Image Reconstruction Computer Research Articles

A New CCERT System With Shielding for Gas-Liquid Two-Phase Flow

This work presents a new capacitively coupled electrical resistance tomography (CCERT) system with shielding for gas-liquid two-phase flow. The new system is developed from the aspects of hardware, image reconstruction algorithm and experiments. The hardware includes a 12-electrode CCERT sensor with shielding, a measurement circuit and an image reconstruction computer. The sensor with shielding is designed and the measurement circuit is developed to obtain the resistance information (real part of the impedance). Based on truncated singular value decomposition (TSVD) and density peaks clustering (DPC), a new image reconstruction algorithm is proposed. TSVD is introduced to obtain the initial image. DPC is improved and used to obtain the final image. Image reconstruction experiments were carried out with the new 12-electrode CCERT system with shielding. Experimental results show that the new CCERT system has good imaging performance. The design of the hardware is successful, and the new proposed image reconstruction algorithm is effective. Compared with the conventional image reconstruction algorithms, the proposed algorithm has higher imaging quality. The maximum relative image errors of the new system are 0.2887 under bubble flow and 0.4177 under stratified flow. Research results also indicate that the shielding design contributes to better imaging stability in interference environment.

Optimal Design of Electromagnetic Tomography Flaw Detection System for Train Wheel Based on FPGA

Electromagnetic tomography (EMT) is a new type of nondestructive testing technology that can be used for metal flaw detection. The implementation of the signal demodulation and filtering algorithm of the current electromagnetic tomography flaw detection system relies on the microprocessor MCU, and the reliability is low in real time. To improve the reliability and system integration of signal processing and transmission of the electromagnetic tomography flaw detection system, this paper uses the field programmable gate array chip to integrate the excitation signal generation module and the digital demodulation module based on the EMT train wheel flaw detection system. A digital filter is designed, and the filter parameters are adjusted to achieve a signal-to-noise ratio of 15 dB. UDP communication protocol is utilized to realize Ethernet communication between FPGA and upper computer. Using three algorithms on the host computer for image reconstruction, the train wheel defect information is visualized. The experimental results show that the FPGA chip improves the immunity of the train wheel flaw detection system, realizes the high integration of the system, and achieves the purpose of train wheel defect detection.

Improved dynamic distortion correction for fMRI using single-echo EPI and a readout-reversed first image (REFILL).

The boundaries between tissues with different magnetic susceptibilities generate inhomogeneities in the main magnetic field which change over time due to motion, respiration and system instabilities. The dynamically changing field can be measured from the phase of the fMRI data and corrected. However, methods for doing so need multi-echo data, time-consuming reference scans and/or involve error-prone processing steps, such as phase unwrapping, which are difficult to implement robustly on the MRI host. The improved dynamic distortion correction method we propose is based on the phase of the single-echo EPI data acquired for fMRI, phase offsets calculated from a triple-echo, bipolar reference scan of circa 3-10 s duration using a method which avoids the need for phase unwrapping and an additional correction derived from one EPI volume in which the readout direction is reversed. This Reverse-Encoded First Image and Low resoLution reference scan (REFILL) approach is shown to accurately measure B0 as it changes due to shim, motion and respiration, even with large dynamic changes to the field at 7 T, where it led to a > 20% increase in time-series signal to noise ratio compared to data corrected with the classic static approach. fMRI results from REFILL-corrected data were free of stimulus-correlated distortion artefacts seen when data were corrected with static field mapping. The method is insensitive to shim changes and eddy current differences between the reference scan and the fMRI time series, and employs calculation steps that are simple and robust, allowing most data processing to be performed in real time on the scanner image reconstruction computer. These improvements make it feasible to routinely perform dynamic distortion correction in fMRI.

A heterogeneous hardware scheme for accelerating the image reconstruction process of electrical tomography

Currently, most of the electrical tomography measurement systems are developed on microcontroller units, digital signal processors, or field programmable gate arrays, whereas image reconstruction and display functions are implemented in a separate host computer. Therefore, the complete hardware usually comprises a measurement system and an image reconstruction computer. The current trend is to develop industrial standard electrical tomography systems, which can implement the image reconstruction and measurement functions into an integrated processor/chip. However, most of the above mentioned processors do not provide the necessary computational resources as required by the computationally intensive image reconstruction function. This paper describes a hardware scheme for implementing image reconstruction functions on a heterogeneous hardware platform, wherein the processor system and programmable logics (PLs) are tightly coupled and can achieve better resource utilization and overall system performance. By adopting a high-level synthesis method, the image reconstruction algorithms can be realized jointly by the PLs and processor system. In this hardware scheme, the algorithms are properly optimized to achieve better data throughput and execution efficiency, that is, by utilizing parallel computation in PLs. Details of the hardware scheme and method of accelerating the image reconstruction process are presented in this paper. Implementation results show that the proposed heterogeneous hardware scheme can achieve the image reconstruction rates of 24 and 1700 frames per second while employing the iterative and non-iterative algorithms, respectively.

Computational photography with plenoptic camera and light field capture: tutorial.

Photography is a cornerstone of imaging. Ever since cameras became consumer products more than a century ago, we have witnessed great technological progress in optics and recording mediums, with digital sensors replacing photographic films in most instances. The latest revolution is computational photography, which seeks to make image reconstruction computation an integral part of the image formation process; in this way, there can be new capabilities or better performance in the overall imaging system. A leading effort in this area is called the plenoptic camera, which aims at capturing the light field of an object; proper reconstruction algorithms can then adjust the focus after the image capture. In this tutorial paper, we first illustrate the concept of plenoptic function and light field from the perspective of geometric optics. This is followed by a discussion on early attempts and recent advances in the construction of the plenoptic camera. We will then describe the imaging model and computational algorithms that can reconstruct images at different focus points, using mathematical tools from ray optics and Fourier optics. Last, but not least, we will consider the trade-off in spatial resolution and highlight some research work to increase the spatial resolution of the resulting images.

Trends of Data Path Topologies for Data Acquisition Systems in Positron Emission Tomography

In this paper, we describe current trends in data path topologies for Positron Emission Tomography (PET) data acquisition (DAQ) systems which is used to capture signals from the detector modules and generate coincidence data for a image reconstruction computer. First, the requirements of DAQ systems in PET, such as event throughput, timing resolution, and energy resolution, are analyzed. Then, design issues related to DAQ designs are discussed including multiplexing schemes, DAQ boards interconnection topologies, and transmission protocols to transfer data to the image reconstruction computer. We also discuss how new trends in PET systems, such as time-of-flight (TOF) PET, depth-of-interaction (DOI) information, and PET/MRI, can affect the design of PET DAQ systems.

Design of a Real-Time FPGA-Based Data Acquisition Architecture for the LabPET II: An APD-Based Scanner Dedicated to Small Animal PET Imaging

To achieve submillimetric spatial resolution, a new detection block has been designed for the LabPET II, a small animal PET scanner being developed at Universite de Sherbrooke. Each detection block consists of 2 arrays of 4×8 avalanche photodiodes (APD) individually coupled to an 8×8 scintillator array, to form 64 independent and parallel DAQ channels. This new detection block entails an 8-fold increase in pixel density compared to the LabPET™ I. A 64-channel mixed-signal Application Specified Integrated Circuit (ASIC) was designed to extract relevant PET data in real time from the LabPET II detection blocks. The ASIC is expected to support up to 3000 PET events/sec per channel. In order to interface the ASICs forming the PET camera with the storage units, a real-time FPGA-based digital DAQ system was designed. The DAQ system allows event harvesting, processing and transmission to a distant computer for image reconstruction as well as system programming and calibration. Real-time event processing embedded in the DAQ includes energy computation using a time-over-threshold (TOT) conversion scheme, timing corrections and event sorting trees. A real-time coincidence engine analyzes events and only keeps relevant information to minimize data throughput and post-acquisition data processing. The architecture consists of 3 layers of FPGA-based electronics wired through gigabit links: a Front-End board extracts timing and energy along with a pixel address, a Hub board sorts incoming events chronologically and a Coincidence board matches coincident events and copes with randoms estimation. Every FPGA in the different layers is accessible through an Ethernet link. The real-time digital architecture sustains the required throughput of ~111 Mevents/s for a ∼37000 channels scanner configuration.

Design for source-and-detector configuration of a ring-scanning-based near-infrared optical imaging system

The design scheme of the source-and-detector arrangement of a ring-scanning-based near-infrared optical imaging system prior to the mechanical and optical construction is demonstrated. In terms of the effectiveness and efficiency of design, through the computation of image reconstruction for varied imaging configurations, the influences of the source-and-detector arrangement on the resulting images are evaluated and a formula to estimate the scanning time is provided. The basic idea of our design is to divide circular scanning into several zones, each of which includes n sources and l detectors; i.e., m zones and n sources along with l detectors per zone are defined in the design. Comparison is made among different imaging configurations where their contrast-to-noise ratio measures are evaluated and contrast-and-size detail resolution curves are depicted. Results show that the 2Z3S or 3Z3S configuration is the optimal design in terms of the time consumption of a complete scanning and the resolution of reconstructed optical-property images.

Optical resolution and the duality of light

For 15 years, lensless microscopes have been constructed based on the use of holography, a digital CCD detector, and a computer for image reconstruction by use of, e.g., Fourier transformation. Thus, no lens is involved and therefore the conventional resolution limit of half the wavelength no longer applies. Instead of being limited by the wavelength, the resolution is in this case limited by how exact one can measure the phases of the light. It is remarkable that the interference-limited resolution is approximately 0.01 lambda, whereas the diffraction-limited resolution is only of the order of 0.5 lambda. It is my hope that by combining these two techniques it will be possible to increase the magnification in optical systems by at least an order of magnitude. The calculations also indicate that information does not necessarily decrease with distance.

Dual energy gamma tomography system for high pressure multiphase flow

For physical understanding and detailed modelling of multiphase flow in pipelines, the distributions of the individual phases are of significant importance. For this reason a dual energy gamma tomography system has been designed, constructed and commissioned at the Norsk Hydro multiphase flow laboratory in Porsgrunn. The system is designed for implementation in a high pressure–high temperature crude oil facility for measurements of the gas–oil–water distribution in a 3″ test pipe. Data from the dual energy system will serve as a basis for further mechanistic modelling of multiphase flow. The set-up uses a 133Ba source along with a CdZnTe detector and a digital spectrum analyser to acquire gamma attenuation data for different chordal positions of the pipe cross section. Special attention has been paid to the transparency of the test pipe, to the choice of isotope and to the spectrum analysis for maximizing the signal to noise ratio. Raw data from the dual energy set-up is used as input to an image reconstruction computer program, and this paper presents three stationary commissioning experiments of the system using different fluid configurations in the pipe cross section. The results from these experiments are encouraging with respect to the overall performance of the system, and prove the ability of the system to resolve different flow configurations in the form of reconstructed tomograms of the pipe cross section.

A long-distance high-speed serial link for process tomography systems

Process tomography systems need a long-distance high-speed serial link for data communication between sensing electronics and an image reconstruction computer, normally a PC. Using Transputer link adaptor chips (C011) and optical fibres, a low-cost serial data transmission link has been developed. A PC-XT extension card with an interfacing circuit is embedded in a PC, forming one terminal of the serial link. The other terminal can have either two 8-bit parallel ports (input and output respectively) to interface with logic circuits, or one 8-bit bi-directional port to interface with another microprocessor. The serial link with the optical fibres can transmit data at a speed of 10 or 20 Mbits per second over a distance as long as required. It has been used successfully in an electrical capacitance tomography system.

Digital ultrasonic scanning system for positioning underwater remotely operated vehicles

The design of a digital ultrasonic scanning system for positioning underwater remotely operated vehicles (UROVs) is presented in this paper. Its principle of operation is based on ultrasonic distance measurements (by determining the time of flight) and mechanical scanning. Ultrasonic imaging is used to construct the 3-D image of the environment surrounding the vehicle. The image is then used, in combination with signals coming from a gyroscope, to estimate the actual distances of the vehicle from the objects in the vicinity of the vehicle. The system consists of a 200 KHz point transducer, a scanning transmitter-receiver unit and a computer for image reconstruction and control of the UROV. The main advantages of this system are its simplicity and its accurate large scale measurement capability. The design of the system was carried out in order to conform directly with the computer controlling the UROV, and its operation was experimentally demonstrated.

Video Based X-Ray Computed Tomography

The capabilities of a video based x-ray imaging system are investigated for performing transaxial ccmputed tomography. The detector which was used in the present study was a 12.5? diameter flat screen optically coupled to a light amplifier tube with a photocathode diameter of 3?. The output of the light amplifier was picked up by an isocon camera. The video projection images were digitized and stored in a computer for image reconstruction. A special aluminum field flattening filter was designed and used to reduce both the dynamic range and beam hardening problems. The spatial and density resolution capability as well as the uniformity of the images is discussed.