High-Resolution Three-Dimensional Imaging via X-Ray Reflectometry and Phase-Contrast Computed Tomography

Project Overview

The traditional approach to non-destructive characterization of 3D objects is to use x-ray absorption computed tomography (CT). However, traditional CT has inadequate image contrast for a wide range of low x-ray absorption contrast materials and its resolution is limited to the micron length scales. To address the problem of inadequate contrast, our solution was to create new computational frameworks for reconstruction of object from synchrotron phase contrast CT data (SPCCT). To address the problem of limited resolution, our solution was to use x-ray reflectivity to measure the nanometer scale roughness of curved surfaces.

We proposed and implemented new approaches to reconstruct the refractive index from SPCCT data (holotomography), which enabled us to demonstrate more than 10x improvement in image contrast for certain materials. One of our novel contributions is a new phase retrieval algorithm that avoids linearization of the underlying non-linear physics of phase contrast, which enables us to reconstruct refractive index with reduced artifacts and improved resolution when compared to the state-of-the-art. To enable wide spread adoption, we have also released the software for our methods under open-source licenses for data pre-processing and object reconstruction. For x-ray reflectivity, we expanded and validated a new x-ray reflectivity (XRR) model to include the effect of surface curvature, enabling the extraction of surface topographic information (i.e. roughness and waviness). We created a new ray tracing model for the reversal of radiographs to extract surface features from spheres and cylinders at resolutions that are significantly higher than state-of-the-art. We also incorporate the effects of internal reflections from thin spherical shells such as the National Ignition Facility (NIF) target capsules.

Mission Impact

The project has pioneered a new set of x-ray imaging methods in the fields of x-ray phase contrast, x-ray reflectivity, and inverse problems to take a significant step forward in metrology, and three-dimensional morphological and density characterization. These new capabilities will accelerate the efforts of the Advanced Materials and Manufacturing, High Energy Density Science and Nondestructive Characterization Institute Core Competencies. These techniques will increase the range of materials that can be qualitatively and quantitatively analyzed by researchers for high resolution characterization and metrology applications. We have demonstrated significant contrast enhancement for fill-holes of National Ignition Facility (NIF) targets, interfaces between various plastics, and other materials that are relevant to lab missions using synchrotron x-ray phase contrast tomography. X-ray reflectivity is useful for NIF capsule roughness measurements and can be extended to measurements of high-performance freeform x-ray and visible optics.

Publications, Presentations, and Patents

Cole, J. A., J. A. Cuadra, R. M. Panas, and S. T. Smith. 2021. "The effect of longer-range waviness on X-ray reflectivity measurements," Journal of Synchrotron Radiation 71-77.

Mohan, K. A., R. M. Panas, and J. A. Cuadra. 2020. "SABER: A Systems Approach to Blur Estimation and Reduction in X-ray Imaging." IEEE Transactions on Image Processing 7751-7764.

Mohan, K. A. 2018. "PySABER: Python package for a systems approach to blur estimation and reduction." https://github.com/LLNL/pysaber.

Mohan, K. A., D. Y. Parkinson, and J. A. Cuadra. 2020. "Constrained Non-Linear Phase Retrieval for Single Distance X-ray Phase Contrast Tomography," Computational Imaging 146-1-146-8.

Forien, Jean-Baptiste. 2021. "PhaseCT: Open Source Software for Data Pre-Processing and Phase Retrieval." https://github.com/jbforien/phaseCT.