A comparison of free software implementations of phase retrieval algorithms for propagation-based X-ray microtomographic imaging

Microtomographic (micro-CT) experiments can be performed in the so-called Propagation Based Imaging (PBI) modality by using a sufficiently coherent X-ray beam, such as the one obtained at e.g. third generation synchrotron laboratories or at enhanced liquid-metal-jet-anode micro focus facilities. Then, a quantitative relationship exists between the phase shift induced by the object and the recorded intensity. The inversion of this relationship is called phase retrieval and in PBI this can be performed via digital image processing. Several phase retrieval algorithms have been developed through years and freely available software has also recently appeared. In this paper, preliminary results of a qualitative comparison of the phase retrieval image processing offered by two free software tools are shown by considering two experimental micro-CT PBI datasets acquired at the SYRMEP beamline of the Italian synchrotron radiation facility (Elettra - Sincrotrone Trieste S.C.p.A.). An algorithm based on the solution of the Transport of Intensity Equation (TIE) implemented into the open source software ANKAPhase is compared against the solution based on the first Born approximation offered by the PITRE free software tool. A deep understanding of how these phase retrieval algorithms affect the resulting images is crucial in order to accurately interpret the reconstructed micro-CT PBI datasets.