磁共振成像PROPELLER采样数据重建中的运动估计新算法

PROPELLER（推进器）采样技术能够利用K空间中心重叠采样区域的数据来估计采集过程中受检查者的运动进而加以补偿,对运动伪影的消除效果非常显著。然而,由于其重建时的运动估计是基于最大化频域空间上相关系数的配准算法,该算法为了实现旋转估计与平移估计的分离,在进行旋转估计时,仅仅采用K空间数据的模,在数据量有限的情况下造成估计精度较低,在重建图像上表现为模糊及星条状伪影。本研究基于最大化图像空间上的互信息提出一种PROPELLER采样数据的运动估计新算法,首先由每个K空间带进行傅立叶逆变换后取模重建出系列临时图像,对这些图像进行模糊增强后以互信息作为相似性测度迭代搜索最优的运动参数。实验证明,该方法能显著提高PROPELLER采样数据重建中运动估计与补偿的精度,从而更好地消除伪影,特别是用于有运动时T1加权头部成像时。     

基于先验估计和相关相位的实时超声弹性成像

基于互相关技术的经典超声弹性成像算法,采用启发式穷举搜索和插值法来提高成像速度和位移估计精度,但实时性和估计精度有限。本研究提出一种新算法,在运动追踪阶段使用先验估计加速追踪收敛速度,然后使用复互相关函数的相位进行亚采样点级精度位移估计,避免了启发式穷举搜索以及插值法所带来的较大计算代价。仿真和体模实验表明,新算法与经典的互相关形变估计算法相比,不仅成像速度大大提高,而且形变估计精度也有显著改善。以仿真的1%应变为例,抛物线插值法生成的弹性图像SNRe为4.8,而新算法生成的弹性图SNRe为11.3。结果证明提出的新算法是一种正确可行的高精度实时超声弹性成像方法。     

腔内超声动脉血管壁弹性模量与运动估计

动脉弹性是了解心脑血管系统生理和病理的重要参数,超声弹性成像有希望成为组织病变诊断和力学特性评价的有效手段。本文利用血管内高频超声成像技术估计动脉血管的弹性模量和血管壁的运动,乳胶管及其变化,避免管壁不规则形状的影响;采用光流法估计血管壁的收缩和扩张运动,内外管壁运动的区别使得血管壁分层结构和非均匀管壁的弹性测量与成像成为可能。     

磁共振弹性成像的初步实验研究

目的：研究磁共振弹性成像（MRE）技术。方法：研制外部激发装置，设计成像脉冲序列，制作模拟人体软组织的体模。激发装置由序列控制，于体模表面产生低频率剪切波。脉冲序列采用梯度回波序列，在x、y或z轴上施加运动敏感梯度（MSG）。剪切波导致的介质内的周期性移位可使接收信号产生周期性相位位移，从测得的相位位移就能计算出每个体素的移位值，直接显示介质内剪切波的传播。通过调整相位偏置，获得一个完整周期内剪切波的动态传播图像。相位图经局部频率估算法（LFE）处理后计算出量化的弹性模景图。实验采用浓度为1．0％和1．5％不同弹性的琼脂凝胶体模，激发频率分别采用150Hz、200Hz、250Hz和300Hz。结果：MRE的相位图显示了剪切波在体模内的传播，剪切波的波长随激发频率和体模弹性变化。波长与激发频率呈反比，与体模弹性呈正比。剪切波的波长在不同激发频率和不同浓度体模之间呈严格的比例关系。计算出的弹性模量图清楚显示了两种浓度介质的弹性对比。结论：MRE的相位图可显示剪切波在介质内的传播，弹性图可量化和显示介质的弹性模量。     

基于相位的2D超声弹性成像形变估计

目的探究应用2D分析窗和幅度调制修正(AMC)技术对加权相位分离(WPS)算法性能的影响。方法首先将位移估计公式和WPS算法推广到2D形式,然后仿真一个均匀组织弹性模型并对其施加0.1%、1%和4%的应变:再分别使用1D窗和2D窗,以及使用AMC和不使用AMC技术对仿真模型分别进行弹性成像,并计算对应弹性图像的信噪比(SNR);最后在2D窗情况下,使用AMC和不使用AMC技术对弹性体模Phantom进行了实际成像。结果仿真实验结果表明,与1D窗相比2D窗可使图像的SNR提高;同样AMC技术也使图像的SNR提高且更加显著。弹性体模的实验结果表明,AMC技术使弹性图像更加平滑细腻,伪应变噪声减少,SNR提高。结论 2D窗和AMC技术的使用能提高WPS算法的性能进而提高弹性图像的质量。     

一种超声弹性成像试验数据的快速仿真算法

基于有限元分析和FieldⅡ声场模拟的超声弹性成像试验数据的仿真需要较长时间,本研究基于超声线性系统理论和弹性力学原理,借助数字信号处理与插值技术,提出了一种快速仿真超声弹性成像试验数据的算法。实验结果显示,该算法能仿真不同组织模型在压缩过程中产生的超声回波数据集,使用标准的弹性成像程序在该仿真的数据集上运行,生成的应变图与预期目标一致;原方法仿真一帧128像素×1 039像素的回波数据需6.3 h,而新算法生成相同的一帧只需要35 s。实验结果证明了该算法的正确性和高效性,可为弹性成像研究所需要的试验数据提供有效仿真手段。     

腔内超声动脉血管壁弹性模量与运动估计

动脉弹性是了解心脑血管系统生理和病理的重要参数,超声弹性成像有希望成为组织病变诊断和力学特性评价的有效手段.本文利用血管内高频超声成像技术估计动脉血管的弹性模量和血管壁的运动,乳胶管对比实验验证了该方法的有效性.通过动脉管壁分段结合内外壁拟合,可有效地估计动脉管壁的内径、外径、壁厚及其变化,避免管壁不规则形状的影响;采用光流法估计血管壁的收缩和扩张运动,内外管壁运动的区别使得血管壁分层结构和非均匀管壁的弹性测量与成像成为可能.     

超声弹性成像技术研究现状

超声弹性成像(ultrasound elastography,UE)是以软组织的弹性参量为对象的一种新的成像技术,它弥补了传统超声成像技术不能提供生态学特性的不足,拓宽了超声图像在肿瘤探测及扩散疾病成像方面的应用,具有非常重要的临床应用价值。本文详细介绍了超声弹性成像技术的实现原理、研究现状以及常用的临床衡量指标,如对比度传输率、应变滤波器、时间延时等,并对其发展做出展望。     

超声弹性成像中应变滤波器的理论及其发展

弹性成像能够提供组织弹性这一基本的力学属性，具有很广阔的应用前景。应变滤波器是超声弹性成像的重要理论框架，可广泛应用于超声弹性成像效果的评估、分析和预测。本详细综述了应变滤波器的理论和发展，并对献中的一些笔误作了修正，对实现的一些细节作了说明。通过对应变滤波器的理解，可以加深对超声弹性成像效果的理解，并对采用合适的方法和参数以获得最佳的成像效果以指导。     

应用动态双平面成像技术研究在体肘关节主动屈伸运动特征

目的 探讨健康肘关节屈伸运动时关节的相对位移和旋转角度变化,为肘关节不稳以及严重肘关节损伤的治疗提供参考。方法 选取10名健康并且无上肢外伤史的受试者。应用动态双平面X线透视成像系统,测量右侧肘关节从旋后最大伸直位至旋后最大屈曲位运动过程中,肱桡与肱尺关节6自由度运动学数据。使用相关性分析评价肘关节不同自由度运动的耦合度。结果 从最大伸直位到最大屈曲位,肱尺关节外翻角从15.2°±3.1°降低到5.3°±2.3°,肱桡关节外翻角从19.7°±4.2°减小到8.2°±2.4°, 肱尺与肱桡关节外翻角与屈曲角呈线性相关;肱尺关节内外旋角先内旋后外旋,呈二次非线性相关,在屈曲110°时达到最大内旋值（4.0°±4.9°）,后达到最大外旋值（5.1°±4.2°）;肱桡关节一直呈内旋增大变化,从内旋3.2°±16.0°增加到内旋27.2°±18.0°。结论 在正常肘关节屈伸过程中,肱尺关节存在外翻角线性减小、内外旋角先内旋后外旋的非线性变化,肱桡关节存在外翻角线性减小、内旋角线性增大的变化。在屈伸过程中,肘关节并非单纯铰链关节,并且肱尺、肱桡关节存在运动学差异。临床上治疗复杂肘关节损伤、肘关节不稳以及肘关节置换手术时,应考虑关节间不同运动特征,以提高术后临床效果。     

人手三维运动检测系统

提出了一种基于普通摄像机的人手三维运动检测系统,它包括两部普通摄像机、标定架和标志点识别子系统等。该系统采用直接线性变换（ＤＬＴ）算法、可以对人手运动进行可靠的三维检测。本文叙述了该系统的工作原理以及测试实验,测试结果显示了该系统良好的三维运动检测性能。本系统的研制为更好地进行人体运动质量的分析和评价,更有效地揭示了人体运动规律提供了经济方便的实验手段和研究途径。     

人体运动检测中的标志点识别算法

针对人体运动的特点提出在人体运动检测中的标志点识别的算法。算法主要包括以下三个方面:(1)采用改进的模板匹配方法以改善匹配峰值的尖锐度;(2 )采用目标图像与模板的互相关系数加权平均的方法使识别的分辨率达到亚像素的水平;(3)根据人体运动的连续性的特点来预测和检验标志点的运动、克服标志点遮挡问题。实验结果证明,采用上述的标志点识别算法能够达到比较高的识别精度和速度。基于上述算法的步态分析系统已经投入使用     

甲状腺微小病变应用超声弹性成像检查的诊断价值

目的探讨甲状腺微小病变应用超声弹性成像检查的诊断价值。方法回顾性分析甲状腺微小病变110例(病灶数116个),分为彩色多普勒超声组与超声弹性成像组,比较两组诊断结果。结果通过病理确诊病灶116个,其中66例(病灶数70个)良性病变,44例(病灶数46个)甲状腺微小癌。彩色多普勒超声检出病灶81个;超声弹性成像检出病灶112个。超声弹性成像检出率96.55%(112/116)比彩色多普勒超声检出率78.45%(81/116)高,比较差异具有统计学意义(P0.05)。结论甲状腺微小病变患者应用超声弹性成像具有较高的病灶检出率、疾病诊断特异性和敏感性。     

基于CT图像的颅内血肿检测与分割

目的:为提高血肿分割精度,提出一种基于改进Canny算子的颅内类血肿噪声检测方法。方法:首先用区域生长算 法分割出颅脑组织,去掉颅骨等干扰信息。然后使用基于改进Canny边缘检测的方法检测颅脑边缘类血肿噪声,并与原 图像进行与运算消除该噪声。最后,通过使用OTSU适应度函数的遗传算法精准分割出颅内血肿。结果:该方法在随机 抽取的200例颅脑血肿图像中,血肿检测的准确率达到96.3%,Dice相似度达到93.5%。结论:该方法能准确、有效地检测 并分割出颅内血肿。     

Motion correction and frequency stabilization for MRS of the human spinal cord

Subject motion is challenging for MRS, because it can falsify results. For spinal cord MRS in particular, subject movement is critical, since even a small movement > 1 mm) can lead to a voxel shift out of the desired measurement region. Therefore, the identification of motion corrupted MRS scans is essential. In this investigation, MR navigators acquired simultaneously with the MRS data are used to identify a displacement of the spinal cord due to subject motion. It is shown that navigators are able to recognize substantial subject motion (>1 mm) without impairing the MRS measurement. In addition, navigators are easy to apply to the measurement, because no additional hardware and just a minor additional user effort are needed. Moreover, no additional scan time is required, because navigators can be applied in the deadtime of the MRS sequence. Furthermore, in this work, retrospective motion correction combined with frequency stabilization is presented by combining navigators with non‐water‐suppressed ¹H‐MRS, resulting in an improved spectral quality of the spinal cord measurements. Copyright © 2016 John Wiley & Sons, Ltd.     

Influences of Motion Artifacts on Three-Dimensional Reconstruction Volume and Conformal Radiotherapy Planning

Objective ：To investigate the influences of motion artifacts on three-dimensional （3D） reconstruction volume and conformal radiotherapy planning. Methods： A phantom which can mimic the clip motion of lung tumor along the cranial-caudal direction is constructed by step motor, small ball of polyethylene and potato. Ten different scan protocols were set and CT data of the phantom were acquired by using a commercial GE LightSpeedl6 CT scanner. The 3D reconstruction of the CT data was implemented by adopting volume-rendering technology of GE AdvantageSim 6.0 system. The reconstructed volumes of each target in different scan protocols were measured through 3D measuring tools. Thus, relative deviations of the reconstruction volumes between moving targets and static ones were determined. The three-dimensional conformal radiation therapy （3D- CRT） plans and conformal fields were created and compared for a static/moving target with the WiMRT treatment planning system （TPS）. Results：For a static target, there was no obvious difference among the 3D reconstruction volumes when the CT data were acquired with different pitches and slices. The appearance of 3D reconstruction volume and 3D conformal field of a moving target was quite different from that of static one. The maximum relative deviation is nearly 90% for a moving target scanned with different scan protocols. The relative deviations are variable among the different targets, about from -39.8% to 89.5% for a smaller target and from - 18.4% to 20.5% for a larger one. Conclusion ：The motion artifacts have great effects on 3 D-CRT planning and reconstruction volume, which will greatly induce distorted conformal radiation fields and false DVHs for a moving target.     

Auditory Detection of Motion Velocity in Humans: a Magnetoencephalographic Study

No HeadingSummary: To investigate the cerebral mechanisms of auditory detection of motion velocity in the human brain, neuromagnetic fields elicited by six moving sounds and one stationary sound were investigated with a whole-cortex magnetoencephalography (MEG) system. The stationary sound evoked only one clear response at a latency of 109±6 ms (first response, or M100), but the six moving sounds evoked two clear responses: an earlier response at a latency of 116±7 ms (M100) and a later response at a latency ranging from 180 to 760 ms (magnetic motion response, or MM). The latency and amplitude of the MM were inversely related to the velocity of the moving sounds (p<0.02). The magnetic source of MM was related to the velocity of the moving sounds (p<0.05). A dynamic neuromagnetic response, MM, was elicited by the moving sounds, which likely encoded the neural processing of auditory detection of motion velocity. A specific neural network that processes the motion velocity in the human brain probably includes the bilateral superior temporal cortices and the brainstem. The left posterior and lateral part of the auditory cortex may play a pivotal role in the auditory detection of motion velocity.We thank Dr. Paul Babyn for his help and suggestions in these experiments. This paper was prepared with the assistance of Prof. Sharon Nancekivell, medical editor, Guelph, Ontario, Canada. This study was partially supported by the Savoy Foundation (Research Grant 77227).     

Diagnostic Role of Conventional Ultrasonography and Shearwave Elastography in Asymptomatic Patients with Diffuse Thyroid Disease: Initial Experience with 57 Patients

Purpose

Thyroid ultrasonography (US) is a useful diagnostic tool in the evaluation of diffuse thyroid disease (DTD), whereas shearwave elastography is a dynamic technique that can provide information about tissue hardness by using acoustic shearwaves remotely induced by a focused ultrasonic beam. This study aims at investigating the role of conventional US and shearwave elastography in the diagnosis of asymptomatic patients with DTD.

Materials and Methods

Fifty-seven patients who underwent both conventional US and shearwave elastography were included in this study. Interobserver variability of the three radiologists in assessment of underlying thyroid echogenicity on conventional US was analyzed. Diagnostic performances for diagnosing DTD on conventional US and shearwave elastography were calculated and compared.

Results

Fair agreement was observed in the identification of DTD with conventional US (kappa value=0.27). The area under the receiver operating characteristic curve (A_z) were 0.52-0.585 on conventional US by three radiologists. The A_z values when using the mean and maximum elasticity values as a diagnostic criteria for DTD were 0.619 and 0.59 on shearwave elastography. Patients with DTD showed higher mean [24.1±10 kilo-Pascals (kPa)] and maximum (36.4±13.3 kPa) elasticity values on shearwave elastography when compared to the normal group (23.4±10.8 kPa and 33.7±12.4 kPa, respectively), although without statistical significance (p=0.802 and p=0.452, respectively).

Conclusion

Conventional US did not show reliable interobserver agreement in the diagnosis of DTD. Although not statistically significant, shearwave elastography may provide additional information in the diagnosis of DTD. Therefore, larger prospective studies are needed to define the values of shearwave elastography for diagnosing DTD.     

Cortical EEG Frequency Composition and the Quality of Apparent Motion in Man

Human subjects were asked to rate the quality of apparent motion (beta motion) in trial-wise presentations of stimuli. The interstimulus interval (ISI) between presentation of two adjacent light patches was varied between 10 and 90 msec. EEG activity during stimulus presentation was assessed with a frequency spectral analysis technique. Results with 10 subjects showed that high quality apparent motion was associated with faster EEG activity at short ISI, and lower frequency EEG activity at longer ISI. The results were significant at a midline occipital electrode, with a tendency in the right direction over the right occipital cortex, but not at other occipital and parietal sites. Changes were within the 8-12 Hz frequency band. Results are interpreted in terms of a mechanism associated with components of the spontaneous EEG which serves to pace information processing within the primary visual cortex.