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Vascular and Interventional Radiology |
1 From the Departments of Radiology (O.E.H.E., P.C.B., A.F.J.W., W.P.T.M.M.) and Vascular Surgery (B.C.E.), and the Julius Center for Patient Oriented Research (O.E.H.E., Y.v.d.G.), University Hospital Utrecht, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands. Received September 22, 1998; revision requested November 10; final revision received February 8, 1999; accepted June 8. Address reprint requests to O.E.H.E. (e-mail: o.e.h.elgersma@azu.nl).
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Abstract |
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MATERIALS AND METHODS: Rotational angiography (16 or 32 projections) was performed in addition to DSA in 47 stenotic internal carotid arteries (ICAs) in 38 symptomatic patients. ICA stenosis was measured independently at DSA and at rotational angiography with North American Symptomatic Carotid Endarterectomy Trial criteria. The degree of stenosis was categorized as 0%–29%, 30%–49%, 50%–69%, or 70%–99%.
RESULTS: In three ICAs, rotational angiography was nondiagnostic. In 28 of the remaining 44 ICAs, the degree of stenosis was categorized similarly with DSA and rotational angiography, whereas with rotational angiography, 15 ICAs were classified one category higher and one ICA was classified two categories higher, owing to the increased number of projections available. Seventy percent to 99% stenosis was demonstrated in 18 ICAs with DSA and in 25 ICAs with rotational angiography. Thus, rotational angiography could have facilitated a change in the optimal treatment (from nonsurgical treatment to carotid arterial endarterectomy) in seven ICAs.
CONCLUSION: Compared with DSA in two or three projections, rotational angiography frequently depicts more severe ICA stenosis. This indicates a limitation of DSA in depicting the maximum ICA stenosis.
Index terms: Carotid arteries, angiography, 172.12483 • Carotid arteries, stenosis or obstruction, 172.721 • Digital subtraction angiography, comparative studies, 172.12483 • Digital subtraction angiography, technology, 172.12483
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Introduction |
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In both trials, ICA stenosis was evaluated by using intraarterial digital subtraction angiography (DSA) or conventional angiography, with the carotid arterial bifurcation depicted in a limited number of projections—usually two or three. In practice, often only one or two projections can be used for actual luminal reduction measurements because of overlapping vessels on other projections. In the two trials, the projection that showed the most severe stenosis was used to assess the percentage of ICA stenosis. Because the residual stenotic lumen can have an asymmetric shape (3–7), it is conceivable that the narrowest residual lumen will not always be depicted and, hence, the maximum ICA stenosis will not be assessed with a small number of projections.
A recently available DSA technique that enables visualization of vessels in many projections during one contrast material injection has been introduced (8). This technique, rotational angiography, may provide additional projections of the ICA that show more severe stenosis than does conventional two- or three-projectional DSA and, thereby, possibly affect optimal patient treatment. The purpose of this study was to evaluate the diagnostic quality and reliability of rotational angiography, assess how often it depicts more severe ICA stenosis compared with conventional DSA, and determine how frequently these factors may affect patient treatment. In addition, the safety of rotational angiography performed in addition to conventional DSA in terms of neurologic complications was evaluated.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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At our hospital, all of the symptomatic patients were first screened with carotid arterial duplex ultrasonography (US). If the peak systolic velocities in the ICA were 150 cm/sec or greater, then carotid arterial disease was suspected (9), and the patients were subsequently referred for DSA. DSA was performed by using a commercially available angiographic unit (Integris V3000; Philips Medical Systems, Best, the Netherlands) with an image intensifier matrix of 1,024 x 1,024. By using the Seldinger technique, the tip of a 5-F catheter was guided from the femoral artery to the ascending aorta and positioned in the right and subsequently the left common carotid artery. Two or three projections (lateral, posteroanterior, and/or oblique) were acquired at each carotid arterial bifurcation. For each projection, 6 mL of contrast material (Ultravist [300 mg of iodine per milliliter]; Schering, Berlin, Germany) was injected at a flow rate of 3 mL/sec.
Rotational angiography was performed in addition to conventional DSA when an ICA stenosis of some degree according to NASCET criteria was visible on one of the conventional DSA projections and when the radiologist anticipated that the patient would be able to remain motionless for at least 24 seconds, which is required to perform rotational angiography. In the first 20 patients, rotational angiography was performed in each ICA, whether the artery was symptomatic or asymptomatic, whereas in the remaining 18 patients, rotational angiography was performed in only the symptomatic ICAs, because the clinicians were specifically interested in these arteries.
With the catheter still positioned in the common carotid artery, the angiographic unit began imaging in the lateral position and rotated 180° around the carotid arterial bifurcation to acquire 32 projections in all but four patients (six carotid arteries), in whom 16 projections were obtained. A 512 x 512 image intensifier matrix was used. The field of views in conventional DSA and in rotational angiography were similar; they varied between 20 and 25 cm. It took 8 seconds to obtain the rotational angiographic subtraction mask series, followed by 8 seconds for the angiographic unit to reverse back into the starting position. The contrast-enhanced rotational angiographic series was obtained in the last 8 seconds, during which the contrast material was injected in 9 seconds. The total amount of time to perform rotational angiography was about 5 minutes. Generally, a roentgen ray beam delay of 2 seconds and a flow rate of 3 mL/sec were used; this resulted in a total of 27 mL of contrast material for each injection. In the first five patients (seven carotid arteries), however, the roentgen ray beam delay varied between 1 and 3 seconds, and the flow and total amount of contrast material injected varied between 2.5 and 3.0 mL/sec and 22.5 and 27.0 mL, respectively, to optimize the rotational angiographic protocol.
Rotational angiography was considered to be optimal when the ICA was filled with contrast material and there was sufficient enhancement for the full 8-second duration of the rotational angiographic contrast series. Projections from the initial rotational series were used as individual subtraction masks to provide good subtraction images. In some cases, pixel shifting was necessary to optimize subtraction. Printed hard copies of the images subtracted from the rotational angiographic series were used for evaluation.
One observer (A.F.J.W.) subjectively classified the quality of the rotational angiograms as either excellent (comparable to conventional DSA images), good (slightly lower quality than conventional DSA images but still useful for diagnostic purposes), or poor; excluded those of poor quality; and counted the number of images with adequate contrast material filling without overlapping vessels in each series. Subsequently, two observers (A.F.J.W., P.C.B.) individually assessed the maximum percentage of ICA stenosis on each rotational angiogram by selecting two images that showed the maximum ICA stenosis, both of which had adequate contrast material filling and no overlapping vessels, and measuring the percentage of ICA stenosis on these two images with the NASCET method (stenosis = [1 - (minimal residual luminal diameter/distal ICA luminal diameter)] x 100%) by using a caliper with a digital display unit (PAV electronic [resolution, 0.01 mm]; Precizion Apparatenbau Vaduz, Vaduz, Liechtenstein). The highest percentage of stenosis measured was selected and subsequently categorized as 0%–29%, 30%–49%, 50%–69%, or 70%–99% stenosis. The stenoses on the conventional DSA images were measured and similarly categorized by both observers individually.
For the measurements of the first observer (A.F.J.W.), the highest percentage of stenosis at rotational angiography was compared with the highest percentage of stenosis at conventional DSA. The mean difference in the maximum ICA stenosis at rotational angiography and that at conventional DSA was calculated. Furthermore, we assessed the number of cases in which rotational angiography demonstrated a different category of ICA stenosis compared with conventional DSA and noted the cases when rotational angiography demonstrated 70%–99% stenosis but conventional DSA demonstrated stenosis of less than 70%. In these cases, nonsurgical treatment could be replaced with carotid endarterectomy, because symptomatic ICA stenosis of 70%–99% at either conventional DSA or rotational angiography in our study implied that the patient was referred for carotid endarterectomy.
To evaluate the reproducibility of measurements at rotational angiography and at conventional DSA, the measurements of the first observer were compared with those of the second observer (P.B.C.). The interobserver variabilities in rotational angiography and in conventional DSA were assessed and compared by using 
statistics.
In most patients, the angiographic examination and the evaluation of the images were performed by different radiologists. However, the first observer performed DSA and rotational angiography in five patients, and the second observer performed these examinations in two patients. To avoid the introduction of bias, the interval between the performance of the DSA and rotational angiographic examinations and the evaluation of the studies was substantial (6–11 months). Furthermore, observers were blinded to patient data during the evaluations.
An additional study was performed to evaluate whether rotational angiography is a reliable technique for depicting carotid arteries, with the capability to provide images that are identical to conventional digital subtraction angiograms. For this purpose, all available conventional DSA projections without overlapping vessels were retrieved, and the percentage of ICA stenosis on them was measured by the first observer. Subsequently, rotational angiographic projections in corresponding directions (if available) were selected, and the first observer, blinded to the results of the corresponding measurements obtained at conventional DSA, measured the percentage of ICA stenosis on them. Measurements on the conventional DSA projections were then compared with those on the corresponding rotational angiographic projections.
Neurologic examinations were performed, and National Institutes of Health stroke scale (10) and modified Rankin scale (11) scores were obtained from all patients shortly before and 24 hours after the angiographic examinations to identify possible neurologic deficits due to the procedures. The National Institutes of Health stroke scale is a serial scale of neurologic deficit that is used to measure the following 11 items of a patient's neurologic status: language, motor function in legs, motor function in arms, level of consciousness, negligence of body parts, visual fields, sensory function, extraocular movement, dysarthria, facial palsy, and limb ataxia. We used the 31-point scale proposed by Goldstein et al (10). The modified Rankin scale is a simplified overall assessment of function: A score of 0 indicates no symptoms, and a score of 5 indicates severe disability (11).
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RESULTS |
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Examples of rotational angiograms of excellent image quality are shown in Figure 1; the stenotic lumen is exposed on only a few projections. Figures 2 and 3 show the advantage of obtaining additional rotational angiographic projections compared with obtaining conventional DSA images in two projections. In Figure 4, the maximum percentages of ICA stenosis at rotational angiography are plotted against the maximum percentages of ICA stenosis at conventional DSA. The mean difference in maximum ICA stenosis between conventional DSA and rotational angiography was 9% (range, -6% to 31%; 95% CI: 6.7%, 12.0%).
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= 0.84; 95% CI: 0.71, 0.97. Analysis of the interobserver variability of measurements obtained at rotational angiography yielded the following results: = 0.81; 95% CI: 0.66, 0.97.
A total of 84 conventional DSA projections without overlapping vessels were available. In 69 cases, a corresponding rotational angiographic projection with adequate contrast material filling could be selected. In Figure 5, the percentages of ICA stenosis on rotational angiographic projections are plotted against the percentages of ICA stenosis on conventional DSA projections. A comparison of the conventional DSA projections and the corresponding rotational angiographic projections revealed no significant differences in the percentages of ICA stenosis (mean difference, 0.5%; 95% CI: -1.5%, 2.4%). Table 2 shows the categorized luminal reduction measurements obtained on the conventional DSA projections versus those obtained on the corresponding rotational angiographic projections ( = 0.75).
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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According to the results of the NASCET, carotid endarterectomy is recommended for symptomatic patients with 70%–99% stenosis on the angiographic projection that shows the most severe ICA stenosis. When this criterion was used in our study population, rotational angiography depicted an additional seven (16%) ICAs (a total of 25 depicted) for possible carotid endarterectomy compared with the 18 vessels identified with conventional DSA. Furthermore, our study results demonstrated that rotational angiography provides images that are identical to conventional DSA images: We did not find any consistent differences between the luminal reduction measurements on conventional DSA projections and those on the corresponding rotational angiographic projections.
The results of this study are consistent with those in previous reports (7,12,13) that showed that conventional angiography tends to underestimate the degree of vascular stenosis. By studying ICA specimens removed en bloc during carotid endarterectomy, Pan et al (7) observed that cross sections of the lumen in the stenotic area had a wide variety of shapes and were never circular. Therefore, the limited number of conventional DSA projections of these stenotic areas could not have revealed the maximum percentage of stenosis. It may be argued, however, that the morphologic features of ex vivo plaque material can change during and after surgical removal because of manipulation, shrinkage, or collapse. In our study, however, the tendency of conventional DSA to underestimate the degree of ICA stenosis was demonstrated by using a similar diagnostic technique that was performed in a far greater number of projections. By using this technique, the intertechnique differences that possibly affect the assessed degree of stenosis may be avoided.
To our knowledge, no former studies in which rotational angiography was used to assess ICA stenosis have been published. However, the neuroradiologic applications of rotational angiography have been reported in a limited number of publications (8,14). Tu et al (8) used this technique to evaluate aneurysms of the intracranial carotid arterial circulation. Rotational angiography better demonstrated the definition of the aneurysmal neck and enabled greater clarification of the configuration of the aneurysms compared with conventional DSA. Tu et al (8) considered a contrast material injection with a duration of more than 6 seconds at a flow rate of 4 mL/sec to be optimal for achieving satisfactory vascular detail with minimal postprocessing adjustments. Similar to us in the present study, they did not encounter any adverse effects from the prolonged contrast material injection.
In our study, adequate contrast material filling during the full 180° of the rotation was obtained in most patients by injecting 27 mL of contrast material for 9 seconds at a flow rate of 3 mL/sec and using a roentgen ray beam delay of 2 seconds. Nevertheless, variations in the time the contrast material reached the arteries were sometimes observed among patients, probably because of differences in heart rate, blood flow velocity, and positioning of the catheter in the common carotid artery. With variations in the time the contrast material reached the ICA and in the presence of overlapping vessels (most often the external carotid artery on posteroanterior projections), rotational angiography provided, on average, 13 projections of diagnostic quality, with a range of four to as many as 25 projections in a patient with external carotid arterial occlusion. Images of excellent quality were obtained in 51% of cases, whereas images of good quality were obtained in 43%. In 6% of cases, the rotational angiograms were not of diagnostic quality because of patient movement; thus, they were not sufficient for establishing the percentage of ICA stenosis.
Because rotational angiography provides many projections with varying image quality, the measurements may be susceptible to considerable interobserver variability. Therefore, it is very important that in grading stenosis, the observer uses only those rotational angiographic images on which he or she is confident that the residual stenotic lumen, as well as the distal ICA, is well defined. With this approach, the interobserver variability of measurements obtained on rotational angiograms will be good and not substantially different from that of measurements obtained on conventional DSA images.
In the first 20 patients, we performed rotational angiography in addition to DSA in each ICA, regardless of whether the artery was symptomatic or asymptomatic, when it showed some degree of stenosis on one of the conventional DSA projections. This resulted in the imaging of 10 carotid arteries that were not symptomatic. For such carotid arteries, Asymptomatic Carotid Atherosclerosis Study criteria rather than NASCET criteria should be used when deciding whether to perform carotid endarterectomy (15). Furthermore, because there are no criteria available for determining when to perform rotational angiography, we used the NASCET criteria with both conventional DSA and rotational angiography to categorize ICA stenoses, although NASCET criteria for performing carotid endarterectomy are based on conventional DSA rather than rotational angiographic findings.
A limitation of rotational angiography is that it can be performed successfully in only those patients who are able to remain motionless for at least 24 seconds, because good rotational subtraction images can be obtained only if the projections of the initial mask series are identical to those of the contrast series. In our study, in six (14%) of 44 patients referred for carotid arterial angiography, the radiologist decided that the patient was not eligible for the rotational angiographic examination because he or she did not feel at ease, was not able to follow instructions, or could not remain motionless. Even with this initial selection process, rotational angiography had a failure rate of 6% because of patient movement.
Another limitation of rotational angiography in assessing the maximum ICA stenosis is the inevitable overlap of vascular structures on a number of projections. On such projections, the degree of ICA stenosis cannot be assessed. Thus, the maximum degree of stenosis can still be underestimated with rotational angiography in some cases. Therefore, in this study, the actual number of carotid arteries in which the degree of stenosis was underestimated with conventional DSA may have been even higher than that demonstrated by using rotational angiography.
The results of our study validate the usefulness of rotational angiography, a recently available angiographic technique that enables identification of the maximum ICA stenosis by providing many projections of the carotid artery. We used rotational angiography to address the limitations of conventional two- or three-projectional DSA in depicting the maximum ICA stenosis. Instead of using rotational angiography, the acquisition of multiple additional projections 180° around the vessel with conventional DSA probably would allow an adequate evaluation of maximum ICA stenosis in many cases. In the present study, however, in some carotid arteries, rotational angiography depicted the maximum stenosis on only one or two projections of the, on average, 13 available projections of the ICA without overlapping vessels. In these instances, a radiologist probably would need to obtain too many additional projections and administer too much contrast material to establish the maximum ICA stenosis with DSA. Nonetheless, when using conventional DSA, additional projections should definitely be obtained when superimposed contrast material is seen in the ICA or when duplex US findings suggest more severe stenosis than that initially demonstrated with conventional DSA in only two or three projections.
In conclusion, the results of this study demonstrated that rotational angiography often depicts more severe ICA stenosis compared with conventional DSA in two or three projections; this indicates a limitation of conventional DSA as the reference-standard method for establishing the maximum ICA stenosis. In addition, a lot of effort is now directed toward the design of an optimal diagnostic strategy that involves less invasive or noninvasive techniques, such as magnetic resonance angiography, computed tomographic angiography, and duplex US, to select patients for carotid endarterectomy (16–18). When these techniques, which depict the ICA in many projections, are correlated with conventional DSA, we recommend the use of identical projections of the ICA to allow accurate comparison of the different modalities.
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Footnotes |
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Author contributions: Guarantors of integrity of entire study, O.E.H.E., W.P.T.M.; study concepts, O.E.H.E., B.C.E., W.P.T.M.M.; study design, O.E.H.E., A.F.J.W.; definition of intellectual content, O.E.H.E., Y.v.d.G., B.C.E.; literature research, O.E.H.E.; clinical studies, O.E.H.E., A.F.J.W., P.C.B.; data acquisition, O.E.H.E., A.F.J.W., P.C.B.; data analysis, O.E.H.E.; statistical analysis, O.E.H.E., Y.v.d.G.; manuscript preparation, O.E.H.E.; manuscript editing, O.E.H.E., A.F.J.W.; manuscript review, Y.v.d.G., B.C.E., W.P.T.M.M.
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