Analysis of Radiographic Contrast Markers for X-ray Digital Image Correlation of Tissue-Simulants Under Dynamic Load

Abstract

The study of traumatic brain injury is critical to the improvement of protective equipment. Numerical models of brain deformation require real-world data for validation. In preparation for upcoming cadaver studies, a novel method of measuring displacement and strain fields of optically inaccessible internal planes using high-speed X-ray, embedded contrast markers and digital image correlation (DIC) is presented herein. An uncoupled scintillator and optimally-selected highspeed camera enable continuous X-ray imaging through a human head at 10,000 fps. As varying composition creates radiographic contrast, contrast within a human brain is limited, therefore, artificial contrast markers are required. Markers must be dynamically coupled to the bulk material and provide sufficient X-ray contrast. An analytical tool was developed to design of contrast markers. The impact of contrast-to-noise ratio and out-of-plane motion on DIC accuracy were quantified. Finally, a feasibility study using a biofidelic headform subjected to a NOCSAE drop test is presented.iii Acknowledgments As I turn the page on this chapter of my life, I cannot help but to reflect on the enormous contributions of an incredible team of collaborators that made it all possible. The completion of this work is due in no small part to my advisor, Professor Oren Petel. His support and passion for my research, made this experience enjoyable. You have provided me with unique opportunities to explore my field over the last two years, encouraging personal growth, and leading me to ask the important question. I am sincerely grateful for your insight and guidance in this work. Construction of the high-speed X-ray facility would not have been possible without the technical recommendations of support staff in the department of mechanical and aerospace engineering at Carleton University. Specifically, the expertise and guidance of lowing access to their X-ray system until our facility was operational. Tong, your passion for discussions on X-ray physics helped establish the foundation I required for my research. Unique opportunities to explore other research facilities have complemented my studies and contributed to my personal growth as a researcher. Special thanks iv to Simon Ouellet, of Defence Research and Development Canada (DRDC) Valcatier, for access to the BI 2 PED headform, and discussion of radiographic contrast marker integration; and Rohan Banton and Thuvan Piehler of the U.S. Army Research Laboratory, for headforms and brain surrogate materials.The first people to share in my successes and support my failures were often my coworkers. Specifically, shout-outs to Ashley Mazurkiewicz, for always listening to the latest updates and sharing stellar LOTR memes as encouragement, and to Scott Dutrisac for solving so many of my problems, and helping me with more rebuilds than the Edmonton Oilers.

A Study of the Impact Response of Discrete Regions of the Human Cadaver Brain

“…As images are radiographic projections, their clarity is based on the X-ray attenuation through the different materials present in the specimen. Adjustments to incident X-ray energy can improve image clarity, however this was not always the case, as these adjustments result in a balance between contrast for brightness [47]. At times, certain features were only detectable through qualitative assessments and visual inspection of the images.…”

“…A qualitative method was not feasible for automated software, which relies on quantitative measures for feature detection. Improving the clarity of the features increases the edge-quality, making target detection more effective and efficient [47].…”

“…Much like a spotlight, the X-ray source does not project an even field. Image intensity tends to be greater toward the central focal spot, resulting in less intensity at the periphery [47]. This produces a vignetting effect in the acquired images, reducing the brightness and clarity of the features in the far-field regions.…”

“…as such is commonly used in diagnostic X-ray imaging [47]. Three different elastomeric binders were used to develop high, medium, and low stiffness markers.…”

A Methodology to Evaluate Strain Within Tissue Slabs under Complex Loading

“…Out-of-plane motion is another factor that contributes to sources of error with headform design. A few investigations into out-of-plane error have been performed with the current X-ray system [75,76], but this parameter was not investigated for this thesis work. To reduce the risk of out-ofplane motion, the surrogate neck was inspected between impacts and the tension cable tightened if the head could turn freely out of plane, but this was a rare occurrence, usually after over 5 consecutive impacts.…”