Fast Reconstruction Method Research Articles

A fast and efficient method for sequential cone-beam tomography.

Sequential cone-beam tomography is a method that uses data of two or more parallel circular trajectories of a cone-beam scanner to reconstruct the object function. We propose a condition for the data acquisition that ensures that all object points between two successive circles are irradiated over an angular span of the x-ray source position of exactly 360 degrees in total as seen along the rotation axis. A fast and efficient approximative reconstruction method for the proposed acquisition is presented which uses data from exactly 360 degrees for every object point. It is based on the Tent-FDK method which was recently developed for single circular cone-beam CT. The measurement geometry does not provide sufficient data for exact reconstruction but it is shown that the proposed reconstruction method provides satisfying image quality for small cone angles.

Algebraic PET image reconstruction with pre-computed reconstruction operators using subsets of sensitivity functions

Algebraic reconstruction methods have been successfully used to improve quality of positron emission tomography (PET) images by accurate modeling of measurement system, but they have computational burden. The authors propose a fast PET image reconstruction method based on an algebraic technique. In this method, reconstruction operators are pre-computed approximately using subsets of sensitivity functions. The subsets contain the sensitivity functions that contribute significantly to each point to be reconstructed. The proposed method was applied to simulated data and experimental data for the ECAT EXACT HR+ (Siemens/CTI) scanner operating in 2D mode. These results show that the proposed method produces images with almost the same quality as the conventional algebraic methods do and has a similar computation time to the filtered backprojection method.

A fast EIT image reconstruction method for the two-phase flow visualization

A preliminary investigation is introduced to demonstrate the feasible potentials of the application of the EIT (Electrical Impedance Tomography) to visualize the bubble distribution in two-phase flow field. We expect the required experimental apparatus for the EIT bubble distribution measurement to be rather simple thus much cheaper than the other bubble motion monitoring devices like LDV (Laser Doppler Velocïmetry), PIV (Particle Image Velocimetry) and optical probes. At the present stage, however, the EIT visualization of the bubble distribution takes too long time to be implemented. In this paper, an adaptive mesh grouping method based on fuzzy-GA (Genetic Algorithm) is introduced to reduce the image reconstruction time significantly. Sample reconstructed images by the proposed method are presented with discussion for several ‘artificial’ bubble distributions.

Fast reconstruction of subband-decomposed progressively transmitted signals

We propose a fast reconstruction method for a subband-decomposed, progressive signal coding system. We show that unlike the conventional approach which requires a fixed computational complexity, the computational complexity of the proposed approach is proportional to the number of refined coefficients at each level of progression. Therefore, unrefined coefficients do not add to the computational complexity of the proposed scheme. It is shown, through specific examples, that the proposed approach can lead to significant reductions in reconstruction complexity. Furthermore, the proposed approach provides the capability for an online updating of the reconstructed image based on receiving the refinement of each coefficient.

A new fast method for the reconstruction of 2-D microwave images of rotating objects

In this paper, the problem of microwave imaging of rotating objects is approached from a digital signal processing point of view. Attention is focused on the reconstruction of the two-dimensional (2-D) image of an object obtained by processing complex samples of the continuous wave (CW) signal return received for different object aspect angles covering a 2pi total variation. The effects of a polar sampling of the Fourier transform (FT) of the target reflectivity function on the impulse response of the imaging system are analyzed. A criterion for the choice of the angular sampling interval in order to control the image blurring is given. Finally, a new and fast digital signal processing method for image reconstruction is proposed. This method reconstructs high resolution images of rotating targets illuminated by a CW electromagnetic signal or by a large bandwidth transmitted signal. This algorithm is suitable for processing wideband received signal of targets observed for a large variation of the viewing angle, so it is very attractive for the reconstruction of very high spatial resolution target images in SAR/ISAR systems. To show the performance of the method we finally present and discuss the results obtained by applying the proposed technique on simulated and experimental data.

Une amélioration de la tomographie ultrasonore en réflexion

Via a simple algorithm given by the Born approximation one can reconstruct a tomographic image of the sound speed of an acoustically penetrable body, knowing its scattered sound field. This method is based on the hypothesis of weak contrast between the body and the external medium. Otherwise the image is a distorted version of the object. The distortion is characterised analytically. Thus we propose a modified algorithm that cancels the image defects so as to obtain a fast and reliable reconstruction method.

Fast reconstruction of 3D PET data with accurate statistical modeling

This paper presents the results of combining high sensitivity 3D PET whole-body acquisition followed by fast 2D iterative reconstruction methods based on accurate statistical models. This combination is made possible by Fourier rebinning (FORE), which accurately converts a 3D data set to a set of 2D sinograms. The combination of volume imaging with statistical reconstruction allows improvement of noise-bias trade-offs when image quality is dominated by measurement statistics. The rebinning of the acquired data into a 2D data set reduces the computation time of the reconstruction. For both penalized weighted least squares (PWLS) and ordered-subset EM (OSEM) reconstruction methods, the usefulness of a realistic model of the expected measurement statistics is shown when the data are pre-corrected for attenuation and random and scattered coincidences, as required for the FORE rebinning algorithm. The results presented are based on 3D simulations of whole body scans that include the major statistical effects of PET acquisition and data correction procedures. As the PWLS method requires knowledge of the variance of the projection data, a simple model for the effect of FORE rebinning on data variance is developed.

Fast accurate iterative reconstruction for low-statistics positron volume imaging

A fast accurate iterative reconstruction (FAIR) method suitable for low-statistics positron volume imaging has been developed. The method, based on the expectation maximization-maximum likelihood (EM-ML) technique, operates on list-mode data rather than histogrammed projection data and can, in just one pass through the data, generate images with the same characteristics as several ML iterations. Use of list-mode data preserves maximum sampling accuracy and implicitly ignores lines of response (LORs) in which no counts were recorded. The method is particularly suited to systems where sampling accuracy can be lost by histogramming events into coarse LOR bins, and also to sparse data situations such as fast whole-body and dynamic imaging where sampling accuracy may be compromised by storage requirements and where reconstruction time can be wasted by including LORs with no counts. The technique can be accelerated by operating on subsets of list-mode data which also allows scope for simultaneous data acquisition and iterative reconstruction. The method is compared with a standard implementation of the EM-ML technique and is shown to offer improved resolution, contrast and noise properties as a direct result of using improved spatial sampling, limited only by hardware specifications.

A Fast Surface-Based Procedure for Object Reconstruction from 3D Scattered Points

In this paper, a new fast three-phase method for object reconstruction from 3D scattered points is presented. The first phase is founded on a novel fast triangulation algorithm, which generates a base approximation of the object surface. By inserting bridges, the triangulation algorithm also handles surfaces with genus greater than zero and determines the genus of the reconstructed surface. From results of the first phase, the object surface features, such as sharp edges, silhouette polylines, and corners, are extracted in the next phase. Sharp edges and corners are used as constraints for triangular mesh fairing later in the final phase, where a new improved decimation and a novel mesh refinement procedure are introduced, while silhouette polylines can be applied for generation of a wire-frame model of the reconstructed object. The overall object reconstruction procedure has a tested linear time complexity.

A fast reconstruction method for transmitting images progressively

To transmit an image over narrow bandwidth channels is an important issue in networks. We proposed a new progressive image transmission (PIT) method. We call it the fast reconstruction method (FRM). There are three techniques in this method. First, we use vector quantization (VQ) to compress the image. Then, we design the central sampling technique, and employ it to select the indices of the compressed image. These indices will be transmitted to the receiver phase by phase. Finally, the receiver applies the pixels copy technique and the received indices to reconstruct the image. From the experimental results, we see that FRM just needs 3.6% reconstruction time of the selective progressive image transmission method (SPITM) to reconstruct the image. Besides, the PSNR of our method is better than that of SPITM at the beginning phases. FRM is therefore effective and efficient in PIT.

Future developments in nuclear medicine instrumentation: a review.

This review article forecasts developments in nuclear medicine instrumentation which are on the horizon. Special attention is paid to the physical properties of detectors and multiple-processor parallel processing systems needed for fast and high-quality imaging in emission tomography. Advances in detector technology will improve imaging resolution below 5 mm and will increase sensitivity and quantitative accuracy. In addition, high count rate list-mode acquisition enables 'true' four-dimensional data-sets. A sandwich-like construction of two different crystals allows the simultaneous use of conventional tracers and positron tracers (multiple emission tomography, MET). Transmission-based attenuation and scatter compensation with fast iterative reconstruction methods will further improve image quality. The clinical and scientific importance of improved images and the limits on advances in instrumentation are also reviewed.

Fast analytical flux reconstruction method for nodal space-time nuclear reactor analysis

The reconstruction of the fine-mesh neutron flux distribution using coarse-mesh computational results is an important step in a nodal reactor analysis procedure. In this paper the problem is reformulated as a one-dimensional interpolation along the node boundaries followed by an approximate analytical solution of the associated Dirichlet problem. Finite difference techniques are employed for the calculation of boundary values and their derivatives for Cartesian and hexagonal fuel assemblies. Apart from the fact that this approach can be used for an arbitrary number of energy groups in any geometry an additional advantage is that it yields an estimate of the order of accuracy. The interior solution is based on weak-element approximations to elliptic problems and uses in its simplest variant as points of support only flux corner values in addition to the known surface fluxes. The high computational accuracy and efficiency is demonstrated by some results for Cartesian and hexagonal configurations.

Reconstruction of images from a coded-aperture box camera

Methods for the reconstruction of images from coded-aperture box cameras are discussed. A fast reconstruction method for unbiased reconstruction is presented and examples of its application to simulated and real data are given. An iterative procedure to further reduce coding noise is proposed and its effectiveness quantified.

Measurement of the spin correlation parameter A00 nn and the polarization A00 n0 in elastic p-p scattering between 400 and 600 MeV

We have measured the spin correlation parameter A 00 nn and the polarization A 00 n0 for p-p elastic scattering in the c.m. angular range between 30° and 90° at seven energies between 400 and 600 MeV. The experiment was performed at SIN using a polarized beam and target and a fast on-line event reconstruction method. The results are compared with phase-shift predictions.