Flexible waveguides for IR laser radiation and surgery applications

Flexible plastic waveguides were developed to deliver IR radiation, especially at 10.6 microns, which is the CO2 laser radiation wavelength. The waveguide is made from teflon tube with the inner wall coated with a metal layer and a dielectric overlayer. The internal diameter (ID) is 1.0 mm, length 1.0-1.2 m, and the distal tip decreases moderately to ID approximately 0.6 mm. The distal part on the last 10 centimeters is coated externally with a metal layer. Maximum power that can be delivered at the outlet is approximately 30 W and 10.6 x 10(3) W/cm2. This type of waveguide was used in several medical operations to evaluate its cutting characteristics and the resistances to heat reflection from the tissue while operating in orifices containing liquid substances.     

Flexible waveguides for Er-YAG laser radiation delivery

Flexible plastic waveguides (FPW) were devised for the delivery of Er-YAG laser radiation. The FPW characteristics were studied under various conditions. In vitro studies were carried out to explore the drilling procedure on extracted teeth and the FPW-tissue mutual effects. The results which were obtained proved that the FPW as a delivery device might be a substitute hand applicator for the pneumatic turbine for drilling in teeth     

Laser-induced acoustic stresses under submerged biologicalmembranes

Er:YAG lasers are being widely studied as candidates for surgical procedures in liquid environments, such as in ophthalmology. However, while the Er:YAG laser can be a precise and efficient light scalpel, this surgical method includes accompanying stress waves that must be quantified and evaluated for potential harm. In this study, Er:YAG laser-induced stress waves for free running laser pulses were measured over various consecutive treatment periods. Using a spot-poled PVDF hydrophone, measurements were acquired beneath a biological membrane submerged in a saline bath. Results yielded pressures peaks of 300-600 mbar beneath the uncut membrane, which could be harmful for the optic nerve if located directly below the treatment area. Acoustic waves representative of direct laser-liquid interactions were observed immediately following membrane rupture, and yielded much larger pressures. The morphological changes in the acoustic wave can be used as a feedback signal to indicate when the membrane has been cut     

Signal enhancement using beamforming and nonstationarity withapplications to speech

We consider a sensor array located in an enclosure, where arbitrary transfer functions (TFs) relate the source signal and the sensors. The array is used for enhancing a signal contaminated by interference. Constrained minimum power adaptive beamforming, which has been suggested by Frost (1972) and, in particular, the generalized sidelobe canceler (GSC) version, which has been developed by Griffiths and Jim (1982), are the most widely used beamforming techniques. These methods rely on the assumption that the received signals are simple delayed versions of the source signal. The good interference suppression attained under this assumption is severely impaired in complicated acoustic environments, where arbitrary TFs may be encountered. In this paper, we consider the arbitrary TF case. We propose a GSC solution, which is adapted to the general TF case. We derive a suboptimal algorithm that can be implemented by estimating the TFs ratios, instead of estimating the TFs. The TF ratios are estimated by exploiting the nonstationarity characteristics of the desired signal. The algorithm is applied to the problem of speech enhancement in a reverberating room. The discussion is supported by an experimental study using speech and noise signals recorded in an actual room acoustics environment     

Quantitative fluorescent imaging of specific markers of diseasedtissue

We have developed a random walk theory to relate observable fluorescent intensities on tissue surfaces to the presence of several embedded fluorescent masses. This work is an extension of analysis previously carried out for an isolated fluorescent site. Results depend on the optical properties of tissue at the excitation and emission wavelengths, as well as on the location of fluorescent targets and positions of source and detector. Measurements on tissue-like phantoms were performed to test the theory. Analysis of fluorescent signals, performed in accordance with the theory, yields accurate information about the location of the targets. Prospects of a noninvasive quantitative fluorescent imaging system, to diagnose and monitor salivary glands disease, is presented     

Broadband flexible waveguides for free-electron laser radiation

We refined flexible waveguides previously developed for CO(2) and Er:YAG laser radiation to transmit free-electron-laser (FEL) radiation. One can tune this laser over several segments of the radiation spectrum. This laser has a high peak power of as much as 10 MW with pulse energy of as much as 100 mJ. We made the waveguides of either Teflon or fused-silica tubes internally coated with metal and dielectric layers. We optimized the internal coatings specifications for transmission of various radiation wavelengths in the mid-IR range and enabled transmission of high-peak radiation. We performed experiments in three major FEL sites in the United States over a more than 1-year period when we measured and examined various characteristics of transmission. We used the analysis of these experiments as feedback to further improve these waveguides. The good preliminary results encourage us to invest more effort to further develop these waveguides until a suitable waveguide is obtained for this type of laser and make possible its introduction to the medical field where its characteristics can be exploited in surgical applications.     

Analytical solutions for time-resolved fluorescence lifetime imaging in a turbid medium such as tissue.

An analytical solution is developed to quantify a site-specific fluorophore lifetime perturbation that occurs, for example, when the local metabolic status is different from that of surrounding tissue. This solution may be used when fluorophores are distributed throughout a highly turbid media and the site of interest is embedded many mean scattering distances from the source and the detector. The perturbation in lifetime is differentiated from photon transit delays by random walk theory. This analytical solution requires a priori knowledge of the tissue-scattering and absorption properties at the excitation and emission wavelengths that may be obtained from concurrent time-resolved reflection measurements. Additionally, the solution has been compared with the exact, numerically solved solution. Thus the presented solution forms the basis for practical lifetime imaging in turbid media such as tissue.