Hang Shu

Computed tomography algorithm based on diffraction-enhanced imaging setup

Recently taking advantage of the novel diffraction-enhanced imaging (DEI) method, one very effective and practical phase contrast imaging technique—a new x-ray computed tomography scheme based on DEI (DEI-CT) showed promising results, really superior to those of conventional CT imaging. In this letter, we show that the application of the conventional CT reconstruction algorithm is not always satisfactory for the new DEI-CT imaging and a new mathematical framework for imaging reconstruction is presented. Experimental data collected at the Beijing synchrotron radiation facility are also discussed using the new algorithm.

A new iterative algorithm to reconstruct the refractive index

The latest developments in x-ray imaging are associated with techniques based on the phase contrast. However, the image reconstruction procedures demand significant improvements of the traditional methods, and/or new algorithms have to be introduced to take advantage of the high contrast and sensitivity of the new experimental techniques. In this letter, an improved iterative reconstruction algorithm based on the maximum likelihood expectation maximization technique is presented and discussed in order to reconstruct the distribution of the refractive index from data collected by an analyzer-based imaging setup. The technique considered probes the partial derivative of the refractive index with respect to an axis lying in the meridional plane and perpendicular to the propagation direction. Computer simulations confirm the reliability of the proposed algorithm. In addition, the comparison between an analytical reconstruction algorithm and the iterative method has been also discussed together with the convergent characteristic of this latter algorithm. Finally, we will show how the proposed algorithm may be applied to reconstruct the distribution of the refractive index of an epoxy cylinder containing small air bubbles of about 300 micro of diameter.

Diffraction enhanced imaging: a simple model

Based on pinhole imaging and conventional x-ray projection imaging, a more general DEI (diffraction enhanced imaging) equation is derived using simple concepts in this paper. Not only can the new DEI equation explain all the same problems as with the DEI equation proposed by Chapman, but also some problems that cannot be explained with the old DEI equation, such as the noise background caused by small angle scattering diffracted by the analyser.

Reconstruction of the refractive index gradient by x-ray diffraction enhanced computed tomography.

The computed tomography technique cannot easily be extended to diffraction enhanced imaging (DEI) because, while from DEI we may extract the refractive index gradient in one dimension, from the conventional CT reconstruction algorithm we may reconstruct only a scalar quantity. However, recently we showed that changing the direction of the scan axis, and collecting a set of data related to the three-dimensional distribution of the refractive index gradient of the sample, a CT image was obtained. The algorithm we used is based on the conventional CT algorithm but with a specific pre-processing of the projection data. The mathematical framework of the procedure and a simple CT experiment are presented and discussed.

Diffraction Enhanced X-ray Imaging for Observing Guinea Pig Cochlea

Diffraction enhanced imaging (DEI) is a novel X-ray radiographic imaging method, which derives contrast from absorption, refraction, and extinction. With DEI technique, the spatial resolution of the acquired image can be increased 1000 times over conventional X-ray radiography. Therefore, it is suitable for the observation of biomedical micro-tissues and organs. This paper presents a new imaging method of minute biomedical organs based on DEI technique. In the investigation, the cochleae of guinea pigs were used as the samples. Before imaging, the cochleae of guinea pigs underwent different treatments, including fixation, decalcification, staining with silver nitrate solution, and reduction. Of them, the decalcification of cochleae is very important for improving the imaging quality. Compared with the conventional radiography image much higher contrast is achieved in the obtained DEI images. The fine spiral structure and inner details of the cochlea can be displayed clearly. The results show that compared with the conventional X-ray radiography, DEI is a more effective way of observing the guinea pig cochlear microstructures and other minute biomedical organs, and a potential tool for diagnosing cochlear diseases and morphologic study

Principle of diffraction enhanced imaging （DEI） and computed tomography based on DEI method

In the first part of this article a more general DEI equation was derived using simple concepts. Not only does the new DEI equation explain all the problems that can be done by the DEI equation proposed by Chapman, but also explains the problem that can not be explained with the old DEI equation, such as the noise background caused by the small angle scattering reflected by the analyzer. In the second part, a DEI-PI-CT formula has been proposed and the contour contrast caused by the extinction of refraction beam has been qualitatively explained, and then based on the work of Andos group two formulae of refraction CT with DEI method has been proposed. Combining one refraction CT formula proposed by Dilmanian with the two refraction CT formulae proposed by us, the whole framework of CT algorithm can be made to reconstruct three components of the gradient of refractive index.