***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: PURPOSE To determine the accuracy of gadolinium-enhanced three-dimensional magnetic resonance ( MR ) angiography in the evaluation of  carotid artery stenosis .  MATERIAL S AND METHODS A prospect i ve blinded comparison of first-pass MR angiography with conventional digital subtraction angiography ( DSA ) was performed in 21 patients suspected of having carotid artery stenosis .  MR angiography was performed on a 1.5-T magnet with gradient overdrive equipment , with a coronal radio-frequency-spoiled , three-dimensional , fast low-angle shot sequence after intravenous injection of contrast material . The guidelines of the North America Symptomatic Carotid Endarterectomy Trial for measuring stenosis of the internal carotid artery were applied on maximum intensity projection images and conventional angiograms . RESULTS Grading of stenoses at MR angiography  agreed with that at DSA in 92 % of the 44 carotid arteries . In the 18 carotid arteries with severe stenosis ( 70%-99 % ) , agreement was 94 % . All internal carotid occlusions ( n = 7 ) or pseudo-occlusions ( n = 3 ) were accurately detected with MR angiography . CONCLUSION The accuracy of gadolinium-enhanced MR angiography in characterizing the degree of carotid stenosis was high . Findings with MR angiography were accurate for differentiating between occlusion and pseudo-occlusion A retrospective study was performed to investigate the reliability of colour duplex scanning as a screening method in detecting carotid artery disease . The results of this technique and digital subtraction arteriography of 100 carotid bifurcations in 50 patients undergoing carotid endarterectomy  were compared . In accordance with suggested st and ard reports dealing with cerebrovascular disease , the diameter reduction was classified in one of five categories : < 20 % , 20 - 59 % , 60 - 79 % , 80 - 99 % and total occlusion . In 78 % the gradings determined using digital subtraction arteriography and duplex scanning correlated perfectly , and in 99 % of the studied bifurcations the difference was not more than one grade . The sensitivity and specificity of colour duplex scanning in detecting a stenosis with a diameter reduction of more than 60 % was 98 % and 87.7 % , respectively . The best non-invasive method to identify carotid bifurcation disease is duplex scanning . Although the role of duplex scanning as an alternative to angiography is currently evolving , the authors still advocate carotid angiography when surgery is considered Background and Purpose — Previous studies have suggested that patients with carotid stenosis who are c and i date s for endarterectomy can be effectively identified on the basis of carotid Doppler ultrasound alone . Before widespread acceptance of this policy , the accuracy of carotid Doppler ultrasound outside selected centers and clinical trials needs to be evaluated . We performed a 12-month prospect i ve study to evaluate the accuracy of Doppler ultrasound in identifying patients for carotid intervention in general practice setting s. Methods — Each patient referred to our endovascular service for diagnostic angiography to evaluate for carotid stenosis was interviewed and examined by a neurologist . Subjects consisted of symptomatic patients with ≥50 % stenosis and asymptomatic patients with ≥60 % stenosis by Doppler ultrasound .  Information pertaining to demographic and cerebrovascular risk factors and the results of the carotid Doppler ultrasound were recorded . The severity of stenosis on angiograms was measured with North American Symptomatic Carotid Endarterectomy Trial criteria by a blinded observer . The results of both studies were compared to determine the relative accuracy of ultrasound results . Results — Of 130 patients ( mean age , 69±8.8 years ) who met Doppler ultrasound criteria , 22 ( 17 % ) and 8 patients ( 6 % ) were found to have 30 % to 49 % or < 30 % stenosis by angiography , respectively . The positive predictive value  of carotid Doppler ultrasound for identifying appropriate symptomatic c and i date s for carotid intervention ( angiographic stenosis ≥50 % ) was 80 % , with a false-positive value of 20 % . The positive predictive value  of carotid Doppler ultrasound for identifying appropriate asymptomatic c and i date s for carotid intervention ( angiographic stenosis ≥60 % ) was 59 % , with a false-positive value of 41 % . Carotid endarterectomy or angioplasty and stent placement were undertaken subsequently in 60 ( 46 % ) of the patients . In 94 patients who underwent cerebral angiography alone  , no complications were observed . Conclusions — The present accuracy of carotid Doppler ultrasound in general practice does not justify its use as the sole basis of selecting appropriate patients for carotid intervention . Given the relatively low rate of associated morbidity with present day techniques , additional confirmatory studies such as angiography should be performed in every patient before a decision regarding intervention is made OBJECTIVE The purpose of this study was to compare the abilities of color-coded duplex sonography , CT angiography , and selective digital subtraction angiography to reveal disease requiring surgery in patients with occlusive disease of the carotid bifurcation . MATERIAL S AND METHODS Fifty-six carotid arteries in 28 patients who had 48 carotid stenoses and symptomatic cerebrovascular disease were prospect ively studied by selective digital subtraction angiography , color-coded duplex sonography , and CT angiography . CT data were displayed in maximum intensity projection . The degree of stenoses revealed were grade d as mild , moderate , severe , and occluded according to North American Symptomatic Carotid Endarterectomy Trial criteria . The results of CT angiography and color-coded duplex sonography were correlated with the gold st and ard of digital subtraction angiography . RESULTS Grading of stenoses on CT angiography agreed with grading of stenoses on digital subtraction angiography in 89 % of cases . All high- grade stenoses and occlusions revealed on CT angiography were correctly interpreted by all observers . For stenoses revealed by color-coded duplex sonography and digital subtraction angiography , observers ' agreement was 75 % . Two severe stenoses were incorrectly grade d as occluded by the interpreter of the color-coded duplex sonograms . Also , one occluded carotid artery was misdiagnosed as moderate stenosis . CONCLUSION Our results indicate that CT angiography is superior to color-coded duplex sonography for evaluating carotid disease and determining disease requiring surgery . CT angiography warrants further investigation in a larger group of patients OBJECTIVE The aim of this study was the definition of the duplex scan parameters that best select patients for carotid endarterectomy . METHODS This study was set in a regional vascular unit . Duplex scanning and angiography were performed prospect ively on 50 patients who were symptomatic ( 100 carotid bifurcation ) to identify the most accurate and sensitive duplex scan criteria to identify an 80 % to 99 % stenosis according to the European Carotid Symptomatic Trial . With data from the European Carotid Symptomatic Trial , we estimated the effect of three different approaches used to select patients for carotid endarterectomy . The first approach was the selection of patients for carotid surgery on the basis of duplex scanning alone with the most accurate duplex scan criteria ( approach I ) . The second approach was the selection of patients for carotid surgery on the basis of duplex scanning alone with a 100 % sensitive duplex scan criteria ( approach II ) . The third approach was the selection of patients for angiography with duplex scanning ( 100 % sensitive criteria ) and then the use of angiography to define which patients should undergo surgery ( approach III ) . RESULTS All three approaches appeared to have a similar potential in stroke reduction . However , approach I , which minimized the number of patients who underwent surgery ( 19 % less than approach II ) or invasive imaging ( 65 % less than approach III ) , appeared to be the most appropriate . CONCLUSION These data support the selection of patients for carotid endarterectomy on the basis of duplex scanning alone . The duplex scan criteria should be vali date d against angiography To assess the accuracy of MR angiography for screening vascular stenosis of the extracranial carotid arteries , 20 consecutive patients with suspected extracranial carotid atherosclerotic disease were evaluated with time-of-flight MR angiography and intra-arterial contrast angiography . Both studies were independently review ed by three observers in a blinded manner . The internal carotid arteries were grade d as either normal or mildly stenotic ( 0%-29 % ) , moderately stenotic ( 30%-69 % ) , severely stenotic ( 70%-99 % ) or occluded . Results of the study indicate that time-of-flight MR angiography has a high rate of agreement with contrast angiography and is an accurate screening technique of the common carotid bifurcation in patients with suspected carotid stenosis BACKGROUND AND PURPOSE The accuracy of routine ultrasonography in detecting severe carotid artery stenosis was evaluated in comparison with cerebral angiography . The precision of ultrasonographic criteria in predicting the risk of stroke was also assessed . METHODS A total of 1011 symptomatic carotid bifurcations were studied in patients from the North American Symptomatic Carotid Endarterectomy Trial ( NASCET ) . Given that all patients were considered for entry into the trial , the chance of a verification bias affecting the analyses was minimized . The ultrasonographic data consisted of peak systolic velocities and frequency changes from both the internal and common carotid arteries . Angiographic stenosis was calculated as in NASCET . Receiver operating characteristic ( ROC ) curves were constructed from the ultrasonographic data for the detection of 70 % or greater stenosis on the basis of an angiographic assessment . Kaplan-Meier stroke-free survival curves were used to predict the risk of stroke . RESULTS The areas under the ROC curves ranged from 0.74 to 0.75 ( 95 % confidence interval [ CI ] , 0.69 to 0.79 ) . The sensitivities and specificities ranged from 0.65 to 0.71 . The risk of stroke at 18 months declined sharply as the degree of angiographically defined stenosis declined from 99 % to 70 % . No pattern of decline was apparent on the basis of the ultrasonographic data . CONCLUSIONS The results indicate that the accuracy of  ultrasonography  is moderate when flow parameters are used to assess the degree of stenosis . Ultrasonography should be used as a screening tool to exclude patients with no carotid artery disease from further testing . Conventional angiography remains an essential investigation before assigning the risk of stroke and deciding appropriate treatment for extracranial carotid artery disease It is essential to image the carotid bifurcation adequately in patients with symptomatic carotid territory ischaemia if they are being considered for carotid endarterectomy .  Optimal resolution is achieved by selective intraarterial contrast angiography which is an invasive procedure carrying some risk . The overall risk-benefit of carotid endarterectomy is currently being investigated in several large r and omised trials in Europe and North America . Because cerebral angiography is a prerequisite for carotid endarterectomy , the risks of cerebral angiography will need to be added to those of surgery when considering whether carotid endarterectomy is effective in the management of these patients . This study evaluated prospect ively 382 patients with symptomatically mild carotid ischaemia who had cerebral angiography to visualise a potentially resectable lesion at the carotid bifurcation . Complications followed 14 cerebral angiograms in 13 patients ( 3.4 % ) ; two complications were local ( 0.5 % ) , two systemic ( 0.5 % ) and 10 were neurological ( 2.6 % ) . The neurological complications were transient ( TIA 1 , generalised seizure 1 ) in two patients ( 0.5 % ) , reversible ( stroke ) in three ( 0.8 % ) and permanent ( stroke ) in five patients ( 1.3 % ) . There were no deaths . The significant risk factors for post angiographic stroke were ( 1 ) stroke before angiography compared with transient ischaemic attacks of the eye or brain and ( 2 ) the presence of greater than or equal to 50 % diameter stenosis of the symptomatic internal carotid artery ; unfortunately it may be the latter patients who are most at risk of stroke as part of the natural history of their disease and therefore most in need of prophylactic carotid endarterectomy ( which requires cerebral angiography ) . The absolute risk of post-angiographic stroke of patients for cerebral angiography using clinical evaluation and Duplex carotid ultrasound screening The results of a prospect i ve study comparing ultrasound , intra-arterial digital subtraction angiography , and magnetic resonance angiography in the assessment of the degree of extracranial internal carotid artery stenosis are reported in patients with symptoms of recent carotid territory ischaemia . A total of 70 patients and 137 vessels were examined by all three techniques . The results obtained by each technique were reported blind . The mean difference ( SD ) for the comparison of magnetic resonance angiography and digital subtraction angiography was -0.7 (14)% , for ultrasound and digital subtraction angiography 3.1 (15)% , and for magnetic resonance angiography and ul 
    Output:
    
A multivariable summary receiver-operating characteristic curve ( ROC ) analysis for diagnosing 70 % to 99 % stenosis demonstrated that the type of MR scanner predicted the performance of MRA , whereas the presence of verification bias predicted the performance of DUS .
These results suggest that MRA has a better discriminatory power compared with DUS in diagnosing 70 % to 99 % stenosis and is a sensitive and specific test compared with DSA in the evaluation of carotid artery stenosis .
For detecting occlusion , both DUS and MRA are very accurate