Creation of a volume lesion in the dog prostate using neodymium: YAG laser coagulation: Concepts for clinical treatment

Background and Objective: The purpose of this study was to determine the geometrical development of a coagulated zone in the canine prostate during free beam side fire Nd: YAG laser coagulation. Study Design/Materials and Methods: A series of 10 male dogs underwent endoscopic prostatic Nd: YAG fixed position laser coagulation through a suprapubic cystotomy using a right-angle deflecting delivery catheter (Microvasive, Boston, MA) at times varying from 10 to 120 seconds at 30 watts. In addition, two dogs underwent lasing by pulling the catheter at 1 mm/s in four quadrants. Acute gross and microscopic pathology specimens were prepared and the lesion shape and volume determined. Results: Analysis of the coagulated volume showed that during the initial 15 seconds of lasing, the zone of coagulation approximates a sphere centered on the urothelium opposite the laser fiber. However, as lasing progressed, the lesion changed from a sphere to an expanding ellipse. This changing geometry can be explained by the absorption and scatter characteristics of the laser and the temperature equilibrium that is established within the prostate. Conclusion: An understanding of this time-dependent geometrical shift from a sphere to an ellipse allows the surgeon to supplement the fixed protocols for lasing at certain positions for given amounts of time. Specific plans can then be established for tissue at the bladder neck, apex, anterior stroma, floor, and irregular prostatic regrowth. © 1995 Wiley-Liss, Inc.     

Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of benign prostatic hyperplasia: A comparative study

Objectives

Currently, various side-emitting optical fibers with different tip geometry are used transurethrally to deliver laser radiation for treatment of benign prostatic hyperplasia (BPH). Since fiber tip design could profoundly affect the size and profile of the emitted laser beam, and consequently the tissue response and the extent of tissue coagulation, we evaluated commercially available fibers in regard to their optical characteristics and their ability to coagulate tissue in a controlled experimental setting.

Methods

Thirteen fibers manufactured by different companies and clinically used at the present time were tested using a surgical neodymium:yttrium-aluminum-garnet laser. The profile of the laser beam delivered via each fiber was imaged on a CCD camera at various distances and evaluated by means of a laser beam analyzer. Beam divergence angle was then calculated for each tip. Tissue coagulation effects were assessed by irradiating samples of beef muscle immersed in water at 37 °C. The fiber tip was kept 2.5 mm away from the tissue and irrigation was maintained at flow rate of 350 to 400 cc/min during irradiation. Laser powers of 20, 40, and 60 W were used for 180, 90, and 60 seconds, respectively, delivering a total energy of 3600 J.

Results

The results of the optical evaluation divided the fibers into two major groups: broad beam with large divergence angle and narrow beam with small divergence angle. Statistical analysis of the data (using analysis of variance) showed that volumes of coagulated tissue were significantly larger for broad beam fibers than for narrow beam fibers (1.15 ± 0.32 versus 0.89 ± 0.34 cm³; P <0.05). Also, significantly larger volumes were obtained for 20 W when compared with 60 W (1.08 ± 0.43 versus 0.88 ± 0.27 cm³; P <0.05).

Conclusions

The laser power density delivered by individual fibers to the prostate tissue may vary significantly, thus greatly affecting the extent of tissue coagulation. Therefore, irradiation parameters must be optimized for each fiber type.     

Histopathological Evaluation of Laser Thermocoagulation in the Human Prostate: Optimization of Laser Irradiation for Benign Prostatic Hyperplasia

We have previously shown in a canine prostate model that a noncontact low power neodymium: YAG laser regimen of 15 watts for 180 seconds yields a larger volume of coagulation necrosis than the currently recommended high power regimen of 50 watts for 60 seconds. These 2 regimens have not yet been compared in humans. The objective of this study was to evaluate histopathologically the thermocoagulation effect of these 2 laser regimens in the human prostate and the effect of the spatial distribution of the laser lesions on the extent of coagulation necrosis. The study was conducted in 10 patients undergoing radical prostatectomy or cystoprostatectomy. The laser treatment was given transurethrally 1 hour before removal of the specimen.There were no fractures of the prostate. The coagulation necrosis did not reach the peripheral zone and it was minimal in areas rich in fibromuscular tissue, such as the bladder neck. At times, nodular benign prostatic hyperplasia was unaffected. A 4-quadrant treatment in the same plane often yielded small nonconfluent lesions. Confluent lesions in the same plane yielded approximately 30 percent greater depth of coagulation necrosis, which was achieved when 3 or 4 lesions were created on each side of the prostate (per single transverse plane). Likewise, coagulation necrosis observed with 15 watts for 180 seconds was approximately 40 percent greater than that noted with the 50 watts for 60 seconds regimen. Our findings suggest that noncontact laser prostatectomy is a safe procedure that can be improved by modifying the laser regimen and the spatial distribution of lesions.     

Enhancement of tissue lesion depth by dual wavelength irradiation with the Nd-YAG/KTP laser: Perspectives for laser prostatectomy

The Nd-YAG/KTP laser coagulates and vaporizes prostate tissue. The objective of this study was to investigate the combined effects of both wavelengths and to determine the irradiation parameters allowing the largest lesion volume. Chicken breast tissue was irradiated ex vivo. Consecutive 1064 and 532 nm Nd-YAG/KTP laser irradiations were performed for different combinations (30 W/10 W, 20 W/20 W, 10 W/30 W) with variable total fluence (1200 J, 2400 J, 3600 J) and compared to isofluent single wavelengths at 40 W irradiation. The depths, diameters and volumes of the total lesion as well as the vaporization effects of the 532 nm wavelength on normal and on priorly coagulated tissue were analysed. Maximum total lesion depths (p< 0.001) were found under combined Nd-YAG/KTP (20 W/20 W) irradiation conditions. Ablation efficacy of the 532 nm wavelength was reduced after prior 1064 nm irradiation, but crater depths were increased. Dual wavelength irradiation with the Nd-YAG/KTP laser induces a specific denaturation process. This may represent a new approach to increase the depth of coagulation necrosis, and thus the treated volume, thereby improving long-term results.     

Fluorescence spectroscopy of epithelial tissue throughout the dysplasia-carcinoma sequence in an animal model: spectroscopic changes precede morphologic changes

BACKGROUND AND OBJECTIVE: Recent studies have indicated that chondrocyte viability decreases with prolonged or repeated laser irradiation. To optimize laser-mediated cartilage reshaping, the heating process must be finely controlled. In this study, we use high-power Nd:YAG laser irradiation (lambda = 1.32 microm) combined with cryogen spray cooling (CSC) in an attempt to reshape porcine septal cartilage while enhancing chondrocyte viability. STUDY DESIGN/MATERIALS AND METHODS: Chondrocyte viability was determined after high-power (50 W/cm2) Nd:YAG-mediated cartilage reshaping with and without cryogen spray cooling (CSC) and correlated with dynamic measurements of tissue optical and thermal properties. RESULTS: After 1.5 to 2.0 seconds of laser exposure, characteristic changes in diffuse reflectance (indicating the onset of accelerated stress relaxation) was observed in both laser only and laser with CSC specimens. After 2 seconds of laser exposure, specimens in both groups retained the curved shape for up to 14 days. After one laser exposure, chondrocyte viability was 94.35 +/- 6.1% with CSC and 68.77 +/- 20.1% (P < 0.05) without CSC. After two laser exposures, a similar trend was observed with CSC (70.18 +/- 16.44%) opposed to without CSC (28 +/- 45%; P < 0.05). CONCLUSION: CSC during high-power laser irradiation allows rapid heating while minimizing extreme front surface temperature elevations and axial thermal gradients. Laser irradiation with CSC can be used to effectively reshape cartilage tissue with the additional advantage of increasing chondrocyte viability.     

Preliminary evaluation of a novel side-fire diode laser emitting light at 940 nm, for the potential treatment of benign prostatic hyperplasia: ex-vivo and in-vivo investigations

OBJECTIVES

To evaluate, ex vivo and in vivo, the tissue‐removal capacity and coagulation properties of a diode laser emitting light at 940 nm, as in the search for potential therapeutic strategies for benign prostatic hyperplasia that cause less morbidity than transurethral resection of the prostate (TURP), various types of lasers have been tested.

MATERIALS AND METHODS

A diode laser system (prototype; wavelength 940 nm, Dornier MedTech, Wessling, Germany) was evaluated in an isolated, blood‐perfused ex‐vivo porcine kidney model at 10–60 W (five kidneys). An in‐vivo beagle model was used to investigate the effects on six prostate lobes at a generator output power level of 200 W. After the laser treatment tissue were examined histologically to compare the depth of coagulation and vaporization.

RESULTS

With increasing generator output power levels there was an increasing vaporization and coagulation ability for the diode laser at 940 nm in the ex‐vivo model. At 60 W the mean (sd ) vaporization depth was 1.72 (0.47) mm with a coagulation zone of 9.56 (0.26) mm. In vivo, the diode laser caused rapid ablation with no intraoperative haemorrhage. Histologically, the zone of coagulation had a mean (sd ) depth of 4.25 (0.15) mm at 200 W. The tissue removal capacity was estimated at 0.874–1.583 g/min in vivo.

CONCLUSIONS

Our findings indicate that diode‐laser vaporization at 940 nm is feasible and might be effective for acutely relieving bladder outlet obstruction in an in‐vivo setting. Due to its mean coagulation zone of 4.25 mm the diode laser seems to have effective haemostatic properties.     

Histological study of vas deferens following intravasal laser irradiation

Aim: To study the histologic changes of the vas deferens following Nd: YAG laser irradiation. Methods:Intravasal laser irradiation was given to (i) 52 segments of rabbit (laser dosage: 2 seconds at 40W～50W) and 16 segments of human (3 seconds at 45W～55W) vas deferens in vitro, (ii) 25 rabbit vasa (2 seconds～2.5 seconds at 40W～45W) in vivo and (iii) 2 human vasa (3 seconds at 55W) in vivo. Segments of vasa were removed from the in vivo irradiated vasa deferentia 15 days ～ 180 days (rabbit) or 15 days (man) after the exposure. All vas segments were embedded in methacrylate resin. Serial sections (thickness 25μm～30μm) were obtained and observed under a light microscope. Results: (i) Laser-induced damage reached the muscularis layer in 27% and 94% of the rabbit and human vas segments in vitro, respectively. (ii) Fourteen of the 25 in vivo rabbit vasa were completely occluded by fibrous tissue and the longer the time interval after treatment, the more likely was the vas occluded. Those unoccluded vasa had either a normal histology or a mucosal damage. (iii) One in vivo human vas was almost completely occluded by the fibrous tissue but the other had a relatively large lumen packed with sperm granulomatous tissue and partial destruction of the smooth muscle layer. Conclusion: Laser irradiation can induce long-term vas occlusion; for rapid occlusion, laser doses just completely destroying the mucosal layer will be advisable.     

Theramal, mechanical, optical, and morphologic changes in bovine nucleus pulposus induced by Nd:YAG (lambda = 1.32 microm) laser irradiation

BACKGROUND AND OBJECTIVE To examine the biophysical effects of photothermal heating on herniated intervertebral discs during laser decompression surgery. STUDY DESIGN/MATERIALS AND METHODS: Ex vivo bovine nucleus pulposus specimens were irradiated with a Nd: YAG laser (lambda = 1.32 microm, 100 seconds exposure time, 9-31 W/cm(2), 4.8 mm spot diameter), whereas changes in tissue thermal, mechanical, and optical properties were monitored by using, respectively, infrared radiometry, tissue tension measurements, and diffuse reflectance from a HeNe probe laser. Morphologic changes and mass reduction were monitored by recording shape changes on video and weighing specimens before and after laser exposure. RESULTS: At power densities below 20 W/cm(2), evaporation of water and specimen volume reduction (shrinking) were consistently observed on video during irradiation. In contrast, above 20 W/cm(2), vapor bubbles formed within the specimen matrix and subsequently ruptured (releasing heated vapors). When radiometric surface temperature approaches approximately 60 to 70 degrees C (denaturation threshold for tissue), tissue tension begins to increase, which is consistent with observations of specimen length reduction. The onset of this change in tissue tension is also reflected in characteristic alterations in diffuse reflectance. With cessation of laser irradiation, a sustained increase in tissue tension is observed, which is consistent with changes in specimen length and volume. Higher laser power results in a faster heating rate and subsequently an accelerated tension change. Specimen mass reduction increased with irradiance from 19 to 72% of the initial mass for 9--31 W/cm(2), respectively. Irradiated specimens did not return to their original shape after immersion in saline (48 hours) in contrast to air-dried specimens (24 hours), which returned to their original shape and size. CONCLUSION: These observations suggest that photothermal heating results in irreversible matrix alteration causing shape change and volume reduction (observed on video and evidenced by the increase in tissue tension) taking place at approximately 65 degrees C. Inasmuch as high laser power results in vapor bubble formation and specimen tearing, the heating process must be controlled. Diffuse reflectance measurements provide a noncontact, highly sensitive means to monitor dynamically changes in tension of nucleus purposus.     

Simplified treatment planning for interstitial laser thermotherapy by disregarding light transport: a numerical study.

BACKGROUND AND OBJECTIVE: The objective was to investigate the effect of light transport on the temperature distribution and the coagulated volume under conditions relevant to interstitial laser thermotherapy (ILT) of tumors in the human liver. STUDY DESIGN/MATERIALS AND METHODS: Temperature distributions and coagulated volumes produced with a diffusing laser fiber or a conductive heat source, at equal output power, were numerically calculated for tissue with different optical penetration depths. Four irradiation times (5, 10, 20, and 30 min) were studied. A three-dimensional finite-element model was used to calculate the temperature distribution during heating with four conductive heat sources (no light emission). Results were compared with measured temperature distributions during laser irradiation in a gel phantom with known optical properties. RESULTS: Numerical calculations showed that the influence of light transport on the coagulated volume was negligible in tissue with optical penetration depths below 3-4 mm at all studied irradiation times. The phantom experiment indicated good agreement with the calculated temperature distribution, both with a single diffusing laser fiber and with four fibers. CONCLUSION: Light transport influences coagulated volumes only slightly under conditions presented in this work, which is relevant to ILT of tumors in the human liver.     

Interstitial Laser Photocoagulation with Four Cylindrical Diffusing Fibre Tips: Importance of Mutual Fibre Distance

. Simultaneous application of multiple fibres could increase the volume of coagulation produced with interstitial laser photocoagulation (ILP) for solid tumours. To take full advantage of the presumed synergistic thermal effect between the fibres, the optimal combination of laser power and distance between the fibres was investigated. Four fibres with a cylindrical diffusing tip of 2 cm length were used, coupled to an optical beamsplitter for Nd:YAG light (four channels, maximal variation 9.5%, transmission >85%). The distance between the fibres was 1, 1.5, 2, 2.5 , 3 or 4 cm with a power output of either 4, 5, 6 or 7 W/fibre; energy per fibre was constant at 1800 J by adjusting exposure time. After laser application, dimensions of the coagulated lesions were measured. The optimal mutual fibre distance was 2 cm ( p<0.01) at all power levels. This resulted in lesions with a mean (SD) volume of 44.5 (2.1) cm³ and a largest diameter of 5.1 (0.4) cm at 7 W/fibre. Smaller distances between the fibres resulted in smaller lesions with central carbonisation, whereas larger distances resulted in four separate zones of coagulation. It was concluded that simultaneous application of four interstitial fibres may result in a considerable increase of volume of coagulation. Fibre position and mutual fibre distance determines whether synergism of the coagulative effect occurs. Paper received 14 July 1998; accepted following revision 18 January 1999     

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)     

Technique and results of interstitial laser coagulation

Summary By use of thermal ablation techniques to apply heat to the prostate from the urethra, the coagulation volume is limited by the limited penetration depth of suitable radiation sources, e.g., lasers, and by heat conduction. Secondarily, the coagulated tissue is removed by sloughing. Interstitial heat application was expected to overcome these problems. Our initial in vitro and animal studies using different light guides for interstitial Nd: YAG laser radiation showed that small, carbonized lesions were created by bare fibers, whereas large, homogeneous coagulation zones measuring up to 2 cm in diameter were produced by specially designed ITT (interstitial thermotherapy) fibers, which secondarily resulted in marked volume reduction by atrophy. Further experiments using such applicators resulted in an operation technique suitable for clinical routine in the treatment of symptomatic benign prostatic hyperplasia (BPH). These laser applicators are inserted into the prostate either transurethrally through a cystoscope under direct vision or percutaneously from the perineum under transrectal ultrasound guidance. The number of placements depends on the size and configuration of the gland. Radiation parameters were optimized for each system. To avoid charring, relatively low levels of laser power and long radiation periods (e.g., 7 W for 10 min) or power-formatting programs (e.g., stepwise reduction of power from 20 to 7 W for a total radiation time of 3 min) are applied. Beginning in July 1991, more than 350 unselected patients with BPH were treated with interstitial laser coagulation in our department, of whom 239 were followed for at least 1 year. The following changes in mean values were observed: American Urological Association (AUA) score, from 25.4 to 6.1; urinary peak flow rate, from 7.7 to 17.8 ml/s; residual urinary volume, from 151 to 10 ml; and prostate volume, from 47.4 to 29.1 ml. Retreatment was necessary in 9.6% of cases.     

Effect of simulated CO2 and GaAlAs laser surface decontamination on temperature changes in Ti-plasma sprayed dental implants

BACKGROUND AND OBJECTIVE: To investigate and compare temperature elevations at the implant-bone interface during simulated implant surface decontamination with a CO2 and a GaAlAs laser. STUDY DESIGN/MATERIALS AND METHODS: Stepped cylinder implants (Frialit 2) Friadent GmbH, Mannheim, Germany) with a Titanium plasma sprayed surface were inserted into bone blocks cut from pig femurs. An artificial periimplant bone defect provided access for laser irradiation in the coronal third. Both lasers were operated at 1.0-2.5 W in the cw-mode. The bone block was placed into a 37 degrees C water bath in order to simulate in vivo thermal conductivity and diffusitivity of heat. K-type thermocouples connected to a digital meter were used to register temperature changes at the periimplant bone. RESULTS: In mean, the critical threshold of 47 degrees C was exceeded after 8 seconds at a power output of 2.5 W, 13 seconds at 2.0 W, 18 seconds at 1.5 W, and 42 seconds at 1.0 W with the GaAlAs laser and 15 seconds (2.5 W), 23 seconds (2.0 W), 35 seconds (1.5 W), and 56 seconds (1.0 W) with the CO2 laser. At equal energy fluence, GaAlAs laser irradiation induced significantly higher temperature elevations than CO2 laser irradiation. CONCLUSIONS: In an energy dependent manner implant surface decontamination with both laser types must be limited in time to allow the implant and bone to cool down. Clinical guidelines are presented to avoid tissue damage.     

Effects of argon, dye, and Nd:YAG lasers on epidermis, dermis, and venous vessels

The aim of the present study, which was performed at the dorsal aspects of the ears of guinea pigs, was to compare effects of different lasers on epidermis, dermis, and small venous vessels. Irradiations were performed with argon, dye, and Nd:YAG lasers. In the first series tissue repair processes were studied after argon laser application. Laser defects were excised after 1, 4, 8, and 14 days and were prepared for routine histological examination. The breadth of epidermal defect and extent of dermal coagulation and occlusion of vessels by thrombus formation were examined histologically. In a second series parameters of irradiation (ie, exposure time, laser power) of the three different lasers were changed systematically. Laser-induced morphological tissue changes could be best observed 24 hours after irradiation. Each of the lasers led to occlusion of vessels by thrombus formation and also coagulated epidermis and dermis. The extent of dermal and epidermal coagulation was less pronounced after dye laser application. Using short exposure times it was possible to reduce the extent of epidermal damage caused by argon and Nd:YAG lasers. Only 50-msec dye laser pulses led to intravascular thrombus formation without epidermal and dermal damage.     

Neodymium:YAG Laser in the Treatment of Gynecologic Malignancies

The Nd:YAG laser has been used for tumor volume reduction of recurrent gynecologic malignant tumors after previous radiation therapy. The localization of the tumor did not allow conventional surgical resection or surgery was contra-indicated because of severe medical problems. Hemorrhage caused by recurrent tumor was controlled by tissue coagulation. The laser beam was delivered by means of a handpiece using the Model 8000 of the Molectron Medical Corporation. A power of 40 to 100 W was used with the maximal pulse duration of 9.9 sec and multiple pulse irradiation. The total energy ranged between 620 and 13.105 Ws. Good palliation was achieved in patients with hemorrhaging tumors of the cervix and ovary metastatic to the vagina.     

High-power laser vaporization of the canine prostate using a 110 W Thulium fiber laser at 1.91 microm

INTRODUCTION: The Thulium fiber laser may have several advantages over current urology lasers, including smaller size, more efficient operation, improved spatial beam quality, more precise tissue incision, and operation in pulsed or continuous-wave modes. Previous laser-tissue interaction studies utilizing the Thulium fiber laser have been limited to laser powers of less than 5 W, restricting potential medical applications. This study describes the preliminary testing of a high-power Thulium fiber laser for vaporization of the canine prostate, ex vivo. STUDY DESIGN/MATERIALS AND METHODS: A continuous-wave, 110-W Thulium fiber laser operating at a wavelength of 1.91 microm, delivered 88.5+/-2.3 W of power through a 600-microm-core silica fiber for non-contact vaporization of canine prostates (n = 6). RESULTS: The Thulium fiber laser vaporized prostate tissue at a rate of 0.83+/-0.11 g/minute. The thermal coagulation zone measured 500-2,000 microm, demonstrating the potential for hemostasis. CONCLUSIONS: The high-power Thulium fiber laser is capable of rapid vaporization and coagulation of the prostate. In vivo animal studies are currently being planned for evaluation of the Thulium fiber laser for potential treatment of benign prostate hyperplasia (BPH).     

Ex vivo and in vivo investigations of the novel 1,470 nm diode laser for potential treatment of benign prostatic enlargement

Perioperative haemorrhage is still the major complication of transurethral resection of the prostate (TURP) for benign enlargement of the prostate. Photoselective vaporisation of the prostate (PVP) with the potassium–titanyl–phosphate (KTP) laser has been shown to achieve instant tissue ablation with excellent haemostatic properties. Our aim was to determine the tissue removal capacity, coagulation and haemostatic property of the novel 1,470 nm diode laser, ex vivo and in vivo. We evaluated two prototype diode laser systems at 1,470 nm in an ex vivo, isolated, blood-perfused, porcine kidney model (n = 5; 10 W–50 W) and in an in vivo investigation of beagle prostate (n = 4; 100 W) to assess vaporisation capacities and coagulation properties at different generator settings. The diode laser evaluation was compared with an 80 W KTP laser in the porcine model. After the laser treatment we performed a histological examination to compare the depth of coagulation and vaporisation. The diode laser system (50 W) showed significantly lower (P < 0.0001) capacities for tissue removal than the 80 W KTP laser (0.96 mm ± 0.17 mm and 5.93 mm ± 0.25 mm, respectively, P < 0.0001), while coagulation zones were significantly (P < 0.001) larger in diode laser-treated kidneys (3,39 mm ± 0.93 mm and 1.27 mm ± 0.13 mm, respectively). In vivo, the diode laser displayed rapid ablation of prostatic tissue with no intraoperative haemorrhage. Histological examination revealed coagulation zones of 2.30 mm (±0.26) at 100 W in the diode laser-treated prostates.     

Selecting source locations in multifiber interstitial laser photocoagulation

A theoretical basis and practical algorithm are described for selecting optimal fiber source locations in multifiber interstitial laser photocoagulation (ILP). By analyzing the shape of overlapping coagulation patterns, the optimal separation of adjacent point heat sources inside a flat target volume boundary is shown to be d* = 2√2r_c, where r_c is the coagulation radius of a single source. Against a curved boundary, the algorithm specifies how d* should be altered. To assess the validity of the theory, ILP was conducted in bovine muscle by delivering 1064 nm laser energy through two or four plane-cut optical fibers simultaneously. Delivered power, exposure duration, and source separation were varied. The observed coagulation patterns matched the theorypredicted patterns at delivered powers of 1.60W and 1.85W, but not at 2.40W. Also, the experiments indicate that reciprocity of delivered power and exposure duration is invalid for ILP. © 1993 Wiley-Liss, Inc.     

Interstitial laser photocoagulation: Nd:YAG 1064 nm optical fiber source compared to point heat source.

Interstitial laser photocoagulation (ILP) was performed in vitro in lean bovine and chicken muscle by delivering 1.6 W of continuous-wave Nd:YAG laser energy (1064 nm) from a 400-microns core optical fiber for 300s. The resulting thermal coagulation lesion was consistently larger when the delivered energy was deposited into a small steel sphere than when it was delivered freely into the tissue. Mathematical modelling confirms this result. This preliminary study suggests that a point heat source produces a larger volume of thermal coagulation than a point optical source (1064 nm) delivering the same power.     

Effects of Nd: YAG laser coagulation of myocardium on coronary vessels

Laser coagulation of arrhythmogenic myocardium proved to be an effective surgical therapy for refractory arrhythmias. To determine the influence of Nd: YAG laser coagulation of myocardium on coronary vessels, a total of 48 transcatheter laser impacts (10 W, 10 sec, 7 W mm2) were directed to the left ventricular free wall via endocardial (24 lesions in 2 dogs) or epicardial (24 lesions in 2 dogs) approach. In 8 of 24 endomyocardial lesions (2 and 6 months old) coronary vessels with a diameter of greater than 50 microns were found within the coagulation zones. The volume of these lesions was significantly (P less than 0.01) smaller (139 +/- 43 mm3) than those (n = 16) with coronary vessels measuring less than 50 microns (311 +/- 87 mm3). Volumes of epimyocardial lesions (1-2 hours old) produced by transcoronary irradiation with normal coronary blood flow were significantly (P less than 0.01) smaller (31 +/- 17 mm3) than with reduced (73 +/- 22) or interrupted (119 +/- 34 mm3) blood flow (n = 8, each). Both directly irradiated coronary vessels and those found within the coagulation zones and scars appeared histologically normal through all layers with an intact intima without fibrosis or thrombosis. The ultrastructure of irradiated arteries, even with total interruption of blood flow, was no different from that of non-irradiated controls. Thus, coronary artery blood flow significantly reduces the volume of coagulated myocardium, whereas the vessels themselves appear to remain undamaged by laser irradiation as used for myocardial coagulation.