Diffuse Optical Imaging

Diffuse optical imaging is a functional medical imaging modality which takes advantage of the relatively low attenuation of near-infrared light to probe the internal optical properties of tissue. The optical properties are affected by parameters related to physiology such as the concentrations of oxyand deoxyhemoglobin. Instrumentation that is used for optical imaging is generally able to measure changes in the attenuation of light at several wavelengths, and in the case of timeand frequency-domain instrumentation, the time-of-flight of the photons in tissue. Light propagation in tissue is generally dominated by scattering. Models for photon transport in tissue are generally based on either stochastic approaches or approximations derived from the radiative transfer equation. If a numerical forward model which describes the physical situation with sufficient accuracy exists, inversion methods may be used to determine the internal optical properties based on boundary measurements. Optical imaging has applications in, e.g., functional brain imaging, breast cancer detection, and muscle imaging. It has the important advantages of transportable instrumentation, relatively high tolerance for external electromagnetic interference, non-invasiveness, and applicability for neonatal studies. The methods are not yet in clinical use, and further research is needed to improve the reliability of the experimental techniques, and the accuracy of the models used. Ilkka Nissilä, Tommi Noponen, Jenni Heino, Timo Kajava, and Toivo Katila Laboratory of Biomedical Engineering, Helsinki University of Technology, P.O. Box 2200, 02015 HUT, Finland. Advances in Electromagnetic Fields in Living Systems, Volume 4, edited by James C. Lin, Springer Science+Business Media, New York, 2005.