7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Official reprint from UpToDate www.uptodate.com 2023 UpToDate, Inc. and/or its affiliates. All Rights Reserved. Evaluation of carotid artery stenosis : Brett L Cucchiara, MD : Scott E Kasner, MD, John F Eidt, MD, Joseph L Mills, Sr, MD : John F Dashe, MD, PhD All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Jun 2023. This topic last updated: Jun 01, 2023. INTRODUCTION Four diagnostic modalities are used to directly image the internal carotid artery: Carotid duplex ultrasound (CDUS) Magnetic resonance angiography (MRA) Computed tomography angiography (CTA) Catheter cerebral angiography (often called conventional angiography or digital subtraction angiography) This topic will review the clinical use of these different techniques and their unique advantages and disadvantages. In addition, we will review the different methods of measuring the degree of carotid stenosis used with angiography. Other aspects of carotid disease are discussed separately. (See "Management of symptomatic carotid atherosclerotic disease" and "Management of asymptomatic extracranial carotid atherosclerotic disease".) GOALS OF IMAGING The main goal of carotid artery imaging is to assess for vascular abnormalities that may contribute to stroke, of which the most common is atherosclerotic disease. Determining the degree of atherosclerotic stenosis (or whether complete occlusion is present) has critical management implications. https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 1/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Measurement of stenosis The benefit of carotid revascularization with endarterectomy or stenting is dependent on the severity of the stenosis. The methods of evaluating the degree of carotid stenosis vary in technique and accuracy. If the results of clinical trials are to be generalized, there is a need for uniformity in measurement [1]. Stenosis determination by angiography The two major randomized clinical trials evaluating the utility of endarterectomy in symptomatic patients (NASCET and ECST) used different methods to measure carotid stenosis ( figure 1), though both relied on catheter angiography [2]. An additional method, the common carotid (CC) method, has also been used: NASCET The North American Symptomatic Carotid Endarterectomy Trial (NASCET) method measures the residual lumen diameter at the most stenotic portion of the vessel and compares this with the lumen diameter in the normal internal carotid artery distal to the stenosis [3]. ECST The European Carotid Surgery Trial (ECST) method measures the lumen diameter at the most stenotic portion of the vessel and compares this with the estimated probable original diameter at the site of maximum stenosis [4]. CC The common carotid (CC) method measures the residual lumen diameter at the most stenotic portion of the vessel and compares this with the lumen diameter in the proximal common carotid artery [2,5]. The maximum degree of stenosis is generally in the carotid bulb, which is a wider portion of the artery than the distal segment. As a result, the same degree of stenosis is quantified as a higher percentage stenosis when measured by the ECST or CC methods than when measured by the NASCET method. The ECST methodology also requires an assumption of the true lumen, which increases the risk of interobserver variability ( figure 1). Despite these differences, the results of all three methods have a nearly linear relationship to each other and provide data of similar prognostic value [2]. Equivalent measurements for the three methods have been determined [2,6]: A 50 percent stenosis with the NASCET method is comparable to a 65 percent stenosis for both the ECST and CC methods. A 70 percent stenosis with the NASCET method is comparable to an 82 percent stenosis for both the ECST and CC methods. Given its better interrater reliability, the NASCET method has been most widely adopted over time [7]. All three methods (NASCET, ECST, and CC) were originally devised for use with https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 2/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate catheter angiography, though these methods can also be used with magnetic resonance and computed tomography angiography. Stenosis determination by carotid duplex ultrasound (CDUS) In contrast to the angiographic measurements described above, CDUS generally estimates the degree of stenosis based on elevations in blood flow velocity observed in the target vessel as opposed to anatomic measurements of luminal narrowing. Velocity criteria correlating with specific degrees of angiographically-confirmed stenosis (usually using the NASCET method) have been established; these are typically categorical as opposed to linear (ie, <50 percent stenosis, 50 to 69 percent stenosis, >70 percent stenosis). Diagnosis of complete occlusion No surgical treatment has been proven to be of benefit for preventing a subsequent stroke in patients with complete carotid artery occlusion. Additionally, revascularization in these patients is often technically not feasible. Thus, it is important to adequately distinguish between completely occluded vessels and those with some remaining flow, since the latter group may benefit from carotid revascularization. Identifying other arteriopathies Carotid imaging can also provide crucial information about the presence and characteristics of other arteriopathies that are potential risk factors and mechanisms of ischemic symptoms. These include the following: Dissection (see "Cerebral and cervical artery dissection: Clinical features and diagnosis", section on 'Evaluation and diagnosis') Fibromuscular dysplasia (see "Overview of secondary prevention for specific causes of ischemic stroke and transient ischemic attack", section on 'Fibromuscular dysplasia') Carotid web (see "Overview of secondary prevention for specific causes of ischemic stroke and transient ischemic attack", section on 'Carotid web') Carotid aneurysm (see "Extracranial carotid artery aneurysm") Evaluating carotid plaque characteristics Determination of carotid plaque characteristics (eg, ulceration, plaque area, intraplaque hemorrhage, plaque echogenicity) may be useful to identify patients with asymptomatic carotid occlusive disease who are at higher risk of stroke and therefore likely to benefit from carotid revascularization. This is discussed separately. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Carotid plaque morphology'.) CHOICE OF IMAGING TEST https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 3/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Patients with carotid stenosis are generally identified using one or more of the noninvasive tests, which have largely replaced catheter angiography in the presurgical evaluation of carotid stenosis: Carotid duplex ultrasound (CDUS) Computed tomography angiography (CTA) Time-of-flight magnetic resonance angiography (TOF MRA) Contrast-enhanced magnetic resonance angiography (CEMRA) Catheter cerebral angiography has been considered the gold standard for the evaluation of internal carotid artery stenosis [8]. However, catheter angiography is invasive, time-consuming, resource-intensive, and associated with a small but real risk of procedural stroke and other vascular complications. Selection of initial test The choice among the noninvasive carotid artery imaging methods depends mainly upon the clinical indications for imaging, the availability and expertise at individual centers, and the initial patient presentation [9]. Our approach to patients with suspected carotid stenosis depends on whether the patient is symptomatic or asymptomatic. Symptomatic For patients with stroke or transient ischemic attack (TIA) potentially due to carotid stenosis, we generally perform CTA or MRA of the head and neck initially. This expedites imaging of both the extracranial and intracranial circulation and allows for identification of unusual vascular abnormalities implicated as stroke mechanisms, such as carotid webs or dissections, in addition to more typical atherosclerotic stenosis. However, other experts prefer CDUS as the initial imaging test, followed most often by CTA if carotid revascularization is being considered. In patients presenting with acute stroke or TIA, immediate CTA is often performed in the emergency department to risk-stratify and rapidly guide acute treatment. In patients with stroke or suspected TIA undergoing brain magnetic resonance imaging (MRI) who have not already had CTA, combining brain MRI with MRA of the head and neck can be an efficient diagnostic strategy. In patients with stroke or TIA in whom an obvious stroke mechanism is apparent (eg, atrial fibrillation) and for whom thrombolysis or thrombectomy is not a consideration, CDUS alone may be the efficient strategy. Asymptomatic For asymptomatic patients (eg, when a carotid bruit is heard), we generally use CDUS as our initial imaging modality. CDUS is an accurate and cost-effective imaging test. https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 4/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Confirmation of stenosis Less than 50 percent stenosis CDUS, CTA, or MRA demonstrating less than 50 percent carotid stenosis generally rules out significant atherosclerotic stenosis that would require revascularization, and no further testing is typically needed. Important exceptions to this include carotid stenosis that is unusually distal and beyond the field of insonation for CDUS as well as short-segment stenosis in regions of heavily calcified plaque on CTA in which adequate assessment of the residual lumen may be difficult. Severe calcification may also hamper duplex imaging. Symptomatic 50 to 99 percent stenosis When >50 percent stenosis is identified on any of the above noninvasive tests, confirmation with an alternative modality is generally advisable, as two separate noninvasive diagnostic modalities concordant for high-grade stenosis increase accuracy. For instance, the combination of carotid duplex and MRA is highly specific (range 80 to 90 percent) for high-grade carotid stenosis when concordant [10-13], is cost effective [14,15], and results in an overall error rate (approximately 3 to 6 percent) that is comparable to the interobserver reliability when two radiologists are presented with the same catheter angiogram revealing carotid artery disease [16]. Similar findings are likely with combined CDUS and CTA, though this has been less extensively studied. When these tests are concordant, we proceed to revascularization if appropriate. If discordant results are found, we then consider either catheter angiography or alternate angiographic imaging different than the initial modality (ie, CTA if MRA was done initially, and vice versa) depending on image quality and the suspected reasons for the discordant results. However, other experts disagree about the need for additional imaging, and carotid revascularization is performed in some centers using CDUS as the sole preoperative imaging modality for the cervical carotid artery in some patients [17,18]. If CDUS is to be used as the single modality for identifying patients for carotid revascularization, evidence of extremely elevated velocity parameters or transcranial Doppler results indicating collateral patterns corresponding to hemodynamically significant proximal carotid stenosis (reversal of ophthalmic artery or ipsilateral anterior cerebral artery flow) increase the reliability for identification of high-grade stenosis. Asymptomatic 50 to 99 percent stenosis If a >50 percent carotid stenosis is identified on the initial study, typically CDUS, the next steps depend upon whether carotid https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 5/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate revascularization is being considered. (See "Management of asymptomatic extracranial carotid atherosclerotic disease".) If carotid revascularization will not be pursued (based on assessment of relative risks and benefits in the individual patient), patients with asymptomatic carotid stenosis can be followed with noninvasive vascular imaging of the carotid artery, typically CDUS, particularly if they may be candidates for revascularization in the setting of stenosis progression. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Imaging surveillance'.) If carotid revascularization is being considered, we generally proceed to CTA or MRA, with a similar approach to concordant and discordant results as for symptomatic patients. The role of carotid revascularization for patients with asymptomatic carotid stenosis is reviewed separately. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Role of carotid revascularization'.) Importantly, all patients with carotid stenosis should receive intensive medical therapy including antiplatelet and statin therapy and other measures to address risk factors for atherosclerosis. Specific recommendations are discussed separately. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Intensive medical therapy and follow-up' and "Overview of primary prevention of cardiovascular disease".) Occlusion Both CDUS and MRA are quite accurate at discriminating between occlusion and severe stenosis. One systematic review pooled data across multiple studies and used digital subtraction angiography (DSA) as the gold standard; for determination of complete carotid occlusion, the sensitivity and specificity with CDUS was 96 and 100 percent, respectively, and with MRA was 98 and 100 percent [19]. Some authors have suggested that, as with high-grade stenosis, concordant results from the combination of MRA and CDUS should be considered diagnostic of occlusion, while discordant results should prompt additional imaging modalities such as DSA [20]. Despite a widespread perception that CTA is highly accurate for discrimination between occlusion and severe stenosis, data supporting this are limited and confounded by technical changes in CTA over time and variable timing schemes for image acquisition. Early reports suggested CTA was 97 to 100 percent sensitive and 99 to 100 percent specific for detection of carotid occlusion [21,22], but the increasing speed of image acquisition with multidetector computed tomography (CT) scans has led to recognition of the phenomenon of carotid "pseudo-occlusion," whereby image acquisition occurs with insufficient time for the contrast bolus to fully opacify the affected vessel, creating the https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 6/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate erroneous appearance of complete occlusion [23]. This problem can be avoided with multiphase CTA, but this is not widely used. In the author s practice, carotid occlusion identified by CTA prompts further study with CDUS to confirm the occlusion if the patient would be a candidate for carotid revascularization and if atherosclerotic stenosis at the bifurcation is suspected to be the source of the occlusion. When carotid occlusion is identified by CEMRA or CDUS, additional testing is generally not performed. COMPUTED TOMOGRAPHY ANGIOGRAPHY Computed tomography angiography (CTA) provides an anatomic depiction of the carotid artery lumen and allows imaging of adjacent soft tissue and bony structures ( image 1A-B). Three- dimensional reconstruction allows relatively accurate measurements of residual lumen diameter. Advantages CTA may be particularly useful when carotid duplex ultrasound is not reliable (eg, in cases with severe kinking, short neck, or high bifurcation) or when an overall view of the vascular field is required [24]. Additionally, CTA can be obtained extremely rapidly (typically <1 minute from contrast bolus injection to completion of image acquisition with modern multidetector CT), an important advantage in patients who are uncooperative or claustrophobic. Disadvantages CTA requires a contrast bolus comparable to that administered during a catheter angiogram. As a result, impaired renal function may raise concern for contrast nephropathy, particularly in patients with diabetes, congestive heart failure, or pre-existing kidney disease. (See "Contrast-associated and contrast-induced acute kidney injury: Clinical features, diagnosis, and management".) In addition, radiation exposure is a potential risk, particularly in young patients or those undergoing multiple repeated studies. (See "Radiation-related risks of imaging".) Accuracy A meta-analysis published in 2006 concluded that CTA compared with catheter cerebral angiography for the diagnosis of 70 to 99 percent carotid stenosis had a sensitivity of 0.77 (95% CI 0.68-0.84) and a specificity of 0.95 (95% CI 0.91-0.97) [25]. An earlier systematic review and meta-analysis that compared CTA with arteriography or digital subtraction angiography concluded that CTA is an accurate method for detection of severe carotid artery disease, particularly for detection of carotid occlusion, where CTA had a sensitivity and specificity of 97 and 99 percent, respectively [22]. The accuracy of CTA may be limited when severe calcifications are present. Evolving technologies, such as dual energy CT angiography, may improve accuracy in these situations https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 7/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate [26]. MAGNETIC RESONANCE ANGIOGRAPHY Magnetic resonance angiography (MRA) generates a reproducible three-dimensional image of the carotid bifurcation with good sensitivity for detecting high-grade carotid stenosis ( image 2). Techniques The techniques most often employed for evaluating the extracranial carotid arteries utilize either two- or three-dimensional time-of-flight (TOF) MRA or gadolinium- enhanced MRA (also known as contrast-enhanced MRA or CEMRA). (See "Principles of magnetic resonance imaging".) CEMRA offers several advantages over traditional TOF techniques. The use of a paramagnetic agent acting as a vascular contrast allows for higher-quality images that are less prone to artifacts. CEMRA is superior to TOF MRA at identifying plaque ulceration [27]. Advantages Compared with carotid duplex ultrasound (CDUS), MRA is less operator- dependent and produces an image of the artery throughout its entire cervical course. Disadvantages MRA is more expensive and time-consuming than CDUS and is less readily available. Furthermore, MRA may be difficult to adequately perform if the patient is critically ill, unable to lie supine, or has claustrophobia, a pacemaker, or ferromagnetic implants [28]. In different series, up to 17 percent of MRA studies are incomplete because the patient could not tolerate the study or could not lie still enough to produce an image of adequate quality for interpretation [29]. Accuracy Both TOF MRA and CEMRA are accurate for the identification of high-grade carotid artery stenosis and occlusion, but they appear to be less accurate for detecting moderate stenosis [30]. In a 2008 meta-analysis that compared MRA with catheter angiography, the sensitivities of either MRA technique for the identification of carotid artery occlusion or severe stenosis were similar and ranged from 91 to 99 percent, while specificities ranged from 88 to 99 percent. In earlier studies, MRA was found to generally overestimate the degree and length of stenosis [28,31]. However, a later study of three-dimensional TOF MRA found that it did not overestimate the degree of stenosis when corresponding MRA and digital subtraction angiography (DSA) projections were compared [32]. https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 8/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate CAROTID DUPLEX ULTRASOUND Techniques CDUS Carotid duplex ultrasound (CDUS) uses B-mode (grayscale) ultrasound imaging and Doppler ultrasound to detect focal increases in blood flow velocity indicative of high-grade carotid stenosis [28,33,34]. The peak systolic velocity is the most frequently used measurement to gauge the severity of the stenosis ( image 1A-B), but the end-diastolic velocity, spectral configuration, and the carotid ratio (the peak internal carotid artery velocity to common carotid artery velocity ratio) provide important additional information [35,36]. Consensus criteria on velocity measurements correlating with varying categories of stenosis have been published ( table 1) and are widely used [17,37]. Note that while these categorical criteria were developed to optimize accuracy in clinical practice, the specificity of an elevated velocity for severe carotid stenosis rises steadily with increasing absolute peak systolic velocities. Color Doppler flow imaging may simplify test performance by allowing the technician to more easily identify the lesion, but it has not been shown to improve accuracy [33,34,38,39]. The role of CDUS in the evaluation of carotid plaque morphology is reviewed elsewhere. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Carotid plaque morphology'.) Contrast-enhanced ultrasound Contrast-enhanced ultrasound is performed after intravenous injection of a microbubble contrast agent. This technique may be useful for evaluating carotid plaque neovascularization, a possible marker of plaque instability [40- 42]. In addition, contrast-enhanced ultrasound may help distinguish complete carotid occlusion from near occlusion and improve lumen visualization in carotid arteries that are technically challenging to study by conventional CDUS. 3D ultrasound Three-dimensional ultrasound improves visualization of vascular anatomy [43]. Advantages compared with B-mode ultrasound include the potential for quantitative monitoring of plaque volume changes in all three directions (circumferentially as well as length and thickness) rather than one or two directions [44]. This in turn could allow measurement of plaque volume change, which may be a more sensitive marker of plaque https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 9/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate progression than measurements of plaque area, intima-media thickness, and carotid stenosis. Disadvantages of three-dimensional ultrasound include a tendency for underestimation of vessel stenosis and difficulty imaging areas of calcification [45]. It is also not widely available or utilized in routine clinical care. Advantages CDUS is a noninvasive, safe, and inexpensive technique for evaluation of the carotid arteries. It is generally associated with greater patient comfort than other modalities as it does not require placement of an intravenous line for contrast injection, nor are there issues of claustrophobia as sometimes seen with magnetic resonance angiography (MRA). Using published consensus velocity criteria, diagnosis of carotid stenosis and stratification into relevant categories of degree of stenosis can be performed with high sensitivity and specificity [37]. CDUS is easily repeated to monitor for change in stenosis over time, which may be useful in certain scenarios. Disadvantages The absence of flow in the internal carotid artery may be due to occlusion, but hairline residual lumens can be missed on CDUS (as with other imaging modalities) [46]. In addition, several studies have found that CDUS tends to overestimate the degree of stenosis [10,47]. CDUS is less precise in determining stenoses of <50 percent compared with stenoses of higher degrees [28,33]. However, this rarely impacts its clinical utility as intervention is not indicated for any condition associated with internal carotid artery stenosis at the bifurcation of <50 percent. CDUS may also be less accurate in determining stenoses in the range of 50 to 69 percent compared with 70 percent stenosis [47]. However, this, too, rarely impacts its clinical utility because most patients with asymptomatic carotid stenosis who are considered for endarterectomy have 70 percent stenosis. In addition, while patients with relevant symptoms and 50 to 69 percent stenosis may be appropriate for carotid intervention, most patients with symptomatic internal carotid artery stenosis have 70 percent stenosis. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Carotid endarterectomy' and "Management of symptomatic carotid atherosclerotic disease", section on 'Patients likely to benefit' and "Management of symptomatic carotid atherosclerotic disease", section on 'Patients appropriate for CEA'.) CDUS imaging may be limited by features such as calcific carotid lesions, tortuous or kinked carotid arteries, and patient body habitus. Furthermore, CDUS must be interpreted carefully in patients with contralateral carotid occlusion to avoid overestimation of an ipsilateral carotid stenosis, since the peak systolic velocity may be increased in the presence of a contralateral https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 10/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate internal carotid occlusion [48]. In this scenario, the peak internal carotid to the ipsilateral common carotid artery velocity ratio will usually accurately reflect the degree of stenosis. An additional limitation of CDUS is that only a portion of the cervical internal carotid artery extending just past the carotid bifurcation can be evaluated. Fortunately, the vast majority of atherosclerotic stenoses occur within this region. However, other carotid pathologies, such as carotid dissection, often occur in the more distal portion of the cervical carotid artery and thus will not be accurately identified by CDUS [49]. When suspected, angiographic imaging with computed tomography angiography (CTA), MRA, or catheter angiography should be used instead. Transcranial Doppler may also provide additional information about intracranial vessels that may inform the assessment of carotid disease. (See 'Transcranial Doppler' below.) Accuracy A 2022 Cochrane systematic review concluded that CDUS compared with digital subtraction angiography (DSA) for the diagnosis of 50 to 99 percent carotid stenosis had a sensitivity of 0.97 (95% CI 0.95-0.98) and specificity of 0.70 (95% CI 0.67-0.73) [50]. For the 70 to 99 percent stenosis range, sensitivity was 0.85 (95% CI 0.77-0.91) and specificity 0.98 (95% CI 0.74-0.90). For complete carotid occlusion, sensitivity was 0.91 (95% CI 0.81-0.97) and specificity was 0.95 (95% CI 0.76-0.99). As noted above, studies clearly demonstrate that increasing absolute peak systolic velocities are associated with increasing specificity for high-grade stenosis. For example, while both a peak systolic velocity of 240 and a peak systolic velocity of 500 would meet criteria for >70 percent stenosis, the latter has greater specificity than the former. The accuracy of CDUS relies heavily upon the experience and expertise of the ultrasonographer [34,51]. Measurement threshold properties may vary widely between laboratories, and the magnitude of the variation is clinically important [52,53]. There may be substantial variability in interpretation even when the same scanner and same criteria for carotid stenosis are used [51,54]. Although important, it may be difficult for the clinician to know the accuracy of the local ultrasound laboratory. Accreditation for vascular testing by the multidisciplinary Intersocietal Accreditation Commission (IAC) assures that the ultrasound data meet certain criteria, including correlation against the gold standard of catheter angiography. TRANSCRANIAL DOPPLER As an adjunct to carotid duplex ultrasound (CDUS), transcranial Doppler (TCD) examines the major intracerebral arteries through the orbit, temporal windows, and at the base of the brain. TCD is often used in conjunction with CDUS to evaluate the hemodynamic significance of internal carotid artery (ICA) stenosis, and it can be used to improve the accuracy of CDUS in identifying surgical carotid disease [55]. https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 11/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate TCD can evaluate the intracranial hemodynamic consequences of high-grade carotid lesions, such as the development of collateral flow patterns in the circle of Willis, reversal of flow in the ophthalmic and anterior cerebral arteries, absence of ophthalmic or carotid siphon flow, and reduced MCA flow velocity and pulsatility [56,57]. An assessment of TCD by the American Academy of Neurology (AAN) concluded that TCD is possibly useful for the evaluation of severe extracranial ICA stenosis or occlusion [58]. The AAN report noted that the clinical utility of TCD to detect impaired cerebral hemodynamics distal to high-grade extracranial ICA stenosis or occlusion and assist with stroke risk assessment requires evaluation and confirmation in randomized clinical trials. TCD can also be used for detection of middle cerebral artery microemboli that arise from the carotid artery. These are visualized as high intensity transient signals within the Doppler spectrum and have a characteristic audible "chirp" sound. TCD monitoring for microembolic signals is a powerful tool for risk-stratifying patients with asymptomatic carotid stenosis. This issue is discussed in more detail elsewhere. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Asymptomatic embolism'.) CATHETER CEREBRAL ANGIOGRAPHY Catheter angiography is considered the gold standard for imaging the carotid arteries. However, most patients with suspected carotid stenosis are evaluated using one or more of the noninvasive tests (ultrasound, magnetic resonance angiography, or computed tomography angiography) in lieu of catheter angiography. (See 'Choice of imaging test' above.) Technique The development of intra-arterial digital subtraction angiography (DSA) reduces the dose of contrast, uses smaller catheters, and shortens the length of the procedure. Although there is lower spatial resolution, DSA has largely replaced conventional catheter angiography [59]. The introduction of a radial as opposed to femoral artery approach for DSA has improved patient comfort with the procedure and is likely associated with a reduced risk of local vascular complications [60]. The quality of catheter angiogram images depends upon selective catheterization of the carotid artery with at least two unimpeded views (typically an anteroposterior and lateral view, often with additional oblique views) to identify the projection with the most severe degree of stenosis; this method is consistent with how stenosis was determined in the ECST and NASCET trials. (See 'Measurement of stenosis' above.) https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 12/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Aortic arch injections alone are inadequate; suboptimal studies can lead to misinterpretations as an irregular stenosis can be either underestimated or overestimated in a single projection. Advantages Cerebral angiography permits an evaluation of the entire carotid artery system, providing information about tandem atherosclerotic disease, plaque morphology/ulceration, and collateral circulation that may affect management [61]. The presence of irregular or ulcerated plaque identified on catheter angiography is associated with a greater risk of recurrent stroke and greater benefit from carotid endarterectomy [62]. Disadvantages The disadvantages of catheter angiography include its invasive nature, high cost, and risk of morbidity and mortality. In a 1990 review of prospective studies using cerebral angiography, the risk of all neurologic complications was approximately 4 percent and the risk of serious neurologic complications or death was approximately 1 percent (range 0 to 6 percent) [59]. In a 2003 single-center prospective study of 986 patients undergoing angiography for diagnosis of carotid stenosis or ischemic stroke, an overall neurologic complication rate of 1.7 percent was reported, with a 0.6 percent rate of neurologic complications resulting in permanent sequelae [63]. The risk of morbidity is increased with cerebrovascular symptoms, advanced age, diabetes, hypertension, elevated serum creatinine, and peripheral vascular disease. The size of the catheter, amount of contrast, and procedure duration also affect the likelihood of complications [63,64]. One study found that embolic events following angiography occur more frequently than the apparent neurologic complication rate [65]; the clinical significance of this finding is unclear. Although often considered the "gold standard" of carotid neurovascular imaging methods, conventional DSA has the disadvantage of a limited number of projections, typically two or three, depicting the carotid artery and bifurcation. This limitation could lead to an underestimation of the degree of carotid stenosis in arteries that have asymmetrical rather than concentric stenotic lumens [66,67]. Rotational angiography provides 16 to 32 projections and is far less subject to this problem, but it is less often used in practice. Accuracy As already noted, catheter cerebral angiography has been considered the gold standard for the evaluation of internal carotid artery stenosis [8]. Noninvasive imaging versus catheter angiography In a 2006 meta-analysis of 41 studies and 2541 patients that assessed the accuracy of noninvasive imaging compared with catheter angiography, CDUS, magnetic resonance angiography (MRA), contrast-enhanced MRA (CEMRA), and CTA, all had high sensitivities and specificities for diagnosing 70 to 99 percent internal carotid artery stenosis in patients with ipsilateral carotid territory ischemic symptoms [25]. The https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 13/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate accuracy of the noninvasive tests for 50 to 69 percent carotid stenosis appeared to be substantially reduced compared with 70 to 99 percent stenosis. However, data were limited. SOCIETY GUIDELINE LINKS Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Stroke in adults" and "Society guideline links: Occlusive carotid, aortic, renal, mesenteric, and peripheral atherosclerotic disease".) INFORMATION FOR PATIENTS UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more th th sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon. Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topics (see "Patient education: Carotid artery disease (The Basics)" and "Patient education: Stroke (The Basics)" and "Patient education: Duplex ultrasound (The Basics)") Beyond the Basics topics (see "Patient education: Stroke symptoms and diagnosis (Beyond the Basics)") SUMMARY AND RECOMMENDATIONS Goals The main goal of carotid artery imaging is determining the presence and degree of atherosclerotic stenosis or complete occlusion. In addition, carotid imaging can identify other arteriopathies (eg, dissection) and evaluate carotid plaque characteristics. (See 'Goals of imaging' above.) https://www.uptodate.com/contents/evaluation-of-carotid-artery-stenosis/print 14/30 7/5/23, 11:40 AM Evaluation of carotid artery stenosis - UpToDate Stenosis measurement The main methods of carotid stenosis measurement are the NASCET, ECST, and common carotid (CC) methods. The NASCET method is the most widely adopted. The NASCET and ECST methods were used in two major randomized clinical trials evaluating the utility of endarterectomy in symptomatic patients ( figure 1). The results of all three methods have a nearly linear relationship to each other and provide data of similar prognostic value. (See 'Measurement of stenosis' above.) Choice of imaging test Most patients are evaluated for carotid disease using one of the noninvasive tests (carotid duplex ultrasound [CDUS], time-of-flight magnetic resonance angiography [TOF MRA], contrast-enhanced MRA [CEMRA], or computed tomography angiography [CTA]). These noninvasive imaging modalities all have high sensitivities and specificities for diagnosing 70 to 99 percent internal carotid artery stenosis in patients with ipsilateral carotid territory ischemic symptoms. The accuracy of the noninvasive tests for 50 to 69 percent carotid stenosis is reduced compared with 79 to 99 percent stenosis. (See 'Choice of imaging test' above.) Symptomatic patients For patients with stroke or transient ischemic attack (TIA) potentially due to carotid stenosis, we generally perform CTA or MRA of the head and neck initially. If >50 percent carotid stenosis is identified, we then perform confirmatory CDUS. If discordant results are found, we then consider alternate angiographic imaging different than the initial modality (ie, CTA if MRA was done initially, and vice versa). (See 'Selection of initial test' above and 'Confirmation of stenosis' above.) The management of symptomatic carotid stenosis is reviewed elsewhere. (See "Management of symptomatic carotid atherosclerotic disease".) Asymptomatic patients For patients who have suspected asymptomatic carotid disease, we generally use CDUS as our initial imaging modality. If >50 percent stenosis is identified and carotid revascularization will not be pursued (eg, based on assessment of relative risks and benefits in the individual patient), patients with asymptomatic carotid stenosis can be followed with noninvasive vascular imaging of the carotid artery, typically with CDUS, particularly if they may be candidates for revascularization in the setting of stenosis progression. (See "Management of asymptomatic extracranial carotid atherosclerotic disease", section on 'Imaging surveillance'.)