提高准静态弹性成像运动估计精度的算法及其仿体实验研究

超声弹性成像作为一种新兴的成像技术手段,可以对病理组织和正常组织的结构性弹性差异进行成像。由于各种良恶性肿瘤以及物理治疗形成的损伤会使得局部组织弹性发生明显变化,因此,采用超声弹性成像检测病变组织或者物理治疗形成的损伤具有重要意义。弹性成像的基础建立在对外力作用下组织运动的精确估计上,在准静态弹性成像中,即为检测轴向外力缓慢施压所造成的组织纵向运动。然而由于非纵向运动,边界条件和设备噪声等因素的影响,实际运动估计中需要通过算法消除各种因素的干扰。本研究采用了一系列方法来提高运动估计的精度,即首先采用二维互相关算法,减小组织横向运动对位移估计的干扰;然后采用分段线性拟合的算法剔除了位移估计中的奇异点,并通过二维中值滤波算法平滑了位移数据;最后采用基于小波变换的低通数字差分算法,成功的抑制了位移数据中的高频噪声对应变估计结果的干扰,并比较了该算法相对于数字低通差分滤波器和直接差分算法的应变估计效果。开展了多层仿体实验和包含有柱状硬物的仿体实验验证了这些算法的可行性。研究表明,通过一系列运动估计算法的改进,可以大大提高运动估计的准确性,降低了图像噪声。     

机械臂超声成像结合超声-CT配准技术构建胫股关节在体检测系统的可行性及精度分析

目的 应用机械臂超声成像结合超声-CT配准技术构建胫股关节在体检测系统，并对该系统的测试精度进行评价。方法 采集猪胫股关节及股骨标本的CT及超声图像，分别三维重建后进行手动配准；采集股骨标本六自由度运动超声图像，进行三维重建后与CT三维模型配准，比较CT三维模型间测量的位移与真实位移差值，计算配准精度；配准及精度计算由两名研究人员分别进行，计算组内相关系数。结果 利用三维几何信息进行超声-CT手动配准构建胫股关节在体检测系统具有可行性；平移精度为0.94～1.16 mm，旋转精度为0.63°～1.50°；精度测量结果的组内相关系数为0.794(P=0.014)。结论 本超声-CT配准技术是可行的，其精度能够满足胫股关节动态检测要求，未来需改进机械臂扫描获取超声图像的方法，利用计算机图像处理技术进行快速配准。     

基于关键点的超声图像与磁共振图像多分辨率离散优化配准方法

脑肿瘤手术规划及术中，术前磁共振（MR）图像与术中超声（US）图像的配准甚为关键。考虑到两种模态图像具有不同密度范围及分辨率，且超声图像存在较多的斑点噪声干扰，采用一种基于局部邻域信息的自相似性上下文（SSC）描述子定义图像之间的相似性测度。将超声图像作为参考，使用三维微分运算提取其中角点作为关键点，并采用密集位移采样离散优化算法实施配准。整个配准过程分为仿射配准和弹性配准两个阶段，在仿射配准阶段，对图像进行多分辨率分解，在弹性配准阶段，采取最小卷积和均值场推理策略对关键点的位移向量进行正则化处理。对22名患者的术前MR和术中US图像进行配准实验，仿射配准后的误差为（1.57±0.30）mm，每对图像配准平均耗时1.36 s；弹性配准后的误差为（1.40±0.28）mm，平均用时1.53 s。实验结果证明本文采用的方法具有良好的配准精度和速度。     

二维数字化超声软组织应变成像系统的研制

利用超声散射回波测量生物组织在静态压缩情况下弹性系数的超声弹性成像方法得到了很大的发展.利用国产高速数据采集卡以及商业线阵B型超声诊断仪,建立了一套二维数字化超声软组织应变成像系统.应用这一系统获得了数字化的射频组织超声散射回波信号,并对组织内的应变分布进行成像.实验结果表明,该应变成像系统在获得传统B型超声图像的同时,可以获得组织内部的应变分布图像,从而获取在B超图像上无法得到的组织弹性变化.这一系统的研制成功,不仅为超声弹性成像技术在医学临床上的应用研究打下了基础,同时也为扩宽普通商业B超的应用范围提供了途径.     

基于动态孔径控制的剪切波传播速度检测方法

目的超声剪切波弹性成像临床应用前景广阔,其中剪切波传播速度检测是其技术的核心步骤。针对在小焦距下传统基于静态孔径聚焦超声发射方式的剪切波传播速度检测准确度低的问题,本文提出一种基于动态孔径控制的剪切波传播速度检测方法。方法对不同的焦距以控制活跃阵元数目的方式动态控制孔径大小;采用峰值时间法结合最小二乘法计算剪切波传播速度;利用超声仿真平台FieldⅡ,采用控制变量法对多个小焦距下的声辐射力场、标记点"位移-时间"曲线及剪切波传播速度进行了仿真研究。结果本方法可有效抑制栅瓣的出现,能获取呈现出明显主峰的走势良好的标记点"位移-时间"曲线。剪切波传播速度检测结果与理论值的相对误差更低,例如在焦距为7 mm时,与理论值相对误差降低了16.585%;在焦距为9 mm时,降低了15.205%。结论基于动态孔径控制的剪切波传播速度检测方法能合理控制小焦距下的声辐射力,提升剪切波传播速度检测准确度,为超声剪切波弹性成像技术的进一步发展提供理论依据。     

超声三维成像技术的发展与应用

随着现代生物医学工程技术的迅速发展,工程技术与医学技术的有机结合,使超声二维成像技术向三维成像的发展成为可能。超声三维成像从1974年开始研究,首先采用的是机械臂方法,1976年提出了回声定位法,1977年应用电磁定位法,1986年利用经食道超声探头(IEE)获得静态三维图像,1990年用回拉式IEE探头成功重建了动态心脏三维图像。     

医学超声关键技术研究和进展(二)超声弹性成像技术、超声图像处理与分析

超声弹性成像技术是近20年来在医学超声领域出现的新技术,它利用准静态压力、外加低频振动、声辐射力等形式激励组织振动,然后用超声方法检测组织的形变或者由振动引起的剪切波传播,最终得到组织的生物力学特性.超声弹性成像已经被广泛应用在乳腺、肝脏、前列腺等领域,显示了良好的临床应用前景.此外,超声图像处理与分析是超声成像系统的重要组成部分,主要包括超声图像的三维可视化、预处理、分割、配准及图像理解等,旨在为临床医生诊断提供有效的辅助手段.     

超声多模态技术对非哺乳期乳腺炎与乳腺癌的鉴别诊断价值

目的:探讨常规超声结合超声造影以及弹性成像对非哺乳期乳腺炎和乳腺癌的鉴别诊断价值。方法:回顾性分析58例乳腺癌、52例非哺乳期乳腺炎的常规超声、超声造影和弹性成像的声像图表现。结果:非哺乳期乳腺炎组和乳腺癌组两种病灶的BI-RADS分级及弹性成像评分、造影增强模式比较差异有统计学意义（P<0.05）。结论:仅通过二维超声诊断非哺乳期乳腺炎和乳腺癌经常会导致误诊,而结合超声造影以及超声弹性成像则能够更好地进行鉴别诊断。     

四维STIC成像联合二维超声在胎儿心脏畸形中的应用价值及相关性研究

目的探讨四维STIC成像联合二维超声在胎儿心脏畸形中的应用效果及相关性。方法选来我院进行孕检的孕妇1050名,入院后孕妇均行常规超声检查,对于疑似胎儿心脏畸形者行四维时空关联成像技术(STIC)筛查,将筛查结果与最终诊断结果比较,采用SPSS Pearson相关性分析软件对四维STIC成像联合二维超声在胎儿心脏畸形中的诊断效果与胎儿肢体遮挡、四腔心位置、母体肥胖、胎动相关性进行分析。结果 1050例孕妇胎儿经病理结果最终确诊为32例心脏畸形,发生率为3.05%。心脏畸形类型排在前三位的分别为:完全性房间隔缺损、法洛四联症、左室发育不良综合征;四维STIC成像诊断筛查时成像四腔心、五腔心、三血管气管、左室流出道、右室流出道、动脉导管弓、主动脉弓、腔静脉长轴显示率,均高于二维超声(P0.05);四维STIC成像联合二维超声诊断符合率,高于单一二维超声、四维STIC成像诊断(P0.05);四维STIC成像联合二维超声诊断漏诊率、误诊率,低于单一二维超声、四维STIC成像诊断(P0.05);SPSS Pearson相关性分析结果表明:四维STIC成像联合二维超声诊断胎儿心脏畸形诊断符合率与胎儿肢体遮挡、四腔心位置、母体肥胖、胎动呈正相关性(P0.05)。结论将四维STIC成像联合二维超声用于胎儿心脏畸形筛查中效果理想,能提高筛查精度,且与胎儿肢体遮挡、四腔心位置、母体肥胖、胎动具有一定相关性,诊断时应综合排除干扰,提高诊断准确率。     

超声造影及超声弹性成像技术在睾丸疾病诊断中的应用进展

目的探讨超声造影及超声弹性成像技术在睾丸疾病诊断中的应用进展。方法查阅近年来超声造影及超声弹性成像技术应用于睾丸疾病诊断的相关文献,进行归纳总结。结果在二维高频灰阶超声、彩色多普勒超声检查基础上,超声造影可提高睾丸扭转、表皮样囊肿、梗死和脓肿等睾丸疾病诊断的敏感性和特异性。超声弹性成像能反映组织的相对软硬度,对良恶性病变具有一定的鉴别价值。结论超声造影及超声弹性成像技术可以提高睾丸疾病诊断的符合率,并能进一步提高睾丸良恶性病变诊断的准确性。     

组织多普勒超声心脏图像的动态三维重建

传统的超声心脏图像三维重建技术只限于描述三维及动态三维解剖结构,不能对心脏动态功能做出准确有效的评价。本研究将建立组织多普勒超声心脏图像的动态三维重建方法,通过超声医学图像三维重建技术和组织多普勒超声成像技术的结合,重建心脏运动的动态三维加速度场,为心脏功能的准确评价提供一条新的途径。论文解决了加速度矢量场重建过程中关键的矢量插值和融合显像的问题,从组织多普勒加速度图像中分别重建心肌运动三维加速度场和三维解剖结构,并进行融合显像。试验结果证明了二者之间相对空间位置正确,该方法可以为心脏疾病的诊断和心脏功能的评价提供更多信息,在心脏靶点起搏和心内消融等领域有潜在的应用价值。     

Freehand三维超声体数据重建的最新研究进展

Freehand三维超声成像系统因其扫描方式自由、能提供更大的成像视角和更高的图像分辨率等优点,比较符合医生习惯和手术室环境,成为近年来超声影像引导介入手术的主要研究方向。Freehand三维超声从一系列不规则的二维B超图像入手,重构器脏结构的三维体数据,并进行三维渲染显示。体数据重建是Freehand三维超声成像系统的关键技术,对提高重建图像质量有着重要的作用。对Freehand三维超声体数据的重建算法进行归纳和分类,比较分析其中的典型算法,最后对Freehand三维超声体数据重建算法的研究状况和未来的发展方向进行展望。     

High-Resolution 3D Ultrasound Jawbone Surface Imaging for Diagnosis of Periodontal Bony Defects: An <Emphasis Type="Italic">In Vitro</Emphasis> Study

Although medical specialties have recognized the importance of using ultrasonic imaging, dentistry is only beginning to discover its benefit. This has particularly been important in the field of periodontics which studies infections in the gum and bone tissues that surround the teeth. This study investigates the feasibility of using a custom-designed high-frequency ultrasound imaging system to reconstruct high-resolution (<50 μm) three-dimensional (3D) surface images of periodontal defects in human jawbone. The system employs single-element focused ultrasound transducers with center frequencies ranging from 30 to 60 MHz. Continuous acquisition using a 1 GHz data acquisition card is synchronized with a high-precision two-dimensional (2D) positioning system of ±1 μm resolution for acquiring accurate measurements of the mandible, in vitro. Signal and image processing algorithms are applied to reconstruct high-resolution ultrasound images and extract the jawbone surface in each frame. Then, all edges are combined and smoothed in order to render a 3D surface image of the jawbone. In vitro experiments were performed to assess the system performance using mandibles with teeth (dentate) or without (nondentate). The system was able to reconstruct 3D images for the mandible’s outer surface with superior spatial resolution down to 24 μm, and to perform the whole scanning in <30 s. Major anatomical landmarks on the images were confirmed with the anatomical structures on the mandibles. All the anatomical landmarks were detected and fully described as 3D images using this novel ultrasound imaging technique, whereas the 2D X-ray radiographic images suffered from poor contrast. These results indicate the great potential of utilizing high-resolution ultrasound as a noninvasive, nonionizing imaging technique for the early diagnosis of the more severe form of periodontal disease.     

Three-dimensional ultrasound imaging

Ultrasound is an inexpensive and widely used imaging modality for the diagnosis and staging of a number of diseases. In the past two decades, it has benefited from major advances in technology and has become an indispensable imaging modality, due to its flexibility and non-invasive character. In the last decade, research investigators and commercial companies have further advanced ultrasound imaging with the development of 3D ultrasound. This new imaging approach is rapidly achieving widespread use with numerous applications. The major reason for the increase in the use of 3D ultrasound is related to the limitations of 2D viewing of 3D anatomy, using conventional ultrasound. This occurs because: (a) Conventional ultrasound images are 2D, yet the anatomy is 3D, hence the diagnostician must integrate multiple images in his mind. This practice is inefficient, and may lead to variability and incorrect diagnoses. (b) The 2D ultrasound image represents a thin plane at some arbitrary angle in the body. It is difficult to localize the image plane and reproduce it at a later time for follow-up studies. In this review article we describe how 3D ultrasound imaging overcomes these limitations. Specifically, we describe the developments of a number of 3D ultrasound imaging systems using mechanical, free-hand and 2D array scanning techniques. Reconstruction and viewing methods of the 3D images are described with specific examples. Since 3D ultrasound is used to quantify the volume of organs and pathology, the sources of errors in the reconstruction techniques as well as formulae relating design specification to geometric errors are provided. Finally, methods to measure organ volume from the 3D ultrasound images and sources of errors are described.     

3D current source density imaging based on the acoustoelectric effect: a simulation study using unipolar pulses

It is of importance to image electrical activity and properties of biological tissues. Recently hybrid imaging modality combing ultrasound scanning and source imaging through the acoustoelectric (AE) effect has generated considerable interest. Such modality has the potential to provide high spatial resolution current density imaging by utilizing the pressure-induced AE resistivity change confined at the ultrasound focus. In this study, we investigate a novel three-dimensional (3D) ultrasound current source density imaging approach using unipolar ultrasound pulses. Utilizing specially designed unipolar ultrasound pulses and by combining AE signals associated to the local resistivity changes at the focusing point, we are able to reconstruct the 3D current density distribution with the boundary voltage measurements obtained while performing a 3D ultrasound scan. We have shown in computer simulation that using the present method it is feasible to image with high spatial resolution an arbitrary 3D current density distribution in an inhomogeneous conductive media.     

Measurement of femoral neck anteversion in 3D. Part 2:3D modelling method

Femoral neck anteversion is the torsion of the femoral head with reference to the distal femur. Conventional methods that use cross-sectional computed tomography (CT), magnetic resonance or ultrasound images to estimate femoral anteversion have met with several problems owing to the complex three-dimensional (3D) structure of the femur. A 3D imaging method has been developed that virtually measures femoral anteversion on the 3D computer space with continuous CT slices; this 3D method provides more accurate and reliable results than conventional 2D CT measurements. A 3D modelling method is devised for the measurement of femoral neck anteversion. This method has advantages over the 3D imaging method, such as shorter processing time, reduced number of slices and an objective result compared with the 3D imaging method. The results of the 3D modelling method are compared with the conventional CT methods (2D CT method and 3D imaging method) using 20 dried femurs.     

血管壁面剪切应力的测量及其临床研究进展

总结血管壁面剪切应力(WSS)的几种测量技术和计算方法,主要包括基于磁共振或磁共振结合计算流体动力学(CFD)、计算机断层扫描(CT)、血管内超声、传统超声、超声向量血流成像和超声粒子流的血流速度测量技术,以及根据速度计算WSS的几种不同运算方法。介绍WSS计算时的另一个重要参数--血液黏滞系数(又称“血黏度”),描述该参数在精确测量WSS时的选取和计算。此外,通过现有文献论述三维向量WSS的测量以及WSS相关临床参数的计算方法,对现有的WSS临床研究做综述性的讨论。针对颈动脉、主动脉、冠状动脉、肱动脉、股动脉等不同血管,列举WSS相关的临床研究结果,并从中归纳出绝大多数临床研究认可的3个主要结论。     

Measurement of femoral neck anteversion in 3D. Part 1: 3D imaging method

Femoral neck anteversion is the torsion of the femoral head with reference to the distal femur. Conventional methods that use cross-sectional computed tomography (CT), magnetic resonance or ultrasound images to estimate femoral anteversion have met with several problems owing to the complex, three-dimensional (3D) structure of the femur. These problems include not only the difficulty of defining the direction of the femoral neck axis and condylar line but also the dependency upon patient positioning. In particular, the femoral neck axis, the direction of the femoral head, known as the major source of error, is difficult to determine from either a single or several two-dimensional (2D) cross-sectional images. A new method has been devised for the measurement of femoral anteversion using the 3D imaging technique. 3D reconstructed CT images from the femoral head and trochanter to the distal femur are used to measure the anteversion. It is necessary to remove the soft tissue from the CT images and extract just the bone part. Then, the femoral anteversion is measured from a computer-rendered femur image. The 3D imaging method is compared with both the conventional 2D method and the physical method using 20 dried femurs. For the physical method, which is used as a reference value, a special apparatus is devised. The average difference between the results of the physical method and those of the 2D CT method is 5.33°. The average difference between the results of the physical method and those of the 3D imaging method is 0.45°. Seventy-four patients, who suffer from toe-in-gait disease, are tested to compare the 3D imaging method with the conventional 2D CT method. The average difference between the 2D and 3D methods is 8.6°, and the standard is 7.43°. This method provides a very accurate and reliable measurement of femoral anteversion, as it is virtually equivalent to the direct measurement of bisected dried femur in vitro.     

Determination of heterogeneous thermal parameters using ultrasound induced heating and MR thermal mapping

In this paper, a method for the determination of spatially varying thermal conductivity and perfusion coefficients of tissue is proposed. The temperature evolution in tissue is modelled with the Pennes bioheat equation. The main motivation here is a model-based optimal control for ultrasound surgery, in which the tissue properties are needed when the treatment is planned. The overview of the method is as follows. The same ultrasound transducers, which are eventually used for the treatment, are used to inflict small temperature changes in tissue. This temperature evolution is monitored using MR thermal imaging, and the tissue properties are then estimated on the basis of these measurements. Furthermore, an approach to choose transducer excitations for the determination procedure is also considered. The purpose of this paper is to introduce a method and therefore simulations are used to verify the method. Furthermore, computations are accomplished in a 2D spatial domain.     

一种提高N线模型探头标定精度的解算方法

在超声引导的介入治疗中,为了利用三维定位系统实现对超声成像平面的跟踪,超声探头与定位系统的传感器之间几何关系的标定是影响整体引导精度的重要环节。广泛应用的N线模型和传统最小二乘解算方法在超声探头标定中存在注册点共面性丢失的问题,进而影响标定精度。针对这一问题,提出一种先拟合虚拟成像平面,再进行共面约束下标定的解算方案,以提高利用N线模型进行标定的精度。实际的标定实验结果表明,新的解算方法能够有效地解决共面性丢失带来的精度影响,与传统解算方法相比,标定误差从5.88 mm降低到4.11 mm。