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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The visual computer 14 (1998), S. 83-94 
    ISSN: 1432-2315
    Keywords: Key words: Volume visualization ; Scientific visualization ; Medical imaging ; Shadow Z-buffer ; Shadow map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Z -buffer technique for fast and efficient shadow generation. Volumetric data contain information about the grid points only. Such data do not provide surface information that could be projected immediately onto the shadow map. To solve this problem, we have implemented two techniques. The first uses a modified adaptive version of the well-known marching cubes algorithm for the special characteristics of medical data sets. The algorithm uses material properties for a precise representation of object boundaries, generating volumetric objects quickly and effectively. There are two representations of the same data set: we use a view-independent approximation to display shadows and the original representation of the volume for object visualization in full precision. The second algorithm uses a ray-tracing approach to create shadow maps. The same routine is used for object rendering, but is restricted to depth-value generation. Semitransparent objects are handled by storing an intensity profile in addition to the depth value.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-136X
    Keywords: Arterioles ; Vasomotion ; Angiotensin II ; Vasopressin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of intracerebroventricular (icv) injections of 10 ng angiotensin II (ANG II) on mean arteriolar diameter and spontaneous arteriolar vasomotion were studied in subcutaneous tissue of conscious, restrained hamsters, using the skin fold window chamber preparation. Angiotensin II caused a significant decrease in mean arteriolar diameter which was associated with a significant elevation in the amplitude of vasomotion. The frequency of vasomotion did not change significantly. The central ANG II-induced effects on arteriolar vasomotion were not significantly altered by continuous intravenous (iv) infusion of hexamethonium (1 mg · kg−1 · min−1). In contrast, iv bolus injection of the vascular vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP (10 μg · kg−1) 5 min prior to icv injection of ANG II significantly attenuated the effects of the neuropeptide on mean arteriolar diameter and the amplitude of vasomotion. These data indicate that central ANG II stimulation enhances arteriolar vasomotion in peripheral subcutaneous tissue of conscious hamsters and that this effect may be mediated by release of vasopressin.
    Type of Medium: Electronic Resource
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