Recent Advances in the Laser Radiation Transport through the Head Tissues of Humans and Animals – A Review

Abstract

Modern studies of the penetration of light into biological tissues is becoming very important in various medical applications. This is an important factor for determining the optical dose in many diagnostic and therapeutic procedures. The absorption and scattering properties of the tissue under study determine how deeply the light will penetrate into the tissue. However, these optical properties are highly dependent on the wavelength of the light source and tissue condition. This overview paper analyzes the transmission of light through different areas of human and animal head tissues, and the optimal laser wavelength and power density required to reach different parts of the brain are determined using lasers with different wavelengths by comparing the distribution of fluence, penetration depth and the mechanism of interaction between laser light and head tissues. The power variation in different regions of the head is presented, as estimated using Monte Carlo (MC) simulations. Data are analyzed for the absorption and scattering coefficients of the head tissue layers (scalp, skull, brain), calculated using integrating sphere measurements and inverse problem solving algorithms such as inverse MC (IMC) and adding-doubling (IAD). This study not only offered a quantitative comparison between wavelengths in terms of light transmission efficiency, but also anticipated the exciting opportunity for online, accurate and visible optimization of LLLT lighting parameters.

Transcranial photobiomodulation for brain diseases: review of animal and human studies including mechanisms and emerging trends

“…They found that the Gaussian beam with a similar or larger size as the hemorrhagic region had the best therapeutic outcomes, whereas the top-hat beam performed better when the hemorrhagic region was much bigger than the beam size. 142,218 3.4 tPBM for Alzheimer's Disease AD is a neurodegenerative disease that dramatically reduces the quality of life and ultimately leads to death. 219 However, there is a lack of effective therapeutic strategies for AD in clinical practice.…”

“…optimized the tPBM illumination parameters for hemorrhagic stroke using the Monte Carlo method to stimulate photon propagation within the visible Chinese human head at a different level of intracerebral hemorrhage with varied parameters of light beams. They found that the Gaussian beam with a similar or larger size as the hemorrhagic region had the best therapeutic outcomes, whereas the top-hat beam performed better when the hemorrhagic region was much bigger than the beam size 142 , 218 …”

“…They found that the Gaussian beam with a similar or larger size as the hemorrhagic region had the best therapeutic outcomes, whereas the top-hat beam performed better when the hemorrhagic region was much bigger than the beam size. 142 , 218 …”

Ultra-Short Laser Pulses Propagation Through Mouse Head Tissues: Experimental and Computational Study

“…Nevertheless, the main hurdle of non-invasive treatment is the delivery of sufficient power for photoconversion after light passing through the skin, skull, and brain [20], [21]. These biological tissues significantly absorb visible light, which can lead to their heating and damage [22].…”