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Cerebrovascular or Carotid Ultrasound

Cerebrovascular CPT Codes and the Medicare ICD9 Codes that Support Indications and  Medical Necessity for a Carotid Ultrasound in Florida

Non-invasive tests for cerebrovascular arterial function document the nature, location, extent and severity of disease in extracranial and intracranial vessels including the carotid and vertebral arteries.

Non-invasive extracranial arterial studies involve the use of direct and occasionally indirect methods of ultrasound. The direct tests examine the anatomy and physiology of the carotid artery, while the indirect tests examine hemodynamic changes in the distal beds of the carotid artery (the orbital and cerebral circulations). It is important to note that the names of these tests are not standardized. Examples of acceptable tests include:

Direct Tests:

· Carotid Phonoangiography

· Direct Bruit Analysis

· Spectral Bruit Analysis

· Doppler Flow Velocity

· Ultrasound Imaging including Real Time

· B-Scan and Doppler Devices

Indirect Tests:

· Periorbital directional Doppler ultrasonography

· Oculoplethysmography

· Ophthalmodynamometry

Doppler ultrasonography is used to evaluate hemodynamic parameters, specifically the velocity of blood flow and the pattern or characteristics of flow. The doppler ultrasound involves the evaluation of the supraorbital, common carotid, external carotid, internal carotid, and the vertebral arteries in the extracranial cerebrovascular assessment.

The second key component of vascular diagnostic ultrasound is the B-mode, or brightness-mode image. This real time imaging technique provides a two-dimensional gray-scale image of the soft tissues and vessels based on the acoustic properties of the tissues.

Duplex ultrasonography combines the direct visualization capabilities of B-mode ultrasonography and the blood-flow velocity measurements of doppler ultrasonography.

Definitions:

-A physiologic study implies functional measurement procedures including Doppler ultrasound studies, blood pressure measurements, transcutaneous oxygen tension measurements or plethysmograhy. A complete study includes pressure measurements and an additional physiologic technique (eg, Doppler waveforms or plethysmography).

-Plethysmography implies volume measurement procedures including air, impedance, or strain gauge methods.

-A duplex scan implies an ultrasonic scanning procedure with display of both two-dimensional structure and motion with time and Doppler ultrasonic signal documentation with spectral analysis and/or color flow velocity mapping or imaging.

Indications

FCSO Medicare will consider non-invasive extracranial arterial studies medically reasonable and necessary under the following circumstances:

· To initially evaluate a patient presenting with an asymptomatic carotid bruit identified on physical examination. However, repeatedly using this test for a patient with an asymptomatic carotid bruit with no evidence of carotid stenosis is routine monitoring. As such, it is considered screening and is noncovered.

· To evaluate a symptomatic patient with a carotid bruit(s).

· To monitor a patient with known carotid stenosis. Patients demonstrating a diameter reduction of 30-50% are normally followed on an annual basis, whereas patients with a diameter reduction of greater than 50% are normally followed every six months. It is not necessary to monitor patients with a diameter reduction of less than 30%.

· To initially evaluate a patient who has had a recent stroke (recent is defined as less than six months) to determine the cause of the stroke.

· To evaluate a patient with focal cerebral or ocular transient ischemic symptoms (including, but not limited to, localizing symptoms, weakness of one side of the face, slurred speech, weakness of limb, ocular microembolism, arterial occlusions on retinal examination (branch or central), ischemic optic neuropathy, suspected dural or carotid cavernous fistulae). Ocular transient ischemic attacks are defined as retinal or visual field deficits and not temporarily blurred vision.

· To evaluate a patient with syncope that is strongly suggestive of vertebrobasilar or bilateral carotid artery disease in etiology, as suggested by medical history.

· To evaluate a patient with retinal arterial emboli (Hollenhorst plaques)

· To evaluate a patient with transient monocular blindness (amaurosis fugax).

· To evaluate a patient with signs/symptoms of subclavian steal syndrome. The symptoms usually associated with subclavian steal syndrome are a bruit in the supraclavicular fossa, unequal radial pulses, arm claudication following minimal exercise, and a difference of 20mmHg or more between the systolic blood pressures in the arms.

· To evaluate a patient with proven carotid disease on medical management in whom cerebrovascular symptoms become recurrent.

· To evaluate a patient presenting with an injury to the carotid artery or blunt neck trauma.

· To evaluate a patient with vasculitis involving the extracranial carotid arteries.

· To evaluate a patient with a suspected aneurysm of the carotid artery. This is suspected in patients with swelling of the neck particularly if occurring post carotid endarterectomy.

· To evaluate a patient with suspected dissection.

· To evaluate pulsatile neck masses.

· To monitor patients who are post carotid endarterectomy. These patients are normally followed with duplex ultrasonography on the affected side at 6 weeks, 6 months, 1 year, and annually thereafter.

· To preoperatively validate the degree of carotid stenosis of a patient whose previous duplex scan revealed a greater than 70% diameter reduction. The duplex is only covered when the surgeon questions the validity of the previous study and the repeat test is being performed in lieu of a carotid arteriogram.

· Preoperative evaluation of patients scheduled for major cardiovascular surgical procedures when there is evidence of systemic atherosclerosis.

Non-invasive vascular studies are medically necessary only if the outcome will potentially impact the clinical management of the patient. Services are deemed medically necessary when all of the following conditions are met:

1) Significant signs/symptoms of ischemia are present;

2) The information is necessary for appropriate medical and/or surgical management; and

3) The test is not redundant of other diagnostic procedures that must be performed.

Limitations:

  • Dizziness is not a typical indication unless associated with other localizing signs or symptoms. However, episodic dizziness with symptom characteristics typical of transient ischemic attacks may indicate medical necessity, especially when other more common sources (eg, postural hypotension, arrhythmia or transiently decreased cardiac output as demonstrated by cardiac events monitoring) have been previously excluded.
  • When reporting syncope as an indication for this service, it is necessary to document that other, more common causes have been ruled out.
  • When an uninterpretable study results in performing another type of study, only the successful study should be billed.
  • Non-invasive studies are reasonable and necessary only if the outcome will potentially impact the clinical course of the patient. For example, the studies are unnecessary when the patient is (or is not) proceeding on to other diagnostic and/or therapeutic procedures regardless of the outcome of the non-invasive studies. If it is obvious from the findings of the history and physical examination that the patient is going to proceed to angiography, then non-invasive vascular studies are not medically necessary.
  • Performance of both non-invasive extracranial arterial studies (CPT codes 93880 or 93881) and non-invasive evaluation of extremity veins (CPT codes 93965, 93970 or 93971) during the same encounter is not appropriate as a general practice or standing protocol, and therefore, would not generally be expected (American College of Radiology, 2010). Consequently, documentation must clearly support the medical necessity if both procedures are performed during the same encounter, and be available to Medicare upon request.

Methods Not Acceptable For Reimbursement:

· Pulse delay oculoplethysmography

· Carotid phonoangiography and other forms of bruit analysis are covered services, but are included in the reimbursement for the office visit

· Periorbital photoplethysmography

· Thermography

· Light reflection rheography

· Photoelectric plethysmograph,

· Mechanical oscillometry

· Inductance plethysmography

· Capitance plethysmography

The use of a simple hand-held or other Doppler device that does not produce hard copy output, or that produces a record that does not permit analysis of bidirectional vascular flow, is considered part of the physical examination of the vascular system and is not separately reported (CPT 2010). The appropriate assignment of a specific ultrasound CPT code is not solely determined by the weight, size, or portability of the equipment, but rather by the extent, quality, and documentation of the procedure. If an examination is performed with hand-carried equipment, the quality of the exam, printout, and report must be in keeping with accepted national standards. Since, the standard for the above indications is a color-duplex scan, portable equipment must be able to produce combined anatomic and spectral flow measurements.

TRAINING REQUIREMENTS:

The accuracy of non-invasive vascular diagnostic studies depends on the knowledge, skill and experience of the technologist and the physician performing the interpretation of the study. Consequently, the technologist and the physician must maintain proof of training and experience.

All non-invasive vascular diagnostic studies must be: (1) performed by a qualified physician, or (2) performed under the general supervision of a qualified physician by a technologist who has demonstrated minimum entry level competency by being credentialed in vascular technology, and/or (3) performed in a laboratory accredited in vascular technology.

A qualified physician for this service is defined as follows: 1) A physician who has staff privileges to interpret vascular laboratory studies in a hospital that participates in the Medicare program in the state of Florida and the U.S. territories of Puerto Rico and the U.S. Virgin Islands (as applicable) or; 2) A physician who works in a certified vascular laboratory or; 3) A physician who has the RVT or the RPVI (Registered Physician in Vascular interpretation – provided by the ARDMS) certificate or ASN: Neuroimaging Subspecialty Certification; 4) Physicians who are not covered by one of these criteria will have until 2008 to comply.

Examples of certification in vascular technology for non-physician personnel include:

· Registered Vascular Technologist (RVT) credential

· Registered Vascular Specialist (RVS) credential

· Registered Technologist in Vascular Sonography (R.T. (VS))

These credentials must be provided by nationally recognized credentialing organizations such as:

· The American Registry of Diagnostic Medical Sonographers (ARDMS) which provides RDMS and RVT credentials

· The Cardiovascular Credentialing International (CCI) which provides RVS credential

· The American Registry of Radiologic Technologists (ARRT)

Appropriate nationally recognized laboratory accreditation bodies include:

· Intersocietal Commission for the Accreditation of Vascular Laboratories (ICAVL)

· American College of Radiology (ACR)

General Supervision means the procedure is furnished under the physician’s overall direction and control, but the physician’s presence is not required during the performance of the procedure. Under general supervision, the training of the nonphysician personnel who actually performs the diagnostic procedure and the maintenance of the necessary equipment and supplies are the continuing responsibility of the physician.

 

Coding Information

Bill Type Codes

Contractors may specify Bill Types to help providers identify those Bill Types typically used to report this service. Absence of a Bill Type does not guarantee that the policy does not apply to that Bill Type. Complete absence of all Bill Types indicates that coverage is not influenced by Bill Type and the policy should be assumed to apply equally to all claims.

 

Code Description 999x Not Applicable

Revenue Codes

Contractors may specify Revenue Codes to help providers identify those Revenue Codes typically used to report this service. In most instances Revenue Codes are purely advisory; unless specified in the policy services reported under other Revenue Codes are equally subject to this coverage determination. Complete absence of all Revenue Codes indicates that coverage is not influenced by Revenue Code and the policy should be assumed to apply equally to all Revenue Codes.
Code Description 99999 Not Applicable

CPT/HCPCS Codes

Code Description 93880 DUPLEX SCAN OF EXTRACRANIAL ARTERIES; COMPLETE BILATERAL STUDY 93882 DUPLEX SCAN OF EXTRACRANIAL ARTERIES; UNILATERAL OR LIMITED STUDY

 

ICD-9 Codes that Support Medical Necessity

362.30 RETINAL VASCULAR OCCLUSION UNSPECIFIED
362.31 CENTRAL RETINAL ARTERY OCCLUSION
362.32 RETINAL ARTERIAL BRANCH OCCLUSION
362.33 PARTIAL RETINAL ARTERIAL OCCLUSION
362.34 TRANSIENT RETINAL ARTERIAL OCCLUSION
362.35 CENTRAL RETINAL VEIN OCCLUSION
362.36 VENOUS TRIBUTARY (BRANCH) OCCLUSION OF RETINA
362.37 VENOUS ENGORGEMENT OF RETINA
368.11 SUDDEN VISUAL LOSS
368.12 TRANSIENT VISUAL LOSS
433.10 OCCLUSION AND STENOSIS OF CAROTID ARTERY WITHOUT CEREBRAL INFARCTION
433.11 OCCLUSION AND STENOSIS OF CAROTID ARTERY WITH CEREBRAL INFARCTION
433.30 OCCLUSION AND STENOSIS OF MULTIPLE AND BILATERAL PRECEREBRAL ARTERIES WITHOUT CEREBRAL INFARCTION
433.31 OCCLUSION AND STENOSIS OF MULTIPLE AND BILATERAL PRECEREBRAL ARTERIES WITH CEREBRAL INFARCTION
434.00 CEREBRAL THROMBOSIS WITHOUT CEREBRAL INFARCTION
434.01 CEREBRAL THROMBOSIS WITH CEREBRAL INFARCTION
434.10 CEREBRAL EMBOLISM WITHOUT CEREBRAL INFARCTION
434.11 CEREBRAL EMBOLISM WITH CEREBRAL INFARCTION
434.90 CEREBRAL ARTERY OCCLUSION UNSPECIFIED WITHOUT CEREBRAL INFARCTION
434.91 CEREBRAL ARTERY OCCLUSION UNSPECIFIED WITH CEREBRAL INFARCTION
435.0 BASILAR ARTERY SYNDROME
435.1 VERTEBRAL ARTERY SYNDROME
435.2 SUBCLAVIAN STEAL SYNDROME
435.3 VERTEBROBASILAR ARTERY SYNDROME
435.8 OTHER SPECIFIED TRANSIENT CEREBRAL ISCHEMIAS
435.9 UNSPECIFIED TRANSIENT CEREBRAL ISCHEMIA
436 ACUTE BUT ILL-DEFINED CEREBROVASCULAR DISEASE
442.81 ANEURYSM OF ARTERY OF NECK
443.21 DISSECTION OF CAROTID ARTERY
443.24 DISSECTION OF VERTEBRAL ARTERY
446.5 GIANT CELL ARTERITIS
780.2 SYNCOPE AND COLLAPSE
784.2* SWELLING MASS OR LUMP IN HEAD AND NECK
785.9 OTHER SYMPTOMS INVOLVING CARDIOVASCULAR SYSTEM
900.00 INJURY TO CAROTID ARTERY UNSPECIFIED
900.01 INJURY TO COMMON CAROTID ARTERY
900.02 INJURY TO EXTERNAL CAROTID ARTERY
900.03 INJURY TO INTERNAL CAROTID ARTERY
V67.00 FOLLOW-UP EXAMINATION FOLLOWING UNSPECIFIED SURGERY
V67.09 FOLLOW-UP EXAMINATION FOLLOWING OTHER SURGERY
V72.83 OTHER SPECIFIED PRE-OPERATIVE EXAMINATION

* Use this code to report pulsatile neck mass.

 

ICD-9 Codes that DO NOT Support Medical Necessity

Code Description

General Information

Documentation Requirements

Medical record documentation maintained by the ordering/referring physician/nonphysician practitioner must clearly indicate the medical necessity of the services being billed. In addition, documentation that the service was performed must be included in the patient’s medical record. This information is normally found in the office/progress notes, hospital notes, and/or test results. A hard copy, or a soft copy convertible to a hard copy provides a permanent record of the study performed and must be of a quality that meets accepted radiologic/ultrasonographic standards.If the provider of the service is other than the ordering/referring physician/nonphysician practitioner, that provider must maintain a copy of the test results and interpretation, along with copies of the ordering/referring physician/nonphysician practitioner’s order for the studies. The physician/nonphysician practitioner must state the clinical indication/medical necessity for the study in his/her order for the test.The provider is responsible for ensuring the medical necessity of procedures and maintaining the medical record, which must be available to FCSO Medicare upon request. Non-invasive vascular studies are medically reasonable and necessary only if the outcome will potentially impact the diagnosis or clinical course of the patient. Providers billing Medicare are encouraged to obtain additional information from referring providers and/or patients or medical records to determine the medical necessity of studies performed. Referring physicians are required to provide appropriate diagnostic information to the performing provider.

Performance of both non-invasive extracranial arterial studies (CPT codes 93880 or 93881) and non-invasive evaluation of extremity veins (CPT codes 93965, 93970 or 93971) during the same encounter is not appropriate as a general practice or standing protocol, and therefore, would not generally be expected (American College of Radiology, 2010). Consequently, documentation must clearly support the medical necessity if both procedures are performed during the same encounter, and be available to Medicare upon request.

Per 42 CFR §410.32, all diagnostic tests must be ordered by the physician/nonphysician practitioner who is treating the patient, that is, the physician/nonphysician practitioner who furnishes a consultation or treats a patient for a specific medical problem and who uses the results in the management of the patient’s specific medical problem. Tests not ordered by the physician/nonphysician practitioner who is treating the patient are not reasonable and necessary.

• When reporting syncope as an indication for this service, it is necessary to document that other, more common causes have been ruled out.

• Documentation must support the criteria for coverage as set forth in the ‘Indications and Limitations of Coverage and/or Medical Necessity’ section of this LCD and should reflect how the results of this test will be used in the patient’s plan of care.

 

Appendices

Utilization Guidelines

It is expected that these services would be performed as indicated by current medical literature and/or standards of practice. When services are performed in excess of established parameters, they may be subject to review for medical necessity.Generally, it is not expected that these services would be performed more than once in a year, excluding inpatient hospital (21) and emergency room (23) places of service.

 

Sources of Information and Basis for Decision

Abuhamad, A., Benacerraf, B., Woletz, P., Burke, B. (2004). The accreditation of ultrasound practices – Impact on compliance with minimum performance guidelines. J Ultrasound Med, 23, 1023-1029.American College of Radiology Practice Guidelines (2007). ACR practice guideline for the performance of an ultrasound examination of the extracranial cerebrovascular system. Retrieved from http://www.acr.orgBeers, M., Berkow, R. (Eds.). (2005). Ischemic Syndromes. The Merck Manual of Diagnosis and Therapy (17 ed.), 165-184. Retrieved from http://www.merck.com/mrkshared/mmanual/section14/chapter174/174b.jsp on December 27, 2005.

Brophy, D. (2005). Subclavian Steal Syndrome. Retrieved from http://www.emedicine.com/radio/topic663.htm on September 9, 2005.

Caplan, L. (2004). Clinical diagnosis of patiens with cerebrovascular disease. Prim Care, 31(1), 95-109. Retrieved from http://home.mdconsult.com/das/article/body/53475846-2/jorg on December 30, 2005.

Cina, C., Clase, C., Radan, A. (2004). Aysmptomatic Carotid Bruit. ACS Surgery. Retrieved from http://www.medscape.com/viewarticle/506635 on September 9, 2005.

Hill, M., Foss., Tu., Feasby, T. (2004). Factors influencing the decision to perform carotid endarterectomy. Neurology 62(5). American Academy of Neurology. Retrieved from http://home.mdconsult/das/article/body/50235942-2/jorg on September 9, 2005.

Mettler, F. (2005). Essentials of Radiology, second edition. Page 149. Elsevier, Inc. Retrieved from http://home.mdconsult.com/das/book/body/0/1276/1.html on September 9, 2005.

Purvin, V. (2004). Cerebrovascular disease and the visual system. Ophthalmol Clin North Am, 17(3), 329-355. Retrieved from http://home.mdconsult.com.das/article/body/53475846-2/jorg on December 27, 2005.

Rowe, V. Tucker, S. (2004). Advances in vascular imaging. Surg Clin North Am, 84(5), 1189-1202. Retrieved from http://home.mdconsult.com/das/article/body/53475846-2/jorg on December 27, 2005.

Shah, K., Edlow, J. (2004). Transient ischemic attack: Review for the emergency physician. Annals of Emergency Medicine 43(5). Retrieved from http://home.mdconsult.com/das/article/body/50211775-2/jorg on September 9, 2005.

Society for Vascular Ultrasound – Professional performance guidelines. (2003). Transcranial doppler (non-imaging). Retrieved from http://www.svunet.org/about/positions on December 28, 2005.

Tusa, R. (2003). Dizziness. Med Clin North Am, 87(3), 609-641. Retrieved from http://home.mdconsult.com/das/article/body/53542946-2-jorg on 12/30/2005.

 

Advisory Committee Meeting Notes

This Local Coverage Determination (LCD) does not reflect the sole opinion of the contractor or contractor medical director. Although the final decision rests with the contractor, this LCD was developed in cooperation with advisory groups, which includes representatives from numerous
societiesFlorida Contractor Advisory Committee meeting held October 16, 2010.Puerto Rico and U.S. Virgin Islands Contractor Advisory Committee meeting held October 21, 2010.

 

Revision History Number

2

 

Revision History Explanation

Revision Number:2
Start Date of Comment Period:N/A
Start Date of Notice Period:01/01/2012
Revised Effective Date: 01/01/2012LCR B2012-013
December 2011 ConnectionExplanation of Revision: Annual 2012 HCPCS Update. CPT code 93875 was deleted and the ‘Contractor’s Determination Number’ has been changed to 93880. The effective date of this revision is based on date of service.Revision Number:1
Start Date of Comment Period:09/30/2010
Start Date of Notice Period:12/09/2010
Revised Effective Date: 01/23/2011LCR B2010-080
December 2010 UpdateExplanation of Revision: The ‘Indications and Limitations of Coverage and/or Medical Necessity’ section of the LCD has been revised in the ‘Limitations’ section, under the fourth bullet to indicate CPT code 93875 is of limited usefulness and will only be reimbursed when billed to represent ocular pneumoplethysomography (OPG-GEE) in evaluating a patient with ischemic optic neuropathy. The following statement has also been added to this section of the LCD: Performance of both non-invasive extracranial arterial studies (CPT codes 93880 or 93881) and non-invasive evaluation of extremity veins (CPT codes 93965, 93970 or 93971) during the same encounter is not appropriate as a general practice or standing protocol, and therefore, would not generally be expected (American College of Radiology, 2010). Consequently, documentation must clearly support the medical necessity if both procedures are performed during the same encounter, and be available to Medicare upon request. The ‘Training Requirements’ section of the LCD has been revised in the third paragraph, under the third seriation, regarding a qualified physician to add: ASN: Neuroimaging Subspecialty Certification. The ‘ICD-9 Codes that Support Medical Necessity’ section has been revised to add two new section headers, ‘The following ICD-9-CM code applies only to CPT code 93875’ and ‘The following ICD-9-CM codes apply only to CPT codes 93880 and 93882’. ICD-9-CM code 377.41 has been moved under ‘The following ICD-9-CM code applies only to CPT code 93875’. The ‘Documentation Requirements’ section has been revised to add the following statements: The provider is responsible for ensuring the medical necessity of procedures and maintaining the medical record, which must be available to FCSO Medicare upon request. Non-invasive vascular studies are medically reasonable and necessary only if the outcome will potentially impact the diagnosis or clinical course of the patient. Clinicians billing Medicare are encouraged to obtain additional information from referring providers and/or patients or medical records to determine the medical necessity of studies performed. Referring physicians are required to provide appropriate diagnostic information to the performing provider. Performance of both non-invasive extracranial arterial studies (CPT codes 93880 or 93881) and non-invasive evaluation of extremity veins (CPT codes 93965, 93970 or 93971) during the same encounter is not appropriate as a general practice or standing protocol, and therefore, would not generally be expected (American College of Radiology, 2010). Consequently, documentation must clearly support the medical necessity if both procedures are performed during the same encounter, and be available to Medicare upon request. The ‘Sources of Information and Basis for Decision’ section has also been updated. The effective date of this revision is based on date of service.Revision Number:Original
Start Date of Comment Period:N/A
Start Date of Notice Period:12/04/2008
Revised Effective Date:02/02/2009

LCR B2009-
December 2008 Bulletin

This LCD consolidates and replaces all previous policies and publications on this subject by the carrier predecessors of First Coast Service Options, Inc. (Triple S and FCSO).

For Florida (00590) this LCD (L29235) replaces LCD L6000 as the policy in notice. This document (L29235) is effective on 02/02/2009.

“Indications and Limitations of Coverage and/or Medical Necessity” section of the LCD revised to align with CMS Manual System, Pub. 100-03, Medicare National Coverage Determinations, Chapter 1, Section 20.17.

11/21/2011 – The following CPT/HCPCS codes were deleted:
93875 was deleted from Group 1

 

Last Reviewed On Date

12/06/2011

 

Related Documents

This LCD has no Related Documents.

 

LCD Attachments

Attachments such as Coding Guidelines and Comment Summaries are available in the Medicare coverage database located on the Centers for Medicare & Medicaid Services (CMS) website. To view attachments, go to http://www.cms.gov/MCD/search.asp?clickon=search and enter the LCD ID in the search window; when the LCD is displayed select LCD Attachments from the “Jump to Section” dropdown list.

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The official local coverage determination (LCD) is the version on the Medicare coverage database at www.cms.gov/medicare-coverage-database/ external link. The LCD data hosted on this site is an exact match of what appears on the MCD.

 

1. Evaluation of patients with hemispheric neurologic symptoms, including stroke, transient ischemic attack, and amaurosis fugax.

2. Evaluation of patients with a cervical bruit.

3. Evaluation of pulsatile neck masses.

4. Preoperative evaluation of patients scheduled for major cardiovascular surgical procedures.

5. Evaluation of nonhemispheric or unexplained neurologic symptoms.

6. Follow-up of patients with proven carotid disease.

7. Evaluation of postoperative patients after carotid revascularization, including stenting.

8. Intraoperative monitoring of vascular surgery.

9. Evaluation of suspected subclavian steal syndrome