Correction to: 3D APT and NOE CEST-MRI of healthy volunteers and patients with non-enhancing glioma at 3 T

Magnetic Resonance Materials in Physics, Biology and Medicine -     

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     

北斗高精度兼容接收机精度测试与分析

采用“硬比法”的实验方法对某公司研发的高精度兼容接收机进行了静态/动态精度测试.在使用载波相位数据处理方式下短基线闭合精度可以达到1～2 mm,动态跑车情况下RTK处理结果与GPS数据处理精度结果的比较,水平定位精度达到2 cm左右,高程精度4 cm左右,得出了使用北斗高精度兼容接收机在精度鉴定服务中可行性的结论.对于今后改变目前测控设备精度鉴定对GPS严重依赖的局面,形成新的测量体系及新的设备精度鉴定体系规范与标准,将具有十分重要的军事意义和应用价值.     

Pilot tone-based prospective correction of respiratory motion for free-breathing myocardial T1 mapping

Objective

To provide respiratory motion correction for free-breathing myocardial T1 mapping using a pilot tone (PT) and a continuous golden-angle radial acquisition.

Materials and methods

During a 45 s prescan the PT is acquired together with a dynamic sagittal image covering multiple respiratory cycles. From these images, the respiratory heart motion in head-feet and anterior–posterior direction is estimated and two linear models are derived between the PT and heart motion. In the following scan through-plane motion is corrected prospectively with slice tracking based on the PT. In-plane motion is corrected for retrospectively. Our method was evaluated on a motion phantom and 11 healthy subjects.

Results

Non-motion corrected measurements using a moving phantom showed T1 errors of 14 ± 4% (p < 0.05) compared to a reference measurement. The proposed motion correction approach reduced this error to 3 ± 4% (p < 0.05). In vivo the respiratory motion led to an overestimation of T1 values by 26 ± 31% compared to breathhold T1 maps, which was successfully corrected to an average difference of 3 ± 2% (p < 0.05) between our free-breathing approach and breathhold data.

Discussion

Our proposed PT-based motion correction approach allows for T1 mapping during free-breathing with the same accuracy as a corresponding breathhold T1 mapping scan.

     

An improved PSF mapping method for EPI distortion correction in human brain at ultra high field (7T)

Object  

To further improve the quality and robustness of the point-spread function (PSF) mapping method for fully automatic and accurate correction of geometric distortions in EPI at ultra high field such as 7 Tesla with high fidelity.     

Differential amplifier with improved gain‐accuracy and linearity

A novel circuit design technique is presented which improves gain‐accuracy and linearity in differential amplifiers. The technique employs negative impedance compensation and results demonstrate a significant performance improvement in precision, lowering sensitivity, and wide dynamic range. A theoretical underpinning is given together with the results of a demonstrator differential input/output amplifier with gain of 12 dB. The simulation results show that, with the novel method, both the gain‐accuracy and linearity can be improved greatly. Especially, the linearity improvement in IMD can get to more than 23 dB with a required gain. Copyright © 2009 John Wiley & Sons, Ltd.     

模拟光耦器件HCNR201及其在高精度电压检测中的应用

介绍了HP公司的高精度线性模拟光耦器件HCNR201的基本原理;给出了利用该芯片对模拟电压进行检测与隔离的硬件电路;通过对实验结果的处理及分析,证明了该方法测量电压的线性度好、准确度高。     

3D T 1-mapping for the characterization of deep vein thrombosis

Purpose  

The aim of this work was to investigate fast T ₁-mapping for the characterization of deep vein thrombosis (DVT).     

Fast T1 and T2 mapping methods: the zoomed U-FLARE sequence compared with EPI and snapshot-FLASH for abdominal imaging at 11.7 Tesla

Objective

A newly adapted zoomed ultrafast low-angle RARE (U-FLARE) sequence is described for abdominal imaging applications at 11.7 Tesla and compared with the standard echo-plannar imaging (EPI) and snapshot fast low angle shot (FLASH) methods.

Materials and methods

Ultrafast EPI and snapshot-FLASH protocols were evaluated to determine relaxation times in phantoms and in the mouse kidney in vivo. Owing to their apparent shortcomings, imaging artefacts, signal-to-noise ratio (SNR), and variability in the determination of relaxation times, these methods are compared with the newly implemented zoomed U-FLARE sequence.

Results

Snapshot-FLASH has a lower SNR when compared with the zoomed U-FLARE sequence and EPI. The variability in the measurement of relaxation times is higher in the Look–Locker sequences than in inversion recovery experiments. Respectively, the average T1 and T2 values at 11.7 Tesla are as follows: kidney cortex, 1810 and 29 ms; kidney medulla, 2100 and 25 ms; subcutaneous tumour, 2365 and 28 ms.

Conclusion

This study demonstrates that the zoomed U-FLARE sequence yields single-shot single-slice images with good anatomical resolution and high SNR at 11.7 Tesla. Thus, it offers a viable alternative to standard protocols for mapping very fast parameters, such as T1 and T2, or dynamic processes in vivo at high field.

     

一个高精度简洁后向控制通道解决方案

后向通道是数字控制器不可缺少的重要环节 ,其性能对整个控制系统的控制品质具有重要影响。讨论了AD420内部电路结构以及三线接口时和级连接口时的时序 ,提出了使用AD420实现一个高精度的后向控制通道的解决方案 ,同时给出了使用AD420构造后向通道的几个实例。实验结果表明 ,AD420构造后向通道极易实现 ,应用程序的编制也非常简洁     

Evaluation of variable flip angle,MOLLI, SASHA,and IR-SNAPSHOT pulse sequences for T1 relaxometry and extracellular volume imaging of the pancreas and liver

Magnetic Resonance Materials in Physics, Biology and Medicine - Compare fourT1-mapping pulse sequences for T1 relaxometry and extracellular volume (ECV) fraction of the pancreas and liver In vitro...     

兼顾提升功率分配精度与抑制电压偏差的自适应下垂控制

直流微电网孤岛运行时,为实现下垂参数跟随直流微电网各光伏单元出口线路阻抗和本地负载分布情况自调整,提出一种基于麻雀搜索算法(sparrow search algorithm, SSA)的自适应下垂控制策略。将下垂参数、变换器输出电压参考值以函数变量的形式构成优化目标函数,利用麻雀搜索算法寻找目标函数的极小值,实时找到同时使系统运行过程中的功率偏差、母线电压偏差最小化的解。即利用麻雀搜索算法将下垂参数和电压参考值调节问题转化为函数极值寻优问题,实现了下垂系数可依据光伏出口线路阻抗、本地负载变化及光照强度变化自调整的目标。同时通过动态调节变换器输出电压参考值,减小母线电压偏差,解决了功率分配精度与母线电压偏差的固有矛盾。利用PSCAD/EMTDC建立系统仿真模型,仿真结果证明所提控制策略正确、有效。     

Comparison of T1-weighted 2D TSE, 3D SPGR,and two-point 3D Dixon MRI for automated segmentation of visceral adipose tissue at 3 Tesla

Objectives

To evaluate and compare conventional T1-weighted 2D turbo spin echo (TSE), T1-weighted 3D volumetric interpolated breath-hold examination (VIBE), and two-point 3D Dixon-VIBE sequences for automatic segmentation of visceral adipose tissue (VAT) volume at 3 Tesla by measuring and compensating for errors arising from intensity nonuniformity (INU) and partial volume effects (PVE).

Materials and methods

The body trunks of 28 volunteers with body mass index values ranging from 18 to 41.2 kg/m² (30.02 ± 6.63 kg/m²) were scanned at 3 Tesla using three imaging techniques. Automatic methods were applied to reduce INU and PVE and to segment VAT. The automatically segmented VAT volumes obtained from all acquisitions were then statistically and objectively evaluated against the manually segmented (reference) VAT volumes.

Results

Comparing the reference volumes with the VAT volumes automatically segmented over the uncorrected images showed that INU led to an average relative volume difference of ?59.22 ± 11.59, 2.21 ± 47.04, and ?43.05 ± 5.01 % for the TSE, VIBE, and Dixon images, respectively, while PVE led to average differences of ?34.85 ± 19.85, ?15.13 ± 11.04, and ?33.79 ± 20.38 %. After signal correction, differences of ?2.72 ± 6.60, 34.02 ± 36.99, and ?2.23 ± 7.58 % were obtained between the reference and the automatically segmented volumes. A paired-sample two-tailed t test revealed no significant difference between the reference and automatically segmented VAT volumes of the corrected TSE (p = 0.614) and Dixon (p = 0.969) images, but showed a significant VAT overestimation using the corrected VIBE images.

Conclusion

Under similar imaging conditions and spatial resolution, automatically segmented VAT volumes obtained from the corrected TSE and Dixon images agreed with each other and with the reference volumes. These results demonstrate the efficacy of the signal correction methods and the similar accuracy of TSE and Dixon imaging for automatic volumetry of VAT at 3 Tesla.

     

高精度、低功耗的基准电压源设计

运用高增益的运算放大器进行内部负反馈,采用嵌套式密勒补偿,设计出了一款低温漂、高电源抑制、低功耗的带隙基准电压源。基于HYNIX 0.5μm CMOS工艺,利用HSPICE仿真验证。仿真结果表明,当温度从-40℃~120℃变化时,基准的温度系数为13.7ppm/℃,低频时的电源抑制比为-117dB,静态工作电流为4μA。     

高精度信号调理电路的设计及测试

阐述了基于FPGA数据采集系统高精度信号调理电路的设计过程,利用Altera芯片所支持的软件QuartusⅡ对控制程序进行了仿真,制作了印制电路板并通过测试进行了抗干扰设计,以提高数据采集系统系统的可靠性和稳定性.     

螺纹量规三维数字化计量模型参数计算及精度分析

针对实体螺纹量规加工难、成本高、易磨损、检定工序繁琐等问题,提出了一种基于三维点云的螺纹量规数字化计量模型建立及参数计算方法。为实现实物螺纹量规数字化,首先获得其三维数字化模型,并获取模型大径、中径、小径、螺距与牙型角等关键参数。其次对模型进行单项误差与综合误差分析,得到各参数相对误差均小于5%。最终得到数字化模型各项参数的不确定度与扩展不确定度,证明螺纹量规数字化计量模型的准确性。该结果为螺纹量规数字化发展提供了研究基础,对计量行业的数字化转型具有参考价值。     

Native T1 mapping of the breast in MRI to differentiate fibroadenomas from benign phyllodes tumors: a preliminary study

Magnetic Resonance Materials in Physics, Biology and Medicine - Both fibroadenomas (FAs) and phyllodes tumors (PTs) are classified as fibroepithelial lesions. PTs are rare fibroepithelial neoplasms...     

Identification of myocardial diffuse fibrosis by 11 heartbeat MOLLI <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> mapping: averaging to improve precision and correlation with collagen volume fraction

Objectives

Our objectives involved identifying whether repeated averaging in basal and mid left ventricular myocardial levels improves precision and correlation with collagen volume fraction for 11 heartbeat MOLLI T ₁ mapping versus assessment at a single ventricular level.

Materials and methods

For assessment of T ₁ mapping precision, a cohort of 15 healthy volunteers underwent two CMR scans on separate days using an 11 heartbeat MOLLI with a 5(3)3 beat scheme to measure native T ₁ and a 4(1)3(1)2 beat post-contrast scheme to measure post-contrast T ₁, allowing calculation of partition coefficient and ECV. To assess correlation of T ₁ mapping with collagen volume fraction, a separate cohort of ten aortic stenosis patients scheduled to undergo surgery underwent one CMR scan with this 11 heartbeat MOLLI scheme, followed by intraoperative tru-cut myocardial biopsy. Six models of myocardial diffuse fibrosis assessment were established with incremental inclusion of imaging by averaging of the basal and mid-myocardial left ventricular levels, and each model was assessed for precision and correlation with collagen volume fraction.

Results

A model using 11 heart beat MOLLI imaging of two basal and two mid ventricular level averaged T ₁ maps provided improved precision (Intraclass correlation 0.93 vs 0.84) and correlation with histology (R ² = 0.83 vs 0.36) for diffuse fibrosis compared to a single mid-ventricular level alone. ECV was more precise and correlated better than native T ₁ mapping.

Conclusion

T ₁ mapping sequences with repeated averaging could be considered for applications of 11 heartbeat MOLLI, especially when small changes in native T ₁/ECV might affect clinical management.

     

2D and 3D texture analysis to differentiate brain metastases on MR images: proceed with caution

Objective

To find structural differences between brain metastases of lung and breast cancer, computing their heterogeneity parameters by means of both 2D and 3D texture analysis (TA).

Materials and methods

Patients with 58 brain metastases from breast (26) and lung cancer (32) were examined by MR imaging. Brain lesions were manually delineated by 2D ROIs on the slices of contrast-enhanced T1-weighted (CET1) images, and local binary patterns (LBP) maps were created from each region. Histogram-based (minimum, maximum, mean, standard deviation, and variance), and co-occurrence matrix-based (contrast, correlation, energy, entropy, and homogeneity) 2D, weighted average of the 2D slices, and true 3D TA were obtained on the CET1 images and LBP maps.

Results

For LBP maps and 2D TA contrast, correlation, energy, and homogeneity were identified as statistically different heterogeneity parameters (SDHPs) between lung and breast metastasis. The weighted 3D TA identified entropy as an additional SDHP. Only two texture indexes (TI) were significantly different with true 3D TA: entropy and energy. All these TIs discriminated between the two tumor types significantly by ROC analysis. For the CET1 images there was no SDHP at all by 3D TA.

Conclusion

Our results indicate that the used textural analysis methods may help with discriminating between brain metastases of different primary tumors.