The newest minimally invasive technique to treat abdominal aortic aneurysms (AAA) is called endovascular prosthesis implantation. Professor of Vascular Surgery at the Utrecht University Hospital, Bert C. Eikelboom, is working together with Philips Medical Systems to apply state-of-the-art pre-operative Computed Tomography (CT) and high quality fluoroscopic imaging during the surgical intervention. The patients are carefully selected with use of ultrasonography to detect the typical structure of the arteries. In case the images meet the selection criteria, exact measurements are performed on the segments of the affected vessel by means of CT angiography. The prosthesis is introduced and correctly positioned under fluoroscopic control. CT again is applied to assess the post-operative condition of the aneurysm with regard to the implantation.
The mortal danger for a patient suffering from asymptomatic abdominal aortic aneurysm consists in a sudden rupture. Preventive repair surgery through the endoluminal stent graft procedure substantially reduces the mortality rate. In a few cases, it is even possible to implant bifurcated prostheses. This type of surgical intervention however requires the highest quality and detail in imaging techniques. At the Utrecht University Hospital, the team of Professor Eikelboom combines the Philips Tomoscan SR 7000 CT system with the EasyVision CT/MR workstation and the large format BV 212 mobile X-ray system for full coverage of the implantation procedure, as well as for pre- and post-operative monitoring and control of both aneurysm and prosthesis.
Endovascular prosthesis implantation can only be performed on patients with bilaterally normal iliac arteries, whose ultrasound images display an aneurysm with a diameter of more than 5 cm, that doesn't cover the renal arteries. In addition, the aorta must show a normal diameter without any trace of thrombus, and also have a caudal shape to the renal arteries, and a cranial one to the aortic bifurcation to provide the right proximal and distal necks. In the next phase, the selected patient is submitted to a volumetric CT examination for the 3D imaging of the specific anatomic details. For this purpose, the physician needs a set of exactly contiguous slices, taken in one helical scan. Since the acquisition is continuous, the risk of stepping effects or misregistration is fully annihilated.
The Vascular Surgery Department in Utrecht uses the Tomoscan SR 7000 CT scanner, equipped with the MRC 200 CT tube to perform the CT angiograms. The result of the volumetric CT processing constitutes a three-dimensional reconstruction of the vascular enhancement. In order to properly view the reconstruction at any possible angle, the EasyVision CT/MR workstation is activated to decide on the adequate surgical approach or radiation therapy. If, for instance, the iliac arteries are too tortuous, it simply will be impossible to insert the catheter delivery system into the patient's body. In case the implantation conditions are favourable, the multiplanar reformations facility of the EasyVision CT/MR measures each segment of the vessel in order to produce a tailor-made endoprosthesis to fit the aorta's proximal and distal necks.
At the start of the implantation procedure, a calibrated catheter measures the length of the aneurysm. The BV 212 mobile X-ray system allows the surgical team to cover the whole operative field without having to move the patient. This device consists of a C-arm unit, similar to the conventional fluoroscopy units, and a 12 inch image intensifier. The patient's custom-made prosthesis lies folded in the delivery system, sealed at the upper and lower ends by two capsules. Once the endoprosthesis has been introduced and correctly positioned, the superior capsule is removed to expose a stent provided with a ring of hooks. An inflated balloon expands the ring in order to attach it to the aorta wall. The inferior stent is fixed in a similar manner. Afterwards, the delivery system is removed in order to control the adequate positioning of the endoprosthesis by means of traditional angiography.
Post-operative check ups are performed with CT imaging to assess the future development of the aneurysm as well as the adoption of the prosthesis to the patient's inner body. For more details about the innovative endoluminal stent graft procedure, we refer to the VMW article Endovascular 3D imaging software treats aortic aneurysms in the September issue, reporting on similar surgical interventions in the United States.