Effects of air susceptibility on proton resonance frequency MR thermometry

Object  

The temperature dependence of the proton resonance frequency (PRF) is often used in MR thermometry. However, this method is prone to even very small changes in local magnetic field strength. Here, we report on the effects of susceptibility changes of surrounding air on the magnetic field inside an object and their inferred effect on the measured MR temperature.     

Fast MR thermometry using an echo-shifted sequence with simultaneous multi-slice imaging

Purpose

Real-time monitoring is important for the safety and effectiveness of high-intensity focused ultrasound (HIFU) therapy. Magnetic resonance imaging is the preferred imaging modality for HIFU monitoring, with its unique capability of temperature imaging. For real-time temperature imaging, higher temporal resolution and larger spatial coverage are needed. In this study, a sequence based on the echo-shifted RF-spoiled gradient echo (GRE) with simultaneous multi-slice (SMS) imaging was designed for fast temperature imaging.

Methods

A phantom experiment was conducted to evaluate the accuracy of the echo-shifted sequence using a fluorescent fiber thermometer as reference. The temperature uncertainty of the echo-shifted sequence was compared with the traditional GRE sequence at room temperature through the ex vivo porcine muscle. Finally, the ex vivo porcine liver tissue experiment using HIFU heating was performed to demonstrate that the spatial coverage was increased without decreasing temporal resolution.

Results

The echo-shifted sequence had a better temperature uncertainty performance compared with the traditional GRE sequence with the same temporal resolution. The ex vivo heating experiment confirmed that by combining the SMS technique and echo-shifted sequence, the spatial coverage was increased without decreasing the temporal resolution while maintaining high temperature measurement precision.

Conclusion

The proposed technique was validated as an effective real-time method for monitoring HIFU therapy.

     

High-resolution impedance mapping using electrically activated quantitative phase imaging

Retrieving electrical impedance maps at the nanoscale rapidly via nondestructive inspection with a high signal-to-noise ratio is an unmet need,likely to impact various applications from biomedicine to energy conversion.In this study,we develop a multimodal functional imaging instrument that is characterized by the dual capability of impedance mapping and phase quantitation,high spatial resolution,and low temporal noise.To achieve this,we advance a quantitative phase imaging system,referred to as epi-magnified image spatial spectrum microscopy combined with electrical actuation,to provide complementary maps of the optical path and electrical impedance.We demonstrate our system with high-resolution maps of optical path differences and electrical impedance variations that can distinguish nanosized,semi-transparent,structured coatings involving two materials with relatively similar electrical properties.We map heterogeneous interfaces corresponding to an indium tin oxide layer exposed by holes with diameters as small as~550 nm in a titanium(dioxide)over-layer deposited on a glass support.We show that electrical modulation during the phase imaging of a macro-electrode is decisive for retrieving electrical impedance distributions with submicron spatial resolution-and beyond the limitations of electrode-based technologies(surface or scanning technologies).The findings,which are substantiated by a theoretical model that fits the experimental data very well enable achieving electro-optical maps with high spatial and temporal resolutions.The virtues and limitations of the novel optoelectrochemical method that provides grounds for a wider range of electrically modulated optical methods for measuring the electric field locally are critically discussed.     

Real-time imaging and triggering of 3D contrast-enhanced MR angiograms using MR fluoroscopy

Although a variety of timing techniques and data acquisition strategies have been, used for three-dimensional contrast-enhanced MR angiography, many are still limited by inadequate overall reliability, limited spatial resolution, or complexity. A technique is presented in this work in which contrast arrival is detected in the targeted vasculature in real time using MR fluoroscopy. Upon detection the operator triggers a 3D MR angiographic acquisition which uses an elliptical centric view order. It is shown that the view order intrinsically provides a high degree of venous suppression which in turn allows acquisition times of 30 s or longer. permitting high spatial resolution. The reliability of fluoroscopic triggering in bolus detection is shown to be over 90%. The technique provides high quality contrast-enhanced MR angiograms for many vascular regions.     

Detecting secondary arc extinction time by analyzing low frequency components of faulted phase voltage or sound phase current waveforms

This paper suggests a new adaptive single-pole auto-reclosing technique based on tracking a single harmonic distortion index (HDI) that represents the behavior of the low frequency components of the faulted phase voltage or sound phase current waveforms and a decision-making index that is defined based on properties of the tracked HDI. The advantage of this technique is that the threshold values, set for indices, can be chosen almost independent of pre-fault loading conditions and line parameters.     

基于DDS和外差混频的频率合成器的设计

在过去20年里,为了适应矢量调制通信和先进雷达系统的迅速发展,射频和微波信号发生器的性能和复杂度都有所增长.对于这些应用,最关键的性能参数之一就是相位噪声.设计了一种利用外差混频技术的DDS驱动锁相环的频率合成器,频率输出范围3～6 GHz.DDS作为锁相频率合成器的参考信号发生器,这样频率合成器就有了极快的切换时间和很窄的频带间隔.通过提高鉴相频率和外差混频,整个频率合成器因为分频比的大幅下降,因此拥有极好的相位噪声,在频率3.85 GHz时,相噪达到-105 dBc/Hz@10 kHz.     

数字移相法测量无功功率的频率误差补偿

用定频采样法及数字移相技术测量无功功率的重大障碍是频率影响误差,该短文提出一种校正该项误差的新方法,对其补偿效果进行了分析,并讨论了相关设计方法。     

三维有限元法分析频率对接地电阻的影响

提出了用涡流场的A-V有限元分析方法计算接地系统接地电阻的方法,分析了入地电流频率的变化对接地电阻的影响。计算结果表明,频率对接地体自身电阻的影响较大,但对散流电阻的影响很小。     

1 kHz步进低噪声YIG调谐微波频率综合器

低噪声微波频率综合器在现代电子系统和高性能测试系统中起着非常重要的作用,其实现方式通常以压控振荡器(VCO)和YIG调谐振荡器锁相频率合成为主。基于4~9 GHz YIG调谐振荡器,通过VCO合成小步进可变参考,使锁相环路在不降低鉴相频率的前提下,设计了完成高分辨率、低杂散的宽带低噪声YIG频率综合器。技术验证样品测试结果表明,在4~9 GHz工作带宽内频率步进为1 k Hz,相位噪声优于-95d Bc@10 k Hz,-115 d Bc@100 k Hz,其软硬件设计支持连续扫频和合成扫频功能,工作性能稳定可靠,可满足工程中本振和信号源应用需求。     

WBZ-1 D型低频率保护装置的设计研究

WBZ-1D型微机式低频率保护装置是根据中、小型汽轮发电机组低频率保护的要求而设计研制的。在研究设计过程中,硬件电路采用了DSP构成硬件系统,软件采用C＋＋语言编程。软、硬件设计过程中采用了～系列可靠性措施,因此保护装置具有较高的性能指标和可靠性。     

Accuracy of 3D MR microscopy for trabecular bone assessment: a comparative study on calcaneus samples using 3D synchrotron radiation microtomography

Magnetic resonance (MR) imaging is attractive for a noninvasive and radiation-free assessment of in vivo trabecular bone architecture. However the quantitative evaluation of architectural parameters could be biased by the limited sensitivity of MR. The aim of this study was to determine the accuracy of trabecular bone architectural parameters obtained from 3D high-resolution MR images, by comparison to reference images obtained by high-resolution X-ray microtomography using synchrotron radiation, from 29 samples of human calcaneus. MR images were obtained with a 66 m×66 m×66 m voxel size, using a 8.5 T MR microscope. Microtomography images were acquired with a 10 m×10 m×10 m voxel size, from the same samples. 3D architectural parameters characterizing the morphometry, topology, anisotropy, and orientation were computed from both modalities and carefully compared. To avoid errors, an identical region of interest was selected in the two corresponding images, and the same algorithms were run at identical spatial resolution. Our results establish that network connectivity, orientation and anisotropy are reliable from the MR data. The bone volume fraction, and morphometric parameters measured from the MR data, were found to be biased with respect to their values from the microtomography data, although there was a significant correlation between the two modalities.An erratum to this article can be found at     

基于机制设计理论的调频服务合同的最优设计 (一)合同模型

电力工业的市场化改革在实现资源优化配置的同时也给系统的安全稳定运行带来了更大的挑战.如何保证足够的调频容量是广泛关注的问题之一.针对电力市场环境下电网公司如何激励抽水蓄能电站提供调频辅助服务的问题,运用委托-代理模型研究二者之间最优调频辅助服务合同,得出满足电网公司和抽水蓄能电站双方效用均衡的结果.     

3D true-phase polarity recovery with independent phase estimation using three-tier stacks based region growing (3D-TRIPS)

Objectives

A postprocessing technique termed 3D true-phase polarity recovery with independent phase estimation using three-tier stacks based region growing (3D-TRIPS) was developed, which directly reconstructs phase-sensitive inversion-recovery images without acquisition of phase-reference images. The utility of this technique is demonstrated in myocardial late gadolinium enhancement (LGE) imaging.

Materials and methods

A data structure with three tiers of stacks was used for 3D-TRIPS to directly achieve reliable region growing for successful background-phase estimation. Fifteen patients undergoing postgadolinium 3D phase-sensitive inversion recovery (PSIR) cardiac LGE magnetic resonance imaging (MRI) were recruited, and 3D-TRIPS LGE reconstructions were compared with standard PSIR. Objective voxel-by-voxel comparison was performed. Additionally, blinded review by two radiologists compared scar visibility, clinical acceptability, voxel polarity error, or groups and blurring.

Results

3D-TRIPS efficiently reconstructed postcontrast phase-sensitive myocardial LGE images. Objective analysis showed an average 95% voxel-by-voxel agreement between 3D-TRIPS and PSIR images. Blinded radiologist review demonstrated similar image quality between 3D-TRIPS and PSIR reconstruction.

Conclusion

3D-TRIPS provided similar image quality to PSIR for phase-sensitive myocardial LGE MRI reconstruction. 3D-TRIPS does not require acquisition of a reference image and can therefore be used to accelerate phase-sensitive LGE imaging.

     

一维带限Weierstrass分形粗糙地面电磁散射的FDTD研究

采用一维带限Weierstrass分形函数模拟了实际的粗糙地面,应用时域有限差分方法研究了一维分形粗糙地面电磁散射特性,计算了分形粗糙地面散射的双站散射系数,得出了散射系数随散射角和入射波频率变化的曲线,讨论了高度起伏均方根、分维数、土壤湿度、入射波频率、入射角等参数对散射系数的影响,得到了一维带限Weierstrass分形粗糙地面电磁散射的特性。数值计算结果表明各参数对散射系数均有显著影响,入射波不同极化方式下的散射系数也有明显的变化。     

Volumetric assessment of myocardial viability in rats using 3D double contrast enhanced T1 and T2-weighted MRI

Objective: Volumetric evaluation of the myocardial viability post-infarction in rats using 3D in vivo MR imaging at 7 T using injection of an extracellular paramagnetic contrast agent and intravascular superparamagnetic iron oxide nanoparticles in the same imaging session. Materials and methods: Five hours after induction of permanent myocardial infarction in rats (n=6), 3D in vivo T1- and T2-weighted MR Imaging was performed prior to and after Gd-DOTA injection (0.2 mmol/kg) and prior to and after nanoparticle injection (5 mg Fe/kg) to assess infarct size and myocardial viability. Results: 3D MR Imaging using a successive contrast agent injection showed a difference of infarct size after Gd-DOTA injection on T1-weighted images compared to the one measured on T2-weighted images after Gd-DOTA and nanoparticle injection. Conclusion: The use of 3D T1- and T2-weighted MR Imaging using a double contrast agents protocol made possible the accurate characterization of myocardial infarction volume and allowed the detection of myocardial viability post-infarction in rats