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DESCRIPTIONPerfusion imaging using CT (computed tomography) provides an assessment of cerebral blood flow that may assist in the identification of ischemic regions of the brain. This technology is proposed as a method to aid treatment decisions in patients being evaluated for acute ischemic stroke, subarachnoid hemorrhage, cerebral vasospasm, brain tumors, and head trauma.
The goal of acute stroke thrombolytic treatment is to rescue the ischemic penumbra, an area of brain that surrounds the infarct core and is hypoperfused but does not die quickly. Multimodal CT (computed tomography) and magnetic resonance imaging (MRI) can be used to assess the cerebral parenchyma, vasculature, and tissue viability in the acute ischemic stroke setting, and are used to detect ischemic tissue, and exclude hemorrhage and other conditions that mimic acute cerebral ischemia.
The approved therapy, intravenous tissue plasminogen activator (tPA), requires only a non-contrast CT scan to exclude the presence of hemorrhage (a contraindication to the use of the drug). Current guidelines are to administer (tPA) within the first 3 hours after an ischemic event, preceded by a CT scan. Many patients, however, do not present within the 3-hour window, and thrombolysis carries a risk of intracranial hemorrhage. Thus, more sophisticated imaging may be needed to select the proper use of intra-arterial thrombolysis or mechanical thrombectomy in patients who present more than 3 hours after an ischemic stroke. Perfusion imaging is also being evaluated in the management of other neurological conditions such as subarachnoid hemorrhage and head trauma.
The potential utility of perfusion imaging of acute stroke is described as the following:
Additional potential uses of perfusion CT in acute stroke may include the following:
Similar information can be provided by CT and MRI in terms of infarct core and penumbra. However, multimodal CT has a short protocol time (5-6 min), and since it can be performed with any modern CT equipment is more widely available in the emergency setting. CT perfusion is performed by capturing images as an iodinated contrast agent bolus passes through the cerebral circulation and accumulates in the cerebral tissues. (Older perfusion methodologies such as single-photon emission CT and xenon-enhanced CT scanning use a diffusible tracer.) The quantitative perfusion parameters are calculated from density changes for each pixel over time with commercially available deconvolution-based software, where cerebral blood flow is equal to regional cerebral blood volume divided by mean transit time. CT angiography/CT perfusion requires ionizing radiation and iodinated contrast. It is estimated that a typical perfusion CT deposits a slightly greater radiation dose than a routine unenhanced head CT (approximately 3.3 mSv). CT perfusion covers limited areas of the brain. Commonly used 16- to 64-slice CT scanners can detect an area of 2- to 4-cm of brain tissue. Whole-brain CT perfusion can be performed with greater than 128-detector row CT.
On October 8, 2009, the U.S. Food and Drug Administration (FDA) issued an Initial Communication about excess radiation during perfusion CT imaging to aid in the diagnosis and treatment of stroke from one facility. Together with state and local health authorities, the FDA has identified at least 250 patients who were exposed to excess radiation during CT perfusion scans. The FDA has received reports of possible excess exposures at facilities in other states, involving more than one manufacturer of CT scanners. The FDA has provided recommendations for facilities and practitioners, and is continuing to work with manufacturers, professional organizations, and state and local public health authorities to investigate the scope and causes of these excess exposures and their potential public health impact.
Subarachnoid Hemorrhage and Cerebral Vasospasm
Cerebral vasospasm is one of the major causes of morbidity and mortality following aneurysmal subarachnoid hemorrhage (ASAH) in patients who survive the initial hemorrhage and can be seen in about two thirds of patients with ASAH. The typical onset of cerebral vasospasm occurs at 3 to 5 days after hemorrhage, with maximal narrowing on digital subtraction angiography at 5 to 14 days. Currently, the diagnosis of vasospasm and management decisions rely on clinical examination, transcranial Doppler sonography, and digital subtraction angiography. Although symptomatic vasospasm affects 20% to 30% of patients with ASAH, not all patients with angiographic vasospasm manifest clinical symptoms, and the symptoms can be nonspecific. In addition, patients do not always have both clinical and imaging findings of vasospasm. Due to these limitations, more accurate and reliable methods to detect cerebral vasospasm are being investigated. Two methods being evaluated are CTA and CT perfusion.
The current standard for tumor grading is histopathologic assessment of tissue. Limitations of histologic assessment include sampling error due to regional heterogeneity and interobserver variation. These limitations can result in inaccurate classification and grading of gliomas. Because malignant brain tumors are characterized by neovascularity and increased angiogenic activity, perfusion imaging has been proposed as a method to assess tumor grade and prognosis. In addition, perfusion imaging can be repeated and may help to assess the evolution of tumors and the treatment response. Traditionally, perfusion imaging of brain tumors has been performed with MRI, which can estimate tumor blood volume, blood flow, and permeability. More recently, CT perfusion has been investigated for glioma grading. Potential advantages, compared with MR perfusion, include the wider availability, faster scanning times, and lower cost. CT perfusion may also be useful in distinguishing recurrent tumor from radiation necrosis.
Several post-processing software packages (e.g., Siemens’ syngo® Perfusion-CT, GE Healthcare’s CT Perfusion 4, Philips Medical System’s Brain Perfusion Option) have received 510(k) marketing clearance from the FDA for use with a CT system to perform perfusion imaging. The software is being distributed with new CT scanners.
POLICYCT based perfusion imaging of the brain is considered investigational for all indications including the diagnosis and management of acute cerebral ischemia (stroke).
POLICY EXCEPTIONSFederal Employee Program (FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.
Investigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY4/25/2007: Policy Added
7/19/2007: Reviewed and approved by the Medical Policy Advisory Committee (MPAC)
7/22/2008: Policy reviewed, no changes
06/09/2010: Policy description extensively re-written regarding use of CT perfusion imaging and FDA status of devices. Policy statement unchanged. FEP verbiage added to the Policy Exceptions section.
07/29/2011: Policy reviewed; no changes.
01/09/2013: Policy reviewed; no changes.
11/15/2013: Policy reviewed; no changes to policy statement. Added "of the Brain" to the policy title for clarification purposes.
10/08/2014: Policy reviewed; description updated regarding acute stroke, subarachnoid hemorrhage and cerebral vasospasm, and brain tumors. Added "of the brain" to the policy statement for clarification purposes.
SOURCE(S)Blue Cross Blue Shield Association Policy # 6.01.49
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.