CompanyName: Helsinki University of Technol
Simultaneous estimation of optical anisotropy and absorption
in medical optical tomography
Authors: Jenni Heino 1, Erkki Somersalo 2, Simon Arridge 3
1 Laboratory of biomedical engineering, Helsinki University of Technology,
P.O.Box 2200, 02015 HUT, Finland
2 Laboratory of Mathematics, Helsinki University of Technology,
P.O.Box 1100, 02015 HUT, Finland
3 Department of Computer Science, University College London,
Gower Street, London WC1E 6BT, UK
Optical tomography is a relatively new, non-invasive modality for medical applications such as functional imaging of the brain or breast cancer detection. Techniques using near-infrared light have some advantages over some of the existing modalities. Near-infrared light is non-ionizing and thus harmless to the patient, enabling long term monitoring. Also, the instrumentation can be made relatively light and inexpensive.
At near-infrared wavelengths, most human tissues are highly scattering. The propagation of light is often modelled using the Radiative Transfer Equation (RTE) and its approximations. The simplest approximation often used to model the forward problem in optical tomography is the Diffusion Approximation (DA), which is obtained by first order spherical harmonic expansion of the RTE, and making the additional assumption that the scattering probability depends only on the relative angle of incident and scattered radiation, not on the absolute direction. Such a medium is often referred to as isotropic.
However, for several human tissues, such as the white matter of the brain, muscles, or skin, the assumption of isotropic medium may not hold. It is known, e.g., that the fibres in the white matter of the brain have direction dependent properties for the diffusion of water. Here, we present one approach to model the anisotropic effects of light propagation and some examples of simultaneous reconstruction of optical absorption and anisotropy model parameters.