Effective visualization of complex vascular structures using a non-parametric vessel detection method

The effective visualization of vascular structures is critical for diagnosis, surgical planning as well as treatment evaluation. In recent work, we have developed an algorithm for vessel detection that examines the intensity profile around each voxel in an angiographic image and determines the likelihood that any given voxel belongs to a vessel; we term this the "vesselness coefficient" of the voxel. Our results show that our algorithm works particularly well for visualizing branch points in vessels. Compared to standard Hessian based techniques, which are fine-tuned to identify long cylindrical structures, our technique identifies branches and connections with other vessels. Using our computed vesselness coefficient, we explore a set of techniques for visualizing vasculature. Visualizing vessels is particularly challenging because not only is their position in space important for clinicians but it is also important to be able to resolve their spatial relationship. We applied visualization techniques that provide shape cues as well as depth cues to allow the viewer to differentiate between vessels that are closer from those that are farther. We use our computed vesselness coefficient to effectively visualize vasculature in both clinical neurovascular x-ray computed tomography based angiography images, as well as images from three different animal studies. We conducted a formal user evaluation of our visualization techniques with the help of radiologists, surgeons, and other expert users. Results indicate that experts preferred distance color blending and tone shading for conveying depth over standard visualization techniques.     

Triton X-100 pretreatment of LR-white thin sections improves immunofluorescence specificity and intensity

The staining of intracellular antigenic sites in postembedded samples is a challenging problem. Deterioration of antigenicity and limited antibody accessibility to the antigen are commonly encountered on account of processing steps. In this study preservation of the antigen was achieved by fixing the tissues with mild fixatives, performing partial dehydration, and embedding in a low crosslinked hydrophilic acrylic resin, LR-White. Permeabilization of cell membranes with Triton X-100 is well documented but can affect some antigen conformations. We tested the effect of Triton X-100 on the ED1 antigen present in the lysosomal membrane of the macrophage in cell culture. The ED1 antigen in the lysosome was resistant to extraction by Triton X-100. Interestingly pretreating the LR-White sections of macrophage pellets with Triton X-100 improved the staining intensity of ED1. The most intense and clear specific fluorescent staining was observed when sections were pretreated with 0.2% Triton X-100 for 2 min. Longer exposure of sections to 0.2% Triton or 2 min exposure to 2% Triton lead to reduced ED1 labeling. SEM observations indicated that the detergent extracted a component from the cells and not the resin and was determined to be lipid. This novel technique could be applied in many research areas where postembedding fluorescent immunolabeling with higher labeling intensity is desired.     

Negotiating participation: understanding the "how" in an ergonomic change team

In participatory ergonomic (PE) interventions, "how" effective participation by workplace parties can be achieved remains unclear. We conducted a case study of the dynamics of an ergonomic change team (ECT) process in a medium-sized (175 employees) automotive foam manufacturing plant. We present analyses of observer field notes and post-intervention interviews from which key elements on the dynamics of the "how" emerged: (1) impacts of facilitators' involvement and interests; (2) tensions in delimiting the scope of ECT activities; issues around (3) managing meetings and (4) realizing labour and management participation; and (5) workplace ECT members' difficulties in juggling other job commitments and facing production pressures. We highlight the ongoing negotiated nature of responses to these challenges by labour, management and ergonomic facilitator members of the ECT. We argue for greater examination of the social dynamics of PE processes to identify additional ways of fostering participation in ergonomic project implementation.     

Towards the implementation of text and discourse theory in computer-assisted textual analysis

Humanities computing (HC) has failed to integrate into its practices many of the key theoretical elements of contemporary text and discourse theory. This has in turn contributed to the marginalization of HC in research and teaching. Outdated theoretical models must be abandoned in order to develop a critical discourse based on the insights of HC. HC projects remain far too attached to micro-analyses and have not developed the theoretical and methodological tools necessary to undertake systemic macro-analyses on the level of discourse. Given that texts are a mixture of determinate and dynamic systems, recent developments in chaos theory may be of help in modelling the interrelationship of these elements at discourse level.Donald Bruce is Associate Professor of Romance Languages at the University of Alberta. His research interests include literary theory, XIXth century French literature, science and literature, and translation. He recently edited an issue ofRecherches Sémiotiques/Semiotic Inquiry on Literature and Ideology and is presently working on a project entitled,The Socio-semiotic Nexus: Jules Vallès and the Discourse of the Commune.     

A Framework and Lightweight Protocol for Multimedia Network Management

The increasing complexities of modern networks coupled with the popularity of multimedia applications have placed higher demands on network managers. This paper reviews the main requirements and challenges for effective management of multimedia networks, presents a case study of a thin-client-based multimedia system called CSL (Computer-supported Learning System) and proposes a framework for managing such networks. CSL delivers browser-based assessments and other learning materials to thousands of students at the University of Auckland. This type of demand requires more flexible schemes for the management of the network. In the framework proposed, most of the link management information will be kept in a MIB in the network and a very simple MIB will be maintained in the thin client. The MIB in the network is accessible to the network management application, and a lightweight protocol is proposed for updating of the network MIB using an agent at the thin client.     

Identification of the female-produced sex pheromone of the scarab beetle,Hoplia equina

Hoplia equina LeConte (Coleoptera: Scarabaeidae: Melolonthinae) is a beetle pest of cranberry beds in Massachusetts. Larvae feed on the roots of the cranberry plant, reducing yield as well as vine density. The female sex pheromone was identified as 2-tetradecanone. There were eight compounds found in the airborne volatiles collected from females that elicited antennal responses from males. Of the eight compounds tested (nonanal, decanal, dodecanal, 2-dodecanone, 2-tridecanone, 2-tetradecanone, 2-pentadecanone, and 2-hexadecanone), 2-tetradecanone was the only one that attracted male beetles in the field. Combining any of the other seven antennally active compounds with 2-tetradecanone did not increase male capture.     

A priority queue in which initialization and queue operations takeO(loglogD) time

Many computer algorithms have embedded in them a subalgorithm called a priority queue which produces on demand an element of extreme priority among elements in the queue. Queues on unrestricted priority domains have a running time of (nlogn) for sequences ofn queue operations. We describe a simple priority queue over the priority domain {1,,N} in which initialization, insertion, and deletion takeO(loglogD) time, whereD is the difference between the next lowest and next highest priority elements in the queue. In the case of initialization,D=(N). Finding a least element, greatest element, and the neighbor in priority order of some specified element take constant time. We also consider dynamic space allocation for the data structures used. Space can be allocated in blocks of size (N ^1/p ), for small integerp. This research was supported by the National Science Foundation under grants MCS 77-21092 and MCS 80-002684.     

Texture analysis of poly-adenylated mRNA staining following global brain ischemia and reperfusion

Texture analysis provides a means to quantify complex changes in microscope images. We previously showed that cytoplasmic poly-adenylated mRNAs form mRNA granules in post-ischemic neurons and that these granules correlated with protein synthesis inhibition and hence cell death. Here we utilized the texture analysis software MaZda to quantify mRNA granules in photomicrographs of the pyramidal cell layer of rat hippocampal region CA3 around 1 h of reperfusion after 10 min of normothermic global cerebral ischemia. At 1 h reperfusion, we observed variations in the texture of mRNA granules amongst samples that were readily quantified by texture analysis. Individual sample variation was consistent with the interpretation that animal-to-animal variations in mRNA granules reflected the time-course of mRNA granule formation. We also used texture analysis to quantify the effect of cycloheximide, given either before or after brain ischemia, on mRNA granules. If administered before ischemia, cycloheximide inhibited mRNA granule formation, but if administered after ischemia did not prevent mRNA granulation, indicating mRNA granule formation is dependent on dissociation of polysomes. We conclude that texture analysis is an effective means for quantifying the complex morphological changes induced in neurons by brain ischemia and reperfusion.     

Factorization of multipliers in passivity and IQC analysis

Multipliers are often used to find conditions for the absolute stability of Lur’e systems. They can be used either in conjunction with passivity theory or within the more recent framework of integral quadratic constraints (IQCs). We compare the use of multipliers in both approaches. Passivity theory requires that the multipliers have a canonical factorization and it has been suggested in the literature that this represents an advantage of the IQC theory. We consider sufficient conditions on the nonlinearity class for the associated multipliers to have a canonical factorization.