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Maximum Stenosis of Extracranial Internal Carotid Artery: Effect of Luminal Morphology on Stenosis Measurement by Using CT Angiography and Conventional DSA¹

¹ From the Departments of Radiology (T.H., K.O., Y.M.) and Neurosurgery (K.S., S.U.), Amakusa Medical Center, 854-1 Kameba, Hondo, Kumamoto 863-0046, Japan; and Department of Radiology, Kumamoto University School of Medicine, Japan (Y.K., M.T.). Received November 1, 2000; revision requested December 23; revision received March 13, 2001; accepted April 18. Address correspondence to T.H. (e-mail: toshinor@beige.ocn.ne.jp).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To assess the luminal morphology of the extracranial internal carotid artery at three-dimensional (3D) computed tomographic (CT) angiography and how this factor affects measurement of maximum carotid arterial stenoses at conventional intraarterial digital subtraction angiography (DSA).

MATERIALS AND METHODS: Prospectively, conventional intraarterial DSA and 3D CT angiography were performed in 42 carotid arteries in 21 patients with suspected carotid artery disease. The longest axis length–perpendicular axis length (L/P) ratios of the arterial lumen on the cross-sectional images at the most stenotic area and distal nonstenotic area were analyzed by acquiring multiplanar reconstruction (MPR) images at 3D CT angiography. The maximum stenosis was measured at each modality with North American Symptomatic Carotid Endarterectomy Trial criteria.

RESULTS: The L/P ratios in the most stenotic areas ranged from 1.0 to 3.2 (mean, 1.5 ± 0.5 [SD]). The mean difference in maximum percentage of stenosis between the two modalities for L/P ratios of 2.0 or greater was significantly greater than that for L/P ratios of less than 1.5 (P < .05). Three carotid arteries with 70%–99% stenosis, with grades determined only with 3D CT angiography, had L/P ratios of 2.0 or greater.

CONCLUSION: On MPR images at 3D CT angiography, the lumen of extracranial internal carotid artery stenosis showed a wide range of shapes. When a carotid artery has a high L/P ratio, the luminal morphology of the carotid artery stenosis may affect the assessment of maximum stenosis of the internal carotid artery at conventional DSA.

Index terms: Carotid arteries, angiography, 1722.1247 • Carotid arteries, CT, 1722.12113, 1722.12117 • Carotid arteries, stenosis or obstruction, 1722.721 • Computed tomography (CT), three-dimensional, 1722.12117 • Digital subtraction angiography, 1722.721 • Digital subtraction angiography, comparative studies

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The degree of stenosis of the internal carotid artery is associated with the risk of stroke. Findings in studies from the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the European Carotid Surgery Trial have proved that symptomatic patients with severe stenoses (70%–99%) can benefit from carotid endarterectomy (1–3). Carotid endarterectomy may also be useful for treating asymptomatic patients with carotid artery stenosis greater than 60% (4). In addition, the findings in NASCET studies indicate that some patients with stenosis as low as 50% can benefit from carotid endarterectomy (3). In these studies, maximum internal carotid artery stenosis was assessed by using conventional angiography or intraarterial digital subtraction angiography (DSA) in two or three projections. However, findings in previous studies with color duplex ultrasonography (US) showed that conventional angiography or intraarterial DSA has a tendency to underestimate the degree of carotid artery stenosis (5–9).

Recently, Elgersma et al (10) reported that rotational angiography, compared with DSA in two or three projections, frequently depicts more severe carotid artery stenosis. The stenotic lumen of the carotid artery has a wide variety of shapes and is usually asymmetric (9). Overlapping vessels may interfere with the assessment of the stenosis at conventional angiography or intraarterial DSA. Therefore, the maximum internal carotid artery stenosis may not always be assessed accurately by using a small number of projections at conventional angiography or intraarterial DSA.

Although conventional angiography and DSA are the reference standard for evaluating carotid disease, cerebral angiographic complications still remain. An accurate noninvasive imaging study is necessary to determine the indications for carotid endarterectomy in both symptomatic and asymptomatic patients with significant internal carotid artery stenoses. For the preoperative evaluation, diseases that require surgery (70%–99% stenoses) must be differentiated from diseases that do not require surgery (stenoses less than 70% and occlusions). With current noninvasive imaging modalities, it has been proved that three-dimensional (3D) computed tomographic (CT) angiography correlates well with catheter angiography and has a high discrimination rate between severe stenoses and occlusions (11–17).

On the basis of findings in some investigations (13–17), the diagnostic accuracy of 3D CT angiography for 70%–99% stenosis was considered to have a sensitivity of 100% and a specificity of 94%–100%. At 3D CT angiography, angiogram-like images can be obtained, and the cross-sectional luminal morphology also can be evaluated by using the multiplanar reconstruction (MPR) method. To our knowledge, no studies have been published in which MPR images at 3D CT angiography were used to assess the luminal morphology of the internal carotid artery and to measure the carotid artery stenosis.

The purpose of this prospective study was to assess the luminal morphology of the extracranial internal carotid artery on MPR images at 3D CT angiography and how this factor affects measurement of maximum internal carotid artery stenoses at conventional DSA.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Patients
From June 1998 to May 1999, 456 consecutive patients with neurologic symptoms underwent magnetic resonance (MR) angiographic examination for the screening of neurovascular disease. Hemodynamically significant stenoses involving the extracranial internal carotid artery were identified at MR angiography in 25 of the 456 patients. Criteria for inclusion in the prospective study were presence of hemodynamically significant stenoses involving the extracranial internal carotid artery at MR angiography, clinical evidence of neurologic symptoms or signs, and provision of informed consent by the patients. We excluded patients with the following: high risks, including heart failure and renal failure; poor physical condition; or a history of head and neck surgery. Finally, a total of 21 patients (17 men, four women; age range, 52–82 years; mean age, 68 years) who met all criteria were prospectively examined with both 3D CT angiography and DSA. The maximum stenosis of the extracranial internal carotid artery was measured at examination with the two modalities on the basis of NASCET criteria. This study was approved by the institutional review board. Symptoms and signs of the patients included transient ischemic attack (n = 8), dizziness (n = 5), hemiparesis (n = 3), syncopal attack (n = 2), gait disturbance (n = 2), and amaurosis fugax (n = 1).

Conventional Intraarterial DSA
Conventional intraarterial DSA and 3D CT angiography were performed within 10 days of each other. Conventional intraarterial DSA was performed with a DSA unit (DFA-100; Hitachi, Tokyo, Japan) with an image matrix of 1,024 x 1,024. All catheterizations were performed through a transfemoral approach by using the Seldinger technique. The angiographic procedure was routinely accomplished with a standard diagnostic catheter. Selective common carotid artery angiograms were obtained bilaterally in the anteroposterior and lateral projections. If a bifurcation was not adequately visualized, oblique carotid artery angiograms also were obtained. For each projection, 6 mL of nonionic contrast material (Iopamiron 300 [300 mg of iodine per milliliter]; Schering, Osaka, Japan) was injected at a flow rate of 4–5 mL/sec with a power injector (Auto Enhance A-50; Nemoto Kyorindo, Tokyo, Japan).

Three-dimensional CT Angiography
Three-dimensional CT angiography was performed with a helical CT scanner (W3000 AD; Hitachi, Tokyo, Japan). Before the volume scanning, nonenhanced CT of the neck between C6 and C3 was performed with 5-mm-thick transverse sections to identify the carotid artery bifurcations. The volume scanning began at a level 25 mm caudal to the carotid artery bifurcation and continued cranially. Volume data were acquired in 30 seconds by using a section thickness of 2 mm and a table speed of 2 mm/sec (175 mA, 120 kV). The scanning area was 60 mm in length, and the field of view was 15 cm, with a 512 x 512 matrix. The nonionic contrast material (100 mL) was injected into the antecubital vein at a flow rate of 3.0 mL/sec with the power injector. An automatic triggering system was used to detect a bolus of contrast material in the common carotid artery. This triggering technique consisted of region-of-interest (ROI) measurements in the common carotid artery during low-dose scanning every 2.5 seconds, beginning 10 seconds after contrast medium injection.

One radiologist (T.H.) selected the ROI bilaterally within the common carotid artery. The size of the ROI was approximately one-fourth of the structure selected. When enhancement of the carotid artery reached 80 HU, spiral scanning was initiated after a 4-second delay. In the first seven patients (14 carotid arteries), however, the spiral scanning was started after a 20-second delay without use of the automatic triggering system. Patients were instructed to breathe quietly without swallowing during scanning.

Images were reconstructed every 1.0 mm. Three-dimensional image reconstruction was performed with a voxel transmission method, a kind of volume-rendering technique that permits visualization of minimal differences in attenuation to create 3D angiograms (18). One radiologist manually selected ROIs by drawing them along the outer margin of the common, internal, and external carotid arteries on transverse source images. The bone structures, the enhancing jugular veins, and the distal branches of the external carotid artery were excluded from the ROIs. The 3D CT angiograms were viewed from multiple angles on a monitor and were printed in sequential 15° rotation intervals and in the orientation showing the greatest stenosis.

Image Analysis
The acquisition and evaluation of the DSA images and 3D CT angiograms were performed by different radiologists. One reviewer (T.H.) subjectively classified the quality of the DSA images and 3D CT angiograms as excellent (high quality for diagnostic purposes), good (slightly lower quality but still useful for diagnostic purposes), or poor (suboptimal for diagnostic purposes). When the images were judged to be excellent or good, the arterial lumen was evaluated on DSA images and CT angiograms in a blinded manner by two independent radiologists (K.O., Y.M.). When findings with each modality were analyzed, reviewers were blinded to information from the other modality and to clinical data.

At DSA, the images were magnified by using a loupe with a magnifying power of x5, and the outermost margin of the vessel lumen was selected. Subsequently, vessel lumina on the DSA images were measured by using a commercially available Vernier caliper with 0.1-mm divisions. No measurement was performed when the internal carotid artery appeared to be normal or occluded. If a stenosis was suspected on DSA images, the image that showed the greatest stenosis was chosen for measurement of the stenosis. The percentage of internal carotid artery stenosis was calculated with NASCET criteria and was derived with the following equation: percentage of stenosis = (1 - [minimal residual luminal diameter/distal carotid artery luminal diameter]) x 100%. The percentage of stenosis was classified as 0%–29%, 30%–49%, 50%–69%, 70%–99%, or 100%.

The MPR images were analyzed in conjunction with the corresponding 3D CT angiograms because of the potential for misinterpretation inherent in the evaluation of MPR images alone. In each internal carotid artery, the cross-sectional images perpendicular to the longitudinal axis of the internal carotid artery at the most stenotic area and its distal nonstenotic area were generated with an MPR technique, and the images were magnified and printed for measurement. On the magnified cross-sectional images, the outermost margin of the vessel lumen was selected, and the luminal length of the longest axis and its perpendicular axis were measured by using the same Vernier caliper (Fig 1). The degree of eccentricity of the luminal shape was determined with the longest axis length–perpendicular axis length (L/P) ratio.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Schematic of lumen of internal carotid artery on MPR images. Outer margin (thick circle) indicates the outermost margin of the arterial wall. Inner margin (thin elliptical line) indicates the outermost margin of the residual lumen. L = the longest axis of the arterial lumen, P = the perpendicular axis of the arterial lumen.

The maximum percentage of stenosis on MPR images at 3D CT angiography was compared with the maximum percentage of stenosis at conventional DSA. Subsequently, to evaluate whether the luminal morphology of the extracranial internal carotid artery at 3D CT angiography affected the maximum percentage of internal carotid stenosis measured at conventional DSA, the differences in maximum percentage of stenosis between that on MPR images at 3D CT angiography and at DSA were compared on the basis of L/P ratio grades.

Statistical Analyses
The statistic was used to assess interobserver reliability of each modality for the measurements of internal carotid stenosis (19). The values greater than 0 were considered to indicate positive agreement; those less than 0.4, positive but poor agreement; those 0.41–0.75, good agreement; and those greater than 0.75, excellent agreement (19). Among groups with each L/P ratio grade, the mean differences in maximum percentage of stenosis between MPR images at 3D CT angiography and at conventional DSA were tested with one-way analysis of variance for multiple comparisons. Once a statistically significant difference (P < .05) was identified among the groups, the Scheffé test was performed.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Imaging data at DSA and 3D CT angiography were successfully obtained in all cases. The image quality of DSA images and 3D CT angiograms was excellent in 37 (left, 18; right, 19) and 31 (left, 16; right, 15) and good in five (left, three; right, two) and 11 (left, five; right, six) carotid arteries, respectively. There were no poor-quality data for either modality. Although two patients who underwent 3D CT angiography without use of the automatic triggering system had slightly insufficient attenuation of the carotid lumen, the 3D CT angiograms had quality suitable for diagnostic purposes.

The maximum internal carotid artery stenosis measurements graded from MPR images at 3D CT angiography versus those graded at conventional DSA are shown in the Table. Grading of stenoses by using MPR images at 3D CT angiography agreed with that at conventional DSA in 36 (86%) of 42 internal carotid arteries (Fig 2), while the degree was classified one grade higher in six internal carotid arteries (14%) in five patients, three for the left and three for the right internal carotid artery (Fig 3). Interobserver reliability between reviewers for measurements of MPR images at 3D CT angiography and at conventional DSA was good ( = 0.72) and excellent ( = 0.80). Stenosis of 70%–99% was depicted in seven internal carotid arteries at 3D CT angiography and in four internal carotid arteries at conventional DSA. Thus, 3D CT angiography demonstrated an additional three 70%–99% internal carotid artery stenoses for possible carotid endarterectomy, which were not identified at conventional DSA.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (89K): [in this window] [in a new window] [Download PPT slide]   Figure 2c. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 2d. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 2e. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 2f. Left internal carotid artery stenosis with L/P ratio of grade 1. (a) Frontal and (b) lateral conventional DSA images of the left common carotid artery show 70% stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms depict the residual lumen at the site of the stenosis (arrow) clearly without any interference from surrounding vessel structures. Arrowhead in d indicates a branch of the internal jugular vein along the external carotid artery (E in e and f) that is partially seen. (e, f) MPR images perpendicular to the longitudinal axis of the internal carotid artery. The percentage of stenosis on the MPR images was nearly equal to that on conventional angiograms. Image of (e) most stenotic area demonstrates a nearly circular lumen (arrow) and image of (f) distal nonstenotic area demonstrates a circular lumen (arrow). Branches (arrowheads in e) of the internal jugular vein (I in e and f) and the external jugular vein (e in e) are seen. The L/P ratio of the lumen was 1.2 in e and 1.0 in f.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 3a. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 3b. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 3c. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (92K): [in this window] [in a new window] [Download PPT slide]   Figure 3d. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 3e. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 3f. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 3g. Left internal carotid artery stenosis with L/P ratio of grade 3. (a) Frontal conventional DSA image of the left common carotid artery shows 66% stenosis (arrow) and (b) lateral DSA image demonstrates the heterogeneity of contrast material opacification at the stenosis (arrow). (c) Frontal and (d) lateral 3D CT angiograms clearly depict the residual lumen at the site of stenosis (arrow). In d, the linear structures (arrowheads) crossing the internal carotid artery are artifacts caused by manual selection of ROI in the adjacent regions of the internal carotid artery and the internal jugular vein. (e) Left anterior oblique 3D CT angiogram reveals the greatest stenosis (arrow) at the site of the stenosis. MPR images perpendicular to the longitudinal axis of the internal carotid artery at the (f) most stenotic area demonstrate an eccentric lumen (arrow) and at the (g) distal nonstenotic area show nearly circular lumen (arrow). Image in g was classified one grade higher with MPR images at 3D CT angiography. The L/P ratio was 2.1 in f and 1.1 in g. In f and g, E = external carotid artery, I = internal jugular vein.

The differences in maximum percentage of stenosis between MPR images at 3D CT angiography and at conventional DSA were plotted against L/P ratio grades on the MPR images at 3D CT angiography (Fig 4). The mean difference in maximum percentage of stenosis for each L/P ratio grade was as follows: grade 1 (left, 12; right, 11), 0.5 ± 2.8; grade 2 (left, five; right, four), 5.4 ± 7.4; and grade 3 (left, three; right, four), 8.9 ± 7.5. With multiple comparisons, a statistically significant difference was demonstrated among groups with each L/P ratio grade (P = .001). The mean difference in maximum percentage of stenosis for L/P ratios of grade 3 was significantly greater than that for L/P ratios of grade 1 (P = .002). However, there were no statistically significant differences between groups with grade 1 and groups with grade 2 (P = .06) and between groups with grade 2 and groups with grade 3 (P = .42). All three internal carotid arteries (left, one; right, two) with 70%–99% stenosis, which were identified only at 3D CT angiography, had L/P ratios of grade 3.

View larger version (17K): [in this window] [in a new window] [Download PPT slide]   Figure 4. Scattergram shows the differences in maximum percentage of stenosis between MPR images at 3D CT angiography and at conventional DSA versus L/P ratio grades. Percentage of difference indicates the percentage of stenosis with MPR images obtained at 3D CT angiography minus the percentage of stenosis with MPR images obtained at conventional DSA. The L/P ratio grades were as follows: grade 1, L/P ratio less than 1.5; grade 2, L/P ratio greater than or equal to 1.5 and less than 2.0; and grade 3, L/P ratio greater than or equal to 2.0. The mean difference in maximum percentage of stenosis for each L/P ratio grade was as follows: grade 1, 0.5 ± 2.8; grade 2, 5.4 ± 7.4; and grade 3, 8.9 ± 7.5. The mean difference in maximum percentage of stenosis for L/P ratios of grade 3 was significantly greater than that for L/P ratios of grade 1 (P < .05).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

In this study, in which MPR images at 3D CT angiography were used, findings were similar to the results of previous ex vivo and in vivo studies: A wide range of shapes of the lumen was found, and discrepancies between 3D CT angiography and conventional DSA were observed in some arteries in measurements of the maximum internal carotid artery stenosis. In the maximum percentages of stenosis calculated from MPR images at 3D CT angiography and at conventional DSA, the mean difference for the internal carotid arteries with L/P ratios greater than or equal to 2.0 was significantly greater than that for internal carotid arteries with L/P ratios less than 1.5. All three 70%–99% internal carotid artery stenoses, which were identified only by using MPR images at 3D CT angiography, had L/P ratios greater than or equal to 2.0. These indicate that the internal carotid arteries with a high L/P ratio may affect the assessment of maximum stenosis of the internal carotid artery at conventional DSA and may alter patient treatment.

The orientation of the projection and luminal shape at the most stenotic area may affect the measurement of the maximum percentage of stenosis at conventional DSA. When the luminal shape is circular, the percentage of stenosis should be identical in any projection. In contrast, when the lumen at the most stenotic area has an eccentric shape, theoretically, the greatest stenosis would be obtained in the orientation parallel to the longest axis in the lumen at the most stenotic area. Since carotid stenosis usually has a wide variety of directions of the longest axis in the lumen, the direction of the longest axis in the lumen may not always be consistent with that shown on a conventional angiogram.

Conventional angiography usually is observed in only two or three projections, while 3D CT angiography enables observation of the artery from various angles and planes. Although NASCET guidelines are based on conventional angiographic criteria, they may be applied by using other imaging modalities, such as 3D CT angiography, as long as those modalities are concordant with conventional angiography. Furthermore, in the near future, a new guideline might be necessary for using 3D CT angiography to select the candidate for treatment more precisely and effectively.

When the diameter of the lumen was measured at 3D CT angiography, we used the MPR images perpendicular to the longitudinal axis of the internal carotid artery at 3D CT angiography for the following reasons. First, the apparent diameter of the lumen may change with the angiographic display technique (20). Shaded-surface display can clearly depict 3D relationships by simulating light reflections. However, shaded- surface display images cannot display x-ray attenuation for values in structures within the threshold range. Although images with the maximum intensity projection and volume-rendering methods may be more accurate than those with shaded-surface display, the inherent accuracy of vascular depiction is strongly dependent on the parameters used to generate the angiogram-like images (eg, threshold value, window and level setting). Second, calcifications are the limiting factor on maximum intensity projection images owing to the inability to separate mural calcifications and intramural contrast material. To minimize this limitation, analysis in conjunction with transverse source images may be useful (17). Calcifications also can be removed from transverse sections by using manual segmentation (13) or sophisticated software (11), but this procedure is time-consuming and can result in an overestimation of stenosis severity with the removal of neighboring pixels. Third, the measurement of the stenosis with transverse source images at 3D CT angiography may be inaccurate if the vessel is tortuous and the scanning plane is not perpendicular to the arterial lumen. Findings in a study of Leclerc et al (17) showed that transverse images at 3D CT angiography could not always enable correct evaluation of carotid artery stenosis. In their study, one internal carotid artery could not be assessed because of a short and severe stenosis oriented in the transverse plane. Furthermore, overlapping vessels may interfere with the assessment of the stenosis even on maximum intensity projection or volume-rendered images.

Our imaging technique at 3D CT angiography has a theoretic advantage compared with previously reported techniques. First, automatic triggering with detection of a bolus of contrast material in the cervical carotid artery was used to obtain the optimized imaging delay. This technique may permit clear evaluation of luminal shape by producing a high-contrast interface between the contrast medium and vascular wall. Although we did not evaluate whether this automatic triggering system improved the imaging quality in this study, this technique seems to provide optimal attenuation of the vessels and may yield better visualization of the lumen of the carotid artery. Second, a voxel transmission method, which is a kind of volume-rendering technique that allows visualization of minimal differences in attenuation, was used to create 3D angiograms (18). This probably contributed to the better visualization of internal carotid artery stenosis when cross-sectional areas at the most stenotic and distal nonstenotic regions were selected on the 3D CT angiograms. Third, we used 2-mm-wide beam collimation and 1-mm-thick reconstruction sections to obtain the 3D data. These imaging parameters, compared with the parameters used in previous studies (11–17), were sufficient to generate high-quality CT angiograms.

However, to determine the candidate for carotid endarterectomy on the basis of 3D CT angiographic findings, several limitations of 3D CT angiography must be overcome. First, the scanning coverage of vessels should be large. The evaluation of steno-occlusive disease of the distal portions of the extracranial internal carotid artery, intracranial arteries, and collateral circulation, such as the circle of Willis, may be needed prior to surgery. The scanning coverage of single-section CT is not enough to permit examination of all these vessels, but multi–detector row CT can overcome this issue. Second, the imaging quality of 3D CT angiograms must be excellent. The imaging quality is affected by several factors, such as patient motion, imaging technique, and the speed of administration of contrast material. At the present time, 3D CT angiography and conventional angiography may be complementary to each other, and we recommend that both of them be performed for preoperative evaluation, but in the near future, conventional angiography can be omitted.

This study had some limitations. First, the resolution of 3D CT angiography depends on the orientation of the vessel because the pixels are anisotropic. The resolution is approximately 0.2–0.3 mm in the transverse plane but only 1 mm in the z axis. Although this may limit the measurement of internal carotid artery stenosis, we believe that this measurement technique is reliable because the results of 3D CT angiography correlated well with those of conventional DSA in this study. Dynamic scanning with multisection data acquisition may further increase the resolution of this technique and provide more detailed information about the cross-sectional anatomy. Second, the measurement of vascular stenosis on MPR images may have been subject to interference from dense calcification. Use of adequate window and level settings can usually help differentiate the vessel lumen from the vessel wall and calcification on the MPR images. Third, the measurements with MPR images may be susceptible to considerable interobserver variability. In selecting the cross-sectional areas on MPR images, the images were assessed in conjunction with 3D CT angiograms. With this method, interobserver variability of measurements obtained on 3D CT angiograms was good and not substantially different from that of measurements obtained on conventional DSA images. Finally, the results were acquired in a small group of patients. Further studies are warranted in a larger group of patients to investigate the usefulness of MPR images at 3D CT angiography for assessing carotid artery diseases that require surgery.

In conclusion, in vivo luminal morphology of the extracranial internal carotid artery was assessed by using MPR images at 3D CT angiography. The lumen of the internal carotid artery stenosis had a wide range of L/P ratios on the MPR images at 3D CT angiography. When an internal carotid artery has an increased L/P ratio, the luminal morphology of the internal carotid artery stenosis may affect the assessment of maximum stenosis of the internal carotid artery at conventional DSA. This morphologic factor of the lumen of the internal carotid artery is important for patient treatment and should be taken into account when maximum internal carotid artery stenosis is assessed with conventional angiography or intraarterial DSA.

	FOOTNOTES

 
Abbreviations: DSA = digital subtraction angiography, L/P ratio = longest axis length–perpendicular axis length ratio, MPR = multiplanar reconstruction, NASCET = North American Symptomatic Carotid Endarterectomy Trial, ROI = region of interest, 3D = three-dimensional

Author contributions: Guarantor of integrity of entire study, T.H.; study concepts, T.H.; study design, T.H., Y.K.; literature research, T.H.; clinical studies, T.H., K.S., S.U.; data acquisition and analysis/interpretation, T.H., K.O., Y.M.; statistical analysis, T.H.; manuscript preparation, T.H.; manuscript definition of intellectual content, T.H., Y.K.; manuscript editing and revision/review, Y.K., M.T.; manuscript final version approval, M.T.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. European Carotid Surgery Trialists’ Collaborative Group. MRC European carotid surgery trial: interim results for symptomatic patients with severe (70–99%) or with mild (0–29%) carotid stenosis. Lancet 1991; 337:1235-1243.
2. 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.
3. North American Symptomatic Carotid Endarterectomy Trial Collaborators. Benefit of carotid endarterectomy in patients with symptomatic moderate or severe stenosis. N Engl J Med 1998; 339:1415-1425.
4. Executive Committee for the Asymptomatic Carotid Atherosclerosis Study. Endarterectomy for asymptomatic carotid artery stenosis. JAMA 1995; 273:1421-1428.
5. O’Donnell TF, Erdoes LS, Mackey WC, et al. Correlation of B-mode ultrasound imaging and arteriography with pathologic findings at carotid endarterectomy. Arch Surg 1985; 120:443-449.
6. Rubin JR, Bondi JA, Rhodes RS. Duplex scanning versus conventional arteriography for the evaluation of carotid artery plaque morphology. Surgery 1987; 102:749-755.
7. Schenk EA, Bond MG, Aretz TH, et al. Multicenter validation study of real-time ultrasonography, arteriography, and pathology: pathologic evaluation of carotid endarterectomy specimens. Stroke 1988; 19:289-296.
8. Alexandrov AV, Bladin CF, Maggisano R, Norris JW. Measuring carotid stenosis: time for a reappraisal. Stroke 1993; 24:1292-1296.
9. Pan XM, Saloner D, Reilly LM, et al. Assessment of carotid artery stenosis by ultrasonography, conventional angiography, and magnetic resonance angiography: correlation with ex vivo measurements of plaque stenosis. J Vasc Surg 1995; 21:82-89.
10. Elgersma OEH, Buijs PC, Wust AFJ, et al. Maximum internal carotid arterial stenosis: assessment with rotational angiography versus conventional intraarterial digital subtraction angiography. Radiology 1999; 213:777-783.
11. Schwartz RB, Jones KM, Chernoff DM, et al. Common carotid artery bifurcation: evaluation with spiral CT. Radiology 1992; 185:513-519.
12. Marks MP, Napel S, Jordan JE, Enzmann DR. Diagnosis of carotid artery disease: preliminary experience with maximum-intensity-projection spiral CT angiography. AJR Am J Roentgenol 1993; 160:1267-1271.
13. Dillon EM, Van Leeuwen MS, Fernandez MA. CT angiography: application to the evaluation of carotid artery stenosis. Radiology 1993; 189:211-219.
14. Cumming MJ, Morrow IM. Carotid artery stenosis: a prospective comparison of CT angiography and conventional angiography. AJR Am J Roentgenol 1994; 163:517-523.
15. Link J, Brossmann J, Grabener M, et al. Spiral CT angiography and selective digital subtraction angiography of internal carotid artery stenosis. AJNR Am J Neuroradiol 1996; 17:89-94.
16. Link J, Brossmann J, Penselin V, Gluer CC, Heller M. Common carotid artery bifurcation: preliminary results of CT angiography and color-coded duplex sonography compared with digital subtraction angiography. AJR Am J Roentgenol 1997; 168:361-365.
17. Leclerc X, Godefroy O, Lucas C, et al. Internal carotid arterial stenosis: CT angiography with volume rendering. Radiology 1999; 210:673-682.
18. Takagi R, Hayashi H, Kobayashi H, et al. Three dimensional-CT angiography for intracranial aneurysm: new semiautomated reconstruction technique (abstr). Radiology 1998; 209(P):627.
19. Fleiss JL, ed. Statistical methods for rates and proportions 2nd ed. New York, NY: Wiley, 1981; 212.
20. Dix JE, Evans AJ, Kallmes DF, et al. Accuracy and precision of CT angiography in a model of carotid artery bifurcation stenosis. AJNR Am J Neuroradiol 1997; 18:409-415.

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