Theoretical and experimental investigations prove Nd: YAG laser treatment to be safe

The Evaluation of Laser Application in Surgery: A Review Article

There are several types of surgeries which use lasers in the operating room. Surgeons use lasers in general surgery or surgical specialties to cut, coagulate, and remove tissue. In modern medicine, the application of laser therapy is an attractive subject due to its minimal invasive effect. Today lasers are widely used in the treatment and diagnosis of many diseases such as various cancers, lithotripsy, ophthalmology, as well as dermatology and beauty procedures. Depending on the type of lasers, the wavelength and the delivery system, most lasers have replaced conventional surgical instruments for better wound healing results. Over time, by using many different tools and devices, new lasers have been created; as a result, they are used in a wide range of medical special cases. In this review, laser applications in surgery and its beneficial effects compared to previous surgeries with the aim of providing appropriate therapeutic and non-invasive solutions with minimal side effects after surgery are investigated.

Laser applications in surgery

In modern medicine, lasers are increasingly utilized for treatment of a variety of pathologies as interest in less invasive treatment modalities intensifies. The physics behind lasers allows the same basic principles to be applied to a multitude of tissue types using slight modifications of the system. Multiple laser systems have been studied within each field of medicine. The term "laser" was combined with "surgery," "ablation," "lithotripsy," "cancer treatment," "tumor ablation," "dermatology," "skin rejuvenation," "lipolysis," "cardiology," "atrial fibrillation (AF)," and "epilepsy" during separate searches in the PubMed database. Original articles that studied the application of laser energy for these conditions were reviewed and included. A review of laser therapy is presented. Laser energy can be safely and effectively used for lithotripsy, for the treatment of various types of cancer, for a multitude of cosmetic and reconstructive procedures, and for the ablation of abnormal conductive pathways. For each of these conditions, management with lasers is comparable to, and potentially superior to, management with more traditional methods.

Ultraviolet and laser radiation safety

Both ultraviolet radiation and laser radiation occupy pmt of the Spectrum designated "optical radiation". Thus, measurement techniques are similar and the same organs (eyes and skin) are at risk from accidental exposure. However, the equipment used to produce ultraviolet and laser radiation differs substantially and the harm caused by each type of radiation is also different. Another significant difference arises from the fact that ultraviolet radiation is natural with associated general population exposure. Consequently, the present article reviews the current status of both ultraviolet and laser radiation with the material divided into two sections where each hazard is considered separately.

Nd-YAG laser damage to metal and silicone endobronchial stents: delineation of margins of safety using an in vitro experimental model

STUDY OBJECTIVE

To identify margins of safety within which bronchoscopic Nd-YAG laser resection can be performed without damaging indwelling tracheobronchial stents.

DESIGN

Experimental in vitro study simulating a patient-care environment.

METHODS

Uncovered and covered metal Wallstent (Schneider; Zurich, Switzerland) and Dumon (Bryan Corporation; Woburn, MA) silicone stents were deployed in the tracheobronchial tree of a ventilated and oxygenated (fraction of inspired oxygen, 40%) heart-lung block of a dead canine. Rigid bronchoscopic Nd-YAG (1,064 nm) laser procedures were performed in order to deliver laser energy using fiber-to-target distances of 10 mm and 20 mm, and noncontact, continuous-mode, 1-s pulses at power settings of 10 W, 30 W, and 40 W. The major outcome measure was laser-induced stent damage, defined as discoloration, ignition, or breakage. This was assessed using six power densities: 75 W/cm(2), 172 W/cm(2), 225 W/cm(2), 300 W/cm(2), 518 W/cm(2), and 690 W/cm(2).

RESULTS

The uncovered Wallstent and the silicone stent remained intact at power densities of 75 W/cm(2) (10 W, 20 mm) and 172 W/cm(2) (10 W, 10 mm), but were damaged at power densities > 225 W/cm(2) (30 W, 20 mm). The covered Wallstent was damaged at all power densities tested.

CONCLUSION

Uncovered Wallstent and silicone stents are not damaged when Nd-YAG laser energy is delivered using power densities < or = 72 W/cm(2) (10 W, 10 mm). Covered Wallstents, however, had a high likelihood of ignition at all power densities studied.

Laser evoked potentials using the Nd:YAG laser

Pain-related cortical potentials were evoked by skin stimulation of the face and the limbs with 5-ns-duration laser pulses delivered by a Q-switched Nd:YAG laser. Such laser pulses, in the nanosecond range, were able to induce pinprick pain sensations and to evoke reproducible laser evoked potentials (LEPs) without visible skin lesions for an energy density of less than 18 mJ/mm(2). Low energy densities, around 10 mJ/mm(2), were sufficient to reach the pain threshold and to induce LEP. The mean conduction velocity of the stimulated afferent fibers was close to 20 m/s, consistent with the stimulation of Adelta fibers. The amplitude of LEP correlated with pain perception rather than with energy density. The differences, such as wavelength and stimulus duration, between the Q-switched Nd:YAG laser we used and the lasers that are currently used in LEP studies (i.e., CO(2), argon, or Tm:YAG lasers in the millisecond range) are discussed. Our study opens novel perspectives in the LEP field of research by using a new type of laser with a very short pulse duration.

Dose-related tissue effects of the CO2 and noncontact Nd:YAG lasers in the canine glottis

OBJECTIVES

The CO2 laser is the standard for control of recurrent respiratory papillomatosis because of its predictable action on laryngeal tissue. The noncontact neodymium:yttrium aluminum garnet (Nd:YAG) 1064-nm laser is generally not used in the larynx owing to the lack of data on its tissue effects, and its potential lack of safety in the larynx. Combined Nd:YAG and CO2 laser treatments have been used safely in the tracheobronchial tree to eradicate recurrent respiratory papillomas. The objectives of this study were to describe and evaluate a method for applying the noncontact Nd:YAG laser to the larynx, to compare the tissue effects of the Nd:YAG, CO2, and combined Nd:YAG and CO2 lasers in the canine larynx, and to extrapolate canine tissue data to the human.

METHODS

The CO2, Nd:YAG, and combined Nd:YAG/CO2 lasers were applied to the glottis in four mongrel dogs. Laryngectomy was performed and the tissue was examined histologically. The nature and degree of tissue injury were analyzed relative to laser type and energy data.

RESULTS

In the canine larynx, the CO2 laser vaporized the surface epithelium and caused varying degrees of edema and necrosis of the lamina propria. The Nd:YAG laser did not cause ulceration but did show a greater degree of thermal damage to the lamina propria. Combined Nd:YAG/CO2 applications resulted in separation of the perimysial fibers from the muscle fibers of the vocalis muscle.

CONCLUSION

These findings suggest that the noncontact Nd:YAG laser can be applied in a controlled fashion to the canine larynx at appropriate power densities. Anatomical differences between human and canine larynges are considered. Extrapolation to humans is proposed.

The influence of laser parameter configurations at 9.3 microns on incisional and collateral effects in soft tissue

These investigations were performed to determine histologic and incisional consequences of varying pulse duration, duty cycle, and average powers during laser incision at 9.3 microns in soft tissue. In 19 fresh pigs' jaws six standardized incisions 3 cm long were made per parameter with a template and motorized jig. Laser parameters investigated were average power: 1 to 9 W, duty cycle: 10% to 80%, and pulse duration: 1 to 200 msec. The gated Cw mode was used. Incision width and depth and collateral tissue effects were assessed statistically with general linear procedures. Multiple factors were found to influence the outcome of laser irradiation. Depth of incision correlated positively with average power. Tissue damage correlated strongly and negatively with all three variables. These results demonstrate that a wide range of surgical and collateral effects can be achieved with one specific laser device depending on the parameter configuration selected.

Development and experimental in vivo validation of mathematical modeling of laser coagulation

Most clinical procedures using the laser are based on thermal laser-tissue interactions. The treatment often consists of inducing damage of given degree and extent by heating the tissue. The aim of this study was to develop a model called HELIOS. The ability of HELIOS to predict thermal coagulation was evaluated by comparison with in vivo experimental results. Conversion of laser light in tissue was studied using the beam-broadening model. Temperature was described by the heat conduction equation solved using the finite difference method. The tissue denaturation was modeled by the Henriques equation leading to the determination of the damage coefficient omega. For a given set of laser and tissue parameters, HELIOS makes a graphic representation of coagulation necrosis and temperature evolution in tissue. HELIOS was validated by experimental studies in vivo on rat liver using a CW Nd:YAG laser, a CO2 laser, and an argon laser. For given sets of laser parameters, temperature measurements were performed using an infrared camera. Histological examinations were carried out on samples to quantify the depth of coagulation necrosis. Experimental data obtained in vivo were compared with those calculated using HELIOS and similar sets of parameters. The difference between the predicted temperature evolution on tissue surface and that measured by the infrared camera was < 5 degrees C in all cases. The difference between the predicted coagulation necrosis depth and the corresponding experimental one was < 10%. In conclusion, HELIOS allows good prediction of tissue temperature and coagulation necrosis.

The histopathological effects of the CO2 versus the KTP laser on the brain and spinal cord: a canine model

Because no data are available concerning the histopathological effects of the potassium titanyl phosphate (KTP) laser on central nervous tissue, a study was performed using a canine model to compare the histopathological effects of a commonly used laser (CO2) and the KTP laser on brain and spinal cord tissue. Exposed brain and spinal cord tissue were irradiated with 0.1-s pulses (x10), with spot sizes of 1 mm (in focus) over a range of 1 to 10 W. Wedge-shaped lesions were produced with the CO2 laser, while more blunt, semilunar-shaped lesions were produced by the KTP laser. The depth and width of the lesions were proportional to the energy applied. The lesions ranged in surface diameter from 0.6 to 1.3 mm for CO2 and 0.8 to 1.6 mm for KTP lasers, respectively. The depth of the lesions varied from 0.4 to 2.0 mm for CO2 and 0.3 to 1.1 mm for KTP lesions. Histopathologically, a central zone of tissue destruction and vaporization was surrounded by a zone of coagulative necrosis, in turn surrounded peripherally by a zone of pallor. CO2-induced lesions were histologically more hemorrhagic than KTP-induced lesions. In view of the histopathological findings, the KTP laser appears as safe as the CO2 laser in terms of tissue lateral thermal change (penetration) and tissue absorption. The additional hemostatic advantage observed clinically for the KTP laser is demonstrated histologically as well. Although the wavelength of the KTP and argon laser light are similar, the histopathological effects seem to be less pigment dependent. The KTP laser seems well suited for neurosurgery and has the versatility provided by a fiberoptic delivery system.

Interstitial Nd:YAG laser ablation in normal rabbit liver: trial to maximize the size of laser-induced lesions

In order to apply interstitial laser ablation to relatively small liver tumors in humans, it will be necessary to optimize the irradiation schedule. Nd:YAG laser was applied to normal rabbit liver in vivo at various power and energy outputs, including a protocol in which irradiation was repeated twice, with and without fiber tip advancement during the intermission. Ex vivo and in vivo tissue were also irradiated to determine the effect of perfusion on the lesion size. We obtained the same monotonic relationship between laser settings and lesion size in rabbit liver as we previously reported in rat liver. MR-guided fiber advancement between heating periods increased the transverse diameter of the lesion, and MR monitoring demonstrated this process. Our results suggest that repeated irradiation with brief intermissions, when combined with fiber advancement, may increase the lesion size.

Exogenous chromophores for the argon and Nd:YAG lasers: a potential application to laser-tissue interactions

Chromophore dyes can be employed to modify laser-tissue interaction. A number of dyes have been investigated for their effect on the absorption and transmission of argon and Nd:YAG laser energy by vascular tissue in vitro. Three histological dyes have been assessed as potential chromophores for the argon laser and four infrared dyes for the Nd:YAG. Segments of porcine coronary artery to which dye had been applied were lased (1,064 nm, 2.5 W, 83 W/cm2, 60 s and 488/514 nm, 400 mW, 10.5 W/cm2, 60s) and the tissue temperature measured remotely using an infrared thermometer. In addition, energy transmission was measured with a photodiode and tissue morphological changes assessed histologically. All three argon dyes significantly increased energy absorption (typically 60 degrees C v. 20 degrees C at 60 s, P less than 0.001, 2-way ANOVA). Three of the four infrared dyes behaved similarly (40-70 degrees C v. 20 degrees C, P less than 0.001). All dyes significantly increased the initial rate of rise in tissue temperature during lasing. A reduction in energy transmission was observed for each of the Argon dyes but not for the Nd:YAG dyes. Histological evidence of thermal damage in control tissue first occurred for the argon and Nd:YAG lasers at 800 mW and 7.5 W without chromophore and at 400 mW and 2.5 W with the chromophore, respectively. A number of effective chromophores have therefore been identified at each wavelength.

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

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.

New long-wavelength Nd:YAG laser at 1.44 micron: effect on brain

A wavelength-shifted Nd:YAG laser, tuned to coincide with the infrared absorption peak of water at 1.44 microns, was used to make lesions in normal rabbit brain. A total of 48 lesions were made with power up to 20 W, with energy up to 40 joules, and with two different spot sizes. These lesions were compared to lesions made with 1.06 microns radiation from an Nd:YAG laser under identical operating conditions. Measurements of blood-brain barrier damage and width, depth, and volume of tissue affected were obtained 30 minutes after placement of the lesions. It was found that 1.44-microns lesions produced photoevaporative tissue loss at the highest intensities used. The layer of coagulated tissue remaining after photovaporization had a mean thickness of 0.6 mm irrespective of the volume of tissue removed. There was no photovaporization in the 1.06-microns lesions. In addition, the amount of peripheral edema per unit volume of tissue coagulated was approximately half at the 1.44-microns wavelength. These findings suggest that the 1.44-microns Nd:YAG laser may be a useful surgical instrument since it combines the photoevaporative effect of the CO2 laser while maintaining the advantages of the conventional Nd:YAG laser (quartz fiber delivery and effective hemostasis).

Canine tracheal injury by neodymium-YAG laser irradiation

The relationship between endoscopic graded neodymiumyittrium aluminum garnet (Nd-YAG) laser intensity and the magnitude of effects on the tracheal wall was studied in two mongrel dogs. The dogs were anesthetized and graded Nd-YAG laser burns of 50, 100, and 200 Joules (J) were produced on the distal tracheal walls with a laser fiber inserted through a bronchoscope. One dog was killed immediately after injury and the other 24 hours later. At the time of killing, the trachea was excised and prepared for light microscopic (LM) and scanning electron microscopic (SEM) examination. We found that the injury produced by the 50 J intensity beam was confined to the mucosa and submucosa, with no destruction of the tracheal cartilage; by contrast, transmural penetration of the trachea was observed at intensities of 100 and 200 J. These results indicate that a strong correlation exists between laser intensity and the magnitude of the resulting tracheal injury. We suggest that the intensity of a Nd-YAG laser, endoscopically directed perpendicular to the tracheal wall, should not exceed 50 J in order to minimize the risk of perforating the tracheal wall.

Finite element model of heat flow in biological tissue undergoing laser irradiation

In this paper we present a numerical method to determine thermal effects in biological tissue undergoing laser irradiation. The scattering and absorption of the laser beam have been analysed. Results are compared with experimental observations.

Effects of Nd:YAG laser photoradiation on intra-abdominal tissues: a histological study of tissue damage versus power density applied

Liver, spleen, and pancreas were subjected to laser photoradiation of 50- to 100-Watt power levels. Samples were evaluated by light microscopy at 0 hours and 7, 14, and 21 days. Four zones of cellular damage were visible in liver and pancreas: coagulum, cavitation, acidophilia, and transition. Only the first three zones were clearly visible in the spleen. Mean lateral tissue penetration was 3.1 mm in liver, 3.3 mm in spleen, and 1.0 mm in pancreas. No significant increase in lateral penetration occurred with increasing power. Normal healing was observed in liver and spleen. Pancreatitis was found in all samples at 7 days postoperatively. At power levels of 80 W or less, recovery was observed. Above 80 W, pancreatic pseudocysts and necrosis led to death of the animals.

Histologic study of normal rat brain tissue after neodymium-yttrium aluminum garnet laser irradiation. I. Cerebral hemisphere

We report a histologic study of normal rat brain tissue after neodymium-yttrium aluminum garnet laser irradiation. Morphological changes occurred at a maximum depth of 5 mm after 60-W, 1-second exposure, at a 2-mm distance between the optical fiber tip and the brain surface. Polymorphonuclear leukocyte infiltration into the irradiated area was observed 48 hours after irradiation. After 72 hours, macrophages and fibroblasts appeared; their number increased thereafter. At 1 month, tissue defects attributable to neodymium-yttrium aluminum garnet laser irradiation were small. Gliotic changes were rarely seen. We conclude that 60-W irradiation is harmful to young rats but not to adult rats.

Extent of thermal penetration of Nd-YAG laser--histological considerations

The extent of thermal penetration of Nd-YAG laser was studied histologically. The material was obtained from seven cases of various types of intracranial and extracranial tumours and normal temporal muscle obtained at operation. After irradiation of the tumour surface with the laser, the tumours were removed and depth and width of pathological changes caused by heat were studied. Histologically, materials consisted of a vaporized surface, carbonized, vesicular, necrotic, oedematous layer and surrounding intact brain tumour tissue. There was a direct relationship between the thermal effect and the irradiated thermal energy (watt x exposure time x pulse number). The results showed that the thermal effect was limited to a depth of 6 to 10 mm from the irradiated surface when irradiated 4 times at the power of 90 watts for 2 seconds.

Nd-YAG laser as a surgical tool

As neurological operation has necessitated effective haemostatic devices, CO2 and Nd-YAG lasers have been introduced in this field. The CO2 laser was first studied and used in neurological surgery and many problems, such as safety, mobility, and others, were overcome by pioneers. The Nd-YAG laser has been developed mainly for endoscopic surgery. However, we noticed its strong haemostatic effect, used it in neurosurgery and found it to be quite effective in removing tumours. The following properties of the Nd-YAG laser are especially fitted for neurosurgical surgery: the laser beam is conducted through a light, thin and flexible quartz fibre; penetration of the laser beam into tissues is controlled by the output wattage, and the grade of coagulation is controlled by duration of irradiation time and by the output wattage.

The laser in neurological surgery

The use of lasers in neurosurgical procedures has received a great deal of attention recently. Surgical use of lasers has been viewed with suspicion and skepticism, probably because of (justified) apprehensions about the misuse of lasers in early work and about the ways in which laser light affects tissues, and a lack of understanding of the basic physics and practical operation of lasers. The authors review the physics, biophysics, experimental findings, and operative use of lasers in current neurosurgical practice, and discuss briefly their experience gained in over 150 neurosurgical procedures using the carbon dioxide and argon surgical lasers.

Thermal effects of laser radiation in biological tissue

A theoretical model is presented that simulates the thermal effects of laser radiation incident on biological tissue. The multiple scattering and absorption of the laser beam and the thermal diffusion process in the tissue are evaluated by a numerical technique that is well suited for microcomputers. Results are compared with recent empirical observations.

Beam broadening in dense scattering media

The full 3-D integral equation for the spherically symmetric scattering of light in a medium of densely packed uniformly distributed scattering centers is solved for the case of a cylindrically symmetric laser beam (Gaussian profile) directed normally at the slab. After reduction to a 2-D problem, the discretized integral equation for the intensity (irradiance) of the scattered light is solved by a standard iteration procedure. The resulting 2-D distribution is reconverted to 3-D to obtain the r and z dependence of the irradiance. From the solution the angular distribution of backward and forward scattered light is calculated; special emphasis is placed on the radial dependence of the scattered light emerging normal to the surface in both directions. Spot sizes are defined and calculated for various values of beam radius and material parameters, nominally chosen to represent irradiation of white (translucent) biological tissue by a Nd:YAG laser. The effect of increasing the scattering coefficient on the spot profiles and radii is studied.