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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Medical Biophysics

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Holdsworth, David W.

Abstract

Biocompatible titanium-alloys can be used to fabricate patient-specific medical components using additive manufacturing (AM). These novel components have the potential to improve clinical outcomes in various medical scenarios. However, AM introduces stability and repeatability concerns, which are potential roadblocks for its widespread use in the medical sector. Micro-CT imaging for non-destructive testing (NDT) is an effective solution for post-manufacturing quality control of these components. Unfortunately, current micro-CT NDT scanners require expensive infrastructure and hardware, which translates into prohibitively expensive routine NDT. Furthermore, the limited dynamic-range of these scanners can cause severe image artifacts that may compromise the diagnostic value of the non-destructive test. Finally, the cone-beam geometry of these scanners makes them susceptible to the adverse effects of scattered radiation, which is another source of artifacts in micro-CT imaging.

In this work, we describe the design, fabrication, and implementation of a dedicated, cost-effective micro-CT scanner for NDT of AM-fabricated biomedical components. Our scanner reduces the limitations of costly image-based NDT by optimizing the scanner's geometry and the image acquisition hardware (i.e., X-ray source and detector). Additionally, we describe two novel techniques to reduce image artifacts caused by photon-starvation and scatter radiation in cone-beam micro-CT imaging.

Our cost-effective scanner was designed to match the image requirements of medium-size titanium-alloy medical components. We optimized the image acquisition hardware by using an 80 kVp low-cost portable X-ray unit and developing a low-cost lens-coupled X-ray detector. Image artifacts caused by photon-starvation were reduced by implementing dual-exposure high-dynamic-range radiography. For scatter mitigation, we describe the design, manufacturing, and testing of a large-area, highly-focused, two-dimensional, anti-scatter grid.

Our results demonstrate that cost-effective NDT using low-cost equipment is feasible for medium-sized, titanium-alloy, AM-fabricated medical components. Our proposed high-dynamic-range strategy improved by 37% the penetration capabilities of an 80 kVp micro-CT imaging system for a total x-ray path length of 19.8 mm. Finally, our novel anti-scatter grid provided a 65% improvement in CT number accuracy and a 48% improvement in low-contrast visualization. Our proposed cost-effective scanner and artifact reduction strategies have the potential to improve patient care by accelerating the widespread use of patient-specific, bio-compatible, AM-manufactured, medical components.

Summary for Lay Audience

In medicine, 3D printing technologies are currently changing the way doctors treat patients. Medical images can now be used to produce patient-specific medical components, improving the results of the treatments. These medical components need to be carefully inspected before being used. However, current 3D inspecting methods are too costly for routine quality control. These methods are costly because they require expensive hardware and expensive infrastructure. Furthermore, because these 3D inspecting methods use X-rays to 'see' inside the medical component, they are susceptible to various limitations due to complex interactions between the X-rays and the component's material. The goals of this thesis were (1) to develop a cost-effective solution for quality control of these novel medical components using 3D X-ray imaging and (2) to reduce the impact of non-idealities caused by complex X-ray physics to improve the quality of these inspections.

In this work, I propose using low-cost X-ray equipment to build a cost-effective, 3D, X-ray scanner for quality control of components manufactured using medical 3D printing. First, I showed that these titanium-alloy medical components have characteristics that make them suitable for inspection using non-sophisticated X-ray imaging equipment. Following this, I developed a low-cost X-ray detector using off-the-shelf hardware combined with the previously described X-ray equipment to build a cost-effective 3D scanner. Finally, I describe two advanced methods to improve the quality of the X-ray-based inspection by reducing the negative effects of scattered radiation and photon starvation, which are two well-known sources of error in 3D X-ray imaging. I found that our cost-effective 3D scanner was able to produce inspection images with the required accuracy to be used for quality control in the medical industry. Additionally, I demonstrated that anti-scatter grids and high-dynamic-range radiography are effective means to improve the image quality of this type of scanner. I believe that the work presented in this thesis offers a cost-effective alternative for inspecting medical devices produced using medical 3D printing. The use of this technology will propel the clinical use of these innovative treatment options using 3D printing.

Creative Commons License

Creative Commons Attribution-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-No Derivative Works 4.0 License.

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