Results for “Reference atlas” — Page 29

PubMed2001

Modified Talairach landmarks.

BACKGROUND: Brain atlas-assisted operations, such as targeting in stereotactic and functional neurosurgery, localisation analysis and metanalysis in human brain mapping, or structure segmentation and labelling in neuroradiology, highly depend on the accurate localisation of the landmarks used for atlas-to-data registration. One of practical and widely used registration methods is the Talairach proportional grid system transformation based on the Talairach landmarks. However, there are several problems associated with the original Talairach landmarks. In the Talairach-Tournoux brain atlas, some Talairach landmarks are not available and locations of others contradict their definitions. When dealing with patient-specific data, the definitions of the Talairach landmarks are not constructive enough or make their identification time consuming. Moreover, there is an inconsistency between the Talairach landmarks and Talairach grid. METHOD: The modified Talairach landmarks, conceptually equivalent to the original Talairach landmarks, are introduced here. They have several advantages and overcome some limitations of the original Talairach landmarks. Three various intercommissural distances are defined: central, internal, and tangential, and the formulas determining their lengths and errors associated are derived. An efficient method for calculating the modified cortical landmarks is proposed. FINDINGS: The internal intercommissural distance is the closest to the original Talairach intercommissural distance. Its relative intercommissural error is only 0.5%, as opposed to the central and tangential intercommissural distances resulting in high (about 10%) relative intercommissural errors. On the other hand, the internal and central intercommissural distances result in a high maximum displacement error at cortex amounting to about 11 mm while the tangential intercommissural distance gives only 1 mm error. The sensitivity of the internal intercommissural distance to the actual location of the intercommissural plane is high reaching above 10%. On the other hand, the sensitivity of the central intercommissural distance is below 0.5%. Each of the Talairach cortical landmarks needs three coordinates for its identification that requires the availability of two two-dimensional projections, the generation and analysis of which is computationally expensive. A modified cortical landmark is identified on a single, one-dimensional projection. INTERPRETATION: The modified Talairach landmarks facilitate the rapid and automated calculation of the Talairach transformation and give more flexibility in their use for specific applications. In stereotactic and functional neurosurgery, the internal intercommissural distance is the most suitable to provide a high accuracy for subcortical structures. In localisation analysis in human brain mapping research, a high accuracy has to be achieved at the cortex and the tangential intercommissural line is superior. Human brain mapping metanalysis may benefit from the use of the central intercommissural distance minimising errors due to the intercommissural plane positioning. In neuroradiology, a high accuracy is required both for subcortical and cortical structures and the tangential intercommissural line should be used.

Anthropometry↗

PubMedDate not supplied

Knowing, mapping and understanding St. Lawrence biodiversity, with special emphasis on bird assemblages.

Environment Canada and the Québec Department of the Environment, partners in the St Lawrence Vision 2000 Action Plan, set out to prepare a compendium of knowledge of the flora and fauna of the St Lawrence and to identify potential conservation sites. The resulting Portrait is an Internet site that presents the current knowledge base of the river's ecological and biological diversity (http://lavoieverte.qc.ec.gc.ca/faune/biodiv/index.html). The Portrait provides information on over 5,000 species of flora and fauna. On the website, you will find a detailed ecological analysis of the richness, rarity and vulnerability of several broad groups of plant and animal species. Furthermore, you will find a list of species for each of the 700 survey units and a distribution map for 2,500 species recorded along the St Lawrence., in atlas form, along with a detailed conservation plan. The plan encompasses the most unique and heterogeneous landscapes of the St Lawrence, some of which have no protection at present. The Portrait provides an overview of the sites that are currently protected by public agencies and private-sector organisations and identifies new sites of interest for conserving biodiversity and protecting species at risk. This paper exposes the content of this extensive compendium on the biodiversity of the St. Lawrence. For conciseness, it presents some of the analyses conducted on birds to illustrate a few of the analytical approaches that were used. Then, the information on species richness and concentration areas for priority species of vascular plants, breeding birds and herpetofauna will serve to identify the terrestrial sites of significance for biodiversity. Finally, a similar approach having been applied to the aquatic environnement, we will conclude with a conservation plan that identifies the terrestrial and aquatic ecosystems, and the geographic sites where the most important elements of St. Lawrence biodiversity are concentrated. Our analysis of the biodiversity of the most thoroughly studied taxa of the St. Lawrence clearly shows the importance of wetlands, particularly those located at the mouths of rivers or within archipelagos or delta complexes, such as the groups of islands and channels found at both ends of the Montreal Archipelago. These aquatic landscapes are sites of intense biological production, combining in a small geographical area spawning, nursery and feeding grounds for a large number of fish species and breeding, rearing and foraging areas for aquatic birds. Variable flooding conditions, associated with seasonal flooding or daily tidal fluctuations, create a complex mosaic of wetland and aquatic habitats. Although wetlands occupy only a small area in comparison with terrestrial habitats, they support a large number of rare plant and animal species in relation to their size. At present, 10% of the vascular flora and 27% of the herpetofauna of the St. Lawrence are at risk. In the case of reptiles and amphibians, the situation is especially worrisome because nearly all of the most threatened species live in a narrow band along the river corridor. Not only is this the sector that is under the greatest pressure from human development, very little public land remains here, making it difficult to create protected areas. Increased participation by non-governmental organisations and individuals, through private stewardship arrangements, is an essential precondition for completing the network of conservation areas in this part of the St. Lawrence. Along the estuary and the Gulf, habitat integrity has not been affected as much by the expansion of Québec's human population. This is a vast territory, and sites have been identified with a view to making up for the deficiencies in the present network of protected sites in terms of representing biodiversity.

Animals↗