CT virtual angioscopy in the study of thoracic aortic dissection [Angioscopia virtuale con TC spirale nello studio delle dissecazioni dell'aorta toracica]

Purpose. Virtual endoscopy is a technique in which helical-CT and MR data sets are processed by a special software creating a three-dimensional viewing of the inner surface of hollow viscera that simulates the endoscopic view. We report our 2.5-year experience with virtual intraluminal endoscopy (VIE) in the study of the thoracic aorta in patients with aortic dissection and in patients with normal aorta. Material and methods. From December 1997 to June 2000, CT angiography (CTA) data sets of the thoracic aorta obtained in a series of 43 patients were retrospectively evaluated. Our series included 23 patients with clinical or radiological suspicion of aortic dissection and 20 patients in whom the study of the thoracic aorta was carried out as a necessary completion of an abdominal aortic disease. CTA data sets were processed with a dedicated software (Navigator); the view point and view direction could be set arbitrarily in the vessel, obtaining an intraluminal endoscopic view of the inner surface of the vessel. Multiple views were obtained and visualised consecutively through a "-cine-loop" technique. The entire thoracic aorta was. studied. Results. VIE enabled correct visualisation of the intimal flap in all cases of aortic dissection (n=23) and of its origin at the level of the ascending aorta in 16 cases (Stanford A) and in the descending aorta in the remaining 7 patients (Stanford B). In the control group (n=20) no signs of intimai flap were identified with the VIE. In all patients with aortic dissection false and true lumen were entirely visualised. VIE allowed the understanding of the relation between false lumen and supraaortic vessels that originated from the true lumen in all cases and were found to be dissected in 6 patients. In 16 cases the dissection included thoracic and abdominal aorta. In some cases the endoscopie view was altered by artifacts related to the selected threshold levels and represented by pierced surface and floating shape artifacts. A correlation with axial and multiplanar (MPR) images allowed the correct interpretation of such artifacts. Conclusions. According to our experience, virtual endoscopy represents a useful tool in the evaluation of the dissection of the thoracic aorta, allowing a better definition of anatomical details. A correlation with axial images and multiplanar views remains compulsory for a better understanding of VIE findings, which is nevertheless significantly influenced by the operator's experience.