Signal-to-noise measurements utilizing a novel dual-energymultimedia detector

Dual-energy measurements are presented utilizing a novel slot-scan digital radiographic imaging detector, operating on gaseous solid state ionization principles. The novel multimedia detector has two basic functional components: a noble gas-filled detector volume operating on gas microstrip principles, and a solid state detector volume. The purpose of this study is to investigate the potential use of this multimedia detector for enhanced dual-energy imaging. The experimental results indicate that the multimedia detector exhibits a large subtracted signal-to-noise ratio. Although the intrinsic merit of this device is being explored for medical imaging, potential applications of the multimedia detector technology In other industrial areas, such as aerospace imaging, aviation security, and surveillance, are also very promising     

A novel sensor for X-ray imaging applications

In this study, a novel direct X-ray conversion electronic sensor for X-ray imaging, aimed at the enhancement of the signal characteristics of a cadmium zinc telluride (CdZnTe) detector substrate, is proposed. CdZnTe substrates are promising candidates in detector technology since they have a high stopping power. The novelty of the sensor lies in the material of use as well as in the signal collector design, which exhibits “Frisch-grid” capabilities. As a result, the proposed technology provides an effective mode to shield the electron-collecting electrode from the charge induced on it from moving positive ions and trapped charge. Overall, this technology would allow for a decreased sensor thickness, accompanied with a high collector efficiency, and consequently improved signal characteristics. Therefore, the signal quality of an imaging sensor as applied to medical detector technology, radio astronomy, aviation security, surveillance and nondestructive inspection, and other industrial areas will be significantly improved     

A framework for optimising the radiographic technique in digital X-ray imaging

The transition to digital radiology has provided new opportunities for improved image quality, made possible by the superior detective quantum efficiency and post-processing capabilities of new imaging systems, and advanced imaging applications, made possible by rapid digital image acquisition. However, this transition has taken place largely without optimising the radiographic technique used to acquire the images. This paper proposes a framework for optimising the acquisition of digital X-ray images. The proposed approach is based on the signal and noise characteristics of the digital images and the applied exposure. Signal is defined, based on the clinical task involved in an imaging application, as the difference between the detector signal with and without a target present against a representative background. Noise is determined from the noise properties of uniformly acquired images of the background, taking into consideration the absorption properties of the detector. Incident exposure is estimated or otherwise measured free in air, and converted to dose. The main figure of merit (FOM) for optimisation is defined as the signal-difference-to-noise ratio (SdNR) squared per unit exposure or (more preferably) dose. This paper highlights three specific technique optimisation studies that used this approach to optimise the radiographic technique for digital chest and breast applications. In the first study, which was focused on chest radiography with a CsI flat-panel detector, a range of kV(p) (50-150) and filtration (Z = 13-82) were examined in terms of their associated FOM as well as soft tissue to bone contrast, a factor of importance in digital chest radiography. The results indicated that additive Cu filtration can improve image quality. A second study in digital mammography using a selenium direct flat-panel detector indicated improved SdNR per unit exposure with the use of a tungsten target and a rhodium filter than conventional molybdenum target/molybdenum filter techniques. Finally, a third study focusing on cone-beam computed tomography of the breast using a CsI flat-panel detector indicated that high Z filtration of a tungsten target X-ray beam can notably improve the signal and noise characteristics of the image. The general findings highlight the fact that the techniques that are conventionally assumed to be optimum may need to be revisited for digital radiography.     

Novel electronic readout system for micro-channel plate detector with wedge and strip anode

A micro-channel plate detector with wedge and strip anode can be used for visible and ultraviolet light imaging. In this paper, the imager electronics are designed in order to process specific output charge characteristics. The original signal output from the detector is shaped into a Gaussian pulse signal, and a digital Constant Fraction Discriminator is used to judge the arrival time of the pulse. The resolution of the electronic output image is 1024?×?1024, and the position decoding accuracy is 1 pixel. The experimental imaging resolving power of the detector is as high as 70?µm.     

Photon Fluctuations,Equivalent Quantum Efficiency,and the Information Capacity of Photographic Images

The equivalent quantum efficiency (EQE) enables the signol-to-noise ratio of a detector to be compared with that attainable by an ideal noiseless detector working under the some conditions. It thus provides a scientific basis for the measurement of photographic speed-to-grain ratios. The limitations of an ideal detector are only those imposed by photon fluctuations in the signal. The signal itself may also be measured in terms of these inherent photon fluctuations, and this enables the information capacity of the detector to be expressed in terms only of the EQE and the ratio of the power spectrum of the signal to that of the photon fluctuations. There are several advantages when the information capaCity is expressed in this manner. Not only is the signal specified in a basic farm, but also, since the EQE is the most fundamental of imaging properties, the information capacity of the photographic process can be rapidly compared with that of any other type of detector by substitution of the appropriate value of the EQE. In this way the information capacity can also be compared with the ultimate capacity, which is that of the signal itself and corresponds to an EQE of 100 per cent. Examples are given of the information capacity for a range of values of the EQE and signal size, and its spatial frequency dependence is demonstrated in terms of the transfer function.     

A hybrid radiation detector based on a plasma display panel

Recently, large-area image detectors have been investigated for X-ray imaging in medical diagnostic and other applications. In this paper, a new type of radiation detector is described, based on the integration of a photoconductor into a plasma display panel (PDP). This device, called a hybrid PDP detector, should be quite inexpensive, because it can directly leverage off the fabrication and materials technologies widely used in plasma display panels. Also, these new radiation detectors should operate under the most challenging environmental conditions, because they are inherently rugged and radiation-resistant and insensitive to magnetic fields. In this paper, we describe a hybrid digital radiation detector device, based on plasma display. The PDP panel is 7 in. in size with a 1000-μm pixel pitch, and filled with 700 Torr of Xe gas; the hybrid PDP panel is of the same structure, except for the photoconductor deposit. The glass absorption, dark current, X-ray sensitivity, and linearity as a function of electric field were measured to investigate its electrical properties. From the results, stabilized dark current density and significant X-ray sensitivity were obtained with both panels; however, the hybrid PDP detector showed better characteristics than the PDP detector. It also had good signal response and linearity. The hybrid digital radiation detector device based on a plasma display seems to be a promising technology for use in radiology and dynamic moving imaging.     

Sealed-cell mercury resonance ionization imaging detector

A sealed, compact mercury atomic-absorption resonance ionization imaging detector has been developed and evaluated. The sensitivity of the detector as well as its ability to form two-dimensional images has been demonstrated. Images of faint light (1000 photons) have been recorded by image summation. It is shown that one can obtain high-quality images with a spatial resolution of at least 130 mum by detecting the ionic component of the imaging signal. Distortion, more noise, and poorer spatial resolution were observed when the electron component of the signal was detected. We studied the influence of voltage on the cell electrodes to find the conditions for optimum signal-to-noise ratio.     

Effect of a finite-size pinhole on noise performance in single-, two-, and three-photon confocal fluorescence microscopy

It is known that signal level in single-, two- and three-photon confocal fluorescence microscopy increases with the size of the detector. Here we evaluate the signal-to-noise and the signal-to-background criteria for these microscopes. We investigate the effect of pinhole size on their ability to detect a weakly fluorescent point object in the presence of a uniformly fluorescence background. Numerical results based on a paraxial approximation theory show that optimization of these criteria gives an optimal value for pinhole size, which results in an improved imaging performance. The resulting improvement in noise performance, compared with the use of a large detector, is greater for three-photon than for two-photon confocal fluorescence microscopes.     

Effects of Annular Pupils on Confocal Fluorescent Imaging

Abstract

For a confocal fluorescent microscope with annular lenses, the effects of varying the radii of central obstruction of the annular lenses on three, two and one-dimensional imaging have been investigated in terms of the optical transfer function. In particular, we consider the effects of the central obstruction on the signal strength for a system with either a point or finite-sized detector. The signal level as a function of the detector and the central obstruction sizes is presented for volume, planar and point objects, respectively.     

Timing characteristics of a Cd1-xZnxTedetector-based X-ray imaging system

The timing characteristics of a planar Cd_1-xZn_x Te sample at each frequency of a scanning square-wave test pattern, has been measured. This study is aimed at evaluating the speed characteristics of a Cd_1-xZn_xTe detector for X-ray imaging and computed tomographic (CT) applications. The experimental results of this study indicate that the temporal response of a Cd_1-xZn_xTe detector based X-ray system, improves significantly by optimizing the X-ray tube and detector parameters     

Photon address digital detector system (PADDS): a cost-effective imaging photon detector

We describe the implementation of an imaging photon detector for the photon address digital detector system (PADDS). The concept is based on combining an image intensifier with a position-sensitive photomultiplier tube with crossed-wire anodes. Particular emphasis is placed on modularity and flexibility. A digital signal processor evaluates events in real time. The compact detector system is able to process photon events with high precision in time with only moderate computing power of the host system. Laboratory experiments show the feasibility of the approach presented for observing rapidly varying sources at low light levels.     

基于分数阶功率谱熵的未知水声脉冲信号检测方法

水声侦察的核心问题是在无先验知识条件下捕获其他平台发射的脉冲信号,单频（Continuous Wave,CW）信号和调频（Frequency Modulation,FM）信号是常用的水声探测脉冲。功率谱熵算法能有效检测低信噪比的CW信号,但对FM信号性能不佳,分数阶傅里叶变换（Fractional Fourier Transform,FRFT）则能聚集FM信号能量。利用FRFT的性质,结合功率谱熵算法,设计了分数阶功率谱熵检测器,可在分数阶域实施未知脉冲信号检测。理论分析了FRFT对FM信号的能量聚集作用,优化了FRFT阶数搜索方法。仿真实验以及海试数据处理结果证实检测器对FM信号性能良好,且对CW信号的侦察检测性能无影响。通过门限学习,检测器可实现对未知水声脉冲信号的统一自动检测。     

Theory of near-field magneto-optical imaging

Scanning near-field optical microscopy has been recently applied to the imaging of magnetic samples. It was shown experimentally that an apertureless microscope suffers a substantial loss of resolution when used for magneto-optical imaging compared with that for conventional imaging. No such change is observed for aperture microscopes. We explain this observation by developing a model for the imaging process that incorporates the response of the probe. We calculate real observable properties such as the rotation of polarization at the detector or the circular dichroism signal and thus simulate magneto-optical images of a domain structure in cobalt for both aperture and apertureless microscopes.     

激光相干阵列成象雷达系统光束整形的研究

激光相干阵列成象雷达系统中本振光波前与信号光波前匹配与否直接影响系统的灵敏度和分辨力。采用共轭光栅合成技术对相干成象本振光束作整形处理，以适应探测器件列及合成输出满足最佳信噪比条件。     

Effects of axial, transverse, and oblique sample motion in FD OCT in systems with global or rolling shutter line detector

This study deals with effects on the interference signal caused by axial, transverse, and oblique motion in spectrometer-based Fourier-domain optical coherence tomography (FD OCT). Two different systems are compared-one with a global shutter line detector and the other with a rolling shutter. We present theoretical and experimental investigations of motion artifacts. Regarding axial motion, fringe washout is observed in both systems, and an additional Doppler frequency shift is seen in the system using a rolling shutter. In addition, both systems show the same SNR decrease as a result of a transversely and obliquely moving sample. The possibility of flow measurement by using the decrease in signal power was demonstrated by imaging 1% Intralipid emulsion flowing through a glass capillary. This research provides an understanding of the SNR degradation caused by sample motion and demonstrates the importance of fast data acquisition in medical imaging.     

Relationship between microscanned image quality and fill factor of detectors

Microscanning is an important technique in high-resolution electro-optical imaging. It can increase the resolution and improve the performance of imaging systems. For optimum design of a staring imaging system with microscanning modes it is necessary to choose the optimum microscanning mode according to the fill factor of the detector. Hence it is important to study the effect of the fill factor on the microscanning image quality. With some assumptions, we introduce the sampling-averaging modulation transfer function of a detector array at the spatial Nyquist frequency with which to study quantitatively the improvement in image quality of various microscanning modes for selected fill factors (1, 2/3, and 1/2). Analytical results show that the amount of improvement is closely associated with the fill factor. Finally, typical sampling imaging of focal plane arrays with these fill factors are simulated. Experimental results qualitatively describe the effect of the fill factor on the microscanning image and show good agreement with theoretical analysis.     

Range accuracy limitation of pulse ranging systems based on Geiger mode single-photon detectors

Geiger mode single-photon detectors have been used in pulse ranging system and three-dimensional imaging systems due to high sensitivity and easy integration. The ranging accuracy and precision is influenced by many factors. Based on statistical theory, five main factors are discussed in this article, namely, echo signal intensity, pulse width, detector quantum efficiency, target position, and background noise. An analytical relationship among the ranging accuracy, precision, and these factors is obtained for a Q-switched laser pulse. Through this relationship, it is shown that the echo signal intensity and pulse width are more important than other factors and higher echo signal intensity and narrower pulse width can result in better accuracy and precision.     

Simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed photodisplacement interferogram

A new parallel photodisplacement technique has been developed that achieves simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram, which greatly simplifies the system and the optical alignment. A linear region of photodisplacement is excited on the sample for subsurface imaging by use of a line-focused intensity-modulated laser beam, and the displacement and surface information on reflectivity and topography are detected by a parallel heterodyne interferometer with a charge-coupled device linear image sensor used as a detector. The frequencies of three control signals for excitation and detection, that is, the heterodyne beat signal, modulation signal, and sensor gate pulse, are optimized such that surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions, allowing each to be discretely reproduced from Fourier coefficients. Preliminary experiments demonstrate that this technique is capable of simultaneous imaging of reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects at a remarkable speed of only 0.26 s per 256 x 256 pixel area. This new technique is promising for use in nondestructive hybrid surface and subsurface inspection and other applications.     

Fast wavelet-based multiresolution image registration on a multiprocessing digital signal processor

Image registration is a fundamental task in image processing. It is used in matching two or more images taken at different times, from different imaging modalities, or from different viewpoints. One of the obstacles in achieving practical acceptance of image registration techniques is their computational complexity, which results in a long response time. In this article we present a fast multiresolution image registration algorithm using wavelet transform for the translational and rotational alignment of two-dimensional images. In particular, a novel approach to determine the algorithm parameters to balance the registration accuracy and computational requirement is also described. We implemented this algorithm on a PC-based multimedia and imaging system using a multiprocessing digital signal processor. The algorithm is capable of achieving a subpixel registration accuracy reliably under various noise levels. The multiresolution algorithm implemented on this desktop system was able to register two 256 × 256 images in 466 ms, which is 40 times faster than the uniresolution exhaustive search approach. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 29–37, 1998     

基于CZT探测器的双能X线骨密度测量技术

提出了一种应用碲锌镉(CdZnTe或CZT)晶体探测器的骨矿密度测量方法。该方法通过对被测对象的定位,X射线扫描,应用CZT晶阵对被骨组织吸收、衰减后的双能X射线进行测量。测量信号经分级处理后,实现了骨矿密度定量测量和成像。实验结果表明,CZT探测器具有良好的工作性能,系统测量具有快速,高精度,高空间分辨率等特点。