Effect of detailed cell structure on light scattering distribution: FDTD study of a B-cell with 3D structure constructed from confocal images

Human B-cells play an important role in the immune system, and because of their relatively simple structures with a nearly spherically shaped cell membrane and a large nucleus, they provide a good case to study on how the details of cell structure affect light scattering properties. A finite-difference-time-domain (FDTD) method is used to calculate angle-resolved light scattering distributions from a B-cell. Published FDTD simulations to date have used a smooth shape with a certain degree of symmetry to approximate the actual cell shape. In contrast, for this work, the shapes of the cell and its nucleus were determined from confocal microscopy measurements. An automated procedure was developed to construct a realistic three-dimensional structure of a B-cell from a stack of two-dimensional confocal images. The angle-resolved Mueller matrix elements of the B-cell were calculated and averaged for 30 different angles of incidence using a parallel FDTD code. These results were compared with those from a homogeneous and a coated sphere. Scattering from the two sphere models and the B-cell were very similar for scattering angles less than 5°, and the coated sphere and B-cell agreed well for scattering angles up to 20°. However, at larger angles, the scattering from the B-cell was a much smoother function of angle than scattering from either sphere model. Additionally, the homogeneous sphere results were the most similar to the B-cell results for most angles between 120° and 150°, and at angles greater than 150°, the B-cell scattered more light than either of the spheres. These results yield strong evidence that accurate modeling of light scattering by biological cells requires not only the high accuracy of the employed numerical method but the realistic cellular structure as input information as well.