In this study properties of diffuse light from a spherical media embedded in an infinite media was investigated. Light that migrates through the spherical media is considered as signal and light that does not propagate through the spherical media is considered as noise. The analytical solution of SNR (signal to noise ratio) was derived with diffusion theory. The spatial distributions of the fluence rate were analyzed and the contours of signal to noise ratio were obtained as light source was put in different positions. The relationship between the source detector separation corresponding to maximum SNR and light source position was discussed, which is helpful to determine an appropriate measurement position. The results acquired in this paper are useful for ultrasound-modulated optical tomography and tissue imaging with diffuse photon density waves.
The velocity of capillary blood flow is an important parameter to diagnose some diseases. In this paper, a model was set up to non-invasively measure the capillary blood flow using diffusing temporal light auto-correlation. This method is independent of the direction of blood flow. The distance between the light source and the detector was discussed in order to obtain high SNR (signal to noise ratio). The influences of the Brownian motion and the random flow of scatterers on the auto-correlation of diffusing light were analyzed with Monte Carlo simulation. The simulation results show that the characteristic correlation time exponentially decays as the mean-squared velocity of capillary blood flow increases, which is useful for medical diagnosis.