Theory Of Selective Photothermolysis Research Articles

Experience of using phototherapy (IPL) for prevention and treatment of some dermatoaesthetic problems

Laser therapy is a complex of hardware procedures that involve exposure of the skin to light energy and allows getting rid of a number of skin imperfections. Objective — to study the possibilities, effectiveness and expediency of using laser technologies to solve some dermatoesthetic problems in patients. Materials and methods. The results of the therapy using the Nordlys device, the principle of operation of which is based on the theory of selective photothermolysis, were analyzed and presented. The Dermatology Life Quality Index (DLQI) was used to determine the effectiveness of the treatment. Results and discussion. We observed 118 patients aged 18 to 65 years (42 men and 76 women) with different dermatoesthe­tic problems. The Nordlys narrow-spectrum IPL technologies were used to treat couperose, rosacea, acne and hyperpigmentation. As a result of the comprehensive treatment using laser therapy, the DLQI indicators statistically significantly improved in patients of all groups: in patients with couperose and rosacea — by 48.75 and 72.71 %, respectively, acne and post-acne — by 77.87 and 72.07 %, respectively, superficial and deep pigmentation — by 40.49 and 50.98 %, respectively (p < 0.001). Before treatment, only 30.51 % patients experienced a moderate impact of skin disease on the life quality, while 69.49 % patients noted a significant impact. However, after the combination treatment using laser therapy, only 11.86 % patients felt a significant impact of their skin disease on their life quality, while all the other 88.14 % patients noted a significant improvement in the life quality. Conclusions. Laser therapy in the comprehensive treatment of patients with dermatological and aesthetic problems makes it possible to reduce the clinical manifestations of dermatoses, eliminate some factors of their development, and contributes to a probable (p < 0.05) improvement in quality of life.

Picosecond Laser Treatment for Tattoos and Benign Cutaneous Pigmented Lesions (Secondary publication).

The selective removal of tattoos and benign cutaneous pigmented lesions with laser energy evolved rapidly with the development of the nanosecond-domain Q-switched laser (ns-laser). Recently, however, a series of picosecond-domain lasers (ps-lasers) with pulsewidths less than 1 ns has become commercially available, enabling more efficient and faster removal of pigmented lesions in the field of dermatologic laser surgery. The efficacy of the ns-laser depended on the theory of selective photothermolysis, whereby an extremely short pulse width was delivered less than the thermal relaxation time (TRT) of a target. At sub-ns pulsewidths, i.e. in the ps-domain, this efficacy is dramatically extended through defeating the stress relaxation time (SRT) of a target allowing for even more effective pigment destruction with even less damage to the surrounding normal tissue. This will be discussed in detail. The ps-laser has been reported as achieving tattoo removal in fewer sessions than the ns-laser, with less in the way of unwanted side effects. Tattoos recalcitrant to ns-laser treatment have responded well to the ps-laser, and although true 'color blindness' is not yet completely achieved with the ps-domain pulses currently available, multicolored tattoos have also responded very favorably. The ability to limit damage precisely to the pigment target gives greater efficacy in treatment of epidermal lesions with less induction of post-inflammatory hyperpigmentation in the PIH-susceptible Asian skin, and dermal melanocytosis also respond very well to ps-laser treatment. Illustrative clinical examples from the author's experience are given. Current ps-lasers could be a revolutionary advance for laser tattoo removal but may be less effective for some specific aesthetic indications such as melasma and other cosmetic procedures. Manufacturers must make an effort to reduce the current comparatively long ps-domain pulsewidths to deliver a 'true' ps-domain laser, with more basic studies also being required to allow expansion of the safe and effective use of the ps-laser outside of tattoo removal.

Fractional laser-assisted topical drug delivery

Topical drugs have been widely applied to the treatment of dermatoses, and improving the bioavailability of drugs delivered via traditional transdermal routes is of great value. Recent studies have found that lasers can promote drugs to penetrate the skin with an increase in drug absorbility and penetration depth. Although traditional ablative lasers have remarkable therapeutic effect, there is a high incidence of adverse reactions such as erythema and pain. Based on the theory of selective photothermolysis, fractional lasers can improve skin permeability of drugs with reduced photothermal damage, have broken through the limitations of traditional lasers and shown great potential in clinical application. Key words: Laser therapy; Dermatologic agents; Skin absorption; Osmosis; Fractional lasers; Topical drug delivery

Lasers for nevi: a review.

A nevus is described as a benign, often pigmented, skin growth that can be congenital or acquired. Different types of nevi are located at different depths within the skin. Traditional treatments for nevi include topical treatments, dermabrasion, and excision, which are generally ineffective, invasive, and often result in scars and dyspigmentation. Lately, laser therapy has been used as an alternative. Based on the theory of selective photothermolysis, melanin can be specifically targeted, minimizing adverse effects and increasing effectiveness of laser treatments. Several types of lasers and lights have been studied for this purpose without a concise agreement as to which is the best. In general, quality-switched lasers are preferred for the treatment of pigmented lesions. However, there is controversy about this therapy because certain nevi may have malignant potential. This article serves as a comprehensive review of available laser treatments for nevi and discusses the appropriate measures that should be taken before and after laser therapy. Based on the reviewed literature, laser treatment has generally been proven to be a safe and effective therapy for nevi with minimal side effects.

The role of natural and UV‐induced skin pigmentation on low‐fluence IPL‐induced side effects: A randomized controlled trial

The risk of adverse skin effects following light-based hair removal is greater in pigmented skin based on the theory of selective photothermolysis. Thus sunlight-induced pigment i.e., facultative pigmentation, increases the risk of adverse skin effects, perhaps disproportionately. The aim of this study was to evaluate the influence of constitutive and facultative skin pigmentation on low-fluence intense pulsed light (IPL)-induced adverse skin effects. Twenty-one subjects with Fitzpatrick skin type II-IV were enrolled. Two buttock blocks were randomized to receive 0 or 8 solar simulated ultraviolet radiation (UVR) exposures of consecutively increasing Standard Erythema Doses (2-4 SED). Each block was subdivided into four sites, randomized to receive IPL of 0, 7, 8, or 10 J/cm(2) , once a week for 3 weeks. Biopsies were taken 16-24 hours after the first IPL exposure and subjects were seen 1 and 4 weeks after the last IPL exposure. Outcome measures were: (i) skin reactions, (ii) pain, (iii) mRNA expression of pigment-markers microphthalmia-associated transcription factor (MITF) and pro-opiomelanocortin (POMC), and (iv) clinical appearance of biopsy wounds. Skin pigmentation increased after UVR (baseline median 13.8%, after UVR 28.1%, P = 0.0001) in all skin types. Subjects reported low pain intensities (median 1.5, scale 0-10) and experienced transient erythema immediately after IPL exposure. No persistent erythema, blisters, crusting, textual, or pigment changes were observed. The risk of erythema and pain intensities increased with IPL dose and skin pigmentation (P < 0.03). There was no difference in pain or skin reactions in skin with similar degree of natural and facultative pigmentation (P ≥ 0.104). Expression of cellular pigment-markers was not influenced by IPL exposure, neither in constitutive nor in facultative pigmented skin. Clinical appearance of biopsy wounds was unaffected by IPL exposure. The prevalence and intensity of low-fluence IPL-induced adverse skin effects depended on IPL dose and skin pigmentation regardless of the origin, i.e., constitutive versus UV induced.

A photothermal model of selective photothermolysis with dynamically changing vaporization temperature

The theory of selective photothermolysis (SP) is used in many fields of laser surgery and medicine. As several parameters and a number of complicated photothermal interactions are involved in SP, numerical simulations have been providing an important and effective way in SP studies. However, with different photothermal models of SP, simulated results differ considerably. In addition, insufficient attention has been paid to tissue pressure variation during SP in these models, so that vessel rupture and other clinical phenomena cannot be explained. A novel photothermal model of SP was proposed using a Monte Carlo method to simulate the laser transport in the tissue, a heat transfer equation with dynamically changing vaporization temperature to calculate the temperature distribution, and the Arrhenius equation to predict the thermal damage. A factor of trapped vaporized tissue water k was introduced to describe the effects on tissue pressure, temperature, and other related parameters. It was shown that the simulation results are affected significantly by k. Temperature and thermal damage volume are almost identical, respectively, to those obtained with models with vaporization at 100°C and models without vaporization when k = 0 and 1, while thermal damage volume is close to that obtained with models of vaporization at 110°C and 130°C, respectively, when k = 0.022 and k = 0.18. To some extent, the current models without vaporization and models with vaporization at constant temperature can be regarded as special cases at specific situations of this new photothermal model of SP. In addition, more descriptive simulation results, such as temperature, thermal damage, and pressure, are accessible with this model, although the accuracy depends on the value of k, the estimation of which is planned as future work.

Clinical analysis of port wine stains treated by intense pulsed light

Background: Port wine stains (PWS) are formed by dilation and malformation of dermal capillaries without endothelium proliferation. Despite the improvements in lasers and light therapy for PWS therapy in the past 10 years, the ‘cure’ rate is only about 10%. Intense pulsed light (IPL) is a non-coherent light based on the theory of selective photothermolysis. Objective: To evaluate the efficacy of a new IPL on PWS. Methods: Seventy-two patients with PWS treated with an IPL with synchronous cooling were retrospectively analyzed. According to AQ1: sentence re-punctuated in places. Please check through and confirm correct the Fitzpatrick skin type, color, location of the lesion, and treatment reaction, light filters of 560 nm 590 nmor 640 nmwere used with a single pulse with a pulse width of 6–14 ms and a fluence of 16–29 J/cm2; a double pulse with a pulse width of 3.5–4.0 ms, a pulse delay of 20–30 ms, and a fluence of 17–23 J/cm2; or a triple pulse with a pulse width of 3.0–4.0 ms, a pulse delay of 20–40 ms, and a fluence of 18–22 J/cm2. The adverse effects and the relationships among the lesion type, treatments, ages and location were analyzed. Results: Most of the PWS lesions faded significantly and the response rate in this series was 76.4%. Patients resistant to other forms of therapy also showed good clinical results. Adult lesions were easier to remove than those in younger individuals. Further improvement did not occur after three treatments. We failed to find any relationship between efficacy and location of the PWS. Conclusion: The IPL treatment modality is safe and efficient for the treatment of PWS and for those which may be resistant to other therapies. The IPL is an alternative method for most PWS lesions.

Treatment of Laser Complications

Modern lasers and light-based sources that were developed based on the theory of selective photothermolysis are capable of destroying specific tissue targets while minimizing the risk of scarring and pigmentary changes. This is accomplished through the use of a wavelength and pulse duration that is best absorbed by a specific chromophore such as melanin or hemoglobin. However, not all lasers and light sources adhere to this principle. Continuous wave (CW) lasers are least selective and may produce unwanted tissue damage and scarring through heat conduction to normal skin. Quasi-CW lasers limit excessive thermal destruction by delivery of a series of brief laser pulses but still pose a higher risk of nonspecific tissue damage and thermal injury. The pulsed and Q-switched (QS) systems adhere most closely to the principles of selective photothermolysis and result in the highest degree of selective destruction with the lowest risk of scarring from excessive thermal diffusion. Certainly, any laser system potentially can result in scarring and tissue damage when used incorrectly; therefore, adequate operator education and skill are essential. Side effects and complications that occur as a consequence of laser treatment can be significantly reduced if diagnosed and treated in an expeditious manner.

Treatment of hypertrophic and resistant port wine stains with a 755 nm laser: A case series of 20 patients

Port wine stains (PWS) are heterogeneous vascular malformations that can be treated with vascular-selective pulsed dye lasers (PDL). Hypertrophic PWS, especially in adults, are consistently less responsive to PDL. Furthermore, many PWS that respond well initially to PDL treatment may reach a response plateau, becoming unresponsive to further PDL treatments, a phenomenon termed "treatment resistance." Based on the theory of selective photothermolysis, vessels in such lesions may also be specifically targeted with a 755 nm laser that has selectivity for deoxyhemoglobin as well as oxyhemoglobin and increased depth of skin penetration. Retrospective case review of 20 patients with either hypertrophic or PDL-resistant PWS treated with a 755 nm laser alone or in combination with other lasers, including PDL. Hypertrophic PWS showed significant lightening after treatment with a 755 nm laser in combination with PDL. Most PDL-resistant PWS showed moderate improvement after treatment with either a 755 nm laser alone or in combination with another laser, including PDL. Some lesions showed only mild improvement or did not respond. Serious side effects were infrequent. Most commonly encountered complications included pain, edema, bullae, crusting, and rare scarring. Alexandrite 755 nm laser can be useful for the treatment of hypertrophic and treatment-resistant PWS in adult and pediatric patients. Complications are infrequent and predictable. Careful attention to using a fluence at or near the threshold for clinical response with this deeply penetrating laser is essential to prevent serious sequelae.

量化测量光子嫩肤中皮肤组织的反应

Light dose plays an important role in the non-ablative photorejuvenation based on the theory of selective photothermolysis. However, present techniques for determining the light dose in clinical practice are still not accurate enough. We present a new system which monitors the skin tissue response during the laser irradiation in photorejuvenation by measuring the change of the total attenuation coefficient. We also investigate the relationship between the total attenuation coefficient and the energy density, pulse duration, and pulse repetition. In this procedure, the total attenuation coefficient decreases when the light dose increases and the reduction dependes on the light dose. These experimental results indicate that the new system would be a potential tool for accurate light dose determination.

Meta-analysis of hair removal laser trials

Traditional hair-removal techniques have included shaving, waxing, chemical depilation, and electrolysis. All of these methods result in temporary hair removal. The theory of selective photo thermolysis led to the development of a variety of different laser systems. These lasers range from the short end of spectrum, with the 694-nm ruby laser, to the middle, with the 755-nm alexandrite and 810-nm diode lasers, and to the long end with the 1,064-nm Nd:YAG laser. We made a systematic review on the clinical trials with use of various laser sources for hair removal, so all clinical trials related to hair removal lasers in 1998-2003 were considered after elimination of heterogenite sources in data store. Trial results were synthetized on the basis of kind of laser. Our study clarified that hair reduction at least 6 months after the last treatment and hair reductions were 57.5, 42.3, 54.7, and 52.8% after three sessions for diode, Nd:YAG, alexandrite and ruby, respectively. We compared the result with use of analysis of variance method (Scheffes) and double comparison with use of Student's t test. Our results clarified that diode laser is the most effective, and Nd:YAG has the least effect of hair removal.It seems that diode and alexandrite lasers are proper for hair removal, but as we need high fluence in the darker skin types and this is accompanied with higher complications, diode is advised for lighter skin, and we advised alexandrite laser for darker skin types.

Fractional Photothermolysis for Treatment of Poikiloderma of Civatte

Poikiloderma of Civatte refers to a change in the skin where there is atrophy, hyper- and hypopigmentation, and dilation of fine blood vessels (telangiectasia). These alterations often cause cosmetic disfigurement, most commonly in middle-aged or elderly women with a fair complexion. Several treatment modalities, based on the theory of selective photothermolysis, including argon lasers, KTP lasers, pulsed dye lasers, and intense pulsed light devices, have been used to treat this condition in the past. Clinical experience has shown that complete clearing is difficult to achieve. Moreover, depending on the modality used, adverse effects, such as scarring with irregular hypopigmentation, post-inflammatory hyperpigmentation, post-treatment purpura, mottled appearance, crusting, and erythema, have been reported. Multiple sessions with these treatments are usually necessary to obtain optimal clearing.

A randomised, blinded, controlled study of the clinical relevance of matching pulse duration to thermal relaxation time when treating facial telangiectasia

The theory of selective photo-thermolysis (SP) suggests the occurrence of optimal damage when the laser pulse duration (PD) equals the target thermal relaxation time (Tr). This study examines the clinical relevance of this theory. The study design and methods consisted of prospective, randomised, blinded, controlled study of KTP 532-nm laser treatment of 28 telangiectatic facial vessels. The PD varied from 0.13 to 1.71 times Tr (factor of 13). All vessels achieved marked improvement or clearance. The analysis of proportions reaching clearance over marked improvement for small and large calibre vessels shows a better outcome when the PD is nearer to the Tr (86% vs 57%; P = 0.09, 95% CI for difference -3% to 60%). Logistic regression analysis shows that, as the ratio of PD to Tr increases (PD near to or higher than Tr), the chance of clearing improves (P = 0.169; 95% CI 0.34 to 341). This study has shown that, for the range of vessels investigated: (1) marked improvement or clearance may be achieved using PDs that range between 0.13 and 1.71 times the Tr; and (2) it also reveals an overall trend towards a higher proportion of clearance when the PD is near to or higher than the Tr.

Update on lasers in facial plastic surgery.

Since the theory of selective photothermolysis was described, the field of facial plastic surgery has advanced the science behind laser: tissue interactions. Particular advances in skin cooling, hair removal, intense pulsed light, and uses for aesthetic and nonaesthetic skin problems are described in this review. Continued basic science research in lasers has led to improvements in current technology available to the facial plastic surgeon. Advances in skin cooling have allowed for wider use in all Fitzpatrick skin types without concomitant adverse reaction. Our understanding of laser science continues to expand our knowledge in basic laser: tissue interaction. An improvement in various laser mediums and adjunctive devices provides the facial plastic surgeon with instruments to treat a wider patient population. The benefit is a successful clinical and aesthetic result with improved safety.

Láser y luz pulsada intensa en el tratamiento de hemangiomas infantiles y malformaciones vasculares

The use of the indications of the laser in treating vascular malformations and infantile haemangiomas is based on the theory of selective photothermolysis, in which the oxyhaemoglobin is the target chromophore on which the light of the laser acts, thus avoiding damage to neighbouring tissues. The pulsed dye laser is the most employed and at present is the treatment of choice in capillary malformations (port-wine stains). A variable response is obtained, with a substantial clearing of the colour of the lesion after several sessions. Application at early ages seems to improve the results. Venous malformations, especially those localised in the mucosa, respond better to the Nd:YAG laser; lymphatic malformations to the CO2 laser. Arteriovenous malformations rarely respond. Use of the pulsed dye laser in the phase of proliferation of the haemangiomas is subject to controversy, except where there is ulceration. A rapid re-epithelialization is obtained in these cases following its use. In the involution phase, patients with residual vascular lesions can benefit from other lasers such as KTP or Nd:YAG. If they show an atrophic surface and scars these complications improve with the CO2 laser or Er:YAG. New treatment modalities are emerging, such as photodynamic therapy, whose efficacy and safety, both in the treatment of haemangiomas and vascular malformations, have yet to be confirmed.

Use of Lasers to Treat Port Wine Stain Birthmarks

Before the development of the laser there was no effective treatment for port wine stain birthmarks. This review considers the basic principles of laser-tissue interaction as applied to port wine stain treatment. Developments leading to the theory of selective photothermolysis and its implementation using pulsed dye lasers are described. Treatment results and recent developments in the field are discussed.

A new long pulsed 940 nm diode laser used for hair removal in Asian skin types

BACKGROUND: The theory of selective photothermolysis has led to the development of a variety of different hair removal laser systems.1,2 These lasers use follicular melanin as a target chromophore. At present the delivery of adequate fluences, optimizing wavelengths and pulse duration, and adequate epidermal cooling are the factors required to achieve effective hair removal. To further evaluate these factors a study was initiated to further investigate a new laser system.

A new long pulsed 940 nm diode laser used for hair removal in Asian skin types

BACKGROUND: The theory of selective photothermolysis has led to the development of a variety of different hair removal laser systems.1,2 These lasers use follicular melanin as a target chromophore. At present the delivery of adequate fluences, optimizing wavelengths and pulse duration, and adequate epidermal cooling are the factors required to achieve effective hair removal. To further evaluate these factors a study was initiated to further investigate a new laser system.

Extended theory of selective photothermolysis: A new recipe for hair cooking?

Extended theory of selective photothermolysis: A new recipe for hair cooking?

Overview Of Lasers In Plastic Surgery

The laser used today in plastic surgery has gone through many stages of development. This article examines the history of lasers, including the scientific background and the theory of selective photothermolysis in therapy. In addition, current trends and future developments in laser treatment are discussed.