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Session: Imaging - Cardiac System
Session starts: Thursday 24 January, 13:30
Presentation starts: 13:45
Room: Lecture room 559

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Renate Boekhoven (TU/e)
Richard Lopata (TU/e)
Marc van Sambeek (Catharina Ziekenhuis)
Frans van de Vosse (TU/e)
Marcel Rutten (TU/e)

Abstract:
Endarterectomy is often performed in carotid arteries of patients with advanced atherosclerosis, regardless of knowledge about the stability of the plaque. To date, plaque stability cannot be assessed accurately in vivo, leading to a large number of false positives. To improve the understanding of plaque rupture, techniques to determine the geometrical, morphological, and mechanical properties of atherosclerotic plaques in vitro need to be developed. In this study, as a first step, a new experimental tool to assess 3D plaque geometry using 2D ultrasonography has been evaluated. Micro-CT (µCT) was used for validation. One polyvinyl-alcohol vessel phantom (asymmetric lumen), one porcine carotid artery and four human atherosclerotic carotid specimens, obtained from endarterectomy (approved by the local ethics committee), were studied. The latter two segment types were pressure fixed. To avoid shadowing effects due to plaque calcifications, longitudinal cross-sections were imaged over 360º in steps of 10º. For this purpose, an ultrasound device (MyLab70, Esaote, Maastricht, The Netherlands) equipped with a linear array probe and RF interface, was used. Next, as a validation, the specimens were imaged in a µCT-scanner (Scanco Medical, Brütisellen, Switserland). Polar transverse cross-sections containing 360° of near wall and far wall data were created by combining single RF-lines from each longitudinal position. Segmentation of the inner and outer wall was performed with a so-called sustain-attack-filter (SAF). The polar data were projected and interpolated on a Cartesian grid (taking the rotation axis into account) resulting in smooth transverse cross-sections. Normalized 3D cross-correlation was used to register the µCT and US segmentation results, accounting for both translation and rotation. To quantify the quality of the US-based 3D volume, the 3D similarity index (SI) was calculated, regarding the µCT data as the golden standard. The SAF was able to segment both outer and inner wall of the vessel phantom and carotid segments. The resulting images show the entire arterial wall in 3D at the highest US resolution possible. Results of the image registration indicate good agreement between the ultrasound and the µCT-based geometries of three different segment types. ISI of the phantom was 0.94; ISI of the healthy carotid artery was 0.79; and the average ISI of the human endarterectomy samples was 0.74 (n=4). In contrast to conventional ultrasound imaging, the method proposed in this study does not suffer from acoustic shadowing effects present when imaging stenotic segments. Furthermore, the method allows future dynamic measurements with high temporal and spatial resolution to determine mechanical properties of atherosclerotic plaque in an in vitro setting.