Magnetic-resonance image segmentation based on improved variable weight multi-resolution Markov random field in undecimated complex wavelet domain

To solve the problem that the magnetic resonance (MR) image has weak boundaries, large amount of information, and low signal-to-noise ratio, we propose an image segmentation method based on the multi-resolution Markov random field (MRMRF) model. The algorithm uses undecimated dual-tree complex wavelet transformation to transform the image into multiple scales. The transformed low-frequency scale histogram is used to improve the initial clustering center of the K-means algorithm, and then other cluster centers are selected according to the maximum distance rule to obtain the coarse-scale segmentation. The results are then segmented by the improved MRMRF model. In order to solve the problem of fuzzy edge segmentation caused by the gray level inhomogeneity of MR image segmentation under the MRMRF model, it is proposed to introduce variable weight parameters in the segmentation process of each scale. Furthermore, the final segmentation results are optimized. We name this algorithm the variable-weight multi-resolution Markov random field (VWMRMRF). The simulation and clinical MR image segmentation verification show that the VWMRMRF algorithm has high segmentation accuracy and robustness, and can accurately and stably achieve low signal-to-noise ratio, weak boundary MR image segmentation.     

从IPv4向IPv6转移的过渡策略

本从IPv4的局限性以及IPv6所作的对应改进入手，讨论了如何平稳从现有的IPv4网络结构过渡到IPv6的策略，并对IPv6的发展前景作了预测。     

Nonlinear profile order for three-dimensional hybrid radial acquisition applied to self-gated free-breathing cardiac cine MRI

This paper presents a nonlinear profile order scheme for three-dimensional(3D) hybrid radial acquisition applied to self-gated, free-breathing cardiac cine magnetic resonance imaging(MRI). In self-gated, free-breathing cardiac cine MRI,respiratory and cardiac motions are unpredictable during acquisition, especially for retrospective reconstruction. Therefore,the non-uniformity of the k-space distribution is an issue of great concern during retrospective self-gated reconstruction. A nonlinear profile order with varying azimuthal increments was provided and compared with the existing golden ratio-based profile order. Optimal parameter values for the nonlinear formula were chosen based on simulations. The two profile orders were compared in terms of the k-space distribution and phantom and human image results. An approximately uniform distribution was obtained based on the nonlinear profile order for persons with various heart rates and breathing patterns.The nonlinear profile order provides more stable profile distributions and fewer streaking artifacts in phantom images. In a comparison of human cardiac cine images, the nonlinear profile order provided results comparable to those provided by the golden ratio-based profile order, and the images were suitable for diagnosis. In conclusion, the nonlinear profile order scheme was demonstrated to be insensitive to various motion patterns and more useful for retrospective reconstruction.     

火焰喷雾热解制Pd-Pt/CeO2催化甲烷燃烧的性能研究

火焰喷雾热解法(FSP)是一种简单、快速、可规模化制备纳米催化剂的技术。通过火焰喷雾热解法合成CeO₂和Pt-CeO₂载体、Pd-Pt-CeO₂催化剂,采用浸渍法在CeO₂和Pt-CeO₂载体分别沉积Pd-Pt和Pd而制得Pd-Pt双金属催化剂,并考察其甲烷催化燃烧性能。利用ICP、XRD、TEM、BET、H2-TPR、XPS和Raman对催化剂的物化性质进行分析。TEM结果表明,Pd-Pt/CeO₂催化剂中Pd和Pt物种高分散于CeO₂载体。相比于一步法(one step)制得的Pd-Pt-CeO₂(OS-FSP)催化剂,共浸渍法制得Pd-Pt/CeO₂(0.25)-WI的催化活性更高,其t₅₀降低了60℃,且稳定运行60 h而没有明显失活。这归因于Pd-Pt/CeO₂(0.25)-WI催化剂表面上Pd⁰/Pd^2+...     

三维多回波流动补偿定量磁化率成像(QSM)方法研究

定量磁化率成像(QSM)利用一般成像技术舍弃的相位信息得到局部磁场变化特性,通过复杂的场到源反演计算,可直接得到定量的磁化率图,它广泛应用于测量血氧饱和度、脑部微出血、铁沉积、组织钙化等方面．然而,梯度磁场中流动会引起相位错误,并且产生显著的流动伪影,最终得到错误的QSM图像．为了矫正流动的影响,该文在3 T磁共振系统上实现了三维多回波流动补偿梯度回波序列,并用该序列采集流动水模和志愿者颅脑数据．流动水模和颅脑数据均显示,流动补偿能够明显矫正相位错误,消除流动伪影．颅脑横断位QSM结果证明,流动补偿序列可以消除血液流动引起的QSM的错误,提高QSM的准确性．     

CMMB整机灵敏度测量与数据分析

CMMB已在全国320个地市覆盖了信号,整机灵敏度从一定程度上影响着整体覆盖情况。广播电视规划院电磁兼容与安全检测实验室作为从事该项测试工作的权威机构,自2008年以来连续3年承担了上千台、次的测试任务,积累了翔实的测量数据,同时对整机灵敏度的测量具有较深的理解,本文阐述了CMMB终端灵敏度的技术要求和测量方法,并通过...     

定量肝脏脂肪的波谱自动后处理算法

目前质子磁共振波谱技术可用于肝脏脂肪含量的定量检测.利用快速T₂校正多回波波谱采集序列可一次屏气获得一组不同回波时间的波谱数据,然后通过谱线拟合和分析得到质子密度脂肪分数.波谱数据后处理一般通过第三方软件,处理步骤复杂,需要消耗大量的时间,而且有不可避免的人为控制因素干扰.本文开发了自动波谱后处理算法,可以实现谱线拟合、T₂衰减校正和脂肪分数计算,并进一步采用水脂模型实验和人体肝脏脂肪检测实验对算法的可行性和准确性进行了评估.研究结果显示,本文提出的自动定量算法计算得到的质子密度脂肪分数和jMRUI软件处理得到的结果高度一致,但其操作简单,更适用于脂肪肝临床检测.     

从IPv4向IPv6转移的过渡策略

本文从IPv4的局限性以及IPv6所作的对应改进入手,讨论了如何平稳地从现有的IPv4网络结构过渡到IPv6的策略,并对IPv6的发展前景作了预测。     

定量磁化率成像多回波相位拟合算法研究

定量磁化率成像(quantitative susceptibility mapping,QSM)技术大多采用多回波梯度回波序列采集相位数据,经加权最小二乘法(weighted linear least-square,WLS)拟合得到局部磁场分布.对于组织磁化率分布不均匀的区域,尤其是颅底部位,常规WLS算法拟合得到的局部磁场误差较大,导致相应部位磁化率分布图信噪比较低.针对常规WLS算法的这一不足,该文提出了一种截断WLS算法.对两种算法拟合得到的磁化率分布图对比研究发现,截断WLS算法可有效提高颅底部位定量磁化率分布图的图像质量,使其噪声明显下降.