Analysis of the influence of skull on photon transmission based on Monte Carlo method

The brain is the main part of the central nervous system, which consists of the cerebrum, cerebellum, brainstem and other structures. There are many nerve centers in the brain. Therefore, the brain has the most complex structure and the most perfect function. It is necessary to study the brain. Since the skull has a strong scattering effect on light, it is difficult for photons to reach deeper through the skull. In order to realize the imaging of brain, methods such as optical clearing, thin skull or are commonly used at present. In order to explore the influence of skull on photon transmission, this paper adopts Monte Carlo method, uses MCML simulation program, and studies the transmission of photon in brain tissue under the condition of with skull and without skull respectively by setting appropriate parameters. The influence of skull on photon is analyzed by photon trajectory, optical absorption density and fluence rate. It was found that, from the analysis of the motion trajectory of the photon, compared with that of the photon with skull, the motion ability of the photon without skull was enhanced in the radial direction and depth direction, and the distribution of the photon number increased along the longitudinal and radial direction. The optical absorption distribution and fluence rate distribution obtained without skull are fusiform and fatter than those obtained with skull, while the light distribution obtained with skull is smoother. The optical absorption distribution and fluence rate distribution without skull were more widely distributed in radial direction, with a range of 0.46 cm, 4.6 times that with skull. The depth of transmission was deeper, about 2.1 cm, while the depth of transmission was only 1.9 cm with skull. This research will provide reference and theoretical guidance for brain optical imaging.