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.
We describe a 2-D computational model of the optical propagation of coherent light from a laser diode within human skin to better understand 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 bistatic 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 aberrations different than those of the receiver path. The model predicts signal decreases that are somewhat greater than those seen in experiments. New details on the reflection from a spherical object show that imaging with the theta line scanner leads to somewhat different results than would be seen with a common-path point scanner. The model is used to optimize the design of the theta line-scanning confocal microscope.
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