In the paper we present the results of study of rat skin and rat subcutaneous tumor under the action of dehydrating agents
in terahertz (THz) range (15-30 THz). Frustrated Total Internal Reflection (FTIR) spectra were obtained with infrared
Fourier spectrometer Nicolet 6700 and then they were recalculated in the transmittance spectra with Omnic software.
Experiments were carried out with healthy and xenografted tumor in skin tissue in vitro. As the dehydrating agents
100% glycerol, 40%-water glucose solution, PEG-600, and propylene glycol were used. To determine the effect of the
optical clearing agent (OCA), the alterations of terahertz transmittance for the samples were analyzed. The results have
shown that PEG-600 and 40%-glucose water solution are the most effective dehydrating agent. The transmittance of
healthy skin after PEG-600 application increased approximately by 6% and the transmittance of tumor tissue after PEG-
600 and 40%-glucose water solution application increased approximately by 8%. Obtained data can be useful for further
application of terahertz radiation for tumor diagnostics.
We are proposing a new method for enhancement of optical imaging of proximal interphalangeal (PIP) joints in humans
at skin using optical clearing technique. A set of illuminating laser diodes with the wavelengths 670, 820, and 904 nm
were used as a light source. The laser diodes, monochromatic digital CCD camera and specific software allowed for
detection of the finger joint image in a transillumination mode. The experiments were carried out in vivo with human
fingers. Dehydrated glycerol and hand cream with urea (5%) were used as optical clearing agents (OCAs). The contrast
of the obtained images was analyzed to determine the effect of the OCA. It was found that glycerol application to the
human skin during 60 min caused the decrease of contrast in 1.4 folds for 670 nm and the increase of contrast in 1.5 and
1.7 folds for 820 nm and 904 nm, respectively. At the same time, the hand cream application to the human skin during 60
min caused the decrease of contrast in 1.1 folds for 670 nm and the increase of contrast in 1.3 and 1.1 folds for 820 nm
and 904 nm, respectively. The results have shown that glycerol and the hand cream with 5% urea allow for obtaining of
more distinct image of finger joint in the NIR. Obtained data can be used for development of optical diagnostic methods
of rheumatoid arthritis.
A comparative study of physical, chemical, and combined enhancement of transdermal transport of optical clearing agents (OCAs) is presented. As a physical enhancer of diffusivity, ultrasound (US) with a frequency 1 MHz and a power 1.1 W in the continuous mode was used, and dimethyl sulfoxide (DMSO) was used as a chemical enhancer. OCA (glycerol and polyethylene glycol-400 in equal proportion) was topically applied to the rat skin in vivo as alone or as together with the enhancers. Monitoring of skin optical clearing was implemented using an optical coherence tomography. The results have shown that the attenuation coefficient of intact skin dermis after the application of US-DMSO-OCA, US-OCA (both for 4 min), and DMSO-OCA (for 20 min) combinations decreased approximately by 31%, 19%, and 5%, respectively, while OCA alone did not induce a noticeable clearing effect for 20 min. Control skin sites with removed epidermis were used for modeling the upper limit of dermis optical clearing, i.e., maximal degree of optical clearing, by using the studied enhancers. They demonstrated that the attenuation coefficient decreases by 32%, 30%, 17%, and 16% at the action of US-DMSO-OCA, US-OCA, DMSO-OCA, and OCA, respectively. It can be concluded that US-DMSO-OCA combination only allowed reaching the upper limit of skin optical clearing.
We are proposing a new method for enhancement of optical clearing agent delivery into the skin using fractional laser
microablation of the skin surface. The Palomar Lux2940 erbium laser with the wavelength 2940 nm and pulse duration
of 5 ms was used as a light source. Two regimes of laser action were used in the experiments: the first one realized
microablation of skin upper layer and the second one created microchannels in skin. As optical clearing agents mineral
oil and PEG-300 were used. In vivo studies were carried out with white outbred rats. Both parameters: the permeability
coefficient of the agents in the tissue and the optical probing depth were measured using the OCT system at a wavelength
of 930 nm. The following values of the permeability coefficient of the skin with microablation were obtained:
(3.41±0.46)×10-5 cm/s and (2.35±0.30)×10-5 cm/s for mineral oil and PEG-300, respectively, at the use of the surface
microablation and (3.32±0.09)×10-5 cm/s and (3.61±0.34)×10-5 cm/s for mineral oil and PEG-300, respectively, at the
use of the microporation. The results have shown that the joint application of mineral oil with microablation in the first
regime promotes maximal (nearly 2-folds) increasing of optical probing depth in 30 min. Obtained data can be used for
development of optical diagnostic methods of skin diseases.
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