INVESTIGATION OF A LINEAR ANTI-SCATTER GRID WITH NONCONVENTIONAL GEOMETRY AND A NOVEL INTERSPACE MATERIAL FOR MEDICAL X-RAY IMAGING
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Date
2022-01-01
Type of Work
Department
Mechanical Engineering
Program
Engineering, Mechanical
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This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
Abstract
The objective of this research was to investigate the performance of an anti-scatter grid with a novel interspace material and a nonconventional geometry used in medical x-ray imaging. Anti-scatter grids are used to eliminate scattered radiation that is emitted from the imaged object and that reaches the image receptor. Scattered radiation accumulated in the image receptor degrades the image contrast making it harder to visualize details that might be needed in a diagnosis. The prototype grid, "High-Maintenance Flat Fixed-focus" (HM-FF) grid, developed for this research is comprised of a 2.0 mm interspace width, 0.61 mm absorber thickness, and a height of 38.0 mm. The novelty proposed for the interspace construction was the implementation of a foam spacer for every two absorbers creating a septa pair. The use of the interspace material created an alternating pattern of air and foam interspaces, providing the grid with an increased x-ray transmission due to the low density of the materials used while providing structural support. The nonconventional geometry developed with this research was attributed to the increased height of the grid while maintaining a large grid ratio of 19:1. The thickness of the steel absorbers promoted a lower grid frequency design while maintaining x-ray absorption similar to thinner lead septa. Theoretical simulations narrowed the focus to implementing steel as a suitable lead absorber replacement. The main advantage of using steel was in the ease to handle during the fabrication process, while providing improved structural support for the overall grid assembly. The larger grid geometry was proposed in contrast to where current technology is and suggests that improved materials, for both absorbers and interspaces can significantly impact the performance of a grid. The results of the experiments measured primary transmission (Tp), scatter transmission (Ts) and total transmission (Tt) for three different grids: a conventional grid, a prototype grid called the "50-50" grid, and the focus of this research, the HM-FF grid. The main interest was in the comparison of the conventional grid to the HM-FF grid. The Tp for the conventional grid was 55.18%, while the HM-FF had a Tp of 68.38%. The Ts for the conventional grid was 10.07% and 5.99% for the HM-FF grid. Lastly, the Tt for the conventional and for the HM-FF grids was 19.84% and 18.20%, respectively. The performance values that are of interest to measure how good or bad a grid can be are calculated from those three transmission measurements. Using the latest update to the IEC 60627 standard for grid testing, the Image Improvement Factor (Q), demonstrated that the HM-FF grid was superior compared to the conventional grid with a value of 2.57 over 1.53. The main driver for pursuing this research was to attempt to contribute to improving the quality of life of humans. The prototype HM-FF grid developed in this research suggests that improved quality images are feasible while attempting to reduce the effects of dosage to patients when obtaining radiographs. The increased performance of the prototype grid was due to the larger nonconventional geometry and the implementation of a more x-ray transparent interspace material.