Duplex Doppler sonography of the carotid artery: false-positive results in an artery contralateral to an artery with marked stenosis

Anecdotal reports have described a false-positive "jet effect" or velocity increase in the carotid artery contralateral to an artery with significant stenosis or occlusion when using duplex Doppler sonography. In this study, the frequency, significance, and possible reasons for this finding were evaluated by a retrospective comparison of duplex sonography and angiography. Twenty-three patients with unilateral 81-100% carotid artery stenosis who underwent both duplex sonography (16 Acuson, seven Quantum) and angiography were evaluated. In 14 patients, there was an accurate or slight underestimate (less than 20%) of stenosis present in the internal carotid artery contralateral to an artery with tight stenosis/occlusion. In nine, a velocity increase in the internal carotid artery resulted in overestimation (10-80%) of the actual degree of stenosis. In one of these nine patients, real-time images were sufficient to explain the velocity increase on the basis of vessel tortuosity. In one, falsely elevated velocity resulted from inaccurate assignment of the Doppler angle of incidence in a patient in whom real-time visualization of a distal internal carotid lesion was poor. In four of the nine patients, cross filling via the circle of Willis toward the side of greater stenosis occurred. However, seven of 14 patients in whom there was duplex sonography/angiography agreement or slight duplex sonography underestimation also had cross filling. Vertebral artery patency did not correlate well with the presence of a "jet effect."(ABSTRACT TRUNCATED AT 250 WORDS)     

A prospective comparison of duplex sonography vs angiography of the vertebral arteries

A prospective blind comparison was completed between duplex sonography and angiography of the vertebral arteries. Thirty-two vertebral arteries were studied for direction of flow, degree of origin plaque or stenosis, Doppler characteristics, and vessel size. The vertebral arteries were reliably identified by imaging their course from the subclavian artery into the transverse foramina and by identifying a Doppler signal similar in waveform to the internal carotid artery. With Doppler, a 90% accuracy was obtained for direction of blood flow. Nonvisualization of origins was primarily due to vessel depth and/or tortuosity. In 12 vessel origins that were well seen with both techniques, angiography and sonography agreed in two-thirds of the cases. In four cases, origin plaque was underestimated with duplex imaging. Interestingly, no Doppler frequency or velocity elevation was identified distal to significant stenoses. One false-positive diagnosis of occlusion occurred with sonography, in which a 99% origin stenosis resulted in no detectable Doppler signal. By comparing sonography with angiography, sonography was shown to be 80% accurate in determining vertebral artery size. Our preliminary results indicate that duplex scanning is a reasonably accurate screening technique for size, patency, and direction of blood flow in the vertebral arteries. Duplex evaluation of the vertebral artery origin was limited by vessel depth, tortuosity, and calcifications.     

Duplex sonography in the evaluation of carotid artery disease

High-resolution duplex sonography was compared with biplane magnified carotid angiography in a prospective evaluation of 161 carotid arteries in 86 patients. The duplex scanner combined real-time B-mode imaging (7.5 MHz) with simultaneous range-gated pulsed Doppler frequency analysis (3 MHz). The degree of stenosis was usually determined by the true and residual lumen of the carotid artery at the atherosclerotic plaque on the transverse image. The Doppler frequency signals were automatically converted to velocity data by a minicomputer. The accuracy of the duplex system in detecting and assessing stenoses graded in 20% increments is demonstrated according to specificity, sensitivity, and positive and negative predictive value by both cumulative and subgroup analyses. A 93.7% sensitivity was shown for minimal (0-20%) stenosis and 100% sensitivity for severe (greater than 60%) stenosis. An apparent limitation of duplex sonography is the differentiation of a high-grade stenosis from occlusion (sensitivity, 82.6%; positive predictive value, 90.4%).     

Duplex and color Doppler flow sonography of occlusion and near occlusion of the carotid artery.

PURPOSETo determine whether color Doppler flow imaging with the use of slow-flow sensitivity improves sensitivity and specificity in the differentiation of occlusion and near occlusion of the internal carotid artery.METHODSColor Doppler and duplex sonography were performed in symptomatic patients who had angiographically confirmed occlusion and/or near occlusion of the internal carotid artery. The study consisted of two phases: in the first, we assessed the usefulness of color Doppler flow imaging by retrospectively reviewing the records of 35 patients with 36 angiographically confirmed occlusions or near occlusions of the internal carotid artery who were examined with color Doppler flow imaging at our institution during a period of 4 years; in the second phase, we incorporated color Doppler sonography into the routine scanning protocols of 39 patients with 41 occluded or nearly occluded internal carotid arteries seen over a period of 2 1/2 years.RESULTSOverall, color Doppler imaging correctly showed all 34 of the near occlusions (sensitivity, 100%) and 36 of the 43 occlusions (specificity, 84%). Seven patients with angiographically confirmed occlusion had sonographic findings that suggested near occlusion. In the first phase, eight near occlusions were misinterpreted as occlusions with conventional duplex sonography, but were correctly shown with color Doppler flow imaging. In the second phase, sensitivity increased from 50% to 100% (18 or 18) because of better detection of the nearly occluded lumen. This was at the expense of a decrease in specificity (from 100% to 78%). owing to identification of apparent flow in the internal carotid artery on color Doppler flow images in five of 23 occlusions.CONCLUSIONBecause of its ability to depict slow flow, color Doppler imaging with slow-flow sensitivity is superior to conventional duplex sonography for the noninvasive discrimination of occlusion from near occlusion of the internal carotid artery.     

Colour Doppler and duplex sonography and angiography of the carotid artery bifurcations

We undertook a prospective double-blind study of 128 carotid artery bifurcations using colour Doppler and duplex sonography and angiography. Sixty-four patients with cerebrovascular events were admitted for angiography. All underwent sonography within 24 h of angiography. Standard duplex sonography and colour Doppler imaging without spectral analysis were performed, on the same device, by two sonographers, using defined morphological and haemodynamic criteria. Digital radiological data on vessel diameter were interpreted independently by two radiologists.The two sonographic methods gave similar grading of stenosis, compared to angiography, with an accuracy ranging from 96% in severe to 83% in minor stenoses. Colour Doppler studies gave better area measurements than standard duplex sonography, except for major stenoses. Discrepancies between ultrasonography and angiography were due mainly, to minor stenoses and large plaques of calcification on the vessel walls, which masked very segmental 70% stenoses in 2 cases. Angiography is limited by its own resolution, does not show uncalcified vessel walls and does not give cross-sectional data. It would therefore be inappropriate for showing small plaques, the full extent of ectasia or for defining the carotid bulb accurately.The advantages of colour methods were in investigating sinuous or deep vessels and hypoechoic plaques. Analysis of the residual lumen of a stenosis and its extent could be determined more rapidly. Haemodynamic quantification of stenoses by standard duplex sonography may be difficult because of limited sample volume and error in estimation of angle, whereas colour Doppler allows semiquantitative estimation of haemodynamics. Standard duplex sonography permits good analysis of vessel wall over a limited distance and quantification of velocity; colour Doppler affords overall demonstration of turbulence, acceleration and backward flow.     

Doppler sonography in basilar artery occlusion

Summary We have investigated 6,972 patients with directional continuous-wave Doppler sonography within the last three and a half years, and have derived criteria for the sonographic diagnosis of basilar artery occlusion or tight stenosis in conjunction with 1,071 retrograde brachial angiograms. By sonographic patterns, we have suspected obstruction of the basilar artery or of both distal vertebral arteries in nine cases. Either bilateral sonographic silence or the absence of a diastolic flow component of the vertebral arteries served as criteria in the sonographic evaluation. Angiography of the vertebro-basilar system, performed in eight cases, showed near or complete occlusion in the distal vertebrals or in the proximal basilar artery. Degrees of stenosis less than an 80 percent reduction in lumen diameter could not be detected sonographically. Two further basilar artery occlusions were detected by means of angiography despite negative Doppler sonography: one of these patients showed an extensive collateral circulation between the posterior inferior and the superior cerebellar arteries, and one patient had an occlusion only of the middle and rostral thirds of the basilar artery, the proximal third and the anterior inferior cerebellar arteries being widely patent. Thus, we believe that directional CW Doppler sonography is very useful in the diagnosis of near or complete occlusion of both distal vertebral arteries or of the proximal basilar artery.     

Detection of internal carotid artery stenosis: comparison of MR angiography, color Doppler sonography, and arteriography.

Findings of two-dimensional time-of-flight magnetic resonance (MR) angiography projection angiograms were prospectively compared with those of color Doppler sonography by using angiography as a standard in 23 consecutive patients (42 carotid bifurcations) to evaluate their utility in determining the presence of carotid artery stenosis. MR angiography helped detect 50% or greater lumen diameter stenosis (sensitivity, 0.96; specificity, 0.64). Color Doppler sonography with 1.25 m/sec peak systolic velocity as a threshold had a sensitivity of 0.96 and a specificity of 0.71. Statistical analysis showed a correlation between percentage of lumen diameter narrowing and the length of the zone of signal intensity loss with MR angiography (r = .69; P less than .0001). A stronger relationship was obtained between angiographic narrowing and peak systolic velocity derived from color Doppler sonography (r = .80; P less than .0001). Two-dimensional time-of-flight MR angiography displayed as projection angiograms and combined with carotid artery and combined with carotid artery sonography is a useful approach for helping detect and potentially grade the severity of stenoses of the carotid artery.     

Diagnostic criteria for carotid duplex sonography

Optimal criteria for the duplex sonographic diagnosis of carotid artery stenosis have not yet been defined. We studied 205 vessels in 105 patients with both duplex sonography and angiography. Four diagnostic groups were defined on the basis of Doppler flow characteristics. Receiver-operating-characteristic curves were used to compare diagnostic criteria at significant stenosis levels, and to select threshold values that emphasize specificity as well as sensitivity. Peak systolic velocity, systolic velocity ratios, and end-diastolic velocity were all shown to be equivalent predictors of significant disease. We chose peak systolic velocity in the internal carotid artery as our best parameter because of its ease of measurement. The use of combined parameters offered no significant statistical advantage over the use of a single parameter. The real-time assessment of stenosis and ulceration was not found to be reliable. ROC curves should be used to select Doppler criteria with desired sensitivities and specificities to maximize the benefit in each clinical setting.     

Accuracy of three-dimensional gadolinium-enhanced MR angiography in the assessment of extracranial carotid artery disease

OBJECTIVE: The purpose of this study was to assess three-dimensional (3D) gadolinium-enhanced MR angiography, used alone or in association with duplex Doppler sonography, with a fast acquisition time (8 sec) for evaluating the extracranial carotid arteries. SUBJECTS AND METHODS: In this prospective study, 48 successive patients with carotid artery stenoses were examined with 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Of the 44 eligible patients, conventional angiography was available in 33 and duplex sonography in 27. We used the North American Symptomatic Carotid Endarterectomy Trial technique to quantify stenosis on all angiograms, and a 250 cm/sec threshold at duplex sonography to diagnose stenoses greater than 70%. Image quality of 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography was assessed, as well as sensitivity and specificity for each technique alone and in combination with duplex sonography. Conventional angiography was the gold standard. RESULTS: Three-dimensional gadolinium-enhanced MR angiography yielded good image quality in 90% of cases. When used alone, it yielded a sensitivity and a specificity of 94% and 85%, respectively, in screening stenoses greater than 70% (70-99%). When combined with duplex Doppler sonography, it provided a 100% sensitivity and specificity for detection of stenoses between 70% and 99% and would have obviated 61% of conventional angiography. In comparison, 3D time-of-flight MR angiography used alone yielded a sensitivity of 88% and a specificity of 94%. In combination with duplex Doppler sonography, its use would have obviated conventional angiography in 74% of cases. Three-dimensional gadolinium-enhanced MR angiography provided accurate results in the diagnosis of occlusions and ulcers and can visualize distant stenoses. CONCLUSION: Used alone, 3D gadolinium-enhanced MR angiography is not accurate enough to replace conventional angiography in the evaluation of extracranial carotid arteries. In association with duplex Doppler sonography, however, it is accurate and may obviate a significant number of conventional angiographic examinations.     

Immediate evaluation of angioplasty and stenting results in supra-aortic arteries by use of a Doppler-tipped guidewire

Intra-arterial Doppler sonography may complement arteriography by providing immediate physiological evidence of hemodynamic adequacy and by obviating unnecessary angioplastic dilation. We used a Doppler-tipped guidewire in 16 patients and obtained velocity measurements at the site of stenosis immediately before and after carotid artery stenting (CAS) in 10 patients. Intra-arterial Doppler sonography confirmed hemodynamic improvement immediately after stent placement and correlated well with post-CAS duplex Doppler sonography results. Thus, intra-arterial Doppler sonography can be feasibly incorporated into CAS procedures for hemodynamic evaluation and can provide anatomic information that complements information provided by angiography.     

双侧颈内动脉狭窄的侧枝循环特点分析

目的 :利用血管造影技术分析双侧颈内动脉狭窄或闭塞的形态学特点。方法 :2 0 0 0年 9月～ 2 0 0 4年 4月 ,我们收治了 15 5例单侧大脑中动脉狭窄或闭塞的患者 ,其中男 10 9例 ,女 4 6例 ;年龄 2 9～ 73岁 ,平均 4 7.6± 6 .2 4岁 ,借助血管造影技术对其形态学特点进行评价。结果 :双侧颈内动脉狭窄或闭塞时 ,最常见各种方式的综合代偿 ,单纯依赖Willis环者较少 ,但在单侧闭塞伴对侧狭窄的患者中 ,前交通动脉代偿较多。单侧闭塞伴对侧狭窄的患者多发生狭窄侧脑梗死。侧枝循环代偿尤其是后交通动脉代偿可以防止梗死发生 ,但前交通动脉代偿时梗死的发生率反而增高。结论 :双侧颈内动脉狭窄或闭塞时 ,应该深入分析血管形态学变化 ,判断其发生缺血事件的危险性 ,从而给予针对性的治疗。     

Common carotid artery occlusion: evaluation with duplex sonography.

PURPOSETo demonstrate the efficacy of carotid duplex ultrasound to diagnose common carotid artery occlusion (CCAO) and to define the clinical features of CCAO.METHODSWe reviewed 5400 carotid duplex ultrasonograms obtained over a 7-year period for suspected carotid artery disease. In cases of CCAO, medical records were reviewed.RESULTSThirteen cases (0.24%) of CCAO were diagnosed by carotid duplex ultrasonography, including five cases of isolated CCAO. Seven cases were proved by cerebral angiography. Cerebral angiography failed to demonstrate patent internal carotid arteries in two cases of isolated CCAO. Mean age of onset was 67 +/- 9 years. The main clinical presentation was stroke in nine cases (69%). The most common vascular risk factors were hypertension (62%) and heart diseases (54%). Three patients had a history of radiation therapy to the neck. Two of five patients with isolated CCAO had major stroke, with good recovery in one, whereas five of eight patients with CCAO had major stroke; among them, only one had good recovery.CONCLUSIONPatients with isolated CCAO may have a better outcome than patients with CCAO. Duplex sonography, particularly with color-coded flow imaging, provides an accurate examination to define the patency of the arteries distal to the carotid bifurcation. The clinical features of CCAO are similar to those of internal carotid artery occlusion except for the low prevalence of CCAO.     

Indikationen und Embolie-Monitoring bei lumeneröffnenden Therapien der A. carotis

Carotid endarterectomy (CEA) is proven to be beneficial in symptomatic patients with high-grade carotid stenosis (70% to 99%; residual lumen as a percentage of the normal distal internal carotid artery) on condition that the peri-operative risk for mortality and morbidity is less than 6%. A minority of the "leading experts" in North America (48%) and Western Europe (28%) recommends carotid endarterectomy in asymptomatic patients in general. Most experts suggest to perform surgery only in asymptomatic patients who are at risk for carotid occlusion in the near future or embolism. At its present state, angioplasty and stenting is an experimental although promising technique which will have to be compared to carotid endarterectomy. Criteria for duplex grading of internal carotid stenosis have been established and systematically validated to results of angiography. Pre-surgical use of angiography will more and more be restricted to selected patients in whom the results of duplex sonography remain inconclusive. The detection of microemboli with transcranial doppler sonography seems to be of particular importance before and during carotid angioplasty and stenting.     

Reappraisal of flow velocity ratio in common carotid artery to predict hemodynamic change in carotid stenosis

BACKGROUND AND PURPOSE: Various Doppler criteria have been used to predict hemodynamically significant carotid stenosis. This study was performed to elucidate whether hemodynamically significant stenosis can be predicted indirectly by the blood flow velocity in the common carotid artery (CCA) measured with duplex ultrasonography in patients with unilateral stenosis of internal carotid artery (ICA). METHODS: Eighty-five patients who were scheduled to undergo carotid endarterectomy for unilateral stenosis of ICA origin were analyzed. The flow velocities and their side-to-side ratios in the CCA were calculated. The flow velocities in the CCA were measured with conventional ultrasonography and poststenotic blood flow with transoral carotid ultrasonography. Cerebral angiography was performed to evaluate the intracranial collateral flow. RESULTS: Among the absolute values and side-to-side ratios of Doppler flow velocities in the CCA, the end diastolic flow velocity (EDV) ratio in the CCA best correlated with the residual lumen area (r = 0.35; P = .0009), stenosis of diameter (r = 0.48; P < .0001), and poststenotic flow (r = 0.60; P < .0001). EDV ratios in the CCA were significantly lower in patients with collateral pathways (anterior communicating artery, P = .0005; posterior communicating artery, P = .004; ophthalmic artery, P < .0001; leptomeningeal collateral, P = .004). The optimal threshold value of the EDV ratio in the CCA for the presence of intracranial collateral flow and stenosis of diameter > or = 70% was 1.2. Those for tight stenosis in a cross-sectional area >95%, the reduction of poststenotic flow, and poststenotic narrowing were 1.4, 1.5, and 1.6, respectively. CONCLUSION: The EDV ratio in the CCA appears to be an additional parameter for predicting hemodynamically significant stenosis in patients with unilateral ICA stenosis.     

Extracranial internal carotid artery Salmonella mycotic aneurysm complicated by occlusion of the internal carotid artery: depiction by Color Doppler sonography,CT and DSA

Mycotic aneurysms of the extracranial carotid artery are rare. Seventy-four cases have been described in the medical literature and only eight secondary to Salmonella infection. To our knowledge, color Doppler sonography, computed tomography (CT), and digital subtraction angiography (DSA) findings relating to the diagnosis and follow-up of extracranial internal carotid artery mycotic aneurysm complicated by occlusion have not previously been described in the literature. We present a report of color Doppler sonography, CT, and DSA findings of a mycotic aneurysm of the right extracranial internal carotid artery due to Salmonella associated with occlusion of the internal carotid artery, promptly diagnosed and followed up using these imaging modalities.     

The limitations of carotid sonography: interpretive and technology-related errors

OBJECTIVE: This study compared carotid artery sonography with angiography to determine, in retrospect, which types of sonographic errors arose from incorrect interpretation of sonographic images and which errors could be ascribed to the limitations of sonographic imaging. MATERIALS AND METHODS: A review of all patients who underwent carotid artery sonography and angiography between 1993 and 1997 at our institution revealed 66 patients with complete sets of studies, yielding 132 examinations (right or left). Studies were not reinterpreted and angiography was considered to be the gold standard. Only stenoses of 60% or greater were included in our study. If the degree or location of stenosis differed on the two imaging studies, they were reviewed together to classify the type of sonographic error. RESULTS: We found complete agreement of sonography and angiography in 115 cases (87%) and discrepancies in 17 (13%). Thirteen of 17 sonographic errors were false-positive interpretations and three were false-negative interpretations. One was an error in location. Retrospective review showed seven interpretive errors. In all these cases, the color Doppler image better revealed the degree of stenosis. Other complicating factors included inconsistencies between absolute velocities, velocity ratios, and waveforms obtained while a patient was being treated with an intraaortic balloon pump. In the other 10 discrepancies, the sonographic interpretation was accurate. Seven of these cases were false-positive interpretations in patients with contralateral occlusions or stenoses. The other three cases in this group showed long segments of stenosis, ulcerations, or tortuous vessels on angiography. CONCLUSION: Our study suggests that increased accuracy can be achieved in the interpretation of carotid artery sonography by meticulous attention to the color image. When color Doppler sonography is technically limited by tortuosity or ulceration, or if significant contralateral disease is present, misinterpretation is more likely.     

Comparison of two Doppler ultrasound criteria for grading cervical internal carotid artery stenosis

In a review of 49 carotid arteries that had been assessed by ultrasound and angiography, two Doppler criteria were compared for accuracy in grading internal carotid artery (ICA) stenosis. The Seattle criteria for Doppler spectral analysis and the internal-to-common carotid artery peak systolic velocity ratio were of similar accuracy. When used in combination, there was an increase in sensitivity compared with the use of a single criterion. The velocity ratio had a higher sensitivity for detection of high-grade stenosis, but it tended to overestimate the grade of stenosis more than the Seattle criteria. To increase the sensitivity for detection of severe stenosis, the criteria should be used together and the higher grade of stenosis should be taken if there is a mismatch in assessment.     

Preoperative evaluation of carotid artery stenosis: comparison of contrast-enhanced MR angiography and duplex sonography with digital subtraction angiography

BACKGROUND AND PURPOSE: Contrast-enhanced MR angiography and extracranial color-coded duplex sonography are noninvasive, preoperative imaging modalities for evaluation of carotid artery stenosis. Innovative techniques and improvements in image quality require frequent reassessment of accuracy, reliability, and diagnostic value compared with those of digital subtraction angiography (DSA). We evaluated contrast-enhanced MR angiography and duplex sonography compared with DSA for detection of high-grade carotid artery stenoses. METHODS: Four readers, blinded to clinical symptoms and the outcome of other studies, independently evaluated stenoses on contrast-enhanced MR angiograms in 71 vessels of 39 symptomatic patients. Duplex sonography was also performed in all vessels. The severity of stenosis was defined according to North American Symptomatic Carotid Endarterectomy Trial criteria (0-29%, 30-69%, 70-99%, 100%). Results of both modalities were compared with the corresponding DSA findings. RESULTS: Contrast-enhanced MR angiography had a sensitivity and specificity of 94.9% and 79.1%, respectively, for the identification of carotid artery stenoses of 70% or greater. Sensitivity and specificity of duplex sonography were 92.9% and 81.9%, respectively. Combining data from both tests revealed a sensitivity and specificity of 100% and 81.4%, respectively, for concordant results (80% of vessels). CONCLUSION: Concordant results of contrast-enhanced MR angiography and duplex sonography increase the diagnostic sensitivity to 100%. The reliability of MR angiography is comparable to that of DSA. The combination of contrast-enhanced MR angiography and duplex sonography might be preferable over DSA for preoperative evaluation in most patients, thus reducing the risk of perioperative morbidity and improving the overall outcome.     

Hepatic artery thrombosis after liver transplantation: radiologic evaluation

Hepatic artery thrombosis after liver transplantation is a devastating event requiring emergency retransplantation in most patients. Early clinical signs are often nonspecific. Before duplex sonography (combined real-time and pulsed Doppler) capability was acquired in October 1984, 76% of all transplants in this institution referred for angiography with a clinical suspicion of hepatic artery thrombosis had patent arteries. In an effort to reduce the number of negative angiograms, CT, real-time sonography, and pulsed Doppler have been evaluated as screening examinations to determine which patients need angiography. Of 14 patients with focal inhomogeneity of the liver architecture detected by CT and/or real-time sonography, 12 (86%) had hepatic artery thrombosis, one had slow arterial flow with hepatic necrosis, and one had a biloma with a patent hepatic artery. In 29 patients undergoing duplex sonography of the hepatic artery, six (21%) had absence of a Doppler arterial pulse. All six had abnormal angiograms: Four had thrombosis, one had a significant stenosis, and one had slow flow with biopsy-proven ischemia. Of 23 patients with a Doppler pulse, two had hepatic artery thrombosis at surgery. However, real-time sonography demonstrated focal inhomogeneity in the liver in both cases. Our data demonstrate that pulsed Doppler of the hepatic artery combined with real-time sonography of the liver parenchyma currently is the optimal screening test for selecting patients who require hepatic angiography after liver transplantation. A diagnostic algorithm is provided.     

The detection of intracranial carotid artery disease by continuous-wave Doppler sonography

Summary We have investigated 6,587 patients with directional continuous-wave (c-w) Doppler sonography of the carotid arteries during the last 33 months, and have developed criteria for the diagnosis of a significant increase in peripheral resistance of the internal carotid artery in conjunction with 1,671 retrograde brachial and direct carotid angiograms. We distinguished stenoses proximal (15 cases) and distal (4) to the origin of the ophthalmic artery, supraclinoid internal carotid artery occlusions (8), stenoses (2) and acute occlusions (10) of the middle cerebral artery. Stenoses in the carotid siphon (proximal or distal to the origin of the ophthalmic artery) of at least 60% reduction in lumen diameter showed a reduction of the relative end-diastolic flow velocity (modified Pourcelot's index) of more than 40%; additionally, stenoses proximal to the origin of the ophthalmic artery exhibited a variable alternating flow, or flow reversal, in the supratrochlear artery. Stenoses distal to the origin of the ophthalmic artery rarely revealed the theoretically expected increase in orthograde flow velocity in the supratrochlear artery. Stenoses of the middle cerebral artery consisting of more than atherosclerotic irregularities proved to be an exception. Supraclinoid occlusions of the internal carotid artery were reliably demonstrated by Doppler sonography. However, the majority of acute occlusions of the middle cerebral artery could not be detected by this means, probably due to anastomoses between the anterior and the middle cerebral arteries, which were detected by angiography. Thus, we believe that c-w Doppler sonography is a reliable tool to detect stenoses of the carotid siphon of more than 60% reduction in lumen diameter and supraclinoid carotid artery occlusions. Barriers to the cerebral blood flow located more peripherally cannot be diagnosed reliably with this technique.