Showing papers in "Lasers in Surgery and Medicine in 1991"

Autofluorescence of normal and malignant bronchial tissue.

Abstract: In vivo autofluorescence spectra were obtained in 5 patients with carcinoma in situ, 26 patients with invasive tumors, and 1 patient with severe dysplasia. Significant spectral differences were observed between pre-cancerous, cancerous, and normal bronchial tissues. This difference may afford a method to image and/or detect early lung cancer by using tissue autofluorescence alone.

Micron-resolution ranging of cornea anterior chamber by optical reflectometry

Abstract: Noncontact, high resolution measurements of anterior eye structures using optical coherence domain reflectometry are described. Distances between intraocular structures are measured by directing a beam of short coherence length light onto the eye and performing an interferometric measurement on the optical group delay of reflected signals. Measurements of corneal thickness, corneal excision depth, and anterior chamber depth are demonstrated in vitro, and the location of tissue boundaries is resolved to within +/- 2 microns. The full-width-half-maximum longitudinal resolution is 10 microns. Sensitivities to reflected signals as small as 10(-10) of the incident power are achieved by heterodyne detection.

Use of the pulsed Nd:YAG laser for intraoral soft tissue surgery.

Abstract: Application of a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was compared to conventional scalpel in dental soft tissue surgery. Two surgery sites on 29 patients were randomly selected and treated. An additional 41 patients were exclusively treated with the Nd:YAG laser. The surgical technique was then evaluated for periodontal pocket depths, degree of pain perceived, bleeding, inflammation, procedure time, and anesthesia. Surgical prognosis was made at the time of surgery and compared to actual healing 1 week and 1 month after surgery. No differences were observed between laser and scalpel surgery in terms of pocket depth reduction, postoperative pain, post-operative inflammation, and treatment time. However, operative and postoperative bleeding with laser surgery were significantly less than with conventional surgery. Anesthesia is required for scalpel surgery, the majority of laser-treated sites evoked minimal pain without anesthesia. These results indicate that the Nd:YAG laser can be used successfully for intraoral soft tissue applications are well tolerated without anesthesia and minimal bleeding compared to scalpel surgery.

Presence of human immunodeficiency virus DNA in laser smoke.

Abstract: Concentrated tissue culture pellets infected with human immunodeficiency virus (HIV) containing 1 x 10(7) cells/ml were vaporized by means of a carbon dioxide laser. The vaporous debris resulting from the laser's impact were evacuated through sterile silastic tubing, then bubbled through sterile culture medium (RPMI) positioned in series with a commercial smoke evacuator. No HIV DNA was detected in the culture medium flask. Tissue culture studies of the silastic collection tubing revealed p24 HIV gag antigen in 3 of 12 tube segments at the end of 1 week and in 1 of 12 tube segments at 2 weeks. No sustained infection of HIV cultured cells was observed at the 28th day. Polymerase chain reaction (PCR) analysis of particulate debris obtained from the silastic collection tubing was positive from proviral HIV DNA in both immediately sampled and day 14 cultured material.

Optical properties of human sclera, and their consequences for transscleral laser applications

Abstract: The spectral dependence of the optical properties of human sclera adjacent to the limbus was investigated and related to the potentials of transscleral photocoagulation. The total transmission, absorption, and reflection, as well as the angular distribution of the transmitted and reflected light were measured at five laser wavelengths (442 nm, 514 nm, 633 nm, 804 nm, and 1,064 nm), both for noncontact and contact applications. Absorption and scattering coefficients were determined using the Kubelka-Munk model for light propagation through a scattering tissue. The scleral transmission is only 6% at 442 nm but increases to 35% at 804 nm and to 53% at 1,064 nm. The absorption is high at short wavelengths with 40% at 442 nm but it is only 6% at 804 nm and 1,064 nm. The reflection is generally higher than 40% and shows little wavelength dependence. The transmitted light is scattered diffusely at short wavelengths, but at 804 nm and 1,064 nm it exhibits a fairly narrow angular distribution in forward direction. Fiber contact leads to an increase of transmission, with a factor of 3.5 at 442 nm, of 2.0 at 804 nm, and 1.5 at 1,064 nm. Our results indicate that the diode laser (804 nm) and the Nd:YAG laser (1,064 nm) with contact delivery are best suited for transscleral photocoagulation.

Noncontact tissue ablation by holmium:YSGG laser pulses in blood.

Abstract: To assess the feasibility of intra-arterial tissue ablation by Holmium:YSGG laser pulses (2.1 microns) in a noncontact mode, the transmission of the laser pulses through saline and blood was measured. The temporal interaction between the 500 microseconds laser pulse and saline at the fiber tip was investigated with time-resolved flash photography. The penetration depth in blood, and saline depended on the fiber output energy. In blood at 37 degrees C, the penetration depth varied from 1.2 to 2.1 mm for intensities of 3.1 to 12.4 J/mm2 per pulse, respectively, whereas its theoretical value for water is 0.33 mm, which is based on the measured absorption coefficient of 3.0 +/- 0.1/mm. The large penetration depth was due to the development of a transparent vapour cavity around the fiber tip. In saline, its maximum length was 4.7 mm. Its maximum width was 2.8 mm. The lifetime of the cavity was 450 microseconds. In blood, ablation of porcine aorta was feasible at a distance of 3 mm. Large fissures observed in adjacent tissue are likely to be caused by the expansion of the vapour cavity. We conclude that, due to a "Moses effect in the microsecond region," Holmium:YSGG tissue ablation is possible through at least 2.7 mm of blood.

Excimer laser ablation of fibrocartilage: an in vitro and in vivo study.

Abstract: To date, lasers have found only limited applications in orthopedics. We employed a 308 nm XeCl excimer laser for ablation of fibrocartilage, in order to investigate the feasibility of excimer laser assisted meniscectomy. Experiments were conducted both in vitro and in vivo. For the in vitro study, human menisci, obtained during surgery and autopsy, were irradiated via a 600 microns core fiber at radiant exposures ranging between 20 mj/mm2 and 80 mj/mm2, at 20 Hz. Ablation rate measurements and histological analysis of the samples were performed. The ablation rates were found to range from 3 microns/pulse to 100 microns/pulse depending on the radiant exposure and/or the applied pressure on the fiber delivery system. Thermographic analysis was also performed during pulsed excimer as well as CW Nd:Yag and CW CO2 laser irradiation. Temperatures were lower for excimer laser (Tmax less than 65 degrees) than CW ND: Yag (Tmax less than 210 degrees) or CW CO2 (Tmax less than 202 degrees) laser. For the in vitro study, medial meniscectomy was performed in 15 rabbits with the excimer laser and a CW Nd:Yag laser in the right and left knee respectively. Excimer laser irradiation was performed at 70 mj/mm2. Nd:Yag irradiation was performed via a 600 microns core fiber at power outputs between 20 to 40 W for 10 and 20 seconds duration. The healing response to injury was investigated by histological analysis of the menisci after 1 day, 1, 2, 4, and 8 weeks following the laser procedure. Excimer laser treated menisci showed less inflammatory reaction and noticeable repair with minimal inflammatory response.(ABSTRACT TRUNCATED AT 250 WORDS)

Optical properties of normal, diseased, and laser photocoagulated myocardium at the Nd:YAG wavelength

Abstract: Laser photocoagulation of the myocardium effectively destroys arrhythmogenic foci. The purpose of this study was 1) to compare the optical properties of canine myocardium before and after photocoagulation, 2) to compare the canine model with clinical cases by measuring the optical properties of human myocardium, and 3) to assess the optical properties of human myocardial scar and epicardial fat tissue. Measured optical properties were the absorption coefficient, mu a; scattering coefficient, mu s; and scattering anisotropy factor, g. Optical measurements were performed at 1064 nm wavelength on thin plane parallel tissue slices using the integrating sphere method with glass hemispheres on either side of the sample. The study showed 1) an increase of the scattering coefficient by 40% and a two- to threefold increase in reduced scattering coefficient as a result of photocoagulation; 2) that the mu a (0.035 +/- 0.024 mm-1) and mu s (17.9 +/- 3.8 mm-1) of human myocardium were not significantly different from mu a (0.043 +/- 0.021 mm-1) and mu s (17.3 +/- 2.2 mm-1) of canine myocardium, whereas the human g (0.964 +/- 0.005) was slightly different from the canine g (0.974 +/- 0.008); and 3) that the mu a (0.021 +/- 0.016 mm-1) of epicardial fat and mu s (13.8 +/- 1.1 mm-1) of myocardial scar were significantly lower than those of normal myocardium. A dynamic model of laser-tissue interaction incorporating these changes and inhomogeneities is necessary to better describe light distribution during laser photocoagulation.

Laser trabecular ablation (LTA).

Abstract: As part of a pilot study for glaucoma surgery, the use of 3 infrared solid state lasers with 4 fiber optic delivery systems to ablate human trabecular meshwork was investigated. Laser trabecular ablation (LTA) was attempted with the Erbium:YAG (2.94 microns), Erbium:YSGG (2.79 microns), and Holmium:YSGG (2.1 microns) lasers. Laser energy was delivered as a single pulse (250 microseconds) by tissue fiber optic contact with low hydroxyl-fused silica (200 and 500 microns), zirconium fluoride (250 microns), or sapphire (250 microns) fiber optics. Total energy required and thermal effects decreased as laser wavelength increased. LTA was best achieved at 2.94 microns (4 mJ total energy; energy densities = 8.2-12.7 J/cm2; pulse length 250 microseconds) with average thermal damage zones of 5.3-10.3 +/- 1.3-2.4 microns (means +/- SDs) to contiguous structures. This finding has potential applications in the surgical treatment of open-angle and congenital glaucoma and may minimize failure rates seen in other types of surgery on the trabecular meshwork where disrupted trabecular meshwork is not removed.

Plasma‐mediated ablation of corneal tissue at 1053 nm using a Nd:YLF oscillator/regenerative amplifier laser

Abstract: Plasma-mediated ablations were performed on human donor corneas with a short pulsed Nd:YLF laser system at 1053 nm. The pulses were 60 psec in duration at a repetition rate of 1.0 kHz. The laser beam was oriented perpendicular to the cornea surface. The threshold energy densities for ablation of epithelium, Bowman's membrane and stroma were measured. They were 6.1 +/- 1.8 J/cm2, 21.0 +/- 5.1 J/cm2 and 10.4 +/- 1.8 J/cm2, respectively. The mean rate of tissue removal at the stromal energy density threshold was about 1 micron per pulse. The walls of the laser excisions were smooth with distortions of less than 1 micron. A new quantitative model of plasma-mediated ablation is introduced and found to closely predict the observed results. Based on the promising nature of the experimental data further investigations are planned in the use of a mode locked Nd:YLF laser as an alternative to excimer lasers for refractive corneal surgery.

Technique for cellular microsurgery using the 193-nm excimer laser

Abstract: A new cell surgery technique has been developed to produce well-defined alterations in cells and tissue without detectable heating and/or other structural damage in the surroundings. The technique involves the use of an argon fluoride excimer laser, in the deep ultraviolet (UV) region of the spectrum at 193 nm, which is guided through a glass pipette filled with a positive air pressure. To demonstrate the method, holes were drilled in the zona pellucida of mouse oocytes. The diameter of the drilled hole was determined by the pipette tip size, and its depth by an energy emitted per pulse and number of pulses. Scanning electron microscopy of the drilled mouse oocytes showed uniform, round, well-circumscribed holes with sharp edges. Oocytes that had their zona pellucida drilled with this new method fertilized in vitro and developed to the blastocyst stage in a rate similar to that of control group. These results demonstrate the nonperturbing nature of this cold laser microsurgical procedure. In addition to the extension of our results for clinical in vitro fertilization purposes, such as enhancement of fertilization and embryo biopsy, there are wide-ranging possible uses of our method in fundamental and applied investigations that require submicron accuracy in cellular alteration.

Laser beam diameter for port wine stain treatment.

Abstract: Optimal port wine stain treatment requires the selective absorption of light by the ectatic blood vessels. We investigated whether deeper blood vessels can be coagulated, without damaging other cutaneous structures, by varying the laser beam diameter. The penetration of the light was simulated with a random walk (Monte Carlo) program. Scattering of the light plays a major role: practically all light that is absorbed in a blood vessel in the dermis is scattered light. In the epidermis, where the distribution is more centered, a larger beam diameter does not increase the energy density as much as deeper within the dermis where the blood vessels lie and where the light is totally diffuse. Increasing the laser beam diameter from 200 microns to 1 mm or more, makes a typical blood vessel absorb 2.5 times more energy, while the energy absorbed by the epidermis remains the same. The larger the laser beam diameter the better the treatment.

Temperature response of biological materials to pulsed non-ablative CO2 laser irradiation

Abstract: This paper presents surface temperature responses of various tissue phantoms and in vitro and in vivo biological materials in air to non-ablative pulsed CO2 laser irradiation, measured with a thermocamera. We studied cooling off behavior of the materials after a laser pulse, to come to an understanding of heat accumulation and related thermal damage during (super) pulsed CO2 laser irradiation. The experiments show a very slow decay of temperatures in the longer time regime. This behavior is well predicted by a simple model for one-dimensional heat flow that considers the CO2 laser radiation as producing a heat flux on the material surface. The critical pulse repetition frequency for which temperature accumulation is sufficiently low is estimated at about 5 Hz. Although we have not investigated the ablative situation, our results suggest that very low pulse frequencies in microsurgical procedures may be recommended.

Direct CO2 laser “revascularization” of the myocardium

Abstract: Evidence of regional myocardial perfusion and contractile function after direct CO2 laser myocardial revascularization (DLR) is lacking. We examined myocardial segment shortening, adenine nucleotide concentrations, and regional blood flow after DLR of the left anterior descending coronary artery (LAD) distribution before and after its proximal ligation in seven anesthetized conditioned dogs. Sonomicrometry assessed myocardial fiber shortening and radioactive microspheres were used to estimate baseline regional blood flows. Cardiopulmonary bypass was followed by cardioplegia arrest. Laser channels (1 mm diameter) were made every 3 to 5 mm in the LAD region with an 80 watt Laser-sonics CO2 unit. Bypass was terminated, the LAD occluded, and parameters reassessed. Core samples of myocardium from the lased LAD and control circumflex area were taken to assess adenine nucleotides. After occlusion, LAD distribution blood flow and myocardial shortening were reduced to pre-lasting ischemic controls. Adenine nucleotides were reduced in the LAD region relative to the control CMX area. DLR cannot be relied upon to acutely revascularize the ischemic myocardium.

Selectivity, efficiency, and surface characteristics of hard dental tissues ablated with ArF pulsed excimer lasers.

Abstract: Lasers are finding expanding applications in the field of dentistry. Cutting in soft tissue, hard dental material ablation, caries removal, and root canal therapy are only a few examples of dental laser uses. In this article, the application of short pulse ArF excimer laser to ablation of dentin and enamel is investigated. In particular, the effect of laser pulse repetition rates (PRR) and fluence levels on the efficiency of the ablation process and on the average thermal response of ablated surfaces is investigated. Ablation of dentin was found to be considerably more efficient than the ablation of enamel and depends exponentially on the laser fluence. Both dentin and enamel surfaces showed an increase in surface temperature with repetition rate. At lower PRR, however, temperature increases are very small. Surface temperature was also found to increase with laser fluence, although this increase is very small at laser PRR of 5 Hz or less. Tissue ablation rates were found to be comparable to or better than other nanosecond lasers, and left smooth surfaces, free of thermal damage. Microscopic examination of the ablated surface shows no crack formation, charring, discoloration, or any other thermal damage. The ablated surfaces appear to be very smooth, highly polished, and glossy looking as if they were subjected to thermal melting. This observation is indeed confirmed under scanning electron microscopy (SEM), where evidence of localized melting of the tissue is observed. Furthermore, a close SEM examination of the dentin surface reveals a selectively ablated intertubular dentin, while the remaining pillar-like dentin tubules are sealed off with fused peritubular dentin. At all fluence levels and PRR, the first three to four pulses impinging on an untreated enamel surface produced unusually large plumes of debris which were different in size, texture, and fluorescence emission characteristics from the ablation products of subsequent pulses. It is believed that these different ablation characteristics are a consequence of the pulsed ArF laser's ability to selectively remove residual matter from the more resistant enamel surface.

Comparison of three lasers for dental instrument sterilization.

Abstract: The sterilization of dental instruments is an area of great interest and recent concern in the field of dentistry. The purpose of this study was to compare the ability of three lasers (argon, CO2, and NdYAG) to sterilize dental instruments. Endodontic reamers were contaminated with microorganisms, lased at various levels of energy, placed in Trypticase soy broth, incubated, and read for growth or no growth to determine sterility. Results indicated that the argon laser is capable of sterilizing selected dental instruments at the lowest energy level (1 watt for 120 seconds) of the three lasers tested. The other two lasers were able to sterilize the instruments also, but at higher energy levels. Results indicated all three lasers capable of sterilizing selected dental instruments; however, the argon laser was able to do so consistently at the lowest energy level of 1 watt for 120 seconds.

Wavelength dependence of pulsed laser ablation of calcified tissue.

Abstract: Pulsed laser ablation of calcified biological tissue was studied at several wavelengths in the near-ultraviolet, visible, near- and mid-infrared regions of the spectrum. The primary tissue model was bovine shank bone, while human arterial calcified plaque and normal human artery wall were also studied at selected wavelengths for comparison. Laser irradiances were on the order of MW/mm2, fluences ranged up to 1000 mJ/mm2, and repetition rates varied between 0.3-10 Hz. Spot sizes on the tissue surface ranged from 150 to 850 microns. Laser craters made with wavelengths between lambda = 295 nm and lambda = 375 nm and in the lambda = 3 microns region exhibited the highest quality ablation with clean, sharp cuts following closely the spatial contour of the incident beam. Craters drilled with visible wavelengths between lambda = 450 nm and lambda = 590 nm were generally larger than the incident laser beam spot, irregular in shape and often surrounded by large flakes of tissue debris. Ablation fluence thresholds increased with wavelength through the visible wavelengths and into the mid-infrared, but dropped to their lowest values near lambda = 3 microns. Fluence thresholds obtained with the tissue under a 1 mm depth of saline were approximately twice air thresholds. Ablation yields also varied with wavelength, probably due to increased scattering in the visible region, and were the same under saline as in air.

Effect of low level laser therapy on wound healing after palatal surgery in Beagle dogs

Abstract: The effect of low level laser therapy on wound healing and wound contraction after palatal surgery in Beagle dogs of 12 weeks of age was investigated. A total of 30 Beagle dogs was used and assigned to a control group (Group C; n=6) and two experimental groups (Group L; n=12 and group LL; n=12). In both experimental groups, Von Langenbeck's palatal repair was simulated. Then in the LL group the denuded bony areas were treated with low level laser therapy using a continuous Ga-As-Al laser beam (830 nm) and energy output set at 30 mW. Per treatment a dosage of 1 J/cm2 wound surface area was used. Therapy was carried out three times a week with a total of ten treatments. Wound healing was observed clinically until wound healing was completed at 4 weeks p.o. and wound areas were measured at regular intervals on standardized intra-oral photographs. Wound contraction was measured as the increments of the distances between tattoo points on the opposite wound margins. No significant differences were found in the quality and rate of wound healing between the two experimental groups. The same held true for the increments of the distances between opposite tattoo points. It was concluded that macroscopically low level laser therapy under conditions used in this study did not have an influence on wound closure or wound contraction.

Co:MgF2 laser ablation of tissue: Effect of wavelength on ablation threshold and thermal damage

Abstract: The wavelength dependence of the ablation threshold of a variety of tissues has been studied by using a tunable pulsed Co:MgF2 laser to determine how closely it tracks the optical absorption length of water. The Co:MgF2 laser was tuned between 1.81 and 2.14 microns, a wavelength region in which the absorption length varies by a decade. For soft tissues the ablation threshold tracks the optical absorption length; for bone there is little wavelength dependence, consistent with the low water content of bone. Thermal damage vs. wavelength was also studied for cornea and bone. Thermal damage to cornea has a weak wavelength dependence, while that to bone shows little wavelength dependence. Framing-camera pictures of the ablation of both cornea and liver show explosive removal of material, but differ as to the nature of the explosion.

Laser-induced photoacoustic injury of skin: effect of inertial confinement.

Abstract: Argon-fluoride (ArF) excimer laser-induced acoustic injury was confirmed by ablating the stratum corneum (s.c.) inertially confined by water in vivo. Hairless rats were irradiated through a quartz chamber with flowing distilled water or air and a 2.5 mm aperture. The laser was adjusted to deliver 150 mJ/cm2 at the skin surface for both conditions. Partial and complete ablation of the s.c. was achieved with 12 and 24 pulses, respectively. Immediate damage was assessed by the transmission electron microscopy. Partial ablation of the s.c. through air produced no damage, whereas partial ablation through water damaged skin to a mean depth of 114.5 +/- 8.8 microns (+/- SD). Full thickness ablation of the s.c. through air and water produced damage zones measuring 192.2 +/- 16.2 and 293.0 +/- 71.6 microns, respectively (P less than 0.05). The increased depth of damage in the presence of inertial confinement provided by the layer of water strongly supports a photoacoustic mechanism of damage. The damage induced by partial ablation of the s.c. provides evidence that photochemical injury is not a significant factor in the damage at a depth because the retained s.c. acts as a partial barrier to diffusion of photochemical products. Combined with our previous studies, these experiments demonstrate that pressure transients are responsible for the deep damage seen with 193 nm ablation and that photoacoustic effects must be considered when using short-pulse, high-peak power lasers.

Rate process parameters of albumen.

Abstract: Both egg white and egg yolk are excellent media for studying photocoagulation due to thermal response of tissue to laser light. They are readily available, consistently the same, and provide a standard biological medium for different labs to compare results. The irradiation parameters for laser coagulation of these media depend upon their optical properties and their temperature-dependent rate reactions. Estimates of the rate process damage coefficients were obtained from constant-temperature water bath experiments. The activation energy E for egg white was estimated to be 92,000 (cal/(M*K)) and the integration constant A was found to be 3.8 × 1057 (second−1).

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

Abstract: 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 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). Our data shows that excimer and CO2, laser produce discrete lesions with minimal damage to surrounding structures. It also demonstrates the safety and reliability of endoscopic denervation, particularly for bilateral denervation which can be performed in one sitting without the added morbidity of a thoracotomy incision.

Studies in fiber guided excimer laser surgery for cutting and drilling bone and meniscus

Abstract: Our experiments on transmitting high-power excimer laser pulses through optical fibers and our investigations on excimer laser ablation of hard tissue show the feasibility of using the excimer laser as an additional instrument in general and accident surgery involving minimal invasive surgery. By combining XeCl-excimer lasers and tapered fused silica fibers we obtained output fluences up to 32 J/cm2 and ablation rates of 3 microns/pulse of hard tissue. This enables us to cut bone and cartilage in a period of time which is suitable for clinical operations. Various experiments were carried out on cadavers in order to optimize the parameters of the excimer laser and fibers: e.g., wavelength, pulse duration, energy, repetition rate, fiber core diameter. The surfaces of the cut tissue are comparable to cuts with conventional instruments. No carbonisation was observed. The temperature increase is below 40 degrees C in the tissue surrounding the laser spot. The healing rate of an excimer laser cut is not slower than mechanical treatments; the quality is comparable.

Histochemical evaluation of the coagulation depth after argon laser impact on a port-wine stain.

Abstract: A two-step excisional treatment of a port-wine stain (PWS) on the back of a 43-yr-old female patient was performed. Immediately before the first surgical treatment, two corresponding series of argon laser impacts were performed, each on one PWS half. Different laser parameters with irradiances ranging from 95 to 382 W/cm2 and energy fluences ranging from 19 to 114,6 J/cm2 were used. Laser spots on the first part ot be excised were biopsied 10 min after laser treatment and prepared for histochemical analysis by staining with nitro blue tetrazolium chloride (NBTC). Reduction of this redox dye by nicotinamide adenine dinucleotide diaphorase (NADH-diaphorase) leads on frozen tissue sections to an intense blue precipitate. The activity of NADH-diaphorase subsides immediately upon cell damage. All vital epidermal and dermal cells presented a dense blue granular pigment in their cytoplasm, sparing the nuclei. Laser induced arc-shaped epidermal and dermal necrosis did not stain, showing a clear demarcation from surrounding vital tissue. The depth of the thermal injury ranged from 0.28 to 0.45 mm; it did not correlate with the chosen fluences. With these penetration depths, the vast majority of PWS vessels was affected. Assessment of the remaining part of the PWS 8 months later yielded blanching of all laser-treated areas. With the NBTC method, an accurate definition of laser-induced tissue damage is feasible. It could be shown that the exposure time is the most relevant parameter influencing the penetration depth.

Temperature along the surface of modified fiber tips for Nd:YAG laser angioplasty.

Abstract: For laser angioplasty probes, the thermal properties of the probes will primarily determine their mechanism of action. We examined the absorption, temperature increase, and probe degradation of transparent contact probes (hemispherical contact probe and ball-shaped fibers) and metal laser probes coupled to a continuous-wave Nd-YAG laser. Temperature was recorded by means of thermocouples and the measurements were corrected for direct light absorption by the thermocouple. During 15 W, 1 s exposure, the peak temperature rise of the hemispherical contact probe in contact with tissue dropped from approximately 1,000 degrees C at the front end to below 45 degrees C (95% drop) at the lateral side. In contrast, during continuous exposure the peak temperature rise of metal laser probes in contact with tissue dropped from 560 degrees C at the front end to near 400 degrees C (30% drop) at the 5.5 mm proximal rear end. During exposure in blood or tissue, the transparent contact probes became contaminated. Their absorption increased from 5 to 33% and the probe deteriorated. Repeated use of metal laser probes in blood resulted in a higher temperature at the rear than at the front end due to backburing of the fiber. Owing to the large temperature drop along the surface of transparent contact probes, the area of thermal destruction is limited to the tissue in front of the probe, whereas along the entire surface of metal laser probes the tissue will be affected. The large difference between these temperature distributions should be respected during clinical application of the transparent contact probe and the metal laser probe.

Water-jet-cooled Nd:YAG laser coagulation: selective destruction of rat liver metastases.

Abstract: The photocoagulating properties of the water-jet-cooled Nd:YAG laser (1,064 nm) have been studied in a rat tumor model. A colon carcinoma CC531 was implanted in the liver; 20 days after inoculation, laser therapy was performed with 600 J, 850 J, 1,200 J, 1,700 J, or 2,400 J at a power setting of either 10 or 20 W. Liver damage was determined in tissue specimen on day 1 after treatment and by serum levels of alanine aminotransferase and aspartate aminotransferase on day 1 and 2. Tissue specimen of day 36 were used to evaluate tumor remission. Liver function was assessed by antipyrine clearance on day 2. Light microscopic examination on day 1 showed coagulative necrosis up to 10 mm in diameter at 1,700 J and 20 W. At 20 W, liver damage was 22% larger than at 10 W (P = 0.0001). A significant relationship was found between laser energy and liver damage with complete tumor destruction in all animals at 2,400 J. No deterioration in liver function was found. The results of this study show the ability of the water-jet-cooled Nd:YAG laser to produce tumor coagulation necrosis with minor liver damage.

Comparison of four laser types for experimental pain stimulation on oral mucosa and hairy skin.

Abstract: The use of different lasers for stimulation in human experimental pain research has provided a sensitive method for evaluation of thin nerve fiber functions. In this study, sensory and pain thresholds were compared to argon-, copper vapour-, Nd:YAG-, and CO2 laser stimulation on hairy skin and on oral mucosa. The influence on thresholds with respect to laser type, stimulation site, surface colour, and stimulus parameters (laser beam diameter and pulse duration) was investigated. Significant differences in thresholds between the four lasers were found on both surfaces; however, no significant differences existed between thresholds on the skin and on the tongue when the same laser was used. The observations imply that wavelength-dependent optical properties of the stimulated tissue influence on threshold determinations. Furthermore, the results indicate that temporal and spatial summation mechanisms may exist for laser induced warmth and pain perceptions. Laser stimulation may be a new tool for the investigation of origin and genesis of various orofacial pain syndromes.

Direct comparison of in-vitro and in-vivo Photofrin-II mediated photosensitization using a pulsed KTP pumped dye laser and a continuous wave argon ion pumped dye laser.

Abstract: A pulsed KTP pumped dye laser (25 kHz repetition rate and 470 nsec pulse width) has been compared to a continuous wave argon ion pumped dye laser as the source of 630 nm light during in-vitro and in-vivo Photofrin-II mediated photosensitization studies. Individual experiments documented the effectiveness of each laser system on a) photosensitizer induced cytotoxicity and induction of stress protein synthesis using Chinese hamster fibroblasts; b) photobleaching of Photofrin-II in aqueous solution; c) Photofrin II mediated photosensitization of normal mouse skin; d) Photofrin II mediated photodynamic therapy of a mouse mammary carcinoma; and e) tumor temperature levels generated during laser exposure. Comparable results were obtained for both laser systems in all experiments.

Light dosimetry model for photodynamic therapy treatment planning

Abstract: A light dosimetry model for photodynamic therapy is described leading to the dependence of necrosis depth on incident light dose. Semiempirical dosimetry relations are derived for four modes of light delivery. Results for Photofrin® II at 630 nm are summarized in graphical form. Numerical values of the parameters and necrosis depth calculations are compared with literature data.