Imagem por refletância difusa usando iluminação de intensidade espacialmente modulada (sfdi)

Abstract

Since the discovery of X-rays by Wilhelm Conrad Röntgen in 1895, the diagnosis and treatment of diseases could be done more quickly, clearly and accurately. In most cases, the imaging techniques adopted involve the use of ionizing radiation which, despite the benefits, has an associated risk. This work shows how visible light, that is, non-ionizing radiation, can be used to visualize different structures from the identification of absorption levels and optical scattering of light at different wavelengths in the range 400-800 nm. This is a technique called “Spatial Frequency Domain Imaging” (SFDI), in which an object is illuminated with a pattern of light and dark bands of different thicknesses. The incident photons under these conditions interact with the molecules of the medium and re-emerge from the material, in different directions, being captured by a CCD Camera. The camera records the image in different wavelengths (457, 488, 532, 580 and 650 nm) and a code in MATLAB® identifies the points of greatest and least reflection in a color-intensity map. The technique is applied with tissue-phantoms composed by silicone, Nankin ink and titanium dioxide (TiO2 ) whose optical properties were determined by spectroscopy in the integrating sphere. Diffuse reflectance proved to be inadequate for spatial frequencies above 0.20 pl/mm at wavelengths 532 and 580 nm. It was noticed that image processing takes into account average intensity values of the region of interest and that structures with large differences in concentration of absorbers or scatters compromise their visualization. In the text, the theory behind the SFDI technique is presented, the production and characterization of the produced phantoms and the results obtained with the processing in MATLAB.