Dual phase grating x-ray interferometry is compatible with common imaging detectors, and abandons the use of an absorption analyzer grating to reduce the radiation dose. When using x-ray tubes, an absorbing source grating must be introduced into the dual phase grating interferometer. In order to attain a high fringe visibility, in this work we conduct a quantitative coherence analysis of dual phase grating interferometry to find how the source grating affects the fringe visibility. Theoretical analysis shows that with the generalized Lau condition satisfied, the fringe visibility is influenced by the duty cycle of the source grating and the transmission through the grating bar. And the influence of the source grating profile on the fringe visibility is independent of the phase grating type. Numerical results illustrate that the maximum achievable fringe visibility decreases significantly with increasing transmission in the grating bar. Under a given transmission, one can always find an optimal duty cycle to maximize the fringe visibility. These results can be used as general guidelines for designing and optimizing dual phase grating x-ray interferometers for potential applications.
A three‐image algorithm is proposed to retrieve the sample's transmission, refraction and dark‐field information in hard X‐ray grating interferometry. Analytical formulae of the three‐image algorithm are theoretically derived and presented, and evaluated by proof‐of‐principle synchrotron radiation experiments. The results confirm the feasibility of the proposed algorithm. The novelty of the proposed algorithm is that it allows versatile and tunable multimodal X‐ray imaging by substantially relaxing the existing limitations on the lateral grating position. Furthermore, this algorithm can also be adapted for samples with negligible refraction, reducing the number of required sample measurements to two. Furthermore, the noise properties of the retrieved images are investigated in terms of the standard deviations. Theoretical models are presented and verified by synchrotron radiation measurements. It is shown that the noise standard deviations exhibit strong dependence on the lateral grating position, especially in the case of refraction and dark‐field images. Further noise reduction and dose reduction can thus be possible by optimizing the lateral grating position for a selected region of interest. Those results can serve as general guidelines to optimize the data acquisition scheme for specific applications and problems.
We present a moment-based alternative approach to retrieve multiple scattering contrasts from x-ray analyzer-based imaging. By use of the properties of moments of convolutions, the multiple-image radiography approach is theoretically validated. Furthermore, higher order moments of the object scattering distribution, inaccessible in multiple-image radiography, are simultaneously provided by this alternative approach. It is experimentally demonstrated that the skew and kurtosis information related to the distribution of sub-pixel features within the object can be obtained from those complementary contrasts. Finally, the sensitivity of the retrieved multiple scattering contrasts is investigated experimentally. The finding that the sensitivity is inversely proportional to the square root of the detected photon number essentially indicates that the retrieval of moments with an order higher than two can be achieved without increasing exposure time or dose. The presented alternative approach provides an access to the exploitation of multiple scattering contrasts, which is expected to be useful in biomedical research, materials science, security screening, etc.
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Purpose X‐ray grating interferometry (XGI) provides substantially increased contrast over conventional absorption‐based imaging methods and therefore shows great potential for future biomedical applications. In this work, we propose a single‐shot phase retrieval method for synchrotron‐based high‐energy x‐ray grating interferometry. Contrary to existing retrieval methods, the presented novel approach enables direct retrieval of the object's phase map quantitatively from a single projection image, thus significantly simplifying the experimental procedure and reducing data acquisition times. Methods The phase retrieval method is analytically derived, based on the phase‐attenuation duality of soft tissues when being imaged with high‐energy x rays. The sensitivity of the retrieved phase map, quantified by the standard deviation, is evaluated as a function of the photon number. Numerical experiments are performed to validate the proposed method and provide some quantitative insight. Results The numerical results show that the method can provide high‐quality phase images, where the well‐known streak artifacts are significantly suppressed. Moreover, the retrieved phase maps confirm that the method is highly stable with respect to statistical noise. Conclusions Thanks to simplified experimental procedure and reduced acquisition time and dose deposition to the sample, we believe that this new method can find its potential in biomedical imaging and in vivo studies. Future work will focus on the adaptation of the method to polychromatic x ray from tube source and to computed tomography.
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