An intraluminal coronary stent is a metal scaffold deployed in a stenotic artery during Percutaneous Coronary Intervention (PCI). In order to have an effective deployment, a stent should be optimally placed with regard to anatomical structures such as bifurcations and stenoses. Intravascular Ultrasound (IVUS) is a catheter-based imaging technique generally used for PCI guiding and assessing the correct placement of the stent. A novel approach that automatically detects the boundaries and the position of the stent along the IVUS pullback is presented. Such technique aims at optimizing the stent deployment. The method requires the identification of the stable frames of the sequence and the reliable detection of stent struts. Using this data, a measure of likelihood for a frame to contain a stent is computed. Then, a robust binary representation of the presence of the stent in the pullback is obtained applying an iterative and multi-scale quantization of the signal to symbols using the Symbolic Aggregate approXimation algorithm. The technique was extensively validated on a set of 103 IVUS of sequences of in-vivo coronary arteries containing metallic and bio-absorbable stents acquired through an international multi-centric collaboration across five clinical centers. The method was able to detect the stent position with an overall F-measure of 86.4%, a Jaccard index score of 75% and a mean distance of 2.5 mm from manually annotated stent boundaries, and in bio-absorbable stents with an overall F-measure of 88.6%, a Jaccard score of 77.7 and a mean distance of 1.5 mm from manually annotated stent boundaries. Additionally, a map indicating the distance between the lumen and the stent along the pullback is created in order to show the angular sectors of the sequence in which the malapposition is present. Results obtained comparing the automatic results versus the manual annotation of two observers shows that the method approaches the inter-observer variability. Similar performances are obtained on both metallic and bio-absorbable stents, showing the flexibility and robustness of the method. This article is protected by copyright. All rights reserved.
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