Regional variance of visually lossless threshold in compressed chest CT images: lung versus mediastinum and chest wall

Purpose

The purpose of this study was to characterize the heartbeat-related displacement of the thoracic aorta in patients with chronic aortic dissection type B (CADB).

Materials and methods

Electrocardiogram-gated computed tomography angiography was performed during inspiratory breath-hold in 11 patients with CADB: Collimation 16 mm × 1 mm, pitch 0.2, slice thickness 1 mm, reconstruction increment 0.8 mm. Multiplanar reformations were taken for 20 equidistant time instances through both ascending (AAo) and descending aorta (true lumen, DAoT; false lumen, DAoF) and the vertex of the aortic arch (VA). In-plane vessel displacement was determined by region of interest analysis.

Results

Mean displacement was 5.2 ± 1.7 mm (AAo), 1.6 ± 1.0 mm (VA), 0.9 ± 0.4 mm (DAoT), and 1.1 ± 0.4 mm (DAoF). This indicated a significant reduction of displacement from AAo to VA and DAoT (p < 0.05). The direction of displacement was anterior for AAo and cranial for VA.

Conclusion

In CADB, the thoracic aorta undergoes a heartbeat-related displacement that exhibits an unbalanced distribution of magnitude and direction along the thoracic vessel course. Since consecutive traction forces on the aortic wall have to be assumed, these observations may have implications on pathogenesis of and treatment strategies for CADB.