This paper is about the ring artifacts removal method in cone beam CT. Cone beam CT images often suffer from disturbance of ring artifacts which caused by the non-uniform responses of the elements in detectors. Conventional ring artifacts removal methods focus on the correlation of the elements and the ring artifacts’ structural characteristics in either sinogram domain or cross-section image. The challenge in the conventional methods is how to distinguish the artifacts from the intrinsic structures; hence they often give rise to the blurred image results due to over processing. In this paper, we investigate the characteristics of the ring artifacts in spatial space, different from the continuous essence of 3D texture feature of the scanned objects, the ring artifacts are displayed discontinuously in spatial space, specifically along z-axis. Thus we can easily recognize the ring artifacts in spatial space than in cross-section. As a result, we choose dictionary representation for ring artifacts removal due to its high sensitivity to structural information. We verified our theory both in spatial space and coronal-section, the experimental results demonstrate that our methods can remove the artifacts efficiently while maintaining image details.
This paper is about geometric calibration of the high resolution CT (Computed Tomography) system. Geometric calibration refers to the estimation of a set of parameters that describe the geometry of the CT system. Such parameters are so important that a little error of them will degrade the reconstruction images seriously, so more accurate geometric parameters are needed in the higher-resolution CT systems. But conventional calibration methods are not accurate enough for the current high resolution CT system whose resolution can reach sub-micrometer or even tens of nanometers. In this paper, we propose a new calibration method which has higher accuracy and it is based on the optimization theory. The superiority of this method is that we build a new cost function which sets up a relationship between the geometrical parameters and the binary reconstruction image of a thin wire. When the geometrical parameters are accurate, the cost function reaches its maximum value. In the experiment, we scanned a thin wire as the calibration data and a thin bamboo stick as the validation data to verify the correctness of the proposed method. Comparing with the image reconstructed with the geometric parameters calculated by using the conventional calibration method, the image reconstructed with the parameters calculated by our method has less geometric artifacts, so it can verify that our method can get more accurate geometric calibration parameters. Although we calculated only one geometric parameter in this paper, the geometric artifacts are still eliminated significantly. And this method can be easily generalized to all the geometrical parameters calibration in fan-beam or cone-beam CT systems.
For tomography reconstruction, the iteration methods based on spare regularization have recently emerged and are proven effective especially in the situation that projection data is insufficient or noisy in low radiation dose. Because iterative tomography reconstruction algorithms have heavy computational demanding especially for clinical data sets and is far from being close to real-time reconstruction. So there is incentive to develop fast algorithms of the optimization problem. We present new accelerating iterative shrinkage algorithms for sparse-based tomography reconstruction, which base on the existing shrinkage algorithms and combine with traditional algebra methods, linear search method and preconditioning techniques to solve large dense linear systems. We give two different weighted matrixes as the preconditioner and get the different convergence speeds. From the experimental results it can be seen that using the sparsity in the transform domain as the regularization term can greatly improve the visual effect of the reconstructed images compared with corresponding algebraic algorithms, and the linear search method can obviously accelerates the converge rate.
This paper presents a development of the algorithm for combination of block-merge algorithm and octree algorithm. The memory insufficiency problem, which is caused by heaps of temporary variables when researching pore structure by octree algorithm, has been effectively solved. The pore structure information of cellular metallic material with large area has been extracted, which provides an important method for the study on the relationship between the structure of porous metal material and function. By applying this method to store more data with less memory, an effective and accurate result is achieved. This work would represent a significant advance for research of pore structure using improved octree algorithm.
High-speed digital videoendoscopy system is emerging as a new clinical tool for voice assessment. The system can acquire images of the vibrating vocal folds with simultaneous recording of voice data from the patient. The laryngeal image-based analysis has been proven valuable for objective and quantitative assessment of voice kinematics in health and disease, and meanwhile, acoustic analysis of voice data could assist in the study of phonatory characteristics and reveal useful information related to laryngeal pathophysiology. Contrast to the hardware acquisition systems, the development of effective software for handling such massive visual/sound data has lagged behind. In this paper, a software system is designed to process the laryngeal image sequences and perform image-based analyses as well as acoustic analyses. Our software contains following modules: (1) Import and view Module - to read AVI video data and sound data (wave file), edit/compile and save selected data, make image montages using DirectShow technology and display the acoustic waveform using DirectSound technology; (2) Image Process Module – to perform frame-by-frame image segmentation to delineate the glottis, to extract the GAW and bilateral vocal fold displacements; (3) Image Analysis Module – to adopt Nyquist plot displays that involves the Hilbert transform based analysis of GAW, and to provide instantaneous frequency and amplitude distributions; (4) Acoustic Analysis Module – to perform Fast Fourier Transform (FFT) and Spectrogram analyses of the imported sound data, to display the plot of the sound data and provide instantaneous frequency and amplitude distributions and Nyqiust plot and (5) Dual GAW and sound wave display module. Upon rigorous testing of this software using clinical data samples we demonstrate the applications of the software to the study of dynamic characteristics of the glottis, which may correlate with voice quality and health condition.
High-speed digital imaging (HSDI) of the glottis provides a direct means to capture the actual vocal-fold vibrations.
Subsequent image-based analyses can be used for objective and quantitative assessment of voice kinematics in healthy
and diseased states. HSDI generates massive visual data array, yet the development of effective software for handling
such massive image data has lagged behind. To obtain a robust and clinically relevant analysis, we have implemented a
software system that includes the processing of AVI image sequences from HSDI recordings, a s we l l a s the
spatiotemporal analysis of glottal area waveform (GAW) and vocal fold displacements extracted from these image
sequences. The software contains the following three modules: 1) Import and View Module- to read AVI video data,
edit/compile and save selected image data, and make image montages using DirectShow technology; 2) Process
Module- to perform frame-by-frame image segmentation to delineate the glottis, and to extract GAW and bilateral vocal
fold displacements; 3) Analysis Module- to adopt Nyquist plot displays that involve the Hilbert transform based analysis of
GAW, and to provide instantaneous frequency and amplitude distributions. Upon rigorous testing of this software using
numerous clinical data samples, we demonstrate the validity of this software in delivering accurate and useful vibratory
characteristics of the vocal folds that may correlate with voice condition.