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Original Report |
1
Department of Radiology, St. Antonius Hospital, Koekoekslaan, 1, 3435CM
Nieuwegein, The Netherlands.
2
Department of Surgery, St. Antonius Hospital, 3435CM Nieuwegein, The
Netherlands.
Received January 29, 2001;
accepted after revision July 10, 2001.
Address correspondence to J. C. van den Berg.
Abstract
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CONCLUSION. Our preliminary experience suggests that 3D rotational angiography appears to be a valid tool in the pre- and perprocedural assessment of patients treated endovascularly for arterial aneurysms.
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In all patients, control angiography using 3D rotational angiography (Fig. 1C) and digital subtraction angiography was performed. Follow-up consisted of color Doppler sonography. Patients were placed on acetylsalicyc acid (80 mg daily) and dipyradimole (150 mg twice daily).
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Control angiography using 3D rotational angiography and digital subtraction angiography after stent placement showed exclusion of the aneurysm in all patients and good appositioning of the stent-graft at the proximal and distal landing zones. No procedure-related complications were seen. The procedure was well-tolerated by all patients. At follow-up (range, 3-8 months; mean, 5.5 months), there were no signs of complications, such as endoleak or thrombosis of the endograft. One patient (who underwent coil embolization of the hypogastric artery) complained of ipsilateral buttock claudication.
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With rotational angiography, a continuous rotation around the region of interest is made during continuous infusion of intraarterial contrast. The area of interest is placed in the isocenter in both frontal and lateral planes. In this way, a large number (with our system, a total of 100) of contrast-enhanced images are obtained. To obtain 3D reconstructions from the rotational angiographic images, it is mandatory that the images are precisely matched to each other. The calibration and quality assessment are done during routine maintenance using test phantoms, both by the manufacturer's service representatives and by our institution's clinical physicist. Measurements were performed using well-defined test phantoms that showed in all orientations that the measured size deviated less than 2% from the actual size [4]. Because of precise calibration, accurate length and diameter measurements can be performed without the use of calibrated catheters [5]. Additionally, viewing the volume from different angles allows the physician to determine the optimal projection (angulation and skew) of the X-ray tube needed for an endovascular intervention.
Pre- and perprocedural stent sizing is always important in cases in which placement of self-expanding covered stents is considered. The unwanted complications of undersizing speak for themselves (insufficient seal and migration), but also oversizing of the stent-graft may have deleterious effects on the vessel wall. Wrinkling of the covering may occur because there is too much material for the vessel diameter. This wrinkling may cause a type I endoleak, which is defined as the persistence of bloodflow outside the graft lumen, but within the aneurysm sac or adjacent vessels in which the graft is deployed, and is caused by inappropriate sealing at the proximal or distal attachment site [6].
For pre- or perprocedural stent sizing, a number of imaging modalities are available, including intravascular sonography, calibrated angiography, conventional or spiral CT, CT angiography, and MR imaging. No gold standard has been established, however, and discrepancies occur between the various techniques. In general, length measurements are underestimated by CT as compared with angiography and intravascular sonography [1]. Diameter measurements, however, are overestimated using conventional CT [1, 7]. Most of the drawbacks of conventional CT can be overcome using CT angiography or a computerized 3D model based on axial CT slices. These techniques provide accurate data for preoperative evaluation of the aortoiliac segment before endovascular abdominal aortic aneurysm repair. Satisfactory technical outcomes for aortic endografts can be achieved without the use of preprocedural invasive imaging [8, 9]. Measurements using MR imaging correlate well with those based on CT angiography [10].
Our initial experience shows that 3D rotational angiography is a fast and reliable adjunct modality that allows measurements to be performed on-line. A measurement error of less than 2% is acceptably low with the use of devices that require a 10-20% oversizing. Thus, extensive preinterventional workup can be reduced, and CT angiography is not required.
Although the amount of contrast for one rotational run exceeds the amount for a single, classic angiographic injection, the total amount of contrast is not considerably increased because one run will suffice. In our institution, standard projections of the aortoiliac region include an anteroposterior view and two oblique views, using a total contrast volume of 45 mL (3 x 15 mL at a flowrate of 15 mL/sec). With 3D rotational angiography, visualizing this region takes a total contrast volume of 48 mL (injection rate, 8 mL/sec). The time necessary for performing the 3D reconstruction is relatively short (5 min) and should not be considered a loss of time because the necessity to perform various runs (as with conventional angiography) is lacking with the 3D rotational angiographic technique. In our experience, the time necessary for sizing of covered stents using 3D rotational angiography does not considerably differ from the time consumed with measurements using calibration software, as available on most modern digital subtraction angiography equipment. A disadvantage of the 3D rotational angiographic technique is the nonvisualization of the thrombus that, when present at the site of the proximal or distal landing zones, may be a contraindication for stent-graft placement (causing improper sealing). In general, the thrombus can be seen easily using transabdominal sonography or conventional CT. Calcification, however, can be seen using 3D rotational angiography. In this series, no comparison of measurements with other techniques was made, but this is a subject of ongoing clinical investigation.
Color Doppler sonography in the follow-up of covered stents is a well-established and reliable tool [11]. In our small series, short-term clinical results are promising and compare favorably with results, as described in the literature (with procedure-related minor complications reported to occur in up to 15% of cases, whereas major complications occur in up to 7.5%) [12]. Evaluation of mid- and long-term follow-up was beyond the scope of this paper (patency rates reported up to 94%) [12].
This preliminary report indicates that in the pre- or perinterventional assessment of peripheral arterial aneurysms, 3D rotational angiography is a valuable adjunct tool, allowing proper sizing and facilitating of the procedure without adding substantial procedural time.
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