Monte Carlo simulations of digital diaphanoscopy in spherical geometry: a pilot study
D.A. Shumilin1, E.O. Bryanskaya2, M.Yu. Kirillin3,1
1N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia;
2 Research and Development Center of Biomedical Photonics, Orel State University, Orel, Russia;
3A.V. Gaponov-Grekhov Institute of Applied Physics RAS, Nizhny Novgorod, Russia;
Abstract
Non-invasive optical diagnostics uses light to analyze biological tissue and provide detailed information about its biochemical composition and anatomical structure. This techniques have the unique ability to conduct studies in real-time being safer and more easier to use than traditional laboratory techniques.
Diaphanoscopy is a cutting-edge method of optical diagnosis of ENT organs disorders , primary aimed at diagnostics of nasal sinuses. The diagnostics procedure involves inserting a light source into the patient's oral cavity and measuring the radiation transmitted through the tissues using a CCD camera located in front of the patient’s head. However, estimation of the required probing radiation intensity which should fit the safety requirements and interpretation of the obtained diagnostic diaphanograms require numerical simulations of signal formation in such systems.
The Monte Carlo method, a widely used technique for simulations of light propagation through scattering media, consists in calculation of a large number of random individual photon trajectories within the medium under study. With sufficient number pf the trajectories, this approach can provide quite accurate solution for light transport in tissues and can used to interpret the results of optical diagnostics.
In this study we avoided using traditional planar multilayer model of tissue and proposed using spherical geometry which is more suitable for simulation of light transport in human head. To mimic the anatomical shape, we introduced regions with spherical boundaries within the inspected volume . The probing radiation is emitted from a source located in the region mimicking oral cavity in accordance with the design of a diaphanoscopy system [1]. The simulations consider probing wavelengths of 650 and 850 nm, corresponding to those of the simulated setup. The region corresponding to nasal sinuses is assumed to be filled with air for simulations of patient in norm, while for cases of pathologies, it is assumed that its optical properties correspond to excaudate or tumor.
These simulations aim to support one of the main goals of diaphanoscopy: to assess the condition of the nasal sinuses. If the sinuses are filled with fluid or a tumor has formed, the radiation will scatter and be absorbed in that area, while in the norm the sinuses are air-filled. This results in a lower signal in the case of pathology presence, which appears as a dark region on the diaphanogram.
The results of the simulations are presented as a two-dimensional scan of the surface radiation intensity distribution in polar coordinates. t The obtained scans show that in the presence of pathology, the detected diaphanoscopy signal is significantly reduced as compared to normal state, and the simulations provide the quantitative estimations for both relative signal decrease and the level of the detected signal on the case of pathology. These results allow to provide recommendations on the power of probing radiation in diaphanoscopy systems and help to develop the protocols for differential diagnostics of nasal sinuses.
Speaker
Denis
National Research Lobachevsky State University of Nizhni Novgorod
Russia
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