高档相控阵B超中相控编码方案的实现

本文提出了一种用于高档相控阵Ｂ超中的新型相控编码方案。该方案采用软件控制相延时电路实现相控扫描和四点动态聚焦，不仅大大简化以往相控阵Ｂ超中复杂的相控电路，而且提高了图象的质量和分辨力。     

医学超声图象的处理与拼接

医学超声图象在临床上得到了广泛的应用，但由于超声图象存在着动态范围小，对比度差，而且噪声大和观察范围有限等缺点，影响了超声图象的临床诊断效果。本文提出了Ｂ超图象的自动匹配与拼接方法，实现了表现更大观察范围的Ｂ超图象，从而弥补了手工拼接中的精度低，误差大的缺陷。为提高图象的匹配与拼接精度，文中还讨论了图象的噪声抑制与灰度增强处理方法，提高了Ｂ超图象的再现质量     

相控阵超声显象装置

Hewlett packard公司研制出的相控阵超声显象装置能如实地对人体内脏进行扫描,并能显示出其内部结构图象,系一实时的相控阵超声显象仪。这一装备在医院有着广泛的适用范围,可以对胸部或整个腹部作超声扫描。由于采用了相阵扫描技术,可以使超声换能器体积缩小,能在肋骨间诊断。这种超声换能器具有64阵元,可自动聚焦。由     

B超图象拷贝仪的开发

Ｂ超图象拷贝仪可以与Ｂ超等成象医疗设备配套使用，打印出高清晰度图象。该仪器主要由图象数据采集、图象存贮器、热敏打印机和单片机控制器等部分组成。本文介绍它的系统构成，工作原理以及设计思想。着重讨论图象信号的量化、存贮与数据转换方式。最后给出了实验结果     

高帧率超声成像系统中提高信噪比的一种方法

基于有限衍射波束理论，最近人们发展了高帧率(high frame rate,HFR)超声成像系统，同传统的动态聚焦相比，此系统通过一次发射事件就可得到一帧图像，故可达到极高的帧率。但在实际应用中，由于仅发射一次超声波束来成像，回波信号较弱，易受噪音干扰，使成像质量降低。为了提高系统的信噪比，采用匹配滤波器来抑制噪音，并进行了计算机仿真。结果表明通过匹配滤波器处理，系统信噪比有了一定的提高，成像质量得到了改善。     

遗传算法在256阵元相控阵高强度聚焦超声治疗系统多焦点控制中的应用

阐述了遗传算法优化多点超声聚焦的方法以及球面相控阵声场计算方法。对实验室研发的256阵元相控阵聚焦超声治疗系统作了简介。利用此遗传算法和声场计算方法，对轴上和离轴单焦点以及轴对称六焦点和非轴对称四焦点进行了256阵元相控阵的声场仿真，并观察了实验室研发的256阵元相控阵聚焦超声治疗系统作用于有机玻璃和透明仿体的实验结果。用遗传算法和声场计算方法的仿真和系统实验结果表明，此方法可在实际聚焦手术中准确地控制3维单焦点和3维多焦点。     

阴道B超在妇科生殖医学中的应用

阴道Ｂ型超声是将探头外套一消毒隔膜如避孕套，外涂适量藕合剂伸入阴道后穹窿进行女性生殖器扫查。因阴道探间频率高（５７．５ＭＨＺ），分辨率强（０．３０．６ｃｍ），且直接靠近检查器官，避开了膀胱、肠道气体等干扰及腹壁脂肪的衰减，使图象分辨率高，检查方便迅速，［１］故在妇产科的临床应用愈来愈广泛，尤在生殖医学中占据重要地位，现将这方面的情况综合如下。一、监测卵泡发育，按时进行超声引导下的卵子采集　在生殖医学发展中，试管婴儿及／或宫腔配子移植的成功，阴道Ｂ超起到了极为重要的作用。这项工作的首要任务，是…     

B型超声在异位妊娠诊断中的应用价值（附134例分析）

本文总结分析了１３４例异位妊娠的Ｂ超诊断结果，术前Ｂ超诊断与术后病理诊断符合的２５例，占９３．３％。文章分述了各种类型异位妊娠的超声特点，并对误诊原因进行了分析，强调了Ｂ超在异位妊娠诊断中的重要作用。     

用窄超声波束多普勒信号估算平均血流流速的统计方法

用窄超声波束多普勒信号估算平均血流流速的统计方法［英］／ＷｉｌｌｉｎｋＲ…／／ＩＥＥＥＴｒａｎｓＢＭＥ．－１９９４，４１（３）．－３２２本文给出了一种在满足多普勒光束直径成倍小于脉管半径的条件下由多普勒功率光谱估计值计算脉管交叉处瞬时平均血流流速的统...     

基于GPU并行计算的超声波束合成方法

逐列扫描式的聚焦成像方法会限制超声成像帧频的提高。采用平面波发射模式只需要一次发射和接收即可获得一幅完整的超声图像,平面波成像是可以大幅度地提高成像帧频,从而实现超声超高速成像的方法之一。但是现有的超声波束合成器无法达到超声超高速成像对于计算能力的要求。对基于平面波成像的超声延时-叠加波束合成算法进行并行性分析,在此基础上设计并实现两种基于图形处理器(GPU)并行计算的超声平面波成像波束合成方法——基于2个Kernel和基于1个Kernel的并行波束合成方法。两种方法的主要区别在于波束合成中对延时值的计算和存储策略的不同处理,仿体实验证明两种方法的计算帧频分别达到2 178 和2 453 帧/s。相比于普通的方法,这两种基于GPU的并行波束合成方法的计算帧频分别提速99倍和111倍。实验结果表明,GPU波束合成器相比于传统方法,可以大幅度提高计算能力。     

Area x-ray beam equalization for digital angiography

An area beam equalization technique has been investigated in order to generate patient-specific compensating filters for digital angiography. An initial image was used to generate the compensating filter, which was fabricated using a deformable compensating material, containing CeO2, and an array of square pistons. The CeO2 attenuator thicknesses were calculated using the gray level information from the initial unequalized image. The array of pistons was pressed against a uniform thickness of attenuating material to generate a filter for x-ray beam equalization. The filter was subsequently inserted into the x-ray beam for the final equalized radiograph. It was positioned close to the focal spot (magnification of 8.0) in order to minimize edge artifacts from the filter. The equalization of x-ray transmission across the field exiting from the object significantly improved the image quality by preserving local contrast throughout the image. The contrast-to-noise ratio (CNR) in the equalized images was increased-by up to fivefold. Phantom studies indicate that equalized images using a relatively small array of pistons (e.g., 8 x 8) produce significant improvement in image quality with negligible perceptible artifacts. Animal studies showed that beam equalization significantly improved fluoroscopic and angiographic image quality. X-ray beam equalization produced an image with a relatively uniform scatter-glare intensity and it reduced the scatter-glare fraction in the previously underpenetrated region of the image from 0.65 to 0.50. Also, x-ray tube loading due to the mask assembly itself was negligible. In conclusion, area beam equalization reduces the scatter-glare fraction and significantly improves CNR in the previously underpenetrated region of the image.     

全数字超声成像中采用双脉冲激励时动态滤波器的设计

目的分析数字超声成像中采用双脉冲单极性激励时,超声回波的频谱及其随深度的变化趋势。方法根据在不同深度利用回波的不同频率的分量进行成像的滤波器匹配思想,设计了一组动态滤波器。既保证了近场图像分辨力又能兼顾远场图像的灵敏度。结果此滤波器在现场可编程门阵列（FPGA）芯片中实现。结论研究证明在全数字超声成像设备中,使用此滤波器得到的超声图像比使用常值滤波器得到的超声图像质量有所提高。     

眼科高频环阵超声波数字化成像技术的研究

目的设计眼科高频环阵B超平台,实现超声波全程数字化处理。方法设计环阵换能器发射接收电路,将高频的超声回波信号经过前级放大后直接引出进行高分辨率、高速的模拟数字采样。信号数字化后,通过高速的现场可编程门阵列（field-programmable gatearray,FPGA）完成波束形成、动态聚焦、滤波、检波及对数放大等一系列信号处理。结果通过临床验证,眼科高频环阵B超平台图像横向分辨率0．2mm,侧向分辨率0．4mm,满足临床要求。结论环阵超声波数字化成像技术可提高图像分辨率和疾病检出率。     

X-ray scatter correction algorithm for cone beam CT imaging

Developing and optimizing an x-ray scatter control and reduction technique is one of the major challenges for cone beam computed tomography (CBCT) because CBCT will be much less immune to scatter than fan-beam CT. X-ray scatter reduces image contrast, increases image noise and introduces reconstruction error into CBCT. To reduce scatter interference, a practical algorithm that is based upon the beam stop array technique and image sequence processing has been developed on a flat panel detector-based CBCT prototype scanner. This paper presents a beam stop array-based scatter correction algorithm and the evaluation results through phantom studies. The results indicate that the beam stop array-based scatter correction algorithm is practical and effective to reduce and correct x-ray scatter for a CBCT imaging task.     

高频环阵数字化超声检测技术的研究

目的研究高频环阵技术,克服线阵等扫描技术只能一维聚焦的缺点,提高各方向分辨率,提高数字化成像技术信噪比,最大限度地提高图像质量,提高超声检出率。方法设计高频环阵水浴旋转式超声探头,以及相应的发射、接收电路,经AD9271数字化处理后进行数字信号处理。结果运用高频环阵数字化超声检测,采集回波信号并进行分析,结果表明,高频环阵数字化超声系统可以提高疾病检出率。结论高频环阵数字化超声检测技术可以作为眼科、乳腺等疾病早期诊断的有效方法。     

Resolution and information limitations from transducer arrays.

The factors limiting the resolution achievable with array-based imaging methods are considered. The limitations on beamwidth and field of view for beam scanning systems are first examined using plane wave diffraction theory, treating focusing and any array curvature as separable to the plane wave analysis. It is found that in all cases the number of half-beamwidths (maximum to null) across the field of view cannot exceed the number of electrically addressable elements in the array. The minimum beamwidth achievable by strong focusing is shown to be limited to twice the inter-element pitch. Digital reconstruction is then considered as an alternative to beam scanning. Here the number of image points recoverable across the field of view is equal to the number of elements in the array. The mathematical equivalence of the two methods is demonstrated, and the inference is made that the half-beamwidth represents a fundamental measure of lateral resolution. Alternative array configurations, suitable for CT methods, are then compared to probe arrays and it is found that the total number of resolution cells within a two-dimensional image is dependent on the pulse length and number of elements, rather than on the array configuration and imaging method. This again reveals the fundamental similarity of the various methods, essentially in combining position line information from the separate elements, albeit in different orders. Finally an expression for the information capacity of a scanning system is presented which relates the limitations on spatial and contrast resolution to the bandwidth and dynamic range of the system and the number of elements in the array.     

High-quality 3D correction of ring and radiant artifacts in flat panel detector-based cone beam volume CT imaging

The use of an x-ray flat panel detector is increasingly becoming popular in 3D cone beam volume CT machines. Due to the deficient semiconductor array manufacturing process, the cone beam projection data are often corrupted by different types of abnormalities, which cause severe ring and radiant artifacts in a cone beam reconstruction image, and as a result, the diagnostic image quality is degraded. In this paper, a novel technique is presented for the correction of error in the 2D cone beam projections due to abnormalities often observed in 2D x-ray flat panel detectors. Template images are derived from the responses of the detector pixels using their statistical properties and then an effective non-causal derivative-based detection algorithm in 2D space is presented for the detection of defective and mis-calibrated detector elements separately. An image inpainting-based 3D correction scheme is proposed for the estimation of responses of defective detector elements, and the responses of the mis-calibrated detector elements are corrected using the normalization technique. For real-time implementation, a simplification of the proposed off-line method is also suggested. Finally, the proposed algorithms are tested using different real cone beam volume CT images and the experimental results demonstrate that the proposed methods can effectively remove ring and radiant artifacts from cone beam volume CT images compared to other reported techniques in the literature.     

K-edge digital subtraction imaging based on a dichromatic and compact x-ray source

This work proposes a compact dichromatic imaging system for the application of the K-edge digital subtraction technique based on a conventional x-ray tube and a monochromator system. A quasi-monochromatic x-ray beam at the energy of iodine K-edge is produced by Bragg diffraction on a mosaic crystal. Two thin adjacent beams with energies that bracket the K-edge discontinuity are obtained from the diffracted beam by means of a proper collimation system. They are then detected using an array of Si detectors. A home-made phantom is used to study the image quality as a function of iodine concentration. Signal and signal-to-noise ratio analysis has also been performed. The results are compared with theoretical expectations.     

Acoustically modulated x-ray phase contrast imaging

We report the use of ultrasonic radiation pressure with phase contrast x-ray imaging to give an image proportional to the space derivative of a conventional phase contrast image in the direction of propagation of an ultrasonic beam. Intense ultrasound is used to exert forces on objects within a body giving displacements of the order of tens to hundreds of microns. Subtraction of images made with and without the ultrasound field gives an image that removes low spatial frequency features and highlights high frequency features. The method acts as an acoustic 'contrast agent' for phase contrast x-ray imaging, which in soft tissue acts to highlight small density changes.