TU‐H‐207A‐07: Comparison of Performance of Tube‐Current Modulation of Three Commercial MDCT Scanners

Abstract

Purpose:To compare performance of tube‐current modulation (TCM) of three commercial MDCT scanners (TOSHIBA Aquilion One, SIEMENS SOMATOM Definition AS+, PHILIPS Brilliance iCT) from tube current measurement, image noise measurement, and Monte Carlo (MC) simulation based on time‐resolved air kerma measurement.Methods:CT image acquisitions were performed with and without TCM by means of TCM phantoms with length of 40 cm which consists of three oval phantoms (10×20 cm, 14×28 cm, 18×36 cm) and one cylindrical phantom with diameter of 10 cm. Tube currents for each slice were obtained from the DICOM header information. The image noise was measured as standard deviation of CT numbers in ROI at each CT slice. TCM was tested for two oval phantoms. A time‐resolving ionization chamber was positioned at 0 degree and 270 degree and the time‐resolved air kerma was measured with and without TCM. Three MDCT scanners were modeled using GMctdospp (IMPS, Germany) based on the EGSnrc user code. MC‐calculated dose curves per angle were compared to those measured. MC calculations for TCM were set to maximal tube‐current reduction factors (TCM limit) from 0.3 to 0.8.Results:The tube current changed depending on a phantom size. However, excessive tube current was observed at the boundary of phantoms. This is because the tube current changed gradually in anticipation of thickness change. The variation of image noise was improved by the use of TCM. MC‐calculated dose curves without TCM were in good agreement with the measurement. The variation of dose curves with TCM increased with decreasing TCM limit. The MC‐calculated curve with TCM limit of 0.3 agreed with the measurement in all scanners.Conclusion:TCM is useful to improve the image quality and reduce radiation dose. However, the excessive tube current was observed due to limitation of tube current control.