Chemical agents with high refractive index, hyperosmotic, and biocompatibility are introduced into tissue, which will
reduce the scattering of tissue, and enhance the penetration of light in tissue. Diffuse reflectance, as a common method,
has been applied to assess optical clearing of skin in vivo, but the scattering characteristic during the in-vivo optical
clearing process has not been valuated quantitatively. In this work, a diffuse reflectance spectroscopy, based on a lookuptable (LUT) based inverse model, is applied to calculate the reduced scattering coefficient and absorption coefficient of skin. Optical clearing agents (OCAs) were topically treated on mouse skin in vivo. The diffuse reflectance during optical clearing was recorded, and the optical properties can be extracted by the reflectance spectroscopy. The results show that the diffuse reflectance spectra and the reduced scattering coefficient are decreased obviously, whilst the absorption coefficient is increased after the application of OCAs. This study provides evident directly for explore the mechanisms of optical clearing of skin in vivo.
Optical imaging techniques have shown tremendous potential for assessing cutaneous microcirculation, but the imaging depth and contrast is limited by the strong scattering of skin. Current skin windows have to be fulfilled by surgical operation and suffer from some side effects. In this study, a switchable skin window was developed by topical application of an optical clearing agent (OCA) and saline on rat skin in vivo. The validity of the skin window was evaluated by the laser speckle contrast imaging technique, and the safety of OCA to the body was tested through histologic examinations. The results indicated that administration of OCA or saline on rat skin in vivo can open or close the window of skin repeatedly for three days. With the repair effect of hyaluronic acid and Vaseline, it is able to repeatedly visualize the dermal blood vessels and flow distribution. Long-term observation shows that there is no abnormal reflection in micro-structure, body weight, organ coefficients, histopathologic lesions, or toxic reactions compared with a control group. This switchable window will provide an effective tool not only for cutaneous microcirculation with laser speckle contrast imaging, but also for diagnosis and treatment of peripheral vascular diseases, including tumor research with various optical imaging techniques.
The high incidence and mortality of breast cancer require an effective method for early breast diagnosis. In order to
investigate the optical differences among malignant tumor, benign tumor and normal human breast tissue, a commercial
spectrophotometer combined with single integrating sphere was used to measure the optical properties of different types
of breast tissue in the wavelength range of 400 nm to 2200 nm in vitro. The hematoxylin and eosin staining (H&E
staining) are used as the standard, and to find the find possible optical markers from the corresponding absorption or
scattering spectra. This work is not only used for in vitro rapid optical diagnosis, but very helpful to develop innovative
optical diagnosis of breast tumor in vivo.
The tissue optical clearing technique based on immersion of tissues into optical clearing agents (OCAs) can enhance the
penetration depth of light in tissues, thus improve the capabilities of noninvasive optical diagnosis and therapeutic
treatment. However, the optical clearing efficiency of skin caused by topical application of OCAs usually suffers from
the barrier of stratum corneum and epithelium. The addition of chemical penetration enhancers to OCAs could
significantly improve the optical clearing of skin, but the investigations on their safety are seldom concerned. In this
study, based on the direct observation and histological examinations, the short-term and long-term effects of the mixture
of PEG-400 and Thiazone on morphology and microstructure of in vivo rat skin were investigated. The results
demonstrated that, in the first week, the hair growth was stunted, some degree of abnormal thickens and vacuoles
occurred at the epidermis layer, and the collagen arranged denser. After 2 week, the morphology and microstructure of rat
skin was completely recovered. It means that there is no long-term effect on rat skin by the mixture of PEG-400 and
Thiazone. In addition, this work provides a useful method for assessing the safety of OCAs to skin.
Optical method plays an important role in clinical diagnosis and treatment, but suffers from limited penetration depth of
light in turbid tissue. The optical clearing technique can improve the light delivery significantly through immersion of
tissues into Optical Clearing Agents (OCAs). However, the barrier function of stratum corneum makes it difficult for
optical clearing of skin by topical application of OCAs. Addition of penetration enhancers to OCAs can improve the skin
clearing efficacy, but most investigations were performed on in vitro skin. Here, to evaluate the efficacy of this method
on in vivo skin, direct observation and measurement of diffuse reflectance spectra were performed after topical
application of different mixtures. One OCA, PEG-400, and three penetration enhancers (PEs), Thiazone, Azone and
Propylene Glycol (PG), were used. The results indicated that the addition of penetration enhancers could improve the
optical clearing efficacy of rat skin in vivo significantly, the dermal blood vessels could be observed directly with PEs.
Among the three penetration enhancers, Thiazone induced the largest enhancement of clearing efficacy, and the
enhancement induced by PG is the least. This study is very helpful for in vivo application of OCAs to enhance skin
optical clearing non- invasively.
Noninvasive detection of skin microcirculation is very significant for clinical diagnosis and therapy of peripheral vascular disease. In this study, an optical clearing method enables a laser speckle contrast imaging (LSCI) technique to image dermal blood flow through intact rat skin. The optical clearing effect of rat skin in vitro caused by a mixture of PEG-400 and Thiazone is evaluated by a commercially available spectrophotometer with an integrating sphere. A LSCI system is applied to image the dermal blood flow of in vivo rat skin after topical treatment of the agents. The results show that the reduced scattering coefficient (630 nm) is down to 60% of the initial value after 40 min of topical treatment of the mixture on skin in vitro. In vivo experimental results show that a 12-min treatment of the mixture on the epidermis can make the skin transparent and dermal vessels can be observed, while treatment with pure PEG-400 cannot. The process of skin optical clearing lasts, and the skin can be recovered by treatment of saline solution. Because optical clearing decreases the temporal contrast, dermal blood flow can be obtained by the laser speckle contrast imaging technique.
The occurrence, development and curative effect of many diseases are relative to the structure and function of
hypodermic blood vessels. The optical imaging techniques may be available, but suffer from the limited penetration of
visible and near infrared light caused by the high scattering of skin. The tissue optical clearing technique based on
immersion of tissues into optical clearing agents (OCAs), proposed by Tuchin, can improve the depth to which light
penetrates. However, it is still difficult to meet skin in vivo except for OCAs hypodermic injection. In this study,
THIAZONE as a new penetration enhancer mixed with polyethylene glycol (PEG-400), was typically applied to rats'
skin in vivo. The optical clearing process of skin was monitored with CCD camera, and the deep blood flow information
of skin was acquired by using of laser speckle contrast imaging technique. The results show that the skin became
transparent after 12 minutes, the vessels were clear. After 40 minutes, acting saline on the interested region, we observed
a recovery of the skin. This work is very significant for medical diagnosis since it is able to acquire the structure and
function information of blood vessels in deep skin in vivo with
non-invasive optical method.
The inherent barrier function of the stratum corneum (SC) makes optical clearing agents difficult to penetrate into skin.
To date, several physicochemical methods have been studied to enhance skin optical clearing. In this study, the rat skin
was initially irradiated by various light (Carbon-Dioxide Laser, Intensed Pulse Light, Nd:YAG Laser and its
frequency-doubled laser) with different dose, and then topically applied anhydrous glycerol. A fiber spectrometer was
used to monitor the change of skin diffuse reflectance spectrum so as to evaluate the optical clearing effect on skin. The
results showed that Nd:YAG Laser(1,064 nm) with appropriate pulse width and energy density combined with glycerol
could improve skin optical clearing effectively, and that Q-switched Nd:YAG Laser combining glycerol made the most
significant decrease of skin diffuse reflectance. However, after the irradiation of Carbon-Dioxide Laser (ultra-pulsed),
Intensed Pulse Light (400-700 nm) or frequency-doubled Q-switched Nd:YAG Laser(532 nm), the following application
of glycerol didn't lead to skin optical clearing. Adversely, higher power of the former two light could result in erythema,
the later one may harm skin apparently even lead to blood coagulation dot. This study provids a new idea to find out a
noninvasive but high-effective approach to increase skin optical clearing, and available parameters of laser need to be