Program Information
Effect of Gantry Rotation Time On Spatial Resolution On Clinical CT Scanners
J Wang1*, (1) Stanford University, Stanford, CA
Presentations
TU-C2-GePD-IT-5 (Tuesday, August 1, 2017) 10:00 AM - 10:30 AM Room: Imaging ePoster Theater
Purpose: To study the effect on spatial resolution when gantry rotation time is reduced on clinical CT scanners
Methods: The ACR phantom (Gammex Inc.) was scanned on a clinical CT scanner (FORCE CT, Siemens Healthcare) with a routine chest protocol and a high-resolution CT protocol at different rotation times: 1s, 0.5s, and 0.28s. The phantom was scanned at different locations and orientations within the scan FOV so that the effect of distance from iso-center on spatial resolution can be studied. Images were reconstructed with a sharp kernel (Br69) and 5cm FOV. The number of projections per rotation for each rotation time was obtained from the projection data file. Two bar patterns in the high contrast spatial resolution module (8 and 10 line pairs/cm) were used to evaluate the azimuthal and radial spatial resolution. Line profiles were drawn over the bar patterns for comparison of spatial resolution. MTF at different rotation times were measured using the circular bone object in the ACR phantom.
Results: The number of projections per rotation is 4200, 2100, and 1280, for rotation time at 1s, 0.5s and 0.28s of routine chest protocol, respectively. With routine chest protocol, the azimuthal spatial resolution shows substantial degradation at rotation time of 0.28s, in comparison to 1s and 0.5s rotation time, and the degradation increases with distance from the gantry iso-center. The radial resolution shows much less dependence on rotation time, supporting a conclusion that the resolution loss results from the reduction in the number of projections. MTF of rotation time at 0.28s shows lower values at higher spatial frequency than rotation time at 1s and 0.5s. With the HRCT protocol, a similar, but much weaker trend of degradation was seen.
Conclusion: Azimuthal spatial resolution shows degradation with deceasing rotation time at increasing distance from iso-center.
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