Channel impulse responses collected on the Virginia Tech campus show combinations of specular multipath and diffuse scattering at LMDS frequencies. An algorithm is presented that estimates link performance based on the channel impulse response. Presented and analyzed are representative impulse responses (one is primarily specular in nature and one shows significant diffuse scattering) to show that the proposed algorithm is appropriate for analyzing channels exhibiting either of these characteristics. Monte Carlo simulations logged the sequence number of each bit error to gain an understanding of the distribution of errors over time. The results show that for these static channels the errors occur randomly rather than in bursts, leading to the conclusion that average bit-error rate statistics are appropriate for channel characterization. Zero-Forcing (Z-F) and Minimum Mean Square Error (MMSE) equalizers employed on these channels had a significant impact on the link quality. In many cases, the performance of the MMSE equalizer performed only slightly better than the Z-F equalizer. However, when deep nulls were present in the channel response, the MMSE equalizer performed significantly better. Algorithms for determining the number of taps necessary to approach an optimum equalization are presented for both types of equalizers and a '98%' rule of thumb is presented. The algorithm's role in adaptive and cognitive radio systems is discussed and two applications are presented to illustrate its utility. / Ph. D.

Neoadjuvant chemotherapy (NAC) is a common breast cancer treatment that involves administering chemotherapy for 3-6 months prior to surgery. This treatment enables more breast-conserving surgeries and even allows for the omission of surgery in some cases. However, about 31% of patients receiving NAC do not respond to the treatment. Therefore, there is a need for real-time methods to predict treatment response and improve patient outcomes. Over the last two decades, diffuse optical imaging has been investigated as a potential solution to this problem. This noninvasive and inexpensive technology uses near or shortwave infrared (NIR or SWIR) light to illuminate tissue, and detects multiply-scattered photons. However, bulky instrumentation and complicated imaging procedures have limited the clinical adoption of this technology. Furthermore, measured biomarkers including oxy- and deoxy-hemoglobin (HbO2 and HHb, respectively), water, and lipid, have had mixed results in terms of prognostic capability. To address these limitations, a new wearable optical probe technology was developed and validated in this project, including a high-optode density NIR probe for monitoring hemodynamics and a first-generation SWIR probe for quantifying water and lipid. Measurements on tissue-mimicking channel flow phantoms confirmed the ability of the NIR probe to quantify absorption contrast in vitro, and a cuff occlusion measurement demonstrated sensitivity to HbO2 and HHb in vivo. Hemodynamic oscillations at the respiratory rate were also explored in healthy volunteers and breast cancer patients as a potential new biomarker. It was demonstrated that traditional and novel breathing-related hemodynamic metrics provide tumor contrast and can potentially track treatment response. A deep-learning algorithm was developed to extract water and lipid concentrations from multi-distance SWIR measurements. The SWIR probe was validated by comparing measured water and lipid concentrations against ground truth values in emulsion phantoms. This work represents a significant step toward the development of technologies for frequent breast cancer treatment monitoring in the clinic and potentially at home.

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<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)

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

This thesis assessed the readability of CRT displays viewed under ambient lighting conditions and then evaluated the findings with respect to the ISO 9241-7 standard. More specifically, two phases of work were conducted in this thesis. In Phase 1, seven monitors were evaluated photometrically according to the ISO 9241-7 standard to determine whether they were Class I, II, or III in positive and negative polarity. Additionally, six filters were attached to each of the monitors and their ISO Class also was assessed. All monitor/filter combinations yielded either Class I or II in positive polarity and Class II, III or failed in negative polarity. In Phase 2, fourteen participants were asked to read Tinker passages from seven display/filter combinations (tested in Phase 1) under five lighting conditions and two screen polarities. The purpose of the Phase 2 was to determine if people perform differently for Class I, II, or III monitor/filter combinations. The dependent measures were the time to read the Tinker passage (reading time) and the ability to identify the out of context word in each passage (accuracy). An Analysis of Variance was used to determine the significant effects of reading time and accuracy. The ANOVA results indicate that specular glare interferes significantly more with reading time than does diffuse glare. Diffuse (200 lux) and Specular reading times also were correlated against two ISO metrics: screen image luminance ratio (Diffuse, 200 lux) and specular reflection luminance ratio. Reading times did not correlate with the screen image luminance ratio, but they did correlate with one of the ISO specular reflection luminance ratios. The results of this thesis indicate that the ISO standard should not equally weight the screen image and the specular reflection luminance ratios. Additionally, the results indicate that it is not necessary to have separate ISO Classes for positive and negative polarity. Furthermore, people did not read differently for Class I, II, or III monitor/filter combinations. Finally, the data of this investigation provide an initial human factors database for use in assessing the validity of ISO 9241-7. / Master of Science