Hindawi Publishing Corporation International Journal of Biomedical Imaging Volume 2012, Article ID 509783, 11 pages doi:10.1155/2012/509783 Research Article Quantifying Optical Microangiography Images Obtained from a Spectral Domain Optical Coherence Tomography System Roberto Reif, Jia Qin, Lin An, Zhongwei Zhi, Suzan Dziennis, and Ruikang Wang Department of Bioengineering, University of Washington, Seattle, WA 98195, USA Correspondence should be addressed to Ruikang Wang, wangrk@uw.edu Received 4 January 2012; Accepted 13 April 2012 Academic Editor: Richard H. Bayford Copyright © 2012 Roberto Reif et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The blood vessel morphology is known to correlate with several diseases, such as cancer, and is important for describing several tissue physiological processes, like angiogenesis. Therefore, a quantitative method for characterizing the angiography obtained from medical images would have several clinical applications. Optical microangiography (OMAG) is a method for obtaining three-dimensional images of blood vessels within a volume of tissue. In this study we propose to quantify OMAG images obtained with a spectral domain optical coherence tomography system. A technique for determining three measureable parameters (the fractal dimension, the vessel length fraction, and the vessel area density) is proposed and validated. Finally, the repeatability for acquiring OMAG images is determined, and a new method for analyzing small areas from these images is proposed. 1. Introduction The appearance of tissue vasculatures may be an important biomarker to distinguish healthy from diseased tissues in several medical applications. For example, a change in retinal vessels is an early indicator of coronary heart disease [1, 2] and stroke [3]. Vascular remodeling has also been of interest in several fields including wound healing [4], oncology [5], and tissue regeneration [6]. Numerous techniques have been applied to obtain the vascular morphology from biological tissues. Optical intrinsic signal imaging [7], laser speckle imaging [8], and laser-Doppler flowmetry techniques [9] can obtain microan- giography images; however, they have low spatial resolution which limits their capability for viewing small capillaries. Confocal microscopy provides high spatial resolution; how- ever, it is limited by its penetration depth and requires the use of fluorescent tissue markers [10]. Photoacoustic imaging, based on thermal-acoustic phenomena resulting from the strong light absorption of blood and the subsequent thermo- elastic expansion, provides high-resolution angiography images; however, the acquisition time is slow [11, 12]. Optical microangiography (OMAG) is a method for obtaining three-dimensional images of blood vessels in vivo, using a spectral domain optical coherence tomography (OCT) system [13, 14]. OMAG is based on separating the static from dynamic tissue structures, which is done by detecting the changes in the scattered signal through time, due to the movement of particles such as red blood cells. OMAG has been used in several studies such as visualizing the corneal-sclera limbus [15], the retina [16], the skin [17] and the cerebral [18], and renal microcirculations [19]. OMAG has the advantage that it can capture a large image (2 × 2 mm) within a few seconds with high resolution (∼10 μm) and high penetration depth (∼2.5 mm). Microangiography images provide direct visualization of the blood vessels and capillaries within biological tissues. Usually, these images are interpreted qualitatively [20]. Pre- vious methods to quantify these images include measuring blood vessel diameters [21], the flow velocity [22], and the maximum distance in the tissue to the nearest blood vessel [23]. New methods that can enable the quantification of the blood vessels, such as the vessel tortuosity, will be beneficial for several studies, like angiogenesis. Vessel length fraction and vessel area density are parame- ters which represent a relative value of the total length of the vessels and the total area occupied by the vessels, respectively [24]. Fractal dimension (FD) is an approach that is used