Physical Sciences and Mathematics Commons^™

Prediction Of Laser Ablation In Brain: Sensitivity, Calibration, And Validation, Samuel J. Fahrenholtz

Dissertations & Theses (Open Access)

The surgical planning of MR-guided laser induced thermal therapy (MRgLITT) stands to benefit from predictive computational modeling. The dearth of physical model parameter data leads to modeling uncertainty. This work implements a well-accepted framework with three key steps for model-building: model-parameter sensitivity analysis, model calibration, and model validation.

The sensitivity study is via generalized polynomial chaos (gPC) paired with a transient finite element (FEM) model. Uniform probability distribution functions (PDFs) capture the plausible range of values suggested by the literature for five model parameters. The five PDFs are input separately into the FEM model to gain a probabilistic sensitivity response …

Voxel-Level Absorbed Dose Calculations With A Deterministic Grid-Based Boltzmann Solver For Nuclear Medicine And The Clinical Value Of Voxel-Level Calculations, Justin Mikell

Dissertations & Theses (Open Access)

Voxel-level absorbed dose (VLAD) is rarely calculated for nuclear medicine (NM) procedures involving unsealed sources or 90Y microspheres (YM). The current standard of practice for absorbed dose calculations in NM utilizes MIRD S-values, which 1) assume a uniform distribution in organs, 2) do not use patient specific geometry, and 3) lack a tumor model. VLADs overcome these limitations. One reason VLADs are not routinely performed is the difficulty in obtaining accurate absorbed doses in a clinically acceptable time. The deterministic grid-based Boltzmann solver (GBBS) was recently applied to radiation oncology where it was reported as fast and accurate for both …

Quantification Of Imrt Severity Scores For Improvement Of Fmea Results, Jacqueline T. Faught

Dissertations & Theses (Open Access)

Accurate delivery of intensity modulation radiation therapy (IMRT) requires perfect execution of a long, complicated chain of events; failure of any component of this process may contribute to dose delivery errors, compromising treatment quality and, more importantly, patient safety. Prospective, process-wide risk mitigation techniques are becoming more prevalent in radiotherapy to establish comprehensive quality management (QM) programs, such as failure modes and effects analysis (FMEA). The subjective nature of the ordinal scores used for FMEA leads questionable reliability and validity of the results. Additionally, physics components are commonly grouped together, leaving out valuable details important to physics QM. While the …

Improving Attenuation Correction In Hybrid Positron Emission Tomography, Hua Asher Ai

Dissertations & Theses (Open Access)

Hybrid positron emission tomography imaging techniques such as PET/CT and PET/MR have undergone significant developments over the last two decades and have played increasingly more important roles both in research and in the clinic. A unique advantage PET has over other clinical imaging modalities is its capability of accurate quantification. However, as the most critical component of PET quantification, attenuation correction in hybrid PET systems is challenged in several different aspects, including the spatial- temporal mismatch between the PET emission images and the associated attenuation images provided by the complementary modality, and the difficulty in bone identification in the MR-based …

Quality Assurance Of Advanced Treatment Modalities Using Presage® Dosimeters, Ryan G. Lafratta

Dissertations & Theses (Open Access)

Computer-controlled therapy machines allow for increasingly complex plans, as there are more variables that can be tuned to produce the ideal result. This makes it increasingly difficult to assure the intended calculated dose is being delivered correctly using current techniques that are 2D-based because the resultant dose distributions can differ markedly in various sections of the target. A measurement of composite dose from the entire plan should be included in patient-specific IMRT QA. A volumetric dosimeter such as PRESAGE^® is able to provide a complete 3D measured dosimetry dataset with one treatment plan delivery. It was hypothesized that a …

Feasibility Of Using Virtual Unenhanced Images To Replace Pre-Contrast Images In Multiphase Renal Ct Examinations, Dawn Olivia Popnoe

Dissertations & Theses (Open Access)

Multiphase renal CT exams are a commonly used imaging technique for the diagnosis of renal masses. The pre-contrast, or true unenhanced (TUE), image provides a baseline for enhancement measurements which is an important criteria used to characterize renal lesions, consequently it is crucial that CT numbers measured in TUE images be accurate. The purpose of this work is to assess the feasibility of replacing TUE with virtual unenhanced (VUE) images derived from DECT data in renal CT exams. Eliminating TUE image acquisition would reduce patient dose and increase patient throughput, improving clinical efficiency.

A retrospective study was conducted for 60 …

Computational Modeling Of Rna-Small Molecule And Rna-Protein Interactions, Lu Chen

Dissertations & Theses (Open Access)

The past decade has witnessed an era of RNA biology; despite the considerable discoveries nowadays, challenges still remain when one aims to screen RNA-interacting small molecule or RNA-interacting protein. These challenges imply an immediate need for cost-efficient while predictive computational tools capable of generating insightful hypotheses to discover novel RNA-interacting small molecule or RNA-interacting protein. Thus, we implemented novel computational models in this dissertation to predict RNA-ligand interactions (Chapter 1) and RNA-protein interactions (Chapter 2).

Targeting RNA has not garnered comparable interest as protein, and is restricted by lack of computational tools for structure-based drug design. To test the potential …

Genetics Of Obesity In Starr County, Texas Mexican Americans, Heather M. Highland

Dissertations & Theses (Open Access)

Currently, over two-thirds of Americans are classified as over-weight or obese. Obesity increases risk for many other diseases including type 2 diabetes, heart disease, stroke, and cancer, making obesity the largest public health problem in America and most other Westernized nations. Hispanics have a higher rate of both obesity and type 2 diabetes, making them a particularly interesting population in which to study obesity. For the last 33 years, the Starr County Health Studies has collected an array of phenotypes and biological samples from residents of Starr County, along Texas-Mexico border. This study includes 825 subjects who were not known …

Characterization Of Low Density Intracranial Lesions Using Dual-Energy Computed Tomography, Jessica L. Nute

Dissertations & Theses (Open Access)

Calcific and hemorrhagic foci of susceptibility are frequently encountered on routine brain MR studies. Both etiologies cause variations in local magnetic field strength, leading to dark regions on the MR images that cannot be classified. Single-energy CT (SECT) can be used to identify lesions with attenuation over 100 HU as calcific, however lesions with lower attenuation cannot be reliably identified. While calcific lesions are unlikely to cause harm, hemorrhagic lesions carry a risk of subsequent intracranial bleeding; as such, identification of hemorrhage is vital in preventing the inappropriate use of anticoagulant medications in patients with hemorrhagic lesions.

Given there currently …