How table height influences image quality and radiation dose of chest CT scans with automatic exposure control: a phantom study?

Abstract

To investigate the influence of table height on image quality and radiation dose of chest CT scan with automatic exposure control (AEC) technology. A chest phantom was scanned with AEC technology at 11 different table heights from 100 to 200 mm with 130 mm table height (iso-center was positioned at the midaxillary line of the phantom) used as reference center position. Image quality and radiation doses at different heights were statistically analyzed. Compared with 130 mm table height, the radiation dose of chest CT scan changed about 15% with the table height at 160 mm, or table height at 100 mm. The trend of the tube current–time (mAs) curve at different table heights was the same. In the thoracic inlet area, mAs changed most obviously, compared to the heart area. The noise of the image at higher table heights was not significantly different from the reference table height, but lower table heights increased the noise. When the height of the table was decreased from 130 to 100 mm, the size of the measured phantom changed greatly, by 5.22%, and when the height of the table was increased from 130 to 160 mm, the measured phantom size decreased to 95.07%. The score of the subjective image quality was lower when the table height was lowered. With table height settled between anterior axillary line and midaxillary line of the phantom, acceptable subjective image quality could be obtained with a lower radiation dose.