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  • 2000-2004  (2)
  • 1925-1929
  • Nuklearmedizin  (1)
  • bio-optical modelling  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Der Radiologe 40 (2000), S. 103-110 
    ISSN: 1432-2102
    Keywords: Schlüsselwörter ; Kardiale Bildgebung ; Angiographie ; Nuklearmedizin ; Magnetresonanztomographie ; Computertomographie ; Key word ; Cardiac imaging ; Angiography ; Nuclear imaging ; Magnetic resonance tomography ; Computed tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Purpose: Cardiac imaging includes determination of the size and structure of the cardiac chambers, valves, great vessels and the coronary arteries, chamber and valvular function, myocardial perfusion, viability and metabolism. Material and methods: Chest roentgenography, angiography, echocardiography and nuclear imaging are commonly used but computed tomography and magnetic resonance imaging also offer a promising potential. Results: Coronary angiography is the gold standard in assessing coronary anatomy. Fast CT technologies such as electron-beam and multi-row-CT are promising non-invasive imaging modalities in the assessment of coronary artery disease. With intravascular ultrasound early stages of coronary atherosclerosis can be detected. For the assessment of myocardial perfusion and viability as well as cardiac function, scintigraphic methods are widely accepted. However, MRI methods have also reached a high degree of accuracy. Evaluation of chamber and valvular function is, due to its wide availability, the field of echocardiography. Conclusions: In clinical routine chest roentgenography, angiography, echocardiography and nuclear imaging are well established. The value of computed tomography and magnetic resonance imaging in the evaluation of coronary artery disease, myocardial perfusion, viability and metabolism is yet to be defined.
    Notes: Zusammenfassung Zielsetzung: Anforderungen an die kardiale Bildgebung sind die Darstellung der Anatomie der Herzhöhlen, Herzklappen, Koronararterien und der großen Gefäße, Parameter der Ventrikel- und Klappenfunktion, der Myokardperfusion, Myokardvitalität und des myokardialen Stoffwechsels. Material und Methode: In der Bildgebung kommen neben den etablierten Standardverfahren wie Röntgen, Angiographie, Echokardiographie und nuklearmedizinischen Methoden auch neuere Verfahren der Computer- und Magnetresonanztomographie zum Einsatz. Ergebnisse: Die Koronarangiographie ist der Goldstandard in der Darstellung des gesamten Koronarsystems. In der Diagnostik der koronaren Herzerkrankung zeigen schnelle CT-Verfahren wie die Elektronenstrahltomographie (EBT) und die Mehrzeilendetektor-CT (MDCT) Vorteile gegenüber der Kernspintomographie. Frühstadien der koronaren Arteriosklerose können nur mit dem intravaskulären Ultraschall (IVUS) erkannt werden. Nuklearmedizinische Methoden sind in der Untersuchung der Myokardperfusion und -vitalität etabliert. Mit der MRT scheint eine qualitative und quantitative Bestimmung der regionalen Perfusion, Funktion und Vitalität möglich zu sein. Die Untersuchung der linksventrikulären Funktion und der Herzklappen ist die Domäne der Echokardiographie. Schlussfolgerung: In der klinischen Routine sind die Angiographie, Echokardiographie und die Nuklearmedizin etablierte Methoden. Der Stellenwert der Magnetresonanz- und Computertomographie in der Diagnostik der koronaren Herzerkrankung und der Herzfunktion, Perfusion und Vitaltät ist noch nicht definiert.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-9058
    Keywords: absorption ; bio-optical modelling ; pigments ; quantum yield ; water quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Primary productivity in marine waters is widely estimated by the measurements of 14C incorporation, the underwater light climate, and the absorption spectra of phytoplankton. In bio-optical models the quantum efficiency of carbon fixation derived from 14C incorporation rates, the photosynthetically absorbed radiation derived from the underwater light climate, and the phytoplankton absorption spectra are used to calculate time- and depth-integrated primary productivity. Due to the increased sensitivity of commercially available fluorometers, chlorophyll a in vivo fluorescence became a new tool to assess the photosynthetic activity of phytoplankton. Since fluorescence data yield only relative photosynthetic electron transport rates, a direct conversion into absolute carbon fixation rates is not possible. Here, we report a procedure how this problem can be adressed in freshwater phytoplankton. We adapted a marine bio-optical model to the freshwater situation and tested if this model yields realistic results when applied to a hypertrophic freshwater reservoir. Comparison of primary productivity derived from 14C incorporation to primary productivity derived from Chl a fluorescence showed that the conversion of fluorescence data into carbon fixation rates is still an unsolved problem. Absolute electron transport rates calculated from fluorescence data tend to overestimate primary production. We propose that the observed differences are caused mainly by neglecting the package effect of pigments in phytoplankton cells and by non-carbon related electron flow (e.g., nitrogen fixation). On the other hand, the 14C incorporation rates can be artificially influenced by "bottle effects", especially near the water surface, where photoinhibition, photorespiration, and Mehler reaction can play a major role.
    Type of Medium: Electronic Resource
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