Fiberoptic Delivery System Research Articles

An optical fibre delivery system for pulsed laser particle image velocimetry illumination

We demonstrate the design and implementation of a fibre-optic beam delivery system for particle image velocimetry applications. The system is designed for the transmission of pulses of high peak power from a Q-switched and frequency-doubled Nd:YAG laser with energies typically in the range of 9 mJ; it is hence suitable for illuminating air flows. Practical laser-induced damage thresholds for large-core step-index multimode fibres are determined, and through exploitation of inter-modal dispersion in the fibre, intensity variations in the output from the fibre due to laser speckle are suppressed to a visibility of <3.5%. Effective use of the fibre-optic beam delivery system for particle image velocimetry was demonstrated for a turbulent air flow seeded with corn oil droplets of the order of 1-2 mu m in diameter; the mean air velocity was 5.5 m s-1.

Stimulation Effect of He-Ne Laser Energy on the Ventral Nerve Cord Motor Neurons of the Crayfish via Fiber Optic Delivery

This investigation integrated intracellular recording techniques with a fiber optic laser delivery system to examine the relationship between laser energy irradiation and the ventral nerve cord (VNC) motor neurons excitability of the crayfish. The VNC was used as a model system analogous to motor neurons of vertebrates. Helium-neon laser energy (He-Ne λ 632.8 nm at 3.5 mW) was delivered via fiber optic material directly to point of contact with the nerve cord. The activity of 18 spontaneously active motorneurons from 13 animals was monitored during laser irradiation by means of glass microelectrodes individually placed within each motorneuron. The resultant signal from each individual motor neuron was digitalized and recorded on a MacIntosh LC II computer. Analyzed data demonstrated statistically significant changes, p < this 0.05, in motor neuron membrane potentials following laser irradiation. Observed changes in frequency, amplitude, and duration of spontaneous potentials illustrated a stimulation effect of laser energy on the VNC motor neurons. Individual variations of response to laser irradiation were analyzed in specific specimens. The degree of response variability within separate specimens illustrated evidence of membrane threshold variability. The threshold level of laser energy necessary to evoke an artificial action potential was not seen in this investigation. Increased activity in specific experiments demonstrated a close proximity to membrane threshold levels. Indications were that threshold levels of activation begin above the delivered energy of 3.5 mW. Spontaneously active motorneurons demonstrated photosensitivity to laser irradiation. All indications were that an artificially generated action potential may be produced given adequate energy at the 632.8 nm wavelength; however, delivered energy must exceed 3.5 mW. Further investigation could lead to establishing a threshold level of motor neuron activation.

Dentin ablation by Ho:YAG Laser: Correlation of energy versus volume using stereophotogrammetry

The future use of lasers in endodontics is dependent upon predictable and consistent ablation of dentin. In this pilot study we used an Ho:YAG laser fiberoptic delivery system to apply laser energy to prepared tooth sections in vitro. Longitudinally sectioned single-rooted human teeth were subjected to single-energy pulses varying from 25 to 1750 mJ at a focal length of 1 mm. At different energy levels we observed changes in the dentin surface ranging from minute surface pitting to the formation of large craters. Scanning electron microscopy and stereophotogrammetry were used to determine the relationship between the amount of energy applied to dentin and the extent of dentin ablation. Dentin crater formation was quantified by determining surface area, depth, and volume of craters produced. Increases in laser energy were compared with increases in surface area, depth, and volume of craters produced within the range of 150 to 1200 mJ. The Ho:YAG laser fiberoptic delivery system used in this study provides an effective means of ablating dentin. Three-dimensional stereophotogrammetry may prove to be a useful method for further studies on the effects of laser energy on mineralized tissues.

Comparative study of different laser systems

To review lasers, laser physics, laser-tissue interaction, delivery systems, and their clinical applications relevant to gynecology. Gynecological Service at Massachusetts General Hospital (MGH) and MGH Laser Center. None. Laser literature review and personal experiences of the authors were used to prepare this manuscript. Lasers have been used in gynecologic practice for cutting and coagulating purposes. Photodynamic therapy has been used clinically for malignant conditions and is being investigated for dysplastic lesions of the lower genital tract and for endometrial ablation. Laser welding has potential, but further work is required in this field before it finds a clinical application. The main lasers used in gynecology are CO2, neodymium-yttrium aluminum garnet (Nd:YAG), and potassium tatanyl-phosphate-doubled Nd:YAG. Pulsed Ho:YAG laser looks promising, as does diode lasers. Holmium-yttrium aluminum garnet and diode lasers will be soon available commercially. Improvements in delivery systems have increased user friendliness, and more developments in this area are anticipated, for example, a fiber-optic delivery system for CO2 lasers. We believe that enhanced understanding of laser technology will provide unique applications for development in gynecology.

Experimental study of co2 laser myringotomy with a hand‐held otoscope and fiberoptic delivery system

CO2 laser myringotomy has previously been proven effective in patients with serous otitis media for short-term aeration of the middle ear. However, the system based on a microscope and a coaxially aligned laser is cumbersome and expensive. The advantage of CO2 laser energy is the high absorption coefficient in biological tissue, meaning minimal damage surrounding the desired lesion. The disadvantage is that conventional optical fibers do not transmit CO2 laser energy (lambda = 10.6 microns). We have developed a silver halide optical fiber of diameter 0.9 mm and lengths of several meters, with high transmission at 10.6 microns. Using a hand-held otoscope coupled to a fiberoptic delivery system, CO2 laser myringotomies were performed in guinea pigs. In the animal model the feasibility of the procedure was proven. Different irradiation parameters were studied and a "dose-dependent" relationship was found between the total energy used and the duration of a patent myringotomy. However, conventional histological studies failed to show a difference in circumferential damage with different energy parameters. CO2 laser myringotomy utilizing a hand-held otoscope coupled to an optical fiber capable of transmitting CO2 laser energy may prove simple and effective. The relationship between energy parameters and myringotomy patency may be instrumental in deciding on the optimal duration of aeration of the middle ear in secretory otitis media.

Laser discectomy: a review.

The percutaneous treatment of lumbar disc disease with laser energy has emerged recently as an alternative to open surgical or even mechanical percutaneous methods. Although numerous laser wavelengths have been employed in both the experimental and clinical settings, no consensus exists regarding selection of laser, treatment duration, or energy requirements. Inspection of the disc/water absorption spectrum combined with the limitations of the fiberoptic delivery systems argue for the use of lasers near 2.0 microns, such as the 2.1-microns Ho:YAG. Although recently developed in vitro models have allowed for laser system comparisons, most clinical work has been empiric, uncontrolled, and in very small series.

Pulsed laser energy through fiberoptics for generation of ultrasound

Laser pulses are an effective, noncontacting technique for generating ultrasound in materials. However, for this approach to be practical, a versatile and safe method of delivering the laser pulses must be developed that eliminates exposed beams steered by mirrors and focused by lenses. Investigations by several researchers using fiberoptic delivery systems indicate that fiberoptics may be a viable method for the delivery of laser energy to generate acoustic energy. The main problem experienced with the fiberoptic delivery systems has been the inability to deliver high-energy, short-duration pulses via a fiber for thousands of pulses with no fiber damage and with constant energy output. This paper presents a technique for laser generation of sound using fiberoptics that continuously delivers sustained 20 ns pulses at a pulsing rate of 30 Hz from a doubled, Q-switched Nd:YAG laser operating at 532 nm with output energy from the fiber-optic system up to 26 mJ/pulse. The delivery system is used to excite ultrasound in a molten weld pool as part of a research effort to develop a noncontacting sensing system for real-time weld inspection.

Workpiece position sensing by means of a fiber optical beam delivery system

We report a method of measuring workpiece position in laser material processing and machining that uses a fiber optical beam delivery system. The method is based on a measurement of the power propagating in the cladding of the optical fiber in the direction from the workpiece to the laser. The power reflected from the workpiece and coupled into the cladding is shown to be a function of the position of the workpiece relative to the beam waist formed by the output optics of the beam delivery system.

気管食道領域でのKTPレーザーの応用

Recently developed KTP laser has been used in the various fields of surgical operations due to its superior performance and easiness of manipulation, however few reports of its application for tracheoesophageal surgery have been made. We have operated over fifty patients with the KTP surgical laser system since March 1992, and found it quite useful. KTP laser has advantages over carbon dioxide laser or YAG laser which have been widely used in otolaryngology, head and neck surgery. First of all, KTP laser has a balanced ability of cutting and hemostasis, so hemostatic cutting can be done easily. Second, Its fiber optic delivery system makes it easy for the operator to manipulate the device. 532 nano meter wavelength of KTP laser is well absorbed into hemoglobin, which makes KTP laser ideal for the treatment of hemangioma. Four representative cases are described in this paper. Two patients had an esophageal stenosis, and the other two had pharyngolaryngeal hemangioma. Hemostatic cutting ability of the KTP laser was useful for three patients and photocoagulation was applied to one of the hemangioma patients. No surgical complications occured and the results of the operations were satisfying.

A Comparison of Excimer Laser (308 nm) Ablation of the Human Lens Nucleus in Air and Saline With a Fiber Optic Delivery System

Photoablation with excimer lasers has demonstrated precise tissue cutting and minimal thermal damage. Potential ophthalmic applications of these lasers include remodelling of the corneal surface, glaucoma treatment, and phacoablation. Ablation of human lens with a 308 nm XeCl excimer laser light delivered through a fiber has been demonstrated in preliminary experiments. Intraocular delivery of laser light must be done in a fluid medium to preserve the integrity of ocular structures. However, little information is available on the effect of the fluid media on the ablation process. Therefore, a series of experiments was conducted to determine whether the ablation of human lens nucleus at 308 nm via a fiber differs in air and saline media. Ablation of human lens nuclei (n = 30) was conducted with a XeCI excimer laser (308 nm) coupled to a 600 microns core size fiber. Irradiation was performed at 2.8 mJ/cm2 energy density and 20 Hz. The fiberoptic was brought to contact with the lens nucleus and remained fixed for the duration of irradiation. Variables consisted of the medium (air or saline) and number of pulses delivered (100 to 10,000). Following establishment of the tissue shrinkage ratio, the depth of each crater and the tissue volume removed were measured histologically. The histological features of nucleus ablation in air and in saline were also examined with both light and scanning electron microscopy. Light microscopy revealed that the average zone of thermal damage adjacent to the crater is thinner in the presence of saline (60 microns, SD = 6 microns) than it is in air (90 microns, SD = 12 microns). In both media, the thickness of the zone of thermal damage is greater at the surface than it is at its base. Following irradiation in air, deep sharpedged craters with smooth walls are formed. Craters formed by irradiation in saline are characterized by reduced depth and irregular walls. For the same number of pulses applied (500, 1000, and 2000), the mean depth of ablation per pulse in air (8.6 to 2.7 microns/pulse) was greater by approximately a factor of two than that in saline (4.10 to 1.30 microns/pulse) at P < .01. However, the mean ablated volume removed per pulse was greater in saline (0.00250 to 0.00150 mm3/pulse) than in air (0.00120 to 0.00080 mm3/pulse), for the same number of pulses (1000, 2000) at P < .01. In comparing the data for the same number of pulses applied in air and in saline, it appears that the depth of crater formed by irradiation in air is deeper than that in fluid. The overall volume ablated is greater in fluid than it is in air at 1000 and 2000 pulses. Additionally, the zone of thermal damage is thinner in the presence of saline than it is in air. Smoother crater shapes were observed following irradiation in air than in saline. These results suggest that under this specific experimental setup, the ablation in saline is different from that in air.

Bi-directional cladding power monitor for fibre optic beam delivery systems

A technique is described for the measurement of the power propagating in either the forward or the reverse direction in the cladding of an optical-fibre beam delivery system. The technique is based on the use of a novel fibre component which is analogous to a directional coupler, except that it transfers power from the cladding of the system fibre (rather than its core) to the monitor fibre. Applications are described for the use of the bi-directional cladding power monitor for determining the efficiency with which light is coupled into the beam delivery system, for monitoring its integrity, and when used in material processing applications, for monitoring the power back-coupled into the fibre from the workpiece.

Cleaning and shaping the root canal with a Nd:YAG laser beam: A comparative study

The effectiveness of an experimental Nd:YAG laser fiberoptic delivery system was compared with conventional methods for its ability to cleanse and shape the root canal space in vitro. Thirty-two teeth were divided into two groups. In the first group, the canals were instrumented with K files, in the second the initial preparation was done with a K file and completed with a laser beam. Scanning electron microscopic evaluations showed that preparation with a laser beam is possible and results in an improvement in the cleanliness of the canal walls when compared with conventional techniques.

Fibre optic beam delivery: launching efficiency measurement by dual-detector cladding power monitoring

In the design and operation of high-power fibre optic beam delivery systems, a primary consideration is the efficiency with which power can be launched from the laser source into the core of the fibre. Techniques for the measurement of launching efficiency, based on monitoring power guided by the fibre cladding, are discussed, and advantages over direct measurement methods are indicated. An extension of the cladding power monitoring technique is introduced, which involves the use of two cladding power detectors separated by a controlled bend in the fibre. It is shown that it is hence possible to normalize the cladding power measurement by the core power, and thus to determine the launch efficiency independent of the laser power.

閉塞性動脈硬化症に対するLaser thermal angioplastyの臨床的検討

Laser thermal angioplasty (LTA) was performed in 34 patients with the occlusive disease of the femoropopliteal artery. Argon laser and an optical fiber delivery system with metal tip probe with thermal feedback control system were used for LTA. Initial success was achieved in 35 (85%) of all 41 lesions, 14 (88%) of 16 in the stenotic lesions and 21 (84%) of 25 in the occlusive lesions. The length of the lesions was significantly longer in a group of the 6 lesions without clinical improvement, and also, the number of the calcified lesions increased remarkably in these patients. At the follow-up of 55 months, the cumulative patency rate (CPR) was 74% in 30 cases with clinical success. In the 12 stenotic and 18 occlusive lesions, the CPR were 80% and 69%, respectively. These results suggested that LTA was useful for the management of patients with chronic occlusion of the peripheral arteries and provided good long-term patency rates by reducing restenosis.

Holmium-YAG Laser Surgery on Experimental Vitreous Membranes

We used a pulsed holmium-YAG laser that emitted in the midinfrared (2.12 microns) to cut experimental vitreous membranes in rabbits via an intraocular fiberoptic delivery system. Thirty-five membranes were treated at distances of 0.5 to 3.8 mm from the retina. All of the membranes that were treated were transected or partially cut. In cases that were treated with the optical fiber encased in a retinal-shielding pick, membranes could be readily transected without retinal injury. Laser vitreous membrane cutting may offer the advantage of near-tractionless membrane segmentation. The combination of a moderately strong target tissue absorption and the ready availability of commercial optical fibers for transmission of 2.12-microns laser energy suggests that the holmium-YAG laser merits further investigation for this application.

Nd:YAG laser with sapphire tip combined with balloon angioplasty in peripheral arterial occlusions. Long-term results.

In 167 patients with complete occlusion (greater than 3 cm) of the femoropopliteal artery, percutaneous transluminal laser angioplasty (PTLA) was performed after an unsuccessful attempt at crossing with a guide wire and was immediately followed by balloon dilatation. An Nd-YAG laser and an optical fiber delivery system with a sapphire tip serving as a contact probe were used for PTLA. In 132 of 167 (79%) patients, the occluded segment was successfully reopened. Clinical symptoms improved in 126 of 167 (75%) patients. PTLA was unsuccessful in 35 patients, and in 15 of these, injury of the vessel wall occurred. In one patient, surgical drainage of a large hematoma became necessary. All patients in whom recanalization had been achieved were randomized to receive long-term treatment with either phenprocumarol or acetylsalicylic acid (ASA) plus dipyridamole to prevent rethrombosis. At 36 months of follow-up, the cumulative patency rate (CPR) was 63%. A complete reobstruction in 32 patients (24%) and a partial reobstruction in 15 patients (11%) were found angiographically. The CPR after 36 months was significantly lower (p less than 0.05) in patients younger than 60 years of age (54%) than in patients older than 60 (68%); it was also significantly lower (p less than 0.05) in patients with reduced peripheral runoff (55%) due to obstructed arteries of the lower leg than in patients with unaffected runoff (73%). The CPR was 65% in recanalized segments shorter than 7 cm and was 62% in recanalized segments longer than 7 cm.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser trabecular ablation (LTA).

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

A new 1.9-µ wavelength laser for neurosurgery

The 1.9-mu wavelength component of a 1.9/1.06-mu two-wavelength laser with near-continuous wave properties was tested for its potential use in neurosurgery. The 1.9-mu wavelength has tissue-ablative capabilities, while the 1.06-mu wavelength (Nd:YAG) is suitable for achieving hemostasis. The advantages of the 1.9-mu wavelength over the CO2 laser include its ability to transmit through silica fiberoptic delivery systems and its deeper penetration in water (approximately 100 mu, a depth 10 times greater than for the CO2 laser), which is compatible with irrigation during ablation. To test the effectiveness of the laser, bilateral craniotomies were performed in anesthetized rats immobilized in a stereotactic frame. Under an operating microscope, lesions were made on the cortex by delivering the 1.9-mu laser beam through a 400-mu fiber at an average power of 1 W over a range of fluences. Subjective intraoperative observations were notable for minimal bleeding, absence of charring when the tissue was irrigated with a thin stream of saline, and uniform lesion formation. For comparison, lesions were generated with a commercially available continuous-wave CO2 laser at equivalent power and fluences. Histological specimens were divided into three groups based on the study after laser application: acute (30 minutes), subacute (48 hours), and chronic (14 days). The extent of thermal injury for the 1.9-mu laser in the acute lesions was quantitatively and histologically similar to that generated by the CO2 laser. Regions of injury extended approximately from the apex of the lesion, and crater depths generated by both lasers were similar (250 to 750 mu) in the range of fluences investigated (1.25 to 10 kJ/sq cm). Subacute and chronic histological specimens demonstrated inflammatory and repair responses that correlated with the acute injury regions in both the 1.9-mu and CO2 laser-treated specimens. This study demonstrates a neurosurgical potential for a new two-wavelength laser that ablates tissue effectively with limited thermal injury. The 1.9-mu laser is comparable to the widely used CO2 laser but offers several unique advantages, including the ability for delivery through a fiberoptic system and to irrigate tissue during use.

A comparative study of coagulation effects on the cortex of the rat using Nd-YAG (1.32 μm), Nd-YAG (1.06 μm) and CO2 lasers

This paper represents a comparative study on brain tissue of three lasers: Nd-YAG (1.32μm); Nd-YAG (1.06 μm); and CO2 laser. The experimental studies were performed on rats. They consisted of a comparison between the thermal effects and the consequent histological lesions produced. The surface temperature of the cortex induced by each laser shot was measured with an infrared camera. The results show that there exists an excellent correlation between surface temperature and the histology of the lesions produced. It appears that for equivalent surface temperatures the cortical lesions 8 days after irradiation were similar for Nd-YAG (1.32μm) and for CO2 lasers but significantly different for the Nd-YAG (1.06μm) laser. For example the depth of coagulation necrosis varied between 20 to 250μm with the CO2 laser using the power of 3 to 10 W at an exposure of 0.05 s with a fluence of 5J/cm2 and varied from 210 to 260μm using the Nd-YAG (1.32μm) with the power of 5 to 14 W with an exposure of 0.4 s with a fluence of 50–170 J/cm2. With the Nd-YAG (1.06μm) the depth of coagulation necrosis varied from 490μm to 550μm using a power of 12 to 19 W with an exposure of 0.4 s with a fluence of 150–250 J/cm2. It would appear that the Nd-YAG laser at a wavelength of 1.32μm should be valuable in neurosurgery as this wavelength is highly absorbed by brain parenchyma and is transmissible with a fibre optic delivery system.

A fiberoptic compatable midinfrared laser with CO 2 laser-like effect: Application to atherosclerosis

In theory, pulses of laser light in the 2-μm range should ablate tissue in a manner similar to that of the 10.6-μm CO 2 laser with the added advantage of efficient transmission through flexible quartz fibers. Using 200-μsec pulses of 2.15-μm thulium—holmium—chromium:YAG (THC:YAG) laser light, we were able to create 700-μm-diameter holes through calcific atherosclerosis in vitro. In vivo evaluation of thrombogenicity and healing was accomplished by exposing the luminal surface of rabbit aortas to the THC:YAG laser. Serial histologic examinations of laser-treated rabbit aortae revealed a time course of resolution of the lesions which was very similar to that observed with like-sized lesions created with the same amount of continuous wave CO 2 energy. No significant differences in thrombogenicity nor healing response were noted. The excellent in vivo response observed is due in part to the pulsed nature of the THC:YAG laser output as well as to the efficient tissue absorption at the 2.15-μm wavelength. We feel that excellent ablative effects with minimal collateral thermal damage can be obtained through fiberoptic delivery systems by taking advantage of laser wavelengths corresponding to the infrared absorption peak of water in the 2-μm region and pulsed delivery of the laser energy.