Three-dimensional brain fiber tracking modeling in diffusion tensor imaging

This dissertation establishes the foundation for a new 3-D visual interface integrating Magnetic Resonance Imaging (MRI) to Diffusion Tensor Imaging (DTI). The need for such an interface is critical for understanding brain dynamics, and for providing more accurate diagnosis of key brain dysfunctions in terms of neuronal connectivity. ^ This work involved two research fronts: (1) the development of new image processing and visualization techniques in order to accurately establish relational positioning of neuronal fiber tracts and key landmarks in 3-D brain atlases, and (2) the obligation to address the computational requirements such that the processing time is within the practical bounds of clinical settings. The system was evaluated using data from thirty patients and volunteers with the Brain Institute at Miami Children's Hospital. ^ Innovative visualization mechanisms allow for the first time white matter fiber tracts to be displayed alongside key anatomical structures within accurately registered 3-D semi-transparent images of the brain. ^ The segmentation algorithm is based on the calculation of mathematically-tuned thresholds and region-detection modules. The uniqueness of the algorithm is in its ability to perform fast and accurate segmentation of the ventricles. In contrast to the manual selection of the ventricles, which averaged over 12 minutes, the segmentation algorithm averaged less than 10 seconds in its execution. ^ The registration algorithm established searches and compares MR with DT images of the same subject, where derived correlation measures quantify the resulting accuracy. Overall, the images were 27% more correlated after registration, while an average of 1.5 seconds is all it took to execute the processes of registration, interpolation, and re-slicing of the images all at the same time and in all the given dimensions. ^ This interface was fully embedded into a fiber-tracking software system in order to establish an optimal research environment. This highly integrated 3-D visualization system reached a practical level that makes it ready for clinical deployment. ^

Seasonal and spatial variation in the stable isotopic composition (δ18O and δD) of precipitation in south Florida

Precipitation data collected from five sites in south Florida indicate a strong seasonal and spatial variation in δ18O and δD, despite the relatively limited geographic coverage and low-lying elevation of each of the collection sites. Based upon the weighted-mean stable isotope values, the sites were classified as coastal Atlantic, inland, and lower Florida Keys. The coastal Atlantic sites had weighted-mean values of δ18O and δD of −2.86‰ and −12.8‰, respectively, and exhibited a seasonal variation with lower δ18O and δD values in the summer wet-season precipitation (δ18O = −3.38‰, δD = −16.5‰) as compared to the winter-time precipitation (δ18O = −1.66‰, δD = −3.2‰). The inland site was characterized as having the highest d-excess value (+13.3‰), signifying a contribution of evaporated Everglades surface water to the local atmospheric moisture. In spite of its lower latitude, the lower Keys site located at Long Key had the lowest weighted-mean stable isotope values (δ18O = −3.64‰, δD = −20.2‰) as well as the lowest d-excess value of (+8.8‰). The lower δD and δ18O values observed at the Long Key site reflect the combined effects of oceanic vapor source, fractionation due to local precipitation, and slower equilibration of the larger raindrops nucleated by a maritime aerosol. Very low δ18O and δD values (δ18O < −6‰, δD < −40‰) were observed just prior to the passage of hurricanes from the Gulf of Mexico as well as during cold fronts from the north-west. These results suggest that an oceanic vapor source region to the west, may be responsible for the extremely low δD and δ18O values observed during some tropical storms and cold fronts.

Autumn raptor migration through the Florida Keys

This study documents the 1996 and 1997 autumn migration seasons at Grassy Key for 16 species of raptors (hawks, eagles, and falcons). My results indicate the Florida Keys are a major raptor migration flyway (over 26,000 sightings). I identified factors influencing watch-site location in the Keys. Northbound flights must be included to avoid inflating southbound counts. By removing the "season effect" (natural rise, peak, and wane of raptor numbers during migration), I demonstrate wind has little consistent effect on raptor counts in the Keys. I further demonstrate we do not see more raptors on cold front days than on non-cold front days. However, cold fronts following tropical storms (as in 1996) increase the number of raptors observed for most species. I conducted a nightly roosting survey on Boot Key resulting in near or over 3,000 raptor sightings per season and present a model to predict aerial counts from roosting counts.

Intra-racial relations among blacks in the United States: dissimilarities, partnerships, and common identities

In the wake of a steadily increasing diversity in ethnicity among Blacks in the United States, efforts need to be made to analyze and understand the dynamics of the relations among the various Black ethnic groups in the United States. This thesis explores the present state of relations among these groups by utilizing an extensive literature review on the topic in conjunction with in-depth interviews. What is of particular interest here are the differing and similar intergroup perspectives on self-identity, as well as any cultural similarities and dissimilarities that exist. We find that the cultural dissimilarities create barriers to harmonious relations among the groups, while particular ideologies such as Pan-Africanism and Black nationalism provide the basis for strong unified fronts and partnerships for those who embrace them.