医用B型超声诊断仪超声源剂量和图像质量控制

医用B型超声诊断仪(以下简称“B超仪”)在医学临床上广泛应用以来,合理使用医用超声源的辐射剂量和诊断图像质量的要求越来越受到重视。为了保障患者的安全和诊断结果准确,避免漏诊、误诊引发医疗事故,国家于1999年3月发布了JJG639-1998《医用超声诊断仪超声源》检定规程,对B超仪的图像质量和患者辐射剂量做了明确的规定,并列入强制检定项目。一、超声源剂量控制超声辐射剂量是指超声强度与辐射时间的乘积。B超仪的工作原理是将一束高频超声脉冲波发射到人体内,通过声波辐射后,由人体内不同界面反射回不同波形生成图像,从而判断人体内的…     

医用超声仪器的量化特征与质量保证体现(下)

(接上期)四、质量保证环节中的量值准确性要求如前所述,在许多超声诊断设备的临床应用中,是以获取量化参数作为诊断依据的。不言而喻,所测数值及其导出参数值越准确,则做出的诊断结论越可靠。为此,除在设计制作过程中通过技术措施予以保证外,最终必须通过可以溯源的质量检验环节进行把关。(1)二维灰阶成像系统在B超的脉冲回波成像功能中,扫描系统是按照公认的人体软组织平均声速1540m/s设计的,即以12.99μs对应1cm距离的往返,并据此将屏幕上的扫描时间标尺换成距离标尺,在二维灰阶图像上实现对病灶、器官和其它解剖结构的几何尺寸测量。但…     

基于支持向量回归模型的医学超声图像去噪研究

医学超声成像技术以其固有的时效性、廉价性及无损性等特点被医疗诊断广泛应用。但超声图像存在的斑点噪声增加了图像解译程度,影响了图像分析与诊断。因此,医学超声图像去噪研究成为超声影像预处理中的关键问题。本研究基于目前医学超声图像去噪研究现状,引入支持向量学习理论,通过含斑图像做对数变换和分解,构建基于支持向量回归模型的局部自适应去斑算法。实验仿真表明,基于支持向量回归模型能够成功地去除超声图像的噪点,同时保障了超声图像的细节特征,其优越的性能超过了传统的去噪方法。     

医学B超图像降噪处理的三种方法比较

针对医学B超图像的噪声特点，将采集到的医学B超图像输入计算机，然后用Matlab语言编制中值滤波、自适应滤波和小波阈值降噪程序，分别对同一图像运用3种方法降噪，并比较结果，得出其图像质量都有所改善，且自适应滤波和小波阈值降噪方法处理的效果更好，尤其是小波方法更优越一点．     

基于超声图像特征的肝硬化分析系统

文章首先研究了肝脏M型超声图像和B型超声图像的特征提取，提取了肝脏M型超声图像的运动包络、相隔一定时间的A型扫描线对的相关特征系数以及肝脏B型超声图像的共25个特征参数。在已提取的特征参数中，用特征融合的方法筛选出对肝硬化最敏感的特征组，并利用这20个参数的Fisher判据建立了基于超声图像特征的肝硬化无损自动分析系统。对临床43例的应用表明：该定量分析系统对肝硬化的诊断具有良好的效果。     

改进的灰度级-彩色变换法在B超图像中的应用

B超图像的伪彩色增强在医学临床诊断上具有重要意义。该文提出了一种对灰度级-彩色变换法中分段传递函数阈值重新划分的新算法。该算法首先利用改进的K均值聚类算法对图像的灰度值进行聚类,再根据聚类各簇的灰度值阈值重新设置分段传递函数的节点。通过实验对比,该算法处理后的图像轮廓更清晰,层次感更强,能有效地突出病灶区,有利于医学诊断。     

数字影像技术在超声医学中的应用

实现超声图像的数字化不仅可以完善医疗档案的数字化管理系统,也为网上会诊创造了条件。而且还把计算机图像处理技术引入了超声医学领域,特别是伪色处理技术给超声医学的研究提供了一个新的手段,可以提高图像的分辨率,丰富影像层次,提高B型超声对病理组织变化的可视度。     

有机液非线性声参量B/A的改进算法

1　引　言非线性声参量 B/ A定义为媒质状态方程在绝热条件下作泰勒展开后 ,其二阶项系数与一阶项系数之比。由于和目前广泛应用于超声诊断中的线性声参量相比较 ,它反映了组织的动力学特征 ,可以提供更多的组织结构信息 ,能成为生物组织定征及超声医学诊断的一个重要的新参量 [1-3 ] ,因而对该参量的研究成为近十多年来超声医学研究的持续热点及前沿课题之一。目前对生物媒质的非线性参量 B/ A的研究取得了重要的进展 ,尤其是 B/ A成像技术已越来越接近临床应用的水平 [3 -4 ] ,但是已进行的研究多偏向于实验和技术 ,到目前为止 ,还未见…     

B超仪检定中的注意事项

医用超声诊断仪超声源（以下简称B超仪）在医学临床上被广泛应用，它的诊断图像质量的好坏直接影响医生对病人病情的判断以及随后的治疗活动。为了保障患者的安全和诊断结果准确，国家于1999年发布了JJG6391998《医用超声诊断仪超声源》检定规程，对B超仪的各项指标做了明确的规定。但是，在检定过程中有很多需要主意的问题应引起重视。     

一种基于超声造影剂的微血管灌注检测方法

提出一种利用超声造影剂回波解相关（DCR）特性的微血管灌注检测方法，介绍了该方法的原理和采用的算法，构建血流仿体和微血管仿体实验系统用于方法的讨论和评价；在仿体实验数据的基础上，对4种DCR检测算法进行了分析和比较，并根据各种实验条件下获得的DCR检测图像，进行了DCR方法与B模式成像结果的对比，同时讨论了各种影响DCR检测效果的因素；结果表明DCR方法可以有效检测包含造影剂的微血管区域并获得清晰图像．     

调频信号发射超声成像的参数优化与成像实验

研究调频信号发射超声成像中影响成像质量的各种参数,提高现有超声图像的信号噪声比.用仿真计算和声学实验来研究不同调频超声信号发射参数下的成像质量.增加超声发射能量,提高图像的信号噪声比;同时,采用相关算法对接收的超声信号解码,保证图像的轴向精度不会下降.优化了调频信号发射超声成像的发射参数,并得到了仿体的B型超声图像,此图像的质量优于传统成像方法的图像质量.该成像方法能够提高超声图像的信号噪声比,尤其是提高超声衰减严重的深部组织图像的信号噪声比.     

A single FPGA-based portable ultrasound imaging system for point-of-care applications

We present a cost-effective portable ultrasound system based on a single field-programmable gate array (FPGA) for point-of-care applications. In the portable ultrasound system developed, all the ultrasound signal and image processing modules, including an effective 32-channel receive beamformer with pseudo-dynamic focusing, are embedded in an FPGA chip. For overall system control, a mobile processor running Linux at 667 MHz is used. The scan-converted ultrasound image data from the FPGA are directly transferred to the system controller via external direct memory access without a video processing unit. The potable ultrasound system developed can provide real-time B-mode imaging with a maximum frame rate of 30, and it has a battery life of approximately 1.5 h. These results indicate that the single FPGA-based portable ultrasound system developed is able to meet the processing requirements in medical ultrasound imaging while providing improved flexibility for adapting to emerging POC applications.     

Ultrasound speckle reduction using modified Gabor filters

B-mode ultrasound images are characterized by speckle artifact, which may make the interpretation of images difficult. One widely used method for ultrasound speckle reduction is the split spectrum processing (SSP), but the use of one-dimensional (1-D), narrow-band filters makes the resultant image experience a significant resolution loss. In order to overcome this critical drawback, we propose a novel method for speckle reduction in ultrasound medical imaging, which uses a bank of wideband 2-D directive filters, based on modified Gabor functions. Each filter is applied to the 2-D radio-frequency (RF) data, resulting in a B-mode image filtered in a given direction. The compounding of the filters outputs give rise to a final image in which speckle is reduced and the structure is enhanced. We have denoted this method as directive filtering (DF). Because the proposed filters have effectively the same bandwidth as the original image, it is possible to avoid the resolution loss caused by the use of narrow-band filters, as with SSP. The tests were carried out with both simulated and real clinical data. Using the signal-to-noise ratio (SNR) to quantify the amount of speckle of the ultrasound images, we have achieved an average SNR enhancement of 2.26 times with simulated data and 1.18 times with real clinical data.     

压缩感知在医学超声成像中的仿真应用研究

为了解决医学超声成像系统中面临的采样率高,数据量大的问题,提出将压缩感知理论方法用于医学超声成像。首先建立了超声信号在时域的稀疏表达模型,然后利用模拟信息转换器对信号进行稀疏采样,最后使用最优化方法完成回波信号重建,利用合成发射孔径方式完成最终超声成像。为了验证算法的有效性,利用Field II对点目标以及复杂组织目标进行了仿真实验,在均方误差、分辨率、对比度以及成像质量上与常规成像结果对比分析。结果表明,采用1/2奈奎斯特采样频率,以30%原始数据所完成的成像仍然可保证良好的图像质量。采用压缩感知理论可以大幅度降低医学超声系统的采样率及总数据量。     

编码发射技术在医学高频超声成像中的研究进展

高频超声成像以其高分辨和实时性好等优势成为近年来医学超声成像领域研究的热点。但由于超声的衰减随频率增加呈指数级升高,导致高频超声信号幅值小,图像信噪比低。为了增强高频超声成像的信噪比,近年来编码发射（又称编码激励）技术得到了越来越多的研究和应用。文章对近几年国内外编码发射技术在医学高频超声成像方面的应用和研究进展进行了综述,重点分析了Chirp码、巴克（Barker）码和格雷（Golay）码3种主要编码发射技术在高频超声成像方面应用的优缺点,并综合对比了各种编码发射技术在高频成像方面的应用前景。     

基于自动种子区域生长的超声B图像缺陷分割方法

提出一种基于自动种子区域生长的超声图像缺陷分割方法。首先使用最大类间方差（Otsu）分割法对超声B图像进行一次预分割;其次寻到绝对背景区,并且在此区域内自动设置种子起始点;然后利用区域生长法将缺陷从背景中分割;最后通过数字形态学降噪法来进一步提高缺陷的识别度。实验结果表明:该方法不仅能准确地分割出缺陷,且具有较好的缺陷边界信息,提高了对超声B图像的处理效率,有效地抑制了大部分图像噪声。     

Piezoelectric contrast materials for ultrasound imaging

Piezoelectric ceramics and polymers can be used as a type of marker and contrast material for medical ultrasound imaging systems. High-frequency electrical signals are detected from surface electrodes when these materials are introduced into conducting media such as tissue and scanned by ultrasound imaging systems. Detected signals are applied to the imaging circuits of a modified ultrasound system such that they display a unique type of electrical image that shows the piezomaterial's polarization, shape, and position at arbitrarily high contrast compared to the conventional ultrasound acoustic image. The resulting piezoelectric image can be merged in real-time with conventional ultrasound acoustic imaging to form a composite image. This approach is of interest in the development of improved techniques for imaging medical devices that are implanted or otherwise introduced into the body.     

基于经验模态分解的聚焦超声非线性声场检测

为精确检测聚焦超声声场中的谐波成分并得到谐波分布规律,开展了对聚焦超声非线性声场检测的研究,提出基于经验模态分解的聚焦超声谐波检测方法。首先对声场信号进行经验模态分解;然后利用噪声判断准则判断出固有模态函数(IMF)中的噪声分量,滤除噪声分量后将剩余的IMF分量予以重新组合;最后对新信号进行傅里叶变换,得到各次谐波的幅值。结果表明:它能较好地抑制噪声,相比于传统的检测方法可获得更平滑的谐波分布;该方法对开展谐波成像、医学超声检测具有重要意义。     

3-D ultrasound volume reconstruction using the direct frame interpolation method

A new method for 3-D ultrasound volume reconstruction using tracked freehand 3-D ultrasound is proposed. The method is based on solving the forward volume reconstruction problem using direct interpolation of high-resolution ultrasound B-mode image frames. A series of ultrasound B-mode image frames (an image series) is acquired using the freehand scanning technique and position sensing via optical tracking equipment. The proposed algorithm creates additional intermediate image frames by directly interpolating between two or more adjacent image frames of the original image series. The target volume is filled using the original frames in combination with the additionally constructed frames. Compared with conventional volume reconstruction methods, no additional filling of empty voxels or holes within the volume is required, because the whole extent of the volume is defined by the arrangement of the original and the additionally constructed B-mode image frames. The proposed direct frame interpolation (DFI) method was tested on two different data sets acquired while scanning the head and neck region of different patients. The first data set consisted of eight B-mode 2-D frame sets acquired under optimal laboratory conditions. The second data set consisted of 73 image series acquired during a clinical study. Sample volumes were reconstructed for all 81 image series using the proposed DFI method with four different interpolation orders, as well as with the pixel nearest-neighbor method using three different interpolation neighborhoods. In addition, volumes based on a reduced number of image frames were reconstructed for comparison of the different methods' accuracy and robustness in reconstructing image data that lies between the original image frames. The DFI method is based on a forward approach making use of a priori information about the position and shape of the B-mode image frames (e.g., masking information) to optimize the reconstruction procedure and to reduce computation times and memory requirements. The method is straightforward, independent of additional input or parameters, and uses the high-resolution B-mode image frames instead of usually lower-resolution voxel information for interpolation. The DFI method can be considered as a valuable alternative to conventional 3-D ultrasound reconstruction methods based on pixel or voxel nearest-neighbor approaches, offering better quality and competitive reconstruction time.     

Limited-angle spatial compound imaging of skin with high-frequency ultrasound (20 MHz)

In dermatology, high-frequency ultrasound (HFUS) is used for high-resolution skin imaging. The conventional B-scan type approach is to perform lateral scans perpendicular to the direction of sound propagation. Ultrasound spatial compounding enables improvement of the image contrast, suppression of speckle and noise, and reduction of imaging artifacts in comparison with conventional B-mode imaging, but it has not yet found its way into HFUS skin imaging applications. In this paper, the potential of HFUS spatial compounding for skin imaging is systematically evaluated. A new HFUS system with a sophisticated scanner for limited-angle (up to +/-40 degrees) spatial compound imaging was developed and implemented. Echo signals are acquired using a 20 MHz spherically focused single-element transducer with an axial and lateral resolution of 69 mum and 165 mum, respectively, in the focus. A calibration scheme for the estimation of unknown system parameters and precise image reconstruction has been developed. The implemented system has been evaluated using measurements of geometrically well-defined structures, speckle phantoms, and in vivo measurements. The results show the advantage of the proposed spatial compound skin imaging concept compared with conventional B-mode imaging in terms of image contrast, isotropy, and independence from the orientation of surfaces.