Photoepilation. Photoepilation utilizes light to cause thermal or mechanical damage of hair follicles. To achieve hair growth delay, it is sufficient to either damage matrix cells of anagen hair follicles or coagulate blood vessels of the papilla, or possibly destroy part of the outer root sheath [56]. For permanent hair-follicle damage, in accordance with current […]

3.6.2.1 Treatment Parameters for Planar, Cylindrical, and Spherical Targets Heat diffusion is strongly dependent on the heater and target geometry. In this section, we discuss three basic geometries: planar, cylindrical, and spherical (Fig. 3.19). In all cases, we Figure 3.19 Three types of target with different geometry [59]: (a) planar, (b) cylindrical, (c) spherical. 1 […]

Thermal damage of target with separation between part of the target and the pigmented area requires deposition of sufficient heat energy into the absorbing area, and good heat exchange between this area and the targeted external structures. Heat deposition depends on the absorption coefficient of the absorber and the EMR power density. Heat exchange depends […]

3.6.1 Theory of Selective Photothermolysis 3.6.1.1 Basic Principles For many years, electromagnetic radiation (EMR) from lasers, lamps, and other sources (including microwave ones) has been used to treat a variety of medical conditions in oph­thalmology, dermatology, urology, otolaryngology, and other specialties. For example, in dermatology EMR sources have been used to perform a wide variety […]

When photons traveling in a tissue are absorbed, heat is generated. Generated heat induces several effects in tissue which can be presented in the order of amount of heat deposition: temperature increase and reversible and irreversible alterations in tissue. The following types of irreversible tissue damage are expected as tissue temperature rises past Tcrit: coagulation […]

3.5.1 Photochemicals Photochemical interaction of light and tissue is of great interest for the study of tissue damage induced by solar radiation, in particular in skin-aging process, as well as for the designing of controllable technologies for tissue repairing and rejuvenation. Such interac­tion depends on the type of endogenous or exogenous chromophore (photosensitizer) involved in […]

The refractive index variation in tissues, quantified by the ratio m = njn0, determines light scattering efficiency. For example, in a simple tissue model, such as dielectric spheres of equal diameter 2a, the reduced scattering coefficient is described by [40]: m’s = ms (1- g) = 3.28 na2 p(2na/A)0,37 (m – 1)209, (3.14) where p […]

Fluorescence, more generally luminescence, is light not generated at high temperatures alone. It is different from incandescence, in that it usually occurs at low temperatures and is thus a form of cold body radiation. It can be caused by, for example, chemical or biochemical reactions, optical energy absorption; many kinds of luminescence are known: fluorescence, […]

Skin, as many other tissues is a polarization anisotropic (i. e., birefringent) medium [1]. Birefringence is the phenomenon exhibited by certain materials in which an incident ray of light is split into two rays, called an ordinary ray and an extraordinary ray, which are plane – (linear) polarized in mutually orthogonal planes, or circular-polarized in […]