An iterative method for robust in-line phase contrast imaging

Abstract

We present an iterative near-field in-line phase contrast method that allows quantitative determination of the thickness of an object given the refractive index of the sample material. The iterative method allows for quantitative phase contrast imaging in regimes where the contrast transfer function (CTF) and transport of intensity equation (TIE) cannot be applied. Further, the nature of the iterative scheme offers more flexibility and potentially allows more high-resolution image reconstructions when compared to TIE method and less artefacts when compared to the CTF method. While, not addressed here, extension of our approach in future work to broadband illumination will also be straightforward as the wavelength dependence of the refractive index of an object can be readily incorporated into the iterative approach.

An iterative method for near-field Fresnel region polychromatic phase contrast imaging

“…It can be seen that our iterative approach performs as well as the CTF method and both perform slightly better than the TIE approach. However, it should be noted that our iterative approach can operate reliably in regimes where the validity conditions for the CTF and TIE are violated to the extent that they become inaccurate [2]. The combination of extended validity and the 'phase diversity' effect means that our iterative method offers flexibility in the phase contrast image reconstruction process, potentially allowing an optimisation of reconstruction that is not possible with direct analytical approaches.…”

“…We have previously calculated the density of the Au sample to be 13.8 g cm −3 rather than bulk density [2]. Accordingly, this value was used when calculating the β and δ values.…”

“…However, figure 2 and table 1 show qualitatively and quantitatively that the polychromatic CTF and iterative methods can provide a better quality reconstruction than the polychromatic TIE. Furthermore, as we have previously demonstrated [2], an appropriate choice of propagator allows the iterative method to operate in regions where the TIE and CTF begin to fail.…”

“…At the expense of higher computational cost, iterative techniques for monochromatic propagation-based x-ray phase contrast offer the benefit of being able to operate in regimes where analytical techniques fail [2].…”

Evaluation of phase retrieval approaches in magnified X-ray phase nano computerized tomography applied to bone tissue

“…Actually, iterative near-field methods have been recently developed a lot in phase contrast imaging. However, they are mostly based on a single distance and generally use iterative algorithms, such as Fienup's error reduction (ER) [37] or the Gerchberg-Saxton (GS) algorithms [38]. In this work, we used a NLCG algorithm, taking as initialization, the phase maps retrieved from the extended Paganin's or homogeneous CTF method.…”