Biomedical subjects

A Katzir

Publications and source records attributed to A Katzir.

At least 19 recordsLinked to original sources

PubMed2004

Investigations of the structure of water using mid-IR fiberoptic evanescent wave spectroscopy.

Liquid water is one of the most studied but still one of the least understood substances. The absorption spectra of water in the mid-IR were measured from -10 and up to 90 degrees C using fiberoptic evanescent wave spectroscopy. The changes in the spectrum and the existence of an isosbestic point during the ice-liquid phase transition were studied. Based on the spectroscopic data we propose a multispecies model for the structure of liquid water. The new model provides an explanation for the results of the measurements reported in this work. It also provides an explanation for some of the unique thermodynamic and kinetic properties of liquid water and for many of the anomalies of water.

Journal Article↗

PubMed2003

Evanescent-wave infrared spectroscopy with flattened fibers as sensing elements.

Fiber-optic evanescent-wave spectroscopy (FEWS) is a novel method for measuring the absorption spectra of samples in contact with a segment of an optical fiber that serves as a sensing element. We used a cylindrical IR-transmitting AgClBr fiber whose central section, of length L, was flattened to a thickness d. This section was used as the FEWS sensing element. Our theoretical work predicted that the signals obtained in FEWS measurements should be linearly dependent on L and inversely proportional to d. Decreasing the thickness can significantly increase its sensitivity of the sensor. These theoretical results were verified experimentally by measurements of methanol and water.

Journal Article↗

PubMed2003

Direct monitoring of soil and water nitrate by FTIR based FEWS or membrane systems.

The development of silver halide fibers that transmit with minimal loss into the mid-IR (MIR) paved the way to their successful utilization as effective ATR (Attenuated Total Reflectance) elements, promoting the implementation of Fiberoptic Evanescent Wave Spectroscopy (FEWS) for direct monitoring of nitrate in environmental systems. Samples containing nitrate in water, soil extracts, and pastes were used for the determination of nitrate concentration with a common ATR ZnSe crystal and with silver halide fibers (FEWS). Spectra of soil pastes and suspensions and those of phosphate, carbonate, sulfate, ammonium, and soil organic constituents were collected to study possible interference with nitrate determination. The standard error of estimate (SEE) and R2 values obtained with flat fibers, using the simple single-point correlation method, were superior to those obtained for cylindrical FEWS and ZnSe ATR crystals in pure water. A significant improvement in the SEE and R2 was achieved in most soil pastes by applying the simple mode of the Cross Correlation method. Direct transmission of MIR radiation through ion-exchange membranes, partially loaded with nitrate or carbonate, was found an effective alternative for MIR-FTIR determination of these ions. Further development and modification of the FEWS devices should allow in-situ and online determination of nitrate in soil and environmental systems.

Agrochemicals↗

PubMed2003

In situ sensing of volatile organic compounds in groundwater: first field tests of a mid-infrared fiber-optic sensing system.

A prototype mid-infrared sensor system for the determination of volatile organic pollutants in groundwater was developed and tested under real-world conditions. The sensor comprises a portable Fourier transform infrared spectrometer, coupled to the sensor head via mid-infrared transparent silver halide fiber-optic cables. A 10 cm unclad middle section of the 6-m-long fiber is coated with ethylene propylene copolymer in order to enrich the analytes within the penetration depth of the evanescent field protruding from the fiber sensor head. A mixture of tetrachloroethylene, dichlorobenzene, diethyl phthalate, and xylene isomers at concentrations in the low ppm region was investigated qualitatively and quantitatively in an artificial aquifer system filled with Munich gravel. This simulated real-world site at a pilot scale enables in situ studies of the sensor response and spreading of the pollutants injected into the system with controlled groundwater flow. The sensor head was immersed into a monitoring well of the aquifer system at a distance of 1 m downstream of the sample inlet and at a depth of 30 cm. Within one hour, the analytes were clearly identified in the fingerprint region of the IR spectrum (1300 to 700 cm(-1)). The results have been validated by head-space gas chromatography, using samples collected during the field measurement. Five out of six analytes could be discriminated simultaneously; for two of the analytes the quantitative results are in agreement with the reference analysis.

Equipment Design↗

PubMed2003

Online sensing of volatile organic compounds in groundwater using mid-infrared fibre optic evanescent wave spectroscopy: a pilot scale test.

A prototype sensing system for in-situ monitoring of volatile organic compounds in contaminated groundwater was tested at a pilot scale plant. The sensor consists of a commercially available Fourier transform infrared spectrometer, connected to a 6 m long infrared transparent silver halide fibre optic cable. A 10 cm long core-only section at the centre of the fibre is mounted on a sensor head and coated with a hydrophobic polymer layer, while the remaining fibre is protected by Teflon tubing and thus not in contact with the surrounding media. The sensor head was immersed into the monitoring wells of the pilot plant testing the sensor system under circumstances close to field conditions and typical for in-situ measurements. The pilot plant consists of a 1 m3 cubic tank filled with gravel. A pump is used to circulate water horizontally through the tank, simulating a natural aquifer. The evolution of the concentration of analytes injected into the system is monitored with time using the developed prototype sensing system. The results are validated by corresponding sampling and analysis with headspace gas chromatography.

Environmental Monitoring↗

PubMed2001

Thermal-feedback-controlled coagulation of egg white by the CO2 laser.

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated with the egg-white model. We observed the dynamics of photothermal denaturation during CO2 laser irradiation by simultaneously controlling surface temperature and monitoring He-Ne laser transmission of egg-white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. Analysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal damage. Our experiments demonstrated that thermal feedback can effectively control or limit photothermal damage.

Journal Article↗

PubMed2001

Laser soldering of rat skin, using fiberoptic temperature controlled system.

BACKGROUND AND OBJECTIVE: Laser soldering of tissues is based on the application of a biological solder on the approximated edges of a cut. Our goal was to use laser soldering for sealing cuts in skin under temperature feedback control and compare the results with ones obtained using standard sutures. STUDY DESIGN/MATERIALS AND METHODS: Albumin solder was applied onto the approximated edges of cuts created in rat skin. A fiberoptic system was used to deliver the radiation of a CO(2) laser, to heat a spot near the cut edges, and to control the temperature. Laser soldering was carried out, spot by spot, where the temperature at each spot was kept at 65-70 degrees C for 10 sec. RESULTS: The tensile strength of laser-soldered cuts was measured after 3-28 days postoperatively and was found comparable to that of sutured cuts. Histopathological studies showed no thermal damage and less inflammatory reaction than that caused by standard sutures (P = 0.04). CONCLUSIONS: Temperature controlled laser soldering of cuts in rat skin gave strong bonding. The cosmetic and histological results were very good, in comparison to those of standard sutures.

Albumins↗

PubMed2001

Monitoring of the infrared radiation emitted from skin layers during CO2 laser resurfacing: a possible basis for a depth navigation device.

CO2 laser resurfacing is very accurate, but it is not free of complications such as scarring. The objectives of the present study were to evaluate the pattern of the infrared (IR) radiation emitted from skin layers and to use this pattern to distinguish between these layers during resurfacing. A CO2-resurfacing laser (Sharplan SilkTouch) was used for the de-epithelialisation of skin. A silver halide optical fibre delivered the radiation emitted from the skin during resurfacing to an IR photonic detector. Time-dependent curves of the signals emitted from the skin layers were statistically evaluated and showed significant differences between the epidermis and the dermal layers. Similar results were obtained during in-vivo and ex-vivo measurements. The difference between the skin layers emission may be used for depth navigation during laser resurfacing.

Analysis of Variance↗

PubMed2001

Fiberoptic infrared radiometer for real time in situ thermometry inside an MRI system.

A warm body emits radiation whose intensity I is dependent on the surface temperature T. For T near room temperature this radiation is mostly in the mid-IR. Radiometric measurement of I is often used for non contact thermometry. Temperature measurements in situ and in remote locations can be carried out using optical fibers, but one needs fibers that are highly transparent in the mid-IR. Our group has developed fibers made of silver halides. These are flexible, nontoxic, not hygroscopic and highly transparent in the mid IR. These fibers served for the development of a novel fiberoptic radiometer. Using this radiometer we have measured the temperatures of samples while being imaged in an MRI system. The presence of the fibers inside the MRI system did not interfere with the operation of the MRI nor did not the MRI system affect the radiometer. The temperature measurements were made with accuracy of 0.3 degrees C, response time of 1 s and spatial resolution of 1 mm. Fiberoptic radiometers would be highly suitable for temperature measurement of human tissues, for example during surgical procedures done inside an MRI system.

Calibration↗

PubMed2001

Carbon dioxide laser and silver halide infrared transmitting fibers for tympanoplasty: an experimental animal model.

OBJECTIVE: This study evaluates the effectiveness and safety of fiberoptic carbon dioxide (CO2) laser welding for graft closure of tympanic membrane perforations in an animal model. STUDY DESIGN AND SETTING: Tympanic membrane perforation was surgically induced in 11 eardrums of 7 given pigs. A lumbar facial graft was placed over the wound, and albumin drops served as a biologic solder. CO2 laser energy, transmitted through silver halide infrared transmitting fibers, was used for "spot-welding" along the circumference of the graft. The welded sites were evaluated by using a surgical microscope as well as by evaluating the sites histologically. RESULTS: Healing started 3 to 4 days after surgery and was completed within 3 weeks with the formation of a neotympanum. Some inflammation with granulation tissue was noted in 5 eardrums. CONCLUSIONS AND SIGNIFICANCE: These preliminary results indicate that CO2 laser tympanoplasty with a fiberoptic delivery system may be a promising new technique for the clinical setting.

Animals↗

PubMed2000

Temperature controlled CO(2) laser welding of soft tissues: urinary bladder welding in different animal models (rats, rabbits, and cats).

BACKGROUND AND OBJECTIVE: 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. STUDY DESIGN/MATERIALS AND METHODS: We have developed a welding system based on a CO(2) laser and on infrared transmitting AgClBr fibers. This fiberoptic system plays a double role: transmitting laser power for tissue heating and noncontact (radiometric) temperature monitoring and control. The "true" temperature of the heated tissue was determined by using an improved calibration method. We carried out long-studies of CO(2) laser welding of urinary bladders in various animal models. Cystotomies were performed on the animals, and complete closure of the bladder was obtained with a surface temperature of 55 +/- 5 degrees C at the welding site. RESULTS: In early experiments on 31 rats, the success rate was 73%. In later experiments with 10 rabbits and 3 cats, there was an 80% and a 100% success rate, respectively. CONCLUSION: The success rate in these preliminary experiments and the quality of the weld, as determined histologically, demonstrate that temperature controlled CO(2) laser welding can produce effective welding of tissues. The fiberoptic system can be adapted for endoscopic laser welding.

Animals↗

PubMed1999

Comparison of flash lamp pulsed-dye laser (585 nm) and conventional surgery in the delay of random dorsal rat flaps.

BACKGROUND AND OBJECTIVE: Delay is a basic surgical technique used by flap surgeons to improve the blood supply to the distal parts of a random skin flap. The aim of this study was to determine whether a scarless delay can be done by the use of the flash lamp pulsed-dye laser operating at a wavelength of 585 nm. STUDY DESIGN/MATERIALS AND METHODS: The pilot study showed that 6 J/cm(2) had a selective photothermolysis effect and therefore was chosen for testing the delay procedure on 15 rats. The percentage of flap necrosis of this group was compared to the results of 15 rats that underwent delay by surgery and 15 rats that were not treated prior to flap surgery (control group). RESULTS: Laser delay of McFarlane flaps resulted in an average of 15.5% smaller necrotic area compared to the control group (52.7% +/- 14.4% and 68.2% +/- 9.6%, respectively, P < 0.01) and was as effective as surgical delay (53.3% +/- 13.6%). CONCLUSIONS: The results indicate that the flash lamp pulsed-dye laser operating at 585 nm is effective for delaying cutaneous flaps in the rat model.

Analysis of Variance↗

PubMed1999

Bladder welding in rats using controlled temperature CO2 laser system.

PURPOSE: Laser tissue welding has potential advantages over conventional suture closure of surgical wounds. It is a noncontact technique that introduces no foreign body and limits the possibility of infections and complications. The closure could be immediately watertight and the procedure may be less traumatic, faster and easier. In spite of these positives laser welding has not yet been approved for wide use. The problem in the clinical implementation of this technique arises from the difficulty in defining the conditions under which a highly reliable weld is formed. We have assumed that the successful welding of tissues depends on the ability to monitor and control the surface temperature during the procedure, thereby avoiding underheating or overheating. The purpose of this work was to develop a laser system for reliable welding of urinary tract tissues under good temperature control. MATERIALS AND METHODS: We have developed a "smart" laser system that is capable of a dual role: transmitting CO2 laser power for tissue heating, and noncontact (radiometric) temperature monitoring and control. Bladder opening (cystotomy) was performed in 38 rats. Thirty-three animals underwent laser welding. In 5 rats (control group) the bladder wound was closed with one layer of continuous 6-0 dexon sutures. Reliable welding was obtained when the surface temperature was kept at 71 + 5C. Quality of weld was controlled immediately after operation. The rats were sacrificed on days 2, 10 and 30 for histological study. RESULTS: Bladder closure using the laser welding system was successful in 31/33 (94%) animals. Histological examination revealed an excellent welding and healing of the tissue. CONCLUSIONS: Efficiency of laser welding of urinary bladder in rats was confirmed by high survival rate and quality of scar that was demonstrated by clinical and histological examinations. In the future, optimal laser welding conditions will be studied in larger animals, using CO2 lasers and other lasers, with deeper radiation penetration into tissues.

Animals↗

PubMed1997

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.

Animals↗

PubMed1996

Laser irradiation of biological tissue through water as a means of reducing thermal damage.

BACKGROUND AND OBJECTIVE: Reduction of thermal damage inbred with laser surgery is an ongoing challenge. The cavitation effect has been shown to facilitate the transmission of a laser beam through the otherwise opaque water layer. We suggest that by immersing the target tissue in water during laser surgery, thermal damage will be diminished. STUDY DESIGN/MATERIALS AND METHODS: A method of irradiating tissue by CO2 laser through a layer of a few millimeters of water is described. A series of experiments was conducted on fresh bovine cornea immersed in water or in air, histology of thermal damage was compared. RESULTS: We were able to show that irradiation of tissue immersed in water reduces the thermal damage caused to the area surrounding the incision as compared to the damage caused during irradiation of tissue in air (P < 0.001). CONCLUSION: Laser surgery of tissue immersed in water can reduce the inbred thermal damage. Application of this method to clinical use may result in precise, clean cutting, and enable the use of CO2 laser through water.

Animals↗

PubMed1994

Silver halide fiber optic radiometric temperature measurement and control of CO2 laser-irradiated tissues and application to tissue welding.

Tissue heating by laser irradiation has attained importance in many clinical applications. Accurate temperature measurements of laser-irradiated tissues are difficult to achieve, and experiments have produced conflicting results. Fiber optic radiometry allows temperature measurement of laser-irradiated tissues by remote sensing of the emitted infra red (IR) radiation. We have developed an IR fiber optic radiometer capable of accurate tissue temperature measurements (+/- 0.2 degrees C) and utilized it to monitor and control the heating of tissues by CO2 laser irradiation. Tissue temperature control of +/- 2.5 degrees C was achieved. This system was used to control tissue temperature during CO2 laser-assisted welding of urinary bladders in rats. The strength of the welds was recorded for different welding temperatures. A temperature of 55 degrees C was found to be optimal.

Animals↗

PubMed1994

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.

Animals↗

PubMed1992

Immediate retinal adhesion by CO2 laser irradiation using a fiberoptic intraocular probe.

Using an experimental fiberoptically guided CO2 laser system, we produced lesions on fresh bovine retinas. These lesions were shown to achieve immediate measurable chorioretinal adhesion. This model provides preliminary data on the use of a fiberoptic CO2 laser probe to produce chorioretinal lesions and possible future use in intraocular surgery for retinal detachment. The advantages of using CO2 laser energy are minimal damage surrounding desired lesion and its versatility as a coagulator and cutter. With modifications, CO2 endolaser may have a role in intraocular surgery.

Animals↗