A novel continuous arterial spin labeling approach for CBF measurement in rats with reduced labeling time and optimized signal-to-noise ratio efficiency

Objective  To develop a continuous arterial spin labeling (CASL) perfusion imaging method for cerebral blood flow (CBF) measurement in rats with reduced spin-labeling length and optimized signal-to-noise ratio (SNR _f ) per unit time. Materials and methods  In the proposed method, the longitudinal magnetization of brain tissue water in the imaging slice is prepared into a proper state before spin-labeling, and a post-tagging delay is employed after spin-labeling. The method was implemented on a 4.7 T small animal scanner. Numerical simulations and in vivo experiments were used to evaluate the performance of the method proposed. Results  With the proposed method, absolute CBF could be measured accurately from normal rat with a spin-labeling pulse as short as 400 ms, and yet employing the same formula as that used in the conventional CASL perfusion imaging method for calculation. The method also showed improved SNR _f per unit time over the conventional CASL perfusion imaging method and the pulsed arterial spin labeling perfusion imaging method FAIR. Conclusion  Compared to the conventional CASL perfusion imaging method, the proposed method would be advantageous for CBF measurement in small animals having short vascular transit time in terms of SNR _f per unit time and other benefits brought by shortened spin-labeling pulse.     

Accelerated whole brain intracranial vessel wall imaging using black blood fast spin echo with compressed sensing (CS-SPACE)

Objective

Develop and optimize an accelerated, high-resolution (0.5 mm isotropic) 3D black blood MRI technique to reduce scan time for whole-brain intracranial vessel wall imaging.

Materials and methods

A 3D accelerated T₁-weighted fast-spin-echo prototype sequence using compressed sensing (CS-SPACE) was developed at 3T. Both the acquisition [echo train length (ETL), under-sampling factor] and reconstruction parameters (regularization parameter, number of iterations) were first optimized in 5 healthy volunteers. Ten patients with a variety of intracranial vascular disease presentations (aneurysm, atherosclerosis, dissection, vasculitis) were imaged with SPACE and optimized CS-SPACE, pre and post Gd contrast. Lumen/wall area, wall-to-lumen contrast ratio (CR), enhancement ratio (ER), sharpness, and qualitative scores (1–4) by two radiologists were recorded.

Results

The optimized CS-SPACE protocol has ETL 60, 20% k-space under-sampling, 0.002 regularization factor with 20 iterations. In patient studies, CS-SPACE and conventional SPACE had comparable image scores both pre- (3.35 ± 0.85 vs. 3.54 ± 0.65, p = 0.13) and post-contrast (3.72 ± 0.58 vs. 3.53 ± 0.57, p = 0.15), but the CS-SPACE acquisition was 37% faster (6:48 vs. 10:50). CS-SPACE agreed with SPACE for lumen/wall area, ER measurements and sharpness, but marginally reduced the CR.

Conclusion

In the evaluation of intracranial vascular disease, CS-SPACE provides a substantial reduction in scan time compared to conventional T₁-weighted SPACE while maintaining good image quality.

     

Deriving the signal-to-noise ratio probability of error and performance measure matrices for distribution line carrier signals propagation (using bus impedance approach)

The automated distribution system using distribution line carrier (DLC) needs a two way communication between the various controlled terminals and the main substation. Digital data should be transmitted over the distribution power lines from the main substation to the transceivers in the distribution system and vice versa. The distribution system is a hostile medium for data transmission [i.e., high noise levels and standing wave patterns with low voltage nodes (as a result of signal reflections in the system)]. This hostility leads to low signal-to-noise ratio (SNR) locations and subsequently to high probability of bit error at these locations. The bus impedance matrix was developed for medium voltage distribution system. An actual medium voltage distribution line was tested. The actual measurements of the tested line verified the validity of the derived equations. The above mentioned line with the addition of a branch is used as an example in this paper. This paper derives (SNR) probability of bit error and performance measure transfer rate of information bits (TRIB) matrices of any DLC system starting from the bus impedance matrix.     

PRESS-based proton single-voxel spectroscopy and spectroscopic imaging with very short echo times using asymmetric RF pulses

Modified point-resolved spectroscopy (PRESS) sequences for single voxel spetroscopy (MRS) and spectroscopic imaging (SI) with very short echo time (T _E ) are described using asymmetric radio-frequency (RF) pulses as well as an optimized design and timing of the PRESS sequence. The proposed sequences were implemented on a standard 4.7 T imaging system yielding a T _E of 6.0 ms only. Simulations and experimental data measured on phantoms and the rat brain in vivo are presented for MRS and SI showing a high signal-to-noise ratio and hardly any phase distortions caused by J-coupling.     

Detecting small pulmonary nodules with spiral ultrashort echo time sequences in 1.5 T MRI

Magnetic Resonance Materials in Physics, Biology and Medicine - This study investigated ultrashort echo time (UTE) sequences in 1.5 T magnetic resonance imaging (MRI) for small lung nodule...     

Preliminary experience with a new double-echo half-Fourier single-shot turbo spin echo acquisition in the characterization of liver lesions

A new double-echo half-Fourier single-shot turbo spin echo technique has been implemented in which two images are obtained per excitation pulse, one with an echo time (TE) of 60 ms and another with a TE of 438 ms. The acquisition window per image is 380 ms and is determined by the echo spacing of 4.3 ms and the echo train length of 88 for images with resolution of 160×256. No breath holding was performed. The aim of the study was to test whether the additional information of the late TE image improves the characterization of liver lesions. Twenty-eight patients with 39 focal liver lesions (9 cysts, 11 hemangiomas, and 19 solid lesions) were imaged with the new technique, and signal intensity (SI) ratios of lesion and liver were obtained. At-test analysis showed that in the TE 60 ms image, SI ratios of cysts and hemangiomas were not significantly different, whereas in the TE 438 ms images the two types of lesions can be classified. Signal intensity ratios of solid lesions were in both images clearly lower than those of cysts and hemangiomas. The technique, therefore, seems a promising and straightforward new tool for the characterization of liver lesions.     

Application of LCModel for quality control and quantitative in vivo1H MR spectroscopy by short echo time STEAM sequence

The linear combination of model spectra (LCModel) calculation of a parameter for long-term quality control,k _T, was introduced, representing the ratio of the temporal and nominal intensities of CH₃ groups of lactate and acetate in a quality control phantom. This procedure is a part of the quality assurance of the scanner using fully automatic measurement and calculation ofk _T parameters, and utilizing Shewhart regulation control charts for continuous evaluation of the magnetic resonance (MR) scanner setting. The application of thek _T parameter for the correction of in vivo data increases the precision of molar concentration determination by about 4%. This was tested by the quantitative in vivo MR determination of the molar concentrations of 13 prominent metabolites (N-acetylaspartate (NAA),N-acetylaspartylgutamate, creatine and phosphocreatine (Cr), choline-containing compounds (Cho), myo-inositol, scyllo-inositol., γ-aminobutyric acid, glutamine, glutamate, glucose, lactate, alanine, taurine) in the white matter and hippocampus of the brain in groups of volunteers, using a short echo time stimulated echo acquisition mode sequence (echo time =10 ms) and the LCModel technique. The repeatability of the measurement of prominent metabolites such as NAA, Cr and Cho was found to be around 10% (relative standard deviation,n=6); precision in a group of volunteers (n=20 and 28, respectively) was in the range of approximately 13–20%. For other metabolites, which are measured with a lower signal-to-noise ratio, the precision can be much lower.     

Towards Ni(II) complexes with spin switches for 19F MR-based pH sensing

Magnetic Resonance Materials in Physics, Biology and Medicine - Our aim was to demonstrate the potential of exploiting simultaneous changes in coordination geometry and spin state in fluorinated...     

Influence of pulse angle variations onstimulated echo acquisition mode proton nuclear magnetic resonance spectra of AB spin systems: theory and experiments with citrate

The influence of pulse angle variations in the localization sequence stimulated echo acquisition mode (STEAM) on the signal of strongly coupled AB spin systems has been examined. Experimental¹H nuclear magnetic resonance (NMR) spectra of citrate were recorded on a 1.5 T whole-body imager. Theoretically calculated spectra were generated, with good correlation to experimental results. The dependence of the signal intensity on sequence timing and pulse angles was calculated analytically. For longer sequence timings, the ratio of the signal intensity from citrate to the signal intensity from uncoupled nuclei depends strongly on the applied flip angles. The shape of spectra also changes with varying flip angles. These effects are clearly less pronounced for STEAM than for point resolved spectroscopy (PRESS). The results have to be considered for quantitative measurements of citrate in spectroscopic investigations as, e.g. of prostate neoplasms.     

Photonic integration using asymmetric twin-waveguide (ATG) technology: part I-concepts and theory

In this first of two papers (hereinafter called Paper I), we present a universal approach for simply realizing monolithic photonic integration based on asymmetric twin-waveguide (ATG) technology. The concepts and important developments leading to ATG integration technology will be reviewed. The ATG structure consists of active and/or passive devices formed in separate, vertically displaced waveguides. Light is transferred between the waveguides via very low loss, lateral, adiabatic tapered mode transformers, allowing different optical functions to be realized in the different waveguides. The design of the adiabatic tapered mode transformer uses an algorithm based on perturbation theory. We show that the same designs can also be deduced from coupled local mode theory. Using the perturbation algorithm to design the taper coupler in an ATG based high bandwidth photodiode, a transfer efficiency of greater than 90% from the fiber waveguide to the coupling waveguide is achieved while the taper length can be reduced by 35% compared to conventional two-section linear taper couplers. The taper design algorithm is further optimized to make the adiabatic taper couplers tolerant to variations in incident light polarization, operation wavelength, and dimensional control during fabrication. Finally, we propose and design a taper that adiabatically couples light from the fundamental mode to the first-order mode. Such a taper coupler is useful in an integrated semiconductor optical amplifier/p-i-n detector circuit.     

改进GM(1,1)模型在电力负荷预测中的应用

灰色预测技术原理简单、样本量小、计算简便,适合用于负荷预测,但其存在很多局限性。从建模原理出发,利用最小二乘法和积分法,改进影响模型精度最重要的两个因素——初始值和背景值。以北京市1999—2005年的电力消费量数据加以计算,证明改进效果较为显著。     

N位取代聚苯并咪唑酰亚胺薄膜:改善的溶解性与透过率

试验合成了两种新型的N-苯基取代苯并咪唑二胺,区别在于N-苯基的邻位分别由甲基和氟原子取代.将新型二胺分别与二酐4,4′-(六氟异丙烯)二酞酸酐(6FDA)和4,4′-氧双邻苯二甲酸酐(ODPA)通过两步热亚胺法制备聚苯并咪唑酰亚胺(PBII)薄膜,并对新型二胺单体及PBII薄膜进行了性能测试与表征.结果表明:新型PBII薄膜表现出良好的耐热性(玻璃化转变温度Tg=341～381℃)和拉伸强度(σ=95～135 MPa).不同邻位取代的N-苯基破坏了分子的有效堆积,使得PBII薄膜的溶解性和光学透明性得到改善.     

Games with incomplete and asymmetric information in poolco markets

Strategic equilibrium solutions as a result of gaming by electricity market participants have been the subject of various recent studies. Yet, in many of the tools developed for finding those strategic solutions, either information is regarded as being complete, or the complexities of the transmission system are disregarded. Since the assumption of complete information is neither absolutely correct nor absolutely necessary for the more complex models, these models need to be extended. The strategic solutions attained in these incomplete information or Bayesian games are Bayesian Nash equilibria. The central thrust of the paper is on bringing the representation of incomplete and asymmetric information in strategic games together with some of the transmission system constraints. For this purpose, the paper focuses on a specific strategic game model referred to as the IWM. Numerical examples, using the IEEE 57-bus system, that deal with the power flow equality constraints are presented as an illustration of the concepts behind the proposed Bayesian games.     

Spatially resolved kinetics of skeletal muscle exercise response and recovery with multiple echo diffusion tensor imaging (MEDITI): a feasibility study

Objectives

We describe measurement of skeletal muscle kinetics with multiple echo diffusion tensor imaging (MEDITI). This approach allows characterization of the microstructural dynamics in healthy and pathologic muscle.

Materials and methods

In a Siemens 3-T Skyra scanner, MEDITI was used to collect dynamic DTI with a combination of rapid diffusion encoding, radial imaging, and compressed sensing reconstruction in a multi-compartment agarose gel rotation phantom and within in vivo calf muscle. An MR-compatible ergometer (Ergospect Trispect) was employed to enable in-scanner plantar flexion exercise. In a HIPAA-compliant study with written informed consent, post-exercise recovery of DTI metrics was quantified in eight volunteers. Exercise response of DTI metrics was compared with that of T2-weighted imaging and characterized by a gamma variate model.

Results

Phantom results show quantification of diffusivities in each compartment over its full dynamic rotation. In vivo calf imaging results indicate larger radial than axial exercise response and recovery in the plantar flexion-challenged gastrocnemius medialis (fractional response: nT2w?=?0.385?±?0.244, nMD?=?0.163?±?0.130, nλ₁?=?0.110?±?0.093, nλ_rad?=?0.303?±?0.185). Diffusion and T2-weighted response magnitudes were correlated (e.g., r?=?0.792, p?=?0.019 for nMD vs. nT2w).

Conclusion

We have demonstrated the feasibility of MEDITI for capturing spatially resolved diffusion tensor data in dynamic systems including post-exercise skeletal muscle recovery following in-scanner plantar flexion.

     

Sodium (23Na) ultra-short echo time imaging in the human brain using a 3D-Cones trajectory

Object

Sodium magnetic resonance imaging (²³Na-MRI) of the brain has shown changes in ²³Na signal as a hallmark of various neurological diseases such as stroke, Alzheimer’s disease, Multiple Sclerosis and Huntington’s disease. To improve scan times and image quality, we have implemented the 3D-Cones (CN) sequence for in vivo ²³Na brain MRI.

Materials and methods

Using signal-to-noise (SNR) as a measurement of sequence performance, CN is compared against more established 3D-radial k-space sampling schemes featuring cylindrical stack-of-stars (SOS) and 3D-spokes kooshball (KB) trajectories, on five healthy volunteers in a clinical setting. Resolution was evaluated by simulating the point-spread-functions (PSFs) and experimental measures on a phantom.

Results

All sequences were shown to have a similar SNR arbitrary units (AU) of 6–6.5 in brain white matter, 7–9 in gray matter and 17–18 AU in cerebrospinal fluid. SNR between white and gray matter were significantly different for KB and CN (p = 0.046 and <0.001 respectively), but not for SOS (p = 0.1). Group mean standard deviations were significantly smaller for CN (p = 0.016). Theoretical full-width at half-maximum linewidth of the PSF for CN is broadened by only 0.1, compared to 0.3 and 0.8 pixels for SOS and KB respectively. Actual image resolution is estimated as 8, 9 and 6.3 mm for SOS, KB and CN respectively.

Conclusion

The CN sequence provides stronger tissue contrast than both SOS and KB, with more reproducible SNR measurements compared to KB. For CN, a higher true resolution in the same amount of time with no significant trade-off in SNR is achieved. CN is therefore more suitable for ²³Na-MRI in the brain.     

Improved short tau inversion recovery (iSTIR) for increased tumor conspicuity in the abdomen

Object

To develop an improved short tau inversion recovery (iSTIR) technique with simultaneous suppression of fat, blood vessels and fluid to increase tumor conspicuity in the abdomen for cancer screening.

Materials and methods

An adiabatic spectrally selective inversion pulse was used for fat suppression to overcome the reduced signal to noise ratio associated with chemically non-selective inversion pulse of STIR. A motion-sensitizing driven equilibrium was used for blood vessel suppression and a dual-echo single-shot fast spin echo acquisition was used for fluid suppression. The technique was optimized on four normal subjects and later tested on five patients referred for metastatic tumor evaluation.

Results

A velocity encoding of 2 cm/s achieved effective blood suppression even in small vessels. Subtraction of two images (one with 60 ms and the other with 280 ms echo time) acquired in the same echo train achieved excellent fluid suppression (>70 % reduction). Simultaneous suppression of fat, blood vessels and fluid improved the tumor conspicuity compared to corresponding fat-suppressed (STIR) image.

Conclusion

This technique generated two complementary images from a single scan: one that is equivalent to a STIR image and the other that qualitatively resembles a diffusion-weighted image and may have potential for magnetic resonance imaging cancer screening.

     

一种利用暂态响应分析提高电磁层析成像测量信号信噪比的新方法

本文提出了一种提高电磁层析成像测量信号信噪比的新方法。在电磁层析成像的前端测量电路中,最重要的一环是一个含有低通滤波器的相敏解调电路,当激励源从一个线圈切换到另一个线圈时,接收电压值发生变化,从而引起一个暂态响应过程。通常,测量和数模转换要等暂态响应过程完成、电压信号稳定后进行。本文提出了一种利用分析暂态相应过程中所含的信息而提高电磁层析成像测量信号信噪比的新方法。仿真和实验结果肯定了这种方法的有效性,测量到的电感值的标准方差下降多于50%。     

1H MR spectroscopic imaging with short and long echo time to discriminate glycine in glial tumours

OBJECT: To investigate glycine (Gly) concentrations in low- and high-grade gliomas based on (1)H MR spectroscopic imaging (MRSI) with short and long echo time (TE). Myoinositol (MI) and Gly appear at the same resonance frequency of 3.56 ppm, but due to strong coupling the MI signal dephases more rapidly. Therefore, their contribution to the 3.56 ppm signal should be distinguishable comparing MRSI data acquired at short and long TE. MATERIALS AND METHODS: (1)H MRSI (TE = 30 and 144 ms) was performed at 3 T in 29 patients with histopathological confirmed World Health Organization (WHO) grade II-IV gliomas and in FIVE healthy subjects. All spectra from the gliomas revealed increase of the 3.56 ppm resonance in the short TE spectra. Signal intensities of Gly and MI were differentiated either by analysing the short to long TE ratio of the resonance or by performing a weighted difference. Gly concentrations were compared between high-grade (WHO III-IV) and low-grade gliomas. RESULTS: High-grade gliomas showed significantly higher Gly concentrations compared to low-grade gliomas. CONCLUSION: Appropriate data processing of short and long TE (1)H MRSI provides a tool to distinguish and to quantify Gly and MI concentrations in gliomas. As Gly seems to be a marker of malignancy, more dedicated spectroscopic methods to differentiate these metabolites are justified.     

Improved luminescence from quantum-dot nanostructures embedded in structurally engineered (In,Ga)As confining layers

Efficient luminescence of quantum-dot nanostructures embedded in active regions of lasers is important for low-threshold current density devices. This paper discusses an approach for structurally engineering confining (In,Ga)As layers into which InAs quantum dots are inserted to enhance their emission efficiency. It is shown that by inserting the dots at the center of compositionally graded In/sub x/Ga/sub 1-x/As layers, the relative emission efficiency can be increased by nearly an order of magnitude over the emission of dots inside a constant composition (In,Ga)As structure. This enhancement is thought to be a result of the high structural and optical quality of the confining layers.     

感应电机饱和漏抗和挤流效应的改进算法（1）

本文采用一个新的计算模型，以有限元方法为工具，系统研究了影响感应电机饱和漏抗的因素，进而将在电机设计中采用的由Ｎｏｒｍａｎ提出的漏磁导饱和系数（ＫＺ）曲线，区分为谐波漏磁导饱和系数曲线与糟漏磁导饱和系数曲线，并首次提出便于在电机设计中使用的计算这些漏磁导饱和系数的曲线族。试算表明，在电机设计中采用本文的曲线族代替Ｎｏｒｍａｎ曲线可明显提高设计精度。