口腔金属材料与影像学伪影的检测与比较

背景：磁共振成像是常用的临床影像检测方法,口腔金属材料在磁共振成像检查时会出现图像伪影,从而影响图像的质量以及诊断的正确性。目的：分析不同口腔金属材料在磁共振成像中产生的伪影强度以及影响伪影的因素。方法：分析9篇近10年关于口腔金属材料对磁共振成像影响的研究文献,从不同角度分析口腔常削金属材料钴铬合金、镍铬合金、钛合金、金铂合金、银铂合金以及纯钛等在磁共振影像中产生的伪影的大小,比较其影响伪影强度的因素。结果与结论：钴铬合金在磁共振图像中产生的伪影最人,并儿随着磁场强度的增强伪影增大,其中硬质钻铬合会产生的伪影强度大于软质钴铬合金产生的伪影强度,其次足镍铬合金产生的伪影,而金、银合金以及纯钛产生的伪影最小,并且磁场强度增强等外加干扰因素对伪影大小无明届影响。     

一种消除MRI拉链伪影的脉冲序列

背景:磁共振成像会产生各种类型的伪影,经常出现的有运动伪影、卷褶伪影、金属伪影、部分容积效应伪影、化学位移伪影、相位伪影和拉链伪影等,但由自旋回波序列成像过程中形成拉链伪影的控制和校正方法还未见报道.目的:通过分析自旋回波序列成像过程中拉链伪影的产生机制,探索出一种新的消除拉链伪影的脉冲序列.方法:编写标准SE序列得到标准图,编写伪影序列得到直线干扰图像和拉链伪影图,编写改进序列得到改进后的除拉链伪影图.结果与结论:5°一瞬间梯度-120°回波序列可得到直线干扰图像,90°一瞬间梯度-120°回波序列可得到拉链伪影图,而改进后序列90°-120°一瞬间梯度回波可彻底消除拉链伪影.结果提示,改进后的脉冲序列显示的图形效果彻底消除了拉链伪影.     

软、硬质钴铬合金及金合金对磁共振成像伪影的影响

背景:磁共振成像具有高对比度、无骨伪影、任意方位断层等优点,被广泛应用于头颈外科、神经外科和口腔颌面外科疾病的诊断.但某些金属材料在磁共振成像中形成的伪影严重影响了图像质量,这些材料的使用限制了磁共振成像在头颈部的应用和准确诊断.目的:观察硬质钴铬铸造合金、软质钴铬铸造合金、金合金3种金属材料在5种不同头颈部扫描序列中的伪影.方法:采用5种头颈常规及快速成像序列,分别对放置于圆柱型水模中心的3种金属试样进行轴位扫描,测量伪影,并进行统计分析.结果与结论:3种金属在磁共振成像相同成像序列中,金合金产生的伪影最小,硬质钴铬形成的伪影最大,各组间比较差异有显著性意义(P均<0.05);相同金属材料,自旋回波序列产生伪影最小,梯度回波序列产生伪影较大,平面回波序列产生伪影最大并使图像变形.结果提示,与非贵金属口腔修复材料相比,以贵金属作为口腔修复材料,在头颈部磁共振成像过程中产生的伪影最小,因此通过合理选择口腔金属修复材料及成像技术,可得到最佳磁共振成像.     

基于平稳小波变换的减小MR图像截断伪影的方法

如何缩短磁共振成像的时间一直是磁共振成像领域研究的热点问题之一.在实际工作中只采集部分相位编码的磁共振信号进行磁共振图像重建,不但可以缩短成像的时间,而且可以使图像保持较高的信噪比,但在重建的图像上出现了截断伪影.采用平稳小波变换和图像模板技术消除图像截断伪影及噪声,可有效地提高图像质量.     

磁共振Propeller技术消除患者因运动及磁敏感效应造成伪影的作用

背景:运动伪影及磁敏感伪影严重影响MR成像质量,Propeller技术采用填充模式,以辐射状的叶片用螺旋的方式采集数据,在很大程度上解决了运动伪影及磁敏感伪影的问题.目的:探讨Propeller技术在头部伪影消除的应用价值.设计、时间及地点:对比观察实验,于2006-0712007-04在解放军成都军区昆明总医院完成.参试者:21例磁共振头颅日常检查中出现躁动或不能自控患者,5例固定义齿致磁敏感伪影明显者.方法:对21例磁共振头颅日常检查躁动或不能自控患者,常规T2FRFSE序列运动伪影明显,用Propeller技术进行T2WI扫描并进行对比;5例常规扩散加权图像序列磁敏感伪影明显者进行Propeller扩散加权图像扫描并进行对比.主要观察指标:Propeller技术应用后运动伪影与磁敏感伪影的改变情况.结果:21例应用Propeller技术进行T2WI扫描明显减少或消除了运动伪影,5例Propeller扩敞加权图像明显消除磁敏感效应引起的伪影.均生成较满意图像.结论:应用Propeller T2WI及扩散加权图像成像技术可以明显减少或消除患者因运动及磁敏感效应造成的伪影,显著提高图像质量,获得具有临床诊断价值的理想图像.     

基于插值方法去除CT图像中的金属伪影

目的：对比观察线性插值、非线性插值和三次样条插值3种方法消除金属伪影后的CT图像。 方法：首先，利用全局阈值分割的方法把原图分割为金属部分和条状伪影部分。然后用雷登变换把伪影图像变换至弦空间，即得到弦图。然后用线性插值、非线性插值和三次样条插值来对伪影弦图进行处理，得到矫正的弦图。最后利用滤波反投影法重建图像。 结果：线性插值最为明显的消除了放射状条纹伪影，非线性插值在消除条纹的时候带入了噪声，而三次样条插值对伪影的处理最弱。 结论：实验表明，在各种单一插值算法中，线性插值是最为有效的消除金属伪影的插值方法。     

一种快速校正CT环形伪影的方法

背景:环形伪影严重影响了CT图像质量,对图像后处理造成困难以及容易造成误诊断.目前去除环形伪影必不可少.目的:去除CT重建图像中的环形伪影,提高CT图像质量以及后续处理和量化分析的精度,便于诊断.方法:首先把含环形伪影的CT图像进行线性变换,将灰度图像转换成浮点类型的图像.接着由直角坐标变换到极坐标,这样原来的环形伪影就被变换成线形伪影.设计多维滤波器,计算每个象素滤波后均值以及方差,通过与阈值比较确定伪影范围.最后通过对伪影范围进行修正以及对图像进行坐标变换,变为灰度图像.结果与结论:通过Matlab 7.0软件设计程序,处理含环形伪影的CT图像.实验表明,此方法能有效快速地校正CT环形伪影,是一种属于图像后处理的校正方法.     

BLADE刀锋技术详解

磁共振成像中,病人运动会产生相位编码方向明显的伪影。伪影主要因为两次激发之间,组织由于运动导致所处空间位置不同所致。关于运动伪影减轻或者消除方法,目前流行的有一维、二维导航回波等。本文主要介绍一种结合快速自旋回波（TSE）和辐射采集的自导航序列：刀锋序列,又称为螺旋桨序列（PROPELLER）。文章重点介绍其数据采集方式,运动纠正方法以及图像重建方法,最后讨论其扫描时间和优缺点。     

发声任务在功能磁共振成像中的应用及伪影校正方法探讨

目的探讨发声任务对功能磁共振成像的影响,并发展一系列数据处理方法,从而更完全地校正发声伪影.方法 8名被试在磁共振扫描过程中执行汉字阅读任务, 以200个汉字作为刺激材料.每名被试完成两个发声阅读序列和两个默声阅读序列.采用三种不同的数据处理方法,其中前两种方法已有报道,而最后一种方法为本文首次提出.结果与前两种方法相比,本文提出的方法更完全地校正了发声伪影的影响,信号的损失也较小.结论利用适当的数据处理方法,功能磁共振研究中发声伪影可以得到有效校正;发声任务可以应用于功能磁共振成像研究.     

计算机X线摄影废弃图像产生的原因及处理对策

目的分析CR系统废弃图像产生的原因,提出处理对策。方法收集2009～2011年柯达CR900系统产生的废弃图像138例,并进行归类分析。结果 138例废弃图像产生原因有6种:X线量子噪声、饱和伪影、左右侧黑白亮度不均、IP板感光层损坏伪影、黑边框过度遮挡伪影、IP灰尘伪影。结论实施相应处理措施可以明显降低CR废弃图像的产生。     

基于EPI方法的功能磁共振成像质量问题实例分析:主要成因与应对方案

基于回波平面成像(echo planar image,EPI)序列的功能磁共振成像(functional magnetic resonance imaging,fMRI)是当前基础与临床脑功能研究实现快速成像的主要手段。但是,与常规成像序列相比,这种快速成像更容易受到各种噪声和伪影的干扰,从而影响fMRI的数据质量。如何及时发现和解决EPI的伪影和稳定性问题,是fMRI科研数据质量控制的一个核心问题。本文对笔者在过去五年fMRI质量控制工作中发现的成像问题进行整理,总结了fMRI应用中经常遇到的五种主要伪影,包括奈奎斯特鬼影、几何畸变、尖峰噪声、射频噪声和EPI稳定性相关的问题。并为每种伪影选取了具有代表性的案例,分析它们的特点、主要成因和应对方案。希望这些案例和分析结果能为fMRI用户和技术人员提供有益的借鉴。     

磁共振成像在大脑功能研究中的作用及价值

目的:介绍国内、外近15年来功能磁共振成像在人类大脑功能区定位方面的研究概况,以期进一步了解功能磁共振成像的作用与价值。资料来源:应用计算机检索美国MEDLINE数据库1990/2005期间的相关文章,限定文章语言种类为英文,检索词为“功能磁共振,大脑”。资料选择:对资料进行初审,选择大脑功能研究中应用功能磁共振为研究方法的研究文献查找全文。纳入标准:①功能磁共振作为主要研究手段。②探讨大脑的运动、感觉、听觉、视觉、认知功能有关的文章。③针对正常受试者脑功能定位的研究。排除标准:①与大脑的运动、感觉、听觉、视觉、认知功能无关的文章。②仅对于异常受试者所做的研究。③重复研究。④原文无英文文题文章。资料提炼:共收集到相关文献6144篇,按上述标准纳入18篇,其余文献均被排除。资料综合:①运动功能定位有关的2篇,关于改变手指运动方式进行脑功能区的定位。②与感觉功能定位有关的4篇,其中1篇是通过简单触觉刺激进行脑功能区的定位,3篇是观察通过针灸刺激穴位时对脑功能区的定位。③与视觉功能定位有关的3篇,其中2篇是通过简单视觉刺激对视觉中枢的定位,1篇是关于交替刺激双眼时脑功能区的定位。④与听觉功能定位有关的3篇,其中2篇是关于通过不同的听觉刺激方式进行中枢的定位,1篇是关于正常与异常受试者在相同刺激下脑功能区定位的不同。⑤与语言功能定位有关的3篇,均是与1篇与运动语言功能区有关,1篇与听觉语言功能区有关,1与视觉语言功能区定位有关。⑥与认知功能定位有关的2篇。均是与记忆有关的文献。⑦1篇实关于fMRI基本原理介绍方面的文献。结论:功能磁共振对脑功能区的定位对比其他方法相对更准确,更方便,更直观。针对不同脑功能区,不仅能显示脑功能区激活区的部位、大小和范围,而且可直接显示激活区所在确切解剖位置。通过对机体的刺激方法和方式的探索、硬件技术的提高、图像后处理技术的提高,功能磁共振将在阐明人脑的功能方面发挥巨大的作用。     

Discriminant analysis of functional connectivity patterns on Grassmann manifold

The functional brain networks, extracted from fMRI images using independent component analysis, have been demonstrated informative for distinguishing brain states of cognitive function and brain disorders. Rather than analyzing each network encoded by a spatial independent component separately, we propose a novel algorithm for discriminant analysis of functional brain networks jointly at an individual level. The functional brain networks of each individual are used as bases for a linear subspace, referred to as a functional connectivity pattern, which facilitates a comprehensive characterization of fMRI data. The functional connectivity patterns of different individuals are analyzed on the Grassmann manifold by adopting a principal angle based Riemannian distance. In conjunction with a support vector machine classifier, a forward component selection technique is proposed to select independent components for constructing the most discriminative functional connectivity pattern. The discriminant analysis method has been applied to an fMRI based schizophrenia study with 31 schizophrenia patients and 31 healthy individuals. The experimental results demonstrate that the proposed method not only achieves a promising classification performance for distinguishing schizophrenia patients from healthy controls, but also identifies discriminative functional brain networks that are informative for schizophrenia diagnosis.     

Analysis and design of perfusion-based event-related fMRI experiments

Perfusion-based functional magnetic resonance imaging (fMRI) using arterial spin labeling (ASL) methods has the potential to provide better localization of the functional signal to the sites of neural activity compared to blood oxygenation level-dependent (BOLD) contrast fMRI. At present, experiments using ASL have been limited to simple block and periodic single-trial designs. We present here an adaptation of the general linear model to perfusion-based fMRI that enables the design and analysis of more complicated designs, such as random and semirandom event-related designs. Formulas for the least-squares estimate of the perfusion response and the F statistic for the detection of a response are derived. Exact expressions and useful approximations for detection power and estimation efficiency are presented, and it is shown that the trade-off between power and efficiency for perfusion experiments is similar to that previously observed for BOLD experiments. The least-squares estimate is compared with an estimate formed from the running subtraction of tag and control images. The running subtraction estimate is shown to be approximately equal to a temporally low-pass-filtered version of the least-squares estimate. Numerical simulations and results from ASL experiments are used to support the theoretical findings.     

利用独立成分分析实现成组的fMRI信号的盲分离

独立成分分析(ICA)作为盲源分离的一种有效方法已经被成功的用于处理功能磁共振成像(fMRI)数据,但是通常人们只是考虑处理单个被试的数据,对于多个被试的情况却很少有人考虑,本文中分析了目前国际上比较流行的三种用ICA来处理多个被试的fMRI数据的方法,并且利用其中最好的一种方法对我们实验中获得的fMRI数据进行处理,结果表明这种方法可以快速有效地处理多个被试的fMRI数据.     

利用独立成分分析技术和静息fMRI数据对脑功能区进行定位

目的 验证可否利用独立成分分析(ICA)技术和静息fMRI数据对脑功能区进行定位.方法 利用ICA方法,通过研究静息状态的脑功能联结来获取功能区的定位.静息数据的采集采用短TR,在低通滤波(截止频率0.08 Hz)后可以去除生理噪声的主要影响.在数据分析中,对ICA结果进行了可复制性分析,只保留可复制性较高的成分,之后将ICA结果与传统的"种子像素"方法获得的结果进行定量的一致性分析.结果 ICA能够在不设定"种子像素"的情况下从静息fMRI数据中分解出运动系统和初级视觉系统的功能联结图,并在所有被试上都与"种子像素"方法有较高一致性.ICA在同一数据中可以同时分解出上述两个系统的功能联结图. 结论 ICA克服了"种子像素"方法的主观性,稳定、准确地从静息fMRI数据中分解出了脑功能联结图.本研究支持初级功能系统内的联系要明显强于系统间的联系的假设,显示ICA方法具有良好的临床应用潜力.     

Simultaneous 3-T fMRI and high-density recording of human auditory evoked potentials

We acquired simultaneous high-field (3 T) functional magnetic resonance imaging (fMRI) and high-density (64- and 128-channel) EEG using a sparse sampling technique to measure auditory cortical activity generated by right ear stimulus presentation. Using dipole source localization, we showed that the anatomical location of the grand mean equivalent dipole of auditory evoked potentials (AEPs) and the center of gravity of fMRI activity were in good agreement in the horizontal plane. However, the grand mean equivalent dipole was located significantly superior in the cortex compared to fMRI activity. Interhemispheric asymmetry was exhibited by fMRI, whereas neither the AEP dipole moments nor the mean global field power (MGFP) of the AEPs showed significant asymmetry. Increasing the number of recording electrodes from 64 to 128 improved the accuracy of the equivalent dipole source localization but decreased the signal-to-noise ratio (SNR) of MR images. This suggests that 64 electrodes may be optimal for use in simultaneous recording of EEG and fMRI.     

A multiple-plane approach to measure the structural properties of functionally active regions in the human cortex

Advanced magnetic resonance imaging (MRI) techniques provide the means of studying both the structural and the functional properties of various brain regions, allowing us to address the relationship between the structural changes in human brain regions and the activity of these regions. However, analytical approaches combining functional (fMRI) and structural (sMRI) information are still far from optimal. In order to improve the accuracy of measurement of structural properties in active regions, the current study tested a new analytical approach that repeated a surface-based analysis at multiple planes crossing different depths of cortex. Twelve subjects underwent a fear conditioning study. During these tasks, fMRI and sMRI scans were acquired. The fMRI images were carefully registered to the sMRI images with an additional correction for cortical borders. The fMRI images were then analyzed with the new multiple-plane surface-based approach as compared to the volume-based approach, and the cortical thickness and volume of an active region were measured. The results suggested (1) using an additional correction for cortical borders and an intermediate template image produced an acceptable registration of fMRI and sMRI images; (2) surface-based analysis at multiple depths of cortex revealed more activity than the same analysis at any single depth; (3) projection of active surface vertices in a ribbon fashion improved active volume estimates; and (4) correction with gray matter segmentation removed non-cortical regions from the volumetric measurement of active regions. In conclusion, the new multiple-plane surface-based analysis approaches produce improved measurement of cortical thickness and volume of active brain regions. These results support the use of novel approaches for combined analysis of functional and structural neuroimaging.     

Electromyography as a recording system for eyeblink conditioning with functional magnetic resonance imaging

This study was designed to develop a suitable method of recording eyeblink responses while conducting functional magnetic resonance imaging (fMRI). Given the complexity of this behavioral setup outside of the magnet, this study sought to adapt and further optimize an approach to eyeblink conditioning that would be suitable for conducting event-related fMRI experiments. This method involved the acquisition of electromyographic (EMG) signals from the orbicularis oculi of the right eye, which were subsequently amplified and converted into an optical signal outside of the head coil. This optical signal was converted back into an electrical signal once outside the magnet room. Electromyography (EMG)-detected eyeblinks were used to measure responses in a delay eyeblink conditioning paradigm. Our results indicate that: (1) electromyography is a sensitive method for the detection of eyeblinks during fMRI; (2) minimal interactions or artifacts of the EMG signal were created from the magnetic resonance pulse sequence; and (3) no electromyography-related artifacts were detected in the magnetic resonance images. Furthermore, an analysis of the functional data showed areas of activation that have previously been shown in positron emission tomography studies of human eyeblink conditioning. Our results support the strength of this behavioral setup as a suitable method to be used in association with fMRI.     

Atlas-assisted localization analysis of functional images

OBJECTIVE: This paper introduces a method for localization analysis of functional images assisted by a brain atlas. The usefulness of the system developed, based on this method, is analyzed for human brain mapping and neuroradiology. MATERIALS AND METHODS: We use an enhanced and extended electronic Talairach-Tournoux brain atlas, containing segmented and labeled subcortical structures, Brodmann's areas, and gyri. The brain atlas serves as a tool for anatomy referencing, segmentation, labeling, registration, and providing 3D anatomical relationships. The process of localization analysis is decomposed into five steps: data loading, feature extraction, data normalization, identification and editing of loci, and getting labels and values. This analysis is supported by near real-time data-to-atlas warping based on the Talairach transformation. Metanalysis is enabled by merging the current and external lists of activation loci. RESULTS: We have designed, developed, tested, and deployed a commercial system for atlas-assisted localization analysis of functional images. This is the first system where an electronic version of the Talairach-Tournoux brain atlas is used interactively for analysis of functional images. This system runs on personal computers and provides functions for a rapid normalization of anatomical and functional volumetric data, data segmentation and labeling, readout of Talairach coordinates, and data display. It also is empowered with several unique features including: interactive warping facilitating fine tuning of the data-to-atlas fit, a backtracking mechanism to compensate for missing landmarks and enhancing the outcome of the overall process of data analysis, navigation on the triplanar formed by the data and the atlas, multiple-images-in-one display with atlas-anatomy-function blending, a fast locus-controlled generation of results, editing of loci, multiple label display, and saving and reading of loci. The system normalizes a single image in near real-time (0.7 s), so analysis of anatomical and functional datasets can be done on-the-fly regardless of the number of slices. The same task performed by the state-of-the-art non-linear registration methods may require up to several days. CONCLUSIONS: The system is a useful tool for atlas-assisted localization analysis and a helpful adjunct to function/location metanalysis in human brain mapping research. It is also a step forward in bringing the atlas and the clinical data together within a practical and powerful solution that is fast and flexible, yet low-cost and affordable.