Development of lung tissue phantoms for bioluminescent imaging

White nylon material was chosen to make cylindrical tissue phantoms for development of bioluminescence tomography techniques. A low-level light source, delivered through an optic fiber of core diameter 200 μm, was placed at different locations on one phantom surface. The light travels through the phantom, reaches the external surface, and is captured by a liquid nitrogen-cooled CCD camera. The scattering, absorption, and anisotropy parameters of the phantom are obtained by matching the measured light transmission profiles to the profiles generated by the TracePro software. The perturbation analysis, with the homogeneous phantoms, demonstrated that the imaging system is sufficiently sensitive to capture intensity change of higher than 0.5nW/cm2 or a location shift of the light source of more than 200 microns. It is observed that the system can distinguish two point light sources with separation of about 2 mm. The perturbation analysis is also performed with the heterogeneous phantom. Based on our data, we conclude that there is inherent tomographic information in bioluminescent measures taken on the external surface of the mouse, which suggests the feasibility of bioluminescence tomography for biomedical research using the small animals, especially the mice

Biochemical-physical mechanisms of light-tissue interactions.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.Optical tissue phantom samples simulating the optical properties of the human prostates and brain tissues were fabricated. The experimental set-up was designed to be cost-effective but reliable, allowing for convenience in its usage and replication, making it ideal for biomedical optical measurements. Gel agar was the base material, and aluminum oxide (Al 2 O3 ) with black ink was employed as the scatter and absorber, respectively. The latter were mixed in various amounts into the gel agar to simulate the desired phantom tissues. Argon red laser and He-Ne green laser light, with wavelengths of 630 nm and 532 nm were incident on varying thicknesses of the phantom samples. The transmitted and incident light powers were measured to determine the scattering and absorption coefficients, from which the attenuation coefficients, penetration depth, and optical albedo were estimated. The optical penetration depths were found to be 0.30 for brain and 0.15 for prostate tissue phantoms. The fabricated tissues successfully mimicked the brain and prostate tissues, with µ a = 0.69 cm−1and µ a = 0.24 cm−1 absorption coefficients as well as = 1.73 cm−1 and µ s = 5.48 cm−1 scattering coefficients at 532 nm and 630 nm wavelengths, respectively. The optical albedo for brain phantom was found to be a = 0.71 and a = 0.96 for prostate phantom tissue. The results verify the reliability of the experimental technique and suitability of the fabricated tissues for use in biomedical, going forward, thus allowing for future work without the need for experimentally complex and expensive setups

Criteria for the design of tissue-mimicking phantoms for the standardization of biophotonic instrumentation

A lack of accepted standards and standardized phantoms suitable for the technical validation of biophotonic instrumentation hinders the reliability and reproducibility of its experimental outputs. In this Perspective, we discuss general criteria for the design of tissue-mimicking biophotonic phantoms, and use these criteria and state-of-the-art developments to critically review the literature on phantom materials and on the fabrication of phantoms. By focusing on representative examples of standardization in diffuse optical imaging and spectroscopy, fluorescence-guided surgery and photoacoustic imaging, we identify unmet needs in the development of phantoms and a set of criteria (leveraging characterization, collaboration, communication and commitment) for the standardization of biophotonic instrumentation

Investigating the effect detector geometry has on heterodyne to non-heterodyne signal ratio (HNHR) in a low-coherence tissue imaging interferometer

A Monte Carlo simulation is used to simulate the emergent light distribution from a turbid media sample placed in the probe beam arm of a scanning low-coherence interferometer that is used to build-up voxelated images in three-dimensions. The sample is a simple three-layered model with an embedded cylinder which simulates the physical and optical properties of skin for near-infrared light passing through the sample. Coherent light from an input probe beam of variable profile and incidence angle is traced through the sample by means of ray-tracing, and any emergent beams are collected in a sample surface array which also logs any emergent Monte Carlo generated photons reaching the surface. At the surface, the heterodyne to nonheterodyne signal ratio (HNHR) measured by a user-defined variable geometry detector is calculated for each point upon a linear scan of the detector position across the sample surface. A coherence gate is set to image a voxel located at the uppermost point of the blood vessel-simulating cylinder. Monte Carlo simulations are performed for various input probe beam angles and probe beam profiles, and the HNHR analysed for various detector geometries by varying: the detector area, central detector axis angle and the acceptance angle at the detector. The Monte Carlo results confirm the benefit of confocal detection, and indicate that angular decoupling of the light delivery and detection systems can improve differential HNHR measurements at scan extremities by 25 to 30 dB provided that stratum comeum is either removed or the sample index matched to the imaging system. Also presented is the description of a prototype experimental low-coherence interferometer system and some of the results derived from it: at its best this system was able to measure reflected coherent signals with a dynamic range approximating 130 dB

Development of lung tissue phantoms for bioluminescent imaging

White nylon material was chosen to make cylindrical tissue phantoms for development of bioluminescence tomography techniques. A low-level light source, delivered through an optic fiber of core diameter 200 μm, was placed at different locations on one phantom surface. The light travels through the phantom, reaches the external surface, and is captured by a liquid nitrogen-cooled CCD camera. The scattering, absorption, and anisotropy parameters of the phantom are obtained by matching the measured light transmission profiles to the profiles generated by the TracePro software. The perturbation analysis, with the homogeneous phantoms, demonstrated that the imaging system is sufficiently sensitive to capture intensity change of higher than 0.5nW/cm2 or a location shift of the light source of more than 200 microns. It is observed that the system can distinguish two point light sources with separation of about 2 mm. The perturbation analysis is also performed with the heterogeneous phantom. Based on our data, we conclude that there is inherent tomographic information in bioluminescent measures taken on the external surface of the mouse, which suggests the feasibility of bioluminescence tomography for biomedical research using the small animals, especially the mice

Two dimensional angular domain optical imaging in biological tissues

Optical imaging is a modality that can detect optical contrast within a biological sample that is not detectable with other conventional imaging techniques. Optical trans-illumination images of tissue samples are degraded by optical scatter. Angular Domain Imaging (ADI) is an optical imaging technique that filters scattered photons based on the trajectory of the photons. Previous angular filters were limited to one dimensional arrays, greatly limiting the imaging capability of the system. We have developed a 2D Angular Filter Array (AFA) that is capable of acquiring two dimensional projection images of a sample. The AFA was constructed using rapid prototyping techniques. The contrast and the resolution of the AFA was evaluated. The results suggest that a 2D AFA can be used to acquire two dimensional projection images of a sample with a reduced acquisition time compared to a scanning 1D AFA

Cyclic Correlation of Diffuse Reflected Signal with Glucose Concentration and scatterer size

The utility of optical coherence tomography signal intensity for measurement of glucose concentration has been analysed in tissue phantom and blood samples from human subjects. The diffusion equation based calculations as well as in-vivo OCT signal measurements confirms the cyclic correlation of signal intensity with glucose concentration and scatterer size.Comment: Four figures, Five page

The design, calibration and usage of a solid scattering and absorbing phantom for near infra red spectroscopy.

Following a review of methods for measuring the optical properties of tissue, the majority of this thesis is concerned with the design, construction, calibration and use of a solid, tissue equivalent phantom. The phantom material is a clear polyester plastic. This is obtained in unpolymerised form, scattering particles and absorbing dyes are added to it, and it is then polymerised to form a stable solid. Purely scattering and absorbing phantoms were made separately, and their optical properties were measured using a specially built system. This has a co-linear collimated light source and detector, and measures the unscattered light transmitted through a sample as a function of its thickness. Other methods of measuring the optical coefficients of tissue were tested with this phantom. One of these uses integrating spheres to measure the transmitted and reflected light from a sample. A model of light transport (in this case a Monte Carlo model) is used to convert these measurements into scattering and absorption coefficients. It was found that the measurement of scattering coefficient was reasonably accurate, but that the absorption coefficient was overestimated at the low values typical of tissue. A measurement of the optical properties of bone was made with this system. The other system investigated uses the diffusion theory to calculate optical properties from measurements made through a thick slab. The material was also employed to create a test phantom for near infrared spectroscopy machines. This provides a diffusing medium with an attenuation that is variable in discrete steps over three orders of magnitude. The relative attenuation between steps is totally wavelength independent. This phantom was adopted by the EC concerted action on near infrared spectroscopy and imaging. Finally, the phantom was used to create test objects with which to investigate the potential of imaging with infrared light

Thermally induced changes in optical properties of biological tissues

This thesis describes an optical phenomenon which may occur when biological tissues are irradiated with therapeutic laser light at powers above the thermal denaturation threshold. The scattering coefficient of most tissues changes with thermal denaturation. This may alter both the light distributions within and the light distributions emerging from the tissue during the therapy. The former effect may require a non-linear description of the thermal interaction whereas the latter may offer the opportunity to observe the progress of the therapy. The clinical uses of lasers in medical therapy and diagnosis are reviewed in the first chapter and physical background information on light and heat transport in tissues are presented. Existing reports on changes in optical coefficients with temperature are collected and discussed in the second chapter. In the third chapter the mechanisms involved in the thermal damage to tissues are examined by means of transmission electron microscopy, experimental measurements of the denaturation kinetics of tissue and a theoretical modelling of cell survival. In the fourth Chapter, a stochastic model for the calculation of light distributions in tissues is described and validated against analytical solutions. Subsequently, it is used to study the effect of different combinations of absorption and scattering coefficient on the light distributions within and emerging from the tissue. Experimentally determined values of absorption coefficient, scattering coefficient and single scattering phase function of rat liver, human aorta and human prostate are presented in the fifth chapter. The optical coefficients were measured both on native and thermally damaged tissues. The final chapter suggests a model for the calculation of temperature distributions in tissues during pulsed laser irradiation. This model relies on the light distributions given by the stochastic model and uses a finite element approximation to the heat diffusion equation. Examples of changes in temperature distributions with changes in optical coefficients are presented

Elliptically polarized light for depth resolved diffuse reflectance imaging in biological tissues

Cotutela Universitat Politècnica de Catalunya i Institut Fresnel, Aix-Marseille UniversitéPolarization gating imaging is a popular and widely used imaging technique in biomedical optics to sense tissues, deeper volumes, and also selectively probe sub-superficial volumes. Due to the "polarization memory" effect of polarized light, elliptical polarization-gating allows access to tissue layers between those of accessible by linear or circular polarizations. As opposed to the conventional linearly polarized illumination, we focus on polarization gating methods that combine the use of elliptically polarized light to select polarization maintaining photons and eliminate the background while providing superior contrast and depth information. With gating, it has also become possible to access user-defined depths (dependent on optical properties) in biological tissues with the use of images at different ellipticities. Furthermore, this investigation allowed the application of polarization gating in spectroscopy to selectively quantify the concentration of tissue chromophores at userdesired depths. Polarization gating methods have been validated and demonstrated with in vivo experiments on abnormalities of human skin (nevus, burn scar) and also on the exposed cortex of an anaesthetized rat. Finally, as a first step towards the use of coherent illumination, adding the concept of polarimetry to laser-speckle imaging was demonstrated. Preliminary tests on phantoms (solid and liquid) suggested evidence of the influence of polarization ellipticity on the formation and behaviour of speckles, which could pave the way for more insight in the study of blood flow in tissues.L’imagerie de filtrage en polarisation est une technique populaire largement utilisée en optique pour le biomédical pour le sondage des tissus superficiels, pour le sondage de volumes plus profonds, mais aussi pour l’examen sélectif de volumes sub-surfaciques. Du fait de l’effet de ’mémoire de polarisation’ de la lumière polarisée, l’imagerie de filtrage en polarisation elliptique est sensible à des épaisseurs de tissus différentes, depuis la surface, accessible avec la polarisation linéaire, jusqu’à une épaisseur critique accessible par la polarisation circulaire. Nous nous concentrons sur des méthodes utilisant des combinaisons de polarisations elliptiques afin de sélectionner la portion de lumi ère ayant maintenu son état de polarisation et éliminer le fond pour un meilleur contraste avec, de plus, une information sur la profondeur. Avec ce type de filtrage, il est possible d’accéder à des profondeurs de tissus biologiques bien définies (selon ses propriétés optiques) selon l’ellipticité de polarisation. De plus, ces travaux ont permis d’étendre la méthode à la spectroscopie pour quantifier sélectivement la concentration en chromophores à une profondeur spécifique. Les méthodes développées ont été validées in vivo à l’aide d’expériences réalisées sur des anomalies de la peau (grain de beauté, cicatrice de brûlure) et aussi sur le cortex exposé d’un rat anesthésié. Enfin, une étude préliminaire a été réalisée pour examiner la possibilité d’étendre la méthode à l’imagerie de tavelures (speckle). Des tests Préliminaires réalisés sur fantômes (solides et liquides) montrent l’influence de l’ellipticité de polarisation sur la formation et le comportement du speckle, ce qui offre la possibilité d’accéder à des informations sur le flux sanguin à des profondeurs spécifiques dans les tissus."Polarization gating imaging" es una técnica de imagen muy popular y ampliamente empleada en óptica biomédica con el fin de caracterizar tejidos y sondear volúmenes subsuperficiales de manera selectiva incluso a regiones profundas. Debido al efecto conocido como memoria de polarización de la luz polarizada, la técnica de "polarization gating" elíptica permite el acceso a capas de tejido que, de otro modo, no son accesibles mediante polarización lineal y circular. En contra de la iluminación linealmente polarizada convencional, nuestro estudio se centra en los métodos de "polarization gating" en combinación con luz elípticamente polarizada. Esto permite discriminar aquellos fotones que mantienen una polarización concreta, eliminando así el fondo al mismo tiempo que proporciona un mayor contraste y profundidad de campo, incrementando notablemente la información extraída. Gracias a esta técnica es posible el acceso a distintas profundidades en tejidos biológicos definidas por el usuario (dependiendo de las propiedades ópticas) mediante el empleo de imágenes a distinta elipticidad. Es más, este estudio ha permitido la aplicación del método "polarization gating" a la espectroscopia con el fin de cuantificar la concentración de ciertos cromóforos presentes en tejidos biológicos de manera selectiva y a distintas profundidades deseadas. Los métodos de "polarization gating" han sido validados, establecidos y demostrados en experimentos in-vivo sobre anomalías en tejidos epiteliales humanos (nervios, cicatrices por quemadura) y también en el córtex expuesto de una rata anestesiada. Finalmente, como primer paso en el uso de iluminación coherente, se ha añadido y demostrado el concepto de polarimetría a la técnica de speckle imaging por láser. Los test preliminares en "phantoms" (tanto en sólido como en líquido) arrojan indicios sobre una influencia de la polarización elíptica en la formación y comportamiento de la distribución de las motas (speckle), lo cual podría abrir nuevas puertas y dar un nuevo enfoque sobre la comprensión de la circulación de la sangre en los tejidos.Postprint (published version