Author: Hadley Anna DeBrosse, Kevin J. Little 👨🔬
Affiliation: The Ohio State University 🌍
Purpose: This work examines the consistency and pattern of spatial resolution degradation in weekly quality control (QC) testing prior to CT tube failure and replacement and investigates potential correlation between spatial resolution degradation and CT tube failure.
Methods: We collected instances of x-ray tube replacement within the previous two years across six Siemens CT scanners. For these scanners, the spatial resolution component of the weekly QC tests examined at least 3 of 4 previously selected reconstruction kernels, including head, body, high-resolution head, and ultra-high resolution (UHR) filters. For all scanners and reconstruction filters, we plotted 50% modulation transfer function (MTF) values ranging 104 weeks prior to tube failure and up to 47 weeks after tube replacement, and quantified degree of degradation with percent change from starting value. Additionally, we collected reasons for tube replacement.
Results: For all scanners and reconstruction kernels, spatial resolution degradation over time was linear. The UHR kernel displayed a greater percent degradation than other kernels, starting on the date of tube replacement. For a given scanner, the absolute percent resolution change increased with kernel sharpness, consistent with a potential physical mechanism behind resolution loss that is obscured by the lower resolution kernels and is more evident in high resolution kernels. Despite this expected and consistent resolution loss, failure in the weekly MTF values for the UHR kernel was often a reason for tube replacement.
Conclusion: Spatial resolution loss in weekly QC is an expected process often only evident when using an UHR kernel. Tube replacement based on UHR MTF failure alone may unnecessary if this kernel is not used clinically. We aim to discuss clinical significance by examining UHR temporal bones imaged immediately before and after tube replacement on these scanners.