Aortic motion: a potential pitfall in CT imaging of dissection in the ascending aorta

Artefacts complicate the diagnosis of thoracic aortic dissection by CT. Aortic compliance and cardiac motion may be responsible but the precise cause of these artefacts remains unclear.

Fifty consecutive clinical thoracic CT examinations performed on a Siemens Somatom Plus scanner (8 mm slice thickness, 1 s scan time) were reviewed (mean patient age 56 years). For each examination, the presence, position, and displacement of motion artefact from the aortic wall were noted at three ascending aortic levels. Cine ultrafast CT on 10 volunteers (mean age 49 years) was used to assess aortic motion for the same three levels (8 mm slice thickness, 50 ms scan time). Digital subtraction of consecutive cine CT allowed the position of the aortic wall throughout the cardiac cycle to be tracked.

Curvilinear motion artefacts were seen in the ascending aorta in 17 conventional CT scans, occurring left anterior and right posterior in all but one and maximally at the aortic root (mean amplitude 3.5 mm). Ultrafast CT, however, showed no motion artefact and no significant change in aortic area with systole. Aortic motion in the sagittal-oblique plane at the ascending aorta was confirmed.

Motion artefacts simulating ascending aortic dissection occur frequently on conventional CT. Their position is predictable and is related to systolic aortic motion from the left anterior to the right posterior position.