9 research outputs found
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Skin pigmentation characterized by visible reflectance measurements
The epidermal melanin content affects most dermatologic treatments involving light, and can limit the therapeutic success significantly. Therefore, knowledge of the optical properties of skin is required. This study investigates how the concentration of melanin influences visible reflectance spectra of skin and the relationship to threshold radiant energy fluence for melanosomal or melanocyte destruction. Reflectance spectra were measured at 28 pigmented human skin sites in vivo. For Asian and Caucasian subjects, measured reflectance values varied over the same range, while significantly lower values were recorded for African individuals. Epidermal melanin absorption coefficients measured at 694 nm were about 2500 m-1 for African, and 300-1200 m-1 for Caucasian and Asian skin. Twenty-five skin sites were exposed to ruby laser pulses (694 nm), where the pulse duration was long enough to allow heat diffusion between melanosomes. Hypopigmentation occurred, on average, at 12 and 26 J cm-2 for sun-exposed and sun-protected white skin, respectively, while slightly lower threshold values resulted from the measured spectra. As visible reflectance spectra reveal information regarding skin pigmentation and individual threshold doses for melanosomal damage, a use as a diagnostic tool in various dermatological laser treatments is apparent
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Photothermal tomography of subcutaneous chromophores
Photothermal tomography (PU) is applied to characterize diameter and depth of subcutaneous chromophores such as blood vessels that comprise port wine stain (PWS) birthmarks. PU uses a fast infrared detector array to measure temperature rises in a PWS induced by pulsed laser radiation. A FIT record of PWS in response to pulsed laser exposure is composed of a sequence of infrared emission frames, each consisting of elevated temperature regions indicative of subcutaneous blood vessel heating. An analytic expression for recorded infrared emission frames is derived as a convolution integral of a PTF point spread function and the three dimensional temperature distribution in the PWS immediately following laser exposure. Diameters of blood vessels comprising the PWS are best resolved in early infrared emission frames when radial heat diffusion is relatively small. Blood vessel images in subsequent frames increase in amplitude due to heat generated in the subsurface PWS diffusing to the skin surface indicative of a "delayed thermal wave". Influence of diameter and depth of blood vessels on the FVF record is analyzed using an in-vitro PWS model consisting of multilayered collagen films
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Tissue parameters determining the visual appearance of normal skin and port-wine stains
Port-wine stain is a congenital birthmark consisting of an abnormal density of blood vessels in the upper dermis. The enlarged blood volume gives the lesion a red to purple colour. The aim of the treatments is to destroy the vessels to the extent necessary for obtaining a normal skin coloration. Thus, in principle, all relevant information about the lesion should be contained in a reflectance spectrum in the visible. However, the relation between the reflectance spectrum and tissue parameters such as scattering, melanin content and blood distribution is somewhat composite. This work tries to enlighten this relation in terms of a very simple analytical mathematical model, and it is demonstrated that such a model at least will contribute to a qualitative understanding of the relevance of the various parameters. © 1995 W.B. Saunders Company Ltd
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Tissue parameters determining the visual appearance of normal skin and port-wine stains
Port-wine stain is a congenital birthmark consisting of an abnormal density of blood vessels in the upper dermis. The enlarged blood volume gives the lesion a red to purple colour. The aim of the treatments is to destroy the vessels to the extent necessary for obtaining a normal skin coloration. Thus, in principle, all relevant information about the lesion should be contained in a reflectance spectrum in the visible. However, the relation between the reflectance spectrum and tissue parameters such as scattering, melanin content and blood distribution is somewhat composite. This work tries to enlighten this relation in terms of a very simple analytical mathematical model, and it is demonstrated that such a model at least will contribute to a qualitative understanding of the relevance of the various parameters. © 1995 W.B. Saunders Company Ltd
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Photothermal tomography of subcutaneous chromophores
Photothermal tomography (PU) is applied to characterize diameter and depth of subcutaneous chromophores such as blood vessels that comprise port wine stain (PWS) birthmarks. PU uses a fast infrared detector array to measure temperature rises in a PWS induced by pulsed laser radiation. A FIT record of PWS in response to pulsed laser exposure is composed of a sequence of infrared emission frames, each consisting of elevated temperature regions indicative of subcutaneous blood vessel heating. An analytic expression for recorded infrared emission frames is derived as a convolution integral of a PTF point spread function and the three dimensional temperature distribution in the PWS immediately following laser exposure. Diameters of blood vessels comprising the PWS are best resolved in early infrared emission frames when radial heat diffusion is relatively small. Blood vessel images in subsequent frames increase in amplitude due to heat generated in the subsurface PWS diffusing to the skin surface indicative of a "delayed thermal wave". Influence of diameter and depth of blood vessels on the FVF record is analyzed using an in-vitro PWS model consisting of multilayered collagen films
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Therapeutic response during pulsed laser treatment of port-wine stains: Dependence on vessel diameter and depth in dermis
Selective photothermolysis with pulsed lasers is presumably the most successful therapy for port-wine stain birthmarks (flammeus nevi). Selectivity is obtained by using an optical wavelength corresponding to high absorption in blood, together with small absorption in tissues. Further on, the pulse length is selected to be long enough to allow heat to diffuse into the vessel wall, but simultaneously short enough to prevent thermal damage to perivascular tissues. The optical wavelength and pulse length are therefore dependent on vessel diameter, vessel wall thickness and depth in dermis. The present work demonstrates that in the case of a 0.45 ms long pulse at 585 nm wavelength, vessels of 40-60 Μm require minimum optical fluence. Smaller vessels require higher fluence because the amount of heat needed to heat the wall becomes a substantial fraction of the absorbed optical energy. Larger vessels also require a higher dose because the attenuation of light in blood prevents the blood in the centre of the lumen from participating in the heating process. It is shown that the commonly used optical dose in the range of 6-7 J cm-2 is expected to inflict vessel rupture rather than thermolysis in superficially located vessels. The present analysis might serve to draw guidelines for a protocol where the optical energy, wavelength and pulse length are optimized with respect to vessel diameter and depth in dermis. © 1995 W.B. Saunders Company Ltd
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Therapeutic response during pulsed laser treatment of port-wine stains: Dependence on vessel diameter and depth in dermis
Selective photothermolysis with pulsed lasers is presumably the most successful therapy for port-wine stain birthmarks (flammeus nevi). Selectivity is obtained by using an optical wavelength corresponding to high absorption in blood, together with small absorption in tissues. Further on, the pulse length is selected to be long enough to allow heat to diffuse into the vessel wall, but simultaneously short enough to prevent thermal damage to perivascular tissues. The optical wavelength and pulse length are therefore dependent on vessel diameter, vessel wall thickness and depth in dermis. The present work demonstrates that in the case of a 0.45 ms long pulse at 585 nm wavelength, vessels of 40-60 Μm require minimum optical fluence. Smaller vessels require higher fluence because the amount of heat needed to heat the wall becomes a substantial fraction of the absorbed optical energy. Larger vessels also require a higher dose because the attenuation of light in blood prevents the blood in the centre of the lumen from participating in the heating process. It is shown that the commonly used optical dose in the range of 6-7 J cm-2 is expected to inflict vessel rupture rather than thermolysis in superficially located vessels. The present analysis might serve to draw guidelines for a protocol where the optical energy, wavelength and pulse length are optimized with respect to vessel diameter and depth in dermis. © 1995 W.B. Saunders Company Ltd
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Non-invasive determination of port wine stain anatomy and physiology for optimal laser treatment strategies.
The treatment of port wine stains (PWSs) using a flashlamp-pumped pulsed dye laser is often performed using virtually identical irradiation parameters. Although encouraging clinical results have been reported, we propose that lasers will only reach their full potential provided treatment parameters match individual PWS anatomy and physiology. The purpose of this paper is to review the progress made on the technical development and clinical implementation of (i) infrared tomography (IRT), optical reflectance spectroscopy (ORS) and optical low-coherence reflectometry (OLCR) to obtain in vivo diagnostic data on individual PWS anatomy and physiology and (ii) models of light and heat propagation, predicting irreversible vascular injury in human skin, to select optimal laser wavelength, pulse duration, spot size and radiant exposure for complete PWS blanching in the fewest possible treatment sessions. Although non-invasive optical sensing techniques may provide significant diagnostic data, development of a realistic model will require a better understanding of relevant mechanisms for irreversible vascular injury