<p> The rapid development of the use of lasers in therapeutic and diagnostic medicine in the past few years has generated interest in measuring the optical properties of tissue. In particular, the development of photodynamic therapy (PDT) has necessitated studies of the optical properties of tissue at wavelengths around 630nm, this being the wavelength at which the photosensitizer commonly used in PDT, namely dihematoporphyrin ether (DHE), is normally activated.</p> <p> The control of the volume of tissue from which information about the interaction coefficients of the tissue is obtained is an important problem in diffuse reflectance spectroscopy and other applications of light, because it is critical to understanding which tissue volumes are sampled by the injected photons that eventually are re-emitted. This report describes a simple model that predicts the parameters that control the volume of tissue interrogated by photons during reflectance spectroscopy.</p> <p> In optical fiber based diffuse reflectance spectroscopy, incident radiation is applied at one point on a tissue surface and collected at another point, a radial distance, r, away. Information about the light multiply scattered by the tissue is used to deduce optical scattering and absorption coefficients of the tissue. In this report both steady state and pulse techniques are studied. In the steady state method, the spatial dependence of the backscattered light is the measured quantity, while the pulse technique uses the temporal broadening of a picosecond (ps) pulse to determine the interaction coefficients.</p> <p> The relative contribution of a volume element of tissue to the observed signal depends on its location, the measurement geometry and the optical properties of the tissue. Knowledge of this dependence would allow some control of the volume interrogated by reflectance spectroscopy, and would provide insight into the influence of inhomogeneities.</p> <p> In the work reported here a simple diffusion model of light propagation in tissue based on the Boltzmann radiative transfer equation has been used to derive mathematical expressions for the relative time spent by photons in a given tissue volume element. Using optical interaction coefficients typical of mammalian soft tissues, results are presented for both steady state and pulse irradiation in both semi-infinite and infinite media.</p> <p> The residency time depth profile calculated by this model for index matched and zero fluence boundary conditions has the same shape as that predicted by Weiss (1989), who used a somewhat different model based on a 3-dimensional random walk theory. These profiles are characterized by a build-up region near the surface and exponential fall far away from the surface in the 'diffusion region'. The influence of the absorption coefficient μa and the fiber separation on the residency time as predicted by this model is in good agreement to that predicted by the random-walk theory (i.e the depth-profile of the residency time tends to sharpen as the absorption coefficient increases. This is attributed to the fact that long trajectories are less likely with large absorption probabilities. As well, the greater the fiber separation, the wider and flatter the depth distribution of the residency time. This is because photons that reach the surface at greater r values have, in general, migrated farther from the immediate vicinity of the source and detector and hence have sampled a larger volume of tissue). All the integrations in this report were performed numerically using the IMSL/LIB on the Microvax computer system in the Hamilton Regional Cancer Center. The adequacy of this numerical integration was tested and was found to be good.</p> <p> This model therefore suggests that during diffuse reflectance spectroscopy, the volume sampled by re-emitted photons can be controlled by changing parameters such as the fiber separation (in both steady state and time-resolved techniques) and the detection time (in the time-resolved method).</p> / Thesis / Master of Science (MSc)

This thesis analyzes the reflectance behavior of textiles in the short-wave infrared (SWIR) band (1 – 2 microns) in order to identify/design potential diagnostic tools that allow the remote detection of human presence in a scene. Analyzing the spectral response of fabrics in the SWIR band has gained significant interest in the remote sensing community since it provides a potential path to discriminate camouflaged clothing from backgrounds that appear similar to the object of interest in the visible band. Existing research, originating primarily from the textiles community, has thoroughly documented the behavior of clothing fabrics in the visible band. Other work has shown that the differences in spectral response in the SWIR band allows for discrimination of materials that otherwise have the same visible spectral response. This work expands on those efforts in order to quantify the reflectance behavior and to better understand the physical basis for that behavior.

<p>Variations in hemoglobin concentration can be indicative of a number of serious complications, including blood loss and anemia. Rapid, noninvasive measurements of hemoglobin are important in applications where blood status is reflective of patient well-being, such as in the emergency room, operating room, or the battlefield. Probe-based diffuse reflectance spectroscopy is capable of noninvasively quantifying tissue optical properties, including hemoglobin concentration. The quantification of hemoglobin concentration using optical methods is complicated by tissue scattering and the robustness of the algorithm and instrumentation used to interrogate the tissue. The sensing depth of diffuse reflectance spectroscopy can be tailored by the wavelengths of light and probe design used.</p><p>In this thesis, the accuracy and clinical viability of different diffuse reflectance spectroscopy implementations are presented. The robustness of an inverse Monte Carlo model, in which tissue optical properties are determined from measured reflectance using ultraviolet-visible (UV-VIS) wavelengths and a steady-state instrument, was tested using laboratory measurements. From the laboratory measurements, a set of references was identified which provided accurate absorption and scattering measurements, independent of the optical properties of the target. In addition, the ability to quantify hemoglobin concentration and saturation over large ranges and concentrations of multiple absorbers was established. </p><p>Following the laboratory measurements, a clinical study in which UV-VIS spectra were measured from the sublingual mucosa of patients undergoing surgeries was carried out. From this study, the correlations of extracted hemoglobin to expected blood hemoglobin were found to be improved when a simple ratiometric method based on isosbestic wavelengths of hemoglobin was used. During this study, the probe positioning in the mouth was found to be unwieldy, and so the transition to a more secure probe that could be taped to the hand was made. </p><p>In order to penetrate the overlying skin, near-infrared (NIR) wavelengths with a different probe geometry was explored. Further investigation of the inverse Monte Carlo model with NIR wavelengths was executed, and while in theory this combination should yield accurate optical property estimation, laboratory measurements indicated large errors, presumably due to the instrument or low magnitude and reduced spectral features of hemoglobin absorption in the NIR. Instead, the use of a well-established frequency-domain instrument coupled with diffusion approximation was implemented to measure spectra from the thenar eminence of volunteers undergoing induced hypovolemia and subsequent retransfusion. There were some moderate correlations with blood hemoglobin, but because both this method and the Monte Carlo method with mucosal probe placement showed higher variability with probe pressure than the isosbestic ratiometric method, further development of the ratiometric method was made. </p><p>The ratiometric method was developed using simulations and validated with phantoms and clinical data. Monte Carlo modeled reflectance was generated for a large range of biologically-relevant absorption and scattering values. The modeled reflectance was scaled by a calibration spectra obtained from a single laboratory phantom measurement so that linear regression equations relating hemoglobin concentration to ratios could be applied directly to clinical or laboratory measurements. Ratios which could best estimate hemoglobin concentration independent of saturation and scattering were determined through the simulation and laboratory measurements. Three isosbestic ratios - 545/390, 452/390, and 529/390 nm - were determined to best estimate hemoglobin concentration, and ratiometric-extracted hemoglobin was shown to correlate well to Monte Carlo-extracted hemoglobin in clinical measurements. Because only a single calibration measurement (which can be measured on a different day) is required per instrument and probe combination, this method can be implemented in near real-time and is thus appropriate for applications where hemoglobin concentration must be measured rapidly.</p> / Dissertation

This dissertation focuses on the development of computational models and algorithms related to diffuse reflectance spectroscopy. Specifically, this work aims to advance diffuse reflectance spectroscopy to a technique that is capable of measuring depth dependent properties in tissue. First, we introduce the Monte Carlo lookup table (MCLUT) method for extracting optical properties from diffuse reflectance spectra. Next, we extend this method to a two-layer tissue geometry so that it can extract depth dependent properties in tissue. We then develop a computational model that relates photon sampling depth to optical properties and probe geometry. This model can be used to aid in design of application specific diffuse reflectance probes. In order to provide justification for using a two-layer model for extracting tissue properties, we show that the use of a one-layer model can lead to significant errors in the extracted optical properties. Lastly, we use our two-layer MCLUT model and a probe that was designed based on our sampling depth model to extract tissue properties from the skin of 80 subjects at 5 anatomical locations. The results agree with previously published values for skin properties and show that can diffuse reflectance spectroscopy can be used to measured depth dependent properties in tissue. / text

Made available in DSpace on 2014-06-11T19:29:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-31Bitstream added on 2014-06-13T20:18:54Z : No. of bitstreams: 1 gigante_ac_me_araiq.pdf: 810984 bytes, checksum: d628a07a7c532c812f60d96301f7afff (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho propõe o desenvolvimento de um método limpo para determinação de ureia em amostras comerciais de fertilizantes utilizando a Espectroscopia de Reflectância Difusa combinada com spot test. O método desenvolvido é baseado na reação entre a ureia e o reagente cromogênico p-dimetilaminocinamaldeído (p-DAC) em meio de ácido clorídrico diluído, que resulta em um produto de coloração rósea cujo valor máximo de reflectância ocorre no comprimento de onda de 535 nm. Os parâmetros experimentais foram otimizados através dos planejamentos fatorial e composto central para a obtenção da superfície de resposta, os quais indicaram uma maior sensibilidade para o método quando se utiliza o reagente p-DAC na concentração de 0,196% (m/v) em meio de ácido clorídrico de concentração 0,0549 mol L-1, empregando etanol como solvente para as soluções. O suporte sólido para a reação é um papel de filtro qualitativo onde são colocados 20,0μL de solução de ureia seguidos de secagem com ar frio de um secador de cabelos e 20,0μL de solução de reagente p-DAC 0,196% (m/v) em meio de HCl 0,0549 mol L-1 e secagem ao ar livre, submetendo-se então o spot à leitura reflectométrica em máx. = 535 nm. Uma relação linear (R = 0,996) foi estabelecida na faixa de concentração de ureia compreendida entre 50,0 – 300 mg L-1. Os limites de detecção e de quantificação foram determinados em 5,13 mg L-1 e 17,10 mg L-1, respectivamente. O método limpo desenvolvido foi aplicado na determinação de ureia em amostras comerciais de fertilizantes onde demonstrou apresentar ótima precisão e exatidão, evidenciadas pela boa recuperação (94,2 – 107,4%), além de oferecer vantagens como simplicidade de execução e baixo consumo de reagentes, geração de mínima quantidade de resíduos, rapidez e segurança... / This work proposes the development of a clean method for determination of urea in commercial samples of fertilizers using the Diffuse Reflectance Spectroscopy combined with spot test. The method is based on the reaction between urea and the chromogenic reagent p-dimethylaminocinnamaldehyde (p-DAC) in diluted hydrochloric acid medium, which results in a pink colored product whose maximum value of reflectance occurs at a wavelength of 535 nm. The experimental parameters were optimized through a factorial and a central composite experimental design to obtain the response surface, which indicated a higher sensitivity for the method when using the reagent p-DAC in the concentration of 0.196% (w/v) in a hydrochloric acid 0.0549 mol L-1 medium, using ethanol as a solvent for the solutions. The solid support for the reaction is a qualitative filter paper where they are placed 20.0μL of urea solution followed by drying with cold air from a hair dryer and 20.0μL of reagent solution p-DAC 0.196% (w/v) in the HCl 0.0549 mol L-1 medium and drying in the air, then submitting the spot to the reflectometric reading at max = 535 nm. A linear relationship (R = 0.996) was established in the range of urea concentration between 50.0 to 300 mg L-1. The limits of detection and quantification were determined at 5.13 mg L-1 and 17.10 mg L-1, respectively. The method was applied to the clean determination of urea in commercial samples of fertilizers, which has shown to present great precision and accuracy as evidenced by the good recovery (94.2 to 107.4%) and also offers advantages such as simplicity of implementation and low consumption of reagents, generation of minimum quantity of wastes, rapidity and security, producing reliable results. As shown, the method is designed as environmentally friendly for determination of urea, as it is consistent with the Principles advocated by the Green Chemistry.

No description available.

Complete resection is correlated to better patient outcome in aggressive cancers such as glioblastoma. Optical biopsy refers to a family of techniques utilizing optical properties of living targets to make diagnoses where a biopsy would conventionally be used. Such a technology can potentially guide neurosurgeons in removing glioblastomas. Diffuse reflectance (DR) and Time-resolved fluorescence (TRF) have previously been investigated for their ability to measure biomarkers indicative of cancer. One of the difficulties faced in using TRF as a diagnostic tool is that multiple endogenous fluorophores will simultaneously contribute to the signal. This makes it difficult to attribute fluorescence lifetimes or spectral changes to one type of molecule in the tissue. This thesis focuses on the challenge of separating the components in a TRF measurement and their fractional contributions. A DR-TRF instrument was designed and built and characterized using fluorescent dyes. An orthonormal basis deconvolution method combined with a Fourier-domain method were tested for their ability to unmix fluorescent components in a hyperspectral TRF measurement. This method was tested on dye mixtures and retrieved fluorescence lifetimes of 4.6±0.4 ns and 2.7±0.2 ns in a mixture of Fluorescein and Coumarin-6 at concentrations of 5 μM each. It was also tested on an ex-vivo brain tissue where the fluorescence was approximated as a sum of 2 components. / Thesis / Master of Applied Science (MASc)

Tissue optical clearing aims to increase the penetration depth of near-collimated light in biological tissue to enhance optical diagnostic, therapeutic, and cosmetic procedures. Previous studies have shown the effects of chemical optical clearing on tissue optical properties. Drawbacks associated with chemical clearing include the introduction of potentially toxic exogenous chemicals into the tissue, poor site targeting, as well as slow transport of the chemicals through tissue. Thus, alternative clearing methods have been investigated. Mechanical compression is one such alternative tissue optical clearing technique. The mechanisms of action of mechanical compression may be similar to those of chemical clearing, though they have yet to be investigated systematically. This research describes the design and execution of a number of procedures useful for the quantification of the tissue optical clearing effects of localized mechanical compression. The first experimental chapter presents the effects of compression on image resolution and contrast of a target imaged through ex vivo biological tissue. It was found that mechanical optical clearing allowed recovery of smaller targets at higher contrast sensitivity when compared to chemical clearing. Also, thickness-independent tissue clearing effects were observed. In the second experimental chapter, dynamic changes in tissue optical properties, namely scattering and absorption coefficients (?s' and ?a, respectively) were monitored during a controlled compression protocol using different indentation geometries. A reduction in ?s' and ?a was evident for all indentation geometries, with greater changes occurring with smaller surface area. Results indicate that localized mechanical compression may be harnessed as a minimally-invasive tissue optical clearing technique. / Master of Science

Radio frequency (RF) lesioning and deep brain stimulation (DBS) are the two prevailing surgical treatments for movement disorders within the field of stereotactic and functional neurosurgery. For RF-lesioning, a small volume of brain tissue is coagulated and knowledge of the lesion size and growth is of great importance for the safety and outcome of the procedure. This thesis deals with adapting the laser Doppler perfusion monitoring (LDPM) technique for measurements in brain tissue during RF-lesioning. The relation between LDPM signal changes and developed lesion size was investigated. LDPM measurements were evaluated both in vitro (albumin protein solution) and in vivo in the porcine brain during RF-lesioning corresponding to a bilateral thalamotomy in man. The investigated signals from the LDPI measurements can be used for following the lesioning time course and to detect if a lesion was created, both in vitro and in the animal model. For the albumin model, both the total backscattered light intensity and the perfusion signal can be used as markers for estimating the final coagulation size, while in the animal model this conclusion was not statistical verified. Independent on surgical method, RF-lesioning or DBS, intracerebral guidance is an important aspect within stereotactic and functional neurosurgery. To increase the accuracy and precision of reaching the correct target, different methods for intracerebral guidance exist, such as microelectrode recording and impedance methods. In this thesis, the possibility of developing an optical intracerebral guidance method has been investigated. Diffuse reflectance spectroscopy served as technology and all measurements were performed stereotactically in both porcine and human brain. Measurements of white and gray matter showed large differences, with higher reflectivity for white brain matter, both in porcine and in human brain. For the human measurements during DBS-implants, large differences between white matter and functional targets were found. Additionally, differences between native and lesioned porcine brain matter were detected. Both studies support the idea of using diffuse reflectance spectroscopy for developing an intracerebral guidance method.

<p>Diffuse reflectance spectroscopy (DRS) is a simple, yet powerful technique that has the potential to offer practical, non-invasive, and cost effective information for op- tical diagnostics and therapeutics guidance. Any progress towards moving DRS systems from their current laboratory settings to clinical settings, field settings and ambitiously to home settings, is a significant contribution to society in terms of reducing ever growing healthcare expenditures of an aging society. Additionally, im- proving on the existing mathematical models used to analyze DRS signals; in terms of speed, robustness, accuracy, and capability in accounting for larger feature space dimensionality (i.e. extraction of more tissue-relevant information) is equally im- portant for real-time diagnosis in the desired settings and to enable use of DRS in as many biomedical applications (e.g. skin cancer diagnosis, diabetics care, tissue oxygenation monitoring) as possible. Improving the reflectance signal complexity and density through novel DRS instrumentation, would facilitate development of the desired models or put the existing ones built on simulations in practical use; which otherwise could not go beyond being a theoretical demonstration.</p><p>DRS studies tissue morphology and composition through quantification of one or more (ideally all of them) of the tissue- and wavelength-specific optical properties: absorption coefficient (μa), reduced scattering coefficient (μ1s), scattering anisotropy (g), tissue thickness, and scattering phase function details (e.g. higher order moments of the scattering phase function). DRS involves sampling of diffusely reflected photons which experience multiple scattering and absorption as they travel within the tissue, at the tissue surface. Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a subset of general DRS technique, which involves sampling of diffuse reflectance signals at multiple distances to an illumination source. SRDRS provides additional spatial information about the photon path; yielding depth-resolved tissue information critical to layered tissue analysis and early cancer diagnostics. Exist- ing SRDRS systems use fiber optic probes, which are limited in accommodation of large number and high-density collection fibers (i.e. yielding more and dense spa- tially resolved diffuse reflectance (SRDR) measurement data) due to difficulty of fiber multiplexing. The circular shape of the fibers restricts the implementable probe ge- ometries and reduces the fill factor for a given source to detector (i.e. collection fiber) separation (SDS); resulting in reduced light collection efficiency. The finite fiber nu- merical aperture (NA) reduces the light collection efficiency well as; and prevents selective interrogation of superficial tissues where most cancers emerge. Addition- ally, SRDR systems using fiber optic probes for photon collection, require one or more photodetectors (i.e. a cooled CCD); which are often expensive components of the systems.</p><p>This thesis deals with development of an innovative silicon SRDRS probe, which partially addresses the challenge of realizing high measurement density, miniaturized, and inexpensive SRDRS systems. The probe is fabricated by conventional, flexible and inexpensive silicon fabrication technology, which demonstrates the feasibility of developing SRDRS probes in any desired geometry and complexity. Although this approach is simple and straightforward, it has been overlooked by the DRS community due to availability of the conventional fiber optic probe technology. This new probe accommodates large number and high density of detectors; and it is in the form of a concentric semi-annular photodiode (PD) array (CMPA) with a central illumination aperture. This is the first multiple source-detector spacing Si SRDRS probe reported to date, and the most densely packed SRDRS probe reported to date for all types of SRDRS systems. The closely spaced and densely packed detectors enable higher density SRDR measurements compared to fiber-based SRDR probes, and the higher PD NA compared to that of fibers results in a higher SNR increasing light collection efficiency. The higher NA of the PDs and the presence of PDs positioned at very short distances from the illumination aperture center enable superficial tissue analysis as well as depth analysis.</p> / Dissertation