CQDSA in Evaluation of Prognosis After EVAR

Re-hospitalization or re-intervention is sometimes necessary to treat type I and type III endoleaks after EVAR for its persistent increasing of pressure in aneurysm lumen. Color-coded quantitative digital subtraction angiography (CQDSA) provides an easy and quick way to post-process the traditional digital subtraction angiography (DSA) which converts the peak time of the maximal contrast medium intensity into a single polychromatic image. With the help of CQDSA, a quantitative evaluation of the endoleak hemodynamics and a risk analysis of the type I or type III endoleak could be performed during the EVAR procedure. This approach may offer an objective assessment of the needs for immediate re-intervention, conservative therapy or treatment endpoint in the future.

Intra-procedural DSA series are transferred to a research workstation to generate the color-coded images and make quantitative measurements. Region of interest (ROI) measurements are performed equivalently in the endoleak and the aorta after the image generation. There are three kinds of ROIs including a small circle area with the shortest time to peak, a circle area with peak contrast intensity and the whole endoleak area. The ROI and a reference at the same latitude within the aorta are selected to undergo measurement which reflected the endoleak hemodynamics of the endoleak to the utmost extent. The following parameters will be acquired through the CQDSA for analysis. 1. Time-versus-ROI contrast intensity graph. The graph contains one endoleak ROI flow curve and one reference aortic flow curve (Ref). The x-axis shows time from 0 second to the maximum frame time of the image. The y-axis shows the sum of pixel intensities, namely total contrast, representing the contrast concentration within the ROI. 2. ROI Peak/Ref Peak. It is the ratio of intensity peak between the endoleak and the reference in the aorta. 3. ROI TTP (Time to peak). Peak time of ROI in the vicinity of endoleak entry. 4. ROI AUC/Ref AUC. Area under curve (AUC) is calculated through Time-versus-ROI contrast intensity graph. The parameter here is the ratio of ROI AUC in endoleak to the reference.