Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study

OBJECTIVE Cochlear implants (CIs) are standard treatment for postlingually deafened individuals and prelingually deafened children. This human cadaver study evaluated diagnostic usefulness, image quality and artifacts in 1.5T and 3T magnetic resonance (MR) brain scans after CI with a removable magnet. METHODS Three criteria (diagnostic usefulness, image quality, artifacts) were assessed at 1.5T and 3T in five cadaver heads with CI. The brain magnetic resonance scans were performed with and without the magnet in situ. The criteria were analyzed by two blinded neuroradiologists, with focus on image distortion and limitation of the diagnostic value of the acquired MR images. RESULTS MR images with the magnet in situ were all compromised by artifacts caused by the CI. After removal of the magnet, MR scans showed an unequivocal artifact reduction with significant improvement of the image quality and diagnostic usefulness, both at 1.5T and 3T. Visibility of the brain stem, cerebellopontine angle, and parieto-occipital lobe ipsilateral to the CI increased significantly after magnet removal. CONCLUSIONS The results indicate the possible advantages for 1.5T and 3T MR scanning of the brain in CI carriers with removable magnets. Our findings support use of CIs with removable magnets, especially in patients with chronic intracranial pathologies.

Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice–bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica.

Chow–Liu trees are sufficient predictive models for reproducing key features of functional networks of periictal EEG time-series

Seizure freedom in patients suffering from pharmacoresistant epilepsies is still not achieved in 20–30% of all cases. Hence, current therapies need to be improved, based on a more complete understanding of ictogenesis. In this respect, the analysis of functional networks derived from intracranial electroencephalographic (iEEG) data has recently become a standard tool. Functional networks however are purely descriptive models and thus are conceptually unable to predict fundamental features of iEEG time-series, e.g., in the context of therapeutical brain stimulation. In this paper we present some first steps towards overcoming the limitations of functional network analysis, by showing that its results are implied by a simple predictive model of time-sliced iEEG time-series. More specifically, we learn distinct graphical models (so called Chow–Liu (CL) trees) as models for the spatial dependencies between iEEG signals. Bayesian inference is then applied to the CL trees, allowing for an analytic derivation/prediction of functional networks, based on thresholding of the absolute value Pearson correlation coefficient (CC) matrix. Using various measures, the thus obtained networks are then compared to those which were derived in the classical way from the empirical CC-matrix. In the high threshold limit we find (a) an excellent agreement between the two networks and (b) key features of periictal networks as they have previously been reported in the literature. Apart from functional networks, both matrices are also compared element-wise, showing that the CL approach leads to a sparse representation, by setting small correlations to values close to zero while preserving the larger ones. Overall, this paper shows the validity of CL-trees as simple, spatially predictive models for periictal iEEG data. Moreover, we suggest straightforward generalizations of the CL-approach for modeling also the temporal features of iEEG signals.

Flux control of sulphate assimilation in Arabidopsis thaliana : adenosine 5′-phosphosulphate reductase is more susceptible than ATP sulphurylase to negative control by thiols

The effect of externally applied l-cysteine and glutathione (GSH) on ATP sulphurylase and adenosine 5′-phosphosulphate reductase (APR), two key enzymes of assimilatory sulphate reduction, was examined in Arabidopsis thaliana root cultures. Addition of increasing l-cysteine to the nutrient solution increased internal cysteine, γ-glutamylcysteine and GSH concentrations, and decreased APR mRNA, protein and extractable activity. An effect on APR could already be detected at 0.2 mm l-cysteine, whereas ATP sulphurylase was significantly affected only at 2 mm l-cysteine. APR mRNA, protein and activity were also decreased by GSH at 0.2 mm and higher concentrations. In the presence of l-buthionine-S, R-sulphoximine (BSO), an inhibitor of GSH synthesis, 0.2 mm l-cysteine had no effect on APR activity, indicating that GSH formed from cysteine was the regulating substance. Simultaneous addition of BSO and 0.5 mm GSH to the culture medium decreased APR mRNA, enzyme protein and activity. ATP sulphurylase activity was not affected by this treatment. Tracer experiments using 35SO42– in the presence of 0.5 mm l-cysteine or GSH showed that both thiols decreased sulphate uptake, APR activity and the flux of label into cysteine, GSH and protein, but had no effect on the activity of all other enzymes of assimilatory sulphate reduction and serine acetyltransferase. These results are consistent with the hypothesis that thiols regulate the flux through sulphate assimilation at the uptake and the APR step. Analysis of radioactive labelling indicates that the flux control coefficient of APR is more than 0.5 for the intracellular pathway of sulphate assimilation. This analysis also shows that the uptake of external sulphate is inhibited by GSH to a greater extent than the flux through the pathway, and that the flux control coefficient of APR for the pathway, including the transport step, is proportionately less, with a significant share of the control exerted by the transport step.

Hydrolytic behaviour of mono-and dithiolato-bridged dinuclear arene ruthenium complexes and their interactions with biological ligands

The hydrolysis and the reactivity of two dinuclear p-cymene ruthenium monothiolato complexes, [(η6-p-MeC6H4Pri)2Ru2Cl2(µ-Cl)(µ-S-m-9-B10C2H11)] (1) and [(η6-p-MeC6H4Pri)2¬Ru2Cl2(µ-Cl)¬(µ-S¬CH2-p-C6H4-NO2)] (2), and of two dinuclear p-cymene ruthenium dithiolato complexes, [(η6-p-MeC6H4Pri)2Ru2(µ-SCH2CH2Ph)2Cl2] (3) and [(η6-p-Me¬C6H4¬Pri)2¬Ru2(S¬CH2¬C6H4-p-O¬Me)2¬Cl2] (4) towards amino acids, nucleotides, and a single-stranded DNA dodecamer were studied using NMR and mass spectrometry. In aqueous solutions at 37 °C, the monothiolato com¬plexes 1 and 2 undergo rapid hydrolysis, irrespective of the pH value, the predominant species in D2O/acetone-d6 solution at equilibrium being the neutral hydroxo complexes [(η6-p-Me¬C6H4¬Pri)2Ru2(OD)2(µ-OD)(µ-SR)]. The dithiolato complexes 3 and 4 are stable in water under acidic conditions, but undergo slow hydrolysis under neutral and basic conditions. In both cases, the cationic hydroxo complexes [(η6-p-MeC6H4Pri)2Ru2(µ-SR)2¬(OD)¬(CD3CN)]+ are the only spe¬cies observed in D2O/CD3CN at equilibrium. Surprisingly, no adducts are observed upon addition of an excess of L-methionine or L-histidine to the aqueous solutions of the complexes. Upon addition of an excess of L-cysteine, on the other hand, 1 and 2 form the unusual cationic trithiolato complexes [(η6-p-MeC6H4Pri)2¬Ru2{µ-SCH2CH(NH2)COOH}2(µ-SR)]+ containing two bridging cysteinato li¬gands, while 3 and 4 yield cationic trithiolato complexes [(η6-p-MeC6H4Pri)2Ru2[µ-SCH2CH¬(NH2)COOH](µ-SR)2]+ containing one bridging cysteinato ligand. A representative of catio¬nic trithiolato complexes containing a cysteinato bridge of this type, [(η6-p-MeC6H4Pri)2¬Ru2[µ-S¬CH2CH(NH2)COOH](µ-SCH2-p-C6H4-But)2]+ (6) could be synthesised from the di¬thiolato complex [(η6-p-Me¬C6H4¬Pri)2-Ru2(S¬CH2¬C6H4-p-But)2Cl2] (5), isolated as the tetra¬fluo¬ro¬borate salt and fully characterised. Moreover, the mono- and dithiolato complexes 1 - 4 are inert toward nucleotides and DNA, suggesting that DNA is not a target of cytotoxic thiolato-bridged arene ruthenium complexes. In contrast to the trithiolato complexes, monothiolato and dithio¬lato complexes hydrolyse and react with L-cysteine. These results may have im¬portant implications for the mode of action of thiolato-bridged dinuclear arene ruthenium drug candidates, and suggest that their modes of action are different to those of other arene ruthenium complexes.

Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Aims. We study the link between gravitational slopes and the surface morphology on the nucleus of comet 67P/Churyumov-Gerasimenko and provide constraints on the mechanical properties of the cometary material (tensile, shear, and compressive strengths). Methods. We computed the gravitational slopes for five regions on the nucleus that are representative of the different morphologies observed on the surface (Imhotep, Ash, Seth, Hathor, and Agilkia), using two shape models computed from OSIRIS images by the stereo-photoclinometry (SPC) and stereo-photogrammetry (SPG) techniques. We estimated the tensile, shear, and compressive strengths using different surface morphologies (overhangs, collapsed structures, boulders, cliffs, and Philae's footprint) and mechanical considerations. Results. The different regions show a similar general pattern in terms of the relation between gravitational slopes and terrain morphology: i) low-slope terrains (0-20 degrees) are covered by a fine material and contain a few large (>10 m) and isolated boulders; ii) intermediate-slope terrains (20-45 degrees) are mainly fallen consolidated materials and debris fields, with numerous intermediate-size boulders from <1m to 10m for the majority of them; and iii) high-slope terrains (45-90 degrees) are cliffs that expose a consolidated material and do not show boulders or fine materials. The best range for the tensile strength of overhangs is 3-15 Pa (upper limit of 150 Pa), 4-30 Pa for the shear strength of fine surface materials and boulders, and 30-150 Pa for the compressive strength of overhangs (upper limit of 1500 Pa). The strength-to-gravity ratio is similar for 67P and weak rocks on Earth. As a result of the low compressive strength, the interior of the nucleus may have been compressed sufficiently to initiate diagenesis, which could have contributed to the formation of layers. Our value for the tensile strength is comparable to that of dust aggregates formed by gravitational instability and tends to favor a formation of comets by the accrection of pebbles at low velocities.

Unintended pregnancy: Attitudes toward contraception of women obtaining abortions

Forty-nine percent of pregnancies in the United States are unintended and significant numbers of pregnancies are unintended for women of all ages. One possible reason for the high rate is that while 85% of women at risk for an unintended pregnancy use contraception, negative attitudes about the method used make them poor contraceptors. Negative attitudes may prevent the remaining 15% of women from using any method of birth control. This study examined adult women's attitudes toward contraception and its use to see if attitudes correlate with unintended pregnancy. ^ To obtain a sample of women experiencing unintended pregnancies, women obtaining therapeutic abortions were surveyed since almost all women obtaining therapeutic abortions are experiencing an unintended pregnancy. The study used a cross-sectional survey design and included 312 women obtaining abortions at the Planned Parenthood Surgical Services Clinic in Houston in the latter half of 1999. ^ The responses revealed a lack of knowledge about the safety and effectiveness of contraception, particularly for methods other than oral contraceptives and condoms. Thirty-four percent of the participants were uncomfortable buying contraception. While 71% of the participants said their physician recommended their use of contraception, 17% were unsure and 35% did not talk to their physician about contraception on a regular basis. ^ The attitudes of women using contraception were compared with those not using contraception and many differences were seen. Women not using contraception responded with more ‘unsure’ answers and believed contraception was more difficult to use. They felt planning ahead for the use of contraception interfered with the enjoyment of sex (p-value = 0.06). They were less likely to use contraception if their partner disapproved (p-value = 0.01) and more of them believed their church disapproved of contraception (p-value = 0.02). In comparison, women using contraception had negative attitudes about the safety of the pill (p-values = 0.01–0.08) and the effectiveness of the condom (p-value = 0.04). Therefore, the negative attitudes women using contraception had about contraception may interfere with their effective use of birth control. Those not using contraception were found to hold attitudes that may contribute to their non-use of contraception. ^