Coagulation Depth Research Articles

Epidermal Damage and Limited Coagulation Depth with the Flashlamp-Pumped Pulsed Dye Laser: A Histochemical Study

To investigate vessel coagulation depth and tissue damage in therapy with the flashlamp-pumped pulsed dye laser (585 nm, 5 mm spot size, 450 microsecond pulse duration, 6-8 J/cm2), we used the nitroblue-tetrazolium chloride stain in 22 post-treatment biopsy specimens from patients with port wine stain. With this method, thermally damaged tissue can be easily differentiated from unchanged tissue to the level of single cells. The results showed that in superficial port wine stain vessels up to 150 microns in diameter, vessel coagulation was complete and selective without further dermal damage. With the increase of vessel diameter, strong superficial hemoglobin absorption led to only partial vessel-wall coagulation and, in some cases, to superficial dermal damage. Likewise, deeper vessels were not coagulated because of shadow effects by superficial vessel layers. Thus, the overall vessel-wall coagulation depth of the flashlamp-pumped dye laser was limited to a maximum of 0.65 mm (mean 0.37 mm). In addition, some degree of epidermal damage was present in most specimens, which significantly increased with epidermal melanin content and resulted in epidermal coagulation and blistering in pigmented skin. Our results explain the occurrence of crusting, hyperpigmentation, and hypopigmentation in therapy with the flashlamp-pumped dye laser and its limited effect on dark or hypertrophic port wine stains in adults featuring large vessel diameters or multiple vessel layers.

Thermocoagulation effect of diode laser radiation in the human prostate: Acute and chronic study

Objectives To evaluate the safety and efficacy of low-power slow-heating diode laser-induced photocoagulation of prostatic tissue for treatment of benign prostatic hyperplasia, we conducted a series of acute and chronic studies using a diode laser (810 nm) to irradiate human prostate. Methods The study included 6 patients undergoing radical prostatectomy because of malignancy. Laser radiation to the prostate was given transurethrally, in a noncontact mode, at the time of the procedure in 2 patients (acute group): 10 W for 300 seconds on the right side of the prostate and 15 W for 180 seconds on the left. In the remaining 4 patients (chronic group), laser radiation was given at 1, 7, 10, and 12 weeks prior to the prostatectomy. Results In the acute group the average depth of coagulation was 8.5 and 9.0 mm for the laser regimens of 15 W for 180 seconds and the 10 W for 300 seconds, respectively. In the chronic group, the average depth of coagulation was 8.9 mm for both laser regimens studied. In the acute group, there was an ill-defined hemorrhagic ring at the periphery of the lesion. At 1 week, an intact necrotic coagulum was present. At 7 weeks, some of the coagulated tissue had already sloughed off. Longer follow-up at 10 and 12 weeks demonstrated formation of a well-defined cavity with mostly re-epithelialized surface. Conclusions Our findings suggest that noncontact diode laser (810 nm) irradiation can induce in the human prostate significant coagulation necrosis followed by sloughing of tissue and cavitation of the prostatic urethra.

Corneal photocoagulation with continuous wave and pulsed holmium:YAG radiation

In this study, the effectiveness of pulsed and continuous wave (CW) holmium:YAG lasers in coagulating in vitro pig corneas was analyzed. With the CW laser, irradiance and exposure time were varied; irradiance, from 162 to 324 W/cm2 and exposure time, from 200 to 800 ms. With the pulsed laser, number of pulses and radiant exposure were varied; number of pulses per lesion, from 4 to 30 and radiant exposure, from 10 to 25 J/cm2. Laserinduced corneal damage was determined by analyzing histological cross sections of each lesion. Depth and diameter of the lesions were plotted against the varying laser parameters. Light and birefringent photomicrographs of typical lesion histology show that the pulsed laser significantly damaged superficial layers of the cornea and could not achieve the coagulation depths produced by the CW laser. Additional histology demonstrates that minimal surface damage (intrastromal coagulation) occurred when the CW laser beam was delivered with a sapphire-tipped contact probe. The results provide empirical data on the sensitivity of each parameter in producing a range of coagulation end points. In addition, the experimental results describe trends between the parameters of either laser and the extent of coagulation.

Neodymium: Yttrium-aluminum-garnet laser dosimetry for the prolase II side-firing delivery system in the human prostate

Objectives. The objective of this study was to define optimal treatment parameters and quantitative dosimetry for neodymium:yttrium-aluminum-garnet (Nd:YAG) laser coagulation prostatectomy utilizing the ProLase II side-firing laser delivery system. Methods. Transurethral Nd:YAG laser application was performed with the ProLase II side-firing laser fiber in adult human prostates prior to planned radical prostatectomy. Depth and volume of prostatic tissue coagulation for single, continuous laser applications were measured at variable power settings from 40 to 80 W, while holding total energy delivery constant. Holding the power setting constant, the extent of tissue coagulation was similarly measured for variable treatment times from 45 to 90 seconds. Results. Peak tissue coagulation for the ProLase II was observed at 60 W—up to a maximum of 13 mm tissue penetration and 3.92 cc volume coagulation following a single spot laser application. The mean depth of tissue coagulation at 60 W power setting was 12.7 mm, with a mean volume of tissue coagulation of 3.07 cc. Holding the power setting constant at 60 W, and increasing treatment time from 45 to 60 seconds, the extent of tissue coagulation increased significantly. However, beyond 60 seconds continuous laser application at 60 W, a plateau in tissue effects was observed, with minimal increase in tissue coagulation between 60 and 90 seconds. Conclusions. Using the ProLase II side-firing laser fiber, 60-second Nd:YAG spot laser applications at 60 W power setting represent optimal treatment parameters. The quantitative dosimetry curves produced for the ProLase II fiber are compared with prior dosimetry studies with the Urolase delivery system.

Myocardial temperature distribution under cw Nd:YAG laser irradiation in in vitro and in vivo situations: theory and experiment

Tissue samples ranging from 2 to 16 mm in thickness were irradiated at 1064 nm with energies ranging from 40 to 2400 J. Coagulation lesions of in vitro and in vivo experiments were subjected to temperature profiling and submitted for histology. Irreversible damage was calculated with the damage integral formalism, following the bioheat equation solved with Monte Carlo computer light-distribution simulations. Numerical temperature rise and coagulation depth compared well with the in vitro results. The in vivo data required a change in the optical properties based on integrating sphere measurements for high irradiance to make the experimental and numerical data converge. The computer model has successfully solved several light-tissue interaction situations in which scattering dominates over absorption.

Comparison of Thermocoagulation Effects of Low Power, Slow Heating Versus High Power, Rapid Heating Nd: YAG Laser Regimens in a Canine Prostate Model

We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus high power, rapid heating (50 W x 60 seconds) laser regimens in the canine prostate. The study was performed in 20 mongrel canines. On each prostate, the low power regimen was delivered at the 2 and 4 o'clock positions, and the high power at the 8 and 10 o'clock positions. The laser power was measured at the fiber tip. Seven dogs (acute group) were sacrificed 1 hour after the procedure. The other 13 dogs (chronic group) were sacrificed at different time intervals from 3 days to 9 weeks after the procedure. The average depth of coagulation was significantly greater in lesions treated at low power (acute: 10.7 mm., chronic: 13.3 mm.) than in those treated at high power (acute: 8.5 mm., chronic: 11.6 mm.). Another potential benefit of the low power regimen observed in the study was preservation of the integrity and efficiency of the laser probe.

The optimization of laser prostatectomypart I: Free beam side fire coagulation

Objectives. To study laser-tissue interaction and develop unifying principlesfor the optimization of free beam side fire neodymium:yttrium-aluminum-garnet (Nd:YAG) laser coagulation prostatectomy. Methods. The heating patterns and coagulation volumes created by different right angle deflecting fibers were studied at different wattages and times in potato and canine models. Results. In the potato, higher wattage resulted in deeper and more rapid heating. Thehigh power density fibers created lesions of smaller volume which increased less with rising wattage than those fibers of lower power density. In the canine model, carbonization decreased heat penetration, and “popcorn” decreased superficial temperature without altering lesion size as long as it occurred without carbonization. As lasing progressed, smaller incremental increases in coagulation depth were achieved. Conclusions. To optimize coagulation laser prostatectomy, the surgeon should operate at the highest wattage which does not cause carbonization. The visualized intraoperative laser-tissue interaction allows the adjustment of laser power during the case as needed.

Myocardial coagulation by intraoperative Nd:YAG laser ablation and its dependence on blood perfusion.

To investigate whether the efficacy of intraoperative laser ablation therapy is affected by myocardial blood perfusion, we irradiated 11 canine hearts through the epicardium with a Nd:YAG laser (10, 20, and 30 J/mm2) using air as the medium. Compared coagulated myocardial depth, width, and volume obtained in the red beating heart was compared with those in the white nonbeating heart infused with 0 degrees C saline (cardioplegic model) via the coronary artery. Histologically, the macro- and microscopical findings were very similar. At each level of energy, the width and volume of red myocardium coagulated were significantly larger than those of white myocardium (P < 0.01). At 30 J/mm2, the depth of coagulation of red myocardium was significantly larger than that of white myocardium (P < 0.01). The coagulated volume of the white myocardium was about 60% of that of the red myocardium. Nd:YAG laser energy was absorbed by blood (red color = hemoglobin), and more energy was transferred in the higher temperature myocardium. During intraoperative Nd:YAG laser ablation, the presence of blood perfusion in cardiac tissue is thought to be an important factor affecting safe irradiation.

Preliminary assessment of the Con-Bio laser in vivo.

A variety of lasers are available for the treatment of pigmented and vascular lesions. This paper presents our preliminary evaluation of the Q-switched 532 nm Con-Bio laser (Continuum Biomedical, Livermore, CA) in a murine model. Mice were anesthetized with intraperitoneal pentobarbital. Laser impacts (10 nsec, 150 mJ max.) were created on the ears at fluences of 1.5, 2, 3, 4, 5, and 6 J/cm 2. Acute study animals were sacrificed 15 min postinjury. Tissues were fixed in formalin and examined via light microscopy. Chronic study animals were allowed to heal for 3 weeks postoperatively. Parameters analyzed included the presence or absence of blistering, hemorrhage, visual assessment of thermal injury, microscopic evidence of vascular coagulation, or disruption and cosmesis. Acute vascular disruption and coagulation were present in all samples. Healing and cosmesis were good at all fluences tested. Tests of the laser in a prefocused mode produced a tissue cavitation effect with a depth of coagulation of 0.73 +/- 0.44 mm and hemorrhage of 0.68 +/- 0.41 mm. A chronic study of the vascular effect on larger vessels (1-2 mm) was conducted on a rabbit ear. Acute disruption was observed, however, all vessels were recanalized when examined grossly and histologically at 3 weeks. These preliminary results suggest that this new laser may be useful for the treatment of cutaneous vascular lesions. Further studies and clinical trials are warranted.

Effects of surface irrigation on the thermal response of tissue during laser irradiation.

Effects of surface irrigation on the thermal response of tissue during laser irradiation are investigated. In particular, influence of temperature and flow rate of the irrigation fluid on the resulting temperature distributions and coagulation depths are studied. Intraluminal Nd:YAG laser irradiation of bovine muscle is performed in vitro for a fixed value of the irrigation flow rate while the irrigation temperature is varied, and for a fixed irrigation temperature while the irrigation flow rate is kept constant. Thermocouples are used to measure the temperatures within the tissue for various irradiation and irrigation conditions. Higher temperatures and deeper coagulation depths are achieved as the temperature of the irrigation fluid is increased. For sufficiently low values of irradiance and exposure time, the use of cold irrigation is shown to prevent or delay tissue carbonization. Beyond a critical irradiance and an exposure time, use of cold irrigation does not prevent tissue carbonization. Coagulation depths and temperature distributions are not affected by a change in the flow rate of laminar irrigation. Application of stagnant irrigation, however, results in an increase in coagulation depth. Results of this study suggest that the dominating mechanism of heat transfer during application of laminar irrigation is thermal diffusion as compared to the bulk motion of the fluid.

中赤外パルスレーザーによるLTKの基礎的検討: Ho: YAG レーザーとTm: YAG レーザーとの比較

To propose Tm: YAG laser LTK (Laser Thermal Keratoplasty), we compared the porcine corneal coagulation depthes produced by Ho: YAG laser (wavelength=2.10 μm) and Tm: YAG laser (wavelength=2.01μm) in vitro. The radiant exposures of both lasers varied from 2.5to 22J/cm2 and the number of laser pulses ranged from single shot to 20 shots. The corneal coagulation depthes were as thick as the human corneal thickness (0.7mm) for Ho: YAG laser and less than that for Tm: YAG laser in the case of single shot. The corneal coagulation depthes were thicker than the penetration depth of either lasers. In the case of varing the number of laser pulses, the relation between the corneal coagulation depthes and the radiant exposures was independent of the number of laser pulses for Tm: YAG laser (2 Hz), however the corneal coagulation depthes increased with the number of laser pulses for Ho: YAG laser (4 Hz). The energy efficiency of the coagulation gave the reason why the depth of corneal coagulation were thicker than the penetration depth. These results demonstrated the capability of Tm: YAG laser LTK without endothelium injury.

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.

Water-jet-cooled Nd:YAG laser coagulation of experimental liver metastases: correlation between ultrasonography and histology.

To establish the value of ultrasonography in imaging laser coagulation of tumor and surrounding tissue, the relation between measurements on ultrasound and histology was determined in a rat tumor model. A piece of colon carcinoma CC531 was implanted in the liver of 21 Wag/Rij rats; 20 days later, tumors (mean diameter 5.3 mm) were treated with a water-jet-cooled Nd:YAG laser at 10 W and either 150 J, 300 J, 600 J, 1,200 J, 1,700 J, or 2,400 J. Ultrasonography was done just pre- and immediately post-laser treatment. The animals were sacrificed and livers removed for light microscopical evaluation. Depth and width of coagulation were measured directly on ultrasound, and on histological samples by computer-assisted image analysis. Laser treatment did not change the echogenic aspect of the tumor on ultrasound. However, liver damage appeared hypoechoic compared to normal liver. A significant correlation was found between the total size of the lesion on ultrasound and histology (P = 0.015, r = 0.57 for depth; P = 0.012, r = 0.58 for width), suggesting that laser induced tumor destruction may be derived from the amount of surrounding hepatic damage on ultrasound.

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

(Reprint requests to Dr. R. A. Neumann, Laser Unit, Dept. of Dermatol. II, Univ. of Vienna, Alserstr. 4, 1090 Vienna, Austria)

Microwave tissue coagulator in liver resection for cirrhotic patients.

The use of the microwave tissue coagulator was studied on 20 consecutive elective hepatic resections carried out for symptomatic hepatocellular carcinoma with liver cirrhosis. The mean operative blood loss (excluding one patient with hepatic vein injury) was 1132 mL. Five patients required no blood transfusion. The average time taken to coagulate the anticipated liver transection plane was less than 15 min. Apart from the complications similar to those occurring in hepatic resections for cirrhotic patients, higher incidences of intra-abdominal sepsis (20%), sympathetic pleural effusion in the absence of chest or intra-abdominal sepsis (20%), and persistent fever lasting more than 1 week (40%) were encountered. It was considered that these complications were related to the coagulated tissue present in the liver remnants (mean depth of tissue coagulation = 3.8 mm) and concluded that although the hospital mortality rate of 10% and the mean operative blood loss of 1132 mL were acceptably low, microwave liver surgery carried a high morbidity rate which is a drawback in major hepatic resectional surgery.

Vascular Malformations of the Gastrointestinal Tract

The advent of fiberoptic endoscopy, which became widespread in the evaluation of gastrointestinal bleeding throughout the late 1970s and 1980s, has dramatically changed both our understanding of the extent to which vascular malformations account for gastrointestinal blood loss and our ability to treat these lesions at the time of diagnosis. Colonic vascular malformations appear to be the single most common cause of acute or recurrent gastrointestinal bleeding episodes in patients over 60 years of age, being responsible for the bleeding in as many as 35% of such patients. Although less common as a cause of upper gastrointestinal bleeding, these lesions still account for 2% to 5% of bleeding lesions in older patients. Diagnosis is accomplished by endoscopy, and the vascular malformations can then be coagulated via the endoscope using one of a number of thermal systems. The argon laser, the heater probe, and the BICAP system are all effective and safe throughout the gastrointestinal tract, especially in the cecum and right colon, where the majority of sporadic vascular malformations occur. Monopolar cautery and the Nd:YAG laser are equally efficacious, but their greater and less predictable depth of coagulation make them much less safe in the cecum and right colon. There are no apparent advantages in terms of efficacy and safety between laser treatment and the other thermal modalities. The laser has the advantage of being quicker, which is especially important when treating large or multiple lesions. The other modalities have the advantages of portability and low relative cost. Endoscopic therapy with lasers or other thermal devices is nonspecific. The effects are achieved by thermally coagulating the mucosal vascular lesions, allowing the coagulated tissue to slough, and leaving a mucosal ulceration that subsequently heals with re-epithelialization. Endoscopic coagulation has thus been reported effective in the treatment of gastrointestinal mucosal vascular lesions regardless of their etiology or characteristics. It has been effective for sporadic vascular malformations, hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease), radiation proctocolitis, the blue rubber-bleb nevus syndrome, and diffuse gastric antral vascular ectasia (the watermelon stomach). As we move through the 1990s and beyond, these endoscopic modalities offer an effective, relatively safe, and clearly less invasive treatment option for the many patients who experience acute, recurrent, or chronic gastrointestinal bleeding from any of these lesions.

Comparison of thermal injury zones in loop electrical and lasercervical excisional conization

Thirty cervical conization specimens obtained by thin-loop electric excision were compared with 30 carbon dioxide laser excisional cone specimens. Zones of thermal artifact were measured with a precise stage micrometer technique calibrated to a Zeiss standard. The mean depth of coagulation at the ectocervical margin measured 0.187 and 0.164 mm for thin loop and laser, respectively. Thermal artifact at the endocervical margin was greater with electric loop (0.295 mm) than with superpulsed carbon dioxide laser (0.137 mm). The zones of thermal injury induced by both electric loop and laser made no significant impact on the interpretation of margin adequacy.

Determination of the optimal technique for bipolar electrocoagulation treatment: An experimental evaluation of the BICAP and Gold probes

The optimal technique for use of bipolar electrocoagulation has not been established despite its widespread clinical use. This study of the BICAP (Circon-ACMI, Stamford, CT) and Gold (Microvasive, Watertown, MA) probes evaluates the maximal force that can be applied through an endoscope and quantifies the depths of coagulation and sticking at varying parameters in a beef liver model. Maximal forces of application were determined with 3.2- and 2.3-mm probes extended 3 and 6 cm outside the endoscope at 90 ° and 45 °. Depths of coagulation and sticking were measured at 90 combinations of varying forces of application (0, 50, and 100 g), watt settings (1, 3, 5, 7, and 9), and durations (2, 6, 10, and 14 seconds; 3 × 2 seconds, 7 × 2 seconds) for the 3.2-mm BICAP and Gold probes. Mean maximal force of application decreased with greater extension or angulation of the probe outside the scope (3.2-mm BICAP—90 °: 3 cm, 110 g; 6 cm, 56 g; 45 °: 3 cm, 50 g; 6 cm, 30 g; P < 0.001; 3.2-mm Gold—90 °: 3 cm, 130 g; 6 cm, 105 g; 45 °: 3 cm, 62 g; 6 cm, 48 g; P < 0.001). The maximal force was significantly greater with the Gold probe than with the BICAP in seven of eight comparisons. Significant variations among the mean depths of coagulation (in millimeters) for pooled data of each parameter were observed with force of application (BICAP: 0 g, 0.8; 50 g, 1.4; 100 g, 1.7), watt settings (BICAP: 1, 0.6; 3, 1.7; 5, 1.4; 7, 1.4; 9, 1.3), and duration of treatment (BICAP: 2 seconds, 0.8; 6 seconds, 1.1; 10 seconds, 1.4; 14 seconds, 1.5; values for the Gold probe were comparable). The greatest depths of coagulation were observed at 100 g force, watt setting 3, and 14 seconds or 7 × 2 seconds duration. Sticking paralleled depth of coagulation, increasing with force and duration of application. In conclusion, optimal treatment of bleeding gastroduodenal lesions with bipolar electrocoagulation includes (a) placing the tip of the endoscope en face as close as possible to the bleeding lesion, (b) applying the maximal force possible, (c) using a low-watt setting (~ 3), and (d) treating with prolonged periods of coagulation.

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

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.

Reflectance as an indirect measurement of the extent of laser-induced coagulation

Two-dimensional reflectance images and surface thermal distributions were recorded during argon laser induced coagulation. During laser irradiation, coagulated egg yolk formed a white lesion. The whiteness, or reflectance caused by backscattering of light from the forming lesion, would be measured after a short delay from the onset of laser irradiation. In the experiments which covered exposure time from 4.5 to 17.0 s, we found that it started slowly, the reflectance increased rapidly once the surface temperature of the lesion reached approximately 90 degrees C. After this rapid rise, the reflectance began to taper off until no change in reflectance was recorded. There was a 0.98 correlation between lesion diameter measured from a two dimensional reflectance image and the lesion diameter that was measured microscopically. There was a 0.92 correlation between reflectance at the center of the lesion and microscopically measured depth of coagulation at the same point. However, the correlation between microscopically measured coagulation depth and width was only 0.88.