Ophir Eyal

Temperature controlled CO2 laser welding of soft tissues: Urinary bladder welding in different animal models (rats, rabbits, and cats)

Laser welding of tissues is a method of closure of surgical incisions that, in principle, may have advantages over conventional closure methods. It is a noncontact technique that introduces no foreign body, the closure is continuous and watertight, and the procedure is faster and requires less skill to master. However, in practice, there have been difficulties in obtaining strong and reliable welding. We assumed that the quality of the weld depends on the ability to monitor and control the surface temperature of the welded zone during the procedure. Our objective was to develop a “smart” fiberoptic laser system for controlled temperature welding.

Temperature-Controlled CO2 Laser Tissue Welding of Ocular Tissues

Lasers can be used for binding tissues by welding, but the clinical application of this method has been limited by the difficulties in defining and maintaining the optimal conditions. Fiberoptic radiometry allows accurate remote temperature measurements for control of laser tissue welding. We evaluated the use of a temperature-controlled tissue welding system to close corneal and corneoscleral wounds. Eighty ex vivo bovine eyes were used for the determination of welding parameters optimal for corneal wound closure. A 4 mm central corneal cut was closed with use of a CO2 laser (600 mw, 0.9 mm spot size), with tissue temperatures ranging from 45-70 degrees C and welding time ranging from 1-30 seconds. Wound strength was measured as burst pressure of the sealed wound. The welding parameters found to cause the strongest wound binding were used to weld a limbal incision of 4 mm in 10 adult albino rabbits. The fellow eye of each animal was used as a control, and the same wound was closed with one 10/0 mersilen suture. Two animals were killed immediately after the procedure, and the eyes were sent for histologic examination. Eight rabbits were followed for 1 month. Clinical examination and refraction were done 1 day, 1 week, 2 weeks, and 1 month after the procedure. Corneal topographic evaluations were done 1 week after the procedure. After 1 month the animals were killed and the eyes were examined histologically. The optimal results of wound binding by laser welding in the enucleated bovine eyes were achieved with 55-60 degrees C and at a welding time of 12-20 seconds. At these parameters the burst pressure of corneal wounds was 70 mm Hg. All laser-welded limbal wounds in the rabbits were tightly closed at the end of procedure and during the follow-up period. The refractive results after laser welding were equal to those of the controlled suture-closed wound. Laser tissue welding combined with tissue temperature monitoring can be used to close corneal wounds.

Thermal feedback control techniques for transistor–transistor logic triggered CO 2 laser used for irradiation of biological tissue utilizing infrared fiber-optic radiometry

A fiber-optic radiometer is used to monitor and control, in real time, the temperature of samples of biological tissue irradiated with a CO(2) laser. Several control algorithms are investigated and the optimal control mode is obtained. A silver halide infrared fiber is used both to deliver the CO(2) laser radiation needed to irradiate the target and to deliver the thermal radiation emitted from the target back to the radiometer. Such a system can be useful in medical applications of CO(2) lasers.

TEMPERATURE MEASUREMENTS USING PULSED PHOTOTHERMAL RADIOMETRY AND SILVER HALIDE INFRARED OPTICAL FIBERS

A novel technique for measuring temperature, based on pulsed photothermal radiometry and analysis of the spectral and temperature dependence of Planck’s blackbody equation, is described. In this technique a body is irradiated by a laser pulse and its temperature inferred from the time dependence of the emitted infrared signal curve. This technique was used for near ambient temperature measurements using a CO2 laser, an infrared detector, and infrared transmitting silver halide optical fibers. The experimental results are consistent with theory. This technique is independent of changes in emissivity or geometric factors and it will be useful for accurate and fast noncontact temperature measurements.

Single-mode mid-infrared silver halide planar waveguides

A single-mode silver halide symmetric step-index planar waveguide for 10.6 microm is described. We fabricate the waveguide from extruded multimode silver halide fiber by pressing the fiber between metal plates while heating. The device is therefore automatically pigtailed to a fiber, which could ease the difficulties of coupling light into it. We achieved single-mode confinement by suitably adjusting the refractive index of the core and the cladding and by reducing the core thickness to 30 microm. The output radiation from the planar waveguide was measured to confirm single-mode confinement. Silver halide single-mode waveguides for the mid-infrared can be used to enhance sensitivity in fiber-optic evanescent-wave infrared spectroscopy measurements or for the development of mid-infrared single-mode lasers and interferometers.

Fiber-optic infrared radiometer for accurate temperature measurements

A fiber-optic radiometer is developed for accurate noncontact temperature measurements. Of compact and novel design, it is based on replacing the usual chopper with a simple shutter. The radiometer operates in a spectral range of 5-20 microm and uses a silver-halide IR-transmitting optical fiber. The radiometer has a temperature resolution of 0.1 degrees C, a time response of 200 ms, and a spatial resolution of approximately 1 mm. Theory, simulation, radiometer design and construction, and examples of experimental measurements are shown. The novel radiometer can be used in diverse applications in science, medicine, and industry.

FIBER-OPTIC PULSED PHOTOTHERMAL RADIOMETRY FOR FAST SURFACE-TEMPERATURE MEASUREMENTS

Temperature measurement based on pulsed photothermal radiometry is described. In this technique a body is irradiated by a laser pulse and its temperature is inferred from the shape of the emitted photothermal-signal curve. A prototypical system based on a pulsed CO(2) laser, an IR detector, and IR-transmitting silver halide optical fibers was constructed and used to evaluate the feasibility of this technique. An important feature of the technique is that changes in sample emissivity or geometric factors do not introduce errors in the temperature determination. Theory, simulation, and experimental results are given and discussed.

Infrared radiometry using silver halide fibers and a cooled photonic detector

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer is capable of measuring in real time the temperature of tissue irradiated with a CO 2 laser. A silver halide IR fiber is used to deliver the CO 2 laser radiation to the target and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of detector blinding by reflected CO 2 radiation. A theory of operation for this silver halide fiber optic radiometer, based on lock-in amplifier techniques, is presented. A short discussion of the radiometer design and construction is given. This work forms a basis for the subject of measuring, in real time, fast radiometric signals caused by CO 2 laser irradiation. Such a radiometer is very useful when dealing with pulsed photo thermal radiation with 10.6-μm CO 2 laser radiation. This technique is very useful in medicine and industry.

Silver halide midinfrared optical fiber Y coupler

A description of a novel silver halide midinfrared optical fiber Y coupler including the construction method and the optical characteristics of the coupler is given. The coupler was used to irradiate a sample with a CO2 laser and to measure simultaneously the temperature rise of the sample.

Temperature monitoring and control of CO2 laser tissue welding in the urinary tract using a silver halide fiber optic radiometer

Laser welding of tissues is an experimental surgical technique for the binding of tissues. The difficulty in the clinical implementation of this technique arises from the difficulty in defining the optimal conditions under which a satisfactory weld is formed. Temperature measurements of laser irradiated tissues are difficult to perform and experiments have produced conflicting results. Fiber optic radiometry allows temperature measurement of laser irradiated tissues by remote sensing of emitted infra red (IR) radiation. We developed an IR radiometer capable of accurate temperature measurements (+/- 0.2 degree(s)C). Utilizing this radiometer for the monitoring and control of CO2 laser irradiated tissues we achieved temperature control of +/- 2.5 degree(s)C of tissues during welding. This system was used to perform laser welds on the urinary bladders of rats. The strength of the welds was recorded for different welding temperatures, and maximal strength was obtained at 55 degree(s)C and 12 sec.