angioplasty and the infusion of vasodilators. It appears that outcomes are improved if these treatments are instituted as early as possible. Perfusion imaging may aid in this early diagnosis and therapeutic intervention. 19,33,34,84–88
How long does a perfusion MR take?
However, many institutions have developed limited, stroke-specific protocols that can be accomplished within 15 to 20 minutes of actual “in-room” time.
What are the two classes of perfusion techniques?
There are 2 major classes of perfusion techniques: those that utilize a diffusible tracer and those that rely on a nondiffusible agent. The physiological principles underlying these 2 classes of techniques and the mathematical models used to attempt quantification of their data are different.
What is a surrogate of clinical brain death determination?
A surrogate of clinical brain death determination is the demonstration of inadequate cerebral perfusion to maintain tissue viability. Perfusion imaging may be of aid in cases in which the clinical determination cannot be made; eg, when an accurate clinical examination is hampered by the presence of hypnotics or sedatives. 94,95
Why is PET scan excluded?
PET scanning is excluded because it is primarily a research tool in academic institutions. Traumatic head injury is included because of its close relationship to ischemic injury, but the use of perfusion imaging in other diseases, such as neoplasms and inflammatory conditions, has not been evaluated.
How many CTP methods are there?
There are 2 methods of CTP, which differ in the amount of brain that can be imaged, the rate and volume of contrast injected, the type of data that are acquired, and the degree of quantification that is possible.
When was CT used for stroke?
The critical role of nonenhanced CT for stroke evaluation began in 1996 , when the U.S. Food and Drug Administration (FDA) approved intravenous tissue plasminogen activator (tPA) for clot thrombolysis ( 2 ).
What is CT imaging?
CT is the primary imaging modality used for selecting appropriate treatment in patients with acute stroke. Awareness of the typical findings, pearls, and pitfalls of CT image interpretation is therefore critical for radiologists, stroke neurologists, and emergency department providers to make accurate and timely decisions regarding both (a) ...
What causes a cell death in a stroke?
In ischemic stroke, arterial occlusion due to embolism or less commonly in situ thrombosis leads to a cascade of cellular events. These events cause local dysfunction and ultimately cell death, leading to development of an infarct core, which is defined as brain tissue likely to die despite immediate reperfusion.
What is the key to interpreting CT perfusion in the setting of acute ischaemic stroke?
The key to interpreting CT perfusion in the setting of acute ischaemic stroke is understanding and identifying the infarct core and the ischaemic penumbra, as a patient with a small core and a large penumbra is most likely to benefit from reperfusion therapies.
Why are small infarcts poorly visualised on perfusion maps?
Small infarcts (e.g. lacunar infarcts) are poorly visualised on perfusion maps due to their low resolution. In cases of seizures, the ictal region shows hyperperfusion, which may lead to an interpretation of hypoperfusion in the contralateral hemisphere mimicking infarct.
Is MRI more sensitive to stroke?
Although MRI is more sensitive to the early parenchymal changes of infarction (see DWI in acute stroke) its clinical application has been limited by difficulties in accessing MRI in a timely fashion in many institutions; this is especially important in this clinical setting as rapid imaging and treatment are crucial to successful intervention.
Can poor cardiac output cause inaccurate perfusion maps?
In patients with poor cardiac output, atrial fibrillation, severe proximal arterial stenosis or poor placement of arterial and venous density regions of interest, the decreased blood flow can lead to inaccurate perfusion maps and specifically to overestimated MTT (i.e. erroneous diagnosis of extensive ischaemia or global hypoperfusion) and underestimated CBF.