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Session: Cardiac Diagnostics
Session starts: Friday 25 January, 10:30
Presentation starts: 11:15
Room: Lecture room 559

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Rik Hansen ()
Gert Jan de Borst ()
Michiel Bots ()
Gerard Pasterkamp ()
Chris de Korte ()

Abstract:
Introduction: Carotid stenosis with plaque rupture is one of the main underlying causes of stroke. Key issue in the risk assessment is identification of the plaque prone to rupture. Lipid-rich and inflammatory plaques with a thin fibrous cap (vulnerable plaques) have a higher risk at rupture than fibrous plaques (stable plaques). We developed a noninvasive ultrasound based compound elastography method to estimate strains in a plaque caused by the pulsating blood [1], because we expect soft lipid-rich plaques to have higher strains than stiff fibrotic plaques. In this in vivo in patient study we investigate the relation between these strain estimates and vulnerable plaque features. Material and Methods: A Medison Accuvix V10 ultrasound system equipped with an L5-13 linear array transducer was used to acquire ultrasound radiofrequency (RF) data of transverse cross sections of 18 severely stenotic carotid arteries of patients before carotid endarterectomy (CEA; surgical excision of the plaque and inner vessel wall). RF data were acquired at three different insonification angles (0°, +20 and -20 degrees). Radial strains were estimated from the angular RF data using an iterative cross-correlation based search algorithm [2] followed by compounding [1]. The percentage of plaque area with strains above 1.5% was determined. After CEA, segments of the imaged plaque cross section were cut and histologically stained. Based on the staining, the presence of plaque vulnerability features was determined: a thin fibrous cap, a high concentration of lipids and a low concentration of collagen, a high concentration of macrophages, and a lack of smooth muscle cells. The sensitivity and specificity of the strain area parameter for the detection of these features were determined. Results: The developed compound elastography method revealed a positive relation between strain and each of the investigated histology based parameters of vulnerability. The highest sensitivities and specificities were reached for the detection of lipid content and superficial macrophages: 80% and 70%, and 100% and 100%, respectively. Conclusions: Within an in vivo setting, we confirmed that noninvasive compound elastography provides strain parameters that increase with plaque vulnerability. At the moment additional patients are being included to validate the findings in a larger population. REFERENCES [1] H.H.G. Hansen et al., "Full 2D displacement vector and strain tensor estimation for superficial tissue using beam steered ultrasound imaging," Phys. Med. Biol., Vol. 5, pp. 3201-3218, (2010). [2] R.G.P. Lopata et al., "Performance evaluation of methods for two-dimensional displacement and strain estimation using ultrasound radio frequency data," Ultrasound Med. Biol., Vol. 35, pp. 796-812, (2009).