Prototype Er:YAG lasers were used to generate 70-170 usec long pulses of 2.9 urn containing a series of lusec relaxation oscillation spikes which were coupled into prototype zirconium fluoride glass optical fibers of 180-250 urn diameter. Pulse energy densities in excess of 2400 mJ/mm2 were transmitted through these fibers without damage. Systematic studies of tissue damage by the Er:YAG laser pulses delivered to the surface of the tissue in a wet field via the ZrF4 fibers demonstrated effective ablative thresholds of 5 mJ/mm2 and slope ablative efficiency of 0.5 mm3/J for soft tissue such as human cadaver coronary artery. For heavily calcified tissues such as hard human calcified atherosclerotic plaque or rib bone ablative thresholds were increased 3 fold and the slope efficiency was slighlty decreased. Tissue thermal damage zone was confined to a region of 3-5 urn from the edge of the ablated zone for suprathreshold pulses. These studies demonstrate the feasibility of an Er:YAG laser - zirconium fluoride fiber microsurgical system for laser angioplasty and other forms of remote human ablative microsurgery.

Hollow fibers were made of plastic materials with both metallic and dielectric inside coating. Previous theoretical investigation had shown that by the use of optimal metallic and dielectric layers, low attenuation could be achieved, even for bent fibers. Experimentally, the attenuation of 2 dB/m was measured for a 3 mm diameter flexible plastic waveguide.

In order to qualify infrared ("IR") fiber materials, components and subsystems for specific medical applications, it is necessary to conduct the appropriate tests to insure that required safety and performance levels are met. Such tests include transmission and power-handling measurements, output characterization, environmental and mechanical analyses, and toxicity evaluation. Several of the test parameters and techniques are different when evaluating fibers for medical applications than for communications or other applications. This paper describes the basic tests which are required for the proper evaluation of IR fibers for medical applications.

The suitable laser power light guide system is neccessary in the medical laser apparatus. In order that the function be must effective, enough flexibility and safety of power laser guide are required. We have developed a non-toxic flexible CO2 laser beam guide with metal and polymer hollow tube. The present experimental results show that the CO2 laser beam tran smission rate about 85% per meter, emitted power was obtained about 81W at 1 meter guide length and any accidents were not happen under the continuous transmission. The emitted light beam spot was focused to about 0.5mm diameter. We have obtained emission beam power density of 40kW/cm2. The amounts of this power density will be practical use for medical applications. The guide tube have flexibility,the tube is bent easily to a round shape at radius above 10cm. The twist of tube is also possible. On the other hand, in order to inprovement of flexibility, we have forward trial product of narrow tube. The hollow guide tube will anticipate development of new medical application of CO2 laser.

An algorithm was developed to calculate the optimal combination of optical fiber and gradient-index lens variables that produces a range of desired spot sizes for laser beam delivery in photocoagulation. This algorithm was used to calculate the optical parameters of endophotocoagulating probes for argon green (514.5 nm) and krypton red (647.1 nm) lasers used in ophthalmology. Prototype endoprobes have been built and tested during intraocular surgery on animals.

The very heart of applications of optical fibre technology in medicine and biology stems primarily from extraordinary reach rea ctions between an optical wave and alive matter. On the other hand, the well known facilities offered by optical fibers working as reliable transmission channels, optical buses, image and optical power channels and sensors,are being still more and more widely recognized for all kinds of medical and biological uses. In the paper we will confine ourselves mainly to the works on applications of the lightguide technology in health service, medicine and biology in this country. We will review some of the recent developments in this domain. The presentation contains the following parts: lightguide communication systems for big hospitals, safety factors of fibre optics in view of internal regulations, fibre optic safety protections in medical and industrial applications, works on optical fibre sensors for medical applications, construction of a multi-task fibre optic micro-probe, optical fibre devices for ophthalmology.

Laser power transmission through fluoride glass fibers is possible, but requires stringent glass processing techniques to avoid laser induced damage. A pulsed Er:Yag laser was used to determine the damage threshold of these fibers.

The purpose of this study was to develop a reproducible method for atrial septostomy in live animals, which would be independent of both atrial septal thickness and left atrial size. Seven mongrel dogs monitored electrocardiographically were anesthetized and instrumented with systemic and pulmonary arterial lines. A modified Mullin's transseptal sheath was advanced under fluoroscopic control to interrogate the left atrium and atrial septum. A 400 micron regular quartz or a laser heated metallic tip fiber was passed through the sheath up to the atrial septum. Lasing of the atrial septum was done with an Argon laser at power output of 5 watts. In three dogs, an atrial septosomy catheter was passed to the left atrium through the laser atrial septostomy and balloon atrial septostomy was performed. The laser atrial septostomy measured 3 x 5 mm in diameter. This interatrial communication could be enlarged with a balloon septostomy to over one cm in diameter. Hemodynamic and electrocardiographic monitoring were stable during the procedure. Engineering problems included: 1) radioluscency of the laser fibers thus preventing fluoroscopic localization of the fiber course; and 2) the inability to increase lateral vaporization of the atrial septum. It is concluded that further changes in the lasing fibers need to be made before the method can be considered for clinical use.

This study quantitates the amount of gas produced when firing an optically shielded argon ion laser into 0.9% saline solution and blood alone, and into atheromatous aorta in either a blood or 0.9% saline medium. Energies from 0.25 to 4 J were used at powers of 2, 5, and 8 watts. We found that total volume of gas produced is small not only at equilibrium (0.3 + 0.1 ul/J when firing in blood alone and also firing in aorta in blood or saline medium), but also at peak (2.5 + 0.2 ul/J firing in blood alone and 1.0 + 0.1 ul/J or 0.9 + 0.1 ul/J when ablating aorta in saline or aorta, respectively). The peak gas volume when firing in blood alone was significantly greater than the other chamber environments. This is thought to be due to increased absorption of argon laser light by hemoglobin. The gas volumes produced by lasing aorta in 0.9% saline or blood were not statistically different. This finding is attributed to the catheter design which has a quartz tip surrounding the optical fiber that acts to displace the media from the lasing field. This catheter design negates the effect the medium might have on the laser light/target interaction.

Calcified human coronary arterial segments obtained at necropsy were irradiated in vitro with continuous wave (CW) argon laser (n=16) and a pulsed (P) excimer laser (n=28). CW laser irradiation accomplished little debridement of calcified plaque. P laser irradiation accomplished extensive ablation of calcific plaque, but was associated with more particulate photoproducts. The quantity and size of the resultant particles varied as a function of the pulse energy employed. Reduction in pulse energy from 80 to 15 mJ/pulse decreased the quantity of particulate debris by 50% and eliminated the largest (>700 microns) particles.

Previous attempts to recanalize obstructed arteries in humans, using laser angioplasty techniques have shown the technique to be feasible but the tunnels created through the arterial obstructions and occlusions were too small, thus facilitating early or late re-occlusion.1-4 Therefore, regardless of the technique used, laser emission through bare fibers shielded by a balloon catheter or thermal angioplasty with a heat metal cap,5,6 a complementary procedure using conventional balloon angioplasty was required to widen the narrow channel left after laser angioplasty.

Nanosecond pulsed lasers have two advantages compared to conventional C. W. lasers. First, they improve the precision of ablation and second, they minimize the thermal effects of laser action. These properties may allow for increased control of the laser beam and safer clinical application of laser angioplasty. Before clinical testing can begin two key problems must be resolved. First, the optimal combination of wavelength, energy density and power density for atheroma ablation must be defined. And second, since the nanosecond pulses of laser energy used generate enormous peak powers, they often destroy the fiberoptic waveguide used to transmit the energy.

This paper reviews our development of a multifiber optically shielded laser catheter for use in laser angiosurgery (LAS). The catheters under development allow both the spectral diagnosis of tissue type and the controlled delivery of therapeutic levels of laser energy within the arterial system. We describe the multifiber catheter device, in-vitro and in-vivo catheter testing and argon ion laser dosimetry. We also discuss the use of the LAS catheter in conjunction with spectral diagnostics.

Angiographically guided balloon dilatation of atherosclerotic vascular lesions is an established non-surgical technique for treating selected patients with occlusive vascular lesions. Balloon angioplasty involves compressing, stretching, and tearing of the arterial intima with subsequent reshaping and healing of the vessel lumen. The atherosclerotic lesion is mechanically displaced but otherwise remains intact. Totally occluding vascular lesions are not amenable to balloon dilatation unless the catheter can be advanced through the occlusion, a practice with inherent complications.

Myocardial ablation is a newly developing technique in the treatment of cardiac arrhythmias. Laser ablation in animal models has been associated with fewer procedural arrhythmias and more focal areas of myocardial injury. The effect of Argon laser ablation on canine epicardial preparations was studied. Single cell, microelectrode techniques were used to record action potential characteristics before and after argon laser ablation. Additionally, infrared micro-thermography was recorded during ablation to establish the superficial thermal characteristics of Argon laser ablation. Focal areas of action potential abnormality were found only at a distance of less than 5 mm from the laser crater edge. Action potential abnormalities occured only in areas where the superficial temperatures exceeded 60 degrees C. The focal nature of the injury as shown by action potential recordings may explain the less frequent association with arrhythmias and myocardial dysfunction.

Balloon angioplasty, while generally successful as a revascularization procedure, has the major drawbacks of abrupt reclosure and chronic restenosis. These problems may be related, at least in part, to a large thrombogenic surface and to abnormal blood flow patterns caused by disrupted vessel wall elements impinging on the lumen following angioplasty. Laser balloon angioplasty (LBA), a method whereby the vessel wall is heated during balloon inflation by a Nd-YAG laser coupled to an optical fiber terminating within the balloon, may help overcome these problems. The major effects of LBA appear to be a welding back of dissected flaps, reduction of the elastic recoil of the vessel wall, and destruction of smooth muscle cells within the wall, so that their exuberant cellular response to angioplasty is less likely to occur.

Canine myocardial lesions of predictable dimensions can be achieved with Nd:YAG laser photocoagulation. These lesions are well demarcated from surrounding normal tissue and heal with homogeneous scar formation. Intraoperative Nd:YAG laser photocoagulation successfully ablated 52 of 55 ventricular tachycardias in 17 patients. Histologic examination of tissues from these arrhythmogenic areas showed differences from lesions produced on canine epicardium. Lesions from the human cases were less predictable and not well circumscribed. These differences are felt to be due to optical inhomogeneities present in diseased, scarred human myocardium, geometric irregularities of the endocardial surface, anatomical constraints on tissue-fiber distance, and the angle of incidence of the beam with the tissue. Modifications of current delivery systems may overcome some of these limitations. Ablation of ventricular tachycardia arising deeper than 4.0 to 6.0 mm. from the irradiated surface may require interstitial probes coupled to the fiberoptic.

This is the first report which describes carbon dioxide laser photocoagulation of upper gastrointestinal bleeding via a flexible endoscope, using an infrared transmitting siver nalide fiber. Various laser parameters were checked to determine the optimal conditions for hemostasis. Both the acute effects of laser irradiation on tissue and the chronic effects on healing process were examined. Preliminary results indicate that carbon dioxide laser beam can successfully photocoagulate moderately bleeding ulcers.

Sensing pH by fiber optics is based on colorimetric method; indicators which change their own colour with the change of acidity of the solution under study 1 or fluorescent substances, whose fluorescence varies with the pH of solution, 2 can be used to modulate the intensity of the light carried by optical fibers.

The Optical Transfer Function of a flexible conventional fibroscope to be used for "in vivo" image transmission has been calculated and numerically analized through available experimental data. The results are derived from an earlier generalized study for gradient index optical media. A criterion to determine the image quality is established and discussed

Hyperthermia in cancer treatment involves heating malignant tumors to 42.5-43.0°C for an extended period (e.g. 30 min) in an attempt to obtain remission. For superficial and some deep seated tumors electromagnetic (microwave or radio frequency) field induced heating is often used. One of the severe problems with this therapeutic modality is the accurate measurement of temperature in the presence of a strong electromagnetic field. We have under development an infrared fiber-radiometer system which quantifies temperatures by measuring black body emission from the surface. This radiometer is based on a non-metallic, infrared fiber probe, which can operate either in contact or in non contact modes. When the fibers are incorporated in endoscopic catheters, internal body temperatures may be measured at those sites accessible via body orifices. In preliminary investigations the radiometer worked well in a strong microwave field, with an accuracy of ±0.5°C.

The use of fiber optics in the field of optical holography is described with emphasis on compensation of fringe instabilities and the ability to select any specified intensity ratio between object and reference beams. After a brief introduction to fiber optic holography, and its advantages over conventional holography, a method of phase compensation using a Michelson interferometer and a piezoelectric phase modulator is described. Also discussed is a method of varying the coupling ratio between outputs of a single mode fiber optic coupler for holographic applications by incorporating a Mach-Zehnder interferometer. Futhermore, a few practical techniques involved in fiber optic holography are discussed.

Oxygen concentration has been measured using fluorescence quenching in solid polymer hosts. The feasibility of generalizing these oxygen transducers to a wider class of chemical sensors through coupling to other chemistries is proposed. An example of such coupling is given in a glucose/oxygen transducer. The glucose transducer is produced by entrapping an enzyme, glucose oxidase, in' the composite matrix of a hydrophilic oxygen transducer. Glucose oxidase catalyzes a reaction between glucose and oxygen, thereby lowering the local oxygen concentration. This transducer yields a glucose modified optical oxygen signal. The specific focus of this research is the development of a theoretical model that describes the coupling of glucose concentration to relative fluorescence intensity, the experimental measurement of the key parameters in this model, and the evaluation of the sensitivity of the variation in relative fluorescence intensity with changes in glucose concentration. The experimental parameters include the diffusivity of oxygen in PHEMA (1.36 x 10-7 cm2/s), the solubility ofoglucose in PHEMA (0.24 g in PHEMA/g in buffer), and the diffusivity of glucose in PHEMA (8.25 x 10-8 cm2/s). When these experimental parameters are incorporated, the model developed predicts critical design requirements of the transducer.

The blood content in cutaneous microvessels shows periodical alterations, the so-called microcirculation oscillations. Depending on measurement conditions they are based on passive reactions (cardial and respiratory oscillations) or on active regulation (e. g. Hering-Traube waves). They can be observed by means of a fiber optic sensor system. Digitized and transfered into a computer the measurement can be analysed (Fourier transformation) and several physiological tests can be evaluated. Effects on the oscillations could be achieved e. g. by temperature changes, several drugs or electromagnetic fields.

An indicator system that responds reversibly to alkali metal ion concentrations has been developed. The components of the indicator system include the Cu(II) complex of aqueous polyethylenimine, an anionic fluorophor, and a neutral ionophore immobilized by adsorption on silica particles. In the absence of alkali metal ion, the anionic fluorophor binds to the Cu(II)-polyethylenimine complex where the presence of the paramagnetic Cu(II) ion causes quenching. When an alkali metal ion is present, it complexes with the ionophore forming a hydrophobic cation which binds to some of the anionic fluorophor rendering it fluorescent. The fluorescence of the indicator can be measured through optical fiber resulting in a reversible sensor for alkali metal ions.

Clinical measurement of coronary flow reserve by means of a fiber-optic laser Doppler catheter requires the measurement of blood flow velocity with minimal interference from the flow disturbance caused by the catheter itself. Study of Doppler scattering in blood by a transport theory approach shows that use of two spatially separated fibers for illumination and collection of light would give greater penetration of the velocity sensing region through the hydrodynamic boundary layer of the catheter. The design of a laser-Doppler velocimeter using dual multimode fibers with frequency shifted heterodyne detection is described. Flow velocity is estimated from the frequency moments of the spectrum, which are determined in realtime by analog signal processing without the use of spectrum analysis. Signal to noise analysis indicates that the output noise of the velocity estimate should be easily adequate to permit measurement of coronary flow reserve and resolution of the phasic characteristics of flow velocity.

A disposable sterile fiber optic probe has been developed to continuously monitor blood gases while residing within a 20 gauge radial artery catheter. Blood pH and dissolved 02 and CO2 are measured independently in three high n.a. 115/100 micron fibers by means of fluorescent indicators embedded in specialized membranes at the probe tip. Excitation of the fluorescent dyes is performed with a pulsed Xenon bulb; fluorescence detection with silicon photodiodes; and separation of excitation and emission is accomplished with a small cube beamsplitter located between two quarter-pitch SELFOC lenses. One of these SELFOC lenses is part of the disposable connector leading to the probe, the other leads to the excitation source via 250/200 micron fibers. The disposable portion is designed to be disconnected and reconnected without loss of calibration, requiring connector throughput reproducibility of 0.25%. System drift is typically less than 2% per 24 hours, after a 30 minute warm-up. Numerous practical problems with the fibers, connectors, SELFOC lenses, background fluorescence, system calibration, accuracy and drift have been encountered and will be discussed.

We have prepared fluorescence-based fiber optic sensors which give rapid and reversible responses. Other investigators have previously prepared sensors in which a membrane, tubing, or a hollow fiber is used to contain a specific reagent near the distal end of the fiber. Such an approach produces fibers with limited signal magnitudes and slow response times. Furthermore, these sensors are cumbersome to assemble, and are difficult to miniaturize and calibrate. We have developed a technique for the covalent chemical modification of the fiber's distal surface which is easily adapted to the smallest diameter glass optical fiber (100 μm). The sensing layer is attached directly to the fiber surface. The layer is extremely thin and highly porous and provides high fluorescence intensity with nearly instantaneous response times. The fibers are moderately stable against bleaching and have long shelf-lives. Our initial efforts have concentrated on the preparation of pH-sensitive optical sensors that are useful in the pH range 4.0 to 8.0. These sensors are reversible in response to pH variation and possess signal-to-noise ratios over 250/1. The fibers are prepared using a glass surface modification followed by a polymerization step for dye immobilization. Both fluorescence and absorbance-based sensors have been prepared using this technique. The absorbance-based pH sensors have 100% response times of less than 3 seconds, are sensitive in the region of pH 6.0 to 8.0, and provide reliable measurement of pH with precision of better than 0.03 pH units.

While fiberoptic thermometry offers a number of inherent advantages for measurement and control during use of rf or microwave-induced hyperthermia as an adjunct to radiation therapy, early fiberoptic thermometry systems exhibited a variety of limitations which have impeded full acceptance and utilization of the technology. Recently, a new technique based on the measurement of the fluorescent decay time of a magnesium fluorogermanate phosphor sensor has been introduced. This paper describes an eight-channel system utilizing the new technology which has been developed specifically for use in hyperthermia and other rf-field applications. The system utilizes a probe made from four small plastic fibers. This probe is available in the form of either a four-sensor linear array or four single-sensor fibers. Performance data taken independently under simulated clinical use indicate that this system substantially overcomes the limitations of previous fiberoptic systems.

The continuous measurement of intratissular NADH concentration allows early detection of cellular respiration arrest during clinical situations, i.e. allows a non-destructive, in situ, continuous measurement of ATP formation. This detection enables the physician or surgeon to intervene during a phase of cellular respiration arrest, before structural cellular alterations occur, thereby preventing potential tissular necrosis. The method has now been validated in experimental cardiac surgery for the monitoring of myocardial preservation techniques in cardiopulmonary by-pass and in cardiac pharmacology. Its industrial development is currently under way. Preliminary investigation strongly suggest the vast potentials of this diagnostic method in both clinical and experimental fields.

A laser melting technique was used to obtain bulb microlens tipped optical fibers. These fibers, along with flat polished optical fibers, were characterized by photometric methods. The effect on arterial tissue produced by the use of these fibers was evaluated in air.

Abela, G.S., and C.R. Conti. Laser revascularization: What are its prospects? J. Cardiovasc. Med. 8, 977-984 (1983) Abela, G.S., C. R. Conti, et al. A new model for investigation of transluminal recanalization: human atherosclerotic coronary artery xenografts. Am. J. Cardiol. 54, 200-205 (1984)

AEI, American Endoscoopy Inc. Diagnostic endoscopes 9350 Progress Parkway, Mentor, OH 44060 219-353-2935 contact: Paul Mucci American Edwards Laboratories Argon laser plus quartz fiber system P.O. box 11150 Santa Ana, CA 92711 714-250-2500 contact: Mike Estes