Light scattering by irregular shaped cell-like objects using the finite difference time domain method (FDTD)

We simulated light scattering by objects similar to biological cells using the FDTD method. The characteristics of the cell-like objects were based on electron micrographs of cells grown in vitro. Three homogeneous cell-like objects were created from micrographs depicting normal prostate cells, and three from micrographs depicting malignant prostate cells. These six models used as the basis of our light scattering simulations led to the following conclusions: (1) The populations of normal and abnormal cell-like objects could be distinguished in terms of forward light scattering in a flow cytometry experiment; (2) The phase functions of light scattered by irregular objects averaged over several angles of incidence and several angles of observations are much smoother than the phase function of a perfect sphere; (3) There is a significant decrease in the ratio of scattering cross section of the non-spherical object to the scattering cross-section of the perfect sphere with equal volume, as the ratio of largest axis to smallest axis of the non-spherical object decreases; (4) For certain cell-like objects the phase functions of the scattered light obtained using the Henyey-Greenstein approximation or Mie theory are very different from those generated by FDTD calculations.; Further calculations compared a homogeneous cell-like object, to a cell-like object of identical shape with heterogeneities added. The following are the results from the comparison of light scattering by a homogeneous cell-like object to heterogeneous cell-like object: (1) There are indications that there is a smoothing effect on the phase function data (for light scattered by the heterogeneous cell-like object) created by organelles both in data averaged over a range of orientations and in data collected at single orientations. This smoothing effect (unlike the one discussed for homogeneous cell-like objects) is observable from a single azimuth angle of observation and a single orientation of the cell relative to the direction incident light. (2) The light scattered by the homogeneous cell-like object based on normal cell A contained significant cross polarization. This effect was greatly suppressed by the introduction of organelles.