Applications of Doppler Optical Coherence Tomography based on zero-crossing detection to flow monitoring inside a stenosis phantom L. Carrion, Z. Xu and R. Maciejko Laboratoire d'Optoélectronique, Département de Génie Physique, Ecole Polytechnique de Montréal, Montreal, QC, H3C 3A7, Canada ABSTRACT Most of the time, arterial stenoses caused by atherosclerosis, hardening of the artery walls, or buildup of fatty deposits prevent the blood from flowing normally. Blood flow characteristics in the vicinity of a stenosis are therefore very important since the restriction may accelerate fatty deposits and thus quickly clog the artery. Doppler Optical Coherence Tomography (DOCT) is a biomedical technique that allows simultaneous structural imaging and flow monitoring inside biological tissues and materials with spatial resolution at least one order of magnitude better than .ultrasound This study deals with the application of a Near Infrared DOCT system for imaging and monitoring of liquid flow inside a stenosis phantom inserted in a glass tube. For the measurement of the Doppler frequency, we use a numerical method based on the detection of the zero-crossing points of the OCT signal. Keywords: Biophotonics, Optical Coherence Tomography, Digital Image Processing. 1. INTRODUCTION As a recent optical imaging modality, Optical Coherence Tomography (OCT) provides depth-resolved structural and morphological information of biological samples and tissues as well as materials [1,2]. The principle of this technique is based on the measurement of the cross-correlation of reflected signals from two arms of an interferometer. Thus, the histology of a sample placed at the end of one of the interferometer arms can be imaged with high resolution (typically several microns) [3]. As an important extension of OCT, Doppler OCT (DOCT) enables the simultaneous evaluation of the structural information and of the blood flow distribution at a localized position beneath the tissue surface [4]. Like Doppler velocimetry, DOCT is based on the measurement of the Doppler frequency shifts contained in the signal scattered back off a moving particle. Since its implementation, DOCT is mostly used to detect blood flow inside small vessels with a resolution as good as several μm/s [5]. Ophtalmic applications are appropriate since blood vessels in the retina are small and easy to reach [6]. Nevertheless, the development of increasingly sophisticated catheters brings new functionalities for OCT in the domain of cardiology, and especially for atherosclerotic plaque characterization on arterial walls [7]. In spite of practical difficulties, DOCT seems to be a promising tool for blood flow characterization inside arteries. In particular, it brings higher spatial and speed resolution than commonly used ultrasound techniques. It has been shown that some DOCT systems could cover a velocity span from 1 μm/s up to 10 to 20 m/s, giving a dynamic range of 60 dB and more [5,8]. Thus, application of DOCT systems to blood flow monitoring near stenoses caused by plaque would certainly reveal detailed information on the mechanism of plaque formation and growth. In this paper, we propose to apply for the first time to our knowledge the DOCT technique to flow monitoring inside a simulated stenosis. For Doppler frequency detection, we will use a numerical method that is based on zero-crossing points detection in the OCT signal. We presented recently this simple and efficient technique. We showed that this method gives more precise results than methods commonly used in DOCT such as short time Fourier transform or Hilbert methods [9]. *lionel.carrion@polymtl.ca; phone 01 514 340 4711 (#4969); fax 01 514 340 3218 Photonics North 2008, Réal Vallée, Michel Piché, Peter Mascher, Pavel Cheben, Daniel Côté, Sophie LaRochelle, Henry P. Schriemer, Jacques Albert, Tsuneyuki Ozaki, Eds., Proc. of SPIE Vol. 7099, 70990G, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.807215 Proc. of SPIE Vol. 7099 70990G-1 2008 SPIE Digital Library -- Subscriber Archive Copy