This issue focuses on the use of optics for non-invasive assessment of tissue structure and dynamics inside the body. Temporal and spatial characteristics of light can be manipulated to reveal information not otherwise seen. The spectral and polarization characteristics of tissue and other body constituents can be combined with spatial localization methods to provide maps of blood flow, blood oxygenation/deoxygenation ratios, and other metrics useful in clinical diagnostics. The field is multidisciplinary, involves optics, engineering, medicine, and biology, and encompasses fundamental research, instrument development, clinical testing, and commercialization. As some of the papers indicate, much attention has to be given to refining those new optical techniques that are well adapted to clinical environments.

Seven papers were accepted for the issue in three general areas: 1) imaging in the multiple scattering regime, 2) imaging in the single scattering regime using optical coherence tomography (OCT), and 3) the determination of the optical properties of highly turbid media. The first three papers are on the multiple scattering regime. Pogue, Testorf, McBride, Osterberg, and Paulsen discuss the implementation and evaluation of a breast cancer imaging system. Boas' paper is a theoretical analysis of the limitation of linear image analysis methods in the diffuse scattering regime. The paper by Rolland and Strickland concerns the development of image processing techniques for treating the background in various medical imaging modalities. The next two papers concern single scattering OCT. A demonstration of high velocity resolution Doppler in OCT imaging is given by Yazdanfar, Kulkarni, and Izatt using Xenopus. In the second paper in this area, Sergeev, Gelikonov, Gelikonov, Feldchtein, Kuranov, Gladkova, Shakhova, Snopova, Shakhov, Kuznetzova, Denisenko, Pochinko, Chumakov, and Streltzova study the use of endoscopic OCT in discriminating precancerous and cancerous mucosa from normal mucosa. Spectroscopy and polarization studies of tissue are the subjects of the last two papers. Hielscher, Eick, Mourant, Freyer, and Bigio, are concerned with developing polarization methods for distinguishing tissue type. The final paper by Marquez and Wang, involves the development of rapid, inexpensive methods for determining the absorption and scattering spectra of tissue.