The number of skin cancer cases reported in the United States is increasing every year and nearly equals the total cancer cases detected from every other part of the body. Current detection strategies of skin cancers include a visual examination followed by a tissue biopsy. This procedure is subjective, invasive and time-consuming. Therefore, considering the number of cancer cases reported and the number biopsies performed, there is a critical need for a non-invasive diagnostic aid to help clinicians reduce the significantly large numbers of unnecessary biopsies. This dissertation presents a quantitative method based on optical spectroscopy for performing a non-invasive ‘optical biopsy’ of melanoma and non-melanoma skin cancers. We have developed the hardware, software and optical algorithms necessary to implement such a device. First, we present a novel lookup table-based model for determining the optical properties of tissue that is valid for fiber-based probe geometries with close source-detector separations and in highly absorbing tissue. These optical properties are quantitative parameters that can be correlated with the physiology of tissue. Second, we present experimental validation of the effects of microvasculature pigment packaging on diffuse reflectance spectra. We have conducted experiments using microfluidic devices over a physiologically relevant range of optical properties and blood vessel sizes. Third, we present the development of a probe-based portable and clinically compatible instrument capable of in vivo spectral measurements. The instrument combines two modalities – diffuse reflectance and intrinsic fluorescence spectroscopy – to provide complementary information regarding tissue morphology, function and biochemical composition. Finally, we present the results of a pilot clinical study using our portable instrument to determine the accuracy of spectral diagnosis of non-melanoma skin cancers. Our results show that the mean optical properties and fluorophore contributions of normal skin and non-melanoma skin cancers are significantly different from each other and can potentially be used as biomarkers for non-invasive diagnosis of skin cancer. / text

<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

<p>Small animal imaging is a valuable tool in preclinical biomedical research which relies on the use of animal models to understand human disease. Newly emerging optical imaging techniques such as bioluminescence tomography offer an inexpensive and sensitive alternative to more established imaging technologies. These techniques are capable of non-invasively imaging a variety of cellular and molecular processes <em>in vivo</em>. As an emerging technology, current bioluminescence imaging methods suffer from several limitations, preventing them from reaching their full potential.</p> <p>In this work, we describe the design and characterization of an integrated imaging system capable of multispectral bioluminescence tomography (BLT), diffuse optical tomography (DOT), and X-ray computed tomography (CT). The system addresses many of the inherent problems encountered in planar bioluminescence imaging techniques, allowing for the recovery of more accurate and quantitative bioluminescence data. The integrated X-ray CT scanner provides anatomical information which aids in the visualization and localization of the recovered bioluminescence distributions and also helps to constrain the inverse reconstruction in the diffuse optical tomography system. It was found that the inclusion of spatial priors from X-ray CT improved the reconstructed image quality dramatically. Four image reconstruction algorithms were evaluated for their ability to recover the effective attenuation coefficients of a series of test phantoms. Two of the algorithms (a modified Levenberg-Marquardt method, and a single-step Tikhonov method) did not use any <em>a priori</em> spatial information. Two other algorithms (hard priors and soft priors) used <em>a priori </em>structural information from X-ray CT to constrain the reconstruction process. The two methods incorporating spatial prior information resulted in recovered optical property distributions with RMS errors ranging from 8 % to 15 % in a series of test phantoms versus errors of 11 % to 26 % for non-spatial methods. The soft priors method was shown to be more resilient to imperfect <em>a priori</em> information.</p> <p>The multispectral BLT component was used to recover accurate bioluminescence distributions in test phantoms using <em>a priori</em> background optical properties recovered from the DOT system. Multispectral measurements were shown to provide an accurate method for estimating the position of a bioluminescence source due to the wavelength dependent attenuation of tissue. Experimental measurements are presented which explore the importance of accurate estimates of background optical properties in BLT. The hard spatial prior method was found to provide the best overall recovery of total source strength, position, and fidelity at all source depths up to 12.5 mm. The total source strength was recovered to within 8 %, while the source position was recovered to within 0.16 mm in all cases. Errors in recovered power and position showed no dependence on depth up to the maximum of 12.5 mm.</p> / Doctor of Philosophy (PhD)

This investigation evaluates the influences of optical property assumptions on nearinfrared diffuse correlation spectroscopy (DCS) flow index measurements. Independent variation is induced in optical properties, absorption coefficient (μa) and reduced scattering coefficient (μs’), of liquid phantoms with concurrent measurements of flow indices. A hybrid instrument is incorporated consisting of a dual-wavelength (785 and 830 nm) DCS flow device to obtain flow indices and a frequency-domain tissue-oximeter for optical properties. Flow indices are calculated with measured μa and μs’ or assumed constant μa and μs’. Inaccurate μs’ assumptions produced much larger flow index errors than inaccurate μa. Underestimated/overestimated μs’ from -35%/+175% lead to flow index errors of +110%/-80% and underestimated/overestimated μa from -40%/+150% lead to -20%/+40%, regardless of wavelength. Analysis of a clinical study involving human head and neck tumors indicates flow index errors due to inter-patient optical property variations up to +280%. Collectively, these findings suggest that studies involving significant μa and μs’ changes should measure flow index and optical properties simultaneously to accurately extract blood flow information. This study provides unique insight through the use of liquid phantoms, hybrid instrumentation, incorporation of measurement errors and a generalization into DCS flow index errors due to the influences of optical properties.

Increased efficacy of light and laser applications in medicine is achieved by accurate light dosimetry. A minimally invasive technique for the determination of the optical coefficients of tissue involves interstitial measurements of the local fluence rate at two or more points in the tissue using isotropic, fibre optic detectors and application of a diffusion model of light propagation. The diffusion models assume simple, homogeneous tissue geometries, possibly oversimplifying the effect of tissue heterogeneities and boundaries. The primary goals of this study were to investigate the influence of realistic finite geometries on the fluence rate distribution and to quantify the systematic errors in the derived optical properties. A Monte Carlo model was developed to predict the fluence rate distribution in any plane of interest in a medium and was verified by comparison with diffusion theory solutions for simple geometries. Fluence rate measurements were made in optically infinite and semi-infinite phantoms for a wide range of optical properties and it was determined that the optical coefficients were derived accurately for phantoms with ueff> 0.2 mm-1 and 2 < ut'<10 mm-1. Measurements were also made in finite spherical volumes with absorbing (Rd = 0.35) and diffuse reflecting (Rd =0.85) boundaries for three optical phantoms and comparisons of the experimental fluence rates with the predictions of the finite volume Monte Carlo model are presented. Boundary effects were observed to be significant within 4 transport mean free paths (mfp') of the boundary. The optical coefficients were derived by applying a diffusion solution for an infinite medium and it was determined that within 2 mfp' of the boundary, the derived ua was overestimated by 40% and underestimated by 20% for the absorbing and reflecting boundaries, respectively. / Thesis / Master of Science (MS)