The role of pulse length in limiting distant damage to vascular tissue caused by the Nd-YAG laser

The total damage caused by equivalent doses of energy given to human cadaver vascular tissue over the same time scale from three Nd-YAG lasers of different pulse lengths is quantified. The continuous wave (c.w.) laser produces vacuolation and coagulation around a vaporized crater; the 100 μs pulsed laser produces less surrounding damage and the 10 ns pulsed laser none at all. The areas of damage in five craters made with 10 J energy were measured from histology slides using a digitising platten, and it was found that in each case the total amount of damage was the same, even though the depth of the craters made varied. The dose response for vaporization of the 10 ns pulsed laser was the greatest at 35 μm/J and that of the c.w. laser was least at 8 μm/J. A pulse length of 100 μs may not be the optimum for limiting surrounding tissue damage during laser angioplasty but it produces much less damage than a c.w. laser and unlike the 10 ns pulses is easily transmissible down an optical fibre.     

Interstitial laser photocoagulation: Evaluation of a 1320 nm Nd-YAG and an 805 nm diode laser: the significance of charring and the value of precharring the fibre tip

Interstitial laser photocoagulation (ILP) is a new percutaneous technique of thermal destruction (necrosis) of deep-seated tumours, using low power laser energy. Our purpose was to investigate: (i) the effects of different laser wavelengths on the extent of thermal damage produced; and (ii) the role of charring around the fibre tip during ILP. Forty-five normal Wistar rats (250–300 g) had ILP to their liver (exposed at laparotomy) by inserting a 400 μm optical fibre into the liver, and activating the laser at 1, 2 or 3W. This was performed at three laser wavelengths (1064 nm Nd-YAG, 1320 nm Nd-YAG, 805 nm diode) using a clean plane-cleaved fibre, and at two wavelengths (1064 nm and 1320 nm Nd-YAG) using a fibre with pre-charring at its tip. The 805 nm and 1320 nm laser wavelengths produced significantly greater necrosis than the 1064 nm, using a clean fibre tip (mean diameters at 2 W were 21.7 mm, 18.3 mm, 8 mm respectively). Pre-charring the fibre significantly increased the necrotic lesion size at 1064 nm (mean diameter at 2 W was 14.7 mm). Using more strongly absorbed wavelengths (805 nm and 1320 nm) and pre-charring the fibre tip give greater thermal damage during ILP, contrary to previously held views that the optimal wavelength for ILP was 1064 nm in the absence of charring.     

Effects of super-pulsed Nd-YAG laser on arterial tissue: comparison with continuous wave

The effects of a super-pulsed Nd-YAG laser at 1.32 μm wavelength on normal or atherosclerotic human arterial tissue were evaluated and compared with those obtained with continuous wave. One joule per pulse was delivered through a 0.2 mm optical fibre with a pulse width of 10 ms at 10 Hz (super-pulse), or 10 W (10 J) were delivered at continuous wave in saline or blood. Ten joules were delivered with super-pulse or continuous wave for each tissue specimen. The aortic specimens were lased either by continuous wave or super-pulse. At super-pulse mode, ablation efficiency (mm³ J⁻¹) was 0.0149±0.0044 for normal tissue in saline, 0.0148±0.0043 for atheroma in saline, 0.0138±0.0062 for normal tissue in blood, and 0.0146±0.0049 for atheroma in blood. There was no significant difference between the groups. At continuous wave mode, ablation efficiency was 0.0507±0.0299 for atheroma in blood (p<0.001 vs super-pulse). However, extensive charring was observed with continuous wave lasing (41% with continuous against 14% with pulsed mode,p<0.001). Heavily calcified plaques were also ablated at 1.5 J per pulse and 15 W (continuous wave), resulting in extensive charring with continuous wave (77% vs 18% with super-pulse,p<0.01). In conclusion, at super-pulse mode, 1.32 μm Nd-YAG laser has neither the selectivity for atheroma nor influence of blood, thermal injury induced by super-pulse is less than that induced by continuous wave (cw), calcified plaques can be ablated by super-pulse, and super-pulsed Nd-YAG laser angioplasty is safer to use than continuous wave.     

Nd-YAG laser thermal effect: Comparative study of coagulation in rat liver in vivo by continuous wave and high power pulsed lasers

The coagulation effect of a continuous-wave neodymium-YAG (Nd-YAG) laser and of a high-power (500 W) pulsed (3–500 ms) microcomputer-controlled Nd-YAG laser are compared in rat liver in vivo. In a series of 68 animals, surface temperature was measured with an infrared camera, and necrosed volume was assessed histologically 24 h after laser irradiation. The high-power pulsed Nd-YAG laser presents two interesting features. First, it gives a better control of surface temperature. Second, a controlled sequence of high-power short pulses produces a predictable coagulated volume which can be comparable to that obtained with continuous-wave Nd-YAG or argon lasers.     

Effects of 1.32-μm Nd-YAG laser on brain thermal and histological experimental data

Considering that the 1.32-μm Nd-YAG laser should have physicothermal properties close to those of the CO₂ laser, a series of experiments were conducted on rat cortex (N = 51). Three laser wavelengths were compared: CO₂ laser (10.6 μm), 1.06-μm Nd-YAG, and 1.32-μm Nd-YAG lasers. For each shot, temperature measurements were recorded with an infrared thermographic videocamera. The digitized signals were figured as thermal profiles and temperature developments. Ninety-five shots were correctly studied and analyzed: CO₂, N = 29; 1.06-μm Nd-YAG, N = 20; 1.32-μm Nd-YAG, N = 46. The histological lesions produced by these three lasers were compared on animals killed 24 hours (N = 20), 8 days (N = 20), and 30 days (N = 5) after the laser impacts. For equivalent densities of energy, the depth of cortical necrosis was comparable for the CO₂ laser (200–250 μm) and the 1.32-μm Nd-YAG laser (210–260μm) whatever the date of death; the 1.06-μm Nd-YAG laser shots were responsible for much more important damage (400–550μm). Because of its important absorption in water and nervous tissue, the authors consider the 1.32-μm Nd-YAG laser most suitable for neurosurgery, particularly because it is conducted through optic fibers, and therefore is easy to handle during neurosurgical procedures.     

Nd-YAG laser for general surgery

We report here our clinical experiences with Nd-YAG laser on general surgery, and evaluate the results of this procedure. From December 1979 to December 1981, we applied Nd-YAG laser to various operations as a hemostatic and cutting tool. For hemostasis, we used conventional quartz fiber which was covered with sterile tube, and hemostatic efficacy was examined especially in the subcutaneous bleeding and the bleeding from solid organs. For cutting, we used special devices, ie, Medilas YAG surgical probe (noncontact-type probe), and a laser blade (contact-type probe), and performed four liver resections. It is concluded that the hemostatic efficacy of Nd-YAG laser to various bleeders was proved in general surgical procedures, and furthermore this laser can cut tissue if we utilize these devices. When comparing these two devices, we would prefer the contact-type probe.     

Low power interstitial Nd-YAG laser photocoagulation in normal rabbit brain

The safe, effective, clinical application of interstitial laser irradiation to destroy brain tumour tissue requires a knowledge of the relation of the extent of laser-induced (thermal) necrosis to the delivered laser power and total energy, and to time post-irradiation. We have conducted experiments to determine these relationships in normal rabbit brain. Irradiation by a Nd-YAG laser (1064 nm), at powers of 0.5–3.0 W and exposures of 200–1333 s produced well-defined necrotic lesions whose size increased with both the power and the total energy delivered. Lesions of 6 mm diameter made by 0.75 W for 1000s were well tolerated by animals allowed to recover from anaesthesia following irradiation. The diameter of the lesion was greatest at 48 h after irradiation. Following evolution of a characteristic healing response to necrosis in brain, the residual damage at 4 weeks was no greater in volume than that of the acute lesion. The results suggest that low power interstitial Nd-YAG laser photocoagulation in brain can be reliably and safely effected.     

Laser induced removal of meniscus cartilage and tendines

This study examines the potential of Nd-YAG lasers with the wavelength 1064 nm or 1320 nm and an Excimer XeCl laser for endoscopic removal of meniscus cartilage and tendon tissue. In vitro irradiation of freshly isolated bovine menisci and tendines with laser light, induced a tissue vaporization and tissue ablation with a highly significant relation to the applied laser energy density. In contrast to the treatment of tissue with the Excimer laser the use of the Nd-YAG laser with both wavelengths provoked carbonization of the lesion surface. Thermic induced changes of tissue integrity as examined by histology and scanning-electron-microscopy were for the Nd-YAG laser with wavelength 1320 nm>Nd-YAG laser with wavelength 1064 nm> Excimer XeCl laser. Due to the smaller thermic induced side effects and the smoother tissue surface after irradiation the pulsed Excimer XeCl laser is favoured for cutting and ablation in meniscus and tendon surgery.     

Potential use of holmium lasers for angioplasty: evaluation of a new solid-state laser for ablation of atherosclerotic plaque

Tissue effects of the mid-IR Holmium laser (emitting at a wave-length of 2130 nm) were evaluated. This wavelength is attractive because it combines high water absorption and easy transmission through standard optical fibres. The laser was pulsed with pulse durations in the range of 100 microseconds and repetition rates between 2 and 6 Hertz. For all experiments a repetition rate of 2 Hertz was used. The laser beam was coupled into waterfree quartz fibers with core diameters of 200 and 800 microns with an efficiency of 70 and 80%, respectively. Ablation of atherosclerotic plaque has been performed at an ablation threshold of 10J/cm2 for the 800 microns and 40J/cm2 for the 200 microns fibre. Removal of calcified plaque was possible. Ablation efficiency increased in a non-linear fashion with increasing pulse energies. The ablation rate per pulse was approximately 2 mm at energy fluences of 1000J/cm2 for the 200 microns fibre and 1.25 mm at energy fluences of 70J/cm2 for the 800 microns fibre; a further increase in energy densities did not result in higher ablation rates. On macroscopic examination only very limited thermal injury was found in crater adjacent tissue structures. Crater edges were even and did not reveal signs of crater charring or debris in the crater lumen. However, the histologic specimens revealed zones of thermal damage extending 100 up to 1000 microns lateral into adjacent tissue. Thermal damage increased with increasing radiant exposures and depended on the medium used.     

Open lung surgery with Nd-YAG Laser

We report on nineteen patients who successfully underwent open lung performance with a Nd-YAG laser in the period December 1987 to August 1988. Reasons for laser operations were lung metastases (twelve cases), lung fibrosis (five patients), one lung cyst and one tuberculoma. We used the Nd-YAG laser in non-contact mode, with focus hand-piece spot size of 1.5 mm, a continual 1064 nm wavelength and a power output 90 W. In these nineteen cases we performed 35 laser photoablations of lung tissue. All patients healed without any serious complications. The major advantage of Nd-YAG laser beam in open lung surgery is in the rapid sealing effect of small airways and of blood vessels up to 3 mm. The Nd-YAG laser seems to be very suitable for operations in lung periphery.     

Application of pulsed and continuous wave 1.32 and 1.06 microns wavelengths of the Nd:YAG laser in the canine tracheobronchial tree: a comparative study

Previous investigations have shown good clinical potential for the use of the 1.32 microns wavelength Nd:YAG laser because its soft tissue absorption is better than that of the 1.06 microns wavelength Nd:YAG laser. The 1.32 microns wavelength Nd:YAG laser has an absorption coefficient in water that is 10 times higher than the 1.06 microns wavelength Nd:YAG laser. A comparative in vivo study of laser soft tissue effects was performed by using the 1.32 microns wavelength and the 1.06 microns wavelength Nd:YAG lasers in a pulsed wave (PW) mode and continuous wave (CW) mode using a non-contact endoscopic delivery system. A standard 5 mm mucosal lesion was made in the canine tracheobronchial tree down to the level of the perichondrium. Soft tissue and cartilage effects were examined by light and scanning electron microscopy, acutely, 1 week and 2 weeks after operation, and a comparison was made between the different laser modalities. To create similar lesions, higher energy was required when using the 1.06 microns wavelength Nd:YAG laser. Soft tissue injury was greater with the 1.06 microns wavelength in CW mode, and no cartilage damage occurred in the PW mode. Soft tissue and cartilage repair after 1 and 2 weeks was better with the 1.32 microns wavelength laser. In comparison, the CO2 laser and the contact Nd:YAG laser proved to be more precise cutting tools than the 1.32 microns wavelength or the 1.06 microns wavelength Nd:YAG lasers. Both Nd:YAG laser wavelengths were useful for coagulation and vaporization of tissues and blood vessels. More studies are needed to determine the effect of the new 1.32 microns wavelengths on endotracheal tumors.     

Arterial response to excimer and argon laser irradiation in the atherosclerotic swine

Injury associated with laser-induced tissue ablation may be reduced by using pulsed energy delivery at low repetition rates, as opposed to using continuous wave energy delivery. This study was designed to examine the similarities and differences between these two systems as regards the healing process, and to examine whether one is superior to the other. In order to test this postulate, the healing response of normal and atherosclerotic aorta were examined after exposure in vivo to argon and excimer (XeCl 308 nm) laser radiation in hypercholesterolemic swine. Swine were fed hyperlipidemic diets for eight months following balloon denudation of the descending aorta. Following general anaesthetic, the descending aorta was isolated and laser burns were made on both normal and atherosclerotic intima using a continuous wave argon laser delivered through a 50 diameter quartz fibre, and a XeCl excimer laser carried through a 1 mm diameter fibre. Energy levels of 3 to 5 J were applied with the argon laser. The pulse duration for the excimer laser was 30 ns and craters were produced using 10 to 60 pulses at a repetition rate of 20 Hz and an energy density of 2 J cm^–2.Forty-eight hours after laser application, craters created by both lasers were filled with thrombus material. Argon burns were surrounded by thermal and acoustic injury which was not seen with excimer burns. Three weeks after laser application all crater surfaces were reconstituted. Unlike the excimer burns, argon craters demonstrated necrosis well beyond the crater margins and were characterized by multinucleate giant-cell reaction surrounding char debris. By nine weeks both excimer and argon laser burns were covered by fibrous tissue but could be distinguished by the fact that char debris and subjacent tissue injury arose with the argon burns.The results suggest that both lasers can be used to remove focal atherosclerotic plaque from arteries without inducing excessive thrombogenicity. Rapid healing is observed with both; however, damage to surrounding tissue is significantly greater with a continuous energy delivery laser as opposed to pulsed energy delivery.Work supported in part by: Heart and Stroke Foundation of Ontario, Grant-in-Aid No. 5-17     

Bare fibre low power Nd-YAG laser interstitial hyperthermia. Comparison between diffuser tip and non-modified tip. An in vitro study

Interstitial low power Nd-YAG laser hyperthermia is a new method with potential for the future treatment of localized neoplasms. A laser fibre is inserted into the tumour. Energy is applied and the tumour is destroyed by heat and phototoxicity. Since most tumours are spherical in shape, the optimal design of the laser fibre tip would be one which caused the light to spread uniformly in all directions. We describe a cone shaped forsted modification of the bare fibre proper (‘the diffuser tip’), that produces coagulation lesions of spherical shape. In vitro experiments show that the lesions were highly reproducible with respect to size and shape, and an excellent doseresponse relationship was observed. The largest lesion produced was achieved with 4 W for 1800 s and measured 44 mm in diameter. By comparison with lesions produced with the non-modified fibre (‘the endfire fibre’) it is concluded that the diffuser tip is superior to the endfire tip, since the latter produces cylinder shaped lesions. Based on these observations it seems that the diffuser tip will be advantageous, e.g. in the treatment of liver metastases.     

Use of the Nd-YAG laser in neurosurgery

Summary After many years of experience, in general we prefere the Nd-YAG laser, although the CO₂ laser is an advantage in a few specific cases (lipomas, cranial synostosis). While the focused CO₂ laser may be used as a cutting instrument in less vascular tissue with little trauma to the surroundings, the Nd-YAG laser produces a homogeneous coagulation with an energy dependent depth effect. Thus, with the Nd-YAG laser residual tumour tissue can be selectively and with a predictable depth effect thermally destroyed. Because of its excellent coagulation property, the use of the Nd-YAG laser is particularly indicated in highly vascular meningeal tumours. The shrinkage of a tumour and its demarcation which is due to the varying absorption properties facilitates the dissection and allows in addition the preservation of normal tissue.     

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.     

Mechanical and thermal effects in striated muscle irradiated by ns-laserpulses

The therapeutic application of laser light is required to minimize defects in the non-irradiated tissue. The primary mechanism of interaction is determined by the duration of laser action. In the case of continuous wave laser light a tissue layer surrounding the irradiated volume is thermally affected. With the pulses of a Q-switched laser (duration some ns) tissue cutting will be obtained by the laser-induced breakdown. To be able to distinguish between thermal and mechanical effects by histological examination, experiments were performed with laser pulse durations of 8ns and 100μs under the same conditions with a Nd-YAG laser at 1064nm. The beam was focused through air below the tissue surface. The beam geometry in the focal region was identical for both cases. The defective region after irradiation could be divided into four zones surrounding a crater. In the μs-experiments the zones corresponded to the temperature distribution in the tissue, so the changes were all classified as thermal. In the ns-experiments, in general larger craters were found. Increasing the number of pulses to 200 the picture is similar to that produced with μs-pulses. These results show that a few ns-pulses suffice to form a crater. Additional ns-pulses lead to heat accumulation and produce thermal lesions like those of the μs-case.     

A new device for inducing deep localized vaporization in liver with the Nd-YAG laser

A new device, composed of a hand-piece (250 mm in length, and 5 mm in diameter) connected to a cooling circulation, has been developed for the purpose of inducing focal coagulation deep in the liver, using a high-power Nd-YAG laser. The device, guiding and protecting the optical fibre, withstands a power-setting of 100 W and allows means transmission of 80% during intrahepatic application with an average power density of 10 200 W/cm². Thirty-six lesions of 12–18 mm in diameter were made in 11 pigs under ultrasound control with laser shorts of 80 W mean power output for 10s duration. Intrahepatic thermocouples showed a high rise in temperature in the core of the lesion, inducing vaporization, while moderate hyperthermia (54.4%C/60s on average), high enough for tumour cell kill, was observed 1 cm from the laser source. Immediately after irradiation ultrasound revealed a central echo-free lesion, well defined on day 3 by a hyperechoic border and invaded from day 20 by internal hyperechoic enhancement. Anatomical examination demonstrated, on day 0, an excavated site of vaporization which was surround, from day 3 on wards, by an increasing ring of connective tissue, and which was covered, from day 30 onwards, by a fibrotic network gaining ground towards the centre of the lesion. Good healing free of complications, was observed after four months' follow-up. The technique is proposed for photocoagulation of deep metastases.     

Diffusing Fibre Tip for the Minimally Invasive Treatment of Liver Tumours by Interstitial Laser Coagulation (ILC): An Experimental Ex Vivo Study

A newly developed diffusing laser applicator was examined for interstitial laser coagulation (ILC) of liver tumours. The applicator consisted of a matted quartz core and a quartz glass dome, also matted on its inner surface and sealed to the fibre. The applicator provided a homogeneous light intensity distribution over an active length of about 20 mm. Lesions were created in an ex-vivo porcine liver model using a Nd-YAG laser comparing the new diffusing tip with a Ringmode^?-ITT applicator in order to find optimal laser parameters and damage thresholds. The lesions were investigated using macroscopic size measurement, volume calculation and histological examination (H&E, NADPH-dehydrogenase). The damage threshold of the diffusing tip was 6 W at 14 min exposure time whereas the Ringmode^?-ITT applicator had its limit at 5 W and 12 min exposure. Comparing various exposure times showed that treatment over a time of more than 840 s did not significantly increase the lesion volume. At 5 W and 720 s the mean lesion volume was 6.9±1.1 cm³ with the diffusing tip and 6.3±0.6 cm³ with the Ringmode^?-ITT applicator, both having a slight ellipsoidal shape. Hence, the created lesions were not significantly different for both applicators when the same laser parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coagulation volumes of up to 7.9±0.5 cm³ at 5 W and 20 min. The experiments showed that lesions with a dimension of 31×22 mm can be achieved with the diffusing applicator which seem suitably sized for treating small human liver metastases in a single laser session. Paper received 25 April 1997; accepted after revision 13 March 1998.     

Interstitial laser thermotherapy: Comparison between bare fibre and sapphire probe

A sapphire probe and a bare fibre were compared with respect to temperature control and distribution and light fluence in interstitial laser thermotherapy. Experiments were performed in processed liver using an Nd-YAG laser and output power levels of 1–4 W. The temperature was controlled at a distance of 10 mm using a feedback circuit with an automatic thermometry system and thermistor probes. With the sapphire probe, carbonization was rare at power levels of 1–2 W but was observed in half of the experiments at 3 W and in all experiments at 4 W. Using the bare fibre, carbonization was seen in almost all experiments. Absence of carbonization was associated with a moderate decrease in the penetration of light and excellent control of the temperature, whereas carbonization led to rapid impairment of light penetration and temperature control. In addition, the temperature gradient was smaller with the sapphire probe than with the bare fibre or when carbonization was absent. It is concluded that a diffuser tip, such as the sapphire probe, may be preferable to the bare fibre for interstitial laser thermotherapy because it gives a smaller temperature gradient and helps to avoid carbonization which results in preserved light penetration and improved temperature control.     

Comparative study of Nd-YAG laser versus electrocautery for liver metastatic resection in the rat

The thermal, hemostatic and lymphostatic effects of the Nd-YAG laser suggest a benefit in the treatment of multiple liver metastases. The aim of this work was to evaluate experimentally this hypothesis in a comparative study with conventional electrocautery resection of liver metastases. The original animal model was represented by syngeneic BDIX rats inoculated under the liver capsule with 1.5×10⁶ DHD/K12 tumour cells originating from a clone of a 1,2 dimethyl hydrazine induced rat colon cancer. One hundred and ten rats bearing three liver metastases were randomly treated by laser volatilization or electrocautery enucleation. The first group of 60 rats was used as a survival group: the laser treated rats survived significantly longer than rats treated by cautery (49.9 days vs 28.9 days) (mean values;p<0.015). In this group, the temperature elevation during operation at the edge of the treated lesion was found higher in the laser group than in the cautery group (56±4.6°C vs 8±3°C) (mean values±s.d.;p<0.001). Nd-YAG laser was also a faster procedure than cautery resection (21±4.2 s vs 57±6.1 s) (mean values±s.d.;p<0.001). At the time of autopsy, the infection rate with laser was found lower than in the cautery group (p<0.025) while no bile leakage was evident. A peritoneal tumour dissemination with ascites was noted in the majority of dead rats. In the second group of 50 rats, the metastatic recurrence was assessed. At day 7, no metastases were found in the laser treated rats while a mean number of 6.5 was found in the cautery group (p<0.001). At the 15th day, more metastases were present in the cautery group. There was a significant correlation between the total number of metastases and the time of death. Those findings suggest that the Nd-YAG laser destruction of experimental liver metastases by its specific effects on tumour cells delayed the recurrence of metastases when compared to the electrocautery resection, contributing to a longer survival of the laser treated rats.