Zhifeng Huang

Quantitative grating-based x-ray dark-field computed tomography

Grating-based x-ray dark-field computed tomography is a functional method that utilizes the scattering contrast mechanism to explore the inaccessible spatially resolved internal structure of the sample. In this letter, we show that the second moment of the scattering angle distribution can be expressed as the minus logarithm of the visibility degradation of the oscillation curve in grating-based imaging. According to the conclusion of Khelashvili et al. [Phys. Med. Biol. 51, 221 (2006)], the minus logarithm of the visibility ratio fulfills the line integral condition; consequently the scattering information can be reconstructed quantitatively by conventional computed tomography algorithms. Results from a computer simulation and from an actual experiment both validate our deduction.

Direct computed tomographic reconstruction for directional-derivative projections of computed tomography of diffraction enhanced imaging

X-ray diffraction enhanced imaging based on synchrotron radiation has extremely high sensitivity of weakly absorbing low-Z samples in medical and biological fields. This letter is dedicated to a direct reconstruction algorithm for directional-derivative projections of computed tomography of diffraction enhanced imaging. It is a “one-step” algorithm and does not require any restoration processing compared with the current “two-step” methods. The actual values of the sample’s refractive index decrement can be estimated from its reconstruction images directly. The algorithm is proven by the actual experiment at the Beijing Synchrotron Radiation Facility and the reconstructed images are described finally.

Low dose reconstruction algorithm for differential phase contrast imaging

Differential phase contrast imaging computed tomography (DPCI-CT) is a novel x-ray inspection method to reconstruct the distribution of refraction index rather than the attenuation coefficient in weakly absorbing samples. In this paper, we propose an iterative reconstruction algorithm for DPCI-CT which benefits from the new compressed sensing theory. We first realize a differential algebraic reconstruction technique (DART) by discretizing the projection process of the differential phase contrast imaging into a linear partial derivative matrix. In this way the compressed sensing reconstruction problem of DPCI reconstruction can be transformed to a resolved problem in the transmission imaging CT. Our algorithm has the potential to reconstruct the refraction index distribution of the sample from highly undersampled projection data. Thus it can significantly reduce the dose and inspection time. The proposed algorithm has been validated by numerical simulations and actual experiments.

Fast X-Ray Phase-Contrast Imaging Using High Resolution Detector

X-ray phase-contrast imaging is a potential nondestructive testing and diagnostic technology in medicine, biology and materials science. It provides high sensitivity and contrast of weakly absorbing low-Z objects by measuring phase shifts of the X-rays. In this paper, we propose a novel phase-contrast imaging method using only one absorption grating and a high-resolution detector. The intensity distribution downstream of the grating is recorded and analyzed by the high-resolution detector directly. We use a spatial phase demodulation method to retrieve the phase information. Only one image is needed. Numerical simulations are performed to validate that the setup of our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming and the unnecessary dose.

Large phase-stepping approach for high-resolution hard X-ray grating-based multiple-information imaging

High-resolution hard X-ray grating-based imaging method with conventional X-ray sources provides attenuation, refraction and scattering information synchronously, and it is regarded as the next-generation X-ray imaging technology for medical and industrial applications. In this letter, a large phase-stepping approach with at least one order of magnitude lower resolution of the movement is presented to equivalently substitute the current high-positioning-resolution phase-stepping approach. Both the theoretical deduction and actual experiment prove that the new approach is available to relax the requirement of high positioning resolution and strict circumstances so as to benefit the future commercial applications of the grating-based multiple-information imaging technology.

Refraction-angle resolution of diffraction enhanced imaging

As a new method, x-ray diffraction enhanced imaging (DEI) has extremely high sensitivity for weakly absorbing low-Z samples in medical and biological fields. Conventional performance parameters, such as spatial resolution and low-contrast resolution, are not enough to describe the characteristics of a DEI system. This paper focuses on refraction-angle resolution which describes the ability of a DEI system to differentiate the x-rays refracted by the sample. The analysis of refraction-angle resolution is composed of two parts: the analysis of the single DEI image measured in a certain position of the rocking curve and the analysis of the refraction-angle image calculated by extraction methods. A 2D computer simulation experiment is performed to prove the results of the analyses. The limitations and conclusions of refraction-angle resolution are described in the end.

Phase-contrast tomosynthetic experiment on biological samples with synchrotron radiation

Tomosynthesis is one of three-dimensional imaging techniques that can remove the effect of overlapping phenomena in radiography, except for computed tomography (CT). In general, CT needs at least hundreds of projections to reconstruct every cross-sectional slice of the samples accurately, while tomosynthesis just requires dozens of projections to reconstruct a series of tomosynthetic slices approximately, Conventional tomosynthesis based on attenuation contrast shows poor results when imaging weakly-absorption objects such as biological samples. In this paper, we present a new type of tomosynthesis, named phase contrast tomosynthesis, combining X-ray phase-contrast imaging mechanism and tomosynthesis, which can obtain higher resolution and image quality for the biological samples with fewer radiation doses and avoid overlapping phenomena. A phase contrast tomosynthetic experiment on a guinea pig cochlea at the Shanghai Synchrotron Radiation Facility (SSRF) was done to evaluate the performances of various reconstruction algorithms integrated with the in-line phase retrieval method.

Local reconstruction in computed tomography of diffraction enhanced imaging

Computed tomography of diffraction enhanced imaging (DEI-CT) based on synchrotron radiation source has extremely high sensitivity of weakly absorbing low-Z samples in medical and biological fields. The authors propose a modified backprojection filtration(BPF)-type algorithm based on PI-line segments to reconstruct region of interest from truncated refraction-angle projection data in DEI-CT. The distribution of refractive index decrement in the sample can be directly estimated from its reconstruction images, which has been proved by experiments at the Beijing Synchrotron Radiation Facility. The algorithm paves the way for local reconstruction of large-size samples by the use of DEI-CT with small field of view based on synchrotron radiation source.

Implement X-ray refraction effect in Geant4 for phase contrast imaging

X-ray phase contrast imaging (PCI) is a hot research field in the last decade. Many novel methods such as diffraction enhanced imaging, grating-based imaging et al come to the fore. The Monte Carlo simulation can simplify the phase contrast system modeling and is useful for system optimization and new method validation. In this paper, a Monte Carlo tool based Geant4 that implements the x-ray refraction effect is proposed. It adds the capability of phase contrast imaging to Geant4. The tool is validated by a simple sphere simulation. The result of the validation is in perfectly accordance with the theoretical value. The tool is also applied to model the grating-based imaging method to present the potential applications in x-ray phase contrast research.

Differential Phase-Contrast Imaging Experimental System Under the Incoherent Condition With Conventional X-Ray Tubes

Hard X-ray phase-contrast imaging provides high sensitivity of weakly absorbing low-Z objects in medicine, biology and materials science. The traditional viewpoint is that coherent X-rays and coherent measurements are essential to hard X-ray phase-contrast imaging. In this paper, a differential phase-contrast imaging experimental system is introduced to obtain refraction-angle images based on the theory of infinite fringe moire deflectometry under the incoherent condition with weakly coherent X-rays from the conventional X-ray tube without Talbot effect. The experiments on material and biological samples prove that differential phase-contrast imaging can be realized under more relaxed condition.