Quantitative analysis of dynamic computed tomography angiography for the detection of endoleaks after abdominal aorta aneurysm endovascular repair: A feasibility study

Abstract

Objectives: To assess the feasibility of quantitative analysis of dynamic computed tomography angiography (dCTA) for the detection of endoleaks in patients who underwent endovascular repair of abdominal aortic aneurysms (EVAR).

Material and methods: Twenty patients scheduled for contrast-enhanced CT angiography (CTA) of the abdominal aorta post-EVAR were prospectively enrolled. All patients received a standard triphasic CTA protocol, followed by an additional dCTA. The dCTA acquisition enabled reconstruction of color-coded maps depicting blood perfusion and a dCTA dataset of the aneurysm sac. Observers assessed the dCTA and dynamic CT perfusion (dCTP) images for the detection of endoleaks, establishing diagnostic confidence based on a modified 5-point Likert scale. An index was calculated for the ratio between the endoleak and aneurysm sac using blood flow for dCTP and Hounsfield units (HU) for dCTA. The Wilcoxon test compared the endoleak index and the diagnostic confidence of the observers.

Results: In total, 19 patients (18 males, median age 74 years [70.5-75.7]) were included for analysis. Nine endoleaks were detected in 7 patients using triphasic CTA as the reference standard. There was complete agreement for endoleak detection between the two techniques on a per-patient basis. Both dCTA and dCTP identified an additional endoleak in one patient. The diagnostic confidence using dCTP for detection of endoleaks was not significantly superior to dCTA (5.0 [5-5] vs. 4.5 [4-5], respectively; p = 0.11); however, dCTP demonstrated superior diagnostic confidence for endoleak exclusion compared to dCTA (1.0 [1-1] vs 1.5 [1.5-1.5], respectively; p <0.01). Moreover, the dCTP endoleak index was significantly higher than the dCTA index (18.5 [10.8-20.5] vs. 3.5 [5-2.7], respectively; p = 0.02).

Conclusions: Quantitative analysis of dCTP imaging can aid in the detection of endoleaks and demonstrates a higher endoleak detection rate than triphasic CTA, as well as a strong correlation with visual assessment of dCTA images.

Fig 1. Post-processing steps involved using the CT Myocardial Perfusion software.

70-year-old man status post EVAR 3 years prior to the dCTA examination. After an initial manual segmentation step of the aorta (A), segmentation propagates automatically. A ROI is positioned in the aortic lumen (B) which is then automatically defined (C) in order to compute the AIF (D).

Fig 2. Case demonstration.

76-year-old man with a BMI of 30.85 kg/m² who had undergone EVAR 2.5 years prior to the CTA examination. The non-contrast, arterial and venous static CTA acquisitions (A, B and C, respectively) do not show the presence of any endoleaks. The dCTA images acquired 2 and 38 seconds after the contrast media injection (D and E, respectively) show a type II endoleak, fed by a lumbar artery, that is also depicted by the color-coded perfusion maps (arrow in E and F). The TAC shows the kinetics of the endoleak (G) characterized by a wash-in that starts after 20 seconds, reaching a peak at 36 seconds, and then a rapid wash-out that does not allow its detection with the static CTA acquisitions.

Fig 3. Case demonstration.

74-year-old man with a BMI of 33.51 kg/m² who had undergone EVAR 1.5 years prior to the CTA examination. The arterial phase of the static CTA shows a type II endoleak fed by a lumbar artery and the inferior mesenteric artery (arrows in A and B, respectively). This is also depicted by the dCTA study during the acquisition performed at 38 seconds after contrast media injection (arrows in C and D). Panels E and F show the color-coded perfusion maps and the TACs (G and H). The TAC (G) corresponding to the cranial portion of the endoleak fed by a lumbar artery (arrow in E) shows a kinetic characterized by a rapid wash-in, a time to peak at 36 seconds, and a delayed washout. The TAC (H) corresponding to the caudal portion of the endoleak fed by the inferior mesenteric artery (arrow in F) shows a kinetic characterized by a rapid wash-in, two time to peaks at 38 and 48 seconds, and a delayed washout.

Fig 4. Discrimination between true and false endoleaks.

This figure shows the same patient as in Fig 2. dCTA images acquired at 2 and 38 seconds after the contrast media injection (A and B, respectively) show a type II endoleak and a suspected inhomogeneous area in the aneurysm sac (thick and thin arrow, respectively in B). The color-coded perfusion map shows the true endoleak and the suspected lesion correspondent to the inhomogeneity in Panel B (thick and thin arrow, respectively in C); the TACs (D) allow to discriminate between the true (ROI 4) and the false endoleak (ROI 5): they demonstrate the typical kinetics for the former while the latter lacks the wash-in, the peak, and the wash out phase, the dots of the correspondent curve being randomly spread on the graph.