Measurement of spatial and density resolutions in x-ray nanocomputed tomography

Abstract

The latest generation of nano computed tomography (nano-CT) systems with sub-micrometer focus X-ray source is expected to yield non-invasive imaging of internal microstructure of objects with isotropic spatial resolution in the range of hundreds nanometers. Most recently commercial systems have become available for purchase. The quantitative characterization of the performance of nano-CT systems is important for evaluating the accuracy of size and density measurements of fine details in nano-CT images. The point spread function (PSF) and modulation transfer function (MTF) are calculated most commonly from the measurement of thin wire phantom for measuring the spatial resolution of clinical CT systems. However, a consistent method for describing the spatial resolution of nano-CT has not been utilized due to the requirement of a nanowire which is a wire of diameter of the order of tens of nanometers. This paper presents a method to characterize the spatial resolution in x/y-scan plane (transversal orientation) of nano-CT systems using a relatively large microwire in the PSF measurement. In this method, the MTF computed from the PSF is estimated on the basis of a two-Gaussian PSF model. Experimenting with microwire images with three different diameter sizes (3μm, 10μm, 30μm) obtained by the synchrotron radiation CT, we demonstrate the potential usefulness of the method for describing the spatial resolutions of nano-CT systems.