Ex Vivo Perfusion-Simulation Measurements of Microbubbles as a Scattering Contrast Agent for Grating-Based X-Ray Dark-Field Imaging.

The investigation of dedicated contrast agents for x-ray dark-field imaging, which exploits small-angle scattering at microstructures for contrast generation, is of strong interest in analogy to the common clinical use of high-atomic number contrast media in conventional attenuation-based imaging, since dark-field imaging has proven to provide complementary information. Therefore, agents consisting of gas bubbles, as used in ultrasound imaging for example, are of particular interest. In this work, we investigate an experimental contrast agent based on microbubbles consisting of a polyvinyl-alcohol shell with an iron oxide coating, which was originally developed for multimodal imaging and drug delivery. Its performance as a possible contrast medium for small-animal angiography was examined using a mouse carcass to realistically consider attenuating and scattering background signal. Subtraction images of dark field, phase contrast and attenuation were acquired for a concentration series of 100%, 10% and 1.3% to mimic different stages of dilution in the contrast agent in the blood vessel system. The images were compared to the gold-standard iodine-based contrast agent Solutrast, showing a good contrast improvement by microbubbles in dark-field imaging. This study proves the feasibility of microbubble-based dark-field contrast-enhancement in presence of scattering and attenuating mouse body structures like bone and fur. Therefore, it suggests a strong potential of the use of polymer-based microbubbles for small-animal dark-field angiography

Measurement of pure PVA bubbles contrast agent.

<p>Grey value scaling is given in brackets. The first column shows the same image with the tube filled with water for three different contrast modalities: (a) transmission [0, 0.9], (d) differential phase [</p><p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (g) dark field [0, 1.0]. The second column shows the same image with the tube filled with pure PVA-microbubbles suspension in three different modalities: (b) transmission [0, 0.9], (e) differential phase [<p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (h) dark field [0, 1.0]. The third column shows the subtraction of the image with contrast agent (second column) from the image with water (first column) for three different contrast modalities: (c) transmission [0, 0.04], (f) differential phase [<p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (i) dark field [0, 0.3].<p></p

Measurement of pure Solutrast contrast agent.

<p>Grey value scaling is given in brackets. The first column shows the same image with the tube filled with water for three different contrast modalities: (a) transmission [0, 0.9], (d) differential phase [</p><p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (g) dark field [0, 1.0]. The second columns shows the same image with the tube filled with pure Solutrast in three different modalities: (b) transmission [0, 0.9], (e) differential phase [<p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (h) dark field [0, 1.0]. The third column shows the subtraction of the image with contrast agent (second column) from the image with water (first column) for three different contrast modalities: (c) transmission [0, 0.2], (f) differential phase [<p></p><p></p><p><mo>−</mo></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>, <p></p><p></p><p></p><p><mi>π</mi><mn>2</mn></p><p></p><p></p><p></p>], (i) dark field [0, 0.13].<p></p

Dark-field signal subtraction and multimodal images.

<p>Left column: dark-field signal subtraction images. Right column: threshold-limited, filtered superimposition of the dark-field subtraction image (in color) on the respective original transmission image (grey values range: [0, 0.9]). (a)-(b) 100% PVA microbubbles suspension, (c)-(d) 10% PVA microbubbles suspension, (e)-(f) 1.3% PVA microbubbles suspension.</p

Sample positioning and preliminary imaging of PVA contrast agent.

<p>(a) Mouse carcass fixated on the animal bed of a preclinical phase-contrast and dark-field CT scanner. A plastic tube was surgically inserted underneath the peritoneum and some spare volume of the tube for flushing the contrast agent downwards was attached to the right side of the mouse. (b) Transmission image of plastic vials containing water (left) and PVA microbubbles (right). Grey values ranging from 0 to 0.35. (c) Dark-field image of plastic vials containing water (left) and PVA microbubbles (right). Grey values ranging from 0 to 0.75. (d) Visible-light brightfield microscopy image of PVA microbubbles.</p

Transmission signal subtraction images.

<p>Left column: transmission signal subtraction images. Right column: threshold-limited, filtered superimposition of the transmission subtraction image (in color) on the respective original transmission image (grey values range: [0, 0.9]). (a)-(b) 100% Solutrast, (c)-(d) 10% Solutrast.</p

Transmission electron microscopy image of a PVA microbubble.

<p>The bubble is coated with iron-oxide nanoparticles, manufactured by Surflay nanotec GmbH, Berlin, Germany. Image courtesy Johan Härmark, School of Technology and Health, KTH Royal Institute of Technology, Sweden.</p

Comparing naturalized alien plants and recipient habitats across an east–west gradient in the Mediterranean Basin

Aim To investigate alien plant species invasion levels in different habitats and alien species traits by comparing the naturalized flora in different areas of the same biogeographical region. Location Spain, Italy, Greece and Cyprus. Methods Comparison of floristic composition, species traits and recipient habitats of naturalized alien neophytes across an east–west gradient comprising four countries in the European Mediterranean basin. Results A total of 782 naturalized neophytes were recorded; only 30 species were present in all four countries. Although floristic similarity is low, the four alien floras share the same patterns of growth form (mostly herbs), life cycle (mostly perennials) and life form (mostly therophytes, hemicryptophytes and phanerophytes). The majority of the recipient habitats were artificial. Wetlands were the natural habitats, with the highest numbers of naturalized species. Floristic similarity analyses revealed: (1) the highest floristic similarity between Italy and Spain, both of which were more similar to Greece than to Cyprus; (2) two groups of floristic similarity between habitat categories in each country (Greece–Cyprus and Italy–Spain); (3) a higher degree of homogenization in the plant assemblages in different habitats in Greece and Cyprus and a lower degree of homogenization in those in Italy and Spain; and (4) a higher degree of homogenization in artificial and natural fresh-water habitats than in the other natural habitats. Main conclusions The floristic similarity of naturalized neophytes between the four countries is low, although the overall analysis indicates that the western group (Italy–Spain) is separated from the eastern group (Greece–Cyprus). Similar patterns emerged regarding the life-history traits and recipient habitats. The artificial habitats and the natural wet habitats are those that are invaded most and display the greatest homogenization in all four countries. Coastal habitats display a lower degree of homogenization but a high frequency of aliens. Dry shrubs and rocky habitats display a lower degree of homogenization and a low frequency of aliensPeer reviewe

Dietary effects on fatty acid composition in muscle tissue of juvenile European eel, Anguilla anguilla (L.)

The role of intracontinental migration patterns of European eel (Anguilla anguilla) receives more and more recognition in both ecological studies of the European eel and possible management measures, but small-scale patterns proved to be challenging to study. We experimentally investigated the suitability of fatty acid trophic markers to elucidate the utilization of feeding habitats. Eight groups of juvenile European eels were fed on eight different diets in a freshwater recirculation system at 20°C for 56 days. Three groups were fed on freshwater diets (Rutilus rutilus, Chironomidae larvae, and Gammarus pulex) and four groups were reared on diets of a marine origin (Clupea harengus, Crangon crangon, Mysis spec., and Euphausia superba) and one on commercial pellets used in eel aquaculture. Fatty acid composition (FAC) of diets differed significantly with habitat. FAC of eel muscle tissue seemed to be rather insensitive to fatty acids supplied with diet, but the general pattern of lower n3:n6 and EPA:ARA ratios in freshwater prey organisms could be traced in the respective eels. Multivariate statistics of the fatty acid composition of the eels resulted in two distinct groups representing freshwater and marine treatments. Results further indicate the capability of selectively restraining certain fatty acids in eel, as e.g. the n3:n6 ratio in all treatments was <4, regardless of dietary n3:n6. In future studies on wild eel, these measures can be used to elucidate the utilization of feeding habitats of individual European eel