Fluorescence tomography (FT) is an emerging non-invasive in vivo molecular imaging modality that aims at quantification and three-dimensional (3D) localization of fluorescent tagged inclusions, such as cancer lesions and drug molecules, buried deep in human and animal subjects. Depth-resolved 3D reconstruction of fluorescent inclusions distributed over the volume of optically turbid biological tissue using the diffuse fluorescent photons detected on the skin poses a highly ill-conditioned problem, as depth information must be extracted from boundary data. Due to this ill-posed nature of FT reconstructions, noise and errors in the data can severely impair the accuracy of the 3D reconstructions. Consequently, improvements in the signal-to-noise ratio (SNR) of the data significantly enhance the quality of the FT reconstructions. Furthermore, enhancing the SNR of the FT data can greatly contribute to the speed of FT scans. The pivotal factor in the SNR of the FT data is the power of the radiation illuminating the subject and exciting the administered fluorescent agents. In existing single-point illumination FT systems, the illumination power level is limited by the skin maximum radiation exposure levels. In this research, a multiplexed architecture governed by the Hadamard transform was conceptualized, developed, and experimentally implemented for orders-of-magnitude enhancement of the SNR and the robustness of FT reconstructions. The multiplexed FT system allows for Hadamard-coded multi-point illumination of the subject while maintaining the maximal information content of the FT data. The significant improvements offered by the multiplexed FT system were validated by numerical and experimental studies carried out using a custom-built multiplexed FT system developed exclusively in this work. The studies indicate that Hadamard multiplexing offers significantly enhanced robustness in reconstructing deep fluorescent inclusions from low-SNR FT data.

This thesis reports on research undertaken in the area of microwave tomography (MWT) where the goal is to find the dielectric profile of an object of interest using microwave measurements collected outside the object. The main focus of this research is on the development of inversion algorithms which solve the electromagnetic inverse scattering problem associated with MWT. Various regularization techniques for the Gauss-Newton inversion algorithm are studied and classified. It is shown that these regularization techniques can be viewed from within a single consistent framework after applying some modifications. Within the framework of the two-dimensional MWT problem, the inversion of transverse magnetic and transverse electric data sets are considered and compared in terms of computational complexity, image quality and convergence rate. A new solution to the contrast source inversion formulation of the microwave tomography problem for the case where the MWT chamber consists of a circular conductive enclosure is introduced. This solution is based on expressing the unknowns of the problem as truncated eigenfunction expansions corresponding to the Helmholtz operator for a homogeneous background medium with appropriate boundary conditions imposed at the chamber walls. The MWT problem is also formulated for MWT chambers made of conducting cylinders of arbitrary shapes. It is shown that collecting microwave scattered-field data inside MWT setups with different boundary conditions can provide a robust set of useful information for the reconstruction of the dielectric profile. This leads to a novel MWT setup wherein a rotatable conductive triangular enclosure is used to generate scattered-field data. Antenna arrays, with as few as only four elements, that are fixed with respect to the object of interest can provide sufficient data to give good reconstructions, if the triangular enclosure is rotated a sufficient number of times. Preliminary results of using the algorithms presented herein on data collected using two different MWT prototypes currently under development at the University of Manitoba are reported. Using the open-region MWT prototype, a resolution study using the Gauss-Newton inversion method was performed using various cylindrical targets.

The Westinghouse FRIGG loop in Västerås, Sweden, has been used to study the distribution of steam in the coolant flow of nuclear fuel elements, which is known as the void distribution. For this purpose, electrically heated mock-ups of a quarter BWR fuel bundles in the SVEA-96 geometry were studied by means of gamma tomography in the late 1990s. Several test campaigns were conducted, with good results, but not all the collected data was evaluated at the time. In this work, tomographic raw data of SVEA-96 geometry is evaluated using two different tomographic reconstruction methods, an algebraic (iterative) method and filtered back-projection. Reference objects of known composition (liquid water) are used to quantify the decrease in attenuation arising from the presence of the void, which is used to create a map of the void in the horizontal cross sections of the fuel at various axial locations. The resulting detailed void distributions are averaged over subchannels and the subchannel steam core for comparison with simulations. The focus of this work is on the void distribution at high axial locations in the fuel, in fuel bundles with part-length fuel-rods. Measurements in the region above the part-length rods are compared with simulations and the reliability of each method is discussed. The algebraic method is found to be more reliable than the filtered back-projection method for this setup. A reasonable agreement between measurements and predictions is shown. The void, in both cases, appears to be slightly lower in the corner downstream the part-length rods.

Iceland provides a unique opportunity to study the processes that occur along mid- ocean ridges. In 1991, thirty temporary seismic stations were installed at the Hengill volcanic complex to record high-quality digital data from local earthquakes. From these data 449 earthquakes have been located, most of them beneath the geothermal area. A local earthquake tomographic inversion was carried out to determine the three- dimensional V(_p) and V(_p) /V(_s) structure to 6 km depth, using P-wave travel times and S-P times from local earthquakes recorded in 1981 and 1991. The resulting models are smoothly varying and give a low data variance. The V(_p) model is similar to that of a previous tomographic inversion in the area, although the models differ in detail. The main high-V(_p) features of these models are interpreted as solidified intrusions, and underlie extinct volcanic centres. A low V(_p) /V(_s) body (-4%) is detected from 0 to 3 km depth that correlates with the surface expression of the geothermal field and is probably due to a combination of effects that include a slightly lower pore fluid pressure (and thus a higher steam content), and rock matrix alteration. Well-constrained moment tensors were determined for 70 local earthquakes by inverting the polarities and amplitude ratios of P and S arrivals. This method works well and is relatively insensitive to wave-speed model and attenuation variations. Most of the earthquakes are non-double-couple with explosive volumetric components. Only 17 (28%) of the earthquakes are consistent with a double-couple model. The remaining earthquakes are modelled as a combination of an opening tensile crack and a shear fault. Two geometries are considered: (1) rupture on two separate fault planes aligned at 45º, and (2) opening-shear rupture on a single fault plane, which is equivalent to coplanar tensile and shear faults. Both models can give the same moment tensors, and the data cannot distinguish between them. They give a good fit to the data, with few polarity misfits for most of the earthquakes. Right-lateral opening-shear strike-slip faulting on near-vertical planes is consistent with the regional seismicity of the South Iceland Seismic Zone. The non-double-couple earthquakes may result from the regional stress regime interacting with the geothermal field.

Stem cell therapy is emerging as a possible method for treating many diseases and disorders, such as cardiovascular disease. In particular, stem cells may be able to revive the dead tissue caused by acute myocardial infarction (heart attack). Adipose-derived stem cells were labelled with 18F-fluorodeoxyglucose (FDG) and superparamagnetic iron oxide (SPIO) particles, for imaging with positron emission tomography (PET) and magnetic resonance imaging (MRI), respectively, and injected into several rats following induced myocardial infarction. Stem cell retention in the heart was investigated following three injection sites; two within the heart (intramyocardial and left intraventricular), and one easily accessible vein (tail vein). The PET and MR images were registered and the initial distributions analyzed using region of interest (ROI) analysis, to determine which injection method would result in the highest stem cell retention in the infarcted heart. The ROI results determined that the intramyocardial injection had the highest % injected dose (%ID) in the heart with 14 +/- 4%, followed by left intraventricular and tail vein with %IDs of 3.6 +/- 0.8% and 1.2 +/- 0.6%, respectively. The results indicate that stem cell delivery via intramyocardial injection should be utilized for optimal retention in the heart.

Electrical impedance tomography is an imaging method with applications to geophysics and medical imaging. A new approximation is presented based on Nachman's 2-dimensional construction for closed domains. It improves upon existing approximations by extending the range of application from resolving 2 times the surface conductivity to imaging perfect conductors and insulators. With perfect knowledge of boundary data, this approximation exactly resolves a single conductive disc embedded in a homogenous domain. The problem, however, is ill-posed, and imaging performance degrades quickly as the distance from the boundary increases. The key to the approximation lies in (a) approximating Fadeev's Green's function (b) pre-processing measured voltages based on a boundary-integral equation (c) solving a linearized inverse problem (d) solving a d-bar equation, and (e) scaling the resulting image based on analytical results for a disc. In the development of the approximation, a new formula for Fadeev's Green's function is presented in terms of the Exponential Integral function. Also, new comparisons are made between reconstructions with and without solving the d-bar equation, showing that the added computational expense of solving the d-bar equation is not justified for radial problems. There is no discernible improvement in image quality. As a result, the approximation converts the inverse conductivity problem into a novel one-step linear problem with pre-conditioning of boundary data and scaling of the resulting image. Several extensions to this work are possible. The approximation is implemented for a circular domain with unit conductivity near the boundary, and extensions to other domains, bounded and unbounded should be possible, with non-constant conductivity near the boundary requiring further approximation. Ultimately, further research is required to ascertain whether it is possible to extend these techniques to imaging problems in three dimensions.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 99 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references.

Thesis (Ph.D.)--Tufts University, 2003. / Adviser: David A. Boas. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references (leaves 215-220). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.)--Tufts University, 2004. / Adviser: David A. Boas. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references (leaves 407-416). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 5 uppsatser.