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(Radiology. 1999;211:775-780.)
© RSNA, 1999

Head and Neck Imaging

Carotid Arterial Stenosis: Evaluation at CT Angiography with the Volume-rendering Technique1

Claude D. Marcus, MD, Viviane J. Ladam-Marcus, MD, Jean-Luc Bigot, MD, Claude Clement, MD, Bernard Baehrel, MD and Bernard P. Menanteau, MD

1 From the Departments of Radiology (C.D.M., V.J.L.M., J.L.B., B.P.M.), Vascular Surgery (C.C.), and Cardiothoracic Surgery (B.B.), Hôpital Robert Debré, C.H.U., Rue du Général Koenig, 51092 Reims, France. Received May 22, 1998; revision requested July 14; revision received September 9; accepted December 15. Address reprint requests to B.P.M.


   Abstract
TOP
 Abstract
Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
PURPOSE: To determine whether computed tomographic (CT) angiography with the volume-rendering technique (VRT) can be used to accurately quantify carotid arterial stenosis and to identify occlusions.

MATERIALS AND METHODS: Spiral CT was performed in 23 patients who were referred for carotid stenosis evaluation. VRT images and shaded-surface display (SSD) images of 46 carotid arterial bifurcations were compared with findings from digital subtraction angiography (DSA).

RESULTS: Agreement on stenosis category between VRT CT angiography and DSA was found in 39 (85%) of the 46 carotid arteries studied. VRT CT angiography was 92% (49 of 53) sensitive and 96% (82 of 85) specific for the detection of grade 2–3 stenoses (>=70% stenosis). Agreement on stenosis category between SSD CT angiography and DSA was found in 38 (83%) of the 46 carotid arteries studied. SSD CT angiography was 91% (48 of 53) sensitive and 93% (79 of 85) specific for the detection of grade 2–3 stenoses. Calcified stenoses were correctly graded at VRT CT angiography in 10 of the 10 cases with heavy mural calcified plaques, while eight of the 10 stenoses were accurately quantified at SSD CT angiography.

CONCLUSION: These results indicate that VRT CT angiography is as accurate as SSD CT angiography in the evaluation of carotid arterial bifurcations.

Index terms: Carotid arteries, angiography, 172.124 • Carotid arteries, CT, 172.12115, 172.12116, 172.12117 • Carotid arteries, stenosis or obstruction, 172.721 • Computed tomography (CT), volume rendering, 172.12117 • Digital subtraction angiography, comparative studies, 172.1211


   Introduction
TOP
 Abstract
 Introduction
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Carotid endarterectomy has proved to be an effective therapy in reducing the risk of ipsilateral stroke at 2 years by 17% in neurologically symptomatic patients with carotid arterial stenosis greater than 70% (1). Three imaging modalities—carotid arteriography, color Doppler ultrasonography, and magnetic resonance angiography—are currently used to evaluate carotid arterial stenosis (2,3). Recently, many authors (4–8) have reported on the clinical utility of computed tomographic (CT) angiography in the noninvasive evaluation of carotid arterial disease. Maximum intensity projection and shaded-surface display (SSD) mainly are used to create three-dimensional images of the vasculature (9,10). The accuracy of stenosis grading with SSD CT angiography ranges from 82% to 92% among studies (11). However, heavy mural calcifications can limit the analysis of CT angiograms (12). In such cases, calcifications can be removed by using segmentation with connectivity algorithms or with subtraction techniques, but these procedures substantially increase the processing time (12,13).

The volume-rendering technique (VRT) has recently been used to display three-dimensional angiographic images when optimal display of the surface or internal detail was needed (14,15). The computer processing for VRT traditionally has been slower than for SSD and for maximum intensity projection display because the entire data set is incorporated into the final VRT image. Recent improvements in computer hardware and software have made VRT a more practical and rapid tool (16). This study was performed to ascertain whether VRT CT angiography could be used to quantify carotid stenosis and identify occlusions accurately, even in severely calcified vessels.


   MATERIALS AND METHODS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Patients
Twenty-three patients (16 men, seven women; mean age, 72 years; age range, 47–85 years) with symptomatic and asymptomatic carotid arterial disease were examined for the CT angiographic study. There was clinical evidence of cerebrovascular disease in 14 patients. In nine patients, there was evidence of carotid stenosis at US, which was performed to evaluate diffuse atherosclerotic disease. Patients were included consecutively in the study without regard to the degree of carotid stenosis or presence of heavy mural calcifications. Individuals were excluded from the study if they had renal disease or a contraindication to intravenous injection of contrast material. The study was approved by our institutional review board, and in all cases written informed consent was obtained from the patient.

Imaging
Digital subtraction angiography (DSA) was performed with use of a Digitron 3 system (Siemens, Erlangen, Germany). Aortic arch injection of 300 mg of iodine per milliliter iopromide (Ultravist; Schering, Lys-Lez-Lannoy, France) was performed by using the standard femoral artery approach. A volume of 40 mL per injection with a maximum rate of 20 mL/sec was used. At least three views of each bifurcation were obtained per patient. Spiral CT angiography was performed with use of a Somatom Plus 4 system (Siemens) within 2 weeks of the DSA examination. We used a standard protocol: 120 kV, 210 mAs, 3-mm section thickness, and 3 mm/sec table feed. Volume acquisition typically covered the region from the inferior margin of the C6 vertebral body to the skull base with a scanning duration of 32–40 seconds. Images were reconstructed every 1.5 mm, which resulted in 75–101 sections. Patients were asked to avoid swallowing, but quiet breathing was allowed throughout the examination.

Contrast material (300 mg of iodine per milliliter iohexol; Omnipaque, Nycomed, Paris, France) was injected intravenously with a power injector through an 18-gauge antecubital intravenous catheter. We used a volume of 140 mL at a rate of 3.5 mL/sec. The mean delay between the injection of the contrast material and the initiation of spiral CT scanning was 18 seconds (range, 15–26 seconds).

Data Processing
The data from the CT sections were transferred to a satellite workstation (Magicview; Siemens) for image processing. The axial CT images were viewed to determine the site of maximal carotid stenosis and the presence of calcified plaques. The attenuation value of the intraluminal contrast material was evaluated to determine the lower and upper thresholds for data exclusion when performing VRT and SSD. The attenuation value of the lumen was calculated on the axial CT images at the narrowest point in the artery and in the surrounding area above and below the stenosis. The segmentation levels were chosen by selecting the upper and lower attenuation values among the three attenuation measurements obtained for the contrast material. Image segmentation was performed with use of a region-of-interest technique for each section to exclude unwanted structures such as bones and veins.

VRT and SSD images were obtained in each patient. For VRT, trapezoidal classification parameters representing vascular contrast material were determined on a voxel-intensity graph (Fig 1). The upper and lower attenuation values found by measuring the attenuation of the intraluminal contrast material were attributed to points B and D (Fig 1). The attenuation values of points A and E, representing areas containing none of the contrast material, were determined by examining the VRT graph and by viewing simultaneously the area of selected voxels on the axial reference section. This area appeared in bright color when the area containing voxels outside the selected range demonstrated normal gray-scale display. We tried to use identical slopes for segments AB and DE in each case to standardize the processing. An opacity value of 75% was assigned to the selected material. We found this value optimal for vascular display from previous spiral CT studies (C.D.M., unpublished data, 1997) of the aortic branches.



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  		Figure 1. Graph of CT scan data as classified by a trapezoid. Point C represents the nominal attenuation value for the contrast material. Points B and D are the maximum variation acceptable for point C such that the voxel number still represents this contrast material entirely. Points A and E correspond to the minimum and maximum attenuation levels, respectively, of a voxel that contains none of the contrast material.

 
For SSD, the upper and lower thresholds were determined by measuring the attenuation value of the intraluminal contrast material. In 10 cases with high-attenuation mural calcifications seen on the axial sections, additional processing was performed to remove the calcifications by tracing a boundary line as described by Dillon et al (6).

Seven views of each carotid artery were obtained about the z axis from a sagittal projection at 30° intervals for VRT and SSD.

Image Analysis
DSA images and spiral CT images of the 23 patients were evaluated by three senior radiologists (C.D.M., V.J.L.M., B.P.M.) independently and in a blinded fashion. Each of the data sets was evaluated separately in a different, randomized order to allow individual assessment for DSA and for each of the CT rendering techniques. Determination of the percentage of stenosis was carried out according to the North American Symptomatic Carotid Endarterectomy Trial, NASCET, criteria (1). The stenoses were graded in four categories: grade 0 was defined as 0%–29%, grade 1 was defined as 30%–69%, grade 2 was defined as 70%–99%, and grade 3 was defined as 100%. The site of maximal stenosis was measured and compared with the more distal part of the postbulbar internal carotid artery (17).

The relationship between CT angiography and DSA with regard to the degree of stenosis was analyzed by using standard linear regression analysis. The sensitivity and specificity of the two CT angiographic techniques were calculated for the presence of hemodynamically significant stenoses (reduction of luminal diameter of 70% or more), with DSA results as the standard of reference. We used the {chi}2 test to determine any statistically significant differences between sensitivity and specificity. A P value less than .05 was considered significant. The results of the individual interpretations for the DSA and CT angiograms were tested for interobserver agreement by using the linear, weighted {kappa} index ({kappa}w) (18). The {kappa}w values can range from -1 (no agreement) to 1 (perfect agreement). Interobserver agreement was classified as follows: poor, {kappa}w = 0.00; slight, {kappa}w = 0.01–0.20; fair, {kappa}w = 0.21–0.40; moderate, {kappa}w = 0.41–0.60; substantial, {kappa}w = 0.61–0.80; or almost perfect, {kappa}w = 0.81–1.00 (18).


   RESULTS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Forty-six carotid arterial bifurcations were evaluated in the current study, representing all degrees of carotid stenosis severity. Of these 46 carotid arteries, a mean of 17.6 was 70% or more stenotic at DSA (Table 1). All carotid arteries were correctly depicted at CT angiography, which allowed us to evaluate the degree of stenosis in each case. The mean attenuation value of the contrast material–filled lumen was 296 HU (range, 249–592 HU). Each of the 46 carotid arteries was graded by the three observers for a total of 138 readings. The results of the three reviewers' interpretations are summarized in Table 2. We found an 85% (39 of 46) agreement for carotid arterial stenosis grade between VRT CT angiography and DSA (Table 2). Agreement for carotid arterial stenosis grade between SSD CT angiography and DSA was 83% (38 of 46) (Table 2).


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  		TABLE 1. Grades of Carotid Artery Stenosis Seen at DSA in 23 Patients
 

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  		TABLE 2. Stenosis Grades with VRT and SSD CT Angiography and with DSA by Reviewer
 
Figure 2 shows the results of the linear regression analysis of the degree of stenosis seen on CT angiograms and on DSA images. The stenosis category at VRT CT angiography was misclassified in 21 (15%) of the 138 individual readings. Fourteen (66%) of these 21 misclassified stenoses appeared less severe on VRT CT angiograms than on DSA images (Table 2). The sensitivity and specificity of VRT CT angiography for the detection of grade 2–3 stenoses (>=70% stenosis) were 89% (16 of 18) and 96% (27 of 28), respectively, for observer 1; 94% (16 of 17) and 97% (28 of 29), respectively, for observer 2; and 94% (17 of 18) and 96% (27 of 28), respectively, for observer 3 (Fig 3). The sensitivity and specificity of SSD CT angiography for the detection of grade 2–3 stenoses were 89% (16 of 18) and 93% (26 of 28), respectively, for observer 1; 88% (15 of 17) and 93% (27 of 29), respectively, for observer 2; and 94% (17 of 18) and 93% (26 of 28), respectively, for observer 3 (Fig 3). There was no statistically significant difference in the sensitivity and specificity calculated for VRT CT angiography and those obtained for SSD CT angiography.



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  		Figure 2. Graph shows linear regression analysis results for the three observers for the degree of stenosis determined with VRT and SSD CT angiograms and DSA images. The dashed line indicates perfect correlation between CT angiography and DSA. The regression lines for VRT and SSD CT angiography are almost identical to each other. CTA = CT angiography.

 


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  		Figure 3a. Left carotid bifurcation in a 75-year-old man with severe stenosis. (a) DSA image, oblique view, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long arrow) of the internal carotid artery. Two small calcifications (short arrows) are seen as filling defects above the stenosis. The internal jugular vein (arrowhead) obscures the distal portion of the internal carotid artery. (c) Spiral SSD CT angiogram in the lateral view shows severe stenosis of the internal carotid artery (arrow). The internal jugular vein (arrowhead) is again noted.

 


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  		Figure 3b. Left carotid bifurcation in a 75-year-old man with severe stenosis. (a) DSA image, oblique view, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long arrow) of the internal carotid artery. Two small calcifications (short arrows) are seen as filling defects above the stenosis. The internal jugular vein (arrowhead) obscures the distal portion of the internal carotid artery. (c) Spiral SSD CT angiogram in the lateral view shows severe stenosis of the internal carotid artery (arrow). The internal jugular vein (arrowhead) is again noted.

 


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  		Figure 3c. Left carotid bifurcation in a 75-year-old man with severe stenosis. (a) DSA image, oblique view, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long arrow) of the internal carotid artery. Two small calcifications (short arrows) are seen as filling defects above the stenosis. The internal jugular vein (arrowhead) obscures the distal portion of the internal carotid artery. (c) Spiral SSD CT angiogram in the lateral view shows severe stenosis of the internal carotid artery (arrow). The internal jugular vein (arrowhead) is again noted.

 
Interobserver agreement between reviewers for VRT and SSD CT angiographic image interpretations is summarized in Table 3. All three observers failed to identify a case with severe carotid arterial stenoses that was underscored by two categories at VRT and SSD CT angiography (Fig 4). However, in this case, the axial images clearly showed the narrowed vessel lumen.


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  		TABLE 3. VRT and SSD CT Angiographic Findings: Interobserver Agreement
 


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  		Figure 4a. Right carotid bifurcation in a 68-year-old man with two stenotic lesions. (a) DSA image, in the oblique projection, shows two severe stenoses (arrows) of the internal carotid artery. (b) Spiral VRT CT angiogram of the right carotid artery in the oblique projection fails to demonstrate hemodynamically significant stenoses of the internal carotid artery (arrows).

 


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  		Figure 4b. Right carotid bifurcation in a 68-year-old man with two stenotic lesions. (a) DSA image, in the oblique projection, shows two severe stenoses (arrows) of the internal carotid artery. (b) Spiral VRT CT angiogram of the right carotid artery in the oblique projection fails to demonstrate hemodynamically significant stenoses of the internal carotid artery (arrows).

 
Mural calcifications were present in 12 (26%) cases, and they were of high attenuation and were extensive in 10 (22%) cases. Large calcified plaques appeared on VRT images as a mural filling defect outlined by the contrast material–opacified lumen (Fig 5). When the plaque was less prominent, VRT permitted the visualization of the contrast material–filled lumen in transparency through the calcification. In two of the 10 cases with high-attenuation calcifications, the circumferential calcified plaque was surrounded by a high-attenuation rim owing to partial volume effects (Fig 5). The brightness of this rim was similar to that observed for contrast material within the vessel lumen. In these cases, measuring the apparent vessel lumen should result in potential underestimation of the carotid stenosis. Therefore, for grading of the stenosis the thickness of the high-attenuation rim was measured at the site opposite to the vascular lumen and then was subtracted from the narrowest diameter of the residual lumen.



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  		Figure 5a. Left carotid arterial bifurcation in a 71-year-old man with hemodynamically significant stenosis. (a) DSA image, anterior projection, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long solid arrow). The calcification (short solid arrow at lower portion) is seen as a mural filling defect and allows analysis of the residual lumen. Note the artifact (arrowhead) due to high-attenuation dental material. The assessment of stenosis severity was achieved by subtracting the high-attenuation rim (open arrows) from the narrowest diameter of the residual vascular lumen. (c) Spiral SSD CT angiogram in the lateral view with segmentation of the calcified plaque shows a severe stenosis (arrow). Note the artifact due to high-attenuation dental material (arrowhead).

 


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  		Figure 5b. Left carotid arterial bifurcation in a 71-year-old man with hemodynamically significant stenosis. (a) DSA image, anterior projection, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long solid arrow). The calcification (short solid arrow at lower portion) is seen as a mural filling defect and allows analysis of the residual lumen. Note the artifact (arrowhead) due to high-attenuation dental material. The assessment of stenosis severity was achieved by subtracting the high-attenuation rim (open arrows) from the narrowest diameter of the residual vascular lumen. (c) Spiral SSD CT angiogram in the lateral view with segmentation of the calcified plaque shows a severe stenosis (arrow). Note the artifact due to high-attenuation dental material (arrowhead).

 


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  		Figure 5c. Left carotid arterial bifurcation in a 71-year-old man with hemodynamically significant stenosis. (a) DSA image, anterior projection, shows severe stenosis (arrow) of the internal carotid artery. (b) Spiral VRT CT angiogram of the left carotid artery in the lateral projection shows severe stenosis (long solid arrow). The calcification (short solid arrow at lower portion) is seen as a mural filling defect and allows analysis of the residual lumen. Note the artifact (arrowhead) due to high-attenuation dental material. The assessment of stenosis severity was achieved by subtracting the high-attenuation rim (open arrows) from the narrowest diameter of the residual vascular lumen. (c) Spiral SSD CT angiogram in the lateral view with segmentation of the calcified plaque shows a severe stenosis (arrow). Note the artifact due to high-attenuation dental material (arrowhead).

 
In 10 of the 10 cases (three grade 2, three grade 1, and four grade 0 stenoses) with extensive high-attenuation calcifications, VRT allowed an accurate grading of the carotid stenosis (Fig 5). However, in two cases, VRT showed a 23% stenosis and a 26% stenosis, although the internal carotid arteries were considered normal at DSA examination. The percentage of stenosis in eight of the 10 cases with severely calcified plaques was evaluated accurately at SSD CT angiography. In the two remaining cases, one moderate stenosis and one mild stenosis were overestimated by one category by the three reviewers.

VRT reconstructions were obtained in approximately 2 minutes (range, 1–3 minutes) for each carotid artery. SSD images were obtained in approximately 1 minute. In the 10 cases with calcified plaques, the additional processing time to segment the calcifications prior to SSD viewing was typically about 15 minutes (range, 9–24 minutes) for each carotid artery.


   DISCUSSION
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
In the present study, an excellent agreement rate of 85% was found between measurements of carotid stenosis on the VRT CT angiograms and those on the DSA images (Fig 2). VRT CT angiography was at least as accurate as SSD CT angiography in the evaluation of carotid arterial bifurcations. The majority of severely stenotic arteries and all occluded carotid arteries were depicted accurately on VRT views (Table 2). However, a severe stenosis on DSA images was misclassified as a mild stenosis on VRT CT angiograms (Fig 4). As this stenosis was correctly identified on axial source images, we therefore recommend careful review of the axial source images in conjunction with three-dimensional reconstructions.

Segmentation with VRT is based on the percentage classification technique (19). The percentage classification is used to estimate the probability for a material to be homogeneously present in a voxel (20). This method provides accurate determination of the amounts of materials when the voxel consists of two or more different materials that are volume averaged. Precise selection of the attenuation values that correspond to the contrast material–filled lumen and assigning opacity to the contrast material allowed us to obtain CT angiograms and to visualize mural calcifications in transparency on the display of the enhanced vessel lumen (Fig 5).

The choice of the minimum and maximum segmentation levels is crucial when using thresholding classification for SSD or percentage classification for VRT, as it is the principal source of error in accurate estimation of the degree of stenosis (6). Schwartz et al (4) measured the attenuation value of the intraluminal contrast material at the narrowest point in the artery. However, it may be difficult to obtain reliable attenuation measurements in cases of severe stenosis because of partial volume effects between the vessel lumen and the atheromatous plaque. Dillon et al (6) addressed this problem when the diameter of the residual lumen was too small by always measuring the attenuation of the lumen in a central portion of the lumen above or below the stenosis. They empirically selected voxels with an attenuation representing 70% lumen and 30% soft tissue (6). By using this method, the stenosis on CT angiograms tended to be less severe than that on angiographic views (6).

Unlike the binary classification system used in these two studies (4,6) with three-dimensional SSD, the percentage classifier algorithm in VRT determines the relative components of each voxel to account for the volume averaging of different tissue types within a single voxel (19). The segmentation problem with VRT has been reduced to determining the values for points A, B, D, and E of the trapezoid. The attenuation values for points B and D were determined by selecting the highest and lowest attenuation values found within three attenuation measurements of the intraluminal contrast material. Points A and E were defined less precisely by viewing the VRT graph. However, in our experience, when making the slopes of segments AB and DE not too large, a change of up to ±30 HU in the attenuation values of points A, B, D, and E did not affect the assessment of stenosis severity.

In our study, the discrepancy between results from DSA and those from spiral CT is probably due to partial volume effects and to an inadequate choice in determining the values for the trapezoids on the VRT graphs. It must be noted that beam-hardening artifacts also may have influenced the apparent attenuation coefficients, which in turn may have affected the tissue classification. These potential errors in attenuation measurements led to an underestimation of the stenosis severity, as 14 (66%) of the 21 stenoses misclassified when adding the individual readings of the three reviewers appeared to be less severe on VRT CT angiograms than on DSA images (Fig 4). Making segments AB and DE vertical will decrease this tendency toward underestimation but conversely will increase the chance of producing three-dimensional images with stenoses that are not real. Because determining the attenuation values for the trapezoids is important to accuracy in VRT CT angiography, further research must be done to optimize this process.

Previous spiral CT studies (4–7) of the carotid bifurcation demonstrated promising results by using SSD and maximum intensity projection displays. Maximum intensity projection is an accurate method for localizing vascular calcifications, but high-attenuation calcified plaques may obscure the vessel lumen and make stenosis measurement impossible. In the majority of the studies (4–7,13), circumferential calcified mural plaques have limited the analysis at CT angiography. To our knowledge, there is currently no reliable method for resolving the problem of mural calcifications. Every technique performed to eliminate high-attenuation mural calcifications may lead to over- or undersegmentation of the calcifications (4,6,7,13). Moreover, segmentation of the calcifications typically requires 18–30 minutes of operator and computer time to segment and remove the calcifications (4,12).

In our study, the computer processing for VRT was slightly slower than for SSD displays. Nevertheless, in cases of calcified bifurcations, VRT CT angiograms were obtained without supplementary processing, whereas the segmentation of calcifications prior to SSD viewing required an additional 15 minutes of processing time for each carotid artery. In our experience, VRT appeared to be sufficiently reliable to allow an accurate evaluation of the degree of carotid stenosis, even in cases of severely calcified carotid bifurcations.

We found that VRT represents a valuable tool for grading carotid arterial stenosis. Because VRT provides excellent visualization of the lumen in calcified vessels, it allows for accurate assessment of high-attenuation circumferential atheromatous plaques. Therefore, in cases with mural calcifications on the source images, we suggest that the VRT technique be used initially, rather than the SSD method, which requires additional time-consuming segmentation or subtraction.


   Acknowledgments
 
Special thanks to Linda Jourdain and Dominique Staumont for technical assistance and to Béatrice Fabritius for photographic assistance.


   Footnotes
 
Abbreviations: DSA = digital subtraction angiography SSD = shaded-surface display VRT = volume-rendering technique

Author contributions: Guarantor of integrity of entire study, C.D.M.; study concepts and design, C.D.M., B.P.M.; definition of intellectual content, B.P.M.; literature research, C.D.M., V.J.L.M.; clinical studies, C.D.M., C.C., B.B.; data acquisition, C.D.M., V.J.L.M., J.L.B.; data analysis, C.D.M., V.J.L.M., B.P.M.; manuscript preparation, C.D.M.; manuscript editing and review, C.D.M., V.J.L.M., J.L.B., C.C., B.B., B.P.M.


   References
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high grade carotid stenosis. N Engl J Med 1991; 325:445-453.[Abstract]
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  7. Cumming MJ, Morrow IM. Carotid artery stenosis: a prospective comparison of CT angiography and conventional angiography. AJR 1994; 163:517-523.[Abstract/Free Full Text]
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3D Digital Subtraction Angiography of Intracranial Aneurysms: Comparison of Flat Panel Detector with Conventional Image Intensifier TV System Using a Vascular Phantom
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L. Saba, G. Caddeo, R. Sanfilippo, R. Montisci, and G. Mallarini
Efficacy and Sensitivity of Axial Scans and Different Reconstruction Methods in the Study of the Ulcerated Carotid Plaque Using Multidetector-Row CT Angiography: Comparison with Surgical Results
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K. Nael, J. P. Villablanca, W. B. Pope, T. O. McNamara, G. Laub, and J. P. Finn
Supraaortic Arteries: Contrast-enhanced MR Angiography at 3.0 T--Highly Accelerated Parallel Acquisition for Improved Spatial Resolution over an Extended Field of View
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K. R. Nandalur, E. Baskurt, K. D. Hagspiel, M. Finch, C. D. Phillips, S. R. Bollampally, and C. M. Kramer
Carotid Artery Calcification on CT May Independently Predict Stroke Risk
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C. de Monye, F. Cademartiri, T. T. de Weert, D. A. M. Siepman, D. W. J. Dippel, and A. van Der Lugt
Sixteen-Detector Row CT Angiography of Carotid Arteries: Comparison of Different Volumes of Contrast Material with and without a Bolus Chaser
Radiology, November 1, 2005; 237(2): 555 - 562.
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M. Berg, Z. Zhang, A. Ikonen, P. Sipola, R. Kalviainen, H. Manninen, and R. Vanninen
Multi-Detector Row CT Angiography in the Assessment of Carotid Artery Disease in Symptomatic Patients: Comparison with Rotational Angiography and Digital Subtraction Angiography
AJNR Am. J. Neuroradiol., May 1, 2005; 26(5): 1022 - 1034.
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M. J.W. Koelemay, P. J. Nederkoorn, J. B. Reitsma, and C. B. Majoie
Systematic Review of Computed Tomographic Angiography for Assessment of Carotid Artery Disease
Stroke, October 1, 2004; 35(10): 2306 - 2312.
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J. W. Olin, J. A. Kaufman, D. A. Bluemke, R. O. Bonow, M. D. Gerhard, M. R. Jaff, G. D. Rubin, and W. Hall
Atherosclerotic Vascular Disease Conference: Writing Group IV: Imaging
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E. G. Grant, C. B. Benson, G. L. Moneta, A. V. Alexandrov, J. D. Baker, E. I. Bluth, B. A. Carroll, M. Eliasziw, J. Gocke, B. S. Hertzberg, et al.
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Radiology, November 1, 2003; 229(2): 340 - 346.
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J. Alvarez-Linera, J. Benito-Leon, J. Escribano, J. Campollo, and R. Gesto
Prospective Evaluation of Carotid Artery Stenosis: Elliptic Centric Contrast-Enhanced MR Angiography and Spiral CT Angiography Compared with Digital Subtraction Angiography
AJNR Am. J. Neuroradiol., May 1, 2003; 24(5): 1012 - 1019.
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R. Corti, M. Alerci, R. Wyttenbach, P. L. Pedrazzi, A. Gallino, T. Hirai, and Y. Korogi
Usefulness of Multiplanar Reconstructions in Evaluation of Carotid CT Angiography * Drs Hirai and Korogi respond:
Radiology, January 1, 2003; 226(1): 290 - 292.
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C. Porsche, L. Walker, D. Mendelow, and D. Birchall
Evaluation of Cross-Sectional Luminal Morphology in Carotid Atherosclerotic Disease by Use of Spiral CT Angiography
Stroke, November 1, 2001; 32(11): 2511 - 2515.
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D. A. Bluemke, A. E. Stillman, K. G. Bis, T. M. Grist, R. A. Baum, R. D’Agostino, E. S. Malden, J. A. Pierro, and E. K. Yucel
Carotid MR Angiography: Phase II Study of Safety and Efficacy for MS-325
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