Digital flashing tomosynthesis: a promising technique for angiocardiographic screening

A system for digital flashing tomosynthesis (DFTS) consists of four ECG-gated simultaneously flashed X-ray tubes, a 14-in image intensifier, a unit for digital subtraction angiography (DSA), a PC-hosted transputer network for three-dimensional (3-D) reconstruction as well as for quantitative coronary angiography and ventriculography, a display unit, and an individual digital archive. A presentation of DFTS tomoangiograms as a single slice or multiple slices of arbitrary thickness is available. DFTS also offers rotating and stereographic presentation of 3-D images. DFTS represents a system for standardized digital angiocardiography with digital archiving, and assures optimal reproducibility and safety. This system is feasible for both an ambulatory basis to allow high-volume cardiovascular angiographic screening by only one X-ray snapshot, and for quantification of natural progression or potential regression of coronary artery disease resulting from interventional or pharmacological therapy.     

Elimination of nonpivotal plane images from x-ray motion tomograms

A method for eliminating the contribution of nonpivotal plane images into a conventional X-ray motion tomogram is described. A set of tomograms, each focused on one of distinct parallel planes, are combined to form a blur-free tomogram. From the mathematical analysis of conventional tomography, it is found that the multisection tomography system reduces to a three-dimensional incomplete linear system with angularly limited frequency response. An iterative constrained reconstruction algorithm incorporating the object boundary constraint is used for reconstruction of a blur-free tomogram without a contribution from nonpivotal planes. Some computer simulations were made for verification of the algorithm. Although the algorithm accomplishes the three-dimensional reconstruction of volume rather than image restoration of a single slice plane, the optimal high-pass spatial filter applying to a single tomogram is derived on the way to solving the inverse problem of the multisection tomography system.     

基于智能型红外焦平面电路液氮成像系统的研究与算法实现北大核心CSCD

提出了一种智能型红外焦平面电路液氮成像系统,系统采用UART转SPI数据传输,上位机VB软件开发SPI配置界面,可提高SPI寄存器批量配置效率和准确率,减少外界干扰产生误码和乱码情况,并结合FPGA、自研的IRCamExpert-CETC图像处理软件和图像采集卡搭建软硬件成像系统,本系统具有红外视频图像在线监测和多芯测试能力。本文进一步提出了基于单片像元级ADC的背景减除、盲元补偿、非均匀性校正、开窗、像素合并、空间滤波、图像均衡变换、时间延迟积分多种图像算法和总体算法结构,并通过对一款640×512阵列的智能型红外焦平面电路进行测试,验证了单片红外焦平面多功能图像算法,并实现了系统对智能型红外焦平面全参数的性能评估。采用像元级进行图像处理的方式,降低了采用算法级进行后续图像处理的难度,减少了图像处理算法消耗的资源。多功能图像算法为智能型红外焦平面的工程化应用提供了新技术途径。     

Reconstruction of 3-D objects from cone beam projections

A true three-dimensional reconstruction (TTR) algorithm which is applicable to a cone beam with 4π detection geometry is introduced. The TTR differs from conventional slice by slice 3-D reconstruction methods. Promising areas of application for the TTR algorithm are position and X-ray computerized tomographic image reconstruction.     

彩色数字全息系统中透镜色差影响的研究

在物光通过透镜系统到达CCD平面的彩色数字全息研究中,将每一色光的像视为像空间中的物体。基于全息图补零的一次傅里叶变换(1-FFT)重建方法,导出既能较好地统一不同色光重建物体的物理尺寸,又能考虑透镜色差影响的彩色数字全息图像重建方法。对该方法的研究结果表明,透镜色差的影响等效于让物体的重建像偏离了理想的重建像平面。然而,数字全息重建图像具有一定的焦深,在多数情况下,可以忽略透镜色差的影响,利用厂家给定的焦距标称值获得满足实际需要的彩色重建图像。     

Personalized body segment parameters from biplanar low-dose radiography

Body segment parameters are essential data in biomechanics. They are usually computed with population-specific predictive equations from literature. Recently, medical imaging and video-based methods were also reported for personalized computation. However, these methods present limitations: some of them provide only two-dimensional measurements or external measurements, others require a lot of tomographic images for a three-dimensional (3-D) reconstruction. Therefore, an original method is proposed to compute personalized body segment parameters from biplanar radiography. Simultaneous low-dose frontal and sagittal radiographs were obtained with EOS system. The upper leg segments of eight young males and eight young females were studied. The personalized parameters computed from the biplanar radiographic 3-D reconstructions were compared to literature. The biplanar radiographic method was consistent with predictive equations based on gamma-ray scan and dual energy X-ray absorptiometry.     

Intrabody three-dimensional position sensor for an ultrasound endoscope

To avoid or reduce the X-ray exposure in endoscopic examinations and therapy, as an alternative to the conventional two-dimensional X-ray fluoroscopy we are developing an intrabody navigation system that can directly measure and visualize the three-dimensional (3-D) position of the tip and the trace of an ultrasound endoscope. The proposed system can identify the 3-D location and direction of the endoscope probe inserted into the body to furnish endoscopic images. A marker transducer(s) placed on the surface of the body transmits ultrasound pulses, which are visualized as a marker synchronized to the scanning of the endoscope. The position (direction and distance of the marker transducer(s) outside the body relative to the scanning probe inside the body) of the marker is detected and measured in the scanned image of the ultrasound endoscope. Further, an optical localizer locates the marker transducer(s) with six degrees of freedom. Thus, the proposed method performs inside-body 3-D localization by utilizing the inherent image reconstruction function of the ultrasound endoscope, and is able to be used with currently available commercial ultrasound image scanners. The system may be envisaged as a kind of global positioning system for intrabody navigation.     

基于离焦光栅的单帧深度学习相位反演算法

针对目前相位差法收敛速度慢以及需要CCD在焦面以及离焦面多次测量的问题,提出了基于离焦光栅的单帧深度学习相位反演算法。该算法用离焦光栅对入射波前进行调制,可同时在透镜焦平面上获得正负离焦以及焦面远场光强分布;此外算法引入卷积神经网络替代原有的多次扰动寻优过程,波前复原算法耗时大大降低。仿真结果表明:算法可根据单帧透镜焦面远场光强分布实现高精度快速波前复原,残差波前的均方根为入射波前均方根的6.7%,算法进行一次波前复原所需时间可小于0.6 ms。     

同轴全息显微镜的三维压缩感知去卷积体积重建

数字同轴全息显微镜是一种二维成像技术,最近已被应用于三维成像,然而在三维图像生成的过程中,物体的失焦图像成为三维体积重建上获取明显三维特征的重要障碍。将压缩感知层析重建算法与去卷积算法相结合,显著减少重建中散斑噪声和失焦伪影对目标的影响。结果显示,与单一的三维去卷积重建图像相比,对于重叠的金属丝,光学标尺,生物棉花切片以及微米级聚苯乙烯颗粒的三维堆积图像具有更好的聚焦效果。     

Parallelized Bayesian inversion for three-dimensional dental X-ray imaging

Diagnostic and operational tasks based on dental radiology often require three-dimensional (3-D) information that is not available in a single X-ray projection image. Comprehensive 3-D information about tissues can be obtained by computerized tomography (CT) imaging. However, in dental imaging a conventional CT scan may not be available or practical because of high radiation dose, low-resolution or the cost of the CT scanner equipment. In this paper, we consider a novel type of 3-D imaging modality for dental radiology. We consider situations in which projection images of the teeth are taken from a few sparsely distributed projection directions using the dentist's regular (digital) X-ray equipment and the 3-D X-ray attenuation function is reconstructed. A complication in these experiments is that the reconstruction of the 3-D structure based on a few projection images becomes an ill-posed inverse problem. Bayesian inversion is a well suited framework for reconstruction from such incomplete data. In Bayesian inversion, the ill-posed reconstruction problem is formulated in a well-posed probabilistic form in which a priori information is used to compensate for the incomplete information of the projection data. In this paper we propose a Bayesian method for 3-D reconstruction in dental radiology. The method is partially based on Kolehmainen et al. 2003. The prior model for dental structures consist of a weighted /spl lscr//sup 1/ and total variation (TV)-prior together with the positivity prior. The inverse problem is stated as finding the maximum a posteriori (MAP) estimate. To make the 3-D reconstruction computationally feasible, a parallelized version of an optimization algorithm is implemented for a Beowulf cluster computer. The method is tested with projection data from dental specimens and patient data. Tomosynthetic reconstructions are given as reference for the proposed method.     

High-Field Magnetic Resonance Imaging With Reduced Field/Tissue RF Artefacts—A Modeling Study Using Hybrid MoM/FEM and FDTD Technique

Due to complex field/tissue interactions, high-field magnetic resonance (MR) images suffer significant image distortions that result in compromised diagnostic quality. A new method that attempts to remove these distortions is proposed in this paper and is based on the use of transceiver-phased arrays. The proposed system uses, in the examples presented herein, a shielded four-element transceive-phased array head coil and involves performing two separate scans of the same slice with each scan using different excitations during transmission. By optimizing the amplitudes and phases for each scan, antipodal signal profiles can be obtained, and by combining both the images together, the image distortion can be reduced several fold. A combined hybrid method of moments (MoM)/finite element method (FEM) and finite-difference time-domain (FDTD) technique is proposed and used to elucidate the concept of the new method and to accurately evaluate the electromagnetic field (EMF) in a human head model. In addition, the proposed method is used in conjunction with the generalized auto-calibrating partially parallel acquisitions (GRAPPA) reconstruction technique to enable rapid imaging of the two scans. Simulation results reported herein for 11-T (470-MHz) brain imaging applications show that the new method with GRAPPA reconstruction theoretically results in improved image quality and that the proposed combined hybrid MoM/FEM and FDTD technique is suitable for high-field magnetic resonance imaging (MRI) numerical analysis     

Mexico 草帽小波与电离层CT反演

电离层ＣＴ技术中由于数据采集系统的几何结构存在局限性,致使探测所得数据不导致其成为不完全数据重建问题。投影中的采样点不均匀,且由投影谱通过Ｆｏｕｒｉｅｒ中心切片原理组合而得的二维谱平面不完全可知,若要用变换方法重建成象,需要对其进行估计。     

A 3D reconstruction of vascular structures from two X-ray angiograms using an adapted simulated annealing algorithm

A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed. Assuming uniform mixing of contrast medium and background subtraction, the cross-section of each vessel is reconstructed through a binary representation. A priori information about both the slice to be reconstructed and the relationships between adjacent slices are incorporated to lessen ambiguities on the reconstruction. Taking into account the knowledge of normal vessel geometry, an initial solution of each slice is created using an elliptic model-based method. This initial solution is then deformed to be made consistent with projection data while being constrained into a connected realistic shape. For that purpose, properties on the expected optimal solution are described through a Markov random field. To find an optimal solution, a specific optimization algorithm based on simulated annealing is used. The method performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles. Results on 2D slice independent reconstruction and 3D reconstruction of a stack of spatially continuous 2D slices are presented for single vessels and bifurcations.     

互相关算法在运动目标距离选通激光三维成像中的应用

在微光成像中,距离选通成像是一种获取目标三维信息的有效手段。对于静止目标而言,可以通过对目标切片成像,获得不同选通距离的目标图像,进而通过二值化算法或质心算法获得目标的三维图像。而对于运动目标而言,在切片成像的同时,目标的空间位置会发生变化,因此需要对不同选通距离的目标图像进行配准,而后才能获得目标的三维图像。搭建了基于像增强电荷耦合器件(ICCD)的距离选通实验系统,提出了一种基于像质评价的互信息配准算法配准激光图像目标的空间位置,然后对配准后的激光图像通过互相关算法获得三维图像,并在保证一定的三维精度基础上,逐渐减少激光图像的像幅数,最后与二值化算法和质心算法三维重构进行了实验对比,实验结果表明,互信息配准算法能够有效配准激光图像,互相关三维成像算法精度高于二值化法和质心法,最少采用2幅图像即可获得目标的三维点云图像,大大降低了对运动目标三维成像的难度。     

红外焦平面条带状非均匀性校正硬件实现方法

红外焦平面阵列条带状非均匀性严重影响了其成像质量,大大限制了它的应用。实现了一种基于FPGA的红外焦平面阵列条带状非均匀性实时校正系统,该系统以中值红外均衡算法为核心,针对算法以及FPGA的特性进行了优化,单帧内可进行条带状非均匀性的校正,硬件仿真结果表明:处理效果显著。系统处理速度快、资源占用量小,可以作为一个独立模块嵌入到红外焦平面成像与处理系统中,实现条带状非均匀性的实时校正,有很高的实用性与可扩展性。     

阵列探测器在成像光谱偏振探测技术中的应用

为了在成像光谱偏振仪中应用近红外焦平面阵列探测器,得到高质量图像信息,结合新型弹光调制型成像光谱偏振探测技术(PEM-ISP),提出了一种基于近红外焦平面阵列探测器的成像光谱偏振探测技术。系统采用FPA-640512 InGaAs焦平面阵列探测器作为光学探测接收元件,采用高速现场可编程门阵列(FPGA)作为信号处理单元,做到对光学信号的快速采集与并行处理,满足高速、实时的信号传输与处理技术等要求。将经高速A/D采集得到的数据存储到FPGA外扩的静态随机存储器中,以保证数据的完整性。数据最终通过通用串行总线传至上位机,上位机通过LabVIEW实现图像还原。结果表明,该系统可以应用于PEM-ISP中,实现对测量信号的精确探测与采集,并得到完整的图像信息。     

宽视场航天相机像面测量技术

宽视场高质量的航天相机是未来有效载荷的发展方向,基于宽视场航天相机的装调需求,提出了一种干涉测量与几何量测量相结合的像面测量方法。搭建了宽视场航天相机像面测量平台,利用激光干涉仪确定各视场的焦点位置,激光跟踪仪获取各焦点位置坐标,通过坐标换算和拟合完成像面的绘制,像面测量误差可控制在0.01 mm内。通过该方法,完成了一款离轴三反航天相机的像面绘制,系统焦距1200 mm,相对孔径1∶2.4,视场角10°×1°。测试的像面与光学设计软件ZEMAX输出的理想像面进行比对,像面形状及位置基本吻合,平面度偏差0.009 mm。测试结果表明光学系统装调到位,为探测器配准工序的完成提供了重要依据。     

Generalized tomosynthesis for focusing on an arbitrary surface

Previous implementations of tomosynthesis used reconstruction algorithms that generate planar tomograms where the structures in one plane are visualized and the structures out of the plane are blurred. In many applications, however, the structures of interest do not reside in a single plane and it is desirable to generalize the reconstruction algorithm to generate a tomogram focused on the structure itself. A procedure that allows such a reconstruction is described, and its usefulness in focusing on a three-dimensional object is demonstrated.     

A reconstruction algorithm from truncated projections

A new tomographic reconstruction method is proposed which permits the reconstruction of a region of interest within a slice from partially truncated scanning data. This method utilizes two types of source data, namely a series of truncated projections and the outline of the object's cross section. The principle of this algorithm is to estimate the outside area of truncation in one projection from the projection data of the other viewing angles and the outline data of the object. The above estimation is accomplished by following two repeated procedures: 1) the modification of the calculated projection data compared each time with the already measured projection data of the truncated area, and 2) the modification of the reconstructed image compared also each time with the shape of the object. Computer simulation shows the convergence of the results obtained by this algorithm thus verifying its validity, and a reconstructed image after iterative processes exhibits good quality.     

Variable pitch reconstruction using John's equation

We present an algorithm to reconstruct helical cone beam computed tomography (CT) data acquired at variable pitch. The algorithm extracts a halfscan segment of projections using an extended version of the advanced single slice rebinning (ASSR) algorithm. ASSR rebins constant pitch cone beam data to fan beam projections that approximately lie on a plane that is tilted to optimally fit the source helix. For variable pitch, the error between the tilted plane chosen by ASSR and the source helix increases, resulting in increased image artifacts. To reduce the artifacts, we choose a reconstruction plane, which is tilted and shifted relative to the source trajectory. We then correct rebinned fan beam data using John's equation to virtually move the source into the tilted and shifted reconstruction plane. Results obtained from simulated phantom images and scanner images demonstrate the applicability of the proposed algorithm.