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Session: Poster session 2 (Odd numbers)
Session starts: Friday 27 January, 10:00
Presentation starts: 10:00

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Rick van Bergen (Eindhoven University of Technology)
Camilo Cano (Eindhoven University of Technology)
Min Wu (Eindhoven University of Technology)
Marc van Sambeek (Catherina Ziekenhuis Eindhoven)
Richard Lopata (Eindhoven University of Technology)

Abstract:
Background, Motivation and Objective The protocol for assessing abdominal aortic aneurysm (AAA) involves measuring the AAA diameter, which is found to introduce ambiguity. Consequently, several studies suggested that intraluminal thrombus (ILT) can be a better predictor for AAA rupture risk. Although the structure and composition of the ILT can contribute to a better assessment of AAA, it is challenging to image and differentiate the three main layers of an ILT, the luminal, medial, and abluminal layers. This difficulty stems from the low contrast between the layers. In this pilot study, we evaluate the feasibility of multispectral photoacoustic imaging (sPAI) on ILT to differentiate between these layers in an experimental setting. Statement of Contribution/Methods Different regions of two excised ILTs were scanned using two scanning schemes. The first is a transverse scan of the ILT where the different layers were imaged using equal optical fluence to explore the possibility of detecting layers based on PA spectral composition. The second is a luminal scan that mimics an intravascular approach. The results from the transverse measurement were spectrally unmixed using the piecewise convex multi-model endmember determination model. For the luminal experiment, an interface detection algorithm was developed. This algorithm detected the layers based on the bandwidth-limited PA signal from interfaces. The results were validated using scanning electron microscopy images of the samples. Results/Discussion In the transverse experiment, the tissue constituents found belonged to blood, fibrin, and the water/fibrin interface. With these endmembers and the corresponding proportion maps, it is possible to observe a correlation between the tissue constituent distributions and the ILT layers. For the luminal experiment, the unmixing results did not provide new insight due to limited optical fluence. However, the proposed interface detection algorithm successfully segmented the luminal layer of the thrombus. Moreover, the medial-abluminal interface was identified, yet a complete surface segmentation requires an improved penetration depth. To conclude, sPAI can be used to differentiate between the different layers of the ILT, although further steps are required, such as increasing penetration depth, to facilitate the translation from bench to bedside.