I133] Impact of scan settings on automatic tube current modulation in CT

Abstract

Purpose Automatic Tube Current Modulation (ATCM) adapts the tube current during a CT scan to provide a target image quality throughout the scan as well as for patients of varying sizes. However, the misapplication of ATCM can result in excessive radiation doses or images of non-diagnostic quality. Furthermore, it is not always intuitive to know which scan settings can affect the resulting ATCM and the ATCM functionality between vendors differs. The purpose of this work was to investigate which variable scan settings can impact the ATCM on CT scanners from the four major vendors. Methods The investigation was categorized into scan setting variations in CT localizer radiographs, exposure parameters, reconstruction parameters, and miscentering. A phantom dedicated to ATCM testing was designed and manufactured. A baseline scan was first made by scanning the ATCM phantom using reference scan settings. The ATCM phantom was subsequently scanned by systematically varying the settings in the four categories of setting variations. The scans with varied settings were compared to baseline and evaluated in terms of differences in applied tube current and image noise. The evaluation included both quantitative and qualitive metrics. Results The impact of scan settings on the applied ATCM will differ greatly between vendors, as each vendor has their own unique ATCM implementation. The impact on ATCM can either be apparent or subtle, depending on which scan setting has been varied. Comprehensive tables, corresponding to the different categories of setting variations, has been compiled highlighting the results. 1 . Conclusions A method (including the design of a phantom) has been developed to systematically evaluate how the choice of scan settings can affect the applied ATCM. The methodology was used to investigate the ATCM from four major CT vendors, highlighting similarities and differences among them.