Development and performance of a sparsity-exploiting algorithm for few-view single photon emission computed tomography (SPECT) reconstruction

<p> Dental implants, otherwise uncompromised, are occasionally found to be date-expired within intact or opened packages, denying their clinical use unless they can be reliably re-sterilized and made equivalent in reaction to new implants within receiving bone sites. This investigation identified an FDA-approved low-temperature gas plasma sterilization approach&mdash;in residual hydrogen peroxide (H2O2) vapor at low pressure&mdash;capable of quickly (within an hour) restoring even grossly contaminated dental implants to sterility and renewing their surface qualities to those of as-manufactured implants with regard to their support for attachment and growth of human alveolar osteoblasts. Pilot studies with flat commercially pure titanium (cpTi) discs used the methods of contact angle measurement, ellipsometry, scanning electron microscopy (SEM), energy-dispersive x-ray analysis (EDS), scanning Auger microscopy, and x-ray photoelectron spectroscopy (XPS) to demonstrate that cpTi surface properties could be optimized for bioadhesion using the H2O2 gas plasma sterilization approach. The main studies then monitored actual date-expired dental implants of three different types, as packaged as well as after deliberate contamination with Candida albicans or adventitious atmospheric organisms, through microbiological broth-based and agar-based assays to prove sterility and through tissue culture assays with human alveolar osteoblasts to prove renewed cellular attachment and growth characteristics. Osteoblast growth and viability was confirmed by statistically equivalent outcomes for as-manufactured implants and clean/re-sterilized (by H2O2 gas plasma) implants, judged by cellular mitochondrial activity assays (MTT), differential interference contrast (DIC) light microscopy, and SEM. These results demonstrated that date-expired dental implants can be safely and effectively restored to conditions generally associated with the good clinical performance of osseointegated cpTi devices.</p>

<p> Focusing medicine to disease locations is a needed ability to treat a variety of pathologies. During chemotherapy, for example, typically less than 0.1% of the drugs are taken up by tumor cells, with the remaining 99.9% going into healthy tissue. Physicians often select the dosage by how much a patient can physically withstand rather than by how much is needed to kill all the tumor cells. The ability to actively position medicine, to physically direct and focus it to specific locations in the body, would allow better treatment of not only cancer but many other diseases. </p><p> Magnetic drug targeting (MDT) harnesses therapeutics attached to magnetizable particles, directing them to disease locations using magnetic fields. Particles injected into the vasculature will circulate throughout the body as the applied magnetic field is used to attempt confinement at target locations. The goal is to use the reservoir of particles in the general circulation and target a specific location by pulling the nanoparticles using magnetic forces. </p><p> This dissertation adds three main advancements to development of magnetic drug targeting. Chapter 2 develops a comprehensive ferrofluid transport model within any blood vessel and surrounding tissue under an applied magnetic field. Chapter 3 creates a ferrofluid mobility model to predict ferrofluid and drug concentrations within physiologically relevant tissue architectures established from human autopsy samples. Chapter 4 optimizes the applied magnetic fields within the particle mobility models to predict the best treatment scenarios for two classes of chemotherapies for treating future patients with hepatic metastatic breast cancer microtumors.</p>

<p> Cell migration is present in virtually all life processes, including fertilization, embryogenic development, immune response, wound healing, and tumor metastasis. To improve the treatment of diseases associated with these various life processes, it is important to understand the underlying mechanisms of cell migration involved. This often requires that we recreate the environment that leads to and supports the continuous migration of cells. Here, we present two engineering approaches toward such a goal, with the additional emphasis that cell migration can be conducted in the absence of fluid flow, a mechanical stimulus that is known to influence cell behaviors. We chose the primary human neutrophil, which is highly motile and sensitive to both fluid flow and chemoattraction, as the model cell type for all our studies. </p><p> In the first approach, we used fluid flow to create a linear and time-invariant gradient of chemoattractants to guide the migration of neutrophils. A thin and porous membrane was used to screen off the associated flow forces while still permitting the diffusion of the gradient to the neutrophils. We showed that the membrane-based system is capable of directing neutrophil migration without the bias from fluid flow, and allowed within minutes the exchange of media to label and wash the migrated neutrophils. To assess the reduction of flow forces enabled by the membrane, we developed an analytical model to predict the direction and the magnitude of flow within the system. The validity of the model was verified both experimentally and numerically with particle tracking and computational fluid mechanic (CFM) simulations. We also performed total internal reflection fluorescence (TIRF) microscopy to verify the preservation of the gradient after v its diffusion through the membrane. </p><p> In the second approach, we created immobilized gradients of the chemoattractant interleukin 8 (IL-8) and the intercellular adhesion molecule 1 (ICAM-1) in the attempt to guide neutrophil migration. A gradient of soluble factors is first established, and the resulting difference of concentration over space leads to a bias in the binding of the soluble factors unto the substrate, forming an immobilized gradient. The immobilization is mediated by a combination of different physicochemical linkages, including electrostatic attraction, protein/protein interactions, and covalent bonding. We showed through labeling with fluorescent antibody that the number of IL-8 or ICAM-1 immobilized in a given area could be controlled, and varied over distances to form different gradient profiles. We further showed that our immobilization procedure does not affect the ability of IL-8 and ICAM-1 to activate and bind the neutrophils. However, with all the immobilized gradients that we have created so far, none were able to effectively promote the directed migration of neutrophils in long distances. Additional work is therefore required to establish if an immobilized gradient of either IL-8 or ICAM-1 alone can direct the migration of neutrophils in long distances, and if it does, what are the required conditions. Currently, our efforts suggest that the membrane-based chemotaxis system is a more attainable platform for promoting a directed migration that is shear-free. </p><p> The presented thesis work offers many potential applications. The membrane-based chemotaxis system, which has the general structure of two compartments separated by a membrane, resembled many physiological structures, including bone marrow, blood vessel, blood-brain barrier, hepatic portal vein, nephron in the kidneys, and alveolus in vi the lungs, and therefore serves as a versatile platform for understanding the transport phenomenon and the biochemical signaling in the aforementioned tissues. With improvements, the membrane-based system can also host larger-scale cell culture for protein production and tissue engineering. The protocols established for the gradient immobilization also provided many valuable references. These include: 1. A 1^st order approximation of the reagents and the times required to fully saturate the substrate to be functionalized. 2. An automated image processing tool to measure the various parameters of cell motility. 3. A statistical framework to detect the presence of a directed migration. In theory, the standard operating procedures established are applicable to the surface functionalization with other peptides and proteins. </p>

<p> Fluorescence molecular imaging will have an important clinical impact in the area of guided oncology surgery, where emerging technologies are poised to provide the surgeon with real-time molecular information to guide resection, using targeted molecular probes. The development of advanced surgical systems has gone hand in hand with probe development, and both aspects are analyzed in this work. A pulsed-light fluorescence guided surgical (FGS) system has been introduced to enable video rate visible light molecular imaging under normal room light conditions. The concepts behind this system design are presented and performance is compared with a commercial system in both phantom and <i> in vivo</i> animal studies using PpIX fluorescence. </p><p> The second critical advance in the emergence of these technologies has been the development of targeted near infrared (NIR) probes. A small, engineered three-helix protein was analyzed for imaging of glioma tumors. The blood brain barrier affects delivery of probes and the superior delivery of a smaller targeted protein (anti-EGFR Affibody) as compared to a full sized antibody is shown using a murine model, <i>ex vivo</i> tissue slices and a commercial imaging system. This small targeted probe is examined further for its possible application in FGS using the pulsed light imaging system. A concentration sensitivity analysis to determine the lower bounds on concentration needed for effective imaging is performed with this culminating analysis carried out in a murine orthotopic glioma tumor model.</p>

<p> The field of immunology has advanced tremendously over the last 40 years, with seminal findings that have guided the development of powerful new therapies. However, the ability to induce safe and long-lasting antigen-specific tolerance has remained elusive. A therapy that could prevent the immune system from aberrantly destroying self-tissues, without impairing its capacity to eliminate dangerous pathogens, would be transformative for the treatment of autoimmune diseases. In addition, such a therapy could also greatly advance the field of organ transplantation by inducing antigen-specific tolerance to prevent graft rejection. </p><p> In this thesis, the overarching goal was to develop a biomaterial delivery system that could recruit and program antigen presenting cells, specifically dendritic cells (DCs), in a non-inflammatory environment, allowing them to orchestrate downstream immune responses that are both antigen-specific and tolerogenic. Gold nanoparticles (AuNPs) were used to deliver a DC recruitment factor, GM-CSF, from an injectable alginate based hydrogel. Both the release of GM-CSF and the physical porous structure of the gel were tuned to achieve effective recruitment of a highly enriched population of DCs. The ability of this system to generate downstream antigen-specific responses in T cells was demonstrated in a mouse model of type 1 diabetes (T1D). Additionally, the DCs recruited in this system were characterized and found to exhibit features that would make them competent to induce tolerance. Finally, a new method was developed for localized delivery and cell-triggered release of a peptide antigen from the material. Over time, antigen-specific T cells expressing FoxP3, a marker of regulatory T cells, which are key mediators of immune tolerance, accumulated in the gels. Together, these findings demonstrate that it is possible to recruit and program DCs in a non-inflammatory context, and that these DCs can induce downstream antigen-specific responses. These promising results suggest that this system may be able to promote tolerance in the setting of autoimmune disease. </p><p> This thesis advances the field of immunomodulatory biomaterials by introducing new methodologies for precisely recruiting and manipulating DCs in a non-inflammatory context. This work may provide the basis for further development of a highly effective and therapeutic antigen-specific tolerogenic vaccine.</p>

<p> The primary goal of this thesis is to develop a combined MR relaxation (T₂ and T_1&rho;), diffusion (ADC, apparent diffusion coefficient), elastography (shear stiffness) method to fully characterize the development of tissue-engineered cartilage in terms of the changes in its composition, structure, and mechanical properties during tissue growth. We do this for the purpose of understanding how we may better use MR-based methodologies to noninvasively monitor and optimize the cartilage tissue engineering process without sacrificing the constructs.</p><p> While conventional T₂ and ADC have been widely used in the studies of engineered cartilage tissues, there were few T_1&rho; and MRE studies related to it. We begin by demonstrating the potential capabilities of T₂, T_1&rho;, ADC, and shear stiffness in characterization of a scaffold-free engineered cartilage tissue. We examine the correlations between MR parameters and biochemical determined macromolecule contents in tissue-engineered cartilage. We show that, in addition to the conventional T₂ and ADC, T_1&rho; and MRE can also be used as potential biomarkers to assess the specific changes in proteoglycan content and mechanical properties of engineered cartilage during tissue growth. </p><p> Secondly, to increase the efficiency of MR characterization of engineered tissues, we develop two new methodologies for simultaneous acquisition of MRI and MRE data: (1) diffusion and MRE (dMRE) and (2) T_1&rho; and MRE (T_1&rho;-MRE), respectively. Conventional T_1&rho;, diffusion, and MRE acquisitions are performed as separate measurements that prolong the imaging protocols. The dMRE and T_1&rho;-MRE are developed to overcome this problem by acquiring two pieces of information in one temporally resolved scan. This allows the simultaneous characterization of both biochemical and mechanical properties of engineered cartilage tissues. We carry out dMRE and T_1&rho;-MRE experiments on tissue-mimicking phantoms to show the feasibilities of two techniques. The results obtained show a good correspondence between simultaneous acquisitions and conventional separate acquisition methods. We expect that the combined MRI/MRE methods will benefit the optimal cartilage tissue engineering process.</p>

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4629. Adviser: Sharmila Majumdar.

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4640. Adviser: Sarah J. Nelson.

Thesis (Ph.D.)--University of California, San Francisco, 2007. / Source: Dissertation Abstracts International, Volume: 68-04, Section: B, page: 2257. Adviser: Kathleen Puntillo.