Análise espectral do biospeckle laser através do momento de inércia, entropia e cross-spectrum

Abstract

Dynamic speckle can be used as a method for analysing activity, biologic or not, from materials illuminated with laser beam. Spatial Temporal Speckle (STS) contains data of time information of dynamic speckle and it is used as input for many techniques that intend to obtain information about the activity that is being monitored. This study presents the Inertia Moment, the Wavelets based Entropy and the Cross-Spectrum analysis as approaches that can be used for evaluating the STS spectral content. STS lines have been created based on many frequencies of the fundamental harmonic. This was done for verifying as each method acts when analysing different frequencies, varying harmonics offset and amplitude. These techniques were applied to real database, to verify their action mechanism in biological samples. The simulated data results present that all techniques are able to verify the spectral content of different harmonics. Inertia Moment was more efficient on analysing high frequencies, because it is a second order moment, being able to obtain more information from high variations on activity. Entropy and Cross-Spectrum, in turn, were better on differing lower frequencies. Probably this has occurred due the convolution method, that filters high frequencies and is part of the implementation process of both techniques. On real database, Inertia Moment and Entropy had their action mechanisms coinciding with the simulated results. Cross-Spectrum was not able of identify the experiment studied. These results show that all techniques can give spectral information about the biospeckle. Althought, any of them returned informations on both high and low frequencies at the same time, they can be used simultaneously, since Entropy and Cross-Spectrum were complementary to Inertia Moment.