超声成像的相位偏差校正

由于人体组织的各向异性，超声成像中存在相位偏差。相差制约了超声成像分辨率的进一步提高。互相关及其类似相位估计技术可以用于相差较正，ｊｉｔｅｒ是此类算法的基本限制。并行自适应接收补偿算法可以校正较小的相差，结合互相关技术能够得到比较理想的相差校正效果     

超声成像的相位偏差校正

由于人体组织的各向异性，超声成像中的存在相位偏关葙差制约超声成像分析分辩率的进一步提高。互相关及其类似相位估计技术可以有于相差较正，ｊｉｔｔｅｒ是此类算法的基本限制。并行自适应接收补偿算法可以校正较上差，结合互相关技术能够得到比较理想的相差校正效果。     

基于幅度相位估计相干系数与幅度相位估计融合的超声成像方法

最小方差(MV)波束形成算法有效提高了成像分辨率,但牺牲了成像对比度和算法稳健性。本研究提出一种融合幅度相位估计(APES)波束形成和基于幅度相位估计的相干系数的成像方法。该方法首先利用APES算法计算出初步结果,然后利用APES波束形成的输出取代相干系数中相干部分,计算相干加权系数,最后对APES波束形成的结果进行加权得到成像结果。为了验证算法的有效性,对点目标和斑目标进行了成像。结果表明提出的算法在成像对比度和稳健性方面优于APES算法和融合APES与相干系数的算法。     

基于一种改进的相位校正算法消除MRI运动伪影

背景：近年来,MRI由于具有高的空间分辨率和软组织对比度,在临床上的运用越来越广泛。但是其成像时间较长,所以容易受到患者身体运动的影响,产生运动伪影。 目的：去除MRI图像成像时产生的伪影,改善图像质量。 方法：使用改进的相位矫正算法,并结合水平集算法去除图像伪影。去除伪影后使用模糊增强改善处理后图像的质量。 结果与结论：实验证明使用改进的相位矫正算法得到的图像比使用原始的相位矫正算法得到的图像效果更加理想。     

NMR中APSL自动相位校正算法的改进

核磁共振仪获取的FID信号采用APSL(自动相位校正算法)进行相位矫正算法时,当相角偏差为45°、135°、225°和315°,计算的相角误差很大.提出了一种改进的APSL方法,通过人为地将原始谱峰相角改变±45°,并在不同的相角偏差下计算相位角,然后对三个角度下的结果进行分析以得到误差最小的相位角.     

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。     

X射线相位衬度成像的研究进展

在临床医学和材料科学等领域,基于吸收衬度的X射线成像技术是一种非常重要的诊断工具.然而,对于生物医学软组织、聚合物或纤维材料等,由于它们对X射线的弱吸收,这种传统X射线成像技术的应用受到了限制.相位衬度成像是目前X射线成像领域的最新前沿技术和研究热点之一,它能检测对X射线弱吸收的轻元素物质,空间分辨率可达微米甚至亚微米量级,与传统X射线吸收成像技术相比具有独特的优势,并且在医学、生物学、材料科学等领域上获得了成功.介绍了X射线相位衬度成像的原理、成像特点和应用情况.     

数字化X线成像系统的成像特性及其校正技术

随着一些新的Ｘ线图像处理方法的出现，对数字Ｘ互图像性能的要求将越来越高，本文从分析数字化Ｘ线成像系统的物理机制出发，提出了数字化Ｘ线成像系统的数学模型，并根据这一模型导出了Ｘ线成像的非线性规律及面不均匀性的规律，给出了对这些不利因素的校正方法，为进行数字Ｘ线图像的后续处理打下了坚实的基础。     

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。     

Spherical aberration correction in multiphoton fluorescence imaging using objective correction collar

Multiphoton microscopy has evolved into a powerful bioimaging tool in three dimensions. However, the ability to image biological specimens in-depth can be hindered by sample spherical aberration and scattering. These two phenomena can result in the degradation of image resolution and the loss of detected multiphoton signal. In this work, we use the correction collar (for cover glass thickness) associated with a water immersion objective in an attempt to improve multiphoton imaging. In the two samples we examined (human skin and rat tail tendon), we found that while the improvement in image resolution was not visible qualitatively, the measured axial fluorescence or second harmonic generation signal profiles indicate that the use of the correction collar can help to improve the detected multiphoton signals. The maximum increases are 36% and 57% for the skin (sulforhodamine B fluorescence) and tendon (second harmonic generation) specimens, respectively. Our result shows that for in-depth multiphoton imaging, the correction collar may be used to correct for spherical aberration. However, each tissue type needs to be examined to determine the optimal correction collar setting to be used.     

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.     

3-Dimensional ultrasound imaging for meniscal lesions

PURPOSE: The aim of this prospective study was to evaluate preoperative three-dimensional ultrasound scans for the detection of meniscal lesions with a special focus on interobserver reliability. METHODS: Forty one patients with clinical signs of meniscal lesions were preoperatively examined by ultrasound using the 3-D technique (11.7 MHz linear transducer). The 3-D dataset was stored and examined by a second orthopaedic surgeon. The second ultrasound examiner was blinded to the results of the first. Any meniscal pathology was confirmed arthroscopically and documented. RESULTS: At arthroscopy eight lateral meniscal lesions and 57 medial meniscal lesions were detected at different locations. The sensitivity and specificity of the original ultrasound examination was acceptable whereas the results of the second ultrasound session were not as sensitive. CONCLUSION: Three-D-ultrasound with a high resolution transducer, in the hands of an experienced operator, provides acceptable results in the detection of meniscal lesions, however, analysis of the volume dataset from the 3-D ultrasound investigation indicates that it does not offer sufficient accuracy for clinical use.     

基于超快超声平面波成像的医学超声探头改进

目的基于平面波发射/接收原理的超快超声成像技术近年来已成为国际医学超声领域的研究热点,有望取代传统的聚焦扫描式超声成像技术。传统方式受其成像模式的限制,无法实现高帧频成像,而通过平面波发射以及相干复合方法,可大大提高超声成像的帧频。本文提出一个新的设想,即采用高程方向无聚焦换能器(non-elevation-focused probe,NEFP),相对于传统的高程方向有聚焦换能器(elevation-focused probe,EFP),可能有助于进一步提高超快超声成像技术的成像效果。方法首先简要介绍平面波相干复合成像的原理和方法,进而通过FieldⅡ软件仿真,验证相干复合成像方法对平面波成像图像质量的提升效果。最后,通过仿真和实验实现探头高程方向的发射声束聚焦模式,并对上述2种模式换能器的平面波成像效果进行了对比分析。结果使用平面波复合成像算法得到很好的成像效果,两种探头经对比,NEFP探头成像图像的对比度相对于EFP探头明显增强。结论对于超快超声成像方法,使用NEFP超声探头可以取得更优的成像效果。     

Diagnosis of ovarian tumors by transvaginal Doppler ultrasound with color flow imaging]

Ovarian carcinoma is a silent disease with few symptoms. Early detection of ovarian cancer is difficult. Transvaginal Doppler ultrasound with color flow imaging is a new technique in the evaluation of gynecological diseases. This method was used in the diagnosis of ovarian tumors in 39 women who were treated in the Department of Obstetrics and Gynecology, Nagoya University Hospital. Wave forms of the parenchymal tumor arteries or tumor surface arteries were compared by according to the pulsatility index (PI). 1/PI was 0.69 +/- 0.04 in benign tumor and 2.33 +/- 1.36 in malignant tumors (p less than 0.01). When the cutoff value of 1/PI was set at 0.8 (cutoff value of PI: 1.25), the accuracy of diagnosis was 84.6% (33/39). The accuracy of ultrasonographic pattern classification and CA125 were 74.4% (29/39) and 53.8% (21/39), respectively. In 18 tumors with low CA125 (less than 35 U/ml), 5 of 7 malignant tumors (71.4%) had high 1/PI (greater than 0.8), and benign tumor, low 1/PI (less than 0.8) or non-detectable wave forms. This procedure should prove to be useful in the diagnosis of ovarian cancer.     

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.     

A stimulus-responsive contrast agent for ultrasound molecular imaging

Complement activation by targeting ligands is an important issue that governs the fate of targeted colloidal contrast agents for molecular imaging. Here, we extend previous work on a stimulus-responsive microbubble construct, in which the ligand is normally buried by a polymeric overbrush and transiently revealed by ultrasound radiation force, to show reduced complement activation and focused adhesion to cells using a physiological peptide ligand. Attachment of C3/C3b in vitro and production of soluble C3a anaphylotoxin in vitro and in vivo decreased significantly for the buried-ligand architecture vs. the conventional exposed-ligand motif and no-ligand control. Additionally, the buried-ligand architecture prevented adhesion of Arg-Gly-Tyr (RGD)-bearing microbubbles to integrin-expressing human umbilical vein endothelial cells (HUVEC) when driven by buoyancy in a static chamber, but it did not affect adhesion efficiency when activated by ultrasound radiation force pulses. These results show, for the first time, the molecular mechanism for reduced immunogenicity for the buried-ligand architecture and feasibility of targeting with this motif using a physiological ligand-receptor pair.     

Second harmonic inversion for ultrasound contrast harmonic imaging

Ultrasound contrast agents (UCAs) are small micro-bubbles that behave nonlinearly when exposed to an ultrasound wave. This nonlinear behavior can be observed through the generated higher harmonics in a back-scattered echo. In past years several techniques have been proposed to detect or image harmonics produced by UCAs. In these proposed works, the harmonics generated in the medium during the propagation of the ultrasound wave played an important role, since these harmonics compete with the harmonics generated by the micro-bubbles. We present a method for the reduction of the second harmonic generated during nonlinear-propagation-dubbed second harmonic inversion (SHI). A general expression for the suppression signals is also derived. The SHI technique uses two pulses, p' and p″, of the same frequency f(0) and the same amplitude P(0) to cancel out the second harmonic generated by nonlinearities of the medium. Simulations show that the second harmonic is reduced by 40?dB on a large axial range. Experimental SHI B-mode images, from a tissue-mimicking phantom and UCAs, show an improvement in the agent-to-tissue ratio (ATR) of 20?dB compared to standard second harmonic imaging and 13?dB of improvement in harmonic power Doppler.