Background

Measurements of the light scattering properties of cells have focused primarily on flow cytometry applications rather than tissue optics. In flow cytometry the light scattered at a fixed number of angles (usually 0 and $90^\circ$) from a stream of cells flowing through a laser beam is measured and used to differentiate between cell types [75]. One of the first measurements of the scattering patterns of cells was conducted by Brunsting, et al [13], who measured the patterns of Chinese hamster ovary cells for $\theta<12^\circ$ and compared the results with Mie theory. They concluded that the intensity at angles above $12^\circ$ contains information about the internal cell morphology.

A method for cell classification using a flow system was described by Salzman in 1975 [86], where they demonstrated that using measurements of the scattered intensity at 0 and $90^\circ$, they could differentiate between lymphocytes, monocytes and granulocytes. Jovin et al [87] were able to distinguish between spheres of different sizes (0.8 and $1.0\: \mu\text{m}$) from the ratio of scattered light at 12 and $19^\circ$.

Steinke et al [88], measured the anisotropy values (g=0.98-0.99) and scattering cross sections (20-80 $\mu\text{m}^2$) for red blood cells and found good agreement with Mie theory. Measurements of the scattering pattern with a flow cytometer capable of recording the scattered intensity at 32 angles simultaneously from 0 to $22^\circ$ were made by Salzman [89]. Using this instrument they observed an increase in the scatter at angles above $12.75^\circ$ for mutant fibroblasts compared with normal fibroblasts. They concluded that abnormal lysomal storage inclusions in the cytoplasm of the mutant cells were responsible for the increase in scatter.

A more recent study by Doornbos et al [90], used an optical trap to isolate single particle and a second laser to measure the scattering pattern of the trapped particle. They obtained excellent agreement with Mie theory for trapped $7\: \mu\text{m}$ spheres, but were only able to measure the pattern of a human lymphocyte from $15-60^\circ$ due to the lower trapping efficiency of the cells.