基于超声相控线阵的缺陷全聚焦三维成像

在无损检测领域,缺陷三维成像能够还原材料内部缺陷的空间信息,与传统的二维成像相比有着明显的优势。目前实现超声相控阵缺陷三维成像主要依靠面阵探头,而这些设备往往十分复杂和昂贵。通过采取适当的数据采集方法和后处理成像算法,超声相控线阵系统能够实现低成本、高效率的三维超声检测成像。采用断层扫描和全矩阵捕捉的方法获取成像数据;再利用全聚焦成像算法绘制高分辨率的断层图像;根据这些图像在三维空间中真实的位置关系,插值还原出缺陷的三维图像。此外,针对全聚焦成像算法计算量大的问题,提出了一种加速算法。实验表明,这种检测方法能够快速得到目标空间区域的高质量三维图像,准确体现缺陷的空间分布情况,相比于借助B扫查图像和C扫查图像材料内部缺陷的方法,具有更强的直观性。     

基于稀疏采样的电力接地网雷达检测系统成像算法

接地网隐蔽的敷设位置造成检测的局限性,而利用雷达系统能够实现无开挖情况下的便捷检测。论文针对接地网雷达智能检测系统的成像处理问题展开研究,结合接地网检测场景的目标分布特点,以稀疏采样理论为基础,利用接地导体强反射性所呈现的信号稀疏性实现了有效的数据低维投影测量,提高了系统检测与数据处理的效率。在低维数据基础上,利用信号重建获取目标的二维轮廓,得到二维成像输出。通过仿真实验验证了成像算法的有效性,在获得高分辨率输出的同时,大幅度降低了系统的数据处理量。此外,由于距离向的信号重建处理,使距离向旁瓣得到有效抑制。     

微波三维成像离散点目标回波数据模拟

成像雷达一般可分为合成孔径雷达(SAR)和逆合成孔径雷达(ISAR).研究目标的RCS特性当前普遍应用ISAR成像技术,而这些目标的成像能力都依赖于目标的回波信号.在ISAR三维成像理论的基础上,模拟离散点目标的回波信号,为三维成像软件提供三维空间的模拟数据,用来验证成像软件的正确性.基于已有的一维和二维成像软件对模拟数据进行了分析.从三维数据中提取出一维和二维数据,成像结果证明了模拟数据在一维和二维的有效性,从而保证了模拟数据三维成像可靠性.     

融合相机与激光雷达的目标检测与尺寸测量

针对三维场景下的目标检测与尺寸测量任务,设计了一种融合激光雷达和相机传感器的三维目标检测和尺寸测量算 法。 使用基于卷积神经网络的二维目标检测器提取目标的二维检测框,结合图像中的二维检测框和几何投影关系获取包含物 体的三维视锥点云,由欧氏聚类方法获得物体的聚类点云,实现了物体的三维目标检测。 提出了基于目标二维检测框的改进尺 寸测量方案以替代原有点云聚类后得到的三维框信息,提高了物体尺寸测量的精度。 在现有数据集上评估测试了目标检测与 尺寸测量的精度,实验结果表明,二维目标检测器 YOLOv7 在检测数据集上的平均检测精度达到了 81%,改进尺寸测量方案在 物体尺寸测量时的测量误差在 5%以内,对于较远物体或较小物体的目标检测和尺寸测量也具有很好的效果。     

采用LCD投影实现三维曲面测量技术研究

本文研究了采用LCD光栅投影形成结构光的立体视觉传感器进行三维曲面测量的方案。通过LCD光栅编码,投射规则的序列图案到被测曲面,实现被测曲面上点的空间编码,然后对投影点由粗到细进行匹配,从而获得高精度空间匹配点,经过标定的传感器即可计算出空间匹配点的三维坐标,从而完成曲面测量。由于LCD投影图案易于控制,速度快,定位精度高,机械结构简单,所以该方案测量速度快,同时可获得较高的测量精度。     

注入电流式磁声成像平面模型的逆问题研究

注入电流式磁声成像是电阻抗成像和超声成像相结合的一种新型成像技术,具有电阻抗成像的高对比度和超声成像高分辨率的优势,是一种有望获得高质量图像的生物电阻抗成像技术,在生物医学成像领域具有广阔的应用前景。作为一种新型成像技术,目前在电导率的重建方面还没有形成完整的体系。针对二维平面模型,提出一种由声场信号准确重建被测样品电流密度的方法。首先采用维纳滤波反卷积方法由超声换能器测量的声场信号重建被测样品原始声场p(r,t),接着利用时间反演法获取声源分布0??(J×B),然后考虑到二维平面模型只有电流密度的两个分量,结合电流连续性定理,从而重建电流密度的两个分量xJ、yJ,最后设计并搭建注入式磁声成像实验平台,利用生物组织进行实验,最终得到猪肉组织的电导率图像,重建结果证明了重建方法的可行性。     

一维距离像的仿真研究

本文对目标一维距离像进行电磁散射仿真研究。通过图形电磁计算,在计算机仿真环境下,利用OpenGL图形处理技术实现。仿真结果能够真实反映出高分辨率下的目标一维散射中心分布。本文所用方法可以进一步用于目标的二、三维成像及目标识别研究。     

基于转台的中场ISAR成像技术研究

在中场区通过对相位弯曲补偿进行微波成像与远场成像效果相当,且能大大降低对测试距离的要求,所以具有很强的工程应用价值.基于经典的转台成像模型,本文提出球面波聚焦卷积积分法和中场滤波-逆投影算法,实现了中场区目标的微波成像.球面波聚焦卷积积分法能实现360°范围的二维成像,且运算速度快,适用于各向同性目标,中场滤波-逆投影算法针对小转角范围内对目标进行精密的二维成像,适用于各种复杂目标.仿真和实验结果表明,这两种算法的有效性.     

矢网仪与滑轨联合控制合成孔径成像系统

基于实验室通用设备矢量网络分析仪和滑轨的合成孔径成像系统可以获取低成本实测数据,验证成像原理和算法;可以通过设置不同系统参数评估系统性能,为实际系统的搭建提供有效的论证。介绍了如何采用 C#编程联合控制矢量网络分析仪和滑轨,以及对目标“一步一停”测量的方法。最后通过实测数据 S21参数获得目标延时特性,分别进行距离向和方位向处理对目标进行二维成像,通过对目标成像结果和实际空间位置的比对,验证了该方案的可行性和有效性。     

水下主动激光扫描系统中光场记录及散射背景分离研究

传统水下主动激光扫描系统采用普通相机对反射光接收记录,反射激光点被掩埋在背景噪声中无法分离,影响成像质量。该文在水下激光主动扫描成像系统中采用光场相机记录了包括激光反射光线和各种散射背景杂光的位置和方向信息,为抑制散射背景杂光提供了可能。在后续光场记录图像处理中,首先,对记录的光场图像进行前后两次重聚焦,第一次是对激光照射到物面激光光点的重聚焦,第二次是对激光光点前景散射光的重聚焦,再对两幅图像进行差分处理;提出一种计算机自动判断流程,使得差分所得图像上激光点的衬度最大,或足够大。实验结果表明,上述方法可以达到较好的散射背景抑制作用,是对现有同步扫描主动激光成像系统空间分离散射背景抑制技术的必要补充。     

Clinical role of diffusion-weighted imaging: neonatal studies

The application of diffusion-weighted imaging to the early diagnosis of neonatal cerebral infarction and hypoxic ischemic encephalopathy is illustrated. Diffusion-weighted images showed early infarction before conventional imaging in both cases. These were subsequently seen with conventional imaging on follow-up. In four cases of grades I and II hypoxic-ischemic encephalopathy (HIE) no abnormality was seen with either diffusion-weighted or conventional imaging. In four other cases of grades II and III HIE, much more extensive changes were seen with diffusion-weighted imaging than with conventional imaging. Follow-up scans with conventional imaging confirmed the abnormalities in the two surviving infants. Diffusion-weighted imaging may be particularly useful for the early diagnosis of ischemic-anoxic injury in infants.     

MR imaging of degenerative disc disease in the lumbar spine with ultrashort TE pulse sequences

Objective The objective of this study was to assess the feasibility of using ultrashort TE (UTE) pulse sequences to image the lumbar spine.Materials Pulse sequences of TE=0.08 ms were used to image the lumbar spine in 5 normal subjects and 14 patients with degenerative disease. Contrast enhancement was administered in 11 cases.Results The sequences showed high signal in the anterior and posterior longitudinal ligaments, the cartilaginous end plate, the annulus fibrosus, the ligamentum flavum, interspinous ligaments and insertions of ligaments. Normal contrast enhancement was seen in these structures. Enhancement of hypertrophied ligaments and scar tissue was readily identified. Long T2 suppression techniques were useful in distinguishing enhancement of scar tissue from veins. Enhancement in discs was more obvious than with conventional sequences. In a case of thalassaemia bands of high signal were seen in the intervertebral discs parallel to the end plates.Conclusion The UTE sequences offer new options for visualizing discs, scar tissue, ligaments and other structures of the lumbar spine in health and disease.     

Preliminary experience with a new double-echo half-Fourier single-shot turbo spin echo acquisition in the characterization of liver lesions

A new double-echo half-Fourier single-shot turbo spin echo technique has been implemented in which two images are obtained per excitation pulse, one with an echo time (TE) of 60 ms and another with a TE of 438 ms. The acquisition window per image is 380 ms and is determined by the echo spacing of 4.3 ms and the echo train length of 88 for images with resolution of 160×256. No breath holding was performed. The aim of the study was to test whether the additional information of the late TE image improves the characterization of liver lesions. Twenty-eight patients with 39 focal liver lesions (9 cysts, 11 hemangiomas, and 19 solid lesions) were imaged with the new technique, and signal intensity (SI) ratios of lesion and liver were obtained. At-test analysis showed that in the TE 60 ms image, SI ratios of cysts and hemangiomas were not significantly different, whereas in the TE 438 ms images the two types of lesions can be classified. Signal intensity ratios of solid lesions were in both images clearly lower than those of cysts and hemangiomas. The technique, therefore, seems a promising and straightforward new tool for the characterization of liver lesions.     

Evaluation of ultrafast phase-contrast imaging in the thoracic aorta

Purpose: Two ultrafast phase-contrast (PC) data acquisition strategies, multishot echo-planar imaging (EPI)-PC and segmentedk-space fast gradient-echo PC (FASTCARD-PC) were evaluated with regard to their measurement accuracy. Materials and Method: Flow measurements of the ascending and descending aorta were acquired in 10 healthy volunteers with an electrocardiogram (ECG)-triggered eight-shot EPI-PC sequence (TR/TE/flip 16/7.4/45°, 32-ms flow-phase interval, 2×2 mm in plane resolution), and FASTCARD-PC (six it-lines per band, TR/TE/flip 11/6.1/45°, 32-ms flow-phase interval, 2 × 1 mm in plane resolution). These were compared to flow-volume data acquired with conventional cine-PC (TR/TE/flip 24/7/45°, 48-ms flow-phase interval, 2 × 1 mm in plane resolution). Using cine-PC as a gold standard, the measurement accuracy of FASTCARD-PC and EPI-PC were determined. Results: Both EPI-PC and FASTCARD-PC significantly reduced data acquisition times compared to cine PC. EPI-PC flow measurements correlated well with aortic cine-PC flow-volume determinations (r=0.98). Reflecting poorer temporal resolution, FASTCARD-PC measurements were less accurate (p<0.05), evidenced by poor correlation with cine-PC data (r=0.62). Conclusion: Ultrafast PC measurements are possible. In contrast to the segmentedk-space PC technique, which is limited in temporal resolution, multishot EPI-PC provides high measurement accuracy in pulsatile vessels while keeping the image acquisition interval short enough for a comfortable breath-hold.     

Dynamic contrast-enhanced MR imaging of the entire breast with spectral-selective inversion fast three dimensional sequence

Dynamic contrast-enhanced images with high spatial and temporal resolutions were acquired with a fast 3D spoiled gradient echo (SPGR) sequence using spectral selective inversion recovery (IR) pulse. Five healthy volunteers and 12 patients with 14 pathologically proven breast lesions were studied. Fat suppressed volume image data covering the entire breast were obtained with a sufficient spatial resolution (0.9×1.5×3.0 mm³) and an imaging time of 57 s. By using the criteria including peripheral enhancement and presence of spiculation, sensitivity, specificity, and accuracy in detecting malignant lesions were 88.9, 80.0 and 85.%, respectively. Although the C/N and S/N ratios were approximately 30% less than those of the conventional fat suppressed 3D technique, fast 3D SPGR imaging with spectral IR method demonstrated sufficient image quality for both time intensity analysis and morphological evaluation of the breast lesions with a data acquisition time less than half of the conventional method. This technique can substantially improve spatial and temporal resolutions of dynamic MR images of the breast and will be useful in evaluating malignant and benign breast lesions.     

In vivo diffusion tensor mapping of the brain of squirrel monkey, rat, and mouse using single-shot STEAM MRI

The purpose was to assess the potential of half Fourier diffusion-weighted single-shot STEAM MRI for diffusion tensor mapping of animal brain in vivo. A STEAM sequence with image acquisition times of about 500 ms was implemented at 2.35 T using six gradient orientations and b values of 200, 700, and 1200 s mm^–2. The use of half Fourier phase-encoding increased the signal-to-noise ratio by 45% relative to full Fourier acquisitions. Moreover, STEAM-derived maps of the relative anisotropy and main diffusion direction were completely free of susceptibility-induced signal losses and geometric distortions. Within measuring times of 3 h, the achieved resolution varied from 600×700×1000 m³ for squirrel monkeys to 140×280×720 m³ for mice. While in monkeys the accessible white matter fiber connections were comparable to those reported for humans, detectable fiber structures in mice focused on the corpus callosum, anterior commissure, and hippocampal fimbria. In conclusion diffusion-weighted single-shot STEAM MRI allows for in vivo diffusion tensor mapping of the brain of squirrel monkeys, rats, and mice without motion artifacts and susceptibility distortions.     

Optimized EPI for fMRI studies of the orbitofrontal cortex: compensation of susceptibility-induced gradients in the readout direction

Object Most functional magnetic resonance imaging (fMRI) studies record the blood oxygen leveldependent (BOLD) signal using gradient-echo echo-planar imaging (GE EPI). EPI can suffer from substantial BOLD sensitivity loss caused by magnetic field inhomogeneities. Here, BOLD sensitivity losses due to susceptibility- induced gradients in the readout (RO) direction are characterized and a compensation approach is developed. Materials and Methods Based on a theory describing the dropout mechanism, an EPI sequence was optimized for maximal BOLD sensitivity in the orbitofrontal cortex (OFC) using a specific combination of an increased spatial resolution in the RO direction and a reduced echo time. Using measured BOLD sensitivity maps and a breath hold experiment, the model and compensation approach were tested. Results Using typical fMRI EPI parameters, susceptibility-induced gradients in the RO direction caused dropouts in the OFC and the inferior temporal lobe. Optimizing the echo time and spatial resolution effectively reduced the dropout as predicted by the theory. Conclusion The model-based compensation approach effectively reduces BOLD sensitivity losses due to susceptibility-induced gradients in the RO direction. It retains the high temporal resolution of single-shot EPI and can be readily combined with methods for the compensation of susceptibility-induced field gradients in the phase-encoding and through-plane direction.     

The Role of Connectivity in Thermal Imaging

This paper demonstrates the role of connectivity, a concept originally developed by Newnham two decades ago, in improving image quality of infrared (IR) imaging systems by enhancing the thermal modulation transfer function (MTF). IR imaging in the medium wavelength range (7.5 to 14 m), corresponding to the thermal black body maximum near room temperature and to the atmospheric window, is desirable for a wide range of applications. Night vision, target recognition, reconnaissance, driving aids, and navigation in foggy and poor visibility weather are among the applications of this technology. 1:3 arrays fabricated from ceramic barium strontium titanate (BST) have made it possible to produce compact, low-cost, uncooled infrared cameras that are capable of delivering television quality images.     

A keyhole echo planar hybrid imaging technique

A hybrid keyhole imaging method is presented which demonstrates theccombination of two distinctly different MR imaging techniques. In this work single shot EPI was used as a dynamic update scan for a conventional high resolution gradient echo acquisition. Problems associated with the integration of MR data from distinctly different imaging techniques are addressed. Illustration is provided by way of diffusion weighted imaging. This novel development requires further investigation which need not be limited to the hybridization of strictly Cartesian based scanning methods.     

红外成像技术在诊断变压器储油柜中油位的应用探讨

分析了胶囊式真空储油柜的结构特点和工作原理,结合一起变压器储油柜油位指示为零的缺陷处理,介绍利用红外成像诊断技术快速、准确地判断变压器储油柜油位的方法。