Quantitative magnetic resonance imaging phantoms: A review and the need for a system phantom.

The MRI community is using quantitative mapping techniques to complement qualitative imaging. For quantitative imaging to reach its full potential, it is necessary to analyze measurements across systems and longitudinally. Clinical use of quantitative imaging can be facilitated through adoption and use of a standard system phantom, a calibration/standard reference object, to assess the performance of an MRI machine.

Response of water to electric fields at temperatures below the glass transition: a molecular dynamics analysis.

The electric field dependence of the structure and dynamics of water at 77 K, i.e., below the glass transition temperature (136 K), is investigated using molecular dynamics simulations.

Diffusion simulation-based fiber tracking using time-of-arrival maps: a comparison with standard methods.

Object: We propose a new tracking method based on time-of-arrival (TOA) maps derived from simulated diffusion processes.

Materials And Methods: The proposed diffusion simulation-based tracking consists of three steps that are successively evaluated on small overlapping sub-regions in a diffusion tensor field. First, the diffusion process is simulated for several time steps.

Comparison of gradient encoding directions for higher order tensor diffusion data.

Recently, higher order tensors were proposed for a more advanced representation of non-Gaussian diffusion. These advanced diffusion models have new requirements for the gradient encoding schemes used in the diffusion weighted image acquisition. The influence of the gradient encoding schemes on the estimated standard second order diffusion tensor was previously investigated.

Evolution of Athletic Records: Statistical Effects versus Real Improvements.

Athletic records represent the best results in a given discipline, thus improving monotonically with time. As has already been shown, this should not be taken as an indication that the athletes' capabilities keep improving. In other words, a new record is not noteworthy just because it is a new record, instead it is necessary to assess by how much the record has improved.

White matter fiber tractography via anisotropic diffusion simulation in the human brain.

A novel approach to noninvasively tracing brain white matter fiber tracts is presented using diffusion tensor magnetic resonance imaging (DT-MRI). This technique is based on successive anisotropic diffusion simulations over the human brain, which are utilized to construct three dimensional diffusion fronts. The fiber pathways are determined by evaluating the distance and orientation from the fronts to their corresponding diffusion seeds.

Top-down attentional processing enhances auditory evoked gamma band activity.

In contrast to animal studies, relatively little is known about the functional significance of the early evoked gamma band activity in humans. We investigated whether evoked and induced 40 Hz activity differentiate automatic, bottom-up aspects of attention from voluntary, top-down related attentional demands. An auditory novelty-oddball task was applied to 14 healthy subjects.

Repetitive transcranial magnetic stimulation induces different responses in different cortical areas: a functional magnetic resonance study in humans.

Repetitive transcranial magnetic stimulation (TMS) for 1 s at 4 Hz and 150% of the individual motor threshold was applied to primary motor cortex and adjacent cortical regions where no motor response could be produced. The hemodynamic reaction was measured using an event-related functional magnetic resonance setup. While all volunteers showed a typical signal increase beneath the coil during motor cortex stimulation, no consistent signal changes were present during frontal or parietal stimulation apart from activation of auditory cortex.

Trends and random fluctuations in athletics.

Improvements in the results of athletic competitions are often considered to stem from better training and equipment, but elements of chance are always present in athletics and these also contribute. Here we distinguish between these two effects by estimating the range into which athletic records would have fallen in the absence of systematic progress and then comparing this with actual performance results. We find that only 4 out of 22 disciplines have shown a systematic improvement, and that annual best results worldwide show saturation in some disciplines.