284 research outputs found
X-ray backscatter radiography with lower open fraction coded masks
Copyright 2017 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.Single sided radiographic imaging would find great utility for medical, aerospace and security applications. While coded apertures can be used to form such an image from backscattered X-rays they suffer from near field limitations that introduce noise. Several theoretical studies have indicated that for an extended source the images signal to noise ratio may be optimised by using a low open fraction (<0.5) mask. However, few experimental results have been published for such low open fraction patterns and details of their formulation are often unavailable or are ambiguous. In this paper we address this process for two types of low open fraction mask, the dilute URA and the Singer set array. For the dilute URA the procedure for producing multiple 2D array patterns from given 1D binary sequences (Barker codes) is explained. Their point spread functions are calculated and their imaging properties are critically reviewed. These results are then compared to those from the Singer set and experimental exposures are presented for both type of pattern; their prospects for near field imaging are discussed
A Compact Neutron Scatter Camera Using Optical Coded-Aperture Imaging
The detection and localization of fast neutron resources is an important capability for a number of nuclear security areas such as emergency response and arms control treaty verification. Neutron scatter cameras are one technology that can be used to accomplish this task, but current instruments tend to be large (meter scale) and not portable. Using optical coded-aperture imaging, fast plastic scintillator, and fast photodetectors that were sensitive to single photons, a portable neutron scatter camera was designed and simulated. The design was optimized, an experimental prototype was constructed, and neutron imaging was demonstrated with a tagged 252Cf source in the lab
Image Processing Applications in Real Life: 2D Fragmented Image and Document Reassembly and Frequency Division Multiplexed Imaging
In this era of modern technology, image processing is one the most studied disciplines of signal processing and its applications can be found in every aspect of our daily life. In this work three main applications for image processing has been studied.
In chapter 1, frequency division multiplexed imaging (FDMI), a novel idea in the field of computational photography, has been introduced. Using FDMI, multiple images are captured simultaneously in a single shot and can later be extracted from the multiplexed image. This is achieved by spatially modulating the images so that they are placed at different locations in the Fourier domain. Finally, a Texas Instruments digital micromirror device (DMD) based implementation of FDMI is presented and results are shown.
Chapter 2 discusses the problem of image reassembly which is to restore an image back to its original form from its pieces after it has been fragmented due to different destructive reasons. We propose an efficient algorithm for 2D image fragment reassembly problem based on solving a variation of Longest Common Subsequence (LCS) problem. Our processing pipeline has three steps. First, the boundary of each fragment is extracted automatically; second, a novel boundary matching is performed by solving LCS to identify the best possible adjacency relationship among image fragment pairs; finally, a multi-piece global alignment is used to filter out incorrect pairwise matches and compose the final image. We perform experiments on complicated image fragment datasets and compare our results with existing methods to show the improved efficiency and robustness of our method.
The problem of reassembling a hand-torn or machine-shredded document back to its original form is another useful version of the image reassembly problem. Reassembling a shredded document is different from reassembling an ordinary image because the geometric shape of fragments do not carry a lot of valuable information if the document has been machine-shredded rather than hand-torn. On the other hand, matching words and context can be used as an additional tool to help improve the task of reassembly. In the final chapter, document reassembly problem has been addressed through solving a graph optimization problem
An Adaptive Optimal Bandwidth Sensor for Video Imaging and Sparsifying Basis
Many compressive sensing architectures have shown promise towards reducingthe bandwidth for image acquisition significantly. In order to use these architectures for video acquisition we need a scheme that is able to effectively exploit temporal redundancies in a sequence. In this thesis we study a method to efficiently sample and reconstruct specific video sequences. The method is suitable for implementation using a single pixel detector along with a digital micromirror device (DMD) or other forms of spatial light modulators (SLMs). Conventional implementations of single pixel cameras are able to spatially compress the signal but the compressed measurements make it difficult to exploit temporal redundancies directly. Moreover a single pixel camera needs to make measurements in a sequential manner before the scene changes making it inefficient for video imaging. In this thesis we discuss a measurement scheme that exploits sparsity along the time axis for video imaging. After acquiring all measurements required for the first frame, measurements are only acquired from the areas which change in subsequent frames. We segment the first frame and detect magnitude and direction of change for each segment and acquire compressed measurements for the changing segments in the predicted direction. TV minimization is used to reconstruct the dynamic areas and PSNR variation is studied against different parameters of proposed scheme. We show the reconstruction results for a few test sequences commonly used for performance analysis and demonstrate the practical utility of the scheme. A comparison is made with existing algorithms to show the eeffectiveness of proposed method for specific video sequences. We also discuss use of customized transform to improve reconstruction of submililimeter wave single pixel imager. We use a sparseness inducing transformation onthe measurements and optimize the result using l1 minimization algorithms. We demonstrate improvement in result of several images acquired and reconstructed using this technique
Adaptive Imaging with a Cylindrical, Time-Encoded Imaging System
Most imaging systems for terrestrial nuclear imaging are static in that the design of the system and the data acquisition protocol are defined prior to the experiment. Often, these systems are designed for general use and not optimized for any specific task. The core concept of adaptive imaging is to modify the imaging system during a measurement based on collected data. This enables scenario specific adaptation of the imaging system which leads to better performance for a given task. This dissertation presents the first adaptive, cylindrical, time-encoded imaging (c-TEI) system and evaluates its performance on tasks relevant to nuclear non-proliferation and international safeguards.
We explore two methods of adaptation of a c-TEI system, adaptive detector movements and adaptive mask movements, and apply these methods to three tasks, improving angular resolution, detecting a weak source in the vicinity of a strong source, and reconstructing complex source scenes. The results indicate that adaptive imaging significantly improves performance in each case.
For the MATADOR imager, we find that adaptive detector movements improve the angular resolution of a point source by 20% and improve the angular resolution of two point sources by up to 50%. For the problem of detecting a weak source in the vicinity of a strong source, we find that adaptive mask movements achieve the same detection performance as a similar, non-adaptive system in 20%-40% less time, depending on the relative position of the weak source. Additionally, we developed an adaptive detection algorithm that doubles the probability of detection of the weak source at a 5% false-alarm rate.
Finally, we applied adaptive imaging concepts to reconstruct complex arrangements of special nuclear material at Idaho National Laboratory. We find that combining data from multiple detector positions improves image uniformity of extended sources by 38% and reduces the background noise by 50%. We also demonstrate 2D (azimuthal and radial) imaging in a crowded source scene. These promising experimental results highlight the potential for adaptive imaging using a c-TEI system and motivate further research toward specific, real-world applications.PHDNuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163009/1/nirpshah_1.pd
Study of the tracking performance of a liquid Argon detector based on a novel optical imaging concept
The Deep Underground Neutrino Experiment (DUNE) is a long-baseline accelerator experiment designed to make a significant contribution to the study of neutrino oscillations with unprecedented sensitivity. The main goal of DUNE is the determination of the neutrino mass ordering and the leptonic CP violation phase, key parameters of the
three-neutrino flavor mixing that have yet to be determined. An important component of the DUNE Near Detector complex is the System for on-Axis Neutrino Detection (SAND) apparatus, which will include GRAIN (GRanular Argon for Interactions of Neutrinos), a novel liquid Argon detector aimed at imaging neutrino interactions using only scintillation light. For this purpose, an innovative optical readout system based on Coded Aperture Masks is investigated. This dissertation aims to demonstrate the feasibility of reconstructing particle tracks and the topology of CCQE (Charged Current Quasi Elastic) neutrino events in GRAIN with such a technique. To this end, the development and implementation of a reconstruction algorithm based on Maximum Likelihood Expectation Maximization was carried out to directly obtain a three-dimensional distribution proportional to the energy deposited by charged particles crossing the LAr volume. This study includes the evaluation of the design of several camera configurations and the simulation of a multi-camera optical system in GRAIN
VOLUMETRIC AND VARIFOCAL-OCCLUSION AUGMENTED REALITY DISPLAYS
Augmented Reality displays are a next-generation computing platform that offer unprecedented user experience by seamlessly combining physical and digital content, and could revolutionize the way we communicate, visualize, and interact with digital information. However, providing a seamless and perceptually realistic experience requires displays capable of presenting photorealistic imagery, and especially, perceptually realistic depth cues, resulting in virtual imagery being presented at any depth and of any opacity. Today's commercial augmented reality displays are far from perceptually realistic because they do not support important depth cues such as mutual occlusion and accommodation, resulting in a transparent image overlaid onto the real-world at a fixed depth. Previous research prototypes fall short by presenting occlusion only for a fixed depth, and by presenting accommodation and defocus-blur only for a narrow depth-range, or with poor depth or spatial resolution. To address these challenges, this thesis explores a computational display approach, where the display’s optics, electronics, and algorithms are co-designed to improve performance or enable new capabilities. In one design, a Volumetric Near-eye Augmented Reality Display was developed to simultaneously present many virtual objects at different depths across a large depth range (15 - 400 cm) without sacrificing spatial resolution, frame rate, or bitdepth. This was accomplished by (1) synchronizing a high-speed Digital Micromirror Device (DMD) projector and a focus-tunable lens to periodically sweep out a volume composed of 280 single-color binary images in front of the user's eye, (2) a new voxel-oriented decomposition algorithm, and (3) per-depth-plane illumination control. In a separate design, for the first time, we demonstrate depth-correct occlusion in optical see-through augmented reality displays. This was accomplished by an optical system composed of two fixed-focus lenses and two focus-tunable lenses to dynamically move the occlusion and virtual image planes in depth, and designing the optics to ensure unit magnification of the see-through real world irrespective of the occlusion or virtual image plane distance. Contributions of this thesis include new optical designs, new rendering algorithms, and prototype displays that demonstrate accommodation, defocus blur, and occlusion depth cues over an extended depth-range.Doctor of Philosoph
Reconstruction algorithms for multispectral diffraction imaging
Thesis (Ph.D.)--Boston UniversityIn conventional Computed Tomography (CT) systems, a single X-ray source spectrum is used to radiate an object and the total transmitted intensity is measured to construct the spatial linear attenuation coefficient (LAC) distribution. Such scalar information is adequate for visualization of interior physical structures, but additional dimensions would be useful to characterize the nature of the structures. By imaging using broadband radiation and collecting energy-sensitive measurement information, one can generate images of additional energy-dependent properties that can be used to characterize the nature of specific areas in the object of interest.
In this thesis, we explore novel imaging modalities that use broadband sources and energy-sensitive detection to generate images of energy-dependent properties of a region, with the objective of providing high quality information for material component identification. We explore two classes of imaging problems: 1) excitation using broad spectrum sub-millimeter radiation in the Terahertz regime and measure- ment of the diffracted Terahertz (THz) field to construct the spatial distribution of complex refractive index at multiple frequencies; 2) excitation using broad spectrum X-ray sources and measurement of coherent scatter radiation to image the spatial distribution of coherent-scatter form factors.
For these modalities, we extend approaches developed for multimodal imaging and propose new reconstruction algorithms that impose regularization structure such as common object boundaries across reconstructed regions at different frequencies. We also explore reconstruction techniques that incorporate prior knowledge in the form of spectral parametrization, sparse representations over redundant dictionaries and explore the advantage and disadvantages of these techniques in terms of image quality and potential for accurate material characterization.
We use the proposed reconstruction techniques to explore alternative architectures with reduced scanning time and increased signal-to-noise ratio, including THz diffraction tomography, limited angle X-ray diffraction tomography and the use of coded aperture masks. Numerical experiments and Monte Carlo simulations were conducted to compare performances of the developed methods, and validate the studied architectures as viable options for imaging of energy-dependent properties
A design and evaluation of a miniaturised position-sensitive energetic particle detector for small satellites
This thesis is concerned with the design and evaluation of an in-situ energetic particle detector for space weather measurements consisting of a position-sensitive solid state detector and a coded aperture mask. The combination of the two presents a novel technique that provides far higher resolution angular information of supra-thermal particles in low-flux environments in two dimensions than previously possible, over a wide field of view. After consideration of the historical and current status of in-situ plasma instruments and coded aperture techniques, a proposed design was modelled with the Geant4 toolkit. A proof-of-concept instrument has been designed and assembled and then tested in the laboratory with three electron sources and the results have been analysed. While the available hardware limited the amount of characterisation possible, the instrument made impressive strides in understanding the setup itself and demonstrated its potential within the tested energy ranges. Further to this, a simulation of such an instrument or its descendants in a space plasma environment was completed and an outlook on the use of the concept in space was discussed. In some configurations this will allow simultaneous energy and high-resolution angular measurements of energetic particle fluxes on small satellites. If such an instrument were flown on a swarm mission, the possibilities for multi-point directional measurements of energetic particles would be hugely increased, especially at low altitudes
Recommended from our members
Free-moving Omnidirectional 3D Gamma-ray Imaging and Localization
The ability to localize and map the distribution of gamma-ray emitting radionuclides in 3D has applications in medical imaging, nuclear contamination remediation, and nuclear security and safeguards. The deployment of freely moving detection systems, such as hand-held instruments or ground/aerial-based vehicles, are critical in overcoming the inverse square law and complex shielding scenarios. Using auxiliary contextually-aware sensors, capable of perceiving spatiotemporal characteristics of the environment, these systems can simultaneously generate 3D maps of the surroundings and track the position and orientation of the gamma-ray sensitive detectors in the scene. The fusion of contextual scene data and gamma-ray detector data to facilitate real-time 3D gamma-ray image reconstruction has previously been demonstrated with mobile germanium and CdZnTe-based Compton cameras for gamma-ray energies ranging from a few hundred keV to several MeV. This concept is applied here for lower energy (50-400 keV) gamma-rays using an active coded mask imaging modality. The platform for demonstration is the Portable Radiation Imaging Spectroscopy and Mapping (PRISM) system, which is a hand-held spherical active coded array of many 1 cm3 coplanar-grid CdZnTe detectors designed for omnidirectional coded mask and Compton imaging and uniform directional sensitivity. This work presents the design, development, and coded mask optimization of PRISM, as well as the methodologies developed for real-time reconstruction using a scene data constrained, GPU-accelerated, list-mode maximum likelihood expectation maximization (ML-EM) algorithm. Experimental results from several measurements in the lab and in the field are shown.A novel approach to 3D gamma-ray image reconstruction for scenarios where sparsity in the source distribution may be assumed, for example radiological source search, is also presented. While the generality of ML-EM enables use in a wide variety of scenarios, it is susceptible to overfitting, limited by the discretization of spatial coordinates, and can be computationally expensive. A more well-conditioned Point-Source Localization (PSL) approach is formulated as an optimization problem where both position and source intensity are continuous variables. This formulation is then extended and generalized to an iterative algorithm for sparse parametric 3D image reconstruction called Additive Point-Source Localization (APSL), where the image is considered the sum of multiple point-sources whose position and intensity are continuous in nature. APSL mitigates overfitting in its iterative bottom-up nature and statistically-founded stopping criteria and, because of the inherent point-source assumption and continuous variables, results in images with improved accuracy and interpretability as compared with ML-EM. A set of simulated source search scenarios using a single non-directional detector is considered to demonstrate the concept and compare ML-EM and APSL. Experimental results using a nearly isotropic, contextually-aware, LaBr3 detector system are then presented, finding improved localization accuracy and computational efficiency with APSL
- …