Physical limits to human brain B0 shimming with spherical harmonics,engineering implications thereof

Magnetic Resonance Materials in Physics, Biology and Medicine - As the MRI main magnetic field rises for improved signal-to-noise ratio, susceptibility-induced B0-inhomogeneity increases...     

Presurgical brain mapping in epilepsy using simultaneous EEG and functional MRI at ultra-high field: feasibility and first results

Magnetic Resonance Materials in Physics, Biology and Medicine - The aim of this study was to demonstrate that eloquent cortex and epileptic-related hemodynamic changes can be safely and reliably...     

Towards an integrated neonatal brain and cardiac examination capability at 7 T: electromagnetic field simulations and early phantom experiments using an 8-channel dipole array

Objective

Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T.

Methods

The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array.

Results

The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom.

Conclusion

The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.

     

Improving the clinical potential of ultra-high field fMRI using a model-free analysis method based on response consistency

Objective

To develop an analysis method that is sensitive to non-model-conform responses often encountered in ultra-high field presurgical planning fMRI. Using the consistency of time courses over a number of experiment repetitions, it should exclude low quality runs and generate activation maps that reflect the reliability of responses.

Materials and methods

7 T fMRI data were acquired from six healthy volunteers: three performing purely motor tasks and three a visuomotor task. These were analysed with the proposed approach (UNBIASED) and the GLM.

Results

UNBIASED results were generally less affected by false positive results than the GLM. Runs that were identified as being of low quality were confirmed to contain little or no activation. In two cases, regions were identified as activated in UNBIASED but not GLM results. Signal changes in these areas were time-locked to the task, but were delayed or transient.

Conclusion

UNBIASED is shown to be a reliable means of identifying consistent task-related signal changes regardless of response timing. In presurgical planning, UNBIASED could be used to rapidly generate reliable maps of the consistency with which eloquent brain regions are activated without recourse to task timing and despite modified hemodynamics.

     

MR venography of the human brain using susceptibility weighted imaging at very high field strength

Objective We investigate the implications of high magnetic field strength on MR venography based on susceptibility-weighted imaging (SWI) and estimate the optimum echo time to obtain maximum contrast between blood and brain tissue. Materials and methods We measured tissue contrast and relaxation times at 7 T of gray matter, white matter, and venous blood in vivo. Results relaxation times of gray matter, white matter, and venous blood in vivo yielded 32.9 ± 2.3, 27.7 ± 4.3, and 7.4 ± 1.4 ms, respectively. Optimum TE was found to be 15 ms which is supported by theoretical considerations. Using this optimum TE, we acquired 3D high resolution datasets with a large volume coverage in a short measurement time that show very detailed microanatomical structures of the human brain such as intracortical veins and laminar cortical substructures. Conclusions By applying optimised vessel filters (vesselness filter and vessel enhancing diffusion) whole brain MR venograms can be obtained at 7 T with a significantly reduced measurement time compared to 3 T.     

PT二次侧B相接地时微机保护自产和外接3_0的剖析

用相量图分析的方法,当电压互感器PT二次侧B相接地时,在正常运行状态和电力系统中发生单相接地、两相短路和两相接地短路微机保护自产3·U0与外接3·U0的一致性     

基于S3C4480＋uClinux的嵌入式系统多串口的实现

对基于S3C4480微处理器和uClinux操作系统的嵌入式系统，利用异步串行通讯芯片TL16C554A实现了多串行通讯接口的扩展。针对半双工RS-485通信方式，在串口驱动程序中采用直接判断TL16C554A的缓冲区状态的方法，实现了数据收发的自动控制。本文的设计和方法已经成功应用在远程监控系统中，系统性能稳定可靠。     

基于S3C44B0+uClinux的嵌入式系统多串口的实现

对基于S3C44B0微处理器和uClinux操作系统的嵌入式系统,利用异步串行通讯芯片TL16C554A实现了多串行通讯接口的扩展.针对半双工RS-485通信方式,在串口驱动程序中采用直接判断TL16C554A的缓冲区状态的方法,实现了数据收发的自动控制.本文的设计和方法已经成功应用在远程监控系统中,系统性能稳定可靠.     

Integrated RF probe for in vivo multinuclear spectroscopy and functional imaging of rat brain using an 11.7 Tesla 89 mm bore vertical microimager

To acquire high quality in vivo NMR data from rat brain using a vertical 89-mm bore magnet, specially designed NMR probes with integrated RF coils and animal handling capability are required. An RF probe design that is also capable of rat head fixation, body support and suitable for physiology monitoring and maintenance was constructed for an 89 mm bore, 11.7 T, vertical microimager which is equipped with a 57-mm i.d. gradient insert. Design concept and practical aspects of probe construction are described in detail. The device allows accurate and highly reproducible positioning of rat head inside the magnet while providing excellent RF performance. Typical results from fMRI, localized in vivo proton and multinuclear spectroscopy using this probe system are presented.     

Water proton T 1 measurements in brain tissue at 7, 3, and 1.5T using IR-EPI, IR-TSE, and MPRAGE: results and optimization

Method This paper presents methods of measuring the longitudinal relaxation time using inversion recovery turbo spin echo (IR-TSE) and magnetization-prepared rapid gradient echo (MPRAGE) sequences, comparing and optimizing these sequences, reporting T ₁ values for water protons measured from brain tissue at 1.5, 3, and 7T. T ₁ was measured in cortical grey matter and white matter using the IR-TSE, MPRAGE, and inversion recovery echo planar imaging (IR-EPI) pulse sequences. Results In four subjects the T ₁ of white and grey matter were found to be 646±32 and 1,197±134ms at 1.5T, 838±50 and 1,607±112ms at 3T, and 1,126±97, and 1,939±149ms at 7T with the MPRAGE sequence. The T ₁ of the putamen was found to be 1,084±63ms at 1.5T, 1,332±68ms at 3T, and 1,644±167ms at 7T. The T ₁ of the caudate head was found to be 1,109± 66ms at 1.5T, 1,395±49ms at 3T, and 1,684±76ms at 7T. Discussion There was a trend for the IR-TSE sequence to underestimate T ₁ in vivo. The sequence parameters for the IR-TSE and MPRAGE sequences were also optimized in terms of the signal-to-noise ratio (SNR) in the fitted T ₁. The optimal sequence for IR-TSE in terms of SNR in the fitted T ₁ was found to have five readouts at TIs of 120, 260, 563, 1,221, 2,647, 5,736ms and TR of 7 s. The optimal pulse sequence for MPRAGE with readout flip angle = 8° was found to have five readouts at TIs of 160, 398, 988, 2,455, and 6,102ms and a TR of 9 s. Further optimization including the readout flip angle suggests that the flip angle should be increased, beyond levels that are acceptable in terms of power deposition and point-spread function.     

Quantitative analysis of the influence of conductors and ferromagnetic structures in power facilities on an ELF magnetic field environment using the finite element method

Recently, electric power transmission/substation systems need to be extended and they tend to be more compact. From the backgrounds of electromagnetic field environment, especially the magnetic field environment in and around electric power facilities becomes more important. However, many factors must be considered when investigating it, such as complicated current conditions, configurations of conductors and ferromagnetic structures, and so on. For more precise investigation of magnetic field environments, we must understand the quantitative influence of conductors and ferromagnetic structures. In this paper we describe how conductive and ferromagnetic materials influence the ELF magnetic field distribution. We carried out the measurement and finite element analysis of magnetic flux density distribution around an aluminum plate, a soft magnetic iron plate, and a 1/40 reduced model of an actual transmission tower. Based on the results, we clarified the influence of conductors and ferromagnetic substances on the magnetic flux density distribution around them. Finally, we showed the effectiveness of finite element analysis for evaluating the magnetic field around actual power facilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 44–52, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10021