4
1 Methods Describing the Interaction of Laser Radiation with Biological Tissues
in the dermis includes collagen and elastin fibers with a diameter of about 60 nm,
packed in bundles of fibers with a diameter about 60 nanometers called - lamels, and
an amorphous substance (interfibrilyarny gel), of salt and water. Connective tissue
contains widely branched vascular structures of the skin, the nervous network and
epithelial glands. Derma is randomly divided into two anatomical areas: papillary
(Stratum papillary dermis) and reticular (Stratum reticulare dermis) [9]. More subtle
is the so-called papillary dermis, the outer part of the dermal connective tissue that
is formed under the epidermis.
Papillary dermis contains more free distribution of elastin and collagen fibers than
the reticular layer. Bundles of collagen fibers of papillary dermis are 0.3–3.0 µm in
diameter. Papillary dermis also contains lymphatic plexus and blood vessels. The
second major part of derma, and the underlying papillary dermis, is called the reticular
dermis. Vascular structure of the skin is clearly divided into two systems: a system
of vessels that provide nourishment skin and deep, mainly subcutaneous, and arterial
and larger venous capillaries which perform the function of heat exchangers of blood
with the environment [2].
Biological tissues, such as skin, are optically inhomogeneous absorbing media
with an average refractive index greater than that of air, so the boundary between
biological object-air part of the radiation is reflected (Fresnel reflection), and the
remaining part penetrates the tissue. The skin is characterized by a significant light
scattering, i.e., it is highly scattering turbid medium, because it consists of a large
number of scattering centers randomly distributed in the volume. The degree of
scattering depends on the wavelength of the radiation and the optical properties of
biological tissues.
Absorption of light is a physical phenomenon, which characterizes the energy
loss when light passes through the biological structure (skin) [10]. The energy of the
absorbed light transfered into heat is spent on photochemical reactions or released in
the form of radiation luminescence. The absorption spectra of any tissue, including
skin, determined by the presence of all biologically important molecules involved in
double bonds (chromophores of skin), and containing water in biological tissues. In
the epidermis the role of chromophores perform various fragments comprising the
amino acids and nucleic acids, absorbing light in the ultra-violet wavelength range
[11]. In the visible spectrum one of the most prevailing chromophores of skin is
the pigment melanin [2]. The absorption spectrum of melanin has no pronounced
absorption bands; however, it effectively absorbs in all spectral regions from 300 to
1200 nm.In the near ultraviolet radiation and visible regions of the spectrum, aside
from melanin, the basic skin chromophores are bilirubin, vitamins, flavins, flavin
ferments, carotenoids, phycobilins, phytochrome, and others, as well as elastin and
collagen fibers [12].
The dermis of the skin include blood vessels, which contain hemoglobin, the
absorption spectrum of which significantly affects the absorption spectrum of the
skin. The higher the content of blood in the dermis, the greater absorption of its
radiation at corresponding to the absorption of blood. Therefore, when calculating
the optimal parameters of the radiation blood content in the dermis and the diameter of
blood vessels should be considered. In the in vivo biological tissue hemoglobin binds
1 Methods Describing the Interaction of Laser Radiation with Biological Tissues
in the dermis includes collagen and elastin fibers with a diameter of about 60 nm,
packed in bundles of fibers with a diameter about 60 nanometers called - lamels, and
an amorphous substance (interfibrilyarny gel), of salt and water. Connective tissue
contains widely branched vascular structures of the skin, the nervous network and
epithelial glands. Derma is randomly divided into two anatomical areas: papillary
(Stratum papillary dermis) and reticular (Stratum reticulare dermis) [9]. More subtle
is the so-called papillary dermis, the outer part of the dermal connective tissue that
is formed under the epidermis.
Papillary dermis contains more free distribution of elastin and collagen fibers than
the reticular layer. Bundles of collagen fibers of papillary dermis are 0.3–3.0 µm in
diameter. Papillary dermis also contains lymphatic plexus and blood vessels. The
second major part of derma, and the underlying papillary dermis, is called the reticular
dermis. Vascular structure of the skin is clearly divided into two systems: a system
of vessels that provide nourishment skin and deep, mainly subcutaneous, and arterial
and larger venous capillaries which perform the function of heat exchangers of blood
with the environment [2].
Biological tissues, such as skin, are optically inhomogeneous absorbing media
with an average refractive index greater than that of air, so the boundary between
biological object-air part of the radiation is reflected (Fresnel reflection), and the
remaining part penetrates the tissue. The skin is characterized by a significant light
scattering, i.e., it is highly scattering turbid medium, because it consists of a large
number of scattering centers randomly distributed in the volume. The degree of
scattering depends on the wavelength of the radiation and the optical properties of
biological tissues.
Absorption of light is a physical phenomenon, which characterizes the energy
loss when light passes through the biological structure (skin) [10]. The energy of the
absorbed light transfered into heat is spent on photochemical reactions or released in
the form of radiation luminescence. The absorption spectra of any tissue, including
skin, determined by the presence of all biologically important molecules involved in
double bonds (chromophores of skin), and containing water in biological tissues. In
the epidermis the role of chromophores perform various fragments comprising the
amino acids and nucleic acids, absorbing light in the ultra-violet wavelength range
[11]. In the visible spectrum one of the most prevailing chromophores of skin is
the pigment melanin [2]. The absorption spectrum of melanin has no pronounced
absorption bands; however, it effectively absorbs in all spectral regions from 300 to
1200 nm.In the near ultraviolet radiation and visible regions of the spectrum, aside
from melanin, the basic skin chromophores are bilirubin, vitamins, flavins, flavin
ferments, carotenoids, phycobilins, phytochrome, and others, as well as elastin and
collagen fibers [12].
The dermis of the skin include blood vessels, which contain hemoglobin, the
absorption spectrum of which significantly affects the absorption spectrum of the
skin. The higher the content of blood in the dermis, the greater absorption of its
radiation at corresponding to the absorption of blood. Therefore, when calculating
the optimal parameters of the radiation blood content in the dermis and the diameter of
blood vessels should be considered. In the in vivo biological tissue hemoglobin binds