Browsing by Subject "3D"

Now showing 1 - 3 of 3
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    Reconstructing the bay-side geomorphic evolution of a freshwater baymouth bar in response to lake level change using three dimensional (3D) ground-penetrating radar (GPR) data
    (2019-11) Kremmin, Todd
    Situated at the southwestern tip of Lake Superior, Minnesota and Wisconsin Points' form a 16-kilometer baymouth bar between Duluth, Minnesota and Superior, Wisconsin, providing the breakwater for the largest and farthest inland freshwater seaport in North America. Comprised of sandy sediment, this baymouth bar's formation is attributed largely to littoral drift from the Wisconsin South Shore and minor sediments from the outflows of the St. Louis and Nemadji River's. Due to continuing differential isostatic rebound of the basin, local lake level at Duluth is presently rising at approximately 25 centimeters/century. The objective of this thesis was to understand the geomorphic evolution of the bay-side of the baymouth bar in response to lake level change in relation to the system overall. Using an approach akin to energy industry seismic studies, the geomorphic expression of the bay-side baymouth bar’s response to lake level change was investigated with 39.62 kilometers of Three-Dimensional (3D) Ground-Penetrating Radar (GPR) data. 8 vibracores’, 11.24 meters’ in total, were advanced within the 3D GPR data to supplement subsurface understanding both spatially and temporally. Radiocarbon material taken from the vibracores were analyzed, dated, and used to establish a chronology for the evolution of the study area (~520.50 Cal yrs. BP to 181.25 Cal yrs. BP). Whole core logger data (including p-wave amplitude and velocity, gamma ray density, acoustic impedance, and fractional porosity) along with Loss on Ignition (LOI) samples taken from each core were used in conjunction with the GPR data to supplement the subsurface stratigraphic and facies identification. In total, 5 facies units were interpreted on the bay side of the baymouth bar, exhibiting a thick clay layer, shoreface ridge and shallow offshore sediments, overwash deposition, fluvial-flood like deposition, and man-made dredge deposits. Historical information and photographs dating back to the 1930’s provide evidence supporting interpretations of dredge material versus natural material. Although this baymouth bar is a young, non-marine system, reconstructing its geomorphic evolution in response to lake level change has become a useful analogue for similar, larger systems involved with base level change. In addition, stratigraphic findings of how such a system’s architecture is configured yield insightful clues towards vintage conventional exploration reservoirs. Finally, these data support a stronger understanding of how such a system geomorphically evolved in the context of the Lake Superior region post glaciation and aid in reshaping knowledge of how other geomorphic features and processes have developed throughout the region, perhaps providing tangible framework for future engineering and environmental management undertakings.
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    Stability of The Mental Foramen And Its Potential Use As A Landmark For Three-Dimensional Superimposition of Human Mandibles on Cone-Beam Computed Tomograms
    (2018-06) Hamdan, Hani
    The purpose of this study was to examine the mental foramina as possible stable landmarks for three-dimensional superimposition of 2 cone-beam computed tomography (CBCT) images of the same human mandible taken during a long period of growth. The ultimate goal was to use the mental foramina as landmarks in a superimposition protocol. This retrospective study used CBCT scans taken at the University of Minnesota’s Department of Orthodontics, which were oriented and measured using Dolphin 3D Imaging software. 55 patients were selected. For each CBCT, the distance between the two mental foramina as well as the distance between protuberance menti (PM) and each mental foramen were measured. Differences in these measurements between the earlier (T1) scan and the later (T2) scan were then tested for statistical significance using a paired t-test. The results showed a significant distal movement of the mental foramen in growing patients, enough to hamper superimposition accuracy. The increase in the distance between each mental foramen and PM was symmetrical. Therefore, it can be concluded that the mental foramina are not suitable landmarks for three dimensional superimposition of the mandible in growing patients. However, the symmetry in the increase in the distance between PM and each mental foramen is a significant finding and indicates that the mental foramina can be used indirectly for 3D superimposition, helping to detect and quantify posterior mandibular growth asymmetry.
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    Three-dimensional dosimetry around small distributed high-Z materials
    (2016-05) Warmington, Leighton
    Patients are increasingly undergoing radiotherapy procedures, in which small metals are implanted in the body for target localization for IGRT or targeted therapies. Previous, interface dosimetry studies focused high-Z materials irradiated by low energy beams where the dose enhancement is large. In the majority of the cases, they used one or two dimensional detectors. Therapeutic beams, however, are mostly 6 MV and higher with significantly less dose enhancement. Over the last decade, significant improvements in polymer gel dosimetry have been made allowing for improved 3D dose measurements. The purpose of this study was to better understand the dose around distributed high-Z materials irradiated by high energy photon beams and investigate the feasibility of 3D dose measurements. A Monte Carlo code was used to determine the effect of various foil configurations. The dosimetric effect of foil thickness, separation, energy and other factors were investigated. Software tools were also developed to process the data. These results were used to help identify suitable experimental setups. The dose around two foils was compared to the dose resulting from adding the dose of two single foils. The dose around a single foil was also compared to the dose around a fiduciary marker. Later on, we looked at how distributing the thickness of the high-Z foil over a wider area affected dose and how that compared to a to the dose around a single foil. Finally, we looked at the effect of pair production and how it affected the distribution of dose in select configurations. Several polymer gel dosimeter (PGD) were evaluated and two were selected for further study. Various formulations were investigated and procedures developed to meet the needs of the project. Materials compatibility studies were performed to ensure that there were no reactions between the PGD and inserted materials within the time frame of the studies. PGDs were manufactured and thin lead foils with the configuration determined earlier were inserted into the polymer gel. The PGDs was irradiated with 18 MV photons and the dose was quantified using MRI with a multiple spin echo technique for the measurement of the spin-spin relaxation rate (R2). The measured dose data were compared to theoretical data obtained from Monte Carlo experiments. The dose profiles around the foils from the PGD were in agreement with dose values from simulation. This project demonstrated that it is feasible to use polymer gel dosimetry to measure the fine dosimetric structures around a small metallic object. We also determined that material, foil thickness, separation and photon energy had the largest effect on the dose in-between a two foil configuration. When the foils were close, we found that the dose around the two foils was larger but not significantly different from the combined dose of two single foils with the same separation. We also found that the dose upstream and downstream of a distributed foil is less that the upstream and downstream dose around a single foil of equivalent thickness.