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1
Department of Radiology, Hopital Cardiovasculaire et Pneumologique L. Pradel,
28 rue du Doyen Lepine, 69500 Bron, France.
2
Johns Hopkins University, Outpatient Center, Rm. 4250, 601 N. Caroline St.,
Baltimore, MD 21287-0845.
3
Department of Vascular Surgery, Hopital Edouart Herriot, 5 place d'Arsonval,
69437, Lyon Cedex 03, France.
4
Department of Biostatistics, CMI, Hopital Hotel Dieu, 1 place de l'Hopital,
69288, Lyon Cedex 02, France.
Received August 18, 1999;
accepted after revision January 20, 2000.
Address correspondence to J. M. Serfaty.
Abstract
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SUBJECTS AND METHODS. In this prospective study, 48 successive patients with carotid artery stenoses were examined with 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Of the 44 eligible patients, conventional angiography was available in 33 and duplex sonography in 27. We used the North American Symptomatic Carotid Endarterectomy Trial technique to quantify stenosis on all angiograms, and a 250 cm/sec threshold at duplex sonography to diagnose stenoses greater than 70%. Image quality of 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography was assessed, as well as sensitivity and specificity for each technique alone and in combination with duplex sonography. Conventional angiography was the gold standard.
RESULTS. Three-dimensional gadolinium-enhanced MR angiography yielded good image quality in 90% of cases. When used alone, it yielded a sensitivity and a specificity of 94% and 85%, respectively, in screening stenoses greater than 70% (70-99%). When combined with duplex Doppler sonography, it provided a 100% sensitivity and specificity for detection of stenoses between 70% and 99% and would have obviated 61% of conventional angiography. In comparison, 3D time-of-flight MR angiography used alone yielded a sensitivity of 88% and a specificity of 94%. In combination with duplex Doppler sonography, its use would have obviated conventional angiography in 74% of cases. Three-dimensional gadolinium-enhanced MR angiography provided accurate results in the diagnosis of occlusions and ulcers and can visualize distant stenoses.
CONCLUSION. Used alone, 3D gadolinium-enhanced MR angiography is not accurate enough to replace conventional angiography in the evaluation of extracranial carotid arteries. In association with duplex Doppler sonography, however, it is accurate and may obviate a significant number of conventional angiographic examinations.
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Duplex sonography with the color Doppler technique is widely used to screen patients with suspected carotid artery disease. Numerous studies have shown its accuracy [5, 6] as well as its limitations, which include operator dependency [7], hospital variations [8, 9], variability in parameter choice [10], susceptibility to artifacts from calcified plaque, and difficulty in distinguishing near-total occlusion.
MR angiography using two-dimensional (2D) and three-dimensional (3D) time-of-flight has also shown a high accuracy in diagnosing stenoses greater than 70% (70-99%). However, on the basis of flow enhancement, MR angiography is limited by enhacing slow or turbulent flows. This limitation leads to overestimation of the severity of a stenosis and difficulty in distinguishing severe stenosis and total occlusions; these difficulties preclude the use of MR angiography alone [11]. To overcome these problems, investigators currently use a protocol that dictates that patients will undergo surgery when duplex Doppler sonography and MR angiography (2D or 3D time-of-flight) findings agree [12,13,14], whereas patients with discordant results will undergo conventional angiography.
More recently, improvements in gradients and sequences have made possible the use of 3D gadolinium-enhanced MR angiography [15,16,17]. This recent technique, which uses a contrast medium injection, has major advantages: rapid acquisition time with a subsequent reduction in flow- and patient-related motion artifacts and a large acquisition volume. This allows good estimation of carotid artery stenosis and differentiation between occlusion and pseudoocclusion. Few studies exist that assess the potential of this technique to quantify carotid atherosclerotic stenosis. Our hypothesis is that 3D gadolinium-enhanced MR angiography, using a fast acquisition time (8 sec) alone or in combination with duplex Doppler sonography, is accurate for the noninvasive preoperative assessment of extracranial carotid arteries.
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All 44 patients underwent 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Of the total group, 33 also underwent conventional angiography, and 27 underwent duplex Doppler sonography. Twenty-three patients underwent all four examinations. Carotid endarterectomy was subsequently performed on 23 arteries in 21 patients.
Imaging Protocol
MR angiography was performed on a 1.5-T system (Vision; Siemens Medical
Systems, Erlangen, Germany) equipped with gradient overdrive with an ultrafast
180 mT(m·msec) slew rate and a high 25 mT/m peak amplitude whole-body
gradient, capabilities that are not available on all clinical MR imaging
units. A 4 x 2 circularly polarized phased array neck coil was placed
around the neck. After obtaining classic fast spoiled gradient-echo axial,
coronal, and sagittal localizers, 3D time-of-flight MR angiography and 3D
gadolinium-enhanced MR angiography were successively performed (Magnetic
Vision; Siemens Medical Systems). Because of better anatomic coverage, better
spatial resolution in the slice thickness, and the potential to use short TEs
in our scanner (which diminishes dramatically any artifacts caused by slow
flows), 3D time-of-flight MR angiography was chosen for our study rather than
2D time-of-flight MR angiography. The multislab 3D time-of-flight technique
comprised seven slabs, each with 32 axial sections, 1.41 mm thick, with a
superior saturation band, and imaging parameters of 39/7 (TR/TE), one
excitation, 25° flip angle, 160 x 256 matrix size, and a 250 x
250 x 90 mm field of view. Acquisition time was 13 min. Examinations
were centered on the carotid bifurcation, which could be visualized easily on
the localizer.
Three-dimensional gadolinium-enhanced MR angiography was subsequently performed. Because the technique is not based on a flow entrance effect but on a T1 lowering of the blood (compared with the surrounding tissues) by prescribing slabs in the coronal plane, it was possible to cover the region from the aortic arch to the carotid siphon. Turbo MR angiography was a spoiled gradient-recalled echo sequence performed with a 3.2-msec TR, a 1.1-msec TE, a 20° flip angle, a 300 x 225 mm field of view, a 96 x 256 matrix, and 64 partitions each 2 mm thick with zero filling in the z-axis, which resulted in an imaging time of 8 sec. The K-space was filled in sequential order. Twenty milliliters of contrast medium was hand-injected at a rate between 2 and 3 mL/sec into an antecubital vein at the beginning of the scan, followed by a 20-mL saline flush. Five consecutive 3D sequences were performed (40-sec total acquisition time). No breath-holding was used. No bolus test preceded the acquisition. The contrast medium was gadopentetate dimeglumine (Magnevist; Berlex, Wayne, NJ).
MR angiography studies were reviewed after postprocessing with a maximum-intensity-projection algorithm with targeted maximum intensity projection used to display 13 projections of each carotid bifurcation separately (14° angle). For the 3D gadolinium-enhanced studies, the maximum-intensity-projection algorithm was applied after subtracting the sequence that showed the best arterial enhancement from the sequence showing no arterial enhancement (the mask). In cases of venous enhancement, subtraction was performed with the last sequence containing low arterial signal intensity and intermediate venous signal intensity.
Sonographic evaluation of bifurcations included 2D sonography, color Doppler sonography, and duplex spectral analysis with a 10-MHz linear array transducer (SD 800; Philips, Shelton, CT). The first step consisted of 2D sonography and color Doppler imaging of the common carotid artery and the extracranial internal and external carotid arteries. This examination made possible the rapid identification of atherosclerotic plaque and associated areas of flow disturbance. Whenever a region of flow disturbance or visible evidence of stenosis was identified, the second step, a duplex spectral analysis at the narrowest point of the lumen, was performed. Peak systolic velocity at the point of maximum acceleration greater than 250 cm/sec was used as the determinant of the presence of a 70-99% stenosis [6, 18]. For peak systolic velocity lower than 250 cm/sec (because of the nonlinear relation between the peak systolic velocity and the degree of stenosis [19]), only axial 2D sonography measurements were considered for stenosis grading. The minimal luminal diameter at the stenosis site was divided by the diameter of the internal carotid artery 1 cm above the bulb. Sonography was performed and the images reviewed by a single experienced observer who was unaware of clinical information and the results of other imaging studies.
Percutaneous catheter angiography was the gold standard for determining the degree of stenosis. Conventional angiography was performed on a digital biplane angiographic system. In 32 examinations, both common carotid arteries were selectively catheterized, and one examination was performed with a nonselective aortic arch injection because selective catheterization was impossible. Both carotid bifurcations were studied in a minimum of two projections. The images of each injection were displayed and processed on a monitor with a 1024 x 1024 matrix, and representative images were recorded on film using a laser printer.
Imaging Analysis
MR angiograms and conventional angiograms were each reviewed independently
by two experienced radiologists who were unaware of clinical, sonographic, and
contrast angiographic findings. The 44 3D gadolinium-enhanced MR angiograms
were analyzed separately by each radiologist during two sessions. The 44 3D
time-of-flight MR angiograms (axial slices and reconstructed images) were
analyzed 2 weeks later, and the conventional angiography 4 weeks later in the
same manner. For conventional angiography results, in cases of disagreement,
images were reevaluated for a final consensus grade. The kappa statistic was
used to assess interobserver reliability.
The image quality of 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography at the carotid bifurcation was scored on a scale of A-D (A = examination without artifacts, B = artifacts not hindering interpretation, C = artifacts hindering interpretation, D = noninterpretable examination). Factors such as image blurring, venous enhancement, and insufficient arterial enhancement that degraded image quality were reported on a worksheet. Bifurcations with a score of D were excluded from the statistical analysis to avoid misinterpretation that would result from the quality of an examination rather than from actual technical limitations of the MR angiography technique.
The percentage of stenosis (by diameter) was determined using the North American Symptomatic Carotid Endarterectomy Trial measurement technique [20] and a jeweler's eyepiece for all the angiographic techniques. Measurements were performed on maximum-intensity-projection reconstructions only. The projection showing the greatest degree of stenosis was used for analysis. No attempt was made to select one maximum intensity projection to match it with the conventional angiography. A signal void on MR angiography was assumed to represent a greater than 70% stenosis, whatever the MR technique [21], because this assumption is used in clinical practice by many radiologists when interpreting MR angiograms. All results were categorized into five grades according to the degree of stenosis: grade 1, stenosis less than 30%; grade 2, 30-49.99%; grade 3, 50-69.99%; grade 4, 70-99.99%; and grade 5, 100% occlusion.
Conventional angiographic and MR angiographic images were also evaluated for the presence of ulceration, occlusion, and other significant stenoses from the aortic arch to the circle of Willis. A plaque was classified as ulcerated if it fulfilled the radiographic criteria of an ulcer niche, seen in profile as a crater penetrating into a stenotic plaque, and double density on an en face view (the latter criterion applicable for conventional angiography only). The irregular plaque or uncertain ulceration category was used either for wall irregularity or multiple small possible craters, or when it was difficult to distinguish a true crater from a normal wall between two plaques. A plaque was considered occluded in the absence of internal carotid signal.
Statistical Methods
The degree of agreement between observers in the interpretation of MR and
conventional angiographic images with regard to quality of an examination and
diagnosis of stenoses greater than 70% was determined using pairwise kappa
statistics. The degree of agreement was interpreted as follows: very good, a
kappa value equal to or greater than 0.81; good, 0.80-0.61; moderate,
0.60-0.41; poor, 0.40-0.21; and bad, less than 0.21.
To assess the precision to detect stenoses greater than 70% (70-99%), sensitivities, specificities, and positive and negative predictive values were calculated for 3D gadolinium-enhanced MR angiography, 3D time-of-flight MR angiography, and duplex Doppler sonography. Receiver operating characteristic curve analysis (sensitivity versus 1 - specificity) was used to compare the accuracy of 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Conventional angiography was the gold standard. We used MedCalc software (version 4.16g; MedCalc Software, Mariakerke, Belgium) to estimate the receiver operating characteristic curves and the statistical significance of the differences between the averaged areas under the receiver operating characteristic curves.
The combination of 3D gadolinium-enhanced MR angiography and duplex Doppler sonography was also studied and was compared with the combinations of 3D time-of-flight MR angiography and duplex sonography, and 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography. Sensitivities and specificities of concordant findings for each combination in the detection of stenosis greater or less than 70% were calculated. The number of discordant results was reported.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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= 0.95).
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Assessment of Stenosis on 3D Gadolinium-Enhanced MR Angiography and
3D Time-of-Flight MR Angiography
One noninterpretable carotid bifurcation on conventional angiography was
excluded from the study, leaving 63 arteries for comparison. The excluded
examination corresponded to the only patient in the study who could not be
successfully injected selectively in the right carotid artery because contrast
material in the aortic arch did not provide sufficient enhancement.
Conventional angiography revealed 37 carotid stenoses (59%) of 0-49%, seven
carotid stenoses (11%) of 50-69%, 17 carotid stenoses (27%) of 70-99%, and two
carotid occlusions (3%). Interobserver reliability for the presence of disease
requiring surgery was very good ( = 0.85). Compared with conventional
angiography, 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR
angiography showed a high accuracy in diagnosing high-grade stenosis (Fig.
2A,2B,2C,2D,2E)
despite an overestimation of stenosis degree (Tables
1 and
2). Of the two MR angiography
techniques, 3D gadolinium-enhanced MR angiography yielded a higher sensitivity
in screening 70-99% stenosis than 3D time-of-flight MR angiography (94% versus
88%) but a lower specificity (94% versus 85%). However, no significant
difference in areas under the curves between the two was detected by receiver
operating characteristic curve analysis (p = 0.62)
(Fig. 3). In our data, neither
MR angiography technique yielded 100% sensitivity because of one stenosis that
was greatly underestimated (25% versus 70% on conventional angiography) and
one near-occlusion that was confused with a total occlusion on 3D
time-of-flight MR angiography. The underestimation was made on the only
nonselective conventional angiography included in the study.
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Assessment of Stenosis on Duplex Sonography
Of the 46 arteries explored with both conventional angiography and duplex
sonography, only seven of 10 arteries with 70-99% stenoses were correctly
graded with duplex sonography (Table
3). This technique yielded a sensitivity and specificity of 64%
(95% confidence interval [CI], 48-77%) and 97% (95% CI, 88-100%), a positive
predictive value of 89% (95% CI, 76-96%), and a negative predictive value of
88% (95% CI, 75-96%).
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Assessment of Stenosis by Combining Noninvasive Techniques
Table 4 summarizes the
results of the comparison of 3D gadolinium-enhanced MR angiography with duplex
sonography, 3D time-of-flight MR angiography with duplex sonography, and 3D
gadolinium-enhanced MR angiography with 3D time-of-flight MR angiography
compared with conventional angiography. The results show that both 3D
gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography,
combined with duplex sonography, yielded a 100% sensitivity and specificity in
screening for 70-99% stenosis. However, the combination of 3D
gadolinium-enhanced MR angiography and duplex sonography yielded a greater
number of discordant results than the combination of 3D time-of-flight MR
angiography and duplex sonography. Thus, conventional angiography was
necessary in more patients (17 versus 14). This may be explained by the
tendency of 3D gadolinium-enhanced MR angiography to more frequently
overestimate intermediate stenosis (50-69%) than 3D time-of-flight MR
angiography (for 44 arteries, six versus three), thus giving more discordant
results with duplex sonography, which, in our study, was very specific.
Another result is the enhancement of MR angiography performance when 3D
gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography were
used together, a combination that yielded a 95% sensitivity and 91%
specificity, with 84% of conventional angiographic examinations avoided.
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Diagnosis of Occlusion and Ulcers
In the 63 carotid arteries analyzed with conventional angiography, two
carotid occlusions were diagnosed. Three-dimensional gadolinium-enhanced MR
angiography and 3D time-of-flight MR angiography confirmed both (Fig.
2A,2B,2C,2D,2E).
However, 3D time-of-flight MR angiography reported a false-positive case of
occlusion, which, on both conventional angiography and 3D gadolinium-enhanced
MR angiography, was a near-occlusion (90-99% stenosis).
Of these 63 carotid arteries, conventional angiography depicted three ulcers. All were diagnosed on 3D gadolinium-enhanced MR angiography, but only one on 3D time-of-flight MR angiography (Fig. 4A,4B,4C,4D).
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Anatomic Coverage and Associated Lesions
Three-dimensional gadolinium-enhanced MR angiography revealed six severe
subclavian stenoses on maximum-intensity-projection subvolume images. Only one
of the six was confirmed on conventional angiography. The analysis of source
images corrected these five errors by showing an insufficient field of view
that partially excluded the subclavian artery wall, thereby simulating
stenosis.
For the internal carotid siphon, three stenoses were diagnosed using 3D gadolinium-enhanced MR angiography, with one confirmed on conventional angiography. The two false-positive cases of thin diaphragm stenoses were artifacts.
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Efficacy of 3D Gadolinium MR Angiography Associated with Duplex
Sonography
Our results show high sensitivity (94%) and specificity (85%) for 3D
gadolinium-enhanced MR angiography, similar to 3D time-of-flight MR
angiography (88% and 94%, respectively). All false-positive cases resulted
from overestimations of intermediate stenosis (50-70%), which lower
specificity. Thus, the quantification of stenosis of 50-70% is inaccurate
using MR angiography techniques. When we calculated the sensitivity and
specificity of 3D gadolinium-enhanced angiography and 3D time-of-flight MR
angiography for stenosis quantified as 50-70% with conventional angiography,
we found a sensitivity of 14% (95% CI, 0-40%) and specificity of 86% (95% CI,
77-95%) with 3D gadolinium-enhanced MR angiography, and a sensitivity of 43%
(95% CI, 6-80%) and specificity of 84% (95% CI, 75-94%) with 3D time-of-flight
MR angiography.
Moreover, the results for the quantification of stenosis greater than 70% are not representative of the ultimate ability of a technique to accurately diagnose a high-grade stenosis. As Kallmes et al. [11] reported, the problem is to find a technique that can distinguish moderate stenosis (30-69%) from high-degree stenosis (>70%). If we exclude data from normal arteries (often contralateral) and mild stenosis data from our study, 3D gadolinium-enhanced MR angiography yields a revised sensitivity of 94% (95% CI, 83-98%) and a revised specificity of 72% (95% CI, 54-90%). These results are close to those of 3D time-of-flight MR angiography (100% and 74%, respectively). Thus, both 3D gadolinium-enhanced MR angiography and 3D time-of-flight MR angiography are not accurate enough when used alone to replace conventional angiography [12, 25, 26].
To increase the specificity of MR angiography, previous articles proposed that only concordant 3D time-of-flight MR angiography and duplex sonography data for the presence or absence of surgical disease be considered [26, 27], whereas discordant findings indicate the necessity for conventional angiography. Our data confirm this strategy for 3D time-of-flight MR angiography and also validate it for the association between 3D gadolinium-enhanced MR angiography and duplex sonography and 3D time-of-flight MR angiography and 3D gadolinium-enhanced MR angiography. Of the three combinations, 3D time-of-flight MR angiography with duplex sonography was the most powerful association, yielding a 100% sensitivity and specificity, with a high percentage (74%) of conventional angiographic examinations avoided. Surprisingly, if the two 3D MR angiography techniques are considered together and show concordance, then up to 84% of carotid angiographic examinations could be avoided, without the need for duplex sonography, in patients with 70-99% stenosis.
However, this strategy should not be extended to patients with 50-70% stenosis. For those patients, duplex sonography alone showed a sensitivity of 80% (95% CI, 45-100%) and a specificity of 80% (95% CI, 68-93%). When duplex sonography was combined with one of the two MR angiography methods, neither sensitivity nor specificity improved. Duplex sonography and 3D time-of-flight MR angiography yielded a sensitivity of 55% and a specificity of 37%. Duplex sonography and 3D gadolinium-enhanced MR angiography yielded a sensitivity of 50% and a specificity of 20%.
Depicting Occlusion and Ulcers with 3D Gadolinium-Enhanced MR
Angiography
For carotid occlusions, the small number of cases we had did not enable us
to reach a conclusion. However, the cases we did evaluate suggest a high
accuracy for 3D gadolinium-enhanced MR angiography for diagnosis of carotid
occlusion [22,
24] and confirm the
limitations of 3D time-of-flight MR angiography and duplex sonography despite
the addition of color Doppler sonography, as described in previous articles
[12,
28]. The time-of-flight method
requires adequate inflow of unexcited protons to generate increased signal
compared with stationary tissues. When the flow is quite slow, as seen in
pseudoocclusion, saturation effects occur, severely diminishing the
inflowrelated signal increase and making the time-of-flight method insensitive
to pseudoocclusion or occlusion. When 3D gadolinium-enhanced MR angiography is
used, these saturation effects are overcome because gadolinium shortens T1
relaxation of the blood, permitting recovery of longitudinal magnetization for
the slow-moving blood protons. The ability to depict occlusions accurately is
important because a patient with a nearly occluded artery would benefit from
carotid endarterectomy, whereas a patient with a carotid occlusion would
not.
Depicting ulcers also is of great importance because the North American Symptomatic Carotid Endarterectomy Trial showed a threefold greater risk of cerebral ischemia in patients who present with a deep ulcer with a high-grade stenosis [6, 29]. Many studies have emphasized the inaccuracy of 3D time-of-flight MR angiography in the detection of ulcers because of flow artifacts [12, 30]. Duplex sonography is also recognized as poor in this regard [31]. Our study agrees with these findings and suggests that results may be improved with 3D gadolinium-enhanced MR angiography.
Anatomic Coverage and Associated Lesions
An important consideration in the evaluation of a new technique for the
assessment of extracranial arteries is the ability of the technique to explore
the aortic arch and the origin of the great vessels. Our data show that 3D
gadolinium-enhanced MR angiography with a classic neck coil can obtain
sufficient signal to image the vessels from the aortic arch to the internal
carotid siphon. For the arch and the origin of the great vessels, the main
problem is the limited acquisition volume in the anteroposterior axis, which
leads to partial arterial exclusion from the field of view and pseudostenosis.
Errors resulting from a small postprocessing field of view may also occur.
Thus, careful examination of native images is recommended because it helps to
differentiate these artifacts from true stenosis. For the siphon arteries, our
results show the great potential of this technique but suggest the need to
improve spatial resolution.
Study Limitations
The choice of conventional angiography as our gold standard may be
interpreted as a limitation of our study. We chose conventional angiography as
the reference standard on the basis of international randomized trials, which
have used and still use conventional angiography as the reference technique.
However, the two views generally provided by this technique are insufficient
for fine quantification because eccentric plaques lead to an oval appearance
of the lumen which, in the case of radiographs not perpendicular to the
borders, give an underestimation of the stenosis. It is therefore not
surprising to find, in our study, an overestimation of MR angiography
techniques, which always quantify stenosis through the ideal angle (Fig.
5A,5B,5C,5D).
One possible way to avoid this bias would be to use endarterectomy plaques as
a gold standard, as Pan et al.
[32] did in a previous study.
However, as they pointed out, this method cannot be retained as a reference
because the lack of arterial pressure probably modifies the measures, and the
internal carotid artery is not measurable 1 cm past the end of the bulb.
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Another limitation of our study was the choice of a peak systolic velocity of 250 cm/sec as a diagnostic threshold. Compared with the North American Symptomatic Carotid Endarterectomy Trial study [6], our sensitivity was lower (64% versus 67%) but our specificity higher (97% versus 67%). This high specificity is uncommon and was specific to our laboratory. However, to validate the association with other duplex sonography sensitivities and specificities, we recalculated using 145 cm/sec as the Doppler threshold. This resulted in a sensitivity of 100% and a specificity of 86% (95% CI, 70-95%) for duplex sonography alone, a sensitivity of 100% and specificity of 91% (95% CI, 77-97%) with duplex sonography combined with 3D gadolinium-enhanced MR angiography (79% conventional angiographic examinations avoided), and a sensitivity of 100% and specificity of 94% (95% CI, 82-99%) with duplex sonography combined with 3D time-of-flight MR angiography (74% of conventional angiography avoided).
Therefore, combining concordant data from noninvasive tests increased their overall accuracy whatever the Doppler threshold. However, the importance of this increase depends on criteria and should be evaluated in each laboratory.
In conclusion, our study shows that 3D gadolinium-enhanced MR angiography alone is not accurate enough to replace conventional angiography for the assessment of extracranial carotid arteries. However, when 3D gadolinium-enhanced MR angiography is combined with duplex sonography, it achieves optimal sensitivity and specificity and makes close to two thirds of conventional angiographic examinations unnecessary. Therefore, to diminish the number of patients undergoing conventional angiography, the clinician can now choose, in association with duplex sonography, either 3D time-of-flight MR angiography or 3D gadolinium-enhanced MR angiography, with specific advantages for each technique. Three-dimensional gadolinium-enhanced MR angiography is fast for MR acquisition, better than 3D time-of-flight MR angiography at differentiating occlusion and subocclusion, and more accurate than 3D time-of-flight MR angiography in diagnosing plaque ulcers. It also allows the study of wide fields of view, which offers the potential to screen associated stenosis, when careful analysis of native images is performed. However, 3D time-of-flight MR angiography provides the major advantage of avoiding a greater percentage of conventional angiographic examinations.
Acknowledgments
We thank Mary McAllister and Charles Clausen for editorial assistance.
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D. C.C. Johnston, J. D. Eastwood, T. Nguyen, and L. B. Goldstein Contrast-Enhanced Magnetic Resonance Angiography of Carotid Arteries: Utility in Routine Clinical Practice Stroke, December 1, 2002; 33(12): 2834 - 2838. [Abstract] [Full Text] [PDF]
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P. J. Nederkoorn, Y. van der Graaf, B. C. Eikelboom, A. van der Lugt, L. W. Bartels, and W. P.T.M. Mali Time-of-Flight MR Angiography of Carotid Artery Stenosis: Does a Flow Void Represent Severe Stenosis? AJNR Am. J. Neuroradiol., November 1, 2002; 23(10): 1779 - 1784. [Abstract] [Full Text] [PDF]
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P. J. Nederkoorn, W. P.Th.M. Mali, B. C. Eikelboom, O. E.H. Elgersma, E. Buskens, M.G. M. Hunink, L. J. Kappelle, P. C. Buijs, A. F.J. Wust, A. van der Lugt, et al. Preoperative Diagnosis of Carotid Artery Stenosis: Accuracy of Noninvasive Testing Stroke, August 1, 2002; 33(8): 2003 - 2008. [Abstract] [Full Text] [PDF]
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J. H. Gillard, B. D. M. Tom, W. Hollingworth, B. Randoux, B. Marro, F. Koskas, M. Duyme, M. Sahel, A. Zouaoui, and C. Marsault Validation of the Effectiveness and Efficiency of Newer Techniques * Dr Randoux and colleagues respond: Radiology, May 1, 2002; 223(2): 586 - 587. [Full Text]
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L. Remonda, P. Senn, A. Barth, M. Arnold, K.-O. Lovblad, and G. Schroth Contrast-Enhanced 3D MR Angiography of the Carotid Artery: Comparison with Conventional Digital Subtraction Angiography AJNR Am. J. Neuroradiol., February 1, 2002; 23(2): 213 - 219. [Abstract] [Full Text] [PDF]
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 F. A. Fellner, J. M. Serfaty, and P. C. Douek Different MR Angiography Techniques Provide Different Results in Assessing Extracranial Carotid Artery Disease Am. J. Roentgenol., August 1, 2001; 177 (2): 468 - 469. [Full Text] [PDF]
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