Objective quantification of epidermal melanin concentration (EMC) should be useful in laser dermatology to determine the individual maximum safe radiant exposure (IMSRE). We propose a single-wavelength remittance measurement at 390 nm as an alternative optical method to determine EMC and IMSRE. Remittance spectra (360 to 740 nm), melanin index (MI) measurements and the transient radiometric temperature increase, T(t), upon skin irradiation with an Alexandrite laser (755 nm, 3-ms pulse duration, 6 J/cm2) were measured on 749 skin spots (arm and calf) on 23 volunteers (skin phototypes I to IV). Due to the shallow penetration depth and independence of blood oxygen saturation (isosbestic point), remittance at 390 nm appears to provide better estimates for EMC and IMSRE than MI.
KEYWORDS: Skin, In vivo imaging, Reflectivity, Optical spheres, In vitro testing, Diffuse reflectance spectroscopy, Laser therapeutics, Color difference, Visualization, Spectrometers
For quantitative prediction and evaluation of pulsed dye laser therapy of port wine stain (PWS) skin, the CIE L*a*b* color difference, ΔE*, has been utilized to characterize numerically the color differences between normal untreated and treated PWS skin. Three optical instruments (Minolta chromameter CR-200, a cross-polarized diffuse reflectance imaging system, and visual reflectance spectrometers) are compared to investigate their clinical feasibility for quantitative color assessment. Compared to the chromameter as a standard measurement instrument, other instruments also provide valuable measurements of skin color for the relative quantification of PWS treatment outcome. The fiber-optic visual reflectance spectrometer is preferable for continuous measurement of a small area of skin. The cross-polarized imaging system is useful as a simple non-contact measurement technique to provide spatially resolved color difference images.
Human skin prepared with an optical clearing agent manifests reduced scattering as a result of de-hydration and refractive index matching. This has potentially large effects for laser therapies of several skin lesions such as port wine stain, hair removal and tattoo removal. With most topically applied clearing agents the clearing effect is limited because they penetrate poorly through the intact superficial skin layer (stratum corneum). Agent application modi other than topical are impractical and have limited the success of optical clearing in laser dermatology. In recent reports, however, a mixture of lipofylic and hydrofylic agents was shown to successfully penetrate through the intact stratum corneum layer which has raised new interest in this field. Immediately after application, the optical clearing effect is superficial and, as the agent diffuses through the skin, reduced scattering is manifested in deeper skin layers. For practical purposes as well as to maximize therapeutic success, it is important to quantify the reduced scattering as well as the trans-cutaneous transport dynamics of the agent. We determined the time and tissue depth resolved effects of optically cleared skin by inserting a microscopic reflector array in the skin. Depth dependent light intensity was measured by quantifying the signal of the reflector array with optical coherence tomography. A 1-dimensional mass diffusion model was used to estimate a trans-cutaneous transport diffusion constant for the clearing agent mixture. The results are used in Monte Carlo modeling to determine the optimal time of laser treatment after topical application of the optical clearing agent.
We present an initial study on applying genetic algorithms (GA) to retrieve human skin optical properties using visual reflectance spectroscopy (VRS). A three-layered skin model consisting of 13 parameters is first used to simulate skin and, through an analytical model based on optical diffusion theory, we study their independent effects on the reflectance spectra. Based on a preliminary analysis, nine skin parameters are chosen to be fitted by GA. The fitting procedure is applied first on simulated reflectance spectra with added white noise, and then on measured spectra from normal and port wine stain (PWS) human skin. A normalized residue of less than 0.005 is achieved for simulated spectra. In the case of measured spectra from human skin, the normalized residue is less than 0.01. Comparisons between applying GA and manual iteration (MI) fitting show that GA performed much better than the MI fitting method and can easily distinguish melanin concentrations for different skin types. Furthermore, the GA approach can lead to a reasonable understanding of the blood volume fraction and other skin properties, provided that the applicability of the diffusion approximation is satisfied.
Pulsed photothermal radiometry (PPTR) can be used for non- invasive depth profiling of port wine stain (PWS) birthmarks, aimed towards optimizing laser therapy on an individual patient basis. Reconstruction of laser-induced temperature profile from the experimentally obtained radiometric signal involves the skin absorption coefficient in the infrared detection band. In the commonly used 3 - 5 micrometer detection band (InSb), the absorption coefficient varies by two orders of magnitude, while assumed to be constant in the reconstruction algorithms used thus far. We discuss the problem of choosing the effective absorption coefficient value to be used under such conditions. Next, we show how to account explicitly for the strong spectral variation of the infrared absorption coefficient in the image reconstruction algorithm. Performance of such improved algorithm is compared to that of the unaugmented version in a numerical simulation of photothermal profiling. Finally, we analyze implementation of a bandpass filter which limits the detection band to 4.5 - 5 micrometer. This reduces the absorption coefficient variation to a level that permits the use of unaugmented algorithm. An experimental test of the latter approach for in vivo characterization of the depth of PWS lesion and epidermal thickness will be presented, including a novel technique that uses two laser excitation wavelengths in order to separate the epidermal and vascular components of the radiometric signal.
Goal is to investigate how delivery nozzle design influences the cooling rate of cryogen spray as used in skin laser treatments. Cryogen was sprayed through nozzles that consist of metal tubes with either a narrow or wide diameter and two different lengths. Fast-flashlamp photography showed that the wide nozzles, in particular the long wide one, produced a cryogen jet (very small spray cone angle) rather than a spray (cone angles of about 15 degrees or higher) and appeared to atomize the cryogen less finely than the narrow nozzles. We measured the cooling rate by spraying some cryogen on an epoxy-block with thermocouples embedded. The heat extraction rate of the wide nozzles was higher than that of the narrow nozzles. The results suggest that finely atomized droplets produced by the narrow nozzles do not have enough kinetic energy to break through a layer of liquid cryogen accumulated on the object, which may act as a thermal barrier and, thus, slow down heat extraction. Presumably, larger droplets or non- broken jets ensure a more violent impact on this layer and therefore ensure an enhanced thermal contact. The margin of error for the heat extraction estimate is analyzed when using the epoxy-block. We introduce a complementary method for estimating heat extraction rate of cryogen sprays.
We used a novel phase-resolved optical Doppler tomographic (ODT) technique, with very high flow velocity sensitivity and high spatial resolution, to image blood flow in port wine stain (PWS) birthmarks in human skin. The variance of blood flow velocity is used to locate the PWS vessels in addition to the regular ODT images. Our device combines an ODT system and laser so that PWS blood flow can be monitored in situ before and after treatment. To our knowledge, this is the first clinical application of ODT to provide a fast semi-quantitative evaluation of the efficacy of PWS laser therapy in situ and in real-time.
The presently most promising treatment modality for port wine stains is selective photothermolysis. This technique is based on exposure of the lesion to yellow laser light of high energy density and long pulse-length, typically 5 - 10 J/cm2 and 0.5 ms, respectively. Although promising clinical results have been reported, only a small percentage of the patients obtains full fading of their lesions. This might in part be due to the fact that most clinicians treat port wine stains with rather standardized settings of the laser parameters. However, clinical response can, hopefully, be improved if these setting are adjusted to each individual lesion. This paper gives a brief discussion of the importance of parameters such as depth, diameter and vessel wall thickness, together with a presentation of non-invasive methods for determination of these values.
Changes of coefficients of scattering ((mu) s), absorption ((mu) a) and average cosine of scattering (g) depending on shear rate of moving whole blood are described. The most interesting result is observed nonlinear dependence between absorption coefficient and shear rate of moving blood with maximum of (mu) a at 135 s-1 which is close connected with erythrocytes orientation and deformation in the cuvette. Phenomenon takes place for 488 and 587 nm within blood layer thickness form 100 to 200 micrometers . Theoretical analysis for angular dependence of coefficient of absorption whole blood from erythrocyte orientation and is presented.
In order to investigate histological results produced by laser wavelengths 514 and 585 nm (Monoline Argon Laser and cw Dye Argon Laser), tests were carried out on a haemangioma situated on the neck of a male adult. The tests were done using the hexascan, previously modified to receive two fibers, which could separately direct the wavelengths 514 and 585 nm (1 watts and 30 ms pulses), with slight pauses during the treatment of one area and another, but both areas having identical characteristics. Random histological samples were taken previous to treatment, immediately after, and a month following treatment, processing them with Mason's Trichromic. Analysis and evaluation of the samples were performed by two researchers, strange to the investigation. In addition to the typical tissue reactions to relatively long Argon pulses (longer than 100 ms), it was found that there were no significant differences in the skin and vessels histological reactions, when both wavelengths 514 and 585 nm were used.
A dichroic filter was adjusted in order to make use of the green line of an argon laser for the treatment of pigmented lesions (actinic and senile lentigo, ephelis, cafe-au-lait marks and spilus nevus). Using a power of 1.5 W, a spot size of 0.5 mm and pulse lengths of 200 or 300 ms, satisfactory elimination of 620 pigmented cutaneous lesions was achieved. Although the pulse lengths used were much longer than the thermal relaxation time of the melanosomes, the histology after treatment showed little damage of adjacent structures. Good restoration of the epidermis and a return of normal pigmentation led to excellent cosmetic results, with few complications.
Dark colored stains, ranging from light blue to black, are disorders which often arise in the gums. Effective elimination of these melanotic disorders can be attempted by destroying the superficial layers of the gingiva. Treatment with monoline 514 nm green light (1.5 W, 300 ms, 0.5 mm spot size) produced by an Argon laser demonstrates, in clinical and histological controls, that due to good 514 nm light absorption by the pigment, elimination of the stains can be obtained and, in spite of the fact that the first layers of the tissue are destroyed, restoration of the mucosa status is optimal, giving excellent aesthetic results.
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