Simulation of imaging with a θ line-scanning confocal microscope

We describe a 2-D computational model of the optical propagation of coherent light from a laser diode within human skin to improve our understanding of the performance of a confocal reflectance theta microscope. The simulation uses finite-difference time-domain (FDTD) computations to solve Maxwell's equations in a synthetic skin model that includes melanin, mitochondria, and nuclei. The theta line-scanning confocal microscope configuration experiences more localized decreases in the signal than the confocal common-path point scanning microscope. We hypothesize that these decreases result. from the bi-static imaging configuration, the imaging geometry, and the inhomogeneity of the index of refraction of the skin. All these factors result in the source path having different aberrations than those of the receive path. Our previous work showed a wide variability on received signals in a realistic tissue model with a small scattering object below the epidermis. Here we present synthetic images in the epidermis to evaluate the effect of various tissue parameters on overall image quality. Additionally, the model shows that correction of low-order aberrations result in an improvement in focus at the image plane. Changes in the model will be used to optimize the design of the theta line-scanning confocal microscope.