[Optimization of the chest computed tomography scan by varying the position of the arms]

Computed tomography automatic exposure control (CT-AEC) technique is calculated from a localizer radiograph. When we perform neck and chest CT examination, at first, we acquire localizer radiograph and neck images by placing the arm in a lowered position. Next, the arm is raised for the chest scan. Therefore, the localizer radiograph and subject information are different in the chest scan. In this situation, the chest scan with the use of the CT-AEC causes radiation over-dose. The purpose of this study is to optimize the CT-AEC by controlling noise index (NI), and make a chest CT scan condition considering the position of the arms. We measured the image noise (SD) in the phantom by using CT-AEC. In addition, dose length product (DLP) was recorded. Moreover, we examined the correlation with the clinical images. The results of our experiments show that radiation dose can be reduced with the image quality kept by controlling NI.