OSA / CLEO/QELS 2010 a2319_1.pdf JWA86.pdf
Optical Coherence Tomography Imaging of Stenotic Aortic Valve Samples Kátia C. Rodrigues1, Cláudia C. B. de O. Mota2, Jamil Saade3, Cid B. de Araújo1, Renato A. Zângaro4, Newton S. da Silva5, Renato E. de Araujo6, and Anderson S. L. Gomes1,* 1 Departamento de Física, Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil Programa de Pós-Graduação em Odontologia, Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil 3 Programa de Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, 50670-901, Recife, PE, Brazil 4 Instituto de Engenharia Biomédica, Universidade Camilo Castelo Branco, 12247-004, São José dos Campos, SP, Brazil 5 Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraíba, 12244-000, São José dos Campos, SP, Brazil 6 Departamento de Eletrônica e Sistemas, Universidade Federal de Pernambuco, 50740-530, Recife, PE, Brazil *
[email protected] 2
Abstract: Aortic valve samples, classified into normal, mild, moderate and severe fibrous calcific tissue based on Raman Spectroscopy, were analyzed with Optical Coherence Tomography. Results point OCT as a powerful diagnostic tool for aortic valve stenosis. ©2010 Optical Society of America OCIS codes: (170.4500) Optical coherence tomography; (170.5660) Raman spectroscopy
1. Introduction Optical Coherence Tomography (OCT) is an optical technique that enables micro-scale, cross-sectional and threedimensional (3D) in situ imaging of biological tissues in practically real time. Exploiting the interference phenomena between a back-reflected reference wave and a wave back-scattered from a medium, this technique measures the echo time delay and intensity of backscattered light using broadband light sources or frequency swept optical sources [1]. The growing interest in medical fields is because the technique is safe, has the potential to be economically viable, is contact-free and noninvasive, and has the possibility to create various functionalities in the imaging process [2]. The OCT images of human coronary atherosclerotic plaques obtained in vivo provide additional, more detailed structural information than Intravascular Ultrasound (IVUS). All fibrous plaques, macrocalcifications and echolucent regions identified by IVUS were visualized in corresponding OCT images by Jang et al [3]. Aortic valve disease is a progressive disorder that ranges from mild valve thickening to severe calcification. Clinic-pathological studies of human stenotic aortic valves identified lesions similar to those in atherosclerotic plaques that contained inflammatory cells and calcific deposits [4-6]. In this study we report for the first time the use of OCT to evaluate stenotic valves. The samples obtained from different cusps of cardiac valves were classified according to the calcification severity using the biochemical composition measured by Raman spectroscopy. An excellent agreement between the Raman spectra and the OCT images was obtained, which was complemented by visual inspection of the samples. 2. Methodology The samples were obtained by aortic valve transplantations. They were portioned in 13 different specimens and analyzed by Raman spectroscopy to identify the presence or not of calcium mineralization. Bovine pericardium organic biological valve prosthesis (manufactured by Braile Biomédica, Brazil) was used as normal tissue reference for Raman and OCT analyses. 3. Results and discussion The samples were classified as normal, mild, moderate and severe stenotic aortic valve tissue by observing the relative intensities of the Raman bands associated to calcium mineralization, elastic lamina and collagen. The OCT images were acquired by scanning the light beam in a vertical plane through the aortic valve samples. For each sample we acquired a set of OCT images or scans. The OCT images, Figure 1, were colored and postprocessed by the Image J software. The hot colors (red and yellow) represent regions where the reflected beam is more intense, whereas colder colors (green and blue) indicate regions where the signal is weaker.
OSA / CLEO/QELS 2010 a2319_1.pdf JWA86.pdf
Fig. 1. OCT images for normal (a), mild (b), moderate (c) and severe fibrous calcific samples (d). Two OCT scans of the respective sample.
In this study the biological aortic valve prosthesis was employed as the normal valve tissue. It is macroscopically smooth, thin and opalescent as normal human aortic valve [7]. In Fig. 1(a), normal sample, the red and yellow are regions closer to the sample surface, whereas the deeper region (less signal) is blue. The penetration depth was about 1.2 mm (directly measured, not corrected for refractive index). The normal tissue shows a homogeneous loss of backscattered intensity over all the tissue extension. The abnormal tissues, obtained by transplantations, contains disorganized collagen fibers, lipid accumulation and calcium mineralization displaying hallmarks of atherosclerosis [4,5]. In Fig. 1(b) the OCT image of a mild stenotic tissue, which are rich in fibrosis and lipids and with no calcium peak in the Raman spectrum, is presented. This morphology directly affects the OCT image, as the increasing amount of fibrous tissue scatters light in a nonuniform way over the sample extension. The OCT signal is even weaker for moderate, Fig. 1(c), and severe fibrous calcific samples, Fig. 1(d), that are characterized by increase in lipids, fibrous tissue and calcification, as confirmed in the Raman analysis. In this case, the regions of higher intensity close to the surface represent a high concentration of fibrotic tissue. These features are represented by large, heterogeneous, sharply delineated regions with absence of intense signals, leading to colder light in the OCT images. However, in the severe tissue the calcium crystals are represented by alternating regions of intense (red/yellow) and weak (green/blue) or by sharply delineated regions of intense red, as can see in Fig. 1(d). 4. Conclusion This ex-vivo study demonstrated the viability of OCT to discriminate different severity stages of stenotic aortic valve. We observed that the features finding in OCT images of abnormal aortic valve samples have great similarity with those finding in atherosclerotic plaques. This study demonstrated the use of OCT to open up new avenues of research combining the stenotic heart valve and vascular atherosclerosis in order to enhance risk factors comprehension and difference and similarities lesions understanding. 5. References [1] M. R. Hee, “Optical Coherence Tomography: Theory,” in Handbook of Optical Coherence Tomography, B. E. Bouma and G. J. Tearney, ed (Marcel Dekker, Inc., New York, 2002). [2] F. Fercher, W. Drexler, C. K. Hitzenberger, and T. Lasser, “Optical coherence tomography—principles and applications,” Rep. Prog. Phys. 66, 239–303 (2003). [3] I-K. Jang, B. E. Bouma, D-H. Kang, S-J. Park, S.W. Park, K-Bo Choi, M. Shishkov, K. Schlendorf, E. Pomerantsev, S. L. Houser, T. Aretz, and G. J. Tearney, “Visualization of Coronary Atherosclerotic Plaques in Patients Using Optical Coherence Tomography: Comparison With Intravascular Ultrasound,” J. Am. Coll. Cardiol. 39, 604-609 (2002). [4] M. A. Allison, P. Cheung, M. H. Criqui, R. D. Langer, and C. M. Wright, “Mitral and aortic annular calcification are highly associated with systemic calcified atherosclerosis,” Circulation 113, 861– 866 (2006). [5] E. R. Mohler III, “Mechanisms of aortic valve calcification,” Am. J. Cardiol. 94, 1396 –1402 (2004). [6] S. J. Sui, M. Y. Ren, F. Y. Xu, and Y. Zhang, “A high association of aortic valve sclerosis detected by transthoracic echocardiography with coronary arteriosclerosis,” Cardiology 108, 322–330 (2007). [7] S. J. Cowell, D. E. Newby, N. A. Boon, and A. T. Elder, “Calcific aortic stenosis: same old story?,” Age and Ageing. 33, 538-544 (2004).
