This study aims to develop a photothermal imaging system through a coherent infrared bundle. This system will be used
to determine the oxygenation level of various tissues, suspected malignant tissues in particular. The oxygenation
estimation is preformed using a computerized algorithm. In order to evaluate the system, different bundle configurations
were used for the determination of the optimal one. Bundle transmittance and the algorithm's estimation ability were
measured, measurements were performed using agar phantoms consisting of varying ratios of Methylene Blue and ICG.
A bundle consisting of 19 Teflon waveguides with a of 1.1mm was found to be the optimal configuration with an RMS
of the error of 9.38%. At a second stage the system was validated on blood samples with varying oxygenation levels and
there oxygenation levels were estimated. This stage had an RMS of the error of 10.16% for the oxygenation level
estimation for samples with a 50% oxygenation level and higher.
Once the basic system was validated successfully on agar phantoms and blood samples a portable system was designed
and built in order to fit the system for portable use. The portable system consists of a white light illuminating source
followed by filters transmitting certain wavelengths, a transmitting fiber, a thermal imaging bundle and a portable
thermal camera. This portable system will be evaluated in order to have an adequate portable system for implementing
the method out of the lab.
The objective of this study is to develop a minimal invasive thermal imaging method to determine the oxygenation level of an internal tissue. In this method, the tissue is illuminated using an optical fiber by several wavelengths in the visible and near-IR range. Each wavelength is absorbed by the tissue and thus causes increase in its temperature. The temperature increase is observed by a coherent waveguide bundle in the mid-IR range. The thermal imaging of the tissue is done using a thermal camera through the coherent bundle. Analyzing the temperature rise allows estimating the tissue composition in general, and specifically the oxygenation level. Such a system enables imaging of the temperature within body cavities through a commercial endoscope. As an intermediate stage, the method is applied and tested on exposed skin tissue. A curve-fitting algorithm is used to find the most suitable saturation value affecting the temperature function. The algorithm is tested on a theoretical tissue model with various parameters, implemented for this study, and on agar phantom models. The calculated saturation values are in agreement with the real saturation values.
This study aims to develop a minimal invasive photothermal imaging method to determine the oxygenation level of an
internal tissue. In this method, the tissue is illuminated using an optical fiber by several wavelengths in the visible and
the near IR range. The absorption of the illuminated radiation causes an increase in the tissue's temperature which is
observed by a thermal camera through a coherent waveguide bundle in the mid-IR range. Analyzing the temperature rise
allows estimating the tissue composition in general, and specifically the oxygenation level. This system will enable to
measure the saturation on superficial tissues as well as within body cavities through a commercial endoscope.
A theoretical model of this problem was implemented to help design the experimental setup and develop the
experimental procedures. A curve-fitting algorithm is used to find the most suitable saturation value affecting the
temperature function. The estimated saturation was calculated on different simulated model parameters and was in good
agreement with the simulated saturation value.
The use hollow core waveguides (HCW's) in biomedicine includes two different tasks: Power delivery in order to
facilitate clinical procedures and measurement of beam parameters in order to sense the surrounding tissue and create a
diagnosis.
To study the interaction between light and waveguide a computer simulation of ray propagation inside a HCW was
developed. The simulation is based on the statistical method of Monte Carlo repeated trials and of ray tracing optics. The
simulation accounts for both meridional and skew rays, rough fiber surface, Imperfect reflection, arbitrary fiber geometry
and the insertion of absorbing molecular clusters inside the fiber lumen for sensing purposes.
Here we test skew rays. At first the effect of skewness on the number of wall hits and the optical distance is investigated.
Then different beam profiles are tested to fulfill different tasks: Sensing and power delivery. The role of skew rays in
each scenario is discussed.
Continuous efforts to develop low-loss flexible waveguides, to transmit mid-IR laser energy for minimally invasive surgical and diagnostic procedures, have been carried out by us and other groups. We have introduced sulfide dielectric films coated over an Ag reflecting layer as another potential solution. The metal sulfides used have high transparency in the IR spectrum, and their thickness can be tailored to minimize the attenuation over a selected wavelength range. The high refractive index contrast of the two metal sulfide materials enables us to produce multilayer hollow waveguides. These waveguide will have low attenuation in both straight and bent conditions, low sensitivity to coupling and to surface roughness, and a broad wavelength range. The lowest loss for a straight guide, measured at 1.55 µm for a 1,000-µm-bore Ag/CdS/PbS/CdS hollow glass waveguide (HGW), was 0.06 dB/m. This loss is three times less than that measured for a single-layer Ag/CdS-coated HGW at 1.55 µm. A theoretical simulation applying the same conditions showed the same pattern with a good potential for improvement.
Continues efforts to develop low loss flexible waveguides, to transmit mid IR laser energy for minimal invasive surgical and diagnostic procedures, have been carried out by us and other groups in this area. We have introduced sulfide dielectric films coated over an Ag reflecting layer as another potential solution. The metal sulfides used, have high transparency in the infra red spectrum and their thickness can be tailored to minimize the attenuation over a selected wavelength range. The high refractive index contrast of the two metal sulfide materials enable to produce multi layer hollow waveguides. These waveguide will have low attenuation in both straight and bent conditions, low sensitivity to coupling and to surface roughness and a broad wavelength range. The straight lowest loss measured at 1.55μm for a 1,000-μm bore Ag/CdS/PbS/CdS HGW was 0.06 dB/m. This loss is three times less than that measured for a single layer Ag/CdS coated HGW at 1.55μm. A theoretical simulation applying the same conditions showed the same pattern with a good potential for improvement.
Hollow waveguides are very sensitive to bending and coupling conditions, which cause large losses. In order to overcome these limitations we suggest to develop a multilayer hollow waveguide based on one-dimensional photonic crystal. Photonic crystals have been investigated for many years. The most common photonic crystal structure is the one- dimensional photonic crystal. For over a decade many companies and research groups have been manufacturing 'perfect mirrors' made of alternating pairs of dielectric materials with different index of refraction. These mirrors are made of a large number (approximately 10) of pairs. Applying the same type of coating techniques, with large number of pairs, to tubular shapes is very difficult and hollow waveguides based on this technology cannot be manufactured. We suggest an alternative method of coating flat surfaces with a pairs of layers of high ratio of index of refraction that can be applied later with minimal difficulties for tubes (hollow waveguides). We used a thin transparent metal layer (silver) as one of the dielectric materials of the pair. The thin metal layers have a large index of refraction in the MIR and the dielectric layer (silver iodine) has lower refractive index. Using these materials enables us to achieve a large ration of index of refraction, which is required for creating photonic crystal properties with a low number of pairs. We developed a mirror from alternating pairs of silver and silver iodine using an electroless chemical method. A mirror made of 4 pairs has reflectance close to 100% and omnidirectional behavior over a wide spectral region (6 - 10 micrometers ). This experimental result is in agreement with our theoretical model as well as other approaches. Using a ray model we have shown that a hollow waveguide based on the same structure of layers will have negligible attenuation when bent and will not be sensitive to the focal length of the coupling lens (omnidirectional).
The study of output laser beam shape as a function of losses, internal diameter, off-center coupling and scattering is presented in this paper. The conditions where the beam shape has good correlation with the source beam shape were found (low losses, center alignment coupling and low scattering). A theoretical model of the mechanism of propagation of the radiation through the hollow waveguides was developed and the conditions under which the shape of beam is changed was calculated. Good agreement between the theoretical and experimental results was found.
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