High-dynamic-range micro-CT for nondestructive testing of titanium 3D-printed medical components

Santiago Fabian Cobos; Christopher James Norley; Steven Ingo Pollmann; David Wayne Holdsworth

doi:10.1117/1.JMI.9.4.044004

High-dynamic-range micro-CT for nondestructive testing of titanium 3D-printed medical components

J Med Imaging (Bellingham). 2022 Jul;9(4):044004. doi: 10.1117/1.JMI.9.4.044004. Epub 2022 Aug 1.

Authors

Santiago Fabian Cobos¹, Christopher James Norley², Steven Ingo Pollmann², David Wayne Holdsworth^{1

2}

Affiliations

¹ University of Western Ontario, Schulich School of Medicine and Dentistry, Department of Medical Biophysics, London, Ontario, Canada.
² University of Western Ontario, Robarts Research Institute, Imaging Research Laboratories, London, Ontario, Canada.

Abstract

Purpose: Industrial microcomputed tomography (micro-CT) scanners are suitable for nondestructive testing (NDT) of metal, 3D-printed medical components. Typically, these scanners are equipped with high-energy sources that require heavy shielding and costly infrastructure to operate safely, making routine NDT of medical components prohibitively expensive. Alternatively, fixed-current, low-cost x-ray units could be implemented to perform CT-based NDT of 3D-printed medical parts in a subset of cases, if there is sufficient x-ray transmission for the CT reconstruction. A lack of signal-caused by areas of high attenuation in two-dimensional-projection images of metal objects-leads to artifacts that can make an image-based NDT unreliable. We present the implementation of a dual-exposure technique devised to extend the dynamic range (DR) of a commercially available CT scanner equipped with a low-cost low-energy (80 kV) x-ray unit, increasing the signal-to-noise ratio of highly attenuated areas for NDT of 3D-printed medical components. Approach: Our high-dynamic-range CT (HDR-CT) technique adequately combines projection images acquired at two exposure levels by modifying the integration times of each protocol. We evaluate the performance and limitations of this HDR-CT technique by imaging a series of titanium-alloy test-samples. One of the test-samples was a resolution and conspicuity phantom designed to assess the improvements in void visualization of the proposed methodology. The other test-samples were four porous cylinders, $17 \times 40 mm$ , with 60%, 70%, 80%, and 90% nominal internal porosities. Results: Our HDR-CT technique adequately combines projection images acquired at two exposure levels by modifying the integration times of each protocol. Our results demonstrate that the 12-bit native DR of the CT scanner was increased to effective values of between 14 and 16 bits. Conclusions: The HDR-CT reconstructions showed improved contrast-to-noise and void conspicuity, when compared with conventional CT scans. This extension of DR has the potential to improve defect visualization during NDT of medium-size, titanium-alloy, 3D-printed medical components.

Keywords: additive manufacturing; high-dynamic-range radiography; laser powder bed fusion; micro-CT imaging; nondestructive testing; x-ray imaging.