Tools
Doppler Extra-Cranial Carotid Assessment, Protocols, and Interpretation
Introduction
Over the past few decades, Doppler ultrasound has become a primary modality for extracranial carotid assessment because it is readily available, noninvasive, and relatively inexpensive.[1] The sonographic evaluation of extracranial carotids aids in the screening, diagnosis, and monitoring of atherosclerotic disease, as well as postintervention analysis.[2] The evaluation is crucial since the stroke risk increases with the degree of atherosclerotic narrowing, leading to flow disturbances.[3] Doppler imaging provides a quantitative determination of velocity, which, in combination with grayscale imaging, provides a qualitative and quantitative assessment of plaque and stenosis. This evaluation is of utmost clinical importance for stroke risk stratification, as well as identifying indications for surgical intervention.[4]
Anatomy and Physiology
Register For Free And Read The Full Article
Search engine and full access to all medical articles- 10 free questions in your specialty
- Free CME/CE Activities
- Free daily question in your email
- Save favorite articles to your dashboard
- Emails offering discounts
Learn more about a Subscription to StatPearls Point-of-Care
Anatomy and Physiology
Extracranial vessels are located outside the brain and skull. The most common configuration is the 3-vessel arch anatomy, where the 1st branch is the brachiocephalic artery, which further branches into the right common carotid (CCA) and right subclavian arteries. The 2nd branch is the left CCA, and the left subclavian artery is the 3rd branch.[5]
The most frequent anatomical variant involves a common origin of the brachiocephalic artery and the left CCA from the aortic arch. The CCAs bifurcate into the external carotid (ECA) and internal carotid (ICA) arteries at the upper border of the thyroid. The carotid bulb marks the site of bifurcation and the ICA origin.[6] The ICA is generally posterior and lateral to the ECA and has a larger caliber (see Image. Carotid Bifurcation on Ultrasonography). The ECA supplies the face and neck musculature, tapering distally as it branches into the extracranial regions.[7]
Indications
Indications for extracranial carotid Doppler ultrasound include hemispheric and nonhemispheric neurologic symptoms, cervical bruit, pulsatile neck mass, preoperative evaluation for major cardiovascular surgery, follow-up of known carotid disease, and subclavian steal syndrome.[8]
Equipment
Since carotid vessels are superficial, a high-frequency linear transducer operating between 5.0 and 7.5 MHz is used. The rationale for this choice is that the frequency of the ultrasound probe is inversely proportional to the depth of insonation. Doppler ultrasound is usually performed in combination with grayscale imaging. Grayscale images are obtained with a 5.0- to 12.0-MHz transducer.
Preparation
The patient should be placed supine with the head slightly extended and turned 45° away from the examined side. The sonographer's position is based on individual preference; some prefer to sit behind the patient’s head facing caudally, while others prefer sitting to the side facing superiorly. The patient’s bed height should be adjusted according to the sonographer’s comfort level to avoid hunching over.
Technique or Treatment
The technique relies on the Doppler effect, measuring changes in the frequency and wavelength of sound waves transmitted and reflected by moving red blood cells within the vessel. This phenomenon is known as Doppler frequency shift.[9] Velocity is calculated using the Doppler formula, where frequency shift is proportional to the velocity multiplied by the cosine of the Doppler angle.[10] The speed and direction of blood flow are then determined.
Grayscale imaging, also referred to as "B-mode," where "B" stands for brightness, typically serves as the initial step. Carotid arteries are examined from the jugular notch to the angle of the mandible in both transverse and longitudinal planes.[11] B-mode imaging evaluates the course and caliber of the vessel, including intimal-media thickness and plaque characteristics.
Plaque morphology correlates with the severity of atherosclerotic disease, with vulnerable plaques carrying a higher risk of rupture and acute thrombosis. Assessment and reporting should include plaque echogenicity, surface characteristics (regular or irregular), and the presence of calcification.[12] Optimizing time-gain compensation is essential to account for ultrasound attenuation from deeper structures. Adjustments to the probe angle are necessary for tortuous vessels. At the jugular notch, the transducer should be angled caudally, while at the angle of the mandible, it should be angled cephalically. Doppler examination is then performed.[13][14]
Several parameters must be adjusted optimally to achieve reliable results. The angle of insonation or Doppler angle should remain below 60° and as close to parallel as possible to enhance measurement accuracy. Calculated velocity becomes less precise when extrapolated from a nearly perpendicular angle.[15] Accurate velocity calculation requires the technologist to set the angle correction parallel to the flow direction. An incorrect angle that does not correspond to the flow direction will result in inaccurate velocity measurements.
The CCA velocity typically ranges from 30 to 40 cm/sec but may vary in diseased vessels.[16] Gain settings must be optimized so that color is confined to the vessel lumen, avoiding bleeding artifacts.[17] The sample volume should be positioned at the center of the lumen and moved along the entire vessel for comprehensive evaluation.
Color Doppler assessment should cover at least the following areas:
- The long axis of the distal CCA
- The long axis of the proximal and mid-ICA
- The long axis of the ECA
- The long axis of the vertebral artery
Abrupt changes in systolic velocity or areas of slow flow require careful evaluation and documentation.[18]
Spectral analysis provides critical parameters, including peak systolic velocity (PSV), peak diastolic velocity (PDV), mean maximum velocity, and pulsatility index. Spectral Doppler waveform evaluation offers detailed insights into flow dynamics at the sampling site, influenced by hemodynamic factors affecting proximal or distal segments of the vessel.[19] The ICA exhibits low-resistance flow, the ECA shows high-resistance flow, and the CCA demonstrates a hybrid pattern of both (see Images. Internal Carotid Artery on Doppler Ultrasonography, External Carotid Artery on Doppler Ultrasonography, and Common Carotid Artery on Doppler Ultrasonography). The resistive index describes waveforms, indicating resistance in the vessel distal to the examined segment.[20]
Pulsus parvus and tardus waveforms, characterized by delayed and diminished arterial pulsation, appear distal to the stenotic area in 91% of cases.[21] Pulsus bisferiens, showing 2 prominent systolic peaks with midsystolic retraction, is associated with hypertrophic cardiomyopathy and aortic valvular disease.[22] Pulsus alternans, characterized by alternating peak systolic heights in synchrony with the cardiac rhythm, occur in conditions such as myocardial disease, metabolic disorders, or inferior vena cava compression.[23]
Complete occlusion of the ICA can cause a shift in the external carotid Doppler waveform from high resistance to low resistance due to the formation of low-resistance collateral pathways, a phenomenon known as the internalization of the external carotid.[24] The CCA may exhibit a "water hammer" spectral appearance in patients with severe aortic regurgitation, characterized by a sharp systolic peak, rapid deceleration of flow in late systole, and flow reversal during diastole.[25]
Spectral Doppler evaluation should include at least the following locations:
- Proximal, mid, and distal segments of the CCA
- Proximal, mid, and distal segments of the ICA
- Proximal ECA
- Vertebral artery
Significant stenosis must be carefully assessed and documented both proximal and distal to the affected area.[26][27]
A PSV exceeding 180 cm/s correlates with 50% or greater ICA stenosis.[28] A PSV above 230 cm/s corresponds to 70% or greater stenosis, which may warrant consideration for surgical endarterectomy.[29] Secondary criteria for stratification include ICA-to-CCA PSV ratios greater than 2.0 and 4.0.
The degree of stenosis is expressed as a percentage based on the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria.[30] Percent stenosis is calculated using the formula:
Percent stenosis = (normal distal vessel diameter - luminal diameter at stenosis)/normal distal vessel diameter
Using the expected luminal diameter of a stenotic carotid bulb as the denominator yields a higher calculated value for the stenosis.[31][32]
The vertebral arteries are evaluated last to determine the direction of blood flow. Located deep within the neck, optimal time-gain compensation is necessary for clear imaging.[33] The vertebral arteries are identified by angling the beam posteriorly and laterally toward the vertebral foramen and applying color and pulsed Doppler. Normal flow in the vertebral artery is antegrade, similar to that of the CCA. The vertebral artery exhibits low resistance, prominent diastolic flow, and spectral broadening.
Altered flow patterns may indicate occlusion or near occlusion of proximal vessels such as the subclavian or brachiocephalic artery. Three subclavian steal patterns are recognized, which are as follows:
- Presteal: Antegrade flow with midsystolic deceleration, potentially reversing to late systolic retrograde flow with ipsilateral arm exercise
- Partial steal: Systolic flow reversal
- Complete steal: Fully reversed flow throughout systole and diastole [34][35]
Comparing vertebral and carotid artery flow on both sides aids in identifying the location of stenosis. Computed tomography angiography offers enhanced accuracy in grading vertebral artery stenosis compared to ultrasound.[36]
Clinical Significance
Stroke is the 3rd leading cause of death and major disability in the United States. Atherosclerosis of extracranial and intracranial cerebral arteries has been identified as the major cause of ischemic stroke. Therefore, the evaluation of atherosclerotic burden is crucial for stroke risk stratification. Grayscale ultrasound imaging, combined with color Doppler and spectral waveform analysis, is a widely available tool that can assess the morphology of plaques and detect hemodynamically significant stenosis. Besides screening, a Doppler examination of the extracranial carotid artery is also beneficial in evaluating the potential complications of vascular interventions, such as pseudoaneurysm formation, restenosis of carotid arteries, fistula formation, and stent deformation and fracture.
Enhancing Healthcare Team Outcomes
Evaluating extracranial arterial atherosclerotic burden for stroke risk stratification has demonstrated improved outcomes. Successful implementation relies on collaboration within an interprofessional team, including primary care providers or internists, midlevel practitioners such as physician assistants and nurse practitioners, interventional radiologists, vascular surgeons, neurologists, and ultrasound technologists. Effective communication among these healthcare professionals is essential for delivering patient-centered care.
Media
(Click Image to Enlarge)
Carotid Bifurcation on Ultrasonography. This grayscale image of the carotid bifurcation shows the common, internal, and external carotid arteries.
Obtained from Providence Hospital, Southfield, Michigan
(Click Image to Enlarge)
Internal Carotid Artery on Doppler Ultrasonography. This image shows the spectral waveform of the internal carotid artery on Doppler ultrasound.
"Contributed by Kirti Dhingra, DO, PhD
(Click Image to Enlarge)
External Carotid Artery on Doppler Ultrasonography. This image shows the spectral waveform of the external carotid artery on Doppler ultrasound.
"Contributed by Kirti Dhingra, DO, PhD
(Click Image to Enlarge)
Common Carotid Artery on Doppler Ultrasonography. This image shows the spectral waveform of the common carotid artery on Doppler ultrasound.
"Contributed by Kirti Dhingra, DO, PhD"
References
Sigel B. A brief history of Doppler ultrasound in the diagnosis of peripheral vascular disease. Ultrasound in medicine & biology. 1998 Feb:24(2):169-76 [PubMed PMID: 9550175]
Fleming SE, Bluth EI, Milburn J. Role of sonography in the evaluation of carotid artery stents. Journal of clinical ultrasound : JCU. 2005 Sep:33(7):321-8 [PubMed PMID: 16196004]
Level 2 (mid-level) evidenceFlaherty ML, Kissela B, Khoury JC, Alwell K, Moomaw CJ, Woo D, Khatri P, Ferioli S, Adeoye O, Broderick JP, Kleindorfer D. Carotid artery stenosis as a cause of stroke. Neuroepidemiology. 2013:40(1):36-41. doi: 10.1159/000341410. Epub 2012 Oct 11 [PubMed PMID: 23075828]
Nezu T, Hosomi N. Usefulness of Carotid Ultrasonography for Risk Stratification of Cerebral and Cardiovascular Disease. Journal of atherosclerosis and thrombosis. 2020 Oct 1:27(10):1023-1035. doi: 10.5551/jat.RV17044. Epub 2020 Aug 29 [PubMed PMID: 32863299]
Kau T, Sinzig M, Gasser J, Lesnik G, Rabitsch E, Celedin S, Eicher W, Illiasch H, Hausegger KA. Aortic development and anomalies. Seminars in interventional radiology. 2007 Jun:24(2):141-52. doi: 10.1055/s-2007-980040. Epub [PubMed PMID: 21326792]
Dungan DH, Heiserman JE. The carotid artery: embryology, normal anatomy, and physiology. Neuroimaging clinics of North America. 1996 Nov:6(4):789-99 [PubMed PMID: 8824131]
Schulz UG, Rothwell PM. Major variation in carotid bifurcation anatomy: a possible risk factor for plaque development? Stroke. 2001 Nov:32(11):2522-9 [PubMed PMID: 11692011]
. AIUM Practice Parameter for the Performance of an Ultrasound Examination of the Extracranial Cerebrovascular System. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 2016 Sep:35(9):1-11. doi: 10.7863/ultra.35.9.1. Epub [PubMed PMID: 27574121]
FRANKLIN DL, SCHLEGEL W, RUSHMER RF. Blood flow measured by Doppler frequency shift of back-scattered ultrasound. Science (New York, N.Y.). 1961 Aug 25:134(3478):564-5 [PubMed PMID: 13701432]
Level 3 (low-level) evidenceBurns PN. The physical principles of Doppler and spectral analysis. Journal of clinical ultrasound : JCU. 1987 Nov-Dec:15(9):567-90 [PubMed PMID: 2960698]
Crişan S. Carotid ultrasound. Medical ultrasonography. 2011 Dec:13(4):326-30 [PubMed PMID: 22132407]
Scoutt LM, Gunabushanam G. Carotid Ultrasound. Radiologic clinics of North America. 2019 May:57(3):501-518. doi: 10.1016/j.rcl.2019.01.008. Epub 2019 Feb 22 [PubMed PMID: 30928074]
Park TH. Evaluation of Carotid Plaque Using Ultrasound Imaging. Journal of cardiovascular ultrasound. 2016 Jun:24(2):91-5. doi: 10.4250/jcu.2016.24.2.91. Epub 2016 Jun 22 [PubMed PMID: 27358696]
Lafont A. Basic aspects of plaque vulnerability. Heart (British Cardiac Society). 2003 Oct:89(10):1262-7 [PubMed PMID: 12975444]
Logason K, Bärlin T, Jonsson ML, Boström A, Hårdemark HG, Karacagil S. The importance of Doppler angle of insonation on differentiation between 50-69% and 70-99% carotid artery stenosis. European journal of vascular and endovascular surgery : the official journal of the European Society for Vascular Surgery. 2001 Apr:21(4):311-3 [PubMed PMID: 11359330]
Meyer JI, Khalil RM, Obuchowski NA, Baus LK. Common carotid artery: variability of Doppler US velocity measurements. Radiology. 1997 Aug:204(2):339-41 [PubMed PMID: 9240517]
Saad AA, Loupas T, Shapiro LG. Computer vision approach for ultrasound Doppler angle estimation. Journal of digital imaging. 2009 Dec:22(6):681-8. doi: 10.1007/s10278-008-9131-2. Epub 2008 May 17 [PubMed PMID: 18488268]
Tahmasebpour HR, Buckley AR, Cooperberg PL, Fix CH. Sonographic examination of the carotid arteries. Radiographics : a review publication of the Radiological Society of North America, Inc. 2005 Nov-Dec:25(6):1561-75 [PubMed PMID: 16284135]
Zwiebel WJ. Spectrum analysis in carotid sonography. Ultrasound in medicine & biology. 1987 Oct:13(10):625-36 [PubMed PMID: 3318070]
Frauchiger B, Schmid HP, Roedel C, Moosmann P, Staub D. Comparison of carotid arterial resistive indices with intima-media thickness as sonographic markers of atherosclerosis. Stroke. 2001 Apr:32(4):836-41 [PubMed PMID: 11283379]
Level 1 (high-level) evidencePark JH, Shin JW, Lee JH. Unilateral Pulsus Parvus et Tardus Waveform Discovered during Carotid Artery Doppler Examination: a Clue of Proximal Carotid Artery Occlusion. Korean circulation journal. 2019 Dec:49(12):1203-1205. doi: 10.4070/kcj.2019.0178. Epub [PubMed PMID: 31760708]
Goudar RB, ElBebawy B. Pulsus Bisferiens. StatPearls. 2025 Jan:(): [PubMed PMID: 33085355]
Walker HK, Hall WD, Hurst JW, Morris DC. The Carotid Pulse. Clinical Methods: The History, Physical, and Laboratory Examinations. 1990:(): [PubMed PMID: 21250154]
Rohren EM, Kliewer MA, Carroll BA, Hertzberg BS. A spectrum of Doppler waveforms in the carotid and vertebral arteries. AJR. American journal of roentgenology. 2003 Dec:181(6):1695-704 [PubMed PMID: 14627599]
Chirinos JA, Akers SR, Vierendeels JA, Segers P. A Unified Mechanism for the Water Hammer Pulse and Pulsus Bisferiens in Severe Aortic Regurgitation: Insights from Wave Intensity Analysis. Artery research. 2018 Mar:21():9-12. doi: 10.1016/j.artres.2017.12.002. Epub 2017 Dec 21 [PubMed PMID: 29576810]
Ginat DT, Bhatt S, Sidhu R, Dogra V. Carotid and vertebral artery Doppler ultrasound waveforms: a pictorial review. Ultrasound quarterly. 2011 Jun:27(2):81-5. doi: 10.1097/RUQ.0b013e31821c7f6a. Epub [PubMed PMID: 21606790]
Horrow MM, Stassi J. Sonography of the vertebral arteries: a window to disease of the proximal great vessels. AJR. American journal of roentgenology. 2001 Jul:177(1):53-9 [PubMed PMID: 11418397]
Gornik HL, Rundek T, Gardener H, Benenati JF, Dahiya N, Hamburg NM, Kupinski AM, Leers SA, Lilly MP, Lohr JM, Pellerito JS, Rholl KS, Vickery MA, Hutchisson MS, Needleman L. Optimization of duplex velocity criteria for diagnosis of internal carotid artery (ICA) stenosis: A report of the Intersocietal Accreditation Commission (IAC) Vascular Testing Division Carotid Diagnostic Criteria Committee. Vascular medicine (London, England). 2021 Oct:26(5):515-525. doi: 10.1177/1358863X211011253. Epub 2021 May 19 [PubMed PMID: 34009060]
Kronick MD, Chopra A, Swamy S, Brar V, Jung E, Abraham CZ, Liem TK, Landry GJ, Moneta GL. Peak systolic velocity and color aliasing are important in the development of duplex ultrasound criteria for external carotid artery stenosis. Journal of vascular surgery. 2020 Sep:72(3):951-957. doi: 10.1016/j.jvs.2019.10.099. Epub 2020 Jan 19 [PubMed PMID: 31964570]
Ferguson GG, Eliasziw M, Barr HW, Clagett GP, Barnes RW, Wallace MC, Taylor DW, Haynes RB, Finan JW, Hachinski VC, Barnett HJ. The North American Symptomatic Carotid Endarterectomy Trial : surgical results in 1415 patients. Stroke. 1999 Sep:30(9):1751-8 [PubMed PMID: 10471419]
Level 1 (high-level) evidenceGrant EG, Benson CB, Moneta GL, Alexandrov AV, Baker JD, Bluth EI, Carroll BA, Eliasziw M, Gocke J, Hertzberg BS, Katanick S, Needleman L, Pellerito J, Polak JF, Rholl KS, Wooster DL, Zierler RE. Carotid artery stenosis: gray-scale and Doppler US diagnosis--Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003 Nov:229(2):340-6 [PubMed PMID: 14500855]
Level 3 (low-level) evidenceNorth American Symptomatic Carotid Endarterectomy Trial Collaborators, Barnett HJM, Taylor DW, Haynes RB, Sackett DL, Peerless SJ, Ferguson GG, Fox AJ, Rankin RN, Hachinski VC, Wiebers DO, Eliasziw M. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. The New England journal of medicine. 1991 Aug 15:325(7):445-53 [PubMed PMID: 1852179]
Level 1 (high-level) evidenceGrogan SP, Mount CA. Ultrasound Physics and Instrumentation. StatPearls. 2025 Jan:(): [PubMed PMID: 34033355]
Osiro S, Zurada A, Gielecki J, Shoja MM, Tubbs RS, Loukas M. A review of subclavian steal syndrome with clinical correlation. Medical science monitor : international medical journal of experimental and clinical research. 2012 May:18(5):RA57-63 [PubMed PMID: 22534720]
Liljeqvist L, Ekeström S, Nordhus O. Monitoring direction of vertebral artery blood flow by Doppler shift ultrasound in patients with suspected "subclavian steal'. Acta chirurgica Scandinavica. 1981:147(6):421-4 [PubMed PMID: 7324774]
Khan S, Cloud GC, Kerry S, Markus HS. Imaging of vertebral artery stenosis: a systematic review. Journal of neurology, neurosurgery, and psychiatry. 2007 Nov:78(11):1218-25 [PubMed PMID: 17287234]
Level 1 (high-level) evidence