Low-dose CT screening for lung cancer with automatic exposure control: phantom study

We conducted a study to determine optimal scan conditions for automatic exposure control (AEC) in computed tomography (CT) of low-dose chest screening in order to provide consistent image quality without increasing the collective dose. Using a chest CT phantom, we set CT-AEC scan conditions with a dose-reduction wedge (DR-Wedge) to the same radiation dose as those for low-tube current, fixed-scan conditions. Image quality was evaluated with the use of the standard deviation of the CT number, contrast-noise ratios (CNR), and receiver-operating characteristic (ROC) analysis. At the same radiation dose, in the scan conditions using CT-AEC with the DR-Wedge, the SD of the CT number of each slice position was stable. The CNR values were higher at the lung apex and lung base under CT-AEC with the DR-Wedge than under standard scan conditions (p < 0.0002). In addition, ROC analysis of blind evaluation by four radiologists and three technologists showed that the image quality was improved for the lung apex (p < 0.009), tracheal bifurcation (p < 0.038), and lung base (p < 0.022) in the scan conditions using CT-AEC with the DR-Wedge. We achieved improvement of image quality without increasing the collective dose by using CT-AEC with the DR-Wedge under low-dose scan conditions.