The conditions pertaining here to the most extreme case (0.2% polystyrene beads, ) are representative of a multiply scattering environment with a scattering coefficient, , of and . For comparison, of biological tissues is in the range ,32,33 and of undiluted homogenized milk and 20% solids Intralipid (an optical phantom of multiple scattering) are , and , respectively.34 Thus, our model system exhibited biologically relevant scattering properties, albeit on the lower end of the spectrum, and allowed us to explore the effect of scattering in a systematic and reproducible manner. For the conditions studied, we found a significant decrease in apparent particle brightness due to attenuation of laser beam intensity [Figs. 5(b) and 6(b)]. We also observed an increase in apparent particle number, , indicating an increase in effective illuminated volume [see Figs. 5(c) and 6(c)]. Equation (1) helps us understand the connection between diffusion and illuminated volume profile. In Eq. (1), for which the illuminated volume is modeled as a Gaussian beam profile in both the radial and axial directions, we see that the correlation function is more sensitive to diffusion into the radial than in the axial direction. Thus, if the volume increase were related to volume distortion predominantly in the axial direction, diffusion time would be minimally affected. Overall, for the system studied here, it appears that a critical loss of intensity happens at a sufficiently low degree of multiple scattering that significant change in diffusion coefficient due to modification of the scattering volume could not be detected.