Estimation of Photon Path Length and Penetration Depth in Articular Cartilage Zonal Architecture over the Therapeutic Window

• Published in: IEEE transactions on biomedical engineering 2024-08, Vol.71 (8), p.1-11
• Main Authors: Kafian-Attari, I., Nippolainen, E., Bergmann, F., George, A., Paakkari, P., Mirhashemi, A., Foschum, F., Kienle, A., Toyras, J., Afara, I. O.
• Format: Article
• Language: English
• Subjects: Articular cartilage; Biomedical optical imaging; Cartilage; Cartilage (articular); Cartilage, Articular - chemistry; Cartilage, Articular - diagnostic imaging; Cartilage, Articular - physiology; Computer Simulation; diffuse optical spectroscopy; Humans; Imaging; Information processing; Light; light propagation; Models, Biological; Monte Carlo Method; Monte Carlo simulation; Optical imaging; Optical propagation; Optical properties; Optical scattering; Optical variables control; Parameter estimation; Penetration depth; photon path length; photon penetration depth; Photonics; Photons; Propagation; Scattering, Radiation; Spectroscopy; tissue optical properties; Tissues; Trajectory analysis
• ISSN: 0018-9294; 1558-2531; 1558-2531
• DOI: 10.1109/TBME.2024.3368012

Objective: The key characteristics of light propagation are the average penetration depth, average maximum penetration depth, and average path length of photons. These parameters depend on tissue optical properties and, thus, on the pathological state of the tissue. Hence, they could provide diagnostic information on tissue integrity. This study investigates these parameters for articular cartilage which has a complex structure. Methods: We utilize Monte Carlo simulation to simulate photon trajectories in articular cartilage and estimate the average values of the light propagation parameters (penetration depth, maximum penetration depth, maximum lateral spread, and path length) in the spectral band of 400-1400 nm based on the optical properties of articular cartilage zonal layers and bulk tissue. Results: Our findings suggest that photons in the visible band probe a localized small volume of articular cartilage superficial and middle zones, while those in the NIR band penetrate deeper into the tissue and have larger lateral spread. In addition, we demonstrate that a simple model of articular cartilage tissue, based on the optical properties of the bulk tissue, is capable to provide an accurate description of the light-tissue interaction in articular cartilage. Conclusion: The results indicate that as the photons in the spectral band of 400-1400 nm can reach the full depth of articular cartilage matrix, they can provide viable information on its pathological state. Therefore, diffuse optical spectroscopy holds significant importance for objectively assessing articular cartilage health. Significance: In this study, for the first time, we estimate the light propagation parameters in articular cartilage.