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We determine the crustal and upper mantle structure within the northern Canadian Cordillera using two complementary Rayleigh wave analysis techniques: ambient noise and teleseismic two-station interferometry. These methods are used to measure Rayleigh waves propagating between all available pairs of seismic stations in northwestern Canada, which are processed to obtain phase velocity dispersion curves. These curves provide information on the inter-station, path-averaged phase velocity as a function of frequency (or period). These inter-station phase velocities are then inverted to produce phase velocity maps. Phase velocity maps for periods between 8 and 80 s show to first-order high velocities within the Shield and low velocities within the Cordillera, supporting the thermal isostasy model for the region. Smaller scale features are observed throughout the Cordillera with high velocities west of the Tintina Fault reflecting the mafic composition of the accreted terranes of the Intermontane belt, and low velocities east of the Tintina fault reflecting the sedimentary rocks of the Selwyn Basin. High velocities extending west past the Cordilleran Deformation Front provide evidence for the existence of regions within the eastern Cordillera underlain by cool cratonic lithosphere. Anisotropy within the upper crust and mantle shows fast-axis orientations in line with the major faults within the region, providing evidence for a shear-zone that extends to lithospheric mantle depths. Lower crustal anisotropy shows an increase in heterogeneity of fast-axis orientations, which provides limited support for the existence of a weak shear zone and detachment within the lower crust. Results of a 1D inversion show approximate Moho depths of 35 km for the region west of the Tintina Fault, 36 km for the Mackenzie Mountains region, and 37 km for the shield. Reduced lower crust velocities observed throughout the Cordillera, provide support for the existence of a weak lower crustal layer.

The authors present an unusual case of a highly mobile gallbladder which simulated a pancreatic mass on computed tomograms. Radiographic features of this interesting variant are illustrated.

Abscesses developing within the retroperitoneal spaces are complicated and serious infections. These abscesses present insidiously, leading to considerable mortality and morbidity. A high clinical suspicion can help diagnose and treat this potentially fatal illness. Computed axial tomography is the best diagnostic modality for retroperitoneal abscess. Computed tomographic scan is useful, not only for diagnosing the retroperitoneal abscess, but can be used for therapeutic drainage of abscesses in high-surgical-risk patients. We present an illustrative case of retroperitoneal abscess and discuss the pathogenesis of retroperitoneal abscess, diagnosis, and treatment.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 530-553. / by David Bruce Laning. / Sc.D.

Indiana University-Purdue University Indianapolis (IUPUI) / An algorithm was developed in to efficiently segment the inner-limiting membrane (ILM) and retinal pigmented epithelium (RPE) from spectral domain-optical coherence tomography image volumes. A deformable model framework is described and implemented in which free-form deformations (FFD) are used to direct two deformable sheets to the two high-contrast layers of interest. Improved accuracy in determining retinal thickness (the distance between the ILM and the RPE) is demonstrated against the commercial state-of-the-art Spectralis OCT native segmentation software. A novel adaptation of the highest confidence first (HCF) algorithm is utilized to improve upon the initial results. The proposed adaptation of HCF provides distance-based clique potentials and an efficient solution to layer-based segmentation, reducing a 3D problem to 2D inference.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Erosive tooth wear (ETW) is the loss of tooth substance due to chemo-mechanical action unrelated to bacteria. ETW affects approximately 46 percent of children/adolescents and 80 percent of adults in the U.S. Visual examination indices are available for the clinical assessment of ETW. Although useful, they are subjective and heavily based on the clinical experience of the examiner. Some quantitative techniques have been proposed and used for clinically assessing erosive tooth wear, including quantitative light-induced fluorescence, ultrasonic measurement, and more recently, polarization-sensitive optical coherence tomography (PS-OCT). Objective: The objective of this study was to explore the ability of PS-OCT to objectively measure erosive tooth wear on occlusal surfaces. Method: This study was conducted in two phases. In the first phase, 10 sound extracted human lower first premolars were selected and then exposed to tooth wear simulation gradually. PS-OCT and micro computed tomography (μ-CT) were used to evaluate enamel thickness of those premolars at the buccal cusp tip during the simulation. In phase 2, 40 extracted human lower first premolars with different severity levels of ETW on occlusal surfaces were selected based on the Basic Erosive Wear Examination (BEWE) index. A total of 10 teeth (n =10) were selected for each BEWE score (0/1/2/3). PS-OCT and μ-CT were used to evaluate the enamel thickness at the highest point on the occlusal surface. Results: There was good agreement between PS-OCT and μ-CT in both phases (phase 1: 0.89 and phase 2: 0.97) with no significant difference between PS-OCT and μ-CT. Conclusion: This result shows the potential of PS-OCT as reliable method for measuring enamel thickness and monitoring tooth wear progression on the occlusal surface

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No description available.