11 research outputs found
Dispersal limitation may result in the unimodal productivity-diversity relationship: a new explanation for a general pattern
Placing local plant species richness in the context of environmental drivers of metacommunity richness
Comparison and evaluation of retrospective intermodality brain image registration techniques
International audiencePURPOSE: The primary objective of this study is to perform a blinded evaluation of a group of retrospective image registration techniques using as a gold standard a prospective, marker-based registration method. To ensure blindedness, all retrospective registrations were performed by participants who had no knowledge of the gold standard results until after their results had been submitted. A secondary goal of the project is to evaluate the importance of correcting geometrical distortion in MR images by comparing the retrospective registration error in the rectified images, i.e., those that have had the distortion correction applied, with that of the same images before rectification. METHOD: Image volumes of three modalities (CT, MR, and PET) were obtained from patients undergoing neurosurgery at Vanderbilt University Medical Center on whom bone-implanted fiducial markers were mounted. These volumes had all traces of the markers removed and were provided via the Internet to project collaborators outside Vanderbilt, who then performed retrospective registrations on the volumes, calculating transformations from CT to MR and/ or from PET to MR. These investigators communicated their transformations again via the Internet to Vanderbilt, where the accuracy of each registration was evaluated. In this evaluation, the accuracy is measured at multiple volumes of interest (VOIs), i.e., areas in the brain that would commonly be areas of neurological interest. A VOI is defined in the MR image and its centroid c is determined. Then, the prospective registration is used to obtain the corresponding point c' in CT or PET. To this point, the retrospective registration is then applied, producing c" in MR. Statistics are gathered on the target registration error (TRE), which is the distance between the original point c and its corresponding point c". RESULTS: This article presents statistics on the TRE calculated for each registration technique in this study and provides a brief description of each technique and an estimate of both preparation and execution time needed to perform the registration. CONCLUSION: Our results indicate that retrospective techniques have the potential to produce satisfactory results much of the time, but that visual inspection is necessary to guard against large errors
Interpreting co-variation in species richness and productivity in terrestrial vegetation: Making sense of causations and correlations at multiple scales
The f2(1565) in anti-p p --> (omega omega) pi0 interactions at rest
Data are presented on the reaction pbar-p -> omega-omega-pizero at rest from
the Crystal Barrel detector. These data identify a strong signal due to
f2(1565) -> omega-omega. The relative production from initial pbar-p states
3P2, 3P1 and 1S0 is well determined from omega-omega decay angular
correlations; P-state annihilation dominates strongly. A combined fit is made
with data on pbar-p -> 3pizero at rest, where f2(1565) -> pizero-pizero is
observed.Comment: Demonstrates that f2(1565) and f2(1640) are two decay modes of the
same resonance, 11 pages, 5 figure