High-dynamic-range X-ray CT imaging method based on energy self-adaptation between scanning angles

High-dynamic-range (HDR) X-ray CT imaging is effective in detecting some complex structures. For previous low-dynamic-range (LDR) imaging detectors, multi-energy LDR image sequence fusion can extend the dynamic range, but the efficiency is decreased. However, with the application of HDR imaging devices, traditional fixed-energy X-ray imaging can cause incongruity within energy, dynamic range, and the equivalent thickness of the workpiece at different projection angles. Then, the projection has a blurred edge, and the CT image quality is poor because of scattering and the inadequate dose. In this paper, a new HDR X-ray CT imaging method with energy self-adaptation between scanning angles for HDR imaging devices is studied. Low-energy prescanning is used to determine the initial scanning energy and obtain the edge contour information with an attenuating effect on scattering. By establishing a mathematical model between the gray level of the projection and the transmission voltage, the transmission energy at each angle is adjusted adaptively. Then, the prescanning and energy self-adaption scanning projections are fused to obtain the complete projection of the complex workpiece. Finally, a conventional reconstruction algorithm is used to reconstruct the HDR CT image. The experimental results show that the proposed imaging method can achieve HDR CT imaging of complex structures with high reconstruction quality, clear edge details, and high completeness.

Narrow-Energy-Width CT Based on Multivoltage X-Ray Image Decomposition

A polychromatic X-ray beam causes the grey of the reconstructed image to depend on its position within a solid and the material being imaged. This factor makes quantitative measurements via computed tomography (CT) imaging very difficult. To obtain a narrow-energy-width reconstructed image, we propose a model to decompose multivoltage X-ray images into many narrow-energy-width X-ray images by utilizing the low frequency characteristics of X-ray scattering. It needs no change of hardware in the typical CT system. Solving the decomposition model, narrow-energy-width projections are obtained and it is used to reconstruct the image. A cylinder composed of aluminum and silicon is used in a verification experiment. Some of the reconstructed images could be regarded as real narrow-energy-width reconstructed images, which demonstrates the effectiveness of the proposed method.

CT Scanning Imaging Method Based on a Spherical Trajectory

In industrial computed tomography (CT), the mismatch between the X-ray energy and the effective thickness makes it difficult to ensure the integrity of projection data using the traditional scanning model, because of the limitations of the object's complex structure. So, we have developed a CT imaging method that is based on a spherical trajectory. Considering an unrestrained trajectory for iterative reconstruction, an iterative algorithm can be used to realise the CT reconstruction of a spherical trajectory for complete projection data only. Also, an inclined circle trajectory is used as an example of a spherical trajectory to illustrate the accuracy and feasibility of this new scanning method. The simulation results indicate that the new method produces superior results for a larger cone-beam angle, a limited angle and tabular objects compared with traditional circle trajectory scanning.

High-Dynamic-Range CT Reconstruction Based on Varying Tube-Voltage Imaging

For complicated structural components characterized by wide X-ray attenuation ranges, the conventional computed tomography (CT) imaging using a single tube-voltage at each rotation angle cannot obtain all structural information. This limitation results in a shortage of CT information, because the effective thickness of the components along the direction of X-ray penetration exceeds the limitation of the dynamic range of the X-ray imaging system. To address this problem, high-dynamic-range CT (HDR-CT) reconstruction is proposed. For this new method, the tube's voltage is adjusted several times to match the corresponding effective thickness about the local information from an object. Then, HDR fusion and HDR-CT are applied to obtain the full reconstruction information. An accompanying experiment demonstrates that this new technology can extend the dynamic range of X-ray imaging systems and provide the complete internal structures of complicated structural components.

[Research on X-ray multispectrum imaging based on variable energy]

In conventional X-ray imaging based on fixed energy, the ray image of the complicated structural component often appears overexposed or underexposed. This is because of the variations in the effective thickness of the component along the orientation of the X-ray penetration that exceed the limit of the dynamic range of the X-ray imaging system. Complete structural information cannot be obtained, and this lack will impact the quality of the X-ray image. To solve this problem, the technology of X-ray multispectrum imaging based on variable energy has advanced. In this new method, the tube voltage is adjusted several times to accommodate the full necessary range of effective thickness, and then, the extracted images are fused to reconstruct the full projection information. Experiment shows that for the 12 bit imaging system, the new technology makes the system's dynamic range expand 4 times, also completely represent the internal structure information of a complicated structural component.

[Virtual design of X-ray multi-spectrum CT imaging based on variable voltage]

In the conventional X-ray imaging, the ray image of the complicated structural component (shape, structure complex and multi-materials) easily exhibits the overexposed and underexposed phenomenon. This is because of the bigger variations in the effective thickness in the orientation of X-ray penetration and the limit of the dynamic range of X-ray imaging system. The complete structure information can't be obtained, and it will impact the quality of X-ray CT image. So the present paper has improved the theory and method of variable voltage X-ray multi-spectrum CT imaging. The new method changes the distribution of X-ray spectrum by changing the voltage, and can realize the matching between the X-ray spectrum and the effective thickness of workpieces. This can expand the dynamic range and ensure the integrity of projection about the workpieces. At the same time, based on the idea of virtual design, the paper has built the variable voltage virtual CT mode based on single-energy and multi-energy, and realized virtual simulation of the variable voltage X-ray CT. At last, the virtual experiment has proved that the theory and method of variable voltage CT imaging is feasible, and the variable voltage CT imaging is the effective method for the complicated structural component.