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At least 343 records · Page 19Linked to original sources
PubMed2002

Laser skin resurfacing treatment outcome of facial scars and wrinkles in Asians with skin type III/IV with the Unipulse CO2 laser system.

OBJECTIVE: To study the efficacy and complications from Unipulse CO2 laser resurfacing system (Nidek, California) for the treatment of scars and wrinkles in patients with Type III and IV skin type. METHODOLOGY: This is a prospective study of patients with skin type III and IV who received laser-resurfacing treatment for facial scars and wrinkles. All patients received topical tretinoin 0.025% cream at least two weeks prior to laser resurfacing. Laser resurfacing was carried out under lidocaine 1% nerve blocks with the Unipulse CO2 laser scanning system. The power at tissue was set at 15 watts (fluence = 6.12 J/cm2; spot size = 1.02 mm, frequency = 300 Hz), with a 20% overlap. Lesions around the eyes were resurfaced with one pass. Those on other parts of the face with two to three passes. Patients were assessed up to 12 months. Treatment response (assessed by patient and dermatologist) was graded as "no change" = no improvement, "minimal improvement" = <25% clearance, "moderate improvement" = 25-50% clearance,"good improvement" = 50-75% clearance and "excellent improvement" = >75% clearance. Complications (assessed by dermatologist only) including erythema, hypopigmentation and hyperpigmentation were scored subjectively as none, minimal, mild, moderate and severe. RESULTS: 16 (nine females, seven males) patients were studied. Thirteen patients were treated for acne scars, two patients for wrinkles and one patient for chicken pox scar. Their mean age was 30.7 years (SD = 9.5 years). Fifteen patients had skin type IV and I had skin type III. TREATMENT RESPONSE: Thirteen patients were assessed at six weeks post laser treatment. One (8%) patient had "minimal improvement" (<25%) improvement, 10 (77%) patients had "moderate improvement" (25-50%) and 2 (15%) patients had "moderate improvement" (50-75%) improvement. At six months, 37% had "minimal improvement", 37% had "moderate improvement" and two had "good improvement and one patient with fine wrinkles had "excellent improvement". COMPLICATIONS: All patients experienced severe erythema at Day 1. Erythema faded over six months. By three months only 22% had minimal erythema and by six months none had erythema. Moderate pigmentation developed in 15% at six weeks. At three months 33% had varying degree of pigmentation. At six months one (12%) patient had residual pigmentation. Only one patient developed mild minimal hypopigmentation at six month, which cleared at 12 months. Another patient developed hypopigmentation at 12 months. CONCLUSION: CO2 laser resurfacing provides minimal to moderate improvements for scars and wrinkles among Asians with darker skin type. Erythema fades over six months after resurfacing. Post-inflammatory pigmentation is common but tends to clear over six months.

Adult↗
PubMed2002

Efficacy of the ramathibodi nasal filter in a simulated human airway evaluated by a laser diode portable dust monitor under low laser smoke particle concentration.

The Ramathibodi nasal filter attached to a simulated human airway was proposed to filter laser smoke particles. The simulated human airway composed of nasal and pharyngeal model, airway passage and lung model machine which mimicked the human respiratory system. The laser smoke particles represented a suspended particulate matter in a highly air-pollutted area such as at a main roadside in Bangkok. The experiment was done in the Department of Otolaryngology, Ramathibodi Hospital, from January to March 2000. The simulated human airway got an equal amount of laser smoke particles in a sealed plastic box for 1 min. The residual amount of laser smoke particles in a closed system of the simulated human airway was measured by a laser diode portable dust monitor for 1 min in each cycle and calculated as a mean and standard deviation. Without the Ramathibodi nasal filter of 39 sample pairs, the amounts of PM15, PM10 and PM2.5 were 52.3 +/- 6.8, 43.0 +/- 4.9 and 37.0 +/- 3.5 mcg/m3 respectively. With the Ramathibodi nasal filter of 39 pairs sample, the amounts of PM15, PM10 and PM2.5 were 48.1 +/- 9.9, 39.1 +/- 9.1 and 33.2 +/- 7.2 mcg/m3 respectively. Ramathibodi nasal filter efficacy for all laser smoke particle sizes evaluated statistically using t-test showed significant differences from those without the filter. Filtration efficacy should be tested further in higher concentrations of laser smoke particles and applied in human nasal vestibules under a critical air-polluted condition.

Air Pollutants, Occupational↗
PubMed1991

Argon laser pretreatment 4 to 6 weeks before Nd:YAG laser iridotomy.

Argon laser pretreatment followed by Nd:YAG laser iridotomy 4 to 6 weeks later was performed in the right eye of 10 patients. Primary Nd:YAG laser iridotomy was performed in the left eye. Significantly more Nd:YAG laser energy was needed to produce an iridotomy in pretreated eyes (P less than .001). Pretreated eyes developed a significantly larger pigment epithelium defect around the iridotomy site and a greater degree of pigmentation of the inferior part of the trabecular meshwork 6 months following treatment. Argon laser pretreatment followed by Nd:YAG laser iridotomy 4 to 6 weeks later appears to offer no advantages over primary Nd:YAG laser iridotomy.

Aged↗
PubMed1990

[A study on the application of Ga-As semiconductor laser to endodontics. The effects of laser irradiation on the activation of inflammatory cells and the vital pulpotomy].

The effects of laser irradiation on the activation of macrophage and fibroblast were examined by determining the rate of glucose utilization into the cell and the activity of lactate dehydrogenase (LDH) in culture supernatant. The laser irradiated macrophages that had been prepared from the peritoneal exudate cells, did not show any enhancement of activity, whereas fibroblast cell line (Gin 1 cell) were activated by laser irradiation. These findings suggest that laser irradiation was effective for the growth of fibroblast and induced suppressive effects for macrophage. In addition, effects of laser irradiation on the vital pulpotomy were investigated. It was observed that laser irradiation induced enhancement of calcification in wound surface and stimulated formation of calcified tissue. These observations indicate that laser irradiation is a useful method for the vital pulpotomy.

Calcification, Physiologic↗
PubMed1989

[Application of lasers in dentistry. Fundamentals of laser material processing in dentistry].

In connection with laser material processing in technical areas since the invention of laser technology it has been attempted to clear the way for the application of laser beams in the clinic itself and within dental technology. It has given a clear view of the fundamentals of the mechanisms of the laser interaction in laser material processing. In view of the first results of laser treatment of nonprecious and precious dental alloys, the possibilities of the application of lasers in the dental laboratory has been illustrated.

Dental Alloys↗
PubMed1995

Development of a new Er: YAG laser conception for laser sclerostomy ab externo: experimental and first clinical results.

The erbium:YAG laser is a preferable energy source for laser sclerostomy ab externo due to the high absorption of its radiation (2940-nm wavelength) in the aqueous parts of scleral tissue. It has thus far been a disadvantage that laser energy has to be transmitted from the laser source to the application site via very susceptible special optical fibers (ZrF). As a consequence of technical improvements, the laser source could be integrated into the application probe. Therefore, only a robust quartz fiber was necessary for contact application. A fiber diameter of 400 microns was chosen according to the experience gained in previous studies. A total of 24 eyes with chronical open-angle glaucoma were treated. A fistula end-point detection unit was developed for safe indication of a full-thickness perforation of the sclera. With a fiber diameter of 400 microns, a postoperative success rate of about 54% was achieved at 6 months follow-up. The automated full-thickness perforation detection prevented the application of additional, surplus laser pulses in the anterior chamber. The postoperative success rate could be improved over that achieved in previous studies. The new device/conception offers more technical reliability and is a further step toward minimally invasive fistulating laser surgery of open-angle glaucoma.

Erbium↗
PubMedDate not supplied

Noncontact laser photothermal keratoplasty. I: Biophysical principles and laser beam delivery system.

BACKGROUND: Thermal shrinkage of stromal collagen is known to produce changes in the corneal curvature. We designed a novel, noncontact laser beam delivery system to perform laser photothermal keratoplasty. MATERIALS AND METHODS: The instrument consisted of a pulsed holmium:YAG laser (2.10-micrometer wavelength, 250-microsecond pulse width, 5-hertz repetition rate) coupled via a monofilament fiber to a common slit-lamp microscope equipped with a polyprism, an adjustable mask, and a projection lens. The system projected an 8-spot annular pattern of infrared laser energy on the cornea to achieve a thermal profile within the stroma and to attain controlled, predictable collagen shrinkage. The system produced treatment patterns of 8 to 32 spots of 150 to 600 microns diameter in concentric rings, continuously adjustable between 3 and 7 mm. The versatility of the system in creating different treatment patterns was tested on thermal paper and human cadaver eyes. RESULTS: A uniform beam profile and different treatment patterns for myopia, hyperopia, and astigmatism were obtained. Myopic correction of 6.00 diopters was demonstrated on cadaver eyes. Corneal topography documented corneal flattening (> 6.00 D) with the following treatment parameters: each spot size on the cornea = 300 microns, radiant exposure of each spot = 18.0 J/cm2, number of pulses = 1, diameter of the treatment ring = 3 mm. CONCLUSIONS: Noncontact slit-lamp microscope laser delivery system for laser photothermal keratoplasty provides flexible and precise selection of laser treatment parameters. It may improve the efficacy of the procedure.

Cadaver↗
PubMed1996

Peroral laser lithotripsy of difficult intrahepatic and extrahepatic bile duct stones: laser effectiveness using an automatic stone-tissue discrimination system.

OBJECTIVES: The use of laser lithotripsy with an integrated stone-tissue discrimination system is an ambitious treatment modality for bile duct stone fragmentation. The aim of our prospective study was to determine the effectiveness and safety of the laser system and to find whether it reduced the need for choledochoscopy. METHODS: Thirty patients with complicated bile duct stones were treated perorally with a flashlamp-pulsed Rhodamine-6G dye laser and an automatic stone-tissue discrimination system. Initial treatment sessions were performed under fluoroscopic guidance in each patient and switched to choledochoscopic control if the stone could not be approached properly. RESULTS: Eighteen of 19 patients with extrahepatic bile stones were treated under fluoroscopic control; 17 of 19 patients were successfully treated through laser therapy. In nine of the patients with intrahepatic stones (n = 11), choledochoscopy was necessary for sufficient laser lithotripsy; seven of those patients became stone-free. Twenty-four of 30 patients (80%) were stone-free after sole laser therapy. Combined with other methods, the overall success rate was 27/30 (90%). Therapy-related mortality was 0%. CONCLUSIONS: Laser lithotripsy is effective and safe. The stone-tissue discrimination system facilitates therapy under fluoroscopic control and precludes the need for choledochoscopy, which is highly significant (p <0.001) if the calculi are extrahepatically located.

Adult↗
PubMed1997

Carbon dioxide laser-assisted hair transplantation. The effect of laser parameters on scalp tissue--a histologic study.

BACKGROUND: "Char-free" carbon dioxide lasers are capable of precise tissue vaporization with minimum residual thermal damage. These lasers deliver very high bursts of energy for extremely short durations, and can vaporize recipient sites during hair transplantation, which are consistent in depth and diameter. OBJECTIVE: To determine the depth of ablation and lateral thermal damage of scalp tissue using various laser parameters with the Sharplan 80XJ Silklaser. METHODS: Two hundred forty laser recipient sites were created, using 24 different laser parameters in each of 10 specimens of scalp tissue removed during scalp reduction. These specimens were evaluated histologically for depth of ablation and lateral thermal damage. RESULTS: While some laser parameters worked better regarding consistent depth of ablation of scalp tissue, lateral thermal damage was quite narrow (average, 20-50 microns). CONCLUSIONS: None of the laser parameters tested in this study should be problematic when used clinically for hair transplantation.

Hair↗
PubMed2004

Improvements in ion signal reproducibility obtained using a homogeneous laser beam for on-line laser desorption/ionization of single particles.

A major factor limiting on-line single particle mass spectrometry techniques from becoming more quantitative is the large shot-to-shot variability in ion intensities observed in the laser desorption/ionization (LDI) mass spectra.1,2 In previous work, lab-generated particles showed fluctuations of up to 152% in the absolute ion intensities in averaged spectra of 200-300 'identical' particles.2 Most of these fluctuations were attributed to inhomogeneities in the laser beam profile, leading to significant differences in the power each particle encountered depending on the position in the LDI laser beam where it underwent analysis. The goal of the work presented herein is to determine whether a fiber optic actually reduces the observed variability in single particle LDI mass spectral data. Initial results are presented for individual single component organic particles composed of 2,4-dihydroxybenzoic acid (2,4-DHB) analyzed using a low-power flat-top laser beam profile created by sending an ultraviolet (266 nm) DI laser through a fiber optic. Relative standard deviations of the total ion intensities for peaks in individual spectra are reduced to 31%. Single particle spectra, compared with and without laser homogenization at the same nominal laser fluence, show a marked enhancement. Specifically, the ion signal patterns of the 2,4-DHB particle spectra obtained using a homogenous LDI beam look identical to one another (i.e. only one particle type was produced with a commonly used neural network grouping algorithm), whereas without beam homogenization 25 different particle types (based on ion intensity patterns) were obtained. Future publications will explore more particle types and matrices but the initial results described herein are quite encouraging.

Journal Article↗
PubMed2002

Femtosecond laser time-of-flight mass spectrometry of labile molecular analytes: laser-desorbed nitro-aromatic molecules.

Femtosecond laser time-of-flight mass spectra of solid samples of trinitrobenzene (TNB), trinitrotoluene (TNT) and trinitrophenol (TNP) have been recorded. Desorption of the solid samples was enacted by the fourth harmonic output (266 nm) of a 5 ns Nd:YAG laser. Subsequent femtosecond post-ionisation of the plume of neutral molecules was achieved using 800 nm laser pulses of 80 fs duration. Mass spectra have been recorded for desorption laser intensities from 2-6 x 10(9) W cm(-2) with ionisation laser intensities between 2 x 10(14) and 6 x 10(15) W cm(-2). Femtosecond laser ionisation has been shown to be capable of generating precursor and characteristic high-mass fragment ions for labile nitro-aromatic molecules commonly used in high-explosive materials. This feature is critical in the future development of femtosecond laser-based analytical instruments that can be used for complex molecular identification and quantitative analysis of environmentally important labile molecules. Furthermore, a comparison of femtosecond post-ionisation mass spectra with standard 70 eV electron impact data has revealed similarities in the spectra and hence the fragmentation processes.

Journal Article↗
PubMed1991

Frequency stabilisation of multimode helium-neon lasers in laser Doppler flowmetry.

Low-frequency noise in laser Doppler recordings can be generated because of thermal instabilities in the gas laser cavity. Mode partition noise can be eliminated by thermal stabilisation of the laser cavity. The paper describes a method for closed loop temperature control of the laser cavity. The method uses orthogonal properties of longitudinal laser modes for the temperature control. The signal-to-noise ratio is considerably improved by the procedure. It is recommended that all gas laser equipped Doppler instruments used for precision blood flow studies should be equipped with stabilised laser sources.

Electricity↗
PubMed1998

XeCl laser surgery of the vocal cords: a histologic comparison with CO2 laser in a porcine model.

Fresh cadaveric pig larynxes were ablated with a CO2 (lambda = 10.6 microm) and a XeCl excimer (lambda = 308 nm) laser. Histologic comparison of the ablation craters created by the two lasers was performed, and ablation crater depth and marginal tissue damage were measured. Crater depth for both laser treatments is correlated with energy deposition and exposure time. The CO2 laser creates three times more nonspecific, marginal tissue damage than the XeCl laser at the ranges of total energy and exposure times used. This study demonstrates the potential of the XeCl laser as an alternative to the CO2 laser in microlaryngeal surgery.

Animals↗
PubMed2001

Dependence of the laser two-photon ionization process in solution on the laser pulse width.

The laser two-photon ionization process has been investigated using simultaneous irradiation of an UV beam and an IR beam. When the laser pulse width was 300 ps, it proceeded through a geminate pair state (a stepwise process), as indicated by the signal enhancement with simultaneous irradiation of the two laser beams. Although no signal enhancement was observed when the laser pulse width was 100 fs, and because molecules with no absorption at the laser wavelength showed an intense signal, the two-photon ionization excited by a femtosecond laser should proceed through a simultaneous two-photon process. The detection limit was quite susceptible to the laser fluctuations.

Journal Article↗
PubMed2004

Laser desorption and matrix-assisted laser desorption/ionization mass spectrometry of 29-kDa Au:SR cluster compounds.

Positive and negative ions generated by laser-based ionization methods from three gold:thiolate cluster compounds are mass analyzed by time-of-flight mass spectrometry. The three compounds have similar inorganic core masses ( approximately 29 kDa, approximately 145 Au atoms) but different n-alkanethiolate ligands associated with each cluster compound (Au:SR, R = butane, hexane, dodecane). Irradiation of neat films (laser desorption/ionization) and films generated by dilution of the cluster compounds in an organic acid matrix (matrix-assisted laser desorption/ionization) with a nitrogen laser (337 nm) produced distinct ion abundances that are relevant to different structural aspects of the cluster compound. Laser desorption/ionization of neat Au:SR compound films produces ions consistent with the inorganic core mass (i.e., devoid of original hydrocarbon content). Matrix-assisted laser desorption/ionization produces either ions with m/z values consistent with the core mass of the cluster compounds or ions with m/z values consistent with the approximate molecular weight of the cluster compounds, depending on ionization conditions. The ion abundances, and ionization conditions under which they are detected, provide insight into desorption/ionization processes for these unique cluster compounds as well as other analytes typically studied by matrix-assisted laser desorption/ionization.

Journal Article↗
PubMed1997

Characterization of a tunable optical parametric oscillator laser system for multielement flame laser excited atomic fluorescence spectrometry of cobalt, copper, lead, manganese, and thallium in buffalo river sediment.

A pulsed (10 Hz) optical parametric oscillator (OPO) laser system based on beta-barium borate (BBO) crystals and equipped with a frequency-doubling option (FDO) was characterized for use in laser excited atomic fluorescence spectrometry (LEAFS). This all-solid-state laser has a narrow spectral line width, a wide spectral tuning range (220-2200 nm), and a rapid, computer-controlled slew scan of wavelength (0.250 nm s-1 in the visible and infrared, and 0.125 nm s-1 in the ultraviolet). The output power characteristics (15-90 mJ/pulse in the visible, 1-40 mJ in the infrared, and 1-11 mJ in the ultraviolet), laser pulse-to-pulse variability (3-13% relative standard deviation, RSD, of the laser pulses), conversion efficiency of the FDO (2-17%), and spectral bandwidth in the visible spectrum (0.1-0.3 cm-1) were measured. The laser was used as the excitation source for a flame LEAFS instrument for which rapid, sequential, multielement analysis was demonstrated by slew scan of the laser. The instrument allowed about 640 measurements to be made in about 6 h, with triplicate measurements of all solutions and aqueous calibration curves, which yielded accurate analyses of a river sediment (National Institute of Standards and Technology, Buffalo River Sediment, 2704) for five elements with precisions < 5% RSD. Comparable or improved flame LEAFS detection limits over literature values were obtained for cobalt (2 ng mL-1), copper (2 ng mL-1), lead (0.4 ng mL-1), manganese (0.2 ng mL-1), and thallium (0.9 ng mL-1) by flame LEAFS.

Calibration↗
PubMed2005

Thermo-kinetics study of laser-induced desorption of self-assembled monolayers from gold: case of laser micropatterning.

Laser-induced desorption of self-assembled monolayers (SAMs) from gold surfaces within context of the direct laser patterning methodology was investigated through combining results of a heat diffusion thermal model with desorption kinetics of alkanethiol SAMs. It was found that contrast plots of experimental scanning electron microscopy (SEM) images, which are correlated to surface coverage of SAMs desorbed after laser irradiation, agreed with the theoretically predicted surface composition of SAMs. The surface composition of SAM was then interpreted in terms of the wetting property of the resulting surface. The effect of incident laser beam power and size on the final spatial coverage of SAMs on the surface and feature sizes was investigated both experimentally and by modeling. Theoretical modeling and experimental evidence showed that the resulting feature sizes are wider when the surface is heated by a laser of higher power. Increasing the laser beam size results in broadening of feature sizes. Considering the correlation of the theoretical and experimental results, we concluded that the feature sizes are controllable in a predictable way (using the presented thermal-kinetics model) through varying laser beam power and beam size.

Journal Article↗
PubMed2005

Stepwise photocleavage of C-O bonds of bis(substituted-methyl)naphthalenes with stepwise excitation by two-color two-laser and three-color three-laser irradiations.

Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2* or ROCH2NpCH2*) in almost 100% yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C-O bond cleavage occurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (T(n)). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C-O bond cleavage from the T(n) states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2NpCH2*) when the T1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2* in the ground state [1,8- and 1,4-ROCH2NpCH2*(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2*(D(n))] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.

Journal Article↗