Time-resolved CT angiography in aortic dissection

Objectives: We performed this study to assess feasibility and additional diagnostic value of time-resolved CT angiography of the entire aorta in patients with aortic dissection.

Materials and methods: 14 consecutive patients with known or suspected aortic dissection (aged 60±9 years) referred for aortic CT angiography were scanned on a dual-source CT scanner (Somatom Definition Flash; Siemens, Forchheim, Germany) using a shuttle mode for multiphasic image acquisition (range 48 cm, time resolution 6s, 6 phases, 100 kV, 110 mAs/rot). Effective radiation doses were calculated from recorded dose length products. For all phases, CT densities were measured in the aortic lumen and renal parenchyma. From the multiphasic data, 3 phases corresponding to a triphasic standard CT protocol, served as a reference and were compared against findings from the time-resolved datasets.

Results: Mean effective radiation dose was 27.7±3.5 mSv. CT density of the true lumen peaked at 355±53 HU. Compared to the simulated triphasic protocol, time-resolved CT angiography added diagnostic information regarding a number of important findings: the enhancement delay between true and false lumen (n=14); the degree of membrane oscillation (n=14); the perfusion delay in arteries originating from the false lumen (n=9). Other additional information included true lumen collapse (n=4), quantitative assessment of renal perfusion asymmetry (n=2), and dynamic occlusion of aortic branches (n=2). In 3/14 patients (21%), these additional findings of the multiphasic protocol altered patient management.

Conclusions: Multiphasic, time-resolved CT angiography covering the entire aorta is feasible at a reasonable effective radiation dose and adds significant diagnostic information with therapeutic consequences in patients with aortic dissection.