Optimal techniques for magnetic resonance imaging of the liver using a respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence

Purpose

To optimize the navigator-gating technique for the acquisition of high-quality three-dimensional spoiled gradient-recalled echo (3D SPGR) images of the liver during free breathing.

Materials and methods

Ten healthy volunteers underwent 3D SPGR magnetic resonance imaging of the liver using a conventional navigator-gated 3D SPGR (cNAV-3D-SPGR) sequence or an enhanced navigator-gated 3D SPGR (eNAV-3D-SPGR) sequence. No exogenous contrast agent was used. A 20-ms wait period was inserted between the 3D SPGR acquisition component and navigator component of the eNAV-3D-SPGR sequence to allow T1 recovery. Visual evaluation and calculation of the signal-to-noise ratio were performed to compare image quality between the imaging techniques.

Result

The eNAV-3D-SPGR sequence provided better noise properties than the cNAV-3D-SPGR sequence visually and quantitatively. Navigator gating with an acceptance window of 2 mm effectively inhibited respiratory motion artifacts. The widening of the window to 6 mm shortened the acquisition time but increased motion artifacts, resulting in degradation of overall image quality. Neither slice tracking nor incorporation of short breath holding successfully compensated for the widening of the window.

Conclusion

The eNAV-3D-SPGR sequence with an acceptance window of 2 mm provides high-quality 3D SPGR images of the liver.     

半直线上Riemann-Liouville型奇异分数阶微分方程边值问题的单调迭代方法

运用不动点定理和单调迭代方法研究半直线上Riemann-Liouville型奇异分数阶微分方程边值问题的正解的存在性.在没有上、下解存在的假设下建立了边值问题存在两个正解的结果,构造了逼近正解的迭代格式,该迭代格式便于应用.     

Heat generation ability in AC magnetic field and their computer simulation for Ti tube filled with ferrite powder

The heat generation ability of needle-type materials was studied for the application of thermal coagulation therapy in an AC magnetic field. Although the Ti tube without the MgFe₂O₄ powder or Ti rod showed poor heat generation abilities in an AC magnetic field, the temperature was significantly increased by the presence of ferrite powder in the Ti tube. We confirmed using a computer simulation that the eddy loss of the Ti tube was increased by the enhanced magnetic flux density due to the ferrite powder in the Ti tube. The heat generation of the ferrite filled Ti tube was increased by utilization of the quenched MgFe₂O₄ powder from elevated temperature. The relative magnetic permeability of the quenched ferrite was enhanced with the decrease in the inverse ratio of the cubic spinel structure. The heat generation ability was increased with the increase in the relative magnetic permeability of the Ti tube with ferrite powder. The calculated joule loss based on the experimental results showed an agreement with those using the computer simulation.     

Interferometric thickness measurement of glass plate by phase-shifting analysis using wavelength scanning with elimination of bias phase error

Optical Review - Phase-shifting fringe analysis using wavelength scanning has been broadly applied to the interferometric profiling of the thickness variation of glass plates. However, the...     

A Series of Dibenzofuran-Based n-Type Exciplex Host Partners Realizing High-Efficiency and Stable Deep-Red Phosphorescent OLEDs

Deep-red to near-infrared (NIR) OLEDs, which yield emission peak wavelengths beyond λ=660 nm, are applicable as unique light sources in plant growth or health monitoring systems. Compared with other visible-spectrum OLEDs, however, research in the field of deep-red OLEDs is not as advanced. In this work, three new types of dibenzofuran-based host materials are developed as n-type exciplex host partners. Combining these with the deep-red iridium complex bis(2,3-diphenylquinoxaline)iridium(dipivaloylmethane) ([(DPQ)₂Ir(dpm)]) and N,N′-di(naphalene-1-yl)-N,N′-diphenylbenzidine (α-NPD) as a p-type exciplex host partner, a highly efficient deep-red OLED can be realized with a maximum external quantum efficiency (η_ext,max) of over 16 % with Comission Internationale de l′Éclairge (CIE) coordinates of (0.71, 0.28). In addition, the effect of the doping concentration and the p/n ratio of the exciplex host on the efficiency and the lifetime of the OLEDs are investigated. Consequently, the optimized device exhibits a η_ext,max of over 15 % and a six-time longer lifetime operating at high brightness of 100 cd m⁻² compared with other state-of-the-art deep-red OLEDs.     

Highly efficient asymmetric conjugate addition of 5-benzylfurfurals to nitroalkenes using a thiourea organocatalyst

The asymmetric direct bisvinylogous conjugate addition of 5-benzylfurfural derivatives to nitroalkenes using a thiourea organocatalyst resulted in a corresponding ε-regioselective addition products in high yields and up to 95% enantiomeric excess.