Transition from the ballistic to the diffusive regime in a turbid medium

Abstract

By varying the absorption coefficient and width of an intralipid-India ink solution in a quasi one-dimensional experiment, the transition between the ballistic and the diffusive regimes is investigated. The medium's attenuation coefficient changes abruptly between two different values within a single mean-free-path. This problem is analyzed both experimentally and theoretically, and it is demonstrated that the transition location depends on the scattering coefficient as well as on the measuring solid angle.

Gaussian beam in two-photon fluorescence imaging of rat brain microvessel

“…Typical Ltr used in optical coherence tomography is about 0.5 to 1 mm for tissues where the diffusion equation becomes valid for 8× Ltr scattering length. 8,9 The effect of multiscattering in a Gaussian profile is discussed in detail by Ying et al 5 The Ls for brain tissue is about 80 μm and the Ltr is approximately 480 μm. The imaging depth of 500 μm in brain tissue can be achieved in theory.…”

Sensitivity of coded aperture Raman spectroscopy to analytes beneath turbid biological tissue and tissue-simulating phantoms

“…In addition, the transport MFPs of the samples were established with collimated transmission measurements that are most accurate in the ballistic or single-scattering regime (i.e., samples with thicknesses corresponding to less than one MFP); therefore, the transport MFPs of the thickest tissues may have been underestimated because of the effects of multiple forward scattering. 36,37 If the two thickest samples are omitted (chicken breast samples with thicknesses of 1850 and 2250 μm, which each correspond to greater than 8 MFPs) and a linear least-squares fit is performed on the remaining logarithm-transformed tissue data, strong relationships between transport MFPs and relative caffeine signal are recovered (R 2 ¼ 0.95 and 0.84 for the coded aperture and slit-based instruments, respectively). The least-squares fits to the truncated tissue data are overlaid on the fits to the Intralipid data in Fig.…”

In-silico and in-vitro investigation of a photonic monitor for intestinal perfusion and oxygenation

“…Although as shown below for real tissue, the depth reached by light at 630 nm is within the thickness of the tissue for the shorter source-to-detector separation chosen, reducing the possible error. For these simulations, the longer mean free path at 630 nm, representing the probabilistic distance a photon will travel before interacting with a scattering particle and defined as the reciprocal of the scattering coefficient, μ s , combined with the reduced distance to the luminal surface of the tissue results in the photons behaving in a more quasi-ballistic fashion and being lost as transmission [48]. …”