Effect of wavelength and beam width on penetration in light-tissue interaction using computational methods.

Penetration depth of ultraviolet, visible light and infrared radiation in biological tissue has not previously been adequately measured. Risk assessment of typical intense pulsed light and laser intensities, spectral characteristics and the subsequent chemical, physiological and psychological effects of such outputs on vital organs as consequence of inappropriate output use are examined. This technical note focuses on wavelength, illumination geometry and skin tone and their effect on the energy density (fluence) distribution within tissue. Monte Carlo modelling is one of the most widely used stochastic methods for the modelling of light transport in turbid biological media such as human skin. Using custom Monte Carlo simulation software of a multi-layered skin model, fluence distributions are produced for various non-ionising radiation combinations. Fluence distributions were analysed using Matlab mathematical software. Penetration depth increases with increasing wavelength with a maximum penetration depth of 5378 µm calculated. The calculations show that a 10-mm beam width produces a fluence level at target depths of 1-3 mm equal to 73-88% (depending on depth) of the fluence level at the same depths produced by an infinitely wide beam of equal incident fluence. Meaning little additional penetration is achieved with larger spot sizes. Fluence distribution within tissue and thus the treatment efficacy depends upon the illumination geometry and wavelength. To optimise therapeutic techniques, light-tissue interactions must be thoroughly understood and can be greatly supported by the use of mathematical modelling techniques.

Pigmentation: selective photothermolysis or non-specific skin necrosis using different intense pulsed light systems?

BACKGROUND AND OBJECTIVE: This study considers end point tissue responses and side effects to determine whether 'square pulse' IPL is more or less effective than the traditional IPL. Supporting histological data and computational modelling results are provided. It provides guidance for IPL users unfamiliar with constant spectrum IPL devices and redirects attention to treatment end points. MATERIALS AND METHODS: Twenty subjects of Fitzpatrick Skin Types I-III, presenting with various epidermal pigmented lesions, were treated 1-3 times with two different IPLs. Coupling gel was used and firm pressure was applied to exclude blood from the treatment area. Immediate and post-treatment side effects, degree of discomfort and end results at fourteen and thirty days were evaluated by professional observation, digital photography and a patient questionnaire. RESULTS: Both IPLs showed a mean clearance of over 80% after 1-3 treatments but the free discharge IPL demonstrated a greater side effect profile with a higher incidence of ulceration, crusting and erythema. CONCLUSIONS: Clinical observation and mathematical modelling suggests that the square pulse, partial discharge IPL system may provide the IPL operator with greater control over the coagulation of pigment and is therefore the more efficient device for effective pigment lightening with fewer side effects.

Mathematical modeling of the optimum pulse structure for safe and effective photo epilation using broadband pulsed light.

The objective of this work is the investigation of intense pulsed light (IPL) photoepilation using Monte Carlo simulation to model the effect of the output dosimetry with millisecond exposure used by typical commercial IPL systems. The temporal pulse shape is an important parameter, which may affect the biological tissue response in terms of efficacy and adverse reactions. This study investigates the effect that IPL pulse structures, namely free discharge, square pulse, close, and spaced pulse stacking, has on hair removal. The relationship between radiant exposure distribution during the IPL pulse and chromophore heating is explored and modeled for hair follicles and the epidermis using a custom Monte Carlo computer simulation. Consistent square pulse and close pulse stacking delivery of radiant exposure across the IPL pulse is shown to generate the most efficient specific heating of the target chromophore, whilst sparing the epidermis, compared to free discharge and pulse stacking pulse delivery. Free discharge systems produced the highest epidermal temperature in the model. This study presents modeled thermal data of a hair follicle in situ, indicating that square pulse IPL technology may be the most efficient and the safest method for photoepilation. The investigation also suggests that the square pulse system design is the most efficient, as energy is not wasted during pulse exposure or lost through interpulse delay times of stacked pulses.