Comparison of two quantitative proton density mapping methods in multiple sclerosis

Objective

Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MS patients.

Materials/methods

PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PD_ref, bias-field method) and PD_alt (alternative method).

Results

PD_alt-values closely matched PD_ref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PD_ref, and the voxel-wise correlation between PD_ref and ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PD_ref were almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PD_alt and PD_ref.

Conclusion

RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MS patients, in spite of discrepancies between ρ(T1) and actual PD values.

     

Quasi-Adiabatic Investigations of Lead in Indium

The use of melting or freezing temperatures of high-purity substances as thermometric fixed points requires a knowledge of the binary phase diagrams of these substances and remaining impurities at very small impurity concentrations. In this paper, a calorimetric apparatus for the measurement of the change in liquidus temperature of fixed-point metals due to dissolved impurities at quasi-adiabatic conditions is presented. This approach combines advantages of the fixed-point method and adiabatic calorimetry. It is more efficient for the screening of a range of impurity concentrations than a fixed-point cell, requires less constructional and experimental expenditure compared with an adiabatic calorimeter, but provides similar small uncertainties on the millikelvin level. Measurements were carried out to determine the influence of lead on the melting temperature of indium at mass fractions up to 6.93 %. The results are in very good agreement with previous measurements by means of slim fixed-point cells in the Physikalisch-Technische Bundesanstalt and confirm a minimum of the freezing point of \(-\) 178 mK at a mass fraction of about 3.7 %. It was demonstrated that this setup allows the investigation of binary phase diagrams with uncertainties less than 8 mK.     

Enhanced electrochemical performance in lithium ion batteries of a hollow spherical lithium-rich cathode material synthesized by a molten salt method

A high voltage layered Li1.2Ni0.16Co0.08Mn0.56O2 cathode material with a hollow spherical structure has been synthesized by molten-salt method in a NaCI flux. Characterization by X-ray diffraction and scanning electron microscopy confirmed its structure and proved that the as-prepared powder is constituted of small, homogenously sized hollow spheres （1-1.5 μm）. The material exhibited enhanced rate capability and high first cycle efficiency due to the good dispersion of secondary particles. Galvanostatic cycling at different temperatures （20, 40, and 60 ℃） and a current rate of 2 C （500 mA.g-1） showed no significant capacity fade.     

Double-spiral tool path in configuration space

Using a spiral tool path is a common strategy in many NC machining applications. It can be used for high-speed machining of pockets or as a space-filling curve for finish applications. When using spirals for finishing application, a double spiral is desired to avoid having a starting or end-point at the center of the workpiece. In this paper, we present an algorithm to create a double spiral from offset curves in a precomputed configuration space (c-space). CAD/CAM systems that operate on NURBS surfaces or on triangular meshes have to deal with the issues of patch-boundary oscillations or long, stretched triangles, respectively. This can be avoided when operating in c-space. The c-space is given in the form of a regular quadrilateral heightfield mesh, which may be adaptively subdivided, where the slope is large. This simple data structure is memory efficient and has proven to be beneficial in CAD/CAM frameworks. Our algorithm creates a double spiral by blending adjacent offset curves. The center of the spiral is filled by a b-spline curve. When given offset curves split into multiple components, the algorithm creates multiple smaller spirals and connects them appropriately. The resulting tool path is one large intersection-free curve with starting and end-point on the boundary of the workpiece.     

Experimental validation of high-order time integration for non-linear heat transfer problems

An accurate prediction of the temperature distribution in space and time plays an important role in many industrial applications, in particular when phase transformations are involved. In this article the thermo-physical properties of steel 51CrV4 (SAE 6150) are determined and used in numerical simulations. For the simulation of the temperature field a semi-discrete approach is used, consisting of a finite element approximation in space and a high order Runge– Kutta integration in time. Several adaptive high-order time integration method (stiffly accurate diagonally implicit Runge–Kutta methods) are applied and their computational efficiency is investigated. The theoretical rates of convergence are achieved for all problems, including the non-linear case. Whereas the second order accurate method of Ellsiepen with time adaptive step-size control proves to be most efficient. Further, the influence of the material model on the simulation results is studied and the numerical results are verified by experiments. The best correlation of the simulation and experimental data is achieved using temperature-dependent parameters.     

Plasma ion assisted deposition of aluminium oxide and aluminium oxifluoride layers for applications in the ultraviolet spectral range

We present extended experimental material about optical and mechanical properties as well as the water content of aluminium oxide films, deposited by plasma ion assisted electron beam evaporation. A clear correlation between these experimental data is established and understood as being affected by the different degree of the porosity of the films. When adding fluorine as a reactive gas during deposition, aluminium oxifluoride layers can be obtained that appear nearly free of water, and combine UV-transparency with higher UV refractive indices than porous aluminium oxide layers.     

Transparente Barriereschichten auf flexiblen Polymersubstraten

Transparent permeation barrier layers on flexible polymer substrates This paper reviews different vacuum based technologies for manufacturing transparent permeation barrier layers and layer stacks on flexible polymer substrates. With plasma assisted reactive evaporation, a cost‐efficient, highly productive process for food packaging applications is presented. Reactive dual magnetron sputtering is a technology for the deposition of oxide layers with a very low water vapor and oxygen transmission rate at a reasonable deposition rate. Many groups suggest multilayer stacks for the encapsulation of flexible electronic devices. In this paper, an all‐in‐vacuum inline concept for manufacturing such multilayers is presented. It is based on the combination of reactively sputtered barrier layers with interlayers grown by using a magnetron based PECVD process (Magnetron‐PECVD). Both, process parameters, such as deposition rate and process pressure, and important layer properties, such as morphology and the water vapor and oxygen transmission rate are compared for the different single and multi layer technologies.