URA编码孔径的层析成像

URA编码孔径成像是X射线成像的一项新技术.它不但提高了信噪比,而且具有层析分辨能力.本文详细论述了URA编码孔径的层析成像原理,并提供了一种改善层析成像质量的叠代方法.并应用迭代方法成功地进行了计算机模拟实验.     

压缩感知光谱成像技术的编码孔径与探测器匹配优化

编码孔径光谱成像仪在实际应用中存在着编码模板与探测器分辨率不匹配从而降低系统分辨率的问题。针对该问题进行了两种情况分析,并通过数学理论建模给出了相应的解决方案。对于编码模板分辨率高于探测器分辨率这一情况,提出引入邻域嵌入超分辨技术的方法,实现了基于压缩感知的超分辨光谱成像。对于编码模板分辨率低于探测器分辨率这一情况,提出区块阈值划分的编码孔径,将编码微元按照区块阈值重新划分并进行灰度分级,从而实现低分辨率编码模板的高分辨率编码孔径。利用梯度投影稀疏重构(GPSR)算法进行数据立方体重建,实验结果表明:运用基于超分辨理论的编码孔径快照光谱成像系统所测得的光谱图像更精准,内容更丰富;采用基于区块阈值划分的编码孔径的编码孔径快照光谱成像系统具有更高的空间分辨率和光谱分辨率。结果证实优化后的编码孔径快照光谱成像系统,其分辨率和成像质量大幅度提升,并实现了高分辨率元件的100%利用。     

SNR of the coded aperture imaging system

Optical Review - In this paper, the expression for the SNR has been developed through the imaging model. It is concluded that the image SNR decreases with the increase of the number of...     

Tomogram reconstruction using advanced coded aperture imaging

Some possibilities are discussed of an advanced coded imaging method to get tomograms of doped γ-ray sources in the body. This method uses a pair of coherent codes and has many advantages compared with any conventional one. The abilities are clearly shown by theoretical analysis and computer simulation.     

X光环孔编码成像技术研究

 着眼于惯性约束聚变实验研究中的应用，对X光环孔编码成像技术进行了研究。利用数值模拟的手段，分析了环孔的自相关函数及其对环孔编码成像技术图像重建的影响，对不同的图像重建技术进行了初步比较。基于星光II实验装置，利用自行研制的X光环孔编码成像系统进行了激光等离子体X光环孔编码成像技术的演示实验，获得了满意结果。     

Micro coded aperture imaging applied to laser plasma diagnosis

We present a coded aperture imaging method which could be applied to the study of microplasmas obtained by laser. Based on the use of an annular aperture associated with a deconvolution processing, this method gives sections of the X-ray and emitted particle tridimensional distribution. The first experimental result shows the range of possibilities offered by this technique.     

X光环孔编码成像技术研究

着眼于惯性约束聚变实验研究中的应用,对X光环孔编码成像技术进行了研究。利用数值模拟的手段,分析了环孔的自相关函数及其对环孔编码成像技术图像重建的影响,对不同的图像重建技术进行了初步比较。基于星光II实验装置,利用自行研制的X光环孔编码成像系统进行了激光等离子体X光环孔编码成像技术的演示实验,获得了满意结果。     

时域压缩合成孔径超分辨水声成像算法

提出一种针对水下稀疏目标的时域压缩合成孔径声呐成像方法(TC-SAS),实现了水声目标高分辨实时成像。通过多子阵的孔径合成,在时域上构造出成像网格格点到有效孔径内逐帧阵列的格林函数,并给出成像区域散射强度到数据域的映射矩阵;然后利用该区域空域稀疏的先验知识,通过正交匹配追踪的稀疏重构方式,解算出成像区域散射系数矩阵,实现了稀疏目标高分辨成像.同时,针对线性调频信号提出数据缩减的方法,通过对观测数据和字典矩阵同时脉压后截取,减小了数据规模;进一步结合二维矩阵数表查表的方法,以空间换时间,实现了区块实时成像。数值仿真以及湖试试验表明,所提算法能分辨出传统的时延求和算法难以分辨的目标,并且在图像清晰度指标上平均提升4.9 dB.改善了合成孔径声呐的成像质量.     

编码孔径光谱成像仪光学简化彗差对图谱反演误差分析

编码孔径光谱成像技术是近年来发展起来的一种新型光谱成像技术, 该技术在一次像面采用特定的编码模板对目标进行编码, 结合特殊的采样成像方式, 获得满足景物重构的采样数据量, 实现了空间信息和光谱信息的高精度重构, 具有高光通量、高信噪比等优势.但该技术实际的光学系统设计, 以及相应加工和装调过程中各种误差的存在, 将逐一传递反映到探测器精度与编码后图谱采样精度的不匹配, 这会引发最终重构图谱质量降低.本文侧重分析研究光学系统设计和研制装调中光学彗差相对设计值间存在的偏差, 通过几何光线追迹与波前像差联合计算的方法, 在成像面仿真出不同数值程度的彗差矩阵, 并以此来分析不同彗差下对重构图像质量的影响结果.并用其分析结论作为依据, 改进了编码孔径光谱成像仪的设计和研制, 提供了相应图像成像反演结果, 由此确保了编码孔径光谱成像仪的成像优势.     

Optimization of sparse synthetic transmit aperture imaging with coded excitation and frequency division

An effective aperture approach is used for optimization of a sparse synthetic transmit aperture (STA) imaging system with coded excitation and frequency division. A new two-stage algorithm is proposed for optimization of both the positions of the transmit elements and the weights of the receive elements. In order to increase the signal-to-noise ratio in a synthetic aperture system, temporal encoding of the excitation signals is employed. When comparing the excitation by linear frequency modulation (LFM) signals and phase shift key modulation (PSKM) signals, the analysis shows that chirps are better for excitation, since at the output of a compression filter the sidelobes generated are much smaller than those produced by the binary PSKM signals. Here, an implementation of a fast STA imaging is studied by spatial encoding with frequency division of the LFM signals. The proposed system employs a 64-element array with only four active elements used during transmit. The two-dimensional point spread function (PSF) produced by such a sparse STA system is compared to the PSF produced by an equivalent phased array system, using the Field II simulation program. The analysis demonstrates the superiority of the new sparse STA imaging system while using coded excitation and frequency division. Compared to a conventional phased array imaging system, this system acquires images of equivalent quality 60 times faster, when the transmit elements are fired in pairs consecutively and the power level used during transmit is very low. The fastest acquisition time is achieved when all transmit elements are fired simultaneously, which improves detectability, but at the cost of a slight degradation of the axial resolution. In real-time implementation, however, it must be borne in mind that the frame rate of a STA imaging system depends not only on the acquisition time of the data but also on the processing time needed for image reconstruction. Comparing to phased array imaging, a significant increase in the frame rate of a STA imaging system is possible if and only if an equivalent time efficient algorithm is used for image reconstruction.     

Three-dimensional spectrally encoded imaging

A method for three-dimensional surface measurements with phase-sensitive spectrally encoded imaging is demonstrated. Both transverse and depth information is transmitted through a single-mode optical fiber, allowing this scheme to be incorporated into a miniature probe. This approach is demonstrated by measurement of the profile of a lens surface and by three-dimensional imaging of the face of a small doll.     

Scanning optical reconstruction of coded aperture images

A scanning optical technique is described and used to reconstruct coded aperture images obtained with four different kinds of arrays. The feasibility and advantages of the technique are demonstrated experimentally. The results are used to compare the imaging properties of these arrays, i.e.: lateral resolution, background noise and axial (tomographic) resolution.     

Scanning heterodyne reconstruction of coded aperture images

The reconstruction of coded aperture images using an optical scanning heterodyne processor is described for a class of apertures which can be synthesized by two beam interference. The analysis of Fresnel zone apertures indicates that a lateral and longitudinal (tomographic) resolution close to the theoretical limit is achievable. Experimental results of optical simulations confirm this assertion. Advantages of such technique include real-time operation and large multiplexing capability.     

Deconvolution systems for coded aperture images of three-dimensional x-ray objects

A non-redundant distribution of ten point sources is used for coded aperture imaging. The coded image of a simple three-dimensional x-ray object is deconvoluted by means of three different decoding systems: by an optical projection system using spatially incoherent light, by an on-line optical set-up with information input using an electro-optic relay tube, and by a quasi-on-line electronic system using an electronic storage-tube. The three methods are compared with respect to signal-to-noise ratio, resolution, and convenience of handling.     

X光编码孔径成像和处理技术

本文论述了编码孔径成像的基本原理.讨论了孔径编码的方法和相机的制作,侧重于均匀冗余阵列(URA)的编码技术.介绍了编码孔径图像的光学处理和数字处理的研究成果.给出了实验和实际应用的结果.     

Phase-coded aperture for optical imaging

For the optical spectrum region, we describe a novel phase-coded aperture imaging system that can be used in a computational imaging camera. The optical design includes a phase-only screen followed by a detector array. A specific diffraction pattern forms at the detector array when the wavefront from a point source object passes through the phase screen. Since diffraction effects cannot be ignored in the optical regime, an iterative phase retrieval method is used to calculate the phase coded screen. Correlation type processing can be applied for the image recovery. Computer simulation results are presented to illustrate the excellent imaging performance of this camera.     

Spinning disk for compressive imaging

We report the first, to the best of our knowledge, experimental implementation of a spinning-disk configuration for high-speed compressive image acquisition. A single rotating mask (i.e., the spinning disk) with random binary patterns was utilized to spatially modulate a collimated terahertz (THz) or IR beam. After propagating through the sample, the THz or IR beam was measured using a single detector, and THz and IR images were subsequently reconstructed using compressive sensing. We demonstrate that a 32-by-32 pixel image could be obtained from 160 to 240 measurements in both the IR and THz ranges. This spinning-disk configuration allows the use of an electric motor to rotate the spinning disk, thus enabling the experiment to be performed automatically and continuously. This, together with its compact design and computational efficiency, makes it promising for real-time imaging applications.     

Detection of explosives by Terahertz synthetic aperture imaging—focusing and spectral classification

In the adaptation of Terahertz (THz) synthetic aperture imaging to stand-off screening of concealed weapons and explosives, the incoming THz wavefronts exhibit significant curvature that must be considered in the image reconstruction. Consequently, the imaging array must be focused at a specific distance to correct for the wavefront curvature. In addition to the focusing correction, detection of explosives requires spectral analysis of the reconstructed THz image. Kohonen self-organizing maps are shown to be promising tools for differentiating the spectral signature of C4 explosive from the reflection spectra of metal and semi-transparent barrier materials. To cite this article: A. Sinyukov et al., C. R. Physique 9 (2008).     

Mathematical morphology by a defocused convolver with coded aperture

An optoelectronic system is constructed to implement mathematical morphological operations, which is based on optical neighborhood connection by a defocused convolver of coded aperture and electronic thresholding by a PC computer. Theoretical considera tions are given, the operations such as erosion, dilation, opening, closing and edge detection are displayed experimentally.     

Sequential beamforming for synthetic aperture imaging

Synthetic aperture sequential beamforming (SASB) is a novel technique which allows to implement synthetic aperture beamforming on a system with a restricted complexity, and without storing RF-data. The objective is to improve lateral resolution and obtain a more depth independent resolution compared to conventional ultrasound imaging. SASB is a two-stage procedure using two separate beamformers. The initial step is to construct and store a set of B-mode image lines using a single focal point in both transmit and receive. The focal points are considered virtual sources and virtual receivers making up a virtual array. The second stage applies the focused image lines from the first stage as input data, and take advantage of the virtual array in the delay and sum beamforming. The size of the virtual array is dynamically expanded and the image is dynamically focused in both transmit and receive and a range independent lateral resolution is obtained. The SASB method has been investigated using simulations in Field II and by off-line processing of data acquired with a commercial scanner. The lateral resolution increases with a decreasing F#. Grating lobes appear if F# ⩽ 2 for a linear array with λ-pitch. The performance of SASB with the virtual source at 20 mm and F# = 1.5 is compared with conventional dynamic receive focusing (DRF). The axial resolution is the same for the two methods. For the lateral resolution there is improvement in FWHM of at least a factor of 2 and the improvement at −40 dB is at least a factor of 3. With SASB the resolution is almost constant throughout the range. For DRF the FWHM increases almost linearly with range and the resolution at −40 dB is fluctuating with range. The theoretical potential improvement in SNR of SASB over DRF has been estimated. An improvement is attained at the entire range, and at a depth of 80 mm the improvement is 8 dB.