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J Stuart Nelson

Publications and source records attributed to J Stuart Nelson.

At least 55 records · Page 3Linked to original sources
PubMed2004

A comparative study of photoacoustic and reflectance methods for determination of epidermal melanin content.

Although epidermal melanin content has been quantified non-invasively using visible reflectance spectroscopy (VRS), there is currently no way to determine melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency-doubled Nd:YAG (neodymium, yttrium, aluminum, garnet) laser operating at 532 nm to generate acoustic pulses in skin in vivo. The probe contained a piezoelectric element that detected photoacoustic waves that were then analyzed for epidermal melanin content using a photoacoustic melanin index (PAMI). Melanin content was compared between results of photoacoustics and VRS. Spectra from human skin were fitted to a model based on diffusion theory that included parameters for epidermal thickness, melanin content, hair color and density, and dermal blood content. Ten human subjects with skin phototypes I-VI were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2=0.85. Photoacoustic and VRS measurements are shown for a human subject with vitiligo, indicating that melanin was almost completely absent. We present preliminary modeling for photoacoustic probe design and analysis necessary for depth profiling of epidermal melanin.

Acoustics↗
PubMed2004

Confocal microscopy study of nerves and blood vessels in untreated and treated port wine stains: preliminary observations.

BACKGROUND AND OBJECTIVE: Vascular ectasia in port wine stain birthmarks (PWS) might result from reduced innervation with loss of autonomic stimulation. We investigated this theory and evaluated nerve and blood vessel density, and mean blood vessel size in untreated and treated PWS skin. METHODS: Skin biopsy specimens were obtained from uninvolved skin, untreated PWS, PWS with a good response to laser treatment and PWS with a poor response to laser treatment. Confocal microscopy was performed to determine nerve and blood vessel density, and mean blood vessel size. RESULTS: Nerve density was significantly decreased in all PWS sites compared to uninvolved skin. Mean blood vessel diameter was larger in untreated compared to treated PWS. PWS with a good response to treatment had decreased nerve density but blood vessel density and mean diameter was relatively normal. PWS with a poor response to treatment had decreased nerve density but increased blood vessel density and mean blood vessel diameter compared to normal skin. CONCLUSION: Nerve density was decreased in all evaluated PWS sites and this may be a factor in lesion pathogenesis. PWS blood vessel size correlated with pulsed dye laser response and may prove to be a useful prognostic indicator of therapeutic outcome.

Adult↗
PubMed2003

Effect of spurt duration on the heat transfer dynamics during cryogen spray cooling.

Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, optimization of the current cooling approach is needed to permit the safe use of higher light doses, which should improve the therapeutic outcome in many patients. The objective of this study was to measure the effect of spurt duration (delta t) on the heat transfer dynamics during CSC using a model skin phantom. A fast-response temperature sensor was constructed to record the changes in surface temperature during CSC. Temperature measurements as a function of delta t at two nozzle-to-skin distances (z = 50 and 20 mm) were performed. The average surface heat fluxes (q) and heat transfer coefficients (h) for each delta t were computed using an inverse heat conduction problem algorithm. It was observed that q undergoes a marked dynamic variation during the entire delta t, with a maximum heat flux (qc) occurring early in the spurt (5-15 ms), followed by a quick decrease. The estimated qc vary from 450 to 600 kW m(-2), corresponding to h maxima of 10 and 17-22 kW m(-2) K(-1) for z = 50 and 20 mm, respectively. For z = 50 mm, spurts longer than 40 ms do not increase the total heat removal (Q) within the first 200 ms. However, for z = 20 mm, delta t longer than 100 ms are required to achieve the same Q. It is shown that the heat transfer dynamics and the time it takes to reach qc during CSC can be understood through classic boiling theory as a transition from transient to nucleate boiling. Based on the results of this model skin phantom, it is shown that spurts longer than 40 ms have a negligible impact on both q and Q within clinically relevant cooling times (10-100 ms).

Administration, Topical↗
PubMed2003

In vivo port-wine stain depth determination with a photoacoustic probe.

We have designed a photoacoustic probe for port-wine stain (PWS) depth measurements consisting of optical fibers for laser light delivery and a piezoelectric element for acoustic detection. We characterized the capabilities and limitations of the probe for profiling PWS skin. The probe induced and measured photoacoustic waves in acrylamide tissue phantoms and PWS skin in vivo. The optical properties of the phantoms were chosen to mimic those of PWS skin. We denoised acoustic waves using spline wavelet transforms, then deconvolved with the impulse response of the probe to yield initial subsurface pressure distributions in phantoms and PWS skin. Using the phantoms, we determined that the limit in resolving epidermal and PWS layers was less than 70 microm. In addition, we used the phantoms to determine that the maximum epidermal melanin concentration that allowed detection of PWS was between 13 and 20%. In vivo measurements of PWS skin with different epidermal melanin concentrations correlated with the phantoms. Thus the photoacoustic probe can be used to determine PWS depth for most patients receiving laser therapy.

Acoustics↗
PubMed2003

Spectra from 2.5-15 microm of tissue phantom materials, optical clearing agents and ex vivo human skin: implications for depth profiling of human skin.

Infrared measurements have been used to profile or image biological tissue, including human skin. Usually, analysis of such measurements has assumed that infrared absorption is due to water and collagen. Such an assumption may be reasonable for soft tissue, but introduction of exogenous agents into skin or the measurement of tissue phantoms has raised the question of their infrared absorption spectrum. We used Fourier transform infrared spectroscopy in attenuated total reflection mode to measure the infrared absorption spectra, in the range of 2-15 microm, of water, polyacrylamide, Intralipid, collagen gels, four hyperosmotic clearing agents (glycerol, 1,3-butylene glycol, trimethylolpropane, Topicare), and ex vivo human stratum corneum and dermis. The absorption spectra of the phantom materials were similar to that of water, although additional structure was noted in the range of 6-10 microm. The absorption spectra of the clearing agents were more complex, with molecular absorption bands dominating between 6 and 12 microm. Dermis was similar to water, with collagen structure evident in the 6-10 microm range. Stratum corneum had a significantly lower absorption than dermis due to a lower content of water. These results suggest that the assumption of water-dominated absorption in the 2.5-6 microm range is valid. At longer wavelengths, clearing agent absorption spectra differ significantly from the water spectrum. This spectral information can be used in pulsed photothermal radiometry or utilized in the interpretation of reconstructions in which a constant mu(ir) is used. In such cases, overestimating mu(ir) will underestimate chromophore depth and vice versa, although the effect is dependent on actual chromophore depth.

Collagen↗
PubMed2003

Rate process analysis of thermal damage in cartilage.

Cartilage laser thermoforming (CLT) is a new surgical procedure that allows in situ treatment of deformities in the head and neck with less morbidity than traditional approaches. While some animal and human studies have shown promising results, the clinical feasibility of CLT depends on preservation of chondrocyte viability, which has not been extensively studied. The present paper characterizes cellular damage due to heat in rabbit nasal cartilage. Damage was modelled as a first orderrate process for which two experimentally derived coefficients, A = 1.2 x 10(70) s(-1) and Ea = 4.5 x 10(5) J mole(-1), were determined by quantifying the decrease in concentration of healthy chondrocytes in tissue samples as a function of exposure time to constant-temperature water baths. After immersion, chondrocytes were enzymatically isolated from the matrix and stained with a two-component fluorescent dye. The dye binds nuclear DNA differentially depending upon chondrocyte viability. A flow cytometer was used to detect differential cell fluorescence to determine the percentage of live and dead cells in each sample. As a result, a damage kinetic model was obtained that can be used to predict the onset, extent and severity of cellular injury to thermal exposure.

Animals↗
PubMed2003

Effects of mass flow rate and droplet velocity on surface heat flux during cryogen spray cooling.

Cryogen spray cooling (CSC) is used to protect the epidermis during dermatologic laser surgery. To date, the relative influence of the fundamental spray parameters on surface cooling remains incompletely understood. This study explores the effects of mass flow rate and average droplet velocity on the surface heat flux during CSC. It is shown that the effect of mass flow rate on the surface heat flux is much more important compared to that of droplet velocity. However, for fully atomized sprays with small flow rates, droplet velocity can make a substantial difference in the surface heat flux.

Aerosol Propellants↗
PubMed2003

Novel model for evaluation of epidermal preservation and dermal collagen remodeling following photorejuvenation of human skin.

BACKGROUND AND OBJECTIVES: In order to optimize photorejuvenation of human skin, a method must be developed to reliably compare the potential for epidermal preservation and dermal fibroblast stimulation of different laser devices and irradiation parameters. We describe a novel human skin tissue culture model developed for this purpose. MATERIALS AND METHODS: An artificial skin model, consisting of human keratinocytes in the epidermis and human fibroblasts and rat-tail collagen in the dermis, was cultured using the floating collagen gel (RAFT) method. Repetitive low-fluence Er:YAG laser irradiation was applied to test the applicability of our RAFT model for characterization of epidermal preservation and dermal fibroblast stimulation post-laser treatment. RESULTS: Histopathologic evaluation revealed a thin layer of epidermal keratinocyte preservation immediately after low fluence sub-ablative Er:YAG laser irradiation. One-week post-laser irradiation, the average increase in number of dermal fibroblasts as compared to control was statistically significant (P < 0.01). CONCLUSIONS: The RAFT model can be used to assess the potential for epidermal preservation and dermal fibroblast stimulation of different photorejuvenation devices and irradiation parameters and offers several advantages over traditional animal and human skin models.

Animals↗
PubMed2003

Dynamic behavior of cryogen spray cooling: effects of spurt duration and spray distance.

BACKGROUND AND OBJECTIVES: Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery. Since optimization of CSC permits the safe use of higher light doses, which improves therapeutic outcome in many patients with superficial skin lesions, studies have focused on understanding spray-surface interactions and cooling dynamics. The objective of this study is to measure accurately temperature variations at the sprayed surface and the effects of spurt duration (deltat) and nozzle-to-sprayed surface distance (L) on cooling dynamics during CSC. STUDY DESIGN/MATERIALS AND METHODS: A fast-response temperature measurement sensor is built using thin (20 microm) aluminum foil placed on top of a poly methyl-methacrylate resin (Plexiglass) with a 50 microm bead diameter thermocouple positioned in between. Liquid film residence time (t(r)) and minimum surface temperature (T(min)) are systematically measured as a function of deltat and L. RESULTS: Two distinct spray-surface interaction mechanisms are recognized. The transition between them occurs at a critical length L(c) approximately 25-30 mm. Noticeable characteristics include: (1) for spurts at L < L(c), shorter t(r), and lower T(min) are reached as compared to L > L(c), T(min) is dependent on deltat and L, while t(r) is a function of deltat only; (2) for spurts at L > L(c), T(min) still depends on L but not on deltat, while t(r) becomes a function of both deltat and L. Finally, for all deltat, t(r) reaches a maximum at L = 40 mm. CONCLUSIONS: Based on our results, a good choice to achieve low T(min) and t(r) for the treatment of superficial skin lesions may be met by using deltat of approximately 30-50 milliseconds and the shortest spray distance that is tolerable by the patient. Spurt durations (deltat) of more than 30-50 milliseconds at spray distances (L) greater than L(c) lead to higher T(min) and longer t(r). These parameters may be appropriate for laser therapy of deeper targets.

Cryotherapy↗
PubMed2003

Measurements of laser light attenuation following cryogen spray cooling spurt termination.

BACKGROUND AND OBJECTIVES: Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatological surgery. However, while CSC can protect the epidermis from non-specific thermal damage, the cryogen film on the skin surface may pose a potential problem of laser light attenuation due to optical scattering. STUDY DESIGN/MATERIALS AND METHODS: This study is focused on measuring the light transmittance changes that occur following cryogen spurt termination. The wavelengths studied were chosen for their clinical relevance to treatment of hypervascular skin lesions (594 nm) and laser-assisted hair removal (785 nm). Following delivery of cryogen spurts to the surface of an epoxy skin phantom, continuous records of light transmittance for 594 and 785 nm were obtained using an integrating sphere-based light collection apparatus. RESULTS: Shortly after spurt termination, there was negligible light attenuation by the cryogen film at the two wavelengths studied. CONCLUSIONS: For the typical clinical use of a 30 milliseconds spurt duration and 30 milliseconds delay between spurt termination and delivery of the laser pulse, a minimum average transmittance value of approximately 97% was measured.

Cryotherapy↗
PubMed2003

Hair removal with long pulsed diode lasers: a comparison between two systems with different pulse structures.

BACKGROUND AND OBJECTIVES: The aim was to study hair removal efficacy, and possible side effects of two commercially available long pulsed diode lasers. The radiant exposure was selected to a value of 35 J/cm2, which is frequently used in the clinic in accordance with manufacturer's recommendations. STUDY DESIGN/MATERIALS AND METHODS: A prospective clinical study was performed on twenty-nine patients with hair color ranging from light brown to black on the upper lip. One half of the upper lip was randomly selected for treatment with the MedioStar laser; the contralateral half of the lip was treated with the LightSheer laser. Three treatments were performed at 6-8 week intervals. Percent hair reduction and acute- and long-term side effects were evaluated after treatment. RESULTS: The average hair reductions 6 months after the first treatment were 49% with the MedioStar laser and 48% with the LightSheer laser. No scarring or pigmentary change of the skin was observed after any of the treatments with either laser. However, differences in acute side effects such as degree of erythema and burned hairs were observed. CONCLUSIONS: No statistically significant differences in hair removal efficacy were observed. These results agree with mathematical modeling, which also offers a method to estimate hair removal efficacy and adverse effects for a range of hair characteristics and laser parameters.

Adult↗
PubMed2003

Influence of wavelength on response to laser photothermolysis of blood vessels: implications for port wine stain laser therapy.

BACKGROUND AND OBJECTIVE: Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters. We have studied the all-important role of wavelength (lambda) by performing pulsed laser photothermolysis in the vasculature of the chick chorioallantoic membrane (CAM) assay. STUDY DESIGN/MATERIALS AND METHODS: The CAM contains an extensive microvascular network ranging from capillaries with diameter D < 20 microm to blood vessels of D approximately 120 microm. The CAM assay enables observation and real-time video documentation of blood flow in pre-capillary arterioles (A) and post-capillary venules (V). The ScleroPlus trade mark laser (Candela Corp., Wayland, MA) has a smooth output over its fixed 1.5 ms pulse duration and allows the operator to vary several treatment parameters such as wavelength, spot size, and energy. Blood vessels in the CAM were irradiated at two clinically relevant wavelengths, lambda = 587 or 597 nm, constant spot size (7 mm), and at different exposures (E = 5-12 J/cm(2)). Threshold exposure (E(th)) (at which non-reversible damage occurred) were 5 J/cm(2) at 587 nm and 8 J/cm(2) at 597 nm. Mathematical modeling was developed to interpret initial (within 30 seconds) injury of arterioles and venules at both wavelengths as a function of D when varying E. RESULTS: Vessel injury was graded off-line from videotapes. For all combinations of lambda and E, measurable injury was evident within 30 seconds of irradiation and maximal damage was reached in less than 10 minutes. Vessel damage was found to depend strongly on lambda. Damage decreased with increasing vessel size. For all D, damage of arterioles was greater than for corresponding venules. CONCLUSIONS: Selection of the correct wavelength is crucial for successful laser therapy of hypervascular lesions and, ideally, should be based on knowledge of vessel diameters for a specific PWS lesion and of optical penetration depths in blood. As a general statement, smaller blood vessels (D = 10-60 microm) should be treated using shorter wavelengths such as 585 nm. To ensure deposition of sufficient laser energy, irradiation at 585 nm, characterized by lower optical penetration depth in blood, may be preferable for PWS therapy.

Animals↗
PubMed2003

Reversible dissociation of collagen in tissues.

The turbidity of most biologic tissues hinders the use of lasers for diagnostic and therapeutic purposes. Hyperosmotic agents such as glycerol have been used to alter the optical scattering properties of turbid tissues. The mechanism of this effect, "optical clearing", however, remains incompletely understood. Multiphoton microscopy utilizing second harmonic generation can be used to monitor collagen structural changes in the presence of glycerol. This study suggests that the use of glycerol for tissue "optical clearing" screens noncovalent intermolecular interactions between low-order collagen structures, resulting in fiber disassembly. Dissociation of collagen fibers in native and engineered tissues in the presence of glycerol and reassociation with the application of saline are imaged dynamically. Collagen fiber reassembly is governed by the displacement of glycerol by saline in native and engineered skin. These results reveal the assembly process of high-order collagen structures and propose a molecular mechanism for the increase in tissue transparency observed after glycerol application.

Animals↗
PubMed2003

Prospective study of pulsed dye laser in conjunction with cryogen spray cooling for treatment of port wine stains in Chinese patients.

BACKGROUND: Pulsed dye laser (PDL) in conjunction with cryogen spray cooling (CSC) is effective in improving efficacy and safety for treatment of port wine stains (PWSs) in whites. However, for dark-skinned patients such as Chinese, only retrospective studies have been performed. OBJECTIVES: To compare prospectively clinical efficacy in terms of blanching and acute and long-term adverse effects of PDL alone and PDL-CSC for treatment of PWSs in Chinese patients. METHODS: Thirty-five Chinese patients (13 males and 22 females) were recruited, and 131 treatments were performed. Half of the test area on the PWS was treated with PDL alone, and the contralateral half was treated with PDL-CSC. The degree of PWS blanching was objectively assessed by spectrophotometer. Skin textural changes were detected by cutometer. All measurements were taken at baseline and before each subsequent laser treatment. Patients were interviewed immediately after treatment and again the following week using a visual analog scale questionnaire to assess the degree of pain and swelling. Occurrence of blisters was noted during each follow-up visit. Patients were evaluated for evidence of long-term adverse effects such as dyspigmentation and scarring after three treatments. RESULTS: Statistically significant higher fluences were used on the PDL-CSC-treated group. The percentage change in the spectrophotometer a* value was significantly greater using PDL-CSC, indicating that there was more PWS blanching after treatment. There was no significant difference in the incidence of skin textural changes after three treatments with PDL alone or PDL-CSC. The immediate pain scores were significantly higher for PDL alone than with PDL-CSC. Blisters were significantly more common on the area treated using PDL alone than PDL-CSC. The overall incidence of long-term adverse effects was not significantly different between the PDL alone and PDL-CSC treatments. PDL-CSC was also the preferred treatment modality for most patients. CONCLUSIONS: PDL-CSC was more effective than PDL alone for blanching of PWS in Chinese patients. Moreover, PDL-CSC was better tolerated and resulted in a lower incidence of acute adverse effects such as blistering.

Adolescent↗
PubMed2003

Experimental study of cryogen spray properties for application in dermatologic laser surgery.

Cryogenic sprays are used for cooling human skin during laser dermatologic surgery. In this paper, six straight-tube nozzles are characterized by photographs of cryogenic spray shapes, as well as measurements of average droplet diameter, velocity, and temperature. A single-droplet evaporation model to predict average spray droplet diameter and temperature is tested using the experimental data presented here. The results show two distinct spray patterns--sprays for 1.4-mm-diameter nozzles (wide nozzles) show significantly larger average droplet diameters and higher temperatures as a function of distance from the nozzle compared with those for 0.5-0.8-mm-diameter nozzles (narrow nozzles). These results complement and support previously reported studies, indicating that wide nozzles induce more efficient heat extraction than the narrow nozzles.

Administration, Topical↗
PubMed2002

Intermittent cryogen spray cooling for optimal heat extraction during dermatologic laser treatment.

Fast heat extraction is critically important to obtain the maximal benefit of cryogen spray cooling (CSC) during laser therapy of shallow skin lesions, such as port wine stain birthmarks. However, a film of liquid cryogen can build up on the skin surface, impairing heat transfer due to the relatively low thermal conductivity and higher temperature of the film as compared to the impinging spray droplets. In an attempt to optimize the cryogen mass flux, while minimally affecting other spray characteristics, we apply a series of 10 ms spurts with variable duty cycles. Heat extraction dynamics during such intermittent cryogen sprays were measured using a custom-made metal-disc detector. The highest cooling rates were observed at moderate duty cycle levels. This confirms the presence, and offers a practical way to eliminate the adverse effect of liquid cryogen build-up on the sprayed surface. On the other hand, lower duty cycles allow a substantial reduction in the average rate of heat extraction, enabling less aggressive and more efficient CSC for treatment of deeper targets, such as hair follicles.

Aerosol Propellants↗