In diffuse optical tomography reconstructing with two different back projection techniques and comparing reconstructed images

Currently, there are several devices have been used for diagnosis of breast cancer. These devices are X-ray tomography ultrasound and MRI. Because of these devices sending harmful photons to the body, costly, lack of resolution and portability, new methods are searching on diagnosis of breast cancer. One of these methods is Diffuse Optical Tomography (DOT). Diffuse optic tomography system was developed in order to diagnose breast tumors. In this study, 808 nm wavelength laser which has a high penetration to tissue is used. In the DOT system there are 49 source and 49 detector fibers. The source and detector fibers are placed in 10x10 matrix in an order. When photons are sending into the tissue by one source, returning light is collected by 49 detectors fiber and are delivered to the photodiode. At the end of the measurements, there are 49x49 data are taken. In in-vitro experiments, to make similar environment like breast tissue Intralipid with a concentration of 1% was used. Intralipid has very low absorption at 808 nm. To make similar absorption coefficient to the breast tissue Indocyanine green (ICG) was added to make the absorption coefficient 0.04 cm-1. To mimic tumor, a transparent balloon was filled with 1% Intralipid and ICG to set scattering and absorption coefficients 10 cm-1 and 0.16 cm-1. Because of the extensive blood supply of tumor region, absorption is higher in tumor region than normal tissue. In this study, the breast phantom and tumor-like structure's (inclusion) light scattering coefficients (μs) is same but absorption coefficients (μa) are different. Therefore, reconstructed images created based on the difference in the absorption between the background and the inclusion. In the study, measurement were taken breast phantoms for the depth of the inclusion of 0.3 cm to 1.5 cm. 3D Image of breast phantoms were created by using Algebraic Reconstruction Technique (ART) and Truncated Conjugate Gradient (TCG) methods. In the reconstruction, the volume under the probe was divided to 15x15x10 voxels on x-y-z axes respectively and so the total number of voxels in the system became 2250. Images created by different reconstruction algorithms are compared to each other in terms of some parameters such as position and resembling the actual shape. The results obtained by the TCG algorithm are closer to the real, which is the closest of absorber`s dimensions and contains less artifact. The system which we use consists of 2401 measurement and 2250 voxels so it is called as over-determined systems. According to our findings, we inference that TCG algorithm works better for over-determined system.