Abstract
The focusing of light through turbid media like biological tissues is strongly hindered by the scattering of light which limits its safe practice and application in medicine. In order to control this phenomenon, we shaped the incident wavefront using three algorithms including a four-element division algorithm, a partitioning algorithm, and simulated annealing to control, iteratively, a spatial light modulator (SLM). We have tested two different convergence criteria to achieve a focal point inside a turbid environment, made up of a mixture of agar and milk, set to mimic a specific depth of human skin, and provide comparison results. A camera and a lens are used to visualize the focal area and give feedback information to the algorithms. A discussion on the use of these algorithms and convergence criteria is presented, being focused on its convergence time and performance. Depending on the algorithm and operational parameters, improvements of 29% to 46% of the irradiance in the region of interest were accomplished.
Highlights
The development of new diagnostic and treatment techniques that are more efficient and less invasive so that the damage of healthy tissue can be minimized is of major importance in medicine
The power of the laser was set to 1.5 mW and the total number of iterations for Partitioning Algorithm (PA) and Simulated Annealing Algorithm (SAA) were chosen according to the continuous sequential algorithm (CS) with 10 phase values per cycle
All left side intensities correspond to the initial phase matrix projected onto the spatial light modulator (SLM), the middle ones relate to the intensities after the optimization, and the right patterns are the optimal phase distributions achieved
Summary
The development of new diagnostic and treatment techniques that are more efficient and less invasive so that the damage of healthy tissue can be minimized is of major importance in medicine. Due to its destructive effect over malignant tissues, like cancer cells, this has already been used in some superficial skin cancer treatments [3] Despite this latter success, it is of interest that this application can be expanded to the point of acting in regions that surpass the surface of the skin, with its thickness ranging from 0.6 mm to 3.2 mm [4], where the turbid nature of tissues prevents the laser from delivering the necessary dose in destroying the undesired tissues. By changing the phase map of the incident light, it can compensate for the scattering effects that decrease the quality of focus in an iterative way [17] Decreasing this area allows for larger irradiance values, following Equation (1), which in an in-depth tumor phototherapy application combined with GNP will allow to manipulate, by knowing the necessary dose (energy density), both the laser power and its exposure time to a minimum.
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