Propagation properties of 1300-nm light in blood-saline mixtures determined through optical coherence tomography Dan P. Popescu*, Bernhard Schattka, Mark D. Hewko, Jeri Friesen, Michael G. Sowa National Research Council of Canada, Institute for Biodiagnostics, 435 Ellice Avenue, Winnipeg, Manitoba, CANADA, R3B 1Y6 ABSTRACT Establishing when the amount of recorded multiple scattered signal becomes dominant is important for various clinical applications that require optical coherence tomography imaging through a turbid environment such as blood. The profiles of detected signals obtained by compounding coherence tomography images of flowing blood-saline mixtures with various blood concentrations are analyzed. The scattering properties of the studied mixtures influence the corresponding profiles of the recorded signal. Monte Carlo simulations of light propagation through environments with various scattering coefficients are used to support and to explain the experimental data. Keywords: Optical coherence tomography, blood, Monte Carlo, light propagation, signal attenuation, multiple scattering of light, blood cells, blood-saline mixtures 1. INTRODUCTION Optical coherence tomography (OCT) is a serious candidate for becoming the method of choice in assessing and monitoring the plaque developed on the arterial walls. Due to a spatial resolution threshold of ~100 µm the most frequently used intravascular imaging methods, intravascular ultrasound (IVUS) and X-ray angioplasty, provide too little information about plaque characteristics or other vessel wall details like angioplasty balloon injuries. With its superior axial resolution, which can reach as far as 3 µm, OCT could become the technology of choice for arterial surface exploration. One of the possible designs for an OCT arterial catheter collecting images in an in-vivo experimental setting is presented in figure 1. The OCT system is designed around a fiber-based interferometer. Light propagating along the probe arm of the interferometer passes through the catheter sheath and enters an environment that could be exclusively blood or a mixture of blood and isotonic saline in various concentrations. After propagating through blood or blood-saline mixture, the probing light reaches the arterial wall where a part of it is reflected back toward the OCT detection system. Bio- morphological variations in the arterial tissue generate changes in optical properties like scattering, absorption and refractive index. Intrinsic optical properties of the tissue leave their marks on the probing light. Therefore by analyzing the back-reflected OCT signal it could be possible to assess the optical properties of the studied tissue and to establish correlations with specific clinical states like, for example, the presence of plaque or arterial injury on the arterial walls or within the artery itself. In order to perform high quality OCT imaging of the artery it is necessary to eliminate and quench all the signals that are not coming from that region of interest. If the specular reflection occurring at the catheter sheath interface is easy to identify and to eliminate from the recorded signal, the part of the signal generated through light scattering by blood cells presents a much bigger problem. Blood, as well as most of the blood-saline mixtures, are highly turbid environments that strongly scatter light. In the presented context, scattering is damaging to OCT imaging in two ways: first, it decreases the amount of probing light flux that reaches the arterial wall and second, it decreases the amount of light that caries information back to the detection after being back-reflected within the arterial tissue. In addition to these two factors, signal detected after undergoing multiple scattering events decreases the contrast of the OCT image. It could be also necessary that, in order to simplify the design of OCT-based arterial catheters, the OCT imaging in clinical applications to be accomplished through a slab of flowing blood that separates the catheter head from the arterial wall. Therefore the characteristics of OCT signal propagation through blood and blood-saline mixtures should be assessed. *dan.popescu@nrc-cnrc.gc.ca; phone 1 204 984-1845; fax 1 204 984-5472; http://intranet.ibd.nrc.ca/ibdww Biomedical Applications of Light Scattering II, edited by Adam Wax, Vadim Backman Proc. of SPIE Vol. 6864, 686408, (2008) · 1605-7422/08/$18 · doi: 10.1117/12.764074 Proc. of SPIE Vol. 6864 686408-1 2008 SPIE Digital Library -- Subscriber Archive Copy