Medical Policy

Subject: Cerebral Perfusion Studies using Diffusion and Perfusion Magnetic Resonance Imaging
Document #: RAD.00046 Current Effective Date:    09/27/2017
Status: Reviewed Last Review Date:    08/03/2017


This document addresses diffusion-weighted magnetic resonance imaging (DW-MRI or DWI) and perfusion-weighted magnetic resonance imaging (PW-MRI or PWI).  The scope of this document is limited to the use of DWI and PWI for cerebral disorders.

DWI is a specialized imaging technique that measures and generates contrast magnetic resonance images of the degree of diffusion of water molecules over short distances.  The DWI signal is high (bright) when the apparent diffusion coefficient (ADC) is reduced, as occurs in cytotoxic damage from ischemia, inflammation, trauma, or tumor.  DWI has been reported to be helpful in detecting early cerebral ischemia.  

PWI is often used in conjunction with DWI and is a technique used to assess cerebral blood flow and blood volume in various regions of the brain.  PWI is usually performed by injecting a contrast agent and then obtaining a series of rapid MRI images.  The images track the passage of contrast agent through the brain.

Note: For information regarding cerebral perfusion studies using Computed Tomography (CT), please refer to:

Position Statement

Medically Necessary:

Cerebral perfusion studies using diffusion, or perfusion-weighted MRI, are considered medically necessary for the evaluation of acute cerebral ischemia.

Investigational and Not Medically Necessary:

Cerebral perfusion studies using diffusion, or perfusion-weighted MRI, are considered investigational and not medically necessary for all other indications.


Standard MRI sequences are relatively insensitive to the changes of acute ischemia within the first few hours after onset of stroke.  Several studies have provided data suggesting that diffusion-weighted MRI imaging (DWI) allows for the early detection of ischemic lesion size, site, and age.  It can detect relatively small cortical or subcortical lesions that are often poorly visualized with standard CT scans.  The Stroke Council of the American Heart Association (AHA) concluded that DWI has a high sensitivity (88% to 100%) and specificity (95% to 100%) for detecting acute ischemia.  Also, the lesion volumes correlate well with stroke severity, as rated by clinical scales and outcomes (Adams, 2007, Adams, 2005; Adams, 2003).  The AHA Council on Cardiovascular Radiology concluded that DWI and perfusion-weighted MRI imaging (PWI) are techniques that have been proven capable of demonstrating severely ischemic tissue in the acute stroke patient (Latchaw, 2003).  The AHA Scientific Statement on Imaging of Acute Ischemic Stroke states that MR-DWI surpasses nonenhanced CT and other MR sequences in detecting acute ischemia.  The MR sequences accompanying DWI are more sensitive than CT for eliminating some mimics of acute cerebral ischemia.  The authors recommend that for "patients beyond three hours from onset of symptoms, either diffusion-weighted MRI or source imaging CTA should be performed along with vascular imaging and perfusion studies, particularly if mechanical thrombectomy or intra-arterial thrombolytic therapy is contemplated" (Latchaw, 2009). 

A report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology, originally published in 2010 and reaffirmed in 2016, evaluated the evidence for the use of MR-DWI and MR PWI in the diagnosis of individuals with acute ischemic stroke.  A systematic review of the literature from 1966 to January 2008 was carried out to explore the diagnostic and prognostic value of DW and PW-MRI.  The following recommendations and conclusions related to DW-MRI were provided.

DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset. DWI should be performed for the most accurate diagnosis of acute ischemic stroke (Level A); however, the sensitivity of DWI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. The diagnostic accuracy of DWI in evaluating cerebral hemorrhage is outside the scope of this guideline. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C). Baseline DWI lesion volumes probably predict (final) infarct volumes (Level B) and possibly predict early and late clinical outcome measures (Level C). Baseline PWI volumes predict to a lesser degree the baseline stroke severity compared with DWI (Level C). There is insufficient evidence to support or refute the value of PWI in diagnosing acute ischemic stroke (Level U) (Schellinger, 2010).

While there is general agreement that DWI and PWI can be helpful as diagnostic tools, there is limited peer-reviewed, published data on how these modalities affect treatment decisions.  Nonetheless, physicians in primary and tertiary care facilities are currently utilizing diffusion and perfusion MRI in the evaluation of acute cerebral ischemia.  The strong evidence that the technology is highly sensitive for detecting acute ischemia, coupled with its adoption in clinical practice, supports the position that diffusion and perfusion MRI may be medically necessary for the evaluation of acute cerebral ischemia.  At the present time, there is no compelling evidence to suggest the ability of DWI and PWI to provide accurate information on the status of vascular reserves in individuals with chronic ischemia or in individuals with vasospasm.


DWI and PWI are techniques utilizing magnetic resonance that were developed in the 1980s and have been studied as tools to aid in the diagnosis of cerebral ischemia.  The need for the development of these new imaging techniques has arisen out of the persistent diagnostic challenge, posed by both acute and chronic cerebral ischemia.  Non-contrast computed tomography (NCCT), for example, is highly sensitive in the detection of acute intracranial hemorrhage, but is much less sensitive in the identification of ischemic brain lesions within the first few hours of stroke onset.  Chronic, progressive occlusive disease and ischemia from vasospasm are also conditions that have been difficult to diagnose with current imaging techniques. 

It has been shown that the use of DWI and PWI imaging together can provide information about the location and extent of brain infarction within minutes of onset.  When performed in series, this imaging can also provide information about the pattern of evolution of the ischemic lesion, which may be helpful in determining treatment management options (Roldan-Valdez, 2014).


Acute cerebral ischemia: A sudden neurological affliction (injury) resulting from compromise of the cerebral blood flow/supply to brain tissue. This condition will result in reversible/transitory or irreversible neurological deficits, based on the etiology and duration of circulatory compromise.

Cerebral (Ischemic) Infarction: An area of coagulation necrosis in brain tissue, (i.e., tissue death), due to local anemia resulting from obstruction of the circulation to the area.

Diffusion-weighted MRI imaging (DWI): An MRI imaging technique in which the images reflect microscopic random motion of water molecules; water molecule protons, known as the apparent diffusion coefficient (ADC) are measured and captured by this type of imaging.

Perfusion-weighted MRI imaging (PWI): An MRI imaging technique in which hemodynamically weighted MR sequences are based on the passage of contrast material through brain tissue. The signal intensity declines as the contrast material passes through the infarcted area and returns to normal as it exits this area. A curve is derived from this tracing data, which represents and estimates the cerebral blood volume.

Stroke: A generic term used to represent any one or all of a group of disorders, including cerebral infarction, intracerebral hemorrhage, or subarachnoid hemorrhage; stroke is characterized by a non-convulsive, focal, neurologic deficit that lasts greater than 24 hours in duration.


The following codes for treatments and procedures applicable to this document are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services may be Medically Necessary when criteria are met:

76498 Unlisted magnetic resonance procedure (eg, diagnostic, interventional) [when specified as cerebral perfusion MRI studies]
ICD-10 Diagnosis  
G45.0-G45.9 Transient cerebral ischemic attacks and related syndromes
I63.00-I63.9 Cerebral infarction
I67.81 Acute cerebrovascular insufficiency
I67.9 Cerebrovascular disease, unspecified

When services are Investigational and Not Medically Necessary:
When criteria are not met or for all other diagnoses not listed, or when the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary.


Peer Reviewed Publications:

  1. Barboriak DP. Imaging of brain tumors with diffusion-weighted and diffusion tensor MR imaging. Magn Reson Imaging Clin N Am. 2003; 11(3):379-401. 
  2. Beauchamp NJ Jr, Barker PB, Wang PY, vanZijl PC. Imaging of acute cerebral ischemia. Radiology. 1999; 212(2):307-324.
  3. Eastwood JD, Lev MH, Wintermark M, et al. Correlation of early dynamic CT perfusion imaging with whole-brain MR diffusion and perfusion imaging in acute hemispheric stroke. AJNR Am J Neuroradiol. 2003; 24(9):1869-1875.
  4. Fiehler J, Fiebach J, Gass A, et al. Diffusion-weighted imaging in acute stroke- a tool of uncertain value? Cerebrovasc Dis. 2002; 14(3-4):187-196. 
  5. Higashida RT, Furlan AJ, Roberts H, et al.; Technology Assessment Committee of the American Society of Interventional and Therapeutic Neuroradiology, Technology Assessment Committee of the American Society of Interventional Radiology and Therapeutic Neuroradiology; Technology Assessment Committee of the Society of Interventional Radiology. Trial design and reporting standards for intra-arterial cerebral thrombolysis for acute ischemic stroke. Stroke. 2003; 34(8):e109-137. Erratum in:  Stroke. 2003; 34(11):2774.
  6. Huisman TA. Diffusion-weighted imaging: basic concepts and application in cerebral stroke and head trauma. Eur Radiol. 2003; 13(10):2283-2297.
  7. Mukherji SK, Chenevert TL, Castillo M. Diffusion-weighted magnetic resonance imaging. J Neuroophthalmol. 2002; 22(2):118-122.
  8. Parsons MW, Barber PA, Chalk J, et al. Diffusion- and perfusion-weighted MRI response to thrombolysis in stroke. Ann Neurol. 2002; 51(1):28-37.
  9. Roldan-Valadez E, Lopez-Mejia M. Current concepts on magnetic resonance imaging (MRI) perfusion-diffusion assessment in acute ischaemic stroke: a review & an update for the clinicians. Indian J Med Res. 2014; 140(6):717-728.
  10. Schellinger PD, Jansen O, Fiebach JB, et al. Monitoring intravenous recombinant tissue plasminogen activator thrombolysis for acute ischemic stroke with diffusion and perfusion MRI. Stroke. 2000; 31(6):1318-1328.
  11. Schramm P, Schellinger PD, Klotz E, et al. Comparison of perfusion computed tomography and computed tomography angiography source images with perfusion-weighted imaging and diffusion weighted imaging in patients with acute stroke of less than 6 hours duration. Stroke. 2004; 35(7):1652-1658.

Government Agency, Medical Society, and Other Authoritative Publications:

  1. Adams HP, del Zoppo G, Alberts MJ, et al. Guidelines for the early management of adults with ischemic stroke: a guideline from the American Heart Association/American Stroke Association Stroke Council, Clinical Cardiology Council, Cardiovascular Radiology and Intervention Council, and the Atherosclerotic Peripheral Vascular Disease and Quality of Care Outcomes in Research Interdisciplinary Working Groups. Stroke. 2007; 38(5):1655-1711.
  2. American College of Radiology. ACR Appropriateness Criteria. Cerebrovascular Disease (2016). Available at: . Accessed on July 10, 2017.
  3. Centers for Medicare and Medicaid Services. National Coverage Determination: Magnetic Resonance Imaging (MRI). NCD #220.2. Effective March 22, 1994. Available at: Accessed on July 10, 2017
  4. Latchaw RE, Alberts MJ, Lev MH, et al. Recommendations for imaging of acute ischemic stroke: a scientific statement from the American Heart Association. 2009; 40(11):3646-3678.
  5. National Quality Measures Clearinghouse (NQMC). Measure summary: Stroke and stroke rehabilitation: percentage of final reports for CT or MRI studies of the brain performed either in the hospital within 24 hours of arrival or in an outpatient imaging center to confirm initial diagnosis of ischemic stroke, TIA, or intracranial hemorrhage. In: National Quality Measures Clearinghouse (NQMC) [Web site]. Rockville (MD): Agency for Healthcare Research and Quality (AHRQ); 2010. Available at: . Accessed on July 10, 2017.
  6. Schellinger PD, Bryan RN, Caplan LR, et al. Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology. 2010; 75(2):177-185.

Cerebral Perfusion
Diffusion/Perfusion Magnetic Resonance Imaging (MRI)

Document History
Status Date Action
Reviewed 08/03/2017 Medical Policy & Technology Assessment Committee (MPTAC) review. Updated the Rationale, References and History sections.
Reviewed 08/04/2016 MPTAC review. Updated the Description/Scope, Background/Overview, References, History and Index sections of the document. Removed Websites for Additional Information section. Removed ICD-9 codes from Coding section.
Reviewed 08/06/2015 MPTAC review. Updated, References and History sections of the document
Reviewed 08/14/2014 MPTAC review. Updated Description/Scope, Review date, References and History sections of the document.
Reviewed 08/08/2013 MPTAC review.  Updated Review date, References and History sections of the document.
Reviewed 08/09/2012 MPTAC review.  Updated Review date, References and History sections of the document.
Reviewed 08/18/2011 MPTAC review.  Updated Review date, References and History sections of the document.
Reviewed 08/19/2010 MPTAC review.  Updated Review date, Rationale, References and History sections of the document.
Reviewed 08/27/2009 MPTAC review.  Updated review date, references and history sections.
Reviewed 08/28/2008 MPTAC review.  Updated review date, references and history sections of document.
  02/21/2008 The phrase "investigational/not medically necessary" was clarified to read "investigational and not medically necessary." This change was approved at the November 29, MPTAC meeting.
Reviewed 08/23/2007 MPTAC review.  Updated review date, references and history sections of document.
Reviewed 09/14/2006 MPTAC review.  No change to stance.  References were updated.
  11/21/2005 Added reference for Centers for Medicare and Medicaid Services (CMS) – National Coverage Determination (NCD).
Revised 09/22/2005 MPTAC review.  Revision based on Pre-merger Anthem and Pre-merger WellPoint Harmonization. 
Pre-Merger Organizations

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Anthem, Inc.


  No prior document
WellPoint Health Networks, Inc.


4.03.06 Cerebral Perfusion Studies Using Diffusion and Perfusion Magnetic Resonance Imaging