Feasibility of fat-saturated T2-weighted magnetic resonance imaging with slice encoding for metal artifact correction (SEMAC) at 3T

Background and Purpose

Fluid-sensitive MR imaging in postoperative evaluation is important, however, metallic artifacts is inevitable. The purpose is to investigate the feasibility of fat-saturated slice encoding for metal artifact correction (SEMAC)-corrected T2-weighted magnetic resonance (MR) at 3T in patients with spinal prostheses.

Methods

Following institutional review board approval, 27 SEMAC-encoded spinal MRs between September 2012 and October 2013 in patients with spinal metallic prostheses were analyzed. The MR images were scanned on a 3T MR system including SEMAC-corrected and uncorrected fast spin echo (FSE) T2-weighted MR images with fat-saturation. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images using a five-point scale in terms of artifact reduction around the prosthesis, visualization of the prosthesis and pedicle, and intervertebral neural foramina. Quantitative assessments were performed by calculating the ratio of signal intensity from the fixated vertebra and that from upper level vertebra. For statistical analyses, paired t-test was used.

Results

Fat-saturated SEMAC-corrected T2-weighted MR images enabled significantly improved metallic artifact reduction (P < 0.05). Quantitative evaluation of the signal intensity ratio of screw-fixated vertebra and upper level vertebra showed a significantly lower ratio on fat-saturated SEMAC images (P < 0.05), however, the high signal intensity of signal pile-up could be not completely corrected.

Conclusion

SEMAC correction in fat-suppressed T2-weighted MR images can overcome the signal loss of metallic artifacts and provide improved delineation of the pedicle screw and peri-prosthetic region. Signal pile-up, however, could not be corrected completely, therefore readers should be cautious in the evaluation of marrow around the prosthesis.     

基于细菌视紫红质光子逻辑门的实验研究

研究了基于细菌视紫红质(简称BR或菌紫质)变种材料D96N的3种光逻辑操作.在633nm激发光照射下，菌紫质分子会被激发到M态，处于M态的菌紫质对412nm的紫光呈较大吸收，会抑制同时入射的紫光.选择合适的紫光强度，通过CCD观测被抑制的412nm检测光透射强度分布，模拟了“非”、“或非”、“与非”几种基本的光子逻辑操作. 关键词： 细菌视紫红质 光子逻辑门 互补抑制     

Experimental investigation and numerical validation of explosion suppression by inert particles in large-scale duct

A large-scale duct with an explosion suppressor was designed to investigate experimentally the explosion suppression by inert particles for a CH₄/O₂/N₂ mixture. The duct is 25 m long and has an internal diameter of 700 mm. Pressure and flame signals were recorded some distance away from ignitor in the duct. Pressure tracking lines of the shock front for the different inert particle cloud densities and the inert particle diameters were made. The measured results indicate that the shock front is decoupled from the flame front in the inert particle cloud, which leads to a suppression of explosion. Also, the experiments suggest that increasing the inert particle cloud density or decreasing the inert particle diameter can enhance the ability to suppress explosion. For the purpose of validation, a two-dimensional numerical model coupled with the element chemical reaction mechanism for the simulations of the CH₄/O₂/N₂ mixture explosion suppression by the inert particles has been developed. This model makes use of the second-order TVD scheme and the MacCormack scheme to calculate gas-phase and particle-phase equations, respectively. The Strang splitting technique is used to treat the stiffness due to the coupling of the governing equations, while the implicit Gear algorithm is used to treat the stiffness due to the chemical reactions. The effect of inert particle cloud density on explosion suppression was investigated using the model. The calculated results indicate that the accumulation of inert particles slows the propagation of the gas-phase shock front and results in explosion suppression. With increased inert particle cloud density, the explosion suppression is more prominent. The calculated results show a qualitative agreement with the measured results in the large-scale duct experiment.     

STUDIES ON THE CELL PHENOTYPE CHARACTERISTICS OF HYBRID CELLS CROSSED BETWEEN RAT NUCLEATED ERYTHROBLASTS AND MOUSE PLASMOCYTOMA (SP~2/O) CELL LINE

The present study is designed to investigate the regulatory effect of mammalian erythroblasts, prior to naturally-occurring denucleation, on malignancy of mouse plasmocytoma cells and the possibility of reactivation of the pyknotic late erythroblast nuclei in hybrid cells crossed between rat intermediate or late erythroblasts of 15-day Wistar rat embryonic livers, and mouse plasmocytoma (SP~2/O) cell lines. Results indicated that:(ⅰ) Suppression of tumorigenicity and reversion of the malignant phenotype were observed in hybrid cells in a similar way as those of cybrid cells crossed between reticulocytes and myeloma cells as we reported previously, thus providing further evidence to support the hypothesis that some regulatory substances already existed in mammalian intermediate and late erythroblasts long before nuclear extrusion. (ⅱ) Appearance of positive histochemical reaction for hemoglobins in cytoplasm and electrophoretic bands of rat and mouse globin chains in hybrid cell lysate were i. The tran     

How to achieve world-wide mutual recognition of calibration and test results – or: Who accredits the accreditor?

 The ongoing globalization of the economy demands cost- and time-effective conformity assessment procedures through mutual cross-border recognition of calibration and test results. Accreditation is an important tool to ensure the technical competence of laboratories performing calibrations and tests. The question, however, arises as to which mechanisms should be applied to achieve technical equivalence of accreditations throughout the world as a basis for mutual recognition of agreements. To avoid third party "accreditation of accreditors", accreditation bodies have established a specific procedure of regional technical cooperation in order to create a climate of confidence resulting in formal mutual recognition agreements. Key elements of this cooperation are the harmonization of operation procedures in addition to existing international standards, a continuos programme of interlaboratory comparisons, and an extensive procedure for mutual peer assessments. The present article provides detailed information on such cooperation within the European region as an example, describes the present situation with respect to mutual recognition agreements within Europe, and gives a brief look into the future with respect to inter-regional cooperation. Received: 28 September 1996 Accepted: 2 November 1996     

MALDI-TOF mass spectrometry of a combinatorial peptide library: effect of matrix composition on signal suppression

The effect of matrix composition on signal suppression caused by a dominant compound under MALDI ionization was studied using the combinatorial TQTXT pentapeptide library as a model system. The peptide library is composed of 19 components with all proteinogenic amino acids except cysteine in position X. From these compounds, only the Arg peptide (TQTRT) was detected with sufficient intensity in the MALDI-TOF mass spectrum under typical MALDI conditions (CCA matrix). The analysis of a set of compounds utilized as different matrix components, additives and a cationizing agent revealed that the composition of the matrix is a critical point in signal suppression. Highly improved ion yields were achieved by using a CCA/DHB mixture as a matrix. The addition of K(+) as a cationizing agent to the CCA matrix resulted in MALDI-TOF mass spectra with relative ion intensities very similar to those obtained by electrospray ionization.     

时滞反馈控制扭转振动系统的振动

研究了采用时滞反馈来控制扭转振动系统的振动问题.在一个带有非线性动力吸振器的扭转振动系统中,采用时滞反馈来控制主系统的振动.研究了反馈增益系数和时滞对主系统振动的影响.研究结果表明,对某一固定的反馈增益系数,存在时滞的某段调节区间,可以通过调节时滞来抑制主系统的振动.在时滞的调节区间内存在一个最佳点,主系统的振动被抑制到最小值.可以同时调节反馈增益系数和时滞两参数,当反馈增益系数和时滞都调节到最佳值时,主系统振动的振幅由0.24减小到0.03,取得了很好的减振效果. 关键词： 时滞反馈 扭转振动 减振     

An immersed interface method for flow past circular cylinder in the vicinity of a plane moving wall

Two‐dimensional flows past a stationary circular cylinder near a plane boundary are numerically simulated using an immersed interface method with second‐order accuracy. Instead of a fixed wall, a moving wall with no‐slip boundary is considered to avoid the complex involvement of the boundary layer and to focus only on the shear‐free wall proximity effects for investigating the force dynamics and flow fields. To analyze the convergence and accuracy of our implementation, numerical studies have been first performed on a simple test problem of rotational flow, where the second order of convergence is confirmed through numerical experiments and an optimal range of relative grid‐match ratio of Lagrangian to Eulerian grid sizes has been recommended. By comparing the force quantities and the Strouhal number, the accuracy of this method has been demonstrated on the flow past a stationary isolated cylinder. The cylinder is then put in proximity to the wall to investigate the shear‐free wall proximity effects in the low Reynolds number regime (20≤Re≤200). The gap ratio, e/D, where e denotes the gap between the cylinder and the moving wall and D denotes the diameter of the cylinder, is taken from 0.10 to 2.00 to determine the critical gap ratio, (e/D)_critical, for the alternate vortex shedding, where the fluid forces, flow fields and the streamwise velocity profiles are studied. One of the key findings is that the (e/D)_critical for the alternate vortex shedding decreases as the Reynolds number increases. We also find that, in this low Reynolds number regime, the mean drag coefficient increases and peaks at e/D = 0.5 with the increase of e/D and keeps decreasing gently from e/D = 0.5 to e/D = 2.0, while the mean lift coefficient decreases monotonically with the increase of e/D. New correlations are then proposed for computing force coefficients as a function of Re and e/D for a cylinder in the vicinity of a moving plane wall. Copyright © 2015 John Wiley & Sons, Ltd.     

Active vibration control and suppression for integrated structures

Spacesmictures,aircraftstrUctures,satellitesandsoonarerequiredtobelightinweightduetotherequirementofoperation.TheyarealsolightlydampedbecauseofthelowinternaldampingofthematerialsusedintheirconstrUction.Thus,theywillgeneraiClargeamplitudevibration,whichmayreducetheprecisionofoperationandaffectthePerformanceofoperation.Itisessentialtousesuitablecontrolsystemtocontrolthevibrationofsimctures.Sincethesesmicturesaredistributedparametersystemshavinganinfinitesetofvibrationmodes,thecontrolsystemwith…     

水平液─固流中颗粒抑制湍流的行为和条件

用激光多普勒分相测量方法，考察了水平含颗粒水流的主流区，亚毫米颗粒对水流湍流有抑制行为，湍流削弱程度与颗粒浓度、流动发展长度、水流雷诺数等因素有关．按照不出现尾涡脱落和至少能响应一部分大尺度涡的运动这两个基本条件，分析了湍流抑制与有关参量的依赖性．结果表明，流动尺度和颗粒尺寸之比，对于颗粒消耗而不增生湍流起着最主要的作用．在一定的水流雷诺数下，只要这一比值很大，亚毫米颗粒就会表现出对湍流的抑制作用