INITIAL ASSESSMENT OF A SIMPLE SYSTEM FOR FREQUENCY-DOMAIN DIFFUSE OPTICAL TOMOGRAPHY

Diffuse optical tomography is an imaging technique whereby spatial map s of absorption and scattering coefficients are derived from the chara cteristics of multiply scattered light transmitted through the object. The system described here used four intensity-modulated light sources and measurements of the intensity and phase (relative to each source) at 16 or 20 detectors on the surface of a 10 cm diameter cylinder. An iterative Newton-Raphson algorithm was used to estimate the absorptio n and scattering coefficients at each pixel in a 17 x 17 array minimiz ing the difference between measured and calculated values of the inten sity and phase at the measurement sites. Forward calculations of the i ntensity and phase were based on a multigrid finite-difference solutio n of the frequency domain diffusion equation. Numerical simulations we re used to examine the resolution, contrast, and accuracy of the recon tructions as well as the effects of measurement noise, systematic unce rtainties in source-detector location, and accuracy of the initial est imates for the optical properties. Experimental tests also confirmed t hat the system could identify and locate both scattering and absorbing inhomogeneities in a tissue-simulating phantom.