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Proximal Great Vessels of Aortic Arch: Comparison of Three-dimensional Gadolinium-enhanced MR Angiography and Digital Subtraction Angiography¹

¹ From the Department of Neuroradiology, Groupe hospitalier Pitié-Salpêtrière, Bâtiment Babinski, 47–83 Blvd de l’Hôpital, 75651 Paris Cedex 13, France. Received October 9, 2001; revision requested December 20; final revision received February 6, 2003; accepted March 19. Address correspondence to B.R. (e-mail: bruno.randoux@caramail.com).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To prospectively compare dynamic three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography and digital subtraction angiography (DSA) for the detection of ostial stenosis of the craniocervical vessels.

MATERIALS AND METHODS: Thirty-three patients with carotid stenosis of more than 50% at sonography prospectively underwent both MR angiography and DSA. The overall quality of each DSA and MR angiographic study was analyzed. For each craniocervical vessel (brachiocephalic, common carotid, subclavian, and vertebral arteries) (n = 231), ostial stenosis was graded as follows: normal, mild (<50%), moderate to severe (>50%), or occlusion. MR angiographic and DSA results were compared by means of the Spearman rank correlation coefficient (Rs).

RESULTS: The overall diagnostic quality of MR angiography was excellent or adequate. Three studies were inadequate because of a poor signal-to-noise ratio (13 of 231 arteries) or a coverage error (five of 231 arteries). Findings at MR angiography and DSA agreed on the degree of stenosis (Rs = 0.82, P < .001). No cases of stenosis of more than 50% were missed at MR angiography. However, some discrepancies were noted between vertebral arteries and the other craniocervical vessels. The sensitivity and specificity for stenosis of more than 50% in other craniocervical vessels were 100% and 98%, respectively. The sensitivity and specificity for stenosis of more than 50% in the vertebral arteries were 100% and 85%, respectively. Findings at MR angiography tended to result in overestimation of the degree of ostial stenosis, especially in vertebral arteries (10 [15%] of 66 arteries).

CONCLUSION: MR angiography is useful to rule out ostial stenosis of the craniocervical vessels. MR angiography is an adequate diagnostic tool for ostial stenosis, except in the vertebral artery.

© RSNA, 2003

Index terms: Angiography, comparative studies, 90.1222 • Blood vessels, MR, 90.12942 • Blood vessels, stenosis or obstruction, 90.72 • Magnetic resonance (MR), vascular studies, 90.12942 • Vertebral arteries, MR, 90.12942 • Vertebral arteries, stenosis or obstruction, 901.72

	INTRODUCTION

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Digital subtraction angiography (DSA), despite its inherent risks and cost (1,2), is the current reference standard for evaluation of craniocervical vessels. However, the advent of noninvasive methods such as dynamic three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography has resulted in modification of the role of DSA (3).

MR angiography depicts carotid stenosis with good sensitivity and specificity (93% and 100%, respectively, for stenosis of more than 70%) (3,4), but few data are available on the use of this method for ostial stenosis of the craniocervical vessels. This is of clinical importance because vertebral artery stenosis is associated with carotid stenosis in 14.7% of cases (5). Full vascular imaging is required for diagnosis and surgical planning in patients known to have or suspected of having cerebrovascular occlusive disease (6).

The purpose of this prospective study was to compare gadolinium-enhanced MR angiography and DSA for the detection of ostial stenosis in the craniocervical vessels.

	MATERIALS AND METHODS

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Patients
Between October 2000 and May 2001, we investigated 36 consecutive symptomatic patients referred to our institution by a vascular surgeon for endarterectomy on the basis of sonographic findings (internal carotid stenosis, >50%). Patients were excluded (n = 3) if they had contraindications to DSA or MR angiography (creatinine > 120 µmol/L, renal failure, or pacemaker). Thus, the study group comprised eight women and 25 men (age range, 32–83 years; median, 62 years). All patients underwent MR angiography and DSA in random order within a 2-week period. The study protocol was approved by the local medical ethics committee, and all patients gave their written informed consent before entering the study.

Imaging
DSA (Easyvision; Philips; Best, the Netherlands) was performed with femoral artery catheterization. Arch aortograms were obtained in two oblique projections (-45° and +45°) with intraarterial injection of 40 mL of a nonionic contrast material (Omnipaque 300; Nycomed, Oslo, Norway), at a rate of 20 mL/sec via a 4-F pigtail catheter (Cordis; Johnson and Johnson, Roden, the Netherlands). DSA was performed with a 33-cm field of view and a 1,024 x 1,024 matrix. The spatial resolution was 0.32 x 0.32 mm. Arch aortography was followed by selective catheterization of subclavian arteries. Anteroposterior and lateral images were obtained for each catheterization, with a 15-cm field of view. Eight milliliters of the nonionic contrast medium was infused at each injection.

Three-dimensional MR angiography was performed with a 1.5-T device (Signa; GE Medical Systems, Milwaukee, Wis) equipped with a neurovascular head and neck coil. MR angiography was performed in the coronal plane from the arch to the skull base with fast imaging (repetition time msec/echo time msec of 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, imaging time of 32 seconds). The spatial resolution was 1.1 x 1.1 x 1.6 mm. Breath holding was not used. Zero-filling interpolation was used. The centric phase-ordering scheme was used for k-space filling, which is most sensitive to early image contrast enhancement produced by the arrival of the bolus of contrast material. The contrast material (Dotarem [0.5 mmol/mL], Laboratoire Guerbet, Aulnay-su-Bois, France) was infused through a 22-gauge venous angiocatheter in the antecubital fossa by using a power injector (Spectris; Medrad, Pittsburg, Pa). Twenty milliliters of contrast material was injected at a rate of 2.5 mL/sec. Each bolus was immediately followed by a 20-mL saline flush. The MR SmartPrep technique (GE Medical Systems) was used with a 5 x 10-mm tracker volume placed in the aortic arch. All patients but one who did not have right arm venous access received the injection in the right arm.

The images were postprocessed with a Windows Advantage workstation (GE Medical Systems). MR angiograms were generated in lateral rotations by using a maximum intensity projection algorithm and projections every 10° from -90° to +90°. We also used base partitions to analyze stenosis. All views were evaluated.

Image Analysis
Image quality at MR angiography and DSA was reviewed by a neuroradiologist (B.M.). General criteria, including the impression of overall image quality, were graded as follows: 1 = excellent with very good vascular visibility enabling detailed and reliable evaluation, 2 = adequate for diagnosis with average vascular visibility, and 3 = less than adequate for diagnosis with artery barely visible.

Each MR angiogram was interpreted independently by two neuroradiologists with 10 and 4 years of experience, respectively (B.M., B.R.). The DSA studies were reviewed by a neuroradiologist (J.C.) with 25 years of experience. Each neuroradiologist was blinded to the findings of the other examinations. DSA was considered the reference standard. The evaluations were performed with the computer workstation. MR angiographic measurements were based on reconstructed maximum intensity projection images. For each examination (MR angiography and DSA), precise measurements of the degree of stenosis were made at the level of maximum stenosis, with high magnification and a computer caliper. The diameter of the most severe stenosis was divided by that of the normal distal artery. For each craniocervical vessel (brachiocephalic, common carotid, subclavian, and vertebral arteries) (n = 231), ostial stenosis was graded as follows: normal, mild (<50%), moderate to severe (>50%), or occlusion. In MR angiography, failure to visualize the lumen at the level of the stenosis when flow was visible distal to the stenosis was considered to indicate severe stenosis (3).

Statistical Assessment
The relationship between MR angiography and DSA findings, in terms of categorized stenosis, was analyzed by means of the Spearman rank correlation coefficient (Rs). The sensitivity, specificity, and negative and positive predictive values of MR angiography for stenosis of more than 50% were calculated. The degree of agreement between observers was determined by using the statistic. Agreement was classified as moderate ( = 0.40– 0.69), good ( = 0.70–0.89), or excellent ( = 0.90–1.00).

	RESULTS

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Image Quality
The overall quality of DSA studies was excellent (33 of 33 studies with grade 1).

In terms of overall quality, 25 MR angiograms were excellent (grade 1), five were adequate for diagnosis (grade 2, suboptimal signal-to-noise ratio), and three were inadequate for diagnosis (grade 3, very poor signal-to-noise ratio [13 of 231 arteries] or coverage error [five of 231 arteries]). Consequently, 213 of 231 arteries could be evaluated. In the patient (with five arteries) in whom infusion was performed in the left arm, image quality was grade 3.

Degree of Stenosis
There was a significant correlation between MR angiographic and DSA findings (Rs = 0.82, P < .001) about the degree of stenosis (Fig 1). However, some discrepancies were noted between the vertebral arteries and the other craniocervical vessels.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 1. A, Oblique DSA image shows normal appearance (arrow) of postoperative left carotid-subclavian anastomosis and ostial stenosis (arrowhead) of less than 50% of the right vertebral artery. B, C, Oblique gadolinium-enhanced MR angiograms show good correlation with A. MR imaging parameters were 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, and imaging time of 32 seconds.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 2. A, Oblique DSA image depicts stenosis (arrowhead) of less than 50% of the right subclavian artery. B, Findings on oblique gadolinium-enhanced MR angiogram result in overestimation of this stenosis (arrowhead). In A and B, note that the left vertebral artery (arrow), which arises from the aortic arch, is barely seen with MR angiography. Another oblique DSA image (not shown) depicted its origin. MR imaging parameters were 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, and imaging time of 32 seconds.

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   Figure 3. A, Oblique DSA image. B, Oblique gadolinium-enhanced MR angiogram. Both images depict stenosis (arrowhead) of less than 50% of the left subclavian artery and stenosis (arrow) of less than 50% of the vertebral arteries. MR imaging parameters were 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, and imaging time of 32 seconds.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 4. A, Oblique DSA image depicts stenosis of less than 50% of the right vertebral artery (arrowhead). B, Findings on oblique gadolinium-enhanced MR angiogram result in overestimation of this stenosis, with lack of luminal visualization (arrow), which was considered arbitrarily to be a severe stenosis. MR imaging parameters were 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, and imaging time of 32 seconds.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 5. A, Oblique DSA image reveals normal aspect of the ostium (arrowhead) of the left vertebral artery. B, Oblique gadolinium-enhanced MR angiogram depicts a stenosis of less than 50% of this artery (arrow). MR imaging parameters were 6/2 with one-half signal acquired, flip angle of 35°, 52 sections, section thickness of 1.6 mm, field of view of 28 x 22 cm, matrix of 256 x 192, and imaging time of 32 seconds.

	DISCUSSION

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Image Quality
Good image quality is essential in this setting, and most MR angiographic studies were excellent. By using automatic triggering with detection of the contrast material bolus, we were able to selectively obtain an arterial phase MR image. Findings in previous studies show that a combination of optimal tracking volume placement and adjustment of tracking volume size ensures optimal sensitivity to the contrast material bolus (7–9). In our study, bolus arrival was always detected. Thus, venous enhancement is no longer a problem.

We attempted to optimize spatial resolution by decreasing the field of view and section thickness. Although this also reduced the signal-to-noise ratio, coverage errors were rare (five of 231 arteries). Signal-to-noise ratio is an important quality factor (10,11). A dedicated head and neck coil is necessary to avoid signal weakness in the lower part of the acquisition volume (12). However, the signal-to-noise ratio was very poor in 13 of 231 cases. In three cases, this was a result of the presence of sternotomy wires, which caused metallic artifacts. In five cases, the infusion was performed in the left arm of the patient, which might explain the poor signal-to-noise ratio because the high level of gadolinium-based contrast material in the left innominate vein, close to the origin of craniocervical vessels, can cause artifacts (13,14). In the other cases, the low signal-to-noise ratio was a result of respiratory motions or cardiac pulsations. We did not use the breath-hold technique because of the long imaging time (32 seconds) and the relatively old age of the study population. In addition, breath holding itself can cause motion artifacts. On the basis of published data, a non–breath-hold technique is most appropriate for the evaluation of craniocervical vessels (3,4).

Degree of Stenosis
MR angiography was highly sensitive for the detection of ostial stenosis of craniocervical vessels. Specificity was acceptable, except for that for the vertebral artery, where the positive predictive value was 58%. Findings at MR angiography tend to result in overestimation of the degree of stenosis, especially for the vertebral ostia (15,16). This phenomenon in the carotid artery is well known and can be explained by excessive section thickness that causes a partial volume effect (17,18). Intravoxel dephasing can occur despite a short echo time and use of contrast enhancement. Overestimation at MR angiography can also be explained by hemodynamic modifications: The decreased flow caused by stenosis leads to a reduced concentration of contrast agent in the distal arterial lumen (19). This is especially important in the evaluation of the degree of stenosis in small vessels, such as the vertebral artery ostia.

Few data have been published about the use of MR angiography to assess ostial stenosis of craniocervical vessels, possibly as a result of a lack of knowledge about the frequency and clinical features of vertebrobasilar disease. Contrary to severe carotid artery stenosis, where results of the North American Symptomatic Carotid Endarterectomy Trial showed unequivocally the benefits of surgical correction, the benefits of vertebral surgical correction are unknown (20). To our knowledge, previous series of ostial stenosis of craniocervical vessels included few stenoses that exceeded 50% (21–23). Leclerc at al (24) reported one severe stenosis and one occlusion of the vertebral artery. Stone et al (21) described five of 48 significant ostial stenoses of the innominate, left carotid, and left subclavian arteries. We identified 21 of 213 arterial stenoses of more than 50%, probably because of the patient selection criteria (internal carotid stenosis of more than 50%). These findings confirm that ostial stenosis is not rare in selected patients.

This study has certain limitations. Because of the small number of patients, the statistical power of the comparison is limited. Furthermore, we separated stenosis into only three categories rather than the five categories used in the national trial of internal carotid artery stenosis. Given the size of the vertebral artery, however, it is difficult to evaluate stenosis in five categories. Despite these limitations, findings in our study show that MR angiography is a promising tool that cannot yet be used alone for the evaluation of ostial stenosis of the craniocervical vessels, notably because of its limited spatial resolution. Multi–detector row computed tomographic angiography also requires further evaluation in this setting.

MR angiography is useful to rule out ostial stenosis of the craniocervical vessels. However, findings at MR angiography may result in overestimation of stenosis or false-positive results, especially for vertebral ostia. MR angiography is an adequate diagnostic tool for ostial stenosis of the great vessels, except the vertebral artery.

	FOOTNOTES

 
Abbreviation: DSA = digital subtraction angiography

Author contributions: Guarantors of integrity of entire study, B.R., C.M.; study concepts, C.M.; study design, B.M.; literature research, B.R.; clinical studies, F.K.; data acquisition, B.R., B.M.; data analysis/interpretation, J.C., D.D., B.R.; statistical analysis, D.D.; manuscript preparation, B.R.; manuscript definition of intellectual content, C.M.; manuscript editing, B.M.; manuscript revision/review, B.M.; manuscript final version approval, B.R.

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This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2292011648v1 229/3/697    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Randoux, B. Articles by Marsault, C. Search for Related Content PubMed PubMed Citation Articles by Randoux, B. Articles by Marsault, C.