Precise determination of aortic length in patients with aortic stent grafts: in vivo evaluation of a thinning algorithm applied to CT angiography data

The aim of this study was to develop a technique for precise determination of the aortic length using volumetric CT data for potential use prior to en dovascular stent-graft placement. The study population consisted of 20 pati ents (38 measurements) with already performed endoluminal grafting. This al lowed for in vivo evaluation of our technique, Its length according to the graft specifications served as a gold standard for our own measurements, Th e implemented graft length varied between 120 and 195 mm. Computed tomograp hy angiography was performed with 3mm slice collimation, 5-mm table feed an d a reconstruction interval of 2 mm. Following semi-automatic segmentation of the aorta and its large side branches, the median centerline (skeleton) of the vessels was determined employing a modified three-dimensional thinni ng algorithm. The algorithm was validated by comparing the calculated lengt h of the resulting skeleton with the specifications of the grafts. The calc ulated length was sufficiently precise despite the limiting reconstruction interval of 2 mm of our CT data which only permitted an assessment of stent length in 2-mm steps, The differences in the measured length and graft len gth were in the range between 0 and 8 mm ( < 5 %)with a mean fractional err or of 2.46 +/- 2.37 mm. The use of an intelligent region growing algorithm capable of coping with variable arterial enhancement significantly reduced operator post-processing time. The average time necessary for segmentation was 7 min (range 3-10 min). Our algorithm provides a non-invasive method fo r objective and precise measurement of aortic length apparently even in tor tuous vessels. It has the potential to replace angiography for aortic and i liac length measurements with calibrated catheters prior to endovascular in tervention.