David Peri

Spectroscopic Study of Containers and Their Content Using a High-Resolution THz System

High-resolution measurements of spectral absorbance in the THz domain were performed to assess the detection feasibility of concealed materials. Spectral data of common materials used to form containers and some biological materials (DNA, tryptophan) are presented. We study the spectral range of 100-600 GHz, where atmospheric transmission allows remote sensing to reasonable ranges. Special care was taken to avoid the appearance of periodical spectral artifacts caused by the interference of multiple reflections from sample surfaces. They were removed either by algebraic postprocessing or by system adjustment to the Brewster angle that eliminates surface interface reflections of the p -polarization. These spectral measurements form a basis for a spectral library upon which detection and discrimination algorithms can be developed.

Efficacy Assessment of Various Anticholinergic Agents Against Topical Sarin-Induced Miosis and Visual Impairment in Rats

Eye exposure to the organophosphorus (OP) irreversible acetylcholinesterase inhibitor sarin results in long-term miosis and reduction in visual function. Anticholinergic drugs, such as atropine or homatropine, which are used topically in order to counter these effects may produce mydriasis and partial cycloplegia, which may worsen visual performance. This study was aimed to test the efficacy of short-acting anticholinergic drugs against sarin-induced miosis and visual impairment, which will minimally insult vision. Long-Evans rats, exposed topically to various sarin doses from 0 to 10 μg, showed a dose-dependent miosis, which returned to pre-exposure levels within 24-48 h. Tropicamide treatment rapidly widened the miotic effect to a different extent depending on time following treatment and dosage given. Cyclopentolate, however, showed a delayed response that finally widened the pupils in a dose-dependent manner. Atropine treatment showed a rapid widening of the pinpoint pupils exceeding baseline level finally causing mydriasis. Light reflex test showed that the contraction ability of the iris following atropine treatment was impaired, as opposed to the use of tropicamide which facilitated the iris contraction, similar to control. Finally, tropicamide and atropine treatments ameliorated the visual impairment, as opposed to cyclopentolate, which worsened visual performance. Considering that tropicamide treatment against sarin exposure did not cause mydriasis nor did it impair the iris contraction flexibility as a response to light, the use of this drug should be taken into consideration as a first-choice topical treatment against OP intoxication.

Retinal damage following exposure to pulsed Nd:YAG laser radiation in rabbits and its relation to physical parameters

The aim of the present study was to characterize permissible exposure limits (MPE) for safety analysis, with an emphasis on the immediate retinal damage, following Nd:YAG Q-switched laser radiation, and to test its correlation to physical parameters. Pigmented rabbits were exposed to Nd:YAG laser radiation (532nm, pulse duration: 20ns) in various energies. Exposures were conducted in retina tissue, very close to the optic nerve, with a total of 20 exposures per retina. Retinas were viewed during the first 10 min following exposure, using an on-line digital video camera. Thereafter, animals were sacrificed for histological evaluation. A part of the retinas were evaluated 24 hours post exposure. A quantitative analysis of the clinical findings, based on a severity score scale and a morphometric analysis of the extent of the lesions, was used to test the statistical relationship with the laser energy and number of pulses. In addition, hemorrhage threshold values were computed using Probit Analysis. Retinal damage, at various levels of severity, was observed immediately after exposure to energies above 10μJ, characterized by edema and subretinal hemorrhages. The appearance and severity of the lesions varied among animals, between fellow eyes and even within the same retina. The relationship between severity and extent of lesions, and energy levels and number of pulses was evaluated. The ED50 for various, immediate types of hemorrhage was determined, and correlated to physical parameters. Histological observations strengthened the clinical findings. The results were discussed in accordance with photomechanical and thermal theories of laser-tissue interactions.

Retinal damage following exposure to single pulses of Nd:YAG laser radiation in rabbits and its relation to energy levels

Purpose: The aim of the present study was to characterize permissible exposure limits (MPE) for safety analysis, with an emphasis on the immediate retinal damage following SHG of Nd:YAG Q-Switched laser radiation and to test its correlation to physical parameters. Methods: Pigmented rabbits (n=14) were exposed to single pulses of Nd:YAG laser radiation (532nm, pulse duration:8-12ns) in various energies ranging from 10 to 150 μJ. Exposures were conducted in retina tissue, very close to the optic nerve, with a total of 20 exposures per retina. Retinas were viewed during the first 15 min following exposure, using an on-line digital video camera. Thereafter, animals were sacrificed for histological evaluation. A quantitative analysis of the clinical findings, based on a severity score scale and a morphometric analysis of the extent of the lesions, was used to test the relationship with the laser energy. In addition, hemorrhage thresholds were computed using Probit Analysis. Results: Retinal damage, at various levels of severity, was observed immediately after exposure to energies above 26 μJ, characterized by edema and sub-retinal hemorrhages. The appearance and severity of the lesions varied among animals, between fellow eyes and even within the same retina. The ED50 for immediate pre-retinal hemorrhage was determined as 83μJ and the lesions’ diameter ranged from 141-640μ. A significant correlation (R=0.80, P<0.0001) was found between the extent of the lesions and energy levels. The diameter of the lesions showed a linear (P<0.008) increase with the laser energy. The histological observations indicated elevation of retinal layers and extensive damage in the outer segment of the photoreceptors and in the pigmented epithelial cells layer. Conclusions: A linear, laser-retinal tissue interaction was found immediately following exposure to single pulses of Nd:YAG laser radiation. It is suggested that unlike argon laser, which produces a thermal burn to the eye, Nd:YAG laser damage is a result of a combination of photo-mechanical and thermal mechanism.

Optical system for exposure of rabbit eyes to laser light and in situ assessment of retinal damage

An optical system designed for exposure of rabbit eyes to laser radiation and in-situ retinal damage assessment is presented. The laser radiation is of 2nd harmonic Q-switched Nd:YAG laser at 532 nm. The system is designed for multiple exposures at a regular grid array within a pre-determined region of the retina. Damage assessment is done in real time parallel to the exposure process. We present experimental results that demonstrate the versatility of the system for the determination of the threshold for laser-induced retinal damage in rabbit eye.

Comparative open-path environmental monitoring using lidar, IR radiometer, and point detectors

A replacement of point-detector network or its combination with an optical remote sensor is considered. The advantages achieved as well as some unavoidable difficulties, are discussed. The main difficulties arise due to inherent differences in spatial and temporal resolution of detectors considered and the different physical units in which their output data is given. Experimental results to illustrate the main points are presented.

Histological aspects of retinal damage following exposure to pulsed Nd:YAG laser radiation in rabbits: indication for mechanism

The severity and characteristics of retinal injury following laser radiation derived from laser and tissue related factors. We have previously shown that retinal damage following Nd:YAG Q-switched laser radiation in rabbits was related to physical parameters, i.e. energy levels and number of pulses. Yet, an extremely large variability in the severity of the damage was found under similar exposure paradigms, even within the same retina. This emphasizes the role of the biological variables in the pathological mechanism of laser-induced retinal damage. The aim of the present study was to further study histological parameters of the injury in relation to retinal site and to elucidate their role in the initiation and characteristics of the damage, following various energy levels (10-50 &mgr;J) and number of pulses (1-4). Pigmented rabbits were exposed to Nd:YAG laser radiation (532nm, pulse duration: 20ns). Exposures were conducted in retina tissue, adjacent to the optic nerve, with a total of 20 exposures per retina. Animals were sacrificed 15 min or 24 hours post exposure, eyes enucleated and processed for paraffin embedding. 4&mgr;m thick serial sections, stained with hematoxylin and eosin, were examined under light microscopy. Two major types of retinal damage were observed: focal edema confined to the pigmented epithelium and the photoreceptor cells, and hemorrhages, associated with destruction of retinal tissue. While focal edema associated with slight elevation of the photoreceptor layer seems to depend on the pigmented epithelium, hemorrhages were related also to the choroid vasculature at the site of radiation. It is suggested that a thermo-mechanical mechanism is involved in laser induced retinal hemorrhages at energies above 10-30&mgr;J (2-1 pulses, respectively).

Standoff detection in a fixed military installation: some test results

A standoff detection of atmospheric tracer dispersion in a military installation, using active and passive remote sensors, was demonstrated in a field test. System performance was evaluated at various atmospheric conditions, different forms of tracer release and different rates of release. Source locations as well as sensors positions were varied between test. A network of point detectors was used as an additional mean to map tracer concentrations, especially at locations not accessed by the remote sensors due to the complex nature of the installation.The test results are presently in a process of evaluation, some of them are presented here.

Extending the CO2 DIAL capability and incorporating point detectors data in concentration mapping

Both hardware and software methods are used to extend LIDAR detection capability in terms of range resolution and concentration threshold. Non overlapping targets are used at different ranges along the LIDAR line of sight (LOS) to replace the dependence on low aerosol backscattering. Methods of signal processing are used in concentration calculations. Presented experimental data demonstrate the method capability.

Efficient monitoring of toxic gases over an industrial zone using a combination of remote sensors

A study aimed at defining an efficient monitoring technique for an industrial zone coverage, using available scanning remote sensors, is presented. Scanning IR LIDAR and FTIR systems are considered as remote sensors. An analysis to define an optimal positioning of a central system and designing optimal lines of sight distribution is described. The application of this procedure is illustrated as a case study of a typical industrial zone, located near a populated urban zone.