软件化脉冲序列程序器

在核磁共振谱仪中, 射频发射通道、接收机以及数据采集等的实时控制是由“脉冲序列器 ”来完成的. 本文提出了一套可设计任意脉冲序列、由全软件构成的“脉冲序列程序器”,该软件用Delphi 5 实现,用户界面简洁直观. 由其产生的脉冲的最小脉宽为1.3 μs,分辨率为12 ns（CPU工作在333 MHz）.     

一种用于核磁共振的脉冲场梯度单元

给出一种用于核磁共振谱仪的脉冲场梯度单元的详细设计. 它具有结构简洁、性能良好以及成本低廉等特点. 该单元只需外部设备提供两条TTL触发线即可产生任意波形的梯度脉冲，因此可以方便地与商用核磁共振仪器配套使用.     

基于数值计算模拟的仿真核磁共振波谱仪开发

核磁共振（NMR）波谱是研究有机分子结构的重要工具之一，其设备昂贵、仪器数量有限、科研机时安排紧凑、教学实验机时有限；若学生的NMR理论和实验基础较为薄弱，则易发生误操作损坏设备或降低设备性能；另外，NMR实验涉及流程较多、教学耗时较长.因此，针对学生的NMR实验教学难以广泛开展.为将虚拟技术更好地用于辅助NMR实验教学，本文基于数值模拟仿真技术，开发了具备真实NMR波谱仪基本功能的仿真NMR波谱仪——VMRS1.0软件.VMRS1.0软件可实现真实NMR实验须进行的调谐匹配、匀场、锁场、射频脉冲调节、原始数据采集等操作步骤，以及快速傅里叶变换、相位校正、自动寻峰、积分、测距、化学位移校正等基本数据处理功能；除简单的1D ¹H和¹³C NMR波谱采集和数据处理外，还可模拟去偶、DEPT、HSQC等相对复杂的实验；另外，该软件可自行虚拟编辑¹H或¹³C NMR实验样品.VMRS1.0软件摆脱硬件条件的限制，实现了与真实NMR实验类似的教学效果，可以让学生通过反复操作调试，更充分地掌握NMR基本原理和实验技能，再配合在真实NMR谱仪上的少量实际操作，可达到更加令人满意的实验教学效果.     

一体化NMR波谱仪梯度-场频联锁-匀场系统设计

介绍一体化核磁共振波谱仪梯度-场频联锁-匀场系统的设计方案. 该方案使用嵌入式以太网、FPGA(Field Programmable Gate Array,现场可编程门阵列)、EMI(External Memory Interface, 外部存储器接口)和高速串行总线等技术构建了基于以太网的通信系统和使用并行运算的控制系统, 并具备CAN(Controller Area Network,控制器局域网)总线通信的能力. 梯度放大器通过LVDS(Low-Voltage Differential Signaling,低压差分信号传输)接口与主控系统的梯度波形发生器连接,实现与谱仪工作站的交互. 系统采用插板式结构和通用性电路的设计方法,具有很好的扩展能力和适应性,能够满足不同谱仪的需求. 系统在11.7 T(500 MHz)NMR系统中进行了有效的锁场、匀场和梯度特性的测试,证明了该方案的可行性.     

一体化核磁共振谱仪控制台的软件系统设计

提出了一体化核磁共振谱仪控制台的软件系统设计方案,主要包括2部分,一部分是安装在谱仪控制台上的嵌入式Linux操作系统及实时控制软件,另外一部分是PC机上的界面控制软件. 2部分软件之间利用socket网络接口进行数据交互, 采用TCP/IP通信协议,这样既能保证数据传输的可靠性又可以达到较高的数据传输速率. 通过网络通信,该谱仪控制台还可以接受远程操控和系统升级. 该文具体阐述了该软件系统的设计思路和设计方法,对设计的软件系统进行了实验测试,并对实验结果进行了讨论.     

高性能核磁共振弛豫分析仪匀场系统的设计与实现

磁场的高均匀性是高性能核磁共振弛豫分析仪实现短弛豫时间样品和微弱信号核磁共振（NMR）检测的基本保障.该文以0.45 T双极型永磁体作为设计核心部件,在大范围磁体空间-25.4 mm球空间（DSV）内,基于目标场法设计了X、Y、Z、XY、XZ、YZ、Z²共7组有源匀场线圈,根据线圈供电要求,设计了可编程恒流电源,搭建了可用于高性能核磁共振弛豫分析仪磁体的有源匀场系统,介绍了系统的基本结构、设计过程及匀场方法.实验测试结果验证了大范围磁体空间内该匀场系统的实用性.     

高场核磁共振波谱仪宽带前置放大器的研制

宽带前置放大器是磁共振仪器的重要部件,其性能决定了整个仪器X核通道的检测灵敏度. 根据射频电路理论以及磁共振波谱仪整体性能指标的要求,设计并实现了可应用于高场核磁共振波谱仪的高性能宽带前置放大器. 实测结果表明,所研制的核磁共振波谱仪宽带前置放大器在15 MHz~300 MHz频率范围内,其工作性能达到：带内增益>38 dB,带内平坦度<1.5 dB,噪声系数基本保持在1.2 dB以下,射频开关切换时间<1.5 μs,具有带内增益平坦度高,噪声系数小,发射状态下放大器前端保护电路隔离度高,以及工作状态检测电路准确、简洁的特点. 同时高场核磁共振碳和磷等杂核实验显示,利用所研制的宽带前置放大器可检测到具有较高信噪比的NMR信号.     

核磁共振实验辅助设计专家系统

采用CLIPS作为事实推理核心,以Visual C++为界面开发工具,设计开发了核磁共振实验辅助设计专家系统软件．该软件可以根据用户提供的关于实验目的、样品特性和谱仪能等信息,建议所需进行的核磁共振实验．在用户反馈实验结果后,该系统可以进一步提出建议,如此循环往复．对于建议进行的实验,系统也给出脉冲序列、参数设置、注意事项等与实验相关的详细信息．本系统对于核磁共振的教学也可以起到辅助作用．     

用于核磁共振的直接数字合成频率源

直接数字频率源的使用可以简化核磁共振谱仪的设计,降低核磁共振谱仪设计的成本. 文中介绍一种采用Analog Device公司的AD7008芯片设计的基于PC机的直接数字合成频率源,它可实现频率和相位的高速切换,频率分辨率为0.01Hz,相位分辨率为0.09°,最后给出核磁共振实验结果.     

武汉中科波谱技术有限公司新技术交流会

<正>武汉中科波谱技术有限公司位于中国光谷的核心地带——武汉东湖新技术开发区,是国内首家集研制、开发、生产、应用和销售为一体的高场超导核磁共振谱仪高新技术企业.公司依托于中国科学院武汉物理与数学研究所强大的学科背景、技术优势与科研力量,致力于核磁共振谱仪国产化和相关技术的推广运用.通过多年研究探索,成功研制和生产了具备自主知识产权的高场核磁共振谱仪.该项目技术创新点包括:     

Computer simulation studies of the effects of dynamic shimming on susceptibility artifacts in EPI at high field

Dynamic shimming in multi-slice imaging aims to achieve optimal magnetic field homogeneity by updating the shim coil currents for each slice in real time. Dynamic shimming may reduce the signal loss and geometric distortion caused by magnetic susceptibility variations between tissues and is likely to be valuable for fast T2*-sensitive imaging techniques like EPI. A computer simulation of dynamic shimming using real image data has been developed to demonstrate the effectiveness of higher order dynamic shimming for echo planar imaging at high magnetic field, and to investigate the potential benefits of different orders of shim coil. Geometric distortions and signal intensities for different degrees of dynamic shimming were simulated and the results are compared with the images obtained with a conventional shimming technique. These results demonstrate the effectiveness, necessity and difficulty of high order dynamic shimming.     

小型回旋加速器全自动化磁场测量和精密垫补平台研制

针对核医学诊疗对PET医用放射性核素的需求,中国原子能科学研究院正在开展PET医用小型回旋加速器的产业化研究。磁场测量和垫补是回旋加速器生产中的必经环节,小型回旋加速器结构紧凑实现磁场测量仪的全自动化控制是一个难点,解决常规垫补方法加工成本高和周期长的问题是产业化生产的关键。本文详细介绍小型回旋加速器全自动化磁场测量和精密垫补平台的研制,通过多台小型回旋加速器的磁场测量和垫补实践,发展一套快速磁场测量和垫补流程,实现全自动化测量方法缩短磁场测量周期,采用精密垫补算法减少垫补次数。在保证磁场测量和垫补工作高效高质量完成的条件下,极大降低了时间和加工成本,为小型回旋加速器的产业化生产打下基础。目前,中国原子能科学研究院已经完成多台小型回旋加速器的商业化落地。     

基于虚拟样机的回旋加速器主磁铁设计与修正

 磁铁设计对于等时性回旋加速器极为关键。磁场分布需要满足粒子等时性加速和粒子径向、轴向聚集要求，同时避免危险的横向共振。提出了一种计算机辅助的自动化磁铁设计、建模和修正的方法，该方法在基于Python混合编程的虚拟样机集成设计环境中实现。详细描述了利用3维电磁场仿真软件TOSCA和自主开发的粒子束跟踪软件PTP对磁铁的优化过程，并给出了一个16 MeV负氢紧凑型回旋加速器的主磁铁设计实例。     

High-order MR shimming: a simulation study of the effectiveness of competing methods, using an established susceptibility model of the human head

The first step in the process of shimming a magnetic field is to characterize it by obtaining a field map and decomposing that map into a convenient set of basis functions. The strength of each member of the set is then calculated. Finally, a set of correction elements which generate fields corresponding to the same spatial distribution as the basis functions is energized so that the sum of their fields and the error fields is substantially zero. The basis functions used typically are solutions to Laplace’s equation and have been shown to be very effective when the region of interest is substantially free space. This paper addresses issues associated with shimming the magnetic field in a region in which there is a distribution of materials with different susceptibilities and which therefore is not free space. In such a region, Laplace’s equation is no longer valid and in principle cannot be used to describe the magnetic field there. It is demonstrated that in spite of this, the same set of basis functions suffices for analyzing the field and the same set of elements suffices for correcting the field. The motivation for this study stems from the need to improve the magnetic field homogeneity when biological specimens are being imaged by magnetic resonance. In particular, this paper describes a study carried out by various simulated shimming strategies to improve the uniformity of the magnetic field over a multitissue model of susceptibility of the human head. The topics of magnetic susceptibility, the effect of shimming on MR images, shimming hardware and shimming methods are briefly reviewed. Two slices of the human head model were selected for detailed study, both offset inferior to the origin and including the base of the brain and the anterior sinus. The results of the study include comparisons between the strategies of global shimming, local slice-selective shimming and combinations of the two; the effects of shimming to various orders of spherical harmonics; and the effects of rotation and displacement of the head with respect to the shim frame of reference.     

Dynamic B0 shimming at 7 T

Dynamic slice-wise shimming improves B₀ field homogeneity by updating shim coil currents for every slice in a multislice acquisition, producing better field homogeneity over a volume than can be obtained by a single static global shim. The first aim of this work was to evaluate the performance of slice-wise field-map-based second-order dynamic shimming in a human high-field 7 T clinical scanner vis-à-vis image based second order static global shimming. Another goal was to characterize eddy currents induced by second and third order shim switching. A final aim was to compare global and dynamic shimming through shim orders to elucidate the relative benefits of going to higher orders and to dynamic shim updating from a static shimming regime. An external hardware module was used to store and dynamically update slice-optimized shim values during multislice data acquisition. High-bandwidth multislice gradient echo scans with B₀ field mapping and low-bandwidth single-shot echo planar scans were performed on phantoms and humans using second-order dynamic and static global shims. For the measurement of second and third order shim induced eddy currents, step response temporal phase changes of individual shims were measured and fit to shim harmonics spatially and to multiexponential decay functions temporally. Finally, an order-wise field-map-based comparison was performed with first, second and third order global static shimming, first and second order dynamic shimming, as well as combined second or third order global and first order dynamic shim. Dynamic shimming considerably improved B₀ homogeneity compared to static global shimming both in phantoms and in human subjects, reducing image distortion and signal dropout. The unshielded second and third order shims generated strong B₀ and self and cross-term eddy fields, with multiple time constants ranging from milliseconds to seconds. Field homogeneity improved with increasing order of shim, with dynamic shimming performing better than global shimming. Hybrid global and dynamic shimming approach yielded field homogeneity better than global static shims but worse than dynamic shims.     

Combined passive and active shimming for in vivo MR spectroscopy at high magnetic fields

The use of high magnetic fields increases the sensitivity and spectral dispersion in magnetic resonance spectroscopy (MRS) of brain metabolites. Practical limitations arise, however, from susceptibility-induced field distortions, which are increased at higher magnetic field strengths. Solutions to this problem include optimized shimming, provided that active, i.e., electronic, shimming can operate over a sufficient range. To meet our shim requirements, which were an order of magnitude greater than the active shim capacity of our 7T MR system, we developed a combined passive and active shim approach. Simple geometries of ferromagnetic shim elements were derived and numerically optimized to generate a complete set of second-order spherical harmonic shim functions in a modular manner. The major goals of the shim design were maximization of shim field accuracy and ease of practical implementation. The theoretically optimized ferro-shim geometries were mounted on a cylindrical surface and placed inside the magnet bore, surrounding the subject's head and the RF coil. Passive shimming generated very strong shim fields and eliminated the worst of the field distortions, after which the field was further optimized by flexible and highly accurate active shimming. Here, the passive-shimming procedure was first evaluated theoretically, then applied in phantom studies and subsequently validated for in vivo 1H MRS in the macaque visual cortex. No artifacts due to the passive shim setup were observed; adjustments were reproducible between sessions. The modularity and the reduction to two pieces per shim term in this study is an important simplification that makes the method applicable also for passive shimming within single sessions. The feasibility of very strong, flexible and high-quality shimming via a combined approach of passive and active shimming is of great practical relevance for MR imaging and spectroscopy at high field strengths where shim power is limited or where shimming of specific anatomical regions inherently requires strong shim fields.     

光学速调管改造后辐射段磁场垫补和测量

 合肥国家同步辐射实验室正在开展储存环相干谐波自由电子激光研究，并对原来的光学速调管进行了改造。磁场的垫补和测量方法由原来的整体测量改为分段进行，垫补的使用使各段积分场及位相误差都尽可能小。详述了合肥储存环的光学速调管辐射段磁场垫补的三种方式，测量了垫补前后不同间隙下积分场分布、位相误差及横向均匀度，各项指标都达到了要求。同样的方法将用于色散段和调制段磁场垫补与测量中，为相干谐波自由电子激光研究提供实验保障。     

C60与某些萘胺衍生物光诱导电子转移反应的ESR研究

在运用ESR方法对C₆₀与一系列萘胺化合物的光诱导电子转移反应过程的研究中发现,对于不同萘胺衍生物,其反应性随化合物分子结构的变化而改变.由于空间位阻作用和氮原子上的孤对电子与芳环的共轭作用,使得萘胺比脂肪胺较难给出电子,而连接两个芳基的N-苯基取代萘胺则更难给出电子.     

An Optimized Passive Shimming Method for Bi-planar Permanent MRI Magnets

An optimized passive shimming method with iron shims is presented in this paper. First, the influence value of a single iron or magnetized shim is fast calculated and determined by analytic solution with a single practical measurement. Then, the correlation between the influence value and parameters of a single shim is analyzed, and the proper parameters, including the position, polarity, and size (radius and thickness), of the shimming pieces are well selected. Finally, the numbers and locations of the passive shims are optimized by mixed-integer linear programming method based on a modified central magnetic field. The optimized method is applied to a 0.5 T Bi-planar permanent magnet magnetic resonance imaging system, and the presented results prove the efficacy of this optimized passive shimming methodology.     

A new method for variable temperature gradient shimming

Sample convection can severely attenuate the signals observed in pulsed field gradient spin--echo experiments such as those used for gradient shimming. A new class of pulse sequences is proposed, in which a double spin--echo refocuses the phase errors caused by sample convection, enabling gradient shimming to be performed reliably over a wide range of temperatures.