Mr. Santiago F. Cobos Profile

Santiago F. Cobos

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Publications (2)

SPIE Journal Paper | 1 August 2022 Open Access

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

JMI, Vol. 9, Issue 04, 044004, (August 2022) https://doi.org/10.1117/12.10.1117/1.JMI.9.4.044004

KEYWORDS: High dynamic range imaging, Nondestructive evaluation, X-rays, Scanners, CT reconstruction, Titanium, Signal to noise ratio, Sensors, Metals, X-ray computed tomography

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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 × 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.

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Proceedings Article | 16 March 2020 Paper

Reduction of ring artifacts caused by 2D anti-scatter grids in flat-panel CBCT

Santiago Cobos, Hristo Nikolov, Steven Pollmann, David Holdsworth

Proceedings Volume 11312, 1131228 (2020) https://doi.org/10.1117/12.2548778

KEYWORDS: Sensors, Image quality, X-rays, X-ray detectors, Digital filtering, Spatial frequencies, Image filtering, Medicine, Dentistry, Manufacturing

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