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At least 109 records · Page 6Linked to original sources

PubMed2001

The effect of axial length on laser spot size and laser irradiance.

OBJECTIVE: To determine the effect of the axial length of the eye on laser spot size and irradiance. DESIGN: Experimental study using a calibrated Gullstrand-type model eye. METHODS: The model eye, which was fitted with a scale of half circles in the center of the artificial fundus, was first examined using 2 different fundus imaging systems, then with a setup of a slitlamp, 2 indirect condensing laser lenses, and a laser unit with a spot size of up to 7 mm. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the magnifications of the fundus imaging systems and the laser lenses were calculated and compared for a treatment spot with a diameter of 4 mm. The laser irradiance for treating the spot at different axial lengths was also recorded. RESULTS: Whereas the magnification of a fundus imaging system is inversely related to the axial length, the laser spot size is directly related to axial length when using indirect condensing laser lenses. Therefore, the changes of magnification produced by axial ametropia are mostly compensated, so that the intended size of the treatment spot is obtained even in eyes with a high axial ametropia. The laser irradiance, on the other hand, has a significant variation for the observed range of the axial length. CONCLUSION: Axial length has a significant effect on laser spot size and laser irradiance. CLINICAL RELEVANCE: The effect of axial length on laser spot size and laser irradiance may be ignored when administering photodynamic therapy with verteporfin but has to be considered for transpupillary thermal treatment of choroidal neovascular lesions.

Choroidal Neovascularization↗

PubMed1997

Side effects from dermatological laser treatment related to UV exposure and epidermal thickness: a murine experiment with the copper vapor laser.

BACKGROUND AND OBJECTIVE: The intention of the present study was to clarify whether UV-exposure prior to laser treatment of albino mouse skin may influence laser-induced side effects and if a possible influence may be explained by epidermal thickening. STUDY DESIGN/MATERIALS AND METHODS: Albino, hairless mice were irradiated 0, 8, and 22 consecutive times with simulated solar UV (1.4 J/cm2 per treatment). Subsequently, two areas on the back of the mice (1.26 cm2 each) were treated with a copper vapor laser that was connected to a Hexascan. The beam diameter was 1 mm, pulse duration 200 msec, and intensities 0.6 W, 0.8 W, and 1.0 W. Laser-induced wounds, scars, and histologically evaluated fibrosis were evaluated. RESULTS: We found that mice irradiated with UV before laser treatment developed smaller wounds, smaller texture change areas, and less fibrosis as compared with nonirradiated control groups, and significant, negative correlations were demonstrated between epidermal thicknesses (stratum corneum, the cellular part of epidermis, and the entire epidermis) and laser-induced skin reactions. A dose response was obtained between laser intensities and laser-induced skin reactions, which tended to be more severe in the cranial back location as compared with the caudal back location. Epidermal layers increased significantly after eight consecutive times of UV irradiation and increased to a steady level after 22 times of irradiation. CONCLUSION: We conclude that UV exposure prior to laser treatment of albino mice reduced laser-induced side-effects, which could be explained by increased epidermal thickening. Variations in epidermal thickness might thus contribute to variations in clinical response to dermatological laser treatment with the copper vapor laser.

Animals↗

PubMed1997

Comparison of a high power diode laser with the Nd:YAG laser using in situ wound strength analysis of healing cutaneous incisions.

BACKGROUND AND OBJECTIVE: The laser-tissue interaction of a high power semiconductor diode laser was compared to the continuous wave neodymium yttrium aluminum garnet (Nd:YAG) laser by evaluating primary wound healing of cutaneous incisions in rats. STUDY DESIGN/MATERIALS AND METHODS: Full thickness incisions were made in rat skin using a diode laser (805 nm, 10 W, contact mode), an Nd:YAG laser (1,064 nm, 10 W, contact mode), and a stainless steel scalpel blade (control). In situ wound breaking strength measurements were obtained at 7, 14, and 21 days using a specially designed tensiometer. Cross sectional area of non-disrupted wounds was calculated in two groups prior to testing to allow for calculation of tensile strength. Blinded histopathologic analysis was also performed. RESULTS: Analysis of variance (P < or = 0.05) was used to determine differences in breaking strengths and tensile strengths due to incision method. There was no significant difference in the breaking strengths (group 1) or tensile strengths (groups 2 and 3) of the diode and Nd:YAG laser incisions. As predicted, breaking strengths and tensile strengths of scalpel blade incisions were significantly greater than those of incisions made with laser energy. Histopathologic evaluation revealed that through day 14, the degree of inflammation and collagen production was similar for diode and Nd:YAG laser incisions. Laser incisions had greater inflammation and a lag in fibroblast invasion and collagen production compared with scalpel incisions. By day 21, all incisions were similar in fibroblast population and collagen production, but laser incisions had slightly more inflammation than scalpel incisions. CONCLUSION: In the primary wound healing model described, the tissue effect, cellular response, and development of wound strength were essentially the same for the high power diode laser at 10 W and the Nd:YAG laser at 10 W.

Animals↗

PubMed1990

Endometrial laser ablation in rabbits: a comparative study of three laser types.

Endometrial laser ablation is one of the alternatives to hysterectomy in cases of intractable uterine bleeding. It is currently performed using the Nd:YAG laser at 1.06 microns. The aim of this study was to compare the tissue effect of three types of laser irradiation (Nd:YAG laser at 1.06 and 1.32 microns and holmium laser at 2.12 microns) on the rabbit endometrium. Crater formation, coagulation necrosis, and muscle necrosis were evaluated at the time of ablation, as well as at 1 week and 4 weeks postablation. The results were assessed by determining the depth and width of the affected portion in the uterine wall (lumen to serosa). It was shown that Nd:YAG laser at 1.32 microns caused more generalized and extended effects as compared with the other laser types examined. Endometrial regeneration was faster after ablation by the Nd:YAG laser at 1.06 microns and the holmium laser than by the Nd:YAG laser at 1.32 microns. The widest range of "ablation energy" (defined as that causing ablation without muscle damage) was achieved by applying the holmium laser. Further evaluation of the holmium laser for this indication is recommended.

Animals↗

PubMed1999

Laser-assisted hair removal: side effects of Q-switched Nd:YAG, long-pulsed ruby, and alexandrite lasers.

BACKGROUND: Laser-assisted hair removal has become popularized using wavelengths in both the red and infrared regions of the electromagnetic spectrum. These photoepilation devices target follicular melanin or an exogenous pigment placed within the follicle resulting in thermal damage to the hair follicle and shaft. However, melanocytes and keratinocytes located within the superficial layers of the skin also absorb red and infrared laser radiation. This may result in unwanted epidermal injury during the hair removal process. OBJECTIVE: The purpose of this study was to examine a large patient population to determine the frequency of side effects using 3 different hair removal laser systems with various wavelengths, pulse durations, and treatment protocols. METHODS: A retrospective chart review and digital photographic analysis of the side effects resulting from 900 consecutive laser-assisted hair removal treatments delivered over a 24-month study period, by means of either a Q-switched Nd:YAG laser with pretreatment wax-epilation and topical carbon solution, a long-pulse ruby laser with a contact cooling tip, or a long-pulse alexandrite laser are reported. RESULTS: Treatment pain, erythema, edema, hypopigmentation and hyperpigmentation, blistering, crusting, erosions, purpura, and folliculitis were observed. The majority of undesirable tissue effects occurred on tanned skin or in Fitzpatrick skin phototypes III and higher. The ruby and alexandrite laser systems resulted in the majority of side effects seen. The effects of seasonal variations, anatomic treatment location, and sun exposure were striking within the ruby and alexandrite laser groups. No infections, scarring, or long-term complications occurred. CONCLUSION: Laser-assisted hair removal is a safe procedure when patient characteristics such as skin type, anatomic location, and sun-exposed or tanned skin are considered during selection of laser treatment parameters. Lasers emitting wavelengths with high melanin absorption capabilities should be used in a conservative manner when treating patients with dark skin phototypes or suntans. No long-term complications, infections, or scarring occurred in this study population.

Adult↗

PubMed1999

A clinical and histologic prospective controlled comparative study of the picosecond titanium:sapphire (795 nm) laser versus the Q-switched alexandrite (752 nm) laser for removing tattoo pigment.

BACKGROUND: Theory predicts that picosecond lasers should be more effective than the currently available nanosecond lasers in removing tattoo ink. In addition to thermal confinement, such pulse widths cause optimal photomechanical disruption of the target. OBJECTIVE: This study compared the efficacy of the picosecond titanium:sapphire (795 nm, 500 psec) laser and the Q-switched alexandrite (752 nm, 50 nsec) laser in the treatment of tattooed guinea pigs. METHODS: Six albino guinea pigs, each with 6 uniformly 1 cm circular black tattoos, were treated. Three of the tattoos were divided into 2; one half was treated with the titanium:sapphire laser and the other half with the alexandrite laser. Fluences used for both lasers were 6.11, 4.24, and 2.39 J/cm2 with spot sizes of 1.25, 1.5, and 2 mm, respectively. The remaining spots served as control. Clinical evaluation and biopsies were performed at baseline and at 11 and 16 weeks after a single laser treatment. RESULTS: Greater clearance of tattoo was observed in titanium:sapphire laser-treated areas in 2 of the 4 surviving guinea pigs. In some areas total clearing was observed after the single titanium:sapphire laser treatment. Clearing improved with higher fluences. No scarring was present. Histologic results showed similar findings. CONCLUSION: Our findings suggest that the picosecond titanium:sapphire laser is more effective than the Q-switched alexandrite laser in removing tattoo pigment and may be of significant clinical utility.

Animals↗

PubMed2005

Soot particle disintegration and detection by two-laser excimer laser fragmentation fluorescence spectroscopy.

A two-laser technique is used to study laser-particle interactions and the disintegration of soot by high-power UV light. Two separate 20 ns laser pulses irradiate combustion-generated soot nanoparticles with 193 nm photons. The first laser pulse, from 0 to 14.7 J/cm2, photofragments the soot particles and electronically excites the liberated carbon atoms. The second laser pulse, held constant at 13 J/cm2, irradiates the remaining particle fragments and other products of the first laser pulse. The atomic carbon fluorescence at 248 nm produced by the first laser pulse increases linearly with laser fluence from 1 to 6 J/cm2. At higher fluences the signal from atomic carbon saturates. The carbon fluorescence from the second laser pulse decreases as the fluence from the first laser increases, suggesting that the particles fully disintegrate at high laser fluences. We use an energy balance parameter, called the photon/atom ratio, to aid in understanding laser-particle interactions. These results help define the regimes where photofragmentation fluorescence methods quantitatively measure total soot concentrations.

Carbon↗

PubMed1999

[Critical evaluation of indications for the holmium:YAG laser and the neodymium:YAG laser in orthopedic surgery based on an in vitro study].

This is an in vitro study of the biophysical effects of holmium:YAG and neodymium-YAG lasers that was prompted by the poor clinical results obtained with lumbar percutaneous laser discus decompression (PLDD). In the absence of adequate cooling, ablation of tissue with the holmium:YAG laser causes thermal damage to the surrounding tissues. Utilizing the immediate colour-independent laser coupling effect, the holmium:YAG laser removes soft and hard tissue immediately. The low tissue penetrating power (max. 0.32 mm), together with the use of irrigation, avoids thermal problems, and this laser type with its high pulse energy and frequency is to be recommended for arthroscopic surgery. In contrast, the effects of the neodymium:YAG laser are highly dependent on tissue colour. Using this laser on light-coloured tissue only diffuse warming but no ablation of soft tissue was often seen. The depth of tissue penetration seen in our study was 0.58 mm, but is greatly dependent on the duration of application, and is much larger with long application times. In conclusion, we believe that the neodymium:YAG laser is more suitable for percutaneous intradiscal procedures than the holmium:YAG laser. For arthroscopic surgery, the holmium:YAG laser will be the better choice. The effect of each type of laser depends not only on its physical properties, but also on tissue properties (light or dark-coloured, thermal conductivity) and duration of application.

Adult↗

PubMedDate not supplied

Picosecond laser in situ keratomileusis with a 1053-nm Nd:YLF laser.

BACKGROUND: Excimer laser in situ keratomileusis requires a microkeratome to generate an anterior corneal flap, plus an excimer laser to ablate the underlying stromal tissue. In this paper we introduce the concepts of laser flap formation and in situ keratomileusis using a picosecond laser. METHODS: A neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser with a plano-plano quartz applanation lens was used to generate various patterns of intrastromal photodisruption in human donor eyes to fashion anterior corneal flaps and generate intrastromal lenticules. RESULTS: Smooth intrastromal dissections, 6 mm in diameter, were generated 160 microns below the corneal surface when the laser delivered pulses at 1 kHz with energies of either 40 microJ/pulse or 60 microJ/pulse, placed 20 microns apart in an expanding spiral. This enabled us to fashion anterior corneal flaps. The ease of the surgery and quality of the dissection corresponded well, and it was evident that both deteriorated noticeably when the laser pulses were separated by 25 microns or 30 microns, regardless of pulse energy. Using 40 microJ laser pulses placed 20 microns apart we also created a 5-mm diameter, 320 microns thick (130 microns-450 microns deep) stromal lenticule below a corneal flap that was easily extracted when the flap was raised. CONCLUSIONS: Anterior corneal flaps were easily fashioned using a Nd:YLF laser. Picosecond laser in situ keratomileusis with a Nd:YLF laser could offer a favorable alternative to combined microkeratome/excimer laser in situ keratomileusis.

Cornea↗

PubMedDate not supplied

Laser thermal keratoplasty using a continuous wave diode laser.

BACKGROUND: Laser thermal keratoplasty is currently performed with a pulsed Ho:YAG laser at 2.07 microns wavelength. Long-term stability depends critically on the coagulation depth of each cone and thus on emission wavelength (absorption in corneal tissue) and focusing, all contributing to controlled stable collagen shrinkage. To achieve this, a temperature range of 65 degrees to 90 degrees C is needed. A continuous wave laser source meets the coagulation requirements more effectively by avoiding tissue cooling by thermal diffusion as well as the peak temperatures of pulsed lasers, which counteracts the intended central corneal steepening. METHODS: A continuous wave diode laser was developed, emitting at 1.885 microns with a maximal energy output of 450 mW. In a contact focusing application, the absorption depth in water as a function of wavelength was measured. Using laser parameters, comparable to those used for a pulsed Ho:YAG laser in contact mode, coagulation spots in human cornea were applied for the continuous wave diode laser. RESULTS: The macroscopic and microscopic effects of the diode laser coagulation on corneas in vitro and in situ were comparable to those of the Ho:YAG laser, if a comparable amount of total energy per spot was applied. CONCLUSION: Due to better optimized laser-collagen interaction, higher corrections and more stable clinical refractive effects appear achievable using the continuous wave diode laser.

Cadaver↗

PubMed1991

[Reparation of the vascular wall after laser recanalization of the artery (characteristics of changes in the vascular wall at a late period after laser recanalization)].

Chronic experimental studies were carried out on 9 mongrel dogs. To study the reparation processes in the arterial wall after laser intervention, arteries of different anatomic zones were irradiated with laser: descending and abdominal aorta, iliac, femoral and axillary arteries. To make a laser trauma, two types of laser catheters were used: a) with the light guide with diameter of 400 and 600 microns; and b) with a quartz tip at the end. The laser light source was a laser of Cu vapors, and ND; YAG laser. Laser energy was transmitted in the form of individual impulses with the duration of 2-5 sec, and power of 8-10 watt. Histological studies of the preparations of the irradiated arterial wall were performed at periods: 1-3-7-16-28 days, and 2-8 months. Characteristic signs of the vascular wall reparations are given. The analysis of the experimental results showed that by the 28-th day after laser trauma, on the site of laser irradiation a connective tissue scar was formed substituting the defect in the vascular wall and covered from the lumen side with a thin continuous layer of endothelium without any signs of inflammatory infiltration. The development of intimal hyperplasia is not excluded, as well as of inflammatory reaction with the following thrombotic occlusion of the artery lumen. The study results can be used in clinical practice in order to determine the optimum tactics and performance of laser recanalization of the artery, as well as the treatment after the laser intervention.

Angioplasty, Laser↗

PubMed1994

13CO2 isotopic laser used through the operating channel of laser laparoscopes: a comparative study of power and energy density losses.

OBJECTIVE: To evaluate the power transmission, spot size, power density, and energy density of a new isotopic carbon dioxide (13CO2) laser compared with a conventional CO2 laser. METHODS: Experiments were performed in a laboratory using a conventional CO2 laser and an isotopic 13CO2 laser. Two laparoscopes with 5-mm and 7.5-mm operating channels were connected to a standard coupler and to each of the lasers. Standardized measurements were made of power transmission and spot size using both nitrogen purge gas and CO2 purge gas at rates of 1-20 L/minute. Power density and energy density were calculated for continuous mode and ultrapulse mode transmission, respectively. RESULTS: The isotopic 13CO2 laser power transmission was higher and proportional to input power, while spot size was smaller compared with the conventional laser and was insensitive to power level or purge rate. Power density and energy density were markedly higher with the isotopic 13CO2 laser, reaching the threshold for complete ablation, and were much more predictable. The 7.5-mm operating channel generally had superior operating results compared with the 5-mm channel because of the smaller spot size and higher power transmission. CONCLUSIONS: The isotopic 13CO2 laser is associated with much higher power density and energy density capabilities than are conventional CO2 lasers. At surgery, we have noted less thermal injury, faster ablation, more precise and predictable tissue effects, and greater control of tissue effect with the isotopic 13CO2 laser than with other CO2 lasers. These results are attributed to the improved beam propagation through CO2 insufflation gas measured in the laboratory. Thermal injury can be varied according to the required surgical situation and can be kept to an absolute minimum at high-pulse energy.

Carbon Dioxide↗

PubMed2001

[Lasers in dentistry. Part A--Development, characteristics, structure, principles of operation and types of lasers].

Laser technology is developing very quickly. New Lasers with a wide range of characteristics are available today and are being used in the various fields of dentistry. The search for new devices and technologies for dental procedures was always challenging and in the last two decades much experience and knowledge has been gained. The purpose of this series of articles published in the journal of the Israel Dental Association in three parts is to present the Israeli dentist a comprehensive and contemporary overview which will assist him in understanding the potential of the use of laser technology for clinical applications in dentistry. The first part will describe the history and development of lasers in dentistry, the characteristics and structure of lasers as well as their principles of operation. A description of the different types of lasers used today in dentistry will be presented in the first part. The second part will describe the interaction of lasers with biological tissues and their effect on the soft and hard tissues of the oral cavity as well as on the dental pulp. Laser safety in the dental practice will also be discussed. The third part will focus on clinical applications of Lasers in Dentistry: pits and fissures sealing, dentin desensitization, cavity preparations, composite curing, surgical procedures and tooth whitening. Current status of using lasers in periodontics, endodontics and dental implantology will be discussed and possible future clinical applications of lasers in dentistry will be presented.

Argon↗

PubMed2002

Treatment of pigmented hypertrophic scars with the 585 nm pulsed dye laser and the 532 nm frequency-doubled Nd:YAG laser in the Q-switched and variable pulse modes: a comparative study.

BACKGROUND: Pigmented hypertrophic scars are a difficult condition to treat. They may result from traumatic injuries or from surgical and cosmetic procedures. The 585 nm flashlamp-pumped pulsed dye laser (FLPDL) has been used to treat this condition, with significant improvement of varying degrees. It remains to be determined whether other laser modalities may have a similar or even greater success in the treatment of pigmented hypertrophic scars. OBJECTIVE: To determine the efficacy of the 532 nm frequency-doubled Nd:YAG laser in the treatment of pigmented hypertrophic scars as compared to the 585 nm FLPDL. METHODS: Six patients with pigmented hypertrophic scars and skin phototypes II-IV were chosen. A scar was selected for treatment in each patient and divided into four equal 2 cm segments. Three segments were each treated with a different laser modality and one was left untreated to serve as the control. A 585 nm FLPDL was used with an energy of 3.5 J, a pulse duration of 450 microsec, and a 10 mm spot size. A 532 nm Q-switched frequency-doubled Nd:YAG laser was set to an energy of 2.8 J, a 10-nsec pulse, and a 3 mm spot size. The same 532 nm laser was set to the variable pulse mode to treat a 2 cm scar segment, with an energy of 9.5 J, a 10-msec pulse, and a 4 mm spot size. An average of 3.3 treatments were performed on each scar segment, at intervals of 4-6 weeks and long-term follow-up at 22 weeks. Treatment outcome was graded by a blind observer using the Vancouver General Hospital (VGH) Burn Scar Assessment Scale. A SigmaStat t-test was used to determine the statistical significance of the values obtained. RESULTS: Treatment of pigmented hypertrophic scars with the 532 nm Q-switched Nd:YAG laser led to a significant improvement of 38% in the VGH scores when compared to baseline (P =.005). The 585 nm FLPDL also had a favorable effect on the scars, with an average improvement of 36.1% in the VGH scores. There was no significant difference noted between the outcome of treatment with either of these two lasers. Treatment with the 532 nm variable pulse Nd:YAG laser led to a 19% improvement in the VGH scores of scars, which did not differ significantly from the 16.1% improvement observed in control scars on the last follow-up visit. No side effects or complications from treatment were noted or reported during the course of the study. At the conclusion of the study, five of six patients chose the segment treated with the 532 nm Q-switched Nd:YAG laser as the best segment overall. CONCLUSION: The 532 nm Q-switched Nd:YAG laser and the 585 nm FLPDL offer comparable favorable results in the treatment of pigmented hypertrophic scars. The 532 nm Q-switched Nd:YAG laser may be preferred by patients particularly distressed by the dark color of their scars.

Adolescent↗

PubMed1989

Laser physics and laser-tissue interaction.

Within the last few years, lasers have gained increasing use in the management of cardiovascular disease, and laser angioplasty has become a widely performed procedure. For this reason, a basic knowledge of lasers and their applications is essential to vascular surgeons, cardiologists, and interventional radiologists. To elucidate some fundamental concepts regarding laser physics, we describe how laser light is generated and review the properties that make lasers useful in medicine. We also discuss beam profile and spotsize, as well as dosimetric specifications for laser angioplasty. After considering laser-tissue interaction and light propagation in tissue, we explain how the aforementioned concepts apply to direct laser angioplasty and laser-balloon angioplasty. An understanding of these issues should prove useful not only in performing laser angioplasty but in comparing the reported results of various laser applications.

Journal Article↗

PubMed1998

[Postoperative proliferative vitreoretinopathy in rhegmatogenous retinal detachment associated with stage B preoperative proliferative vitreoretinopathy: comparative results of trans-scleral retinopexy with diode laser or trans-pupillary retinopexy with argon laser].

PURPOSE: To compare the rate of severe postoperative PVR in primary rhegmatogenous retinal detachments (RD) associated with preoperative grade B PVR and managed either with transpupillary Argon laser photocoagulation or transscleral Diode laser photocoagulation. MATERIAL AND METHODS: We evaluated 72 primary rhegmatogenous retinal detachment associated with preoperative grade B PVR (retinal tears with curled posterior edges), referred before any failed attempt to reattach the retina. Eleven RD were due to giant tear. The retinopexy was performed using transpupillary Argon laser. photocoagulation in 46 eyes, and transscleral Diode laser photocoagulation in 26 eyes. Follow up was 6 to 30 months. Statistical analysis used Chi-square test, and variance analysis. RESULTS: The overall rate of postoperative PVR was 6.9% (5/72 eyes). The rate of postoperative PVR was 6.5% (3/46) in eyes managed with Argon laser photocoagulation and 7.7% (2/26) in eyes managed with Diode laser photocoagulation (p > 0.05). The rate of postoperative PVR in RD due to horseshoe tears was 5.4% (2/37) in eyes managed with Argon laser and 8.3% (2/24) in eyes treated with Diode laser (p > 0.05). The rate of postoperative PVR in giant tear was 11.1% (1/9) in eyes managed with Argon laser photocoagulation and 0% (0/2) in eyes managed with Diode laser photocoagulation (p > 0.05). CONCLUSION: In the present series the rate of postoperative PVR was not influenced by the method of photocoagulation (transpupillary Argon laser or transscleral Diode laser). Therefore each technique can be used as the retinopexy method in primary rhegmatogenous retinal detachment associated with preoperative grade B PVR.

Adolescent↗

PubMed2005

Possible application of transmitted laser light for the assessment of human pulp vitality. Part 2. Increased laser power for enhanced detection of pulpal blood flow.

The purpose of this study was to investigate the effect of an increase in laser power on the transmitted laser signals from vital and non-vital teeth, in the hope of achieving a better assessment of human pulp vitality with the transmitted laser-light flowmeter. The experiments were carried out on total of 61 vital teeth with no restoration (19 upper central incisors, 16 upper lateral incisors, 16 upper canines, and 10 first premolars) and five non-vital upper central incisors (the root canals of which were filled with gutta-percha) in 15 subjects aged 22-28 years. For use with transmitted laser light, the fibers within the probe of a conventional laser Doppler flowmeter (LDF) apparatus were used, one for transmitting light onto the labial surface, the other for receiving it at the palatal surface of the same tooth, as reported previously. Laser output power was set at the original 2 mW and also at 5, 7, and 10 mW. The number of vital teeth displaying a blood flow (BF) signal at each laser power setting was: 1) 12/19 central incisors at 2 mW, 19/19 at 5, 7, and 10 mW, 2) 19/19 lateral incisors at 2, 5, 7, and 10 mW, 3) 0/16 canines at 2 mW, but eight, 12, and 14 at 5, 7, and 10 mW, 4) 0/10 first premolars at 2, 5, 7, and 10 mW. Thus, an increase in laser power increased BF detection from the thicker teeth (but not from premolars). In addition, clearer BF signals synchronized with heart rate, and greater passive BF changes secondary to blood pressure (BP) changes were observed at higher laser settings. In non-vital teeth, no signals synchronized with heart rate or BP changes were observed, indicating that no BF signal of non-pulpal origin was ever monitored with this ballistic light even when the laser power was increased. These results indicate that high-powered transmitted laser light could be a useful tool both for monitoring pulpal BF and for the assessment of tooth-pulp vitality.

Adult↗

PubMed1993

Efficacy of carbon monoxide laser in selectively intimal thermal welding--implications for laser balloon angioplasty.

Excessive vascular damage causes excessive vascular repair, which results in restenosis. To limit the thickness of the coagulation layer in laser balloon angioplasty, we used a carbon monoxide (CO) laser, which has high tissue absorption, as a therapy laser source instead of a Nd: YAG laser. To investigate the benefit of short-penetration CO laser light to vascular tissue, excised human abdominal aorta was irradiated with a CO laser through a 30 microns polyethylene membrane. The temperature of the vascular tissue was continuously monitored during irradiation. CO laser irradiation of 20 W/cm2 was performed in either a continuous mode or an intermittent mode with various duty ratios (exposure/interval duration). With a total fluence of 200 J/cm2, the adventitial temperature decreased as the duty ratio was reduced. The adventitial temperature at a duty ratio of 1:2 was 43 degrees C. Microscopic examination of aorta which had been intermittently irradiated duty ratio of 1:2 showed thermal coagulation localized within the intima and a flattened intimal surface. These results suggest that intermittent laser irradiation with a CO laser can be used to limit the depth of thermal coagulation, and can selectively weld the intima without excessive thermal damage. Laser balloon angioplasty using a CO laser may help to prevent restenosis.

Angioplasty, Balloon, Laser-Assisted↗