Temat: quantitative reconstruction - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Historia rozwoju dwóch torfowisk mszarnych w Borach Tucholskich
Developmental history of two kettle-hole mires in Tuchola Pinewoods (N Poland)
Autorzy:: Lamentowicz, M.
Obremska, M.
Mitchell, Edward A.D.
Powiązania:: https://bibliotekanauki.pl/articles/2074410.pdf
Data publikacji:: 2006
Wydawca:: Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:: torfowisko
analiza palinologiczna
analiza ameb skorupkowych
analiza makroszczątków roślinnych
kettle-hole mire
Sphagnum mire
Testate amoebae
pollen
plant macrofossils
palaeohydrology
terrestrialization
weighted averaging
quantitative reconstruction
Opis:: Our research confirmed the value of kettle-hole mires for reconstructing Holocene environmental changes. The multi-proxy approach in which three palaeoecological methods were used (analyses of testate amoebae, plant macrofossils and pollen) improved the interpretation potential. We studied two Sphagnum mires situated in Tuchola Pinewoods (N Poland). In Tuchola mire 9000 years of environmental changes (groundwater level and pH) were recorded. Water table changes inferred from Tuchola mire show patterns similar to regional hydrological changes recorded in Polish lakes and mires as well as in other European sites. Jelenia Wyspa mire recorded changes in local vegetation and palaeohydrology during the last 1500 years. A rise in the groundwater table, caused by deforestation in the catchment area, allowed Sphagnum to expand. Consequently, the peatland evolved into an oligotrophic mire dominated by peat mosses. Approx. 200 years ago water pH increased and subsequently decreased, the lowest value being associated with the deforestation maximum. Furthermore, the planting of pine probably also caused an acidification of Jelenia Wyspa mire.
Źródło:: Przegląd Geologiczny; 2006, 54, 1; 76-80
0033-2151
Pojawia się w:: Przegląd Geologiczny
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: System matrix computation for iterative reconstruction algorithms in SPECT based on direct measurements
Autorzy:: Borys, D.
Szczucka-Borys, K.
Gorczewski, K.
Powiązania:: https://bibliotekanauki.pl/articles/907829.pdf
Data publikacji:: 2011
Wydawca:: Uniwersytet Zielonogórski. Oficyna Wydawnicza
Tematy:: SPECT
metoda iteracyjna
obrazowanie ilościowe
iterative reconstruction
quantitative imaging
Opis:: A method for system matrix calculation in the case of iterative reconstruction algorithms in SPECT was implemented and tested. Due to a complex mathematical description of the geometry of the detector set-up, we developed a method for system matrix computation that is based on direct measurements of the detector response. In this approach, the influence of the acquisition equipment on the image formation is measured directly. The objective was to obtain the best quality of reconstructed images with respect to specified measures. This is indispensable in order to be able to perform reliable quantitative analysis of SPECT images. It is also especially important in non-hybrid gamma cameras, where not all physical processes that disturb image acquisition can be easily corrected. Two experiments with an 131I point source placed at different distances from the detector plane were performed allowing the detector response to be acquired as a function of the point source distance. An analytical Gaussian function was fitted to the acquired data in both the one- and the two-dimensional case. A cylindrical phantom filled with a water solution of 131I containing a region of 'cold' spheres as well as a uniform solution (without any spheres) was used to perform algorithm evaluation. The reconstructed images obtained by using four different of methods system matrix computation were compared with those achieved using reconstruction software implemented in the gamma camera. The contrast of the spheres and uniformity were compared for each reconstruction result and also with the ranges of those values formulated by the AAPM (American Association of Physicists in Medicine). The results show that the implementation of the OSEM (Ordered Subsets Expectation Maximization) algorithm with a one-dimensional fit to the Gaussian CDR (Collimator-Detector Response) function provides the best results in terms of adopted measures. However, the fit of the two-dimensional function also gives satisfactory results. Furthermore, the CDR function has the potential to be applied to a fully 3D OSEM implementation. The lack of the CDR in system matrix calculation results in a very noisy image that cannot be used for diagnostic purposes.
Źródło:: International Journal of Applied Mathematics and Computer Science; 2011, 21, 1; 193-202
1641-876X
2083-8492
Pojawia się w:: International Journal of Applied Mathematics and Computer Science
Dostawca treści:: Biblioteka Nauki

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