Laser Doppler flowmetry is a non-invasive method of measuring microcirculatory blood flow in tissue. In this review the technique is discussed in detail. The theoretical and experimental developments to improve the technique are reviewed. The limitations of the method are elaborated upon, and the research done so far to overcome these limitations is critically assessed.

We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced optical breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create optical breakdown in the dermis while leaving the epidermis intact, resulting in lesions due to cavitation and plasma explosion. This stimulates a healing response and consequently skin remodelling, resulting in skin rejuvenation effects. Analysis of ex-vivo and in-vivo treated human skin samples successfully demonstrated the safety and effectiveness of the microscopic lesion creation inside the dermis. Treatments led to mild side effects that can be controlled by small optimizations of the optical skin contact and treatment depth within the skin. The histological results from a limited panel test performed on five test volunteers show evidence of microscopic lesion creation and new collagen formation at the sites of the optical breakdown. This potentially introduces a safe, breakthrough treatment procedure for skin rejuvenation without damaging the epidermis with no or little social down-time and with efficacy comparable to conventional fractional ablative techniques. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Background/Aims: Sensitive skin (SS), a frequently reported condition in the Western world, has been suggested to be underlined by an impaired skin barrier. The aim of this study was to investigate the skin barrier molecular composition in SS subjects using confocal Raman microspectroscopy (CRS), and to compare it with that of non-SS (NSS) individuals as well as atopic dermatitis (AD) and allergic rhinoconjunctivitis (AR) subjects, who frequently report SS. Methods: Subjects with SS (n = 29), NSS (n = 30), AD (n = 11), and AR (n = 27) were included. Stratum corneum (SC) thickness, water, ceramides/fatty acids, and natural moisturizing factor (NMF) were measured by CRS along with transepidermal water loss and capacitance on the ventral forearm, thenar, and cheek. Sebum levels were additionally measured on the forearm and cheek. Results: No differences between SS and NSS subjects were found regarding SC thickness, water, and NMF content, yet a trend towards lower ceramides/fatty acids was observed in the cheek. Compared to AD subjects, the SS group showed higher ceramides/fatty acid content in the forearm, whereas no differences emerged with AR. The correlation of macroscopic biophysical techniques and CRS was weak,yetCRS confirmed the well-known lower content of NMF and water, and thinner SC in subjects with filaggrin mutations. Conclusion: The skin barrier in SS is not impaired in terms of SC thickness, water, NMF, and ceramides/fatty acid content. The failure of biophysical techniques to follow alterations in the molecular composition of the skin barrier revealed by CRS emphasizes a strong need in sensitive and specific tools for in vivo skin barrier analysis.

Abstract:We investigated the influence of thermal initiation pathway on the irradiance threshold for laser induced breakdown in transparent, absorbing and scattering phantoms. We observed a transition from laserinduced optical breakdown to laser-induced thermal breakdown as the absorption coefficient of the medium is increased. We found that the irradiance threshold after correction for the path length dependent absorption and scattering losses in the medium is lower due to the thermal pathway for the generation of seed electrons compared to the laser-induced optical breakdown. Furthermore, irradiance threshold gradually decreases with the increase in the absorption properties of the medium. Creating breakdown with lower irradiance threshold that is specific at the target chromophore can provide intrinsic target selectivity and improve safety and efficacy of skin treatment methods that use laser induced breakdown. Phys. 64(4), 1549-1554 (1976). 11. P. K. Kennedy, "A first-order model for computation of laser-induced breakdown thresholds in ocular and aqueous media. I. Theory," IEEE J. Quantum Electron. 31(12), 2241-2249 (1995). 12. D. X. Hammer, R. J. Thomas, G. D. Noojin, B. A. Rockwell, P. P. Kennedy, and W. P. Roach, "Experimental investigation of ultrashort pulse laser-induced breakdown thresholds in aqueous media," IEEE J. Quantum Electron. 32(4), 670-678 (1996). calculation of thresholds, absorption coefficients, and energy density," IEEE J. Quantum Electron. 35(8), 1156-1167 (1999

An increasing number of applications, including non- or minimally invasive diagnostics and treatment as well as various cosmetic procedures, has resulted in a need to determine the optical properties of hair and its structures. We report on the measurement of the total attenuation coefficient of the cortex and the medulla of blond, gray, and Asian black human scalp hair at a 633-nm wavelength. Our results show that for blond and gray hair the total attenuation coefficient of the medulla is more than 200 times higher compared to that of the cortex. This difference is only 1.5 times for Asian black hair. Furthermore, we present the total attenuation coefficient of the cortex of blond, gray, light brown, and Asian black hair measured at wavelengths of 409, 532, 633, 800, and 1064 nm. The total attenuation coefficient consistently decreases with an increase in wavelength, as well as with a decrease in hair pigmentation. Additionally, we demonstrate the dependence of the total attenuation coefficient of the cortex and the medulla of Asian black hair on the polarization of incident light. A similar dependence is observed for the cortex of blond and gray hair but not for the medulla of these hair types.

We demonstrate the efficacy of a novel minimally invasive nonthermal skin rejuvenation technique for wrinkle and fine-line reduction based on laser-induced optical breakdown. The optical breakdown caused by tightly focused near-infrared laser pulses creates a grid of intradermal lesions without affecting the epidermis, leading to skin rejuvenation. The pilot in vivo efficacy test performed on five subjects successfully demonstrates wrinkle and fine‐line reduction, and improvement of other skin features without pain or any other unpleasant sensations or any social downtime associated with the treatment. The efficacy is evaluated objectively and subjectively by assessing the improvement of wrinkles and/or fine lines or skin texture after the treatment. The treatment is safe without side effects or social downtime, and all test subjects reported that the treatment is “perceptible but not painful.” Four out of the five subjects who participated in this pilot study were assessed to have “minor” to “significant” improvements of wrinkles and fine lines by the professional panels. The results of this clinical study are expected to bring a paradigm shift in the present laser- and light-based skin rejuvenation methods by introducing a safe treatment procedure without damaging the epidermis, with no or little social downtime and with an efficacy that might be comparable to ablative techniques.

Abstract:We report a method on quantitative and simultaneous noncontact in-vivo hydration and sebum measurements of the skin using an infrared optical spectroscopic set-up. The method utilizes differential detection with three wavelengths 1720, 1750, and 1770 nm, corresponding to the lipid vibrational bands that lay "in between" the prominent water absorption bands. We have used an emulsifier containing hydro-and lipophilic components to mix water and sebum in various volume fractions which was applied to the skin to mimic different oily-dry skin conditions. We also measured the skin sebum and hydration values on the forehead under natural conditions and its variations to external stimuli. Good agreement was found between our experimental results and reference values measured using conventional biophysical methods such as Corneometer and Sebumeter. H. Behrendt, and J. Ring, "Skin Surface pH, Stratum corneum Hydration, Trans-epidermal water loss and skin roughness related to atopic eczema and skin dryness in a population of primary school children," Acta Derm. Venereol. 80(3), 188-191 (2000). 11. M. Janssens, J. van Smeden, G. J. Puppels, A. P. M. Lavrijsen, P. J. Caspers, and J. A. Bouwstra, "Lipid to protein ratio plays an important role in the skin barrier function in patients with atopic eczema," Br. J. Dermatol. 170(6), 1248-1255 (2014). 12. J. Kim, J. Jeon, and H. Song, "Evaluation of the degree of skin dryness and the effect of moisturizing therapy in scalp psoriasis", Annual Global Pharma Summit, Philadelphia, USA (2015). #261736Received 23 Dermatol. 96(6), 845-851 (1990 (InTech, Rijeka, 2012). 21. Y. Shirai, "Skin condition observation apparatus," U.S. Patent 10,642,683, Aug. 19, 2003. 22. H. Iwasaki, K. Miyazawa, and S. Nakauchi, "Visualization of the human face skin moisturizing-ability by spectroscopic imaging using two near-infrared bands," Proc. SPIE 6062, 606203 (2006). 23. D. P. Lookingbill and W. J. Cunliffe, "A direct gravimetric technique for measuring sebum excretion rate," Br.

In optical Doppler measurements, the path length of the light is unknown. To facilitate quantitative measurements, we develop a phase-modulated Mach-Zehnder interferometer with separate fibers for illumination and detection. With this setup, path-length-resolved dynamic light scattering measurements of multiple scattered light in static and dynamic turbid media are performed. Optical path length distributions spanning a range from 0 to 11 mm are measured from the area under the phase modulation peak around the modulation frequency in the power spectrum. A Doppler-broadened phase modulation interference peak is observed that shows an increase in the average Doppler shift with optical path length, independent of absorption. Validation of the estimated path length distributions is done by measuring their deformation for increasing absorption and comparing these observations with predictions based on Lambert-Beer's law.