Showing papers in "Lasers in Surgery and Medicine in 2000"

Imaging superficial tissues with polarized light.

Abstract: Objective Polarized light can be used to obtain images of superficial tissue layers such as skin, and some example images are presented. This study presents a study of the transition of linearly polarized light into randomly polarized light during light propagation through tissues. Study Design/Materials and Methods The transition of polarization was studied in polystyrene microsphere solutions, in chicken muscle (breast) and liver, and in porcine muscle and skin. The transition is discussed in terms of a diffusion process characterized by an angular diffusivity (radians2/mean free path) for the change in angular orientation of linearly polarized light per unit optical path traveled by the light. Results Microsphere diffusivity increased from 0.031 to 0.800 for diameters decreasing from 6.04 μm to 0.306 μm, respectively. Tissue diffusivity varied from a very low value (0.0004) for chicken liver to an intermediate value (0.055) for chicken and porcine muscle to a very high value (0.78) for pig skin. Conclusion The results are consistent with the hypothesis that birefringent tissues randomize linearly polarized light more rapidly than nonbirefringent tissues. The results suggest that polarized light imaging of skin yields images based only on photons backscattered from the superficial epidermal and initial papillary dermis because the birefringent dermal collagen rapidly randomizes polarized light. This anatomic region of the skin is where cancer commonly arises. Lasers Surg. Med. 26:119–129, 2000. © 2000 Wiley-Liss, Inc.

Effects of low-energy laser irradiation on bone remodeling during experimental tooth movement in rats.

Abstract: Background and Objective Low-energy laser irradiation has many anabolic effects such as the acceleration of bone formation. However, its effects on tooth movement, performed by bone resorption and formation, have not been well characterized. Study Design/Materials and Methods A total of 10 g of orthodontic force was applied to rat molars to cause experimental tooth movement. A Ga-Al-As diode laser was used to irradiate the area around the moved tooth, and after 12 days, the amount of tooth movement was measured. Calcein was injected subcutaneously to label the newly formed alveolar bone for quantitative analysis. Immunohistochemical staining of proliferating cell nuclear antigen was performed to evaluate cellular proliferation. TRAPase staining was also performed to facilitate the identification of osteoclasts. Results In the laser irradiation group, the amount of tooth movement was significantly greater (1.3-fold) than that of the nonirradiation group in the end of the experiment. The amount of bone formation and rate of cellular proliferation in the tension side and the number of osteoclasts in the pressure side were all significantly increased in the irradiation group when compared with the nonirradiation group (P < 0.01). Conclusion These findings suggest that low-energy laser irradiation can accelerate tooth movement accompanied with alveolar bone remodeling. Lasers Surg. Med. 26:282–291, 2000 © 2000 Wiley-Liss, Inc.

Nonablative treatment of rhytids with intense pulsed light.

Abstract: Background and Objective The aim of this study was to evaluate the efficacy and complication rate of a nonablative nonlaser light source in the treatment of rhytids. Laser resurfacing, in the treatment of facial rhytids, has involved ablative methods, with their associated complications and limitations. Rhytid improvement requires dermal collagen remodeling. Interest has begun to focus on the use of wavelengths that preserve the epidermis but deliver enough energy to promote rhytid improvement. Study Design/Materials and Methods Thirty subjects with class I–II rhytids and Fitzpatrick skin types I–II were treated with up to four treatments with an intense pulsed light source. Subjects were evaluated 6 months after the final treatment. Results Twenty-five subjects showed some improvement in the quality of skin. No subjects were found to have total resolution of rhytids. Conclusion Nonlaser intense pulsed light may effectively improve some facial rhytids. Such improvement can occur without epidermal ablation. Lasers Surg. Med. 26:196–200, 2000. © 2000 Wiley-Liss, Inc.

Origin of retinal pigment epithelium cell damage by pulsed laser irradiance in the nanosecond to microsecond time regimen.

Abstract: Background and Objective: Selective photodamage of the retinal pigment epithelium (RPE) is a new technique to treat a variety of retinal diseases without causing adverse effects to surrounding tissues such as the neural retina including the photoreceptors and the choroid. In this study, the mechanism of cell damage after laser irradiation was investigated. Study Design/Materials and Methods: Single porcine RPE-melanosomes and RPE cells were irradiated with a Nd:YLF laser (wavelength l = 527 nm, adjustable pulse duration t = 250 nsec-3 msec) and a Nd:YAG laser (l = 532 nm, t = 8 nsec). Fast flash photography was applied to observe vaporization at melanosomes in suspension. A fluorescence viability assay was used to probe the cells vitality. Results: The threshold radiant exposures for vaporization around individual melanosomes and for ED50 cell damage are similar at 8-nsec pulse duration. Both thresholds increase with pulse duration; however, the ED50 cell damage radiant exposure is 40% lower at 3msec. Temperature calculations to model the onset of vaporization around the melanosomes are in good agreement with the experimental results when assuming a surface temperature of 150°C to initiate vaporization and a homogeneous melanosome absorption coefficient of 8,000 cm ˛1 . Increasing the number of pulses delivered to RPE cells at a repetition rate of 500 Hz, the ED50 value decreases for all pulse durations. However, the behavior does not obey scaling laws such as the N 1/4 equation. Conclusion: The origin of RPE cell damage for single pulse irradiation up to pulse durations of 3 msec can be described by a damage mechanism in which microbubbles around the melanosomes cause a rupture of the cell structure. The threshold radiant exposure for RPE damage decreases with increasing number of pulses applied. Lasers Surg. Med. 27:451‐464, 2000. © 2000 Wiley-Liss, Inc.

Effects of near-infrared low-level laser irradiation on microcirculation.

Abstract: Background and Objective Recently, there has been an increase in the clinical application of low-level laser irradiation (LLLI) in various fields. The present study was conducted to explore the effects of LLLI on microcirculation. Study Design/Material and Methods We investigated the effects of LLLI on rat mesenteric microcirculation in vivo, and on cytosolic calcium concentration ([Ca2+]i) in rat vascular smooth muscle cells (VSMCs) in vitro. Results LLLI caused potent dilation in the laser-irradiated arteriole, which led to marked increases in the arteriolar blood flow. The changes were partly attenuated in the initial phase by the superfusion of 15 μM L-NAME, but they were not affected by local denervation. Furthermore, LLLI caused a power-dependent decrease in [Ca;2+]i in VSMCs. Conclusion The circulatory changes observed seemed to be mediated largely by LLLI-induced reduction of [Ca2+]i in VSMCs, in addition to the involvement of NO in the initial phase. Lasers Surg. Med. 27:427–437, 2000. © 2000 Wiley-Liss, Inc.

Deep coagulation of dermal collagen with repetitive Er:YAG laser irradiation.

Abstract: Background and Objective: Er:YAG lasers are known to effectively ablate human skin with minimal thermal damage to subjacent dermal tissue. We have investigated whether deep coagulation of dermal collagen, similar to that observed with the CO2 laser, could be achieved with repetitive Er:YAG laser exposures. Study Design/Materials and Methods: Skin on the back of a SpragueDawley rat in vivo was irradiated with sequences of 1‐10 Er:YAG laser pulses at a repetition rate of 10 or 33 Hz and single-pulse fluences from 0.8 to 1.4 J/cm 2 . The resulting lesions were biopsied within 1 hour after laser exposure, and the histologic sections were examined by using optical microscopy. Results: The depth of dermal collagen denaturation increases dramatically when 3‐10 low-fluence Er:YAG laser pulses are stacked at a repetition rate of 10 or 33 Hz. Conclusion: Coagulation of dermal collagen deeper than 200 mm below the epidermal-dermal junction is feasible by using the appropriate settings of a repetitive Er:YAG laser. Lasers Surg. Med. 26:215‐222, 2000. © 2000 Wiley-Liss, Inc.

Collagen Structure and Nonlinear Susceptibility: Effects of Heat, Glycation, and Enzymatic Cleavage on Second Harmonic Signal Intensity

Abstract: Background and Objective Helical macromolecules such as collagen and DNA are characterized by nonlinear optical properties, including nonlinear susceptibility. Because collagen is the predominant component of most biological tissues, as well as the major source of second harmonic generation (SHG), it is reasonable to assume that changes in harmonic signal can be attributed to structural changes in collagen. The purpose of this study is to determine whether various modifications of collagen structure affect second harmonic intensity. Study Design/Materials and Methods SHG was measured in tissues from cows, humans, and chickens. The effects of beam polarization, thermal denaturation, glyco-oxidative damage, and enzymatic cleavage of tissues on second harmonic intensity was studied. Results The second harmonic intensity differed considerably among different tissues, as did the effect of the incident beam polarization. In structurally modified collagen, SHG was significantly degraded from SHG in intact collagen. Conclusion These structural modifications are representative of changes that occur in pathophysiologic conditions such as thermal injury, diabetes, tumor invasion, and abnormal wound healing. The ability to assess these changes rapidly and noninvasively has considerable clinical applicability. SHG analysis might provide a unique tool for monitoring these structural changes of collagen. Lasers Surg. Med. 27:329–335, 2000. Published 2000 Wiley-Liss, Inc.

In vitro effects of low‐level laser irradiation at 660 nm on peripheral blood lymphocytes

Abstract: Background and Objective: The effects of low-level laser light irradiation are still highly contested, and the mechanisms of its action still unclear. This study was conducted to test the effects of low-level laser irradiation at 660 nm on human lymphocytes and to investigate the possible mechanisms by which these effects are produced. Study Design/Materials and Methods: Whole blood obtained by phlebotomy was irradiated at 660 nm by using energy fluences between 0 and 5.0 J/cm 2 . The lymphocytes were isolated after irradiation of the whole blood. For the control experiment, the lymphocytes were first isolated and then irradiated at the same wavelength and energy fluence for comparison. The proliferation of lymphocytes and the formation of free radicals and lipid peroxides were monitored. Hemoglobin was also irradiated in a cell-free environment to test for the production of lipid peroxides. Results: Lymphocyte proliferation was significantly higher (P < 0.05) as expressed by a Stimulation Index in samples irradiated in the presence of whole blood compared with lymphocytes irradiated after isolation from whole blood. Free radical and lipid peroxide production also increased significantly when samples were irradiated in the presence of red blood cells. Conclusion: The present study supports the hypothesis that one mechanism for the photobiostimulation effect after irradiation at 660 nm is the reaction of light with hemoglobin, resulting in oxygen radical production. Lasers Surg. Med. 27:255‐261, 2000 © 2000 Wiley-Liss, Inc.

Nonablative skin remodeling: selective dermal heating with a mid-infrared laser and contact cooling combination.

Abstract: Background and Objective Many of the microscopic changes associated with photodamage reside in the dermis. It follows that subsurface heating of the skin might allow for cosmetic enhancement without loss of the epidermis. Accordingly, we investigated the clinical and microscopic changes produced by a mid-infrared laser coupled with a contact cooling device. Study Design/Materials and Methods Nine patients were treated with an erbium glass laser and sapphire cooling handpiece in contact with the skin. Postauricular sites were irradiated with pulse energies varying from 400–1,200 mJ and numbers of pulses from 4 to 40. Outcome measures included pain, edema, and erythema at predetermined postoperative intervals. Biopsies were performed just after treatment and 2 months postoperatively for selected pulse energy-pulse number combinations. Results Erythema, edema, and pain increased with pulse energy and number of pulses. Likewise, immediate epidermal necrosis and subsequent scarring were observed for larger pulse energy-pulse number combinations. At sites with epidermal preservation, on biopsy, immediate dermal thermal damage was observed in a band-like pattern. The deep boundaries of this band were dependent on pulse energy and pulse number. After 8 weeks, biopsies showed dermal fibroplasia roughly correlating to the band of immediate dermal thermal damage. Conclusion Selective dermal heating can be achieved with a mid-infrared laser coupled to a contact surface cooling device. In this study, the range of fibroplasia and lack of clinically substantial cosmetic enhancement suggest that the dermal thermal damage achieved may be too deep and that the injury should be confined to more superficial levels to alter the most severely photodamaged dermis. Lasers Surg. Med. 26:186–195, 2000. Published 2000 Wiley-Liss, Inc.

Q-switch laser and tattoo pigments: first results of the chemical and photophysical analysis of 41 compounds.

Abstract: Background and Objective In the Western world, there are at least 20–30 million people with tattoos. Improved self-image and social stigmatization are the main reasons for removing tattoos from skin. Q-switched lasers are applied to destroy the tattoo compounds in the skin. The treatment of tattoos containing ink often gives excellent results, whereas the results of treatments for coloured tattoos are not predictable and usually are worse. The chemical structure and the absorption spectra of the tattoo pigments are usually unknown. However, the efficacy of the treatment by using light of different Q-switched lasers (wavelengths 510, 532, 694, 755, 1064 nm) is correlated to both the chemical structure of the tattooed compounds yielding specific absorption spectra and the laser wavelength used. Study Design/Materials and Methods A structural and spectroscopic analysis of 41 coloured pigments was performed. Results The 41 substances were identified, and they consist of 16 individual chemicals of different structured well-known industrial organic pigments. The absorption spectra of the 16 pigments were measured quantitatively. Conclusion The results of the present analysis explain to some extent the outcome of clinical studies regarding laser therapy of coloured tattoos. Because the laser energy used produces a high temperature in the azo or polycyclic pigments, it is necessary to investigate whether that change causes possibly toxic or cancerogenic compounds. Lasers Surg. Med. 26:13–21, 2000. © 2000 Wiley-Liss, Inc.

Evaluation of cooling methods for laser dermatology.

Abstract: Background and Objective: Skin cooling is used to protect the epidermis in a variety of laser dermatology procedures, including leg vein treatment, hair removal, and port wine stain removal. Spray and contact cooling are the two most popular methods, but similarities and differences of these techniques are not well understood. Study Design/Materials and Methods: A theoretical model of skin cooling is presented for two different regimens: “soft” cooling in which freezing of the skin is not permitted and “hard” cooling in which the skin can be frozen to a given depth. Spray and contact cooling were also compared experimentally using an in vitro model. Results: For a fixed skin surface temperature, spray and contact cooling theoretically produce the same cooling profile in the skin. Anatomic depth of cooling depends on the time for which either the spray or contact is applied. In vitro experiments caused temperature at the simulated basal layer to be between ˛5 and +5°C for both spray (tetrafluoroethane, boiling point ˛26°C) and contact (˛27°C sapphire plate) cooling. The theoretical precooling analysis shows hard mode to be faster and more selective than soft mode; however, cooling time for hard mode must be carefully controlled to prevent irreversible epidermal damage caused by freezing. Conclusions: Both spray and contact cooling provide efficient skin cooling. The choice of cooling method depends on other factors such as the target depth, cost, safety, and ergonomic factors. Lasers Surg. Med. 26:130‐144, 2000 © 2000 Wiley-Liss, Inc.

Collagen tightening induced by carbon dioxide laser versus erbium: YAG laser.

Abstract: Background and objective Pulsed CO2 laser resurfacing improves photodamage and acne scarring by ablation of abnormal tissue with subsequent regeneration and remodeling of collagen and through heat induced collagen contraction. Whether collagen contraction persists long-term and helps maintain the skin tightening observed after resurfacing is debated. One possible mechanism of long-term clinical tightening is that of wound contracture that occurs as part of normal wound healing. If normal wound contracture, and not heat induced collagen contraction, is responsible for maintaining the initial skin tightening seen in CO2 laser resurfacing, then equal results would be expected from resurfacing with either CO2 or erbium lasers. The study was performed to determine whether there is a difference in skin tightening secondary to thermally mediated collagen contraction versus that which occurs secondary to tissue contraction of wound healing. The persistence of these changes over 6 months and the histologic characteristics were studied as well. Study design/materials and methods Nine patients had four tattoo dots applied to the upper eyelids, with horizontal axis measuring 18-20 mm and the vertical axis 6-10 mm. One month later, one eyelid was treated with three passes of the UltraPulse CO2 laser and the other eyelid with an erbium laser to the end point of early pinpoint bleeding. Three patients were treated with additional passes after pinpoint bleeding was encountered. The total number of pulses used per patient was recorded. Measurements of the vertical and horizontal distances were made after each pass and monthly for 6 months. The treated skin was then excised in performance of an upper lid blepharoplasty and the tissue submitted for histologic analysis. Results In the vertical plane, the UltraPulse CO2 laser induced an average of 43% tightening intraoperatively and this gradually diminished to an average of 34% by 6 months, whereas the wound contracture of erbium resurfacing was not seen until 1 month postoperatively, at which time 42% tightening was seen, gradually diminishing to 36% at 6 months. Three patients with erbium resurfacing had scarring present. These were the three patients treated most aggressively and also the three patients with the most significant wound contracture. Scarring was not seen on the CO2 treated side in any patients. In the horizontal plane, the CO2 laser caused 31% intraoperative tightening, decreasing to 19% at 6 months. In this plane, the erbium laser induced wound contracture was 12% at 1 month which remained stable and unchanged. Conclusions Although wound contraction secondary to tissue healing may result in nearly the same tissue tightening as heat-induced collagen contraction, the two processes are very different and variable, with increased risk of scarring seen with wound contracture, compared with heat-induced collagen tightening. The tissue tightening seen with thermally induced collagen contraction is long-lasting, if not "permanent."

Preliminary evaluation of two fluorescence imaging methods for the detection and the delineation of basal cell carcinomas of the skin.

Abstract: Background and ObjectiveFluorescence techniques can provide powerful noninvasive means for medical diagnosis, based on the detection of either endogenous or exogenous fluorophores The fluorescence of I´-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) has already shown promise for the diagnosis of tumors The aim of the study was to investigate the localization of skin tumors after the topical application of ALA, by detecting the PpIX fluorescence either in the spectral or in the time domainStudy Design/Materials and MethodsTwo fluorescence imaging systems were used to identify basal cell carcinomas of the skin in humans, after topical application of 20% ALA ointment Both systems rely on the comparison between the exogenous and the endogenous fluorescence, performed either in the spectral domain or in the time domain The first system works by using three images acquired through different spectral filters, whereas the second one measures the spatial map of the average fluorescence lifetime of the sampleResultsA clear demarcation of skin malignancies was successfully performed in vivo noninvasively with both fluorescence imaging systemsConclusionThe two complementary approaches considered in the present study show promise for skin tumor detection and delineation based on specific fluorescence features Lasers Surg Med 26:76–82, 2000 © 2000 Wiley-Liss, Inc (Less)

Laser modulation of angiogenic factor production by T-lymphocytes.

Abstract: BACKGROUND AND OBJECTIVE: In previous investigations, small variations in the energy densities of low level light therapy (LLLT) were found to produce significant differences in the proliferation of resting T-lymphocytes in vitro. Pulsing these cells with mitogen in addition to laser therapy produced inhibitory effects regardless of the amplitude of the energy density used. In the current study, the effect of LLLT on the production of angiogenic factor(s) by T-lymphocytes was investigated in vitro. STUDY DESIGN/MATERIALS AND METHODS: Human T-cells isolated from peripheral blood were prepared in suspension either with or without addition of mitogen. Cell suspensions were irradiated with laser by using the following energy densities: 1.2, 3.6, 6.0, and 8.4 J/cm(2). Wavelength, pulsing frequency, and power output were kept constant at 820 nm, 5,000 Hz, and 50 mW, respectively. After either 3 or 5 days of incubation, lymphocyte supernatants were collected and added as conditioned media to cultured endothelial cells (ECs). The effect on the proliferation of these ECs was assessed over a 72-hour period by using a methylene blue assay. RESULTS: Endothelial cell proliferation increased significantly when incubated with conditioned media collected from resting T-cells exposed to 1.2 and 3.6 J/cm(2). Day 5 conditioned media produced similar patterns of EC proliferation to that of day 3 but at lower magnitude. Pulsing of T-lymphocytes with mitogen in addition to laser irradiation significantly lessened their angiogenic capability. Conditioned media from 3.6 J/cm(2) laser-treated T-cells induced the maximal EC proliferation in all groups studied. CONCLUSION: It would seem that laser therapy stimulates lymphocytes to produce factor(s) that can modulate EC proliferation in vitro; this effect on the lymphocytes is influenced by (1) the amplitude of energy density used for T-cell irradiation, (2) exposing T-cells to both mitogen and laser, and (3) the duration of T-cell incubation in culture.

Effect of low-intensity laser irradiation (660 nm) on a radiation-impaired wound-healing model in murine skin.

Abstract: Background and Objective The use of low-intensity laser therapy (LILT) as a therapeutic modality has become popular in a variety of clinical applications including the promotion of wound repair. Although the clinical evidence base for such application remains sparse, recent studies have demonstrated a number of quantifiable photobiological effects associated with such therapy. In the present study, the effect of laser irradiation at various radiant exposures on a radiation-impaired wound-healing model in murine skin was investigated. Study Design/Materials and Methods The study included two phases; in phase one, male Balb/c mice (n = 36; age-matched at 10 weeks) were randomly allocated to three experimental groups (n = 12, each group). In all groups, a well-defined area on the dorsum was exposed to 20 Gy x-rays. Seventy-two hours postirradiation, all mice were anaesthetised and a 7 × 7 mm area wound was made on the dorsum. All wounds were videotaped alongside a marker scale (three times weekly) until closure was complete. In groups 2 and 3, mice were treated with laser irradiation (0.5 and 1.5 J/cm2, respectively) three times weekly by using a 660-nm GaAlAs laser unit (5 kHz; 15 mW; Omega Laser Systems, London, UK). Wound areas were then calculated by using an image analysis system (Fenestra 2.1), and results were analyzed by using repeated measures and one-factor analysis of variance statistical tests. In phase two, two experimental groups were included (n = 12 each group); the protocol was identical to that described for phase 1; however, mice in group 2 were treated with a radiant exposure of 4 J/cm2. Results Results from this investigation demonstrated that treatment with 0.5, 1.5. and 4 J/cm2 had no beneficial effect on the rate of wound closure (P > 0.05). Conclusion These findings provide little evidence of the putative stimulatory effects of LILT in vivo at the parameters investigated. Lasers Surg. Med. 26:41–47, 2000. © 2000 Wiley-Liss, Inc.

Modulating the Er:YAG laser.

Abstract: Background and Objectives In the past 2 years, there has been some controversy about the optimal laser system, or combination of systems, for cutaneous resurfacing. Initially, it seemed that the Er:YAG laser would have significant advantages over the CO2 laser. In practice, some of those who jumped early onto the Er:YAG bandwagon have been unimpressed with the degree of skin tightening that can be achieved with this system. Also, the excessive bleeding induced by the Er:YAG lasers prevented deeper vaporization. During the past 18 months, three new “modulated” Er:YAG lasers have been produced that are said to be able to achieve CO2 laser-like effects, while maintaining the Er:YAG laser advantages. The purpose of this article is to examine these new systems and to discuss their potential benefits, if any, over the “conventional” Er:YAG lasers, and the CO2 lasers. Study Design/Materials and Methods The author has collected data from his own experience and that of his colleagues in the department of dermatology at University of California at San Francisco. The author has used all three types of modulated Er:YAG laser on patients presenting for cosmetic laser resurfacing and the treatment of many benign conditions over an 18-month period. Results All three modulated forms of Er:YAG lasers have been demonstrated to provide better coagulation than the conventional Er:YAG lasers. The Derma-K and the Contour Er:YAG lasers were able to induce tissue contraction/desiccation similar to the CO2 laser. The author and his colleagues have induced only two cases of permanent hypopigmentation in over 50 cases during the past 18 months while using the Er:YAG laser, significantly less than might be expected with the CO2 lasers. Conclusions If a laser surgeon is happy with the results obtained with a high-energy, short-pulse CO2 laser, then there seems little reason to consider changing to an Er:YAG laser. The modulated Er:YAG lasers have definite advantages over the conventional Er:YAG lasers. They exhibit better control of hemostasis and can ablate tissue to a greater depth than the conventional Er:YAG lasers. The Er:YAG lasers might induce less permanent hypopigmentation than the CO2 lasers. Lasers Surg. Med. 26:223–226, 2000 © 2000 Wiley-Liss, Inc.

New approaches to the treatment of vascular lesions

Abstract: Background and Objective The pulsed dye laser was developed based on the concept of selective photothermolysis. By using a wavelength of light well absorbed by the target and pulse duration short enough to spatially confine thermal injury, specific vascular injury could be produced. Study Design/Materials and Methods Although the pulsed dye laser revolutionized the treatment of port wine stains (PWS) and a variety of other vascular lesions, the ideal thermal relaxation time for the vessels in PWS is actually 1–10 ms, not 450 μs of the original pulsed dye laser machines. These original theoretical calculations recently have been proven correct in a study that used both an animal vessel model and in human PWS. Results Longer wavelengths of light, within the visible spectrum, penetrate more deeply into the skin and are more suitable for deeper vessels, whereas longer pulse durations are required for larger caliber vessels. Conclusion A variety of lasers recently have been developed for the treatment of vascular lesions which incorporate these concepts into their design, including pulsed dye lasers at 1.5 ms, a filtered flash-lamp pulsed light source with pulse durations of 1–20 ms, several 532-nm pulsed lasers with pulse durations of 1 ms to as high as 100 ms, long pulsed alexandrite lasers at 755 nm with pulse durations up to 20 ms, pulsed diode lasers in the 800 to 900 nm range, and long pulsed 1064 Nd:YAG sources. Lasers Surg. Med. 26:158–163, 2000. © 2000 Wiley-Liss, Inc.

Cold air in laser therapy: first experiences with a new cooling system.

Abstract: Background and Objective: Analgesic cooling technologies are firmly established in dermatologic laser therapy. We present cold air as a novel method of cooling and compare it with those methods that are already in use. Study Design/Materials and Methods: We treated 166 patients with the diagnoses hypertrichosis, port wine stains, hemangioma, essential telangiectasias, and tattoos with different laser systems (long-pulsed alexandrite laser [LPIR], pulsed dye laser, Q-switched Nd:YAG laser, Q-switched ruby laser). In a prospective study, we collected data about the analgesia of the cooling method and the thermal protection of the epidermis (reduction of the extent and duration of erythema, purpura, blisters, hyper-/hypopigmentations, edemas, crusting), compared with the cooling method with ice gel. Additionally, we measured air and skin temperatures with an infrared thermometer at different application modalities. Results: Three percent of the treated patients refused the cold air therapy altogether. Eleven percent found that it was as good as the other cooling methods; 86% clearly preferred the cold air therapy. Leaving out the perinasal area, the percentage rises to 97%. On average, the analgesic effect was by 37% better than through cooling with ice gel. The increased thermal protection of the epidermis made it possible to use laser energy levels that were higher by 15‐30% and, at the same time, to reduce the rate of side effects (in 63% of the patients erythema persisted for a shorter period, in 70% the purpura was reduced, 83% had less crusting). Conclusion: In dermatologic laser therapy, the use of cold air in analgesia can be considered as an effective, inexpensive, and well-accepted (by both patients and doctors) alternative to currently applied cooling methods. Nevertheless, further prospective studies are necessary to determine whether treatment results can really be improved by using higher laser energy levels. Lasers Surg. Med. 27:404‐410, 2000. © 2000 Wiley-Liss, Inc.

Variable pulse erbium:YAG laser skin resurfacing of perioral rhytides and side-by-side comparison with carbon dioxide laser†

Abstract: Background and Objective Laser resurfacing of facial rhytides has become a popular treatment option for many patients with wrinkles, photoaging, and acne scarring. Laser wavelength/pulse duration options and new techniques continue to shorten the healing phase associated with laser skin resurfacing while maintaining clinical efficacy. Variable pulse erbium:YAG (Er:YAG) laser systems are now available that offer the surgeon the ability to vary the Er:YAG pulse duration from a pulse that is primarily ablative to one that is more thermal. The objective of this study was to evaluate the histologic effects created with a variable pulse Er:YAG laser. To study prospectively the clinical effects on upper lip rhytides with a variable pulse Er:YAG laser when compared side by side with pulsed carbon dioxide (CO2) laser resurfacing. Study Design/Materials and Methods Forty-two treatment sites on 21 patients were randomized and evaluated after treatment of the upper lip region with CO2 laser resurfacing on one side and a variable pulse Er:YAG laser on the other. Patient diaries were maintained to assess erythema, crusting, pain, and pigmentary changes. Blinded objective grading of improvement was performed. Chromometer measurements were obtained to analyze erythema. Results The variable pulse Er:YAG laser treatment reduced the duration of crusting on average from 7.7 days with CO2 to 3.4 days. Chromometer measurements noted decreased postoperative erythema. Grading by physicians in a blinded manner showed 63% improvement for the CO2 treatment site and 48% improvement in the variable pulse Er:YAG site. No cases of permanent hyperpigmentation, hypopigmentation, or scarring occurred. Conclusion The variable pulse Er:YAG laser resurfacing is a safe and effective resurfacing tool, which combines ablative and thermal modalities. The protocol used in this study approaches but does not equal the results we have traditionally seen with CO2 laser resurfacing. Lasers Surg. Med. 26:208–214, 2000 © 2000 Wiley-Liss, Inc.

In vivo experimental evaluation of skin remodeling by using an Er:Glass laser with contact cooling.

Abstract: Background and objective Selective dermal remodeling consists of inducing collagen tightening, neocollagen synthesis, or both, without damage to the overlying epidermis. This experimental study aimed to evaluate an Er:Glass laser emitting at 1.54 micrometer combined with contact cooling to target the upper dermis while protecting the epidermis. Study design/materials and methods Male hairless rats were used for the study. Different fluences (26-30 J/cm(2)) by using single 3-ms pulse irradiation or pulse train irradiation (1.1 J, 3 Hz) and different cooling temperatures (+5 degrees C, 0 degrees C, -5 degrees C) were screened with clinical examination and histologic evaluation at 1, 3, and 7 days after laser irradiation. Results The clinical effects were clearly dose and temperature cooling dependent. It seemed that single pulse irradiation led to epidermal whitening in most cases, whatever the cooling temperature. Conversely, pulse train irradiation showed reproducible epidermal preservation and confinement of the thermal damage into the dermis. New collagen synthesis was confirmed by a marked fibroblastic proliferation, detected in the lower dermis at day 3 and clearly seen in the upper dermis at day 7. Conclusion This new laser seems to be a promising new tool for the treatment of skin laxity, solar elastosis, facial rhytides, and mild reduction of wrinkles.

Optimal cryogen spray cooling parameters for pulsed laser treatment of port wine stains

Abstract: Background and Objective In dermatologic laser therapy, cryogen spray cooling (CSC) is a means to protect the epidermis while leaving dermal structures susceptible to thermal damage. The purpose of this study was to determine optimal spurt duration, τs, and optimal delay, τd, between the cryogen spurt and laser pulse when using CSC in treatment of port wine stain birthmarks. Study Design/Materials and Methods A finite difference method is used to compute temperature distributions in human skin in response to CSC. Optimal τs and τd are determined by maximizing the temperature difference between a modeled basal layer and an imaginary target chromophore. Results The model predicts an optimal τs of 170–300 msec and approximately 400 msec for shallow (150 μm) and deeper (400 μm) targets, respectively. Spraying for longer than the optimal τs does not critically impair cooling selectivity. For a spurt duration of 100 msec, optimal delays are 5–10 msec and 25–70 msec for a shallow and deep basal layer, respectively. Conclusion In the absence of knowledge about the lesion anatomy, using a τs of 100–200 msec and no delay is a good compromise. A delay is justified only when basal layer and target chromophore are relatively deep and the optimal spurt duration cannot be applied, e.g., to avoid frostbite. Lasers Surg. Med. 27:165–170, 2000. © 2000 Wiley-Liss, Inc.

Morphologic changes correlating to different sensitivities of Escherichia coli and enterococcus faecalis to Nd:YAG laser irradiation through dentin.

Abstract: Background and Objective Previous studies demonstrated the disinfecting potential of Nd:YAG laser irradiation on the root canal system from an overall quantitative viewpoint. The aim of this study was to evaluate the specific effect of irradiation through dentin on gram-negative and gram-positive bacteria with regard to their cell structure. Study Design/Materials and Methods Sterile dentin samples of standardized size were divided into two sets of four groups with eight samples each. The first set was inoculated with Escherichia coli as the gram-negative test strain, the second set was inoculated with Enterococcus faecalis, which served as the gram-positive test organism. The samples were then irradiated on the bacteria-free side in contact mode under constant scanning movement at an angle of 10° by use of the fiber optic of the Nd:YAG laser. Upon laser treatment they were critical point dried and subjected to SEM investigation. Another two sets of samples were prepared and irradiated in the same manner and evaluated by standard microbiological procedures to verify whether the observed morphologic alterations correlated to cell death. Results SEM investigations revealed damage pattens that increased with the amount of energy applied. Whereas the gram-negative test organism showed immediate structural injury, the gram-positive test organism required repeated application of irradiation. The microbiological examination showed reduction of both bacterial strains, yet to different extents. Conclusion Our study demonstrates the different morphologic impact of Nd:YAG laser irradiation through dentin on representatives of the two main groups of bacteria. It shows that the construction of the cell wall is crucial for their individual sensitivity to laser treatment. Lasers Surg. Med. 26:250–261, 2000. © 2000 Wiley-Liss, Inc.

Optic nerve sheath fenestration with a novel wavelength produced by the free electron laser (FEL).

Abstract: Background and Objective To determine whether 6.45-μm free electron laser (FEL) energy can successfully perform optic nerve sheath fenestration and to compare the acute and chronic cellular responses with this surgery. Study Design/Materials and Methods Optic nerve sheath fenestration was performed in rabbits by using either FEL energy (< 2.5 mJ, 10 Hz, 325-μm spot size) or a knife. The optic nerve integrity and glial response were evaluated histologically acutely or 1 month postoperatively. Results The FEL at low energy effectively cut the optic nerve sheaths with minimal reaction in the underlying nerve. With FEL or knife surgical techniques, a mild astrocytic hypertrophy only adjacent to the fenestration was observed acutely in the glial fibrillary acidic protein (GFAP) -immunoreacted sections. The chronic healing responses after either technique appeared similar with: (1) a thin fibrous scar at the fenestration site, (2) cells uniformly distributed (hematoxylin and eosin), and (3) up-regulation of GFAP and S100β in astrocytes adjacent to the fenestration site. Conclusion The FEL at low energy performs an optic nerve sheath fenestration in a small space with ease. Both FEL and knife incisions cause a similar rapid glial response near the fenestration site that remains 1 month later. Lasers Surg. Med. 27:191–205, 2000. © 2000 Wiley-Liss, Inc.

Laser‐tissue interaction with a continuous wave 3‐μm fibre laser: Preliminary studies with soft tissue

Abstract: Background and Objective Lasers operating at wavelengths in the mid-infrared region have become increasingly popular for applications in areas of surgery and medicine Advances in fibre laser technology have introduced a highly efficient, compact, diode-pumped source operating at around the 3-μm wavelength This study examines the effects of this recently developed laser on soft biological tissue Study Design/Materials and Methods Chicken breast and liver tissue samples were exposed to 800 mW continuous wave laser power, at a wavelength of 271 μm, with incident spot sizes of around 150 μm Samples were inspected grossly immediately after laser irradiation and also prepared for histologic processing Results After irradiation, visual assessment of changes at sample surfaces indicated a region of thermally affected tissue surrounding the ablation crater This region was observed to grow in size to around 10 mm in diameter after 3 seconds of laser exposure at 800 mW An ablation velocity of 080 mms−1 was determined in chicken breast for the same incident laser parameters Analysis of samples irradiated at 800 mW and processed for histology revealed minimal damage at hole boundaries and no signs of char formation, providing incident exposure times were restricted to below around 05 seconds Conclusion This fibre laser source has demonstrated its potential to fulfil medical applications, enabling accurate, precise tissue removal to proceed at a rapid ablation rate The efficiency and small size of the laser are attractive features Lasers Surg Med 26:491–495, 2000 © 2000 Wiley-Liss, Inc

Recent developments in cutaneous lasers.

Abstract: Laser surgery is one of the most rapidly advancing fields in medicine. In dermatology and ophthalmology, lasers now routinely provide the most precise form of surgery ever practiced, often for cosmetic goals. Consumer demand has generated intense interest from physicians and industry. This has led to the development of safer and more effective lasers with a wide range of applications. The theory of selective photothermolysis, introduced by Anderson and Parrish in 1981, is the basis for many advancements in dermatological lasers [1]. It allows for highly localized destruction of light-absorbing “targets” in skin, with minimal damage to the surrounding tissue. To achieve selective photothermolysis, appropriate wavelength, exposure duration, and sufficient fluence are necessary. Various targets absorb at different wavelengths, and the wavelength of the laser should be absorbed more by the target structure than by surrounding structures. Light absorbed in the target structure is converted to heat, which immediately begins to diffuse away. In general, exposure duration should be shorter than or about equal to the thermal relaxation time of the target. Thermal relaxation time is the time it takes the target to cool significantly and is proportional to the square of the diameter of the target. Therefore, the thermal relaxation time of a small object is much shorter than that of large objects. A useful approximation is that the thermal relaxation time in seconds of a target is equal to the square of its diameter in millimeters. Thus, a 0.1-mm blood vessel cools significantly in about 0.01 sec (10 msec). Finally, sufficient energy must be delivered to cause the desired effect, destruction of the target. Fluence (energy/area) necessary for treatment is inversely proportional to the fraction of light absorbed by the targets. Thus, higher fluence is necessary when using weakly absorbed wavelengths, treating targets that contain less chromophore (the light absorbing substance), or targets that are deep within the skin. Clinically, selective photothermolysis involves ensuring that a maximum tissue-damaging temperature occurs only in the desired tissue targets. When treating dermal targets (blood vessels, tattoos, hair, etc.), light must pass through the epidermis. Epidermal injury is the most frequent cause of side effects in these settings. A classic example of selective photothermolysis is the use of pulsed lasers in the treatment of port-wine stains (PWS). PWS consist of dilated venules in which the principal chromophore is oxyhemoglobin. The principal absorption peaks of oxyhemoglobin are in the blue–green– yellow portion of the visible range (418, 542, and 577 nm). In general, longer wavelengths penetrate more deeply into skin because of less scattering by dermal collagen, and the wavelengths 577–595 nm, within one absorption band of oxyhemoglobin, are well suited to target vessels in PWS. The first lasers designed for selective photothermolysis of PWS were pulsed dye lasers emitting pulses of about 1 msec duration. This pulse width corresponds to thermal relaxation time of vessels down to about 30 mm in diameter, typical for pediatric PWS. Laser light absorbed by hemoglobin is converted into heat, which damages the endothelium and surrounding vessel wall, followed by thrombosis, a vasculitis, and the removal of the abnormal venules [2]. The ideal pulse duration for PWS treatment is probably approximately 10 msec [3], and several laser systems are emerging that emit longer pulses.

Low‐power laser light in the healing of burns: A comparison between two different wavelengths (635 nm and 690 nm) and a placebo group

Abstract: Background and Objective Studies on the influence of low-power laser light on wound healing have shown inconsistent results, or, as in the case of burns, are very scarce. We have studied the effects of two different low-power diode laser lights on the healing of burns in rats. Study Design/Materials and Methods Thirty rats were burned on both flanks and randomly allocated to one of three study groups. In group A, both wounds remained untreated; in groups B and C, one wound each was irradiated with 635 nm or 690 nm laser light (1.5 J/cm2), whereas the other wound remained untreated. Diameter, redness, and edema of the wounds were examined daily. Results Between and within groups, diameter, redness, and edema of the wounds were similar throughout the entire observation period. Irradiation of the burns did not accelerate wound healing when compared with control wounds. Conclusion We conclude that neither 690 nm nor 635 nm low-power laser light produced any beneficial effects on the healing processes of burns in rats. Lasers Surg. Med. 27:39–42, 2000. © 2000 Wiley-Liss, Inc.

Hyperbaric oxygen and photodynamic therapy in the treatment of advanced carcinoma of the cardia and the esophagus.

Abstract: Background and Objective The photochemical reaction of photodynamic therapy (PDT) depends on the presence of molecular oxygen. Because of anoxic regions in tumor tissue and vascular shutdown during PDT, the efficiency is limited. Therefore, the use of hyperbaric oxygen, which increases the oxygen in tumor tissue, as well as the amount of singlet oxygen, may enhance the efficiency of PDT. Study Design/Materials and Methods After diagnostic work-up, photosensitization was carried out with a hematoporphyrin-derivate 2 mg/kg body weight 48 hours before PDT. The light dose was calculated as 300 J/cm of fiber tip. Twenty-three patients were treated by PDT alone and 29 patients received PDT under hyperbaric oxygen at a level of two absolute atmospheric pressures. Results Improvement regarding dysphagia and stenosis-diameter could be obtained in both treatment arms with no significant difference (P = 0.43 and P = 0.065, respectively). The tumor length also decreased in both groups and showed a significant difference in favour of the PDT/HBO group (P = 0.002). The mean overall survival was 11.3 months. The mean survival time for the PDT group was 8.7 months and for the PDT/HBO group 13.8 months (P = 0.021). Conclusion According to this pilot study, combined PDT/HBO represents a new approach in the treatment of esophageal and cardia cancer, which appears to have enhanced the efficiency of PDT. Lasers Surg. Med. 26:308–315, 2000. © 2000 Wiley-Liss, Inc.

Laser skin welding: in vivo tensile strength and wound healing results.

Abstract: Background and Objective Laser skin welding was investigated as a general model for laser tissue closure. Scanned delivery of near-infrared laser radiation in combination with a dye can produce strong welds with limited thermal damage. Study Design/Materials and Methods Two-centimeter-long, full-thickness incisions were made on the backs of guinea pigs. Wounds were closed either by laser welding or sutures and then biopsied at 0, 3, 6, 10, 14, 21, and 28 days postoperatively. Welding was achieved by using continuous-wave, 1.06-μm, Nd:YAG laser radiation scanned over the incisions to produce a dwell time of ∼80 msec. The cooling time between scans was fixed at 8 seconds. A 4-mm-diameter laser spot was maintained during the experiments, and the power was kept constant at 10 W. The operation time was fixed at 10 minutes per incision. India ink was used as an absorber of the laser radiation at the weld site, and clamps were used temporarily to appose the incision edges. Results Acute weld strengths of 2.1 ± 0.7 kg/cm2 were significantly higher than suture apposition strengths of 0.4 ± 0.1 kg/cm2 (P < 0.01), and weld strengths continued to increase over time. Lateral thermal damage in the laser welds was limited to 200 ± 40 μm near the epidermal surface with less thermal damage deeper within the dermis. Conclusion Our welding technique produced higher weld strengths and less thermal damage than reported in previous skin welding studies and may represent an alternative to sutures. Lasers Surg. Med. 27:55–65, 2000. © 2000 Wiley-Liss, Inc.

Optimal light dose for interstitial photodynamic therapy in treatment for malignant brain tumors.

Abstract: Background and objective The primary goal was to determine the maximal tolerable light dose that can be administered to patients undergoing multifiber interstitial photodynamic therapy (PDT) of malignant brain tumors at a fixed dose of photosensitizer. Study design/materials and methods Eighteen patients (12 glioblastomas, 5 anaplastic astrocytoma, and 1 malignant ependymoma) were included in this study. The total light dose delivered to the tumor was divided into three groups of six patients each: 1,500-3,700 J, 3,700-4,400 J, and 4,400-5,900 J. Results Five patients (all glioblastomas) demonstrated postoperative permanent neurologic deficits. None of the patients in 1,500-3,700 J, two patients in 3,700-4,400 J, and three patients in 4,400-5,900 J had neurologic deficits. Glioblastomas recurred more often than anaplastic astrocytomas. Increasing the light dose did not make a difference in local/regional control of glioblastomas. Patients with anaplastic astrocytomas survived (mean, 493 days) longer than patients with glioblastomas (mean, 116.5 days) after PDT. Four patients had prolonged survival (more than a year) after PDT. Conclusions Increasing the total light dose delivered to the tumor increases the odds of having a permanent neurologic deficit but does not increase survival or time to tumor progression. There was no difference in local or marginal recurrence with increasing light dose. Recurrent anaplastic astrocytomas tend to do better than recurrent glioblastomas with PDT.

Optical and thermal properties of nasal septal cartilage.

Abstract: Backgrounds and Objectives The aim of the study was to measure the spectral dependence of optical absorption and reduced scattering coefficients and thermal conductivity and diffusivity of porcine nasal septal cartilage. Values of optical and thermal properties determined in this study may aid in determining laser dosimetry and allow selection of an optical source wavelength for noninvasive diagnostics for laser-assisted reshaping of cartilage. Materials and Methods The diffuse reflectance and transmittance of ex vivo porcine nasal septal cartilage were measured in the 400- to 1,400-nm spectral range by using a spectrophotometer. The reflectance and transmittance data were analyzed by using an inverse adding-doubling algorithm to obtain the absorption (μa) and reduced scattering (μa′) coefficients. A multichannel thermal probe controller system and infrared imaging radiometer methods were applied to measure the thermal properties of cartilage. The multichannel thermal probe controller system was used as an invasive technique to measure thermal conductivity and diffusivity of cartilage at three temperatures (27, 37, 50°C). An infrared imaging radiometer was used as a noninvasive method to measure the thermal diffusivity of cartilage by using a CO2 laser source (λ = 10.6 μm) and an infrared focal plane array (IR-FPA) camera. Results The optical absorption peaks at 980 nm and 1,180 nm in cartilage were observed and corresponded to known absorption bands of water. The determined reduced scattering coefficient gradually decreased at longer wavelengths. The thermal conductivity values of cartilage measured by using an invasive probe at 27, 37, and 50°C were 4.78, 5.18, and 5.76 mW/cm°C, respectively. The corresponding thermal diffusivity values were 1.28, 1.31, and 1.40× 10−3 cm2/sec. Because no statistically significant difference in thermal diffusivity values with increasing temperature is found, the average thermal diffusivity is 1.32 × 10−3 cm2/sec. The numerical estimate for thermal diffusivity obtained from infrared radiometry measurements was 1.38 × 10−3 cm2/sec. Conclusion Values of the spectral dependence of the optical absorption and reduced scattering coefficients, and thermal conductivity and diffusivity of cartilage were measured. The invasive and noninvasive diffusivity measurements were consistent and concluded that the infrared imaging radiometric technique has an advantage to determine thermal properties, because damage to the cartilage sample may be avoided. The measured values of absorption and reduced scattering coefficients can be used for predicting the optical fluence distribution in cartilage and determining optical source wavelengths for the laser-assisted cartilage reshaping studies. The thermal conductivity and diffusivity values can play role in understanding thermal-dependent phenomenon in cartilage during laser irradiation and determining laser dosimetry for the laser-assisted cartilage reshaping studies. Lasers Surg. Med. 27:119–128, 2000. © 2000 Wiley-Liss, Inc.