Abdominal aortic intimal flap motion characterization in acute aortic dissection: assessed with retrospective ECG-gated thoracoabdominal aorta dual-source CT angiography

Abstract

Objectives: To evaluate the feasibility of dose-modulated retrospective ECG-gated thoracoabdominal aorta CT angiography (CTA) assessing abdominal aortic intimal flap motion and investigate the motion characteristics of intimal flap in acute aortic dissection (AAD).

Materials and methods: 49 patients who had thoracoabdominal aorta retrospective ECG-gated CTA scan were enrolled. 20 datasets were reconstructed in 5% steps between 0 and 95% of the R-R interval in each case. The aortic intimal flap motion was assessed by measuring the short axis diameters of the true lumen and false lumen 2 cm above of celiac trunk ostium in different R-R intervals. Intimal flap motion and configuration was assessed by two independent observers.

Results: In these 49 patients, 37 had AAD, 7 had intramural hematoma, and 5 had negative result for acute aortic disorder. 620 datasets of 31 patients who showed double lumens in abdominal aorta were enrolled in evaluating intimal flap motion. The maximum and minimum true lumen diameter were 12.2 ± 4.1 mm (range 2.6 ∼ 17.4) and 6.7 ± 4.1 mm (range 0 ∼ 15.3) respectively. The range of intimal flap motion in all patients was 5.5 ± 2.6 mm (range 1.8 ∼ 10.2). The extent of maximum true lumen diameter decreased during a cardiac cycle was 49.5% ± 23.5% (range 12% ∼ 100%). The maximum motion phase of true lumen diameter was in systolic phase (5% ∼ 40% of R-R interval). Maximum and minimum intimal flap motion was at 15% and 75% of the R-R interval respectively. Intimal flap configuration had correlation with the phase of cardiac cycle.

Conclusions: Abdominal intimal flap position and configuration varied greatly during a cardiac cycle. Retrospective ECG-gated thoracoabdominal aorta CTA can reflect the actual status of the true lumen and provide more information about true lumen collapse. This information may be helpful to diagnosis and differential diagnosis of dynamic abstraction.

Figure 1. Measurement of lumen short axis diameters A.

Double-oblique multiplanar reformations were adjusted perpendicularly to the longitudinal axis of aortic vessel course, at the level of 2 cm distal to the celiac trunk ostium. Outline the true and false lumen short axis diameter manually with the tool of distance measurement. B. Schematic illustration of short axis diameter measurement. Connecting the end points A and B of the dissected flap can get the segment AB. The perpendicular line through the mid point C intersects with true lumen wall, dissected flap and false lumen wall at point D, E and F respectively. Segment DE and EF are true lumen and false lumen short axis diameters respectively.

Figure 2. The frequency distributions of MMP and intimal flap motion artifacts during a cardiac cycle.

The MMP of all cases was at systolic phase (5%∼40% of R-R interval) and the peak was found at 15% of the R-R interval. Most intimal flap motion artifacts were founded at systolic phase. Datasets acquired at 70% R-R interval had no intimal flap motion artifacts.

Figure 3. Time courses of TLD and FLD during the R-R interval.

Group-averaged TLD, FLD of each phase were plotted against time in percentages of R-R interval. Group-averaged FLD was larger than group-averaged TLD in every phase. Although there was no statistically significant difference in R-R intervals, a peak for group-averaged FLD and a trough for group-averaged TLD were found in 15% of R-R interval.

Figure 4. Time courses of RCTLD during the R-R interval.

Individual (light line) and group-averaged (dark line) RCTLD were plotted against time in percentages of R-R interval. Despite high inter-individual variation, group-averaged RCTLD showed clear biphasic pulsatility in 10%–25% of R-R intervals.

Figure 5. Images in different phases demonstrated different anatomical features.

At the right renal artery origin, 0% and 15% datasets could not demonstrate reentry tear, but 60% datasets can demonstrate reentry tear clearly. It was worthy to note that true lumen was completely collapsed and the flap nearly was invisible in 15% R-R interval. However, it was of reasonable caliber in 60% R-R interval.

Figure 6. Transverse CT images of different phases at the same level.

The intimal flap configuration, position and area of the true and false lumens were extremely variable during a cardiac cycle at the same level.

Figure 7. True lumen completely collapses during the cardiac cycle.

0–95% datasets showed that the true lumen was completely collapsed. The position of internal flap was changed mildly, but the configuration of intimal flap was not changed in different R-R intervals.