Radiation dose and imaging quality of abdominal computed tomography before and scan protocol adjustment: Single-institution experience in three years

To compare radiation dose and image quality of abdominal CT for patients who underwent repeated CT examinations before and after adjustment of scan protocol. We compared radiation dose and image quality of repeated abdominal CT scans (at three-year-interval) of 50 patients with chronic liver disease, 50 patients with early gastric cancer, and 50 patients with uterine cancer. To reduce radiation dose, we optimized CT protocols by omitting unnecessary pre-contrast phase, reducing kVp, and setting higher noise index. Data of dose reports were collected. Objective image quality was evaluated for noise level, signal to noise ratio (SNR), and contrast noise ratio (CNR). For subjective image quality, we evaluated image noise, contrast, and overall diagnostic acceptability. The mean values of dose length product of 2011 CT scans compared to those of 2008 CT scans were 27.6% to 45.7%. The image noise level, SNR, and CNR were significantly (p < 0.05) worse in 2011 CT scans compared to 2008 CT scans. For subjective image quality, image noise was also significantly (p < 0.05) worse in 2011. However, CNR and diagnostic acceptability showed variable results. No CT scans were considered as unacceptable image.We modified abdominal CT protocols to reduce radiation exposure while trying to maintain diagnostic acceptability.