Speckle noise reduction of modulated images generated by spatial frequency domain imaging technique based on interferometric approach

Abstract

Nowadays, optical imaging techniques have been broadly and successfully applied for biological screening and pathogen identification. Spatial Frequency Domain Imaging (SFDI) is a recent non-invasive wide-field optical imaging technique utilized in many medical and clinical procedures such as photodynamic therapy, assessing burn severity, and monitoring wound healing progression. The SFDI technique provides a quantitative mapping of tissue absorption and scattering properties over a wide field of view based on tissue diffuse reflectance/transmittance dependency on the spatial frequency. In a typical SFDI system, broadband light is employed as the illuminating source, whereas in some applications, laser sources could also be used. However, the appearance of laser speckle may influence the captured images and this, in turn, affects the accuracy of the reconstructed optical parameters. Therefore, in the current study, an experimental configuration based on interference has been utilized to reduce the speckle noise contrast of the obtained spatially modulated images. To achieve that, a red laser source with a wavelength of λ = 650 nm is divided into two identical beams using a beam splitter. One beam illuminates a reflecting mirror (reference beam) and the other one illuminates the reflecting window of a spatial light modulator (SLM) (reflected beam). Sinusoidal patterns of different frequencies are displayed on the SLM; hence the reflected beam becomes spatially modulated. The two beams (reference and reflected modulated beams) are combined to pass through a diffuser that simulates a rough tissue and imaged by a CCD camera. The obtained results reveal that the speckle noise contrast has been reduced by an average ratio of 21.89% after applying the interferometric configuration.