Optimization of acquisition conditions in synchrotron X-ray phase micro-tomography

X-ray in-line phase contrast micro-tomography is a relatively new coherent X-ray imaging technique which offers a sensitivity several orders of magnitude higher than standard, attenuation based techniques. In this technique, phase contrast is achieved by simply letting the beam propagate after interaction with the imaged object. More interestingly, the images acquired with this technique can be used to reconstruct the phase shift induced by the object – phase retrieval. Further, the retrieved phase shifts, reconstructed at different rotation angles of the object can be used to reconstruct the 3D refractive index distribution in the sample – phase tomography. Several different phase retrieval algorithms have been presented in literature. Sensitivity to low frequency noise has required the introduction of priors, such as assuming a homogeneous object. One of these algorithms reconstruct the phase from one propagation phase contrast image alone by using such assumptions, whereas other methods use images at several distances to reconstruct the phase, while putting less restrictions on the object. The obvious gain of a single distance technique is the simplicity of the experimental setup, reduced amount of recorded data and reduced use of precious synchrotron beam time. It is believed, however, that recording of images at multiple distances could actually help reduce the damage induced by the dose deposited in the sample, partially by dose fractioning, partly by exploiting the correlations between the phase information in the images and the independence of the noise between the images. This is a very important aspect in X-ray imaging of biomedical samples. Hence, this project aims at quantitatively establishing ideal image acquisition parameters for different imaging conditions. Different imaging conditions, in terms of eg., number of distances and signal to noise ratios in the recorded images, will be explored both using synthetic data and real data acquired at the European Synchrotron Radiation Facility, Grenoble, France. The imaging conditions will be evaluated by applying different phase retrieval algorithms and comparing the descriptive statistics in terms of eg., contrast to noise ratio, resolution and precision in the reconstructed tomograms. The successful candidate should have a background in computer science, electrical engineering or engineering physics, and a strong interest in biomedical imaging, optimization, signal and image processing and related areas. Duration: 3-6 months Contact: Max Langer (max.langer@esrf.fr), Françoise Peyrin (peyrin@esrf.fr).