The effect of optical design on micromanipulator spot size using CO2 laser irradiation

Objective: The study goal was to compare the laser spot size created using reflective and refractive micromanipulators with a CO₂ laser and to determine the sensitivity of spot size to laser power. Study Design and Setting: A CO₂ laser and operating microscope (400-mm focal length) was coupled to either a reflective (Cassegrain-like) or refractive micromanipulator. Laser spot size was determined by measuring the region of ablation created by laser irradiation of wood (dry tongue depressors), exposed photographic film, and agar gel using optical micrometry. Laser power varied from 0.5 to 20 W with pulse durations of 0.1 and 0.5 second. Results: The reflective micromanipulator demonstrated overall smaller spot sizes for a given laser power and lower incremental change in spot size with increasing power. The reflective design demonstrated less sensitivity to increases in laser power. Conclusions: Micromanipulator optical design can result in significant differences in laser spot size. The reflective device used in this study demonstrated less sensitivity to increasing laser power. (Otolaryngol Head Neck Surg 2002;126:593-597.)     

The effect of optical design on micromanipulator spot size using CO2 laser irradiation.

OBJECTIVE: The study goal was to compare the laser spot size created using reflective and refractive micromanipulators with a CO(2) laser and to determine the sensitivity of spot size to laser power. STUDY DESIGN AND SETTING: A CO(2) laser and operating microscope (400-mm focal length) was coupled to either a reflective (Cassegrain-like) or refractive micromanipulator. Laser spot size was determined by measuring the region of ablation created by laser irradiation of wood (dry tongue depressors), exposed photographic film, and agar gel using optical micrometry. Laser power varied from 0.5 to 20 W with pulse durations of 0.1 and 0.5 second. RESULTS: The reflective micromanipulator demonstrated overall smaller spot sizes for a given laser power and lower incremental change in spot size with increasing power. The reflective design demonstrated less sensitivity to increases in laser power. CONCLUSIONS: Micromanipulator optical design can result in significant differences in laser spot size. The reflective device used in this study demonstrated less sensitivity to increasing laser power.     

Diode laser and microvascular carotid anastomosis: A preliminary study

A crossed carotid end-to-end anastomosis was performed in 20 Wistar rats by means of a diode laser device (wavelength 830 nm and power output 3 W in continuous wave). The diode laser energy was delivered into a micromanipulator coupled to an OPMI 1 Zeiss operating microscope with a focused spot of 300 μm diameter. The vessel sealing was effected on common carotids (0.8–1.2 mm) using laser shots (average 9) of 680 mW power and 4.5 s duration and 962 W cm⁻² irradiance each. The good vascular flow was confirmed by Doppler spectral analysis and angiography performed on days 0, 10 and 30. Light and scanning electron microscopy showed that reendothelialization was complete on day 10 whilst collagenous fusion of media and adventitia was obvious. The patency rate was 90% impaired by a lethal thrombosis. The efficiency of the diode laser was compared to that of other types of LAVA and to manual microanastomosis.     

IR Lasers and Application Systems for Myringotomy

. The study examines an Er:YAG laser (2940 nm) and different application systems of the CO₂ laser (10 600 nm) with regard to their suitability for a one-shot laser myringotomy of an adequate perforation size (∼2 mm). The laser–tissue interaction of the Er:YAG laser and the CO₂ laser in fresh tympanic membranes of horses (thickness: 80–100 μm) as well as in formalin-fixed human tympanic membranes (thickness: 100 μm) is studied correlating perforation diameters to the applied power/energy density and the effects demonstrated by light and scanning electron microscopy are analysed. Using the Er:YAG laser with a focused laser beam (spot diameter: 400 μm) or with a maximally defocused laser beam (spot diameter: 1600 μm) perforations of an adequte size (2 mm) can only be achieved with multiple laser pulses. Histological studies disclose only minimal thermic side effects in the adjacent tissue in both specimens. If the CO₂ laser radiation is transmitted via a silver halide polycrystalline fibre (diameter: 900 μm) a maximal perforation diameter of 1300 μm is achieved with significant thermic side effects such as coagulation. Using an Acuspot™ 710 micromanipulator (focused beam diameter: 180 μm) combined with a SilkTouch™ scanner a maximal perforation diameters of 1700 μm can be achieved in horse tympanic membrane with one laser pulse. A prototype of a hand-held CO₂ laser otoscope in combination with the SilkTouch™ scanner is suitable for performing laser myringotomies with a diameter of 2 mm with a single laser pulse in fresh horse tympanic membrane. Paper received July 1999; accepted after revision December 1999.     

Thermal imaging of the temporal bone in CO 2 laser surgery: An experimental model

The unique properties of lasers create an enormous potential for specific treatment of chronic ear disease. Despite the widespread acceptance and use of the laser, however, a complete understanding of the time- and space-dependent temperature distribution in otic capsule bone immediately after pulsed laser exposure has not been elucidated. Using a liquid nitrogen-cooled mercury-cadmium telluride infrared detector, the temperature distribution in human cadaveric otic capsule bone was determined immediately after pulsed (100 msec) carbon dioxide laser exposure (0.3 to 4.0 W; 200 μm spot diameter). The time- and space-dependent temperature increases and thermal diffusion were determined as a function of the laser power density and were found to vary linearly. (Otolaryngol Head Neck Surg 1997;117:610-5.)     

Multifiber gradient-index lens laser angioplasty probe

A novel laser angioplasty probe fabricated with a gradient-index (GRIN) lens positioned at the tip of a seven-fiber bundle is presented. The combination of the GRIN lens and the fiberoptic bundle provides selectable optical directionality in either the axial direction or one of six off-axis directions for illumination of the arterial wall. The probe diameter (1 mm) is small enough for use in coronary laser angioplasty, and the probe is shown to transmit laser light and receive fluorescent signals simultaneously. In a 2 mm diameter lumen, the spot width in a plane normal to the axis of the lens is about 2 mm and the lateral spot size is approximately 10 mm long. The ability to direct the probe's beam pattern angularly should provide flexibility in both diagnosis and treatment.     

Photocoagulation with a copper vapour laser in rabbit liver: A comparative study between the 510 nm and the 578 nm wavelengths

The coagulation effect, penetration depth and healing process of the 510.6 nm (green) and 578.2 nm (yellow) wavelengths of copper vapour laser (CVL) were compared in vivo in rabbit liver (n=15). A pulsed CVL, the Cu 15 from Oxford Laser—pulse repetition 10 kHz, peak-power 70 kW, pulse width 25 ns, and average maximal power 16W—was used connected to a dichroic system. The beam was transmitted through a 1000 μm quartz fibre and focused with a handpiece providing a 2 mm diameter spot size. By means of this delivery system 270 focused lesions are achieved at a power output of 2.65 W (power density 80 W cm⁻²) with irradiation times of 3, 5 and 10 s. The operative and microscopic verifications were achieved at 0 hour, and on days 3, 10, 20 and 30. Immediately after laser application, the lesions were triangular, well demarcated, and characterized by a central vaporization surrounded by four peripheral zones: carbonization; coagulation; oedema; and transition. The penetration depth was noticeably bigger in the yellow wavelength than with green wavelength, evidenced on day 10 by superior size of yellow wavelength photocoagulations and coagulation necrosis. Fibrosis appeared by day 3 and was gaining ground quickly and intensively after yellow wavelength while the fibrotic reaction was delayed on day 10 after green wavelength. The more penetrating effect of yellow wavelength advocates for its use in liver tumour destruction and photoradiation therapy while the green wavelength, inducing less aggressive effect on the surrounding tissue, seems more suitable for liver resection.     

Histological correlation in laser skin resurfacing

Modern CO₂ systems can be programmed to emit high power density short pulses to produce instantaneous conversion of cutaneous tissue to a gaseous state. Tissue ablation occurs so quickly that there is minimal thermal conduction to the adjacent structures. The limits of thermal injury can be minimized to the order of only 50 thick and, in spite of the limited effects of heat conduction, coagulation in vessels can be obtained as well, since small blood vessels are immediately sealed by the laser. Collimated handpieces deliver a fixed beam diameter for more uniform vaporization at a constant energy density, as the handpiece is steadily moved over lesions situated on uneven facial contours. The fluence used is about 250 mJ for a 3 mm spot size and these parameters can be used for clean, repeatable and predictable ablation of tissue, taking advantage of the concept of the known thermal relaxation time of soft tissue.     

Dependence of laser photocoagulation on interstitial delivery parameters

Photocoagulation was performed ex vivo between tissue slabs by delivering continuous-wave laser energy from an optical fiber either directly, or by depositing the energy into a 2.4 mm diameter steel sphere at the fiber tip. The dependence of photocoagulation lesions on the following variables was assessed: (1) energy source: Nd:YAG-532 nm, 1,064 nm ± steel sphere, (2) tissue type: porcine muscle (light), bovine muscle (dark), (3) delivered power: P = 1.5–3.0 W (porcine), 1.0–2.5 W (bovine), (4) exposure duration: T = 300–1500 s. The resulting cross-sectional photocoagulation lesions are summarized as follows: 532 nm: elongated; central charring in all cases; 1,064 nm: circular; central charring only in bovine for P ? 2.0 W, T ? 500 s; sphere: circular; central charring in bovine for P ? 1.5 W and porcine for P ? 2.0 W. These experiments suggest photocoagulation lesion size decreases as optical penetration increases. The results indicate that interstitial laser photocoagulation lesions >10 mm diameter can be made without charring in both lightly and heavily pigmented tissues ex vivo by delivering 1,064 nm laser energy at sufficiently low power for at least 1,000 s from well-polished optical fibers. © 1994 Wiley-Liss, Inc.     

Microarterial anastomosis using a noncontact diode laser versus a control study

A series of direct carotid end-to-end laser anastomosis vs. direct manual suture was carried out on a series of 70 Wistar rats (mean weight 260 g). Both common carotids (0.8–1.2 mm) were sectioned and repaired. The left side (n = 70) was submitted to laser-assisted microvascular anastomosis (LAMA) performed by means of a diode laser device (wavelength 830 nm and power output 3 W in continuous wave) without chromophore. The right side (n = 70) underwent a control manual suture (CMA). The diode laser energy was delivered into a micromanipulator coupled to a Zeiss operating microscope with a focused spot of 300 μm in diameter. After placement of three 10.0 stitches for edge coaptation, the LAMA was achieved using laser shots (average 3) of 500 mW power, 4.5 s duration, and 700 W/cm² irradiance each. The CMA was performed by means of six 10.0 stitches. The good vascular flow was confirmed by Doppler spectral analysis (n = 466) carried out from day 0 to day 90. Light and scanning electron microscopy (n = 82) showed that re-endothelialization after LAMA was gaining ground on day 3, whereas collagenous network developed in the media scar by day 10. In contrast, after CMA the arterial repair was delayed on day 20, inducing a media fibrotic scar. The patency rate was 93% in both anastomoses. The shorter operating time (13 min for LAMA vs. 22 min for CMA) and the noncontact laser technique are the main intraoperative advantages. The technical benefits of the diode laser are pointed out. © 1994 Wiley-Liss, Inc.     

Porcine skin ED50 damage thresholds for 2,000 nm laser irradiation

BACKGROUND AND OBJECTIVES: To gain refinement in safe-exposure limits, indicated by the maximum permissible exposure (MPE) limits, the minimum visible lesion thresholds for three spot sizes (5-15 mm) and four exposure durations (0.25-2.5 seconds) were determined for the skin at 2,000 nm continuous wave laser irradiation. STUDY DESIGN/MATERIALS AND METHODS: A series of experiments were conducted in vivo on female Yucatan mini-pigs to determine the ED50 damage thresholds for 2,000 nm continuous wave laser irradiation. The study employed Gaussian laser beam exposures with spot diameters (1/e2) of 4.83, 9.65, and 14.65 mm and exposure durations of 0.25, 0.5, 1.0, and 2.5 seconds as a function of laser power. The effect of each irradiation was evaluated within 1 minute after irradiation and the final determination was made at 48 hours post-exposure. Probit analysis was conducted to estimate the dose for 50% probability of laser-induced damage (ED50), defined as persistent redness at the site of irradiation for the mini-pig skin after 48 hours. RESULTS: The MPE spot size and exposure duration trends for 2,000 nm laser exposure is consistent for exposure diameters less than 3.5 mm. However, for larger exposure diameters of 4.83, 9.65, and 14.65 mm and exposure duration longer than 0.25 second, the current MPEs are bigger than one tenth of our damage thresholds. For Gaussian laser profile, which is common for many laser output irradiance distributions, lower energy is required to generate a lesion on skin for smaller spot sizes and shorter exposure duration. On the other hand, for spot sizes greater than 4.83 mm and exposure duration over 0.25 second, the average radiant exposure at threshold is inversely proportional to spot size. The irradiance-time and temperature-time power law at the threshold were investigated as well and showed that the irradiance-time power law was a close approximation to estimate laser irradiance at ED50 damage threshold. CONCLUSIONS: The thresholds study shows that consideration for lowering the MPE standards should be explored as the laser beam diameter becomes larger than 3.5 mm. Based on the limited experimental data, the duration and size dependences of the ED50 damage thresholds could be described by an empirical equation: Irradiance at the threshold = (5.669-1.81xspot diameter)xexposure duration -0.794.     

双光纤Nd:YAG激光消融新鲜离体猪肝

目的 观察以双光纤Nd：YAG激光消融（LA）新鲜离体猪肝的价值。方法 将45件新鲜离体猪肝随机分为15组,每组3件;分别以不同消融功率（4、5、6 W）和作用时间（1、2、3、4、5 min）组合行双针双点LA,观察各组消融灶大小和温度,分析以双光纤Nd：YAG激光对猪肝行LA的价值。结果 消融时间设为1 min时,消融灶横径（TD）随功率增加而增大（P均<0.05）;消融时间为1、5 min时,消融灶纵径（LD）及体积（V）均随功率增加而增大（P均<0.05）。不同功率下,消融灶TD、LD及V均基本随消融时间增加而增大,消融灶温度则随消融时间增加而升高;不同消融时间下,消融灶温度基本随消融功率增加而升高。结论 双光纤Nd：YAG用于激光消融新鲜离体猪肝升温迅速且消融范围稳定。     

Bactericidal effects of different laser wavelengths on periodontopathic germs in photodynamic therapy

 This study was an attempt to clarify whether the bactericidal effects of photodynamic therapy (PDT) are wavelength or dose-dependent. We also attempted to create an optimised protocol for a light-based bactericidal modality to eliminate periodontal pathogens. Cultures of Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, Porphromonas gingivalis, Prevotella intermedia, and Streptococcus sanguis, were exposed to a He-Ne laser (632.8 nm) with a 30 mW power output, a 100 mW diode laser at 665 nm, or a 100 mW diode laser at 830 nm, in the presence or absence of methylene blue (MB) as a photosensitiser. A control group was also used with exposure to MB alone without laser exposure. The cultures were analysed by viable counts. The results indicated that exposure to the 100 mW laser light could eliminate up to 40% of bacteria on average. In particular, the most effective killing occurred with exposure to laser light in combination with the MB photosensitiser. The results of kinetic studies indicated that the best PDT response rate was achieved with a 60 s (energy density 21.2 J/cm²) exposure to the 665 nm wavelength diode laser in the presence photosensitiser. In this condition, approximately 95% of A. actinomycetemcomitans and F. nucleatum, and 99–100% of the black-pigmented bacteria (P. gingivalis and P. intermedia) and S. sanguis were eliminated. These results showed that both wavelength and energy density are important factors, and that a low power laser of optimal wavelength and dosage, in combination with an appropriate photosensitiser, is a practical bactericidal modality. We concluded that using a diode laser of proper power and wavelength to deliver 60 s of irradiation could be a useful adjunct with mechanical debridement in the prevention of the re-colonisation of subgingival lesions by pathogenic microorganisms. Received: 29 November 2001 / Accepted: 18 June 2002     

Continuous measurement of hematocrit using an intravascular catheter equipped with a fiberoptic transmission cell

Purpose. The purpose of this study was to measure intravascular hematocrit values continuously by using a fiberoptic probe based on near-infrared photometry. Methods. We produced a catheter 1.5 mm in diameter that use a pair of plastic fibers. One of the fibers, the measuring fiber, was used to measure the optical density of blood, and the other, the reference fiber, was used to decrease the signal-to-noise ratio. We employed an 805-nm laser diode as the light source. Two photodiodes were used to measure the intensity of the light transmitted through the two fibers, and the output signals were amplified and sent to a personal computer through an analog-to-digital converter. Results. The hematocrit values obtained by this fiberoptic continuous measurement agreed well with those obtained by microcentrifugation within physiological ranges. Conclusions. This method is effective for monitoring the rapid changes in hematocrit.     

Nd:YAG laser versus traditional scalpel. A preliminary histological analysis of specimens from the human oral mucosa

Hyperplastic fibro-epithelial lesions are the most common tumor-like swellings in the mouth. The neodymium yttrium aluminium garnet (Nd:YAG) laser appears to be useful for the surgical treatment of these lesions. Some controversies of laser surgery concern the accuracy of pathological diagnosis as well as the control of thermal damage on the target tissue. The aim of this study was to establish if the thermal changes induced by the Nd:YAG laser may affect the histopathological diagnosis and the evaluation of the resection margins. Furthermore, we compared the histological features of oral benign fibro-epithelial lesions excised through Nd:YAG laser and traditional scalpel. Twenty-six benign fibro-epithelial oral lesions from 26 patients, localized in the same oral subsites (cheek and buccal mucosa), were collected at the Unit of Oral Pathology and Oral Laser-assisted Surgery of the Academic Hospital of the University of Parma, Italy. Specimens were subclassified into three groups according to the tool used for the surgical excision. Group 1 included six specimens excised through Nd:YAG laser with an output power of 3.5 W and a frequency of 60 Hz (power density 488,281 W/cm²); Group 2 included nine specimens excised through Nd:YAG laser with an output power of 5 W and a frequency of 30 Hz; Group 3 included 11 specimens excised through a Bard-Parker scalpel blade no. 15c. Epithelial changes, connective tissue modifications, presence of vascular modifications, incision morphology and the overall width of tissue modification were evaluated. Differences between specimens removed with two different parameters of Nd:YAG laser were not significant with regard to stromal changes (p = 0.4828) and vascular stasis (p = 0.2104). Analysis of regularity of incision revealed a difference which was not statistically significant (p = 1.000) between group 1 and group 2. Epithelial and stromal changes were significantly more frequent in specimens with a mean size less than 7 mm (p < 0.0001). Nd:YAG laser induced serious thermal effects in small specimens (mean size less than 7 mm) independently from the frequency and power employed. The quality of incision was better and the width of overall tissue injuries was less in the specimens obtained with higher frequency and lower power (group 1: Nd:YAG laser at 3.5 W and 60 Hz).     

Effect of different power parameters of Er,Cr:YSGG laser on human dentine

The aim of this work was to determine the optimal power setting of an Er,Cr:YSGG laser for cutting human dentine to produce a surface that remains suitable as a foundation on which to build and bond a dental restoration. The cutting efficiency and resulting microhardness of the dentine were evaluated for various laser power settings, and representative samples were examined by SEM. The microhardness of the dentine was significantly reduced by 30–50% (p < 0.05, paired t test) after laser irradiation, irrespective of the power setting used. The mean ablation efficiency increased in proportion to the power setting of the laser. Although the laser power setting did not affect the extent of reduction in microhardness, it did affect the microstructure of human dentine.     

Advanced microspot microslad for the CO2 laser

New advances in instrumentation have facilitated the development of a second generation carbon dioxide (CO2) laser microspot micromanipulator. The 710 Acuspot has unique advantages over the previous generation of microspots. The compact design is easier to handle and has attachment points for sterile draping. The unit produces a spot size of 250 microns at a 400-mm focal length and 160 microns at 250 mm; the maximum de-focus is 3.2 mm at all focal lengths. An innovative dichroic mirror allows use of the laser unit's own HeNe laser as the aiming beam, eliminating possible aiming error introduced with a virtual image-aiming system. The dichroic mirror also allows better light transmission, resulting in a brighter field of view. As with first generation microspots, the laser beam path is coincident with the microscope optical path, eliminating parallax; this feature has been especially advantageous in pediatric and otologic cases. Having used this unit for 6 months on more than 50 patients, we now consider the use of a microspot to be our delivery system of choice for most microlaryngeal laser surgical applications.     

Endoscopic thoracic sympathectomy: evaluation of pulsatile laser, non-pulsatile laser, and radiofrequency-generated thermocoagulation

We describe a modified technique for percutaneous denervation of the thoracic sympathetic chain by laser to treat selected cases of sympathetic causalgia of the upper extremities. The technique involves transpleural ablation with laser under thoracoscopic guidance through the second or third intercostal space-anterior axillary line. We also compare four different modalities of endoscopic denervation: A xenon chloride excimer laser (308 nm, 35 mJ/pulse, 20 pulses/sec, 2.2 mm catheter tip), CO2 laser (14 W, CW, 2 mm spot size), Nd:YAG laser (88 W, CW, 3 mm spot size), and radiofrequency-generated thermocoagulation (3 W, CW, 2.1 mm catheter tip) by performing bilateral thoracic sympathectomy on 12 mongrel dogs (three dogs each). Criteria analyzed included duration of exposure, power density, total energy output, laser penetration and spread, gross morphology, and scanning electron microscopy (SEM) of the destroyed neural tissue. Total ablation of the inferior segment of the stellate ganglion and the T1-T2 nerve roots by excimer laser required 83 +/1 1 Joules over an exposure period of 118 seconds. Ablation by CO2 and Nd:YAG laser required 153 +/- 13 Joules and 554 +/- 47 Joules delivered over 11 and 6 seconds respectively. In contrast, ablation of the same volume of nerve tissue by RF required 810 +/- 50 Joules over 270 seconds. SEM evaluation revealed that excimer and CO2 laser lesions were narrower in configuration compared to RF and Nd:YAG lesions which showed more lateral spread. The actual depth of penetration per 1 second exposure was similar for Excimer and CO2 (1.5 mm) and RF (1.3 mm), but deeper for Nd:YAG (3 mm).(ABSTRACT TRUNCATED AT 250 WORDS)     

Examination of tooth pulp following laser beam irradiation

An attempt was made to determine the maximum amount of laser energy which could be utilized without impairing pulpal vitality. Forty rat molar teeth were irradiated in vivo; the Sharplan CO2 laser modality, focused to a 0.2-mm-diameter spot size was used. The energy output was varied by changing the power and/or the pulse duration. Subsequent histological examination of the irradiated teeth showed that the duration of exposure was more significant than the power. A pulse of 0.2 sec/10 W appears to be the safety limit in preserving pulpal vitality.     

Evaluation of mineral content of dentin prepared by erbium, chromium:yttrium scandium gallium garnet laser

Laser etching has an effect on the mineral content of dentin. The aim of this study was to evaluate the mineral content of dentin prepared at three different power settings with an erbium, chromium:yttrium scandium gallium garnet (Er,Cr:YSGG) laser. The enamel of five, lower, wisdom, molar teeth was removed to expose the dentin surface. Four dentin slabs were obtained, then each tooth was randomly divided into four portions (groups 1 W, 2 W, 3 W and control) so that we could evaluate the effect of laser treatment. The Er,Cr:YSGG laser used for the study had a pulse duration of 140 μs, a pulse repetition rate of 20 Hz and a power output range of 0 W to 6 W. Laser energy was delivered through a fiberoptic system to a sapphire tip terminal 6 mm long and 600 μm in diameter, using a non-contact mode. The levels of five elements: magnesium (Mg), phosphorus (P), calcium (Ca), potassium (K), and sodium (Na), in each slab were measured by inductively coupled plasma–atomic emission spectrometry (ICP-AES). There were significant differences between the groups (1 W, 2 W, 3 W and control) for Ca, Mg, Na, P and Ca/P ratio (P < 0.05); however, there were no significant differences for K (P = 0.43). Laser treatment at 1 W significantly affected the mean percentage weight of all element groups except K. Scanning electron microscopy (SEM) photographs indicated that the surface irregularities increased with increasing power setting.