Comparison of delayed gadolinium enhanced MRI of cartilage (dGEMRIC) using inversion recovery and fast T1 mapping sequences

The delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique has shown promising results in pilot clinical studies of early osteoarthritis. Currently, its broader acceptance is limited by the long scan time and the need for postprocessing to calculate the T1 maps. A fast T1 mapping imaging technique based on two spoiled gradient echo images was implemented. In phantom studies, an appropriate flip angle combination optimized for center T1 of 756 to 955 ms yielded excellent agreement with T1 measured using the inversion recovery technique in the range of 200 to 900 ms, of interest in normal and diseased cartilage. In vivo validation was performed by serially imaging 26 hips using the inversion recovery and the Fast 2 angle T1 mapping techniques (center T1 756 ms). Excellent correlation with Pearson correlation coefficient R2 of 0.74 was seen and Bland-Altman plots demonstrated no systematic bias.

Visual vector inversion during memory antisaccades--a TMS study

In the memory antisaccade task, subjects are instructed to look at an imaginary point precisely at the opposite side of a peripheral visual stimulus presented short time previously. To perform this task accurately, the visual vector, i.e., the distance between a central fixation point and the peripheral stimulus, must be inverted from one visual hemifield to the other. Recent data in humans and monkeys suggest that the posterior parietal cortex (PPC) might be critically involved in the process of visual vector inversion. In the present study, we investigated the temporal dynamics of visual vector inversion in the human PPC by using transcranial magnetic stimulation (TMS). In six healthy subjects, single pulse TMS was applied over the right PPC during a memory antisaccade task at four different time intervals: 100 ms, 217 ms, 333 ms, or 450 ms after target onset. The results indicate that for rightward antisaccades, i.e., when the visual target was presented in the left screen-half, TMS had a significant effect on saccade gain when applied 100 ms after target onset, but not later. For leftward antisaccades, i.e., when the visual target was presented in the right screen-half, a significant TMS effect on gain was found for the 333 ms and 450 ms conditions, but not for the earlier ones. This double dissociation of saccade gain suggests that the initial process of vector inversion can be disrupted 100 ms after onset of the visual stimulus and that TMS interfered with motor saccade planning based on an inversed vector signal at 333 ms and 450 ms after stimulus onset.

Interaction between Meristem Tissue Layers Controls Phyllotaxis

Phyllotaxis and vein formation are among the most conspicuous patterning processes in plants. The expression and polarization of the auxin efflux carrier PIN1 is the earliest marker for both processes, with mathematical models indicating that PIN1 can respond to auxin gradients and/or auxin flux. Here, we use cell-layer-specific PIN1 knockouts and partial complementation of auxin transport mutants to examine the interaction between phyllotactic patterning, which occurs primarily in the L1 surface layer of the meristem, and midvein specification in the inner tissues. We show that PIN1 expression in the L1 is sufficient for correct organ positioning, as long as the L1-specific influx carriers are present. Thus, differentiation of inner tissues can proceed without PIN1 or any of the known polar transporters. On theoretical grounds, we suggest that canalization of auxin flux between an auxin source and an auxin sink may involve facilitated diffusion rather than polar transport.

KrigInv: An efficient and user-friendly implementation of batch-sequential inversion strategies based on kriging

Several strategies relying on kriging have recently been proposed for adaptively estimating contour lines and excursion sets of functions under severely limited evaluation budget. The recently released R package KrigInv 3 is presented and offers a sound implementation of various sampling criteria for those kinds of inverse problems. KrigInv is based on the DiceKriging package, and thus benefits from a number of options concerning the underlying kriging models. Six implemented sampling criteria are detailed in a tutorial and illustrated with graphical examples. Different functionalities of KrigInv are gradually explained. Additionally, two recently proposed criteria for batch-sequential inversion are presented, enabling advanced users to distribute function evaluations in parallel on clusters or clouds of machines. Finally, auxiliary problems are discussed. These include the fine tuning of numerical integration and optimization procedures used within the computation and the optimization of the considered criteria.

Net CO 2 surface emissions at Bern, Switzerland inferred from ambient observations of CO 2 , δ(O 2 /N 2 ), and 222 Rn using a customized radon tracer inversion

The 222Radon tracer method is a powerful tool to estimate local and regional surface emissions of, e.g., greenhouse gases. In this paper we demonstrate that in practice, the method as it is commonly used, produces inaccurate results in case of nonhomogeneously spread emission sources, and we propose a different approach to account for this. We have applied the new methodology to ambient observations of CO2 and 222Radon to estimate CO2 surface emissions for the city of Bern, Switzerland. Furthermore, by utilizing combined measurements of CO2 and δ(O2/N2) we obtain valuable information about the spatial and temporal variability of the main emission sources. Mean net CO2 emissions based on 2 years of observations are estimated at (11.2 ± 2.9) kt km−2 a−1. Oxidative ratios indicate a significant influence from the regional biosphere in summer/spring and fossil fuel combustion processes in winter/autumn. Our data indicate that the emissions from fossil fuels are, to a large degree, related to the combustion of natural gas which is used for heating purposes.

The Frontal Eye Field Is Involved in Visual Vector Inversion in Humans – A Theta Burst Stimulation Study

In the antisaccade task, subjects are requested to suppress a reflexive saccade towards a visual target and to perform a saccade towards the opposite side. In addition, in order to reproduce an accurate saccadic amplitude, the visual saccade vector (i.e., the distance between a central fixation point and the peripheral target) must be exactly inverted from one visual hemifield to the other. Results from recent studies using a correlational approach (i.e., fMRI, MEG) suggest that not only the posterior parietal cortex (PPC) but also the frontal eye field (FEF) might play an important role in such a visual vector inversion process. In order to assess whether the FEF contributes to visual vector inversion, we applied an interference approach with continuous theta burst stimulation (cTBS) during a memory-guided antisaccade task. In 10 healthy subjects, one train of cTBS was applied over the right FEF prior to a memory-guided antisaccade task. In comparison to the performance without stimulation or with sham stimulation, cTBS over the right FEF induced a hypometric gain for rightward but not leftward antisaccades. These results obtained with an interference approach confirm that the FEF is also involved in the process of visual vector inversion.