Optical imaging techniques have become widespread in neuroscience and are now considered valuable tools in both neurovascular and cellular physiology research (Wilt et al., 2009). Macroscopic optical modalities include techniques such as optical intrinsic signal imaging (Grinvald et al., 1986), laser Doppler imaging (Dirnagl et al., 1989), laser speckle imaging (Dunn et al., 2001), diffuse optical imaging (Villringer and Chance, 1997), and laminar optical tomography (Hillman et al., 2004). These techniques typically achieve spatial resolutions on the order of hundreds of microns to millimeters. Two-photon microscopy is capable of resolution on the micron scale, though the imaging speed, penetration depth, and feld of view are somewhat limited. Optical coherence tomography (OCT) (Huang et al., 1991) has been a highly successful optical imaging modality in clinical applications due to the fact that it is label-free and enables high penetration depths, while still maintaining micron-scale resolution. Over the past two decades, OCT has increasingly been employed for the assessment of human tissues in vivo, and is now recognized as an important advancement in the diagnosis and monitoring of many pathologies. Optical coherence microscopy (OCM) is a term used to describe OCT approaches that prioritize high transverse spatial resolution, typically by employing higher numerical aperture (NA) focusing (Beaurepaire et al., 1998; Drexler and Fujimoto, 2008). Quantitative analysis based on 3-D imaging techniques such as OCM allows for the use of histological analysis tools, without the need for biopsy or the usage of contrast agents. More recently, OCT and OCM techniques have begun to expand beyond the clinic to the realm of basic research, including neuroscience. A recent enabling advancement in OCT imaging has been the development of angiography methodologies to selectively image vasculature. Red blood cells (RBCs) within blood vessels are typically seen as scattering and dynamically changing in standard OCT intensity images. Based on this observation, angiography techniques have been developed as a means of visualizing vasculature in vivo (Makita et al., 2006; Wang et al., 2007; Mariampillai et al., 2008; Tao et al., 2008; Vakoc et al., 2009). By using intensity- or phase-based algorithms, OCT angiography techniques enhance the image contrast associated with moving RBCs in comparison to that of the surrounding static tissue. This chapter describes approaches to combine OCM and angiography methods and apply them to the study of vascular architecture in the central nervous system, with particular regard to the brain cortical vasculature. Techniques for the analysis and categorization of vasculature are outlined, with emphasis on working with OCM data. Some discussion of the described methods and their applications is presented, along with suggestions for future research directions.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Biochemistry, Genetics and Molecular Biology(all)