1. / naam faculteit of vakgroep /department of biomedical engineering Identifying Plaque Geometry and Morphology Using Tomography Renate Boekhoven 1, Richard Lopata 1, Marc van Sambeek 2, Frans van de Vosse 1 & Marcel Rutten 1 1 University of Technology Eindhoven, 2 Catharina Hospital, Eindhoven Introduction To distinguish between stable and vulnerable carotid atherosclerotic plaques, geometry and morphology of a plaque and the mechanical properties of its components need to be determined. Previously it was shown that from 2D ultrasound (US) data 3D geometries can be obtained, which showed good agreement with micro computed tomography (µCT) data. The next step is to determine plaque mechanics and morphology. Hereto, possibilities of both US (strain imaging) and µCT (morphology assessment) were investigated. Ultrasound: Plaque Deformation Local deformations were determined by cross-correlating windows of RF-data from frame to frame. Regions with high and low strain can be determined (Fig. 3a-i). These regions should be related to specific plaque components. Figure 2: 3D reconstructed data can be found for an eccentric PVA phantom, a healthy porcine carotid artery, and an endarterectomy segment, imaged with Echo- CT and µCT. Figure 4: Geometry of a plaque imaged with µCT (a), a projection of the calcifications is shown in (b), and a projection of the lipid pools is shown in (c). Future Work Strain imaging results are promising but still need to be projected on the corresponding 3D geometries. Morphology determined from µCT is currently validated with histology. The typical strain regions will be correlated to µCT-based morphology to validate the 3D mechanical and morphologic assessment from echo-CT imaging. Distension, geometry and morphology will eventually serve as input for inverse numerical modeling to extract mechanical properties from the plaque components. Hopefully, these methods and results will enable characterization of vulnerable plaques. US reconstructionµCT reconstruction Eccentric phantom Healthy Plaque Plaque Geometry An automated segmentation tool was developed to segment longitudinal cross-sections, creating 3D geometries. The post-processing method was validated with static µCT (gold standard, Fig. 2). Registration quality was quantified using a similarity index, and showed good agreement for all three types of vessel segments (0.7 – 0.94). Materials A poly vinyl alcohol (PVA) phantom, a healthy porcine carotid artery and an intact carotid plaque, provided by Catharina Hospital, were cannulated and mounted in a set-up (Fig. 1) and loaded with a physiological pressure. Figure 1: Schematic overview of the experimental set-up. (g) (h) (i) (a)(b)(c) µCT: Plaque Morphology Plaques were imaged prior and post OsO 4 staining. OsO 4 specifically binds to unsaturated lipids. Figure 4 reveals a typical plaque including calcifications (Fig. 4b) and lipid pools (Fig. 4c). Figure 3: Strain imaging is applied to a healthy carotid artery (a-c), a PVA phantom (d-f) and an atherosclerotic plaque (g-i), radial strains of up to 0,2 were achieved (yellow indicates compression, purple indicates extension). (g)(h)(i) (d) (e)(f) (a)(b)(c) 80 mmHg100 mmHg120 mmHg 80 mmHg 120 mmHg140 mmHg 0 mmHg 20 mmHg 50 mmHg