Artifact quantification of venous stents in the MRI environment: Differences between braided and laser-cut designs.

PURPOSE: To quantify B0- and B1-induced imaging artifacts of braided venous stents and to compare the artifacts to a set of laser-cut stents used in venous interventions. METHODS: Three prototypes of braided venous stents with different geometries were tested in vitro. B0 field distortion maps were measured via the frequency shift Δf using multi-echo imaging. B1 distortions were quantified using the double angle method. The relative amplitudes B1rel were calculated to compare the intraluminal alteration of B1. Measurements were repeated with the stents in three different orientations: parallel, diagonal and orthogonal to B0. RESULTS: At 1.5 T, the braided stents induced a maximum frequency shift of Δfx<100Hz. Signal voids were limited to a distance of 2 mm to the stent walls at an echo time of 3 ms. No substantial difference in the B0 field distortions was seen between laser-cut and braided venous stents. B1rel maps showed strongly varying distortion patterns in the braided stents with the mean intraluminal B1rel ranging from 63±18% in prototype 1 to 98±38% in prototype 2. Compared to laser-cut stents the braided stents showed a 5 to 9 times higher coefficient of variation of the intraluminal B1rel. CONCLUSION: Braided venous stent prototypes allow for MR imaging of the intraluminal area without substantial signal voids due to B0-induced artifacts. Whereas B1 is attenuated homogeneously in laser-cut stents, the B1 distortion in braided stents is more inhomogeneous and shows areas with enhanced amplitude. This could potentially be used in braided stent designs for intraluminal signal amplification.

Publisher Correction: Real-time magnetic resonance imaging - guided coronary intervention in a porcine model.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Real-time magnetic resonance imaging - guided coronary intervention in a porcine model.

X-ray fluoroscopy is the gold standard for coronary diagnostics and intervention. Magnetic resonance imaging is a radiation-free alternative to x-ray with excellent soft tissue contrast in arbitrary slice orientation. Here, we assessed real-time MRI-guided coronary interventions from femoral access using newly designed MRI technologies. Six Goettingen minipigs were used to investigate coronary intervention using real-time MRI. Catheters were custom-designed and equipped with an active receive tip-coil to improve visibility and navigation capabilities. Using modified standard clinical 5 F catheters, intubation of the left coronary ostium was successful in all animals. For the purpose of MR-guided coronary interventions, a custom-designed 8 F catheter was used. In spite of the large catheter size, and therefore limited steerability, intubation of the left coronary ostium was successful in 3 of 6 animals within seconds. Thereafter, real-time guided implantation of a non-metallic vascular scaffold into coronary arteries was possible. This study demonstrates that real-time MRI-guided coronary catheterization and intervention via femoral access is possible without the use of any contrast agents or radiation, including placement of non-metallic vascular scaffolds into coronary arteries. Further development, especially in catheter and guidewire technology, will be required to drive forward routine MR-guided coronary interventions as an alternative to x-ray fluoroscopy.

Radial MRI with variable echo times: reducing the orientation dependency of susceptibility artifacts of an MR-safe guidewire.

OBJECTIVES: Guidewires are indispensable tools for intravascular MR-guided interventions. Recently, an MR-safe guidewire made from a glass-fiber/epoxy compound material with embedded iron particles was developed. The size of the induced susceptibility artifact, and thus the guidewire's visibility, depends on its orientation against B 0. We present a radial acquisition scheme with variable echo times that aims to reduce the artifact's orientation dependency. MATERIALS AND METHODS: The radial acquisition scheme uses sine-squared modulated echo times depending on the physical direction of the spoke to balance the susceptibility artifact of the guidewire. The acquisition scheme was studied in simulations based on dipole fields and in phantom experiments for different orientations of the guidewire against B 0. The simulated and measured artifact widths were quantitatively compared. RESULTS: Compared to acquisitions with non-variable echo times, the proposed acquisition scheme shows a reduced angular variability. For the two main orientations (i.e., parallel and perpendicular to B 0), the ratio of the artifact widths was reduced from about 2.2 (perpendicular vs. parallel) to about 1.2 with the variable echo time approach. CONCLUSION: The reduction of the orientation dependency of the guidewire's artifact via sine-squared varying echo times could be verified in simulations and measurements. The more balanced artifact allows for a better overall visibility of the guidewire.

Differences in centromere positioning of cycling and postmitotic human cell types.

Centromere positioning in human cell nuclei was traced in non-cycling peripheral blood lymphocytes (G0) and in terminally differentiated monocytes, as well as in cycling phytohemagglutinin-stimulated lymphocytes, diploid lymphoblastoid cells, normal fibroblasts, and neuroblastoma SH-EP cells using immunostaining of kinetochores, confocal microscopy and three-dimensional image analysis. Cell cycle stages were identified for each individual cell by a combination of replication labeling with 5-bromo-2'-deoxyuridine and immunostaining of pKi67. We demonstrate that the behavior of centromeres is similar in all cell types studied: a large fraction of centromeres are in the nuclear interior during early G1; in late G1 and early S phase, centromeres shift to the nuclear periphery and fuse in clusters. Peripheral location and clustering of centromeres are most pronounced in non-cycling cells (G0) and terminally differentiated monocytes. In late S and G2, centromeres partially decluster and migrate towards the nuclear interior. In the rather flat nuclei of adherently growing fibroblasts and neuroblastoma cells, kinetochores showed asymmetrical distributions with preferential kinetochore location close either to the bottom side of the nucleus (adjacent to the growth surface) or to the nuclear upper side. This asymmetrical distribution of centromeres is considered to be a consequence of chromosome arrangement in anaphase rosettes.

Inhibition of the plastidic ATP/ADP transporter protein primes potato tubers for augmented elicitation of defense responses and enhances their resistance against Erwinia carotovora.

Tubers of transgenic potato (Solanum tuberosum) plants with decreased activity of the plastidic ATP/ADP transporter AATP1 display reduced levels of starch, modified tuber morphology, and altered concentrations of primary metabolites. Here, we demonstrate that the spontaneous production of hydrogen peroxide, the endogenous content of salicylic acid, and the levels of mRNAs of various defense-related genes are similar in tuber discs of wild-type and AATP1(St) antisense plants. However, upon challenging the tissue with fungal elicitors or culture supernatants of the soft rot-causing pathogen Erwinia carotovora subsp. atroseptica, the AATP1(St) antisense tubers exhibit highly potentiated activation of defense responses when compared with wild-type tissue. The augmented defense responses comprise enhanced accumulation of transcripts of five defense-related genes (beta-1,3-GLUCANASE B2 and A1, CHITINASE B3 and A2, and Phe AMMONIA-LYASE) and enhanced elicitation (up to 21-fold) of the early hydrogen peroxide burst. The potentiated activation of cellular defense responses in AATP1(St) antisense tubers is not accompanied by a precedent increase in endogenous salicylic acid levels, but is associated with a strongly enhanced resistance of the tissue to E. carotovora. From these results, we conclude that inhibition of primary metabolic reactions induces a primed state that sensitizes the potato tubers for improved elicitation of various cellular defense responses, which likely contribute to enhanced E. carotovora resistance.

Establishment of introduced antagonistic bacteria in the rhizosphere of transgenic potatoes and their effect on the bacterial community.

In a field release experiment, rifampicin resistant mutants of two antagonistic plant-associated bacteria were used for seed tuber inoculation of transgenic T4 lysozyme expressing potatoes, transgenic control potatoes and non-transgenic parental potatoes. The T4 lysozyme tolerant Pseudomonas putida QC14-3-8 was originally isolated from the tuber surface (geocaulosphere) of T4 lysozyme producing plants and showed in vitro antibacterial activity to the bacterial pathogen Erwinia carotovora ssp. atroseptica. The T4 lysozyme sensitive Serratia grimesii L16-3-3 was originally isolated from the rhizosphere of parental potatoes and showed in vitro antagonism toward the plant pathogenic fungus Verticillium dahliae. The establishment of the inoculated bacteria in the rhizosphere and geocaulosphere of the different plant lines was monitored over one growing season to assess the effect of T4 lysozyme produced by transgenic potato plants on the survival of both inoculants. Both introduced isolates were able to colonize the rhizo- and geocaulosphere of transgenic plants and non-transgenic parental plants, and established in the rhizosphere at levels of ca. log(10) 5 colony forming units g(-1) fresh weight of root. During flowering of plants, significantly more colony counts of the T4 lysozyme tolerant P. putida were recovered from transgenic T4 lysozyme plants than from the transgenic control and the parental line. At this time, the highest level of T4 lysozyme (% of total soluble protein) was detected. Effects of the inoculants on the indigenous microbial community were monitored by analysis of PCR-amplified fragments of the 16S rRNA genes of the whole bacterial community after separation by denaturing gradient gel electrophoresis (DGGE). At any sampling time, the DGGE pattern of rhizosphere and geocaulosphere communities did not show differences between the inoculated and non-inoculated potatoes. Neither of the introduced strains became a dominant member of the bacterial community. This work was the first approach to assess the establishment of plant growth promoting rhizobacteria and potential biocontrol agents on transgenic plants.