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A need exists to noninvasively assess renal interstitial fibrosis, a common process to all kidney diseases and predictive of renal prognosis. In this translational study, Magnetic Resonance Imaging (MRI) T1 mapping and a new segmented Diffusion-Weighted Imaging (DWI) technique, for Apparent Diffusion Coefficient (ADC), were first compared to renal fibrosis in two well-controlled animal models to assess detection limits. Validation against biopsy was then performed in 33 kidney allograft recipients (KARs). Predictive MRI indices, ΔT1 and ΔADC (defined as the cortico-medullary differences), were compared to histology. In rats, both T1 and ADC correlated well with fibrosis and inflammation showing a difference between normal and diseased kidneys. In KARs, MRI indices were not sensitive to interstitial inflammation. By contrast, ΔADC outperformed ΔT1 with a stronger negative correlation to fibrosis (R(2) = 0.64 against R(2) = 0.29 p

Die Ausbildung der Cr2O3-Schicht auf Ni20Cr ist bei 850°C in H2/H2O (p(O2) = 10−19 bar) unter gleichzeitiger Kriechverformung an Flachproben untersucht worden. Die Schadigung der schutzenden Oxidschicht durch Risse wurde in Abhangigkeit von der Verformungs-geschwindigkeit und der Dehnung des Grundwerkstoffes beobachtet. Zur Trennung des Einflusses der plastischen Verformung der Oxidschicht und der Risheilung wurden erganzend voroxidierte Proben in reiner Ar-Atmosphare verformt. Unterhalb der Kriechgeschwindigkeit von 10−9s−1 werden keine Risse mehr festgestellt. Bei < etwa 3 × 10−8s−1 treten Risse nur oberhalb Legierungskorngrenzen auf, bei hoheren liegen sie auch in Bereichen uber den Legierungskornern. Fur > etwa 3 × 10−8s−1 hangt die Risdichte nicht mehr von ab. Aus der unterschiedlichen Schadigung der Oxidschicht in den beiden Gasatmospharen kann geschlossen werden, das bei zwischen 10−9s−1 und 10−7s−1 neben einer Plastizitat der Oxidschicht insbesondere die Risheilung mesbare Einflusse bei der Summe der Risoffnungen hervorruft, mit steigendem wird der Beitrag der Plastizitat vernachlassigbar klein. Influence of creep deformation on the formation of the oxide layer on the high temperature alloy Ni20Cr The formation of the Cr2O3-layer on Ni20Cr has been investigated at 850°C in H2/H2O (p(O2) = 10−19 bar) under simultaneous creep deformation with flat samples. The damage of the protecting oxide layer by cracks has been observed in dependence on deformation rate and strain. For additional information about the influence of the plastic deformation of the oxide layer and the healing of the cracks, preoxidized samples have been deformed in pure Ar-atmosphere. At strain rates below 10−9s−1 cracks cannot be observed. When strain rates < about 3 × 10−8s−1 are applied, cracks occur only above grain boundaries of the alloy, at higher strain rates they also lie in regions above the grains of the alloy. For > about 3 × 10−8s−1 the crack density depends no more on but only on strain . The different damages of the oxide layers in the two atmospheres allow the conclusion, that at from 10−9s−1 to 10−7s−1 beside the plasticity of the oxide layer in particular the crack healing influences the sum of the crack openings measurably. With increasing strain rates the contribution of plasticity can be neglected.

The oxidation behavior of the Ni-base alloys IN 617, IN 713 LC, Ni20Cr, and Ni20Cr+Si has been investigated in the temperature range from 850°C to 1000°C in air and at low-oxygen partial pressure p(O2) (10−19 to 10−16 bar). With the exception of alloy IN 713 LC, the materials show no influence of p(O2) on the oxidation mechanisms and the kinetics. This result can be explained by the formation of a dense Cr2O3 layer, the growth rate of which is controlled by the Cr ion interstitial concentration in Cr2O3 at the phase boundary oxide/alloy and the mobility of Cr ions in Cr2O3. For the alloy IN 713 LC which develops a dense Al2O3 layer in air, a modified transition mechanism at low p(O2) leads to the formation of Cr2O3 at the surface and a strong internal oxidation of Al.