The clinically widely used X-ray computed tomography examination has a low-grade radiation effect and recently has attracted much attention concerning the possible adverse effects of radiation on human body [ref. 1-5]. The radiation is harmful to human tissues and cells mainly because it can interact with water (which makes up to 80% of cells) to generate reactive oxygen species (ROS), especially the formation of hydroxyl radicals. So far as we can reach, there is no report concerning the relation between X-ray computed tomography examination and the blood ROS level. Therefore, we wish to conduct this study to clarify if the routinely applied abdominal X-ray computed tomography examination may induce a higher level of ROS in the peripheral blood.

Study subjects will be patients who are admitted to our hospital because of abdominal diseases that need to receive abdominal X-ray computed tomography examination for diagnosis. In total, sixty cases will be enrolled for the study. The formal consent will be delivered and explained to the patients and families several hours before the performance of abdominal X-ray computed tomography. The formal consent will be retrieved and then the peripheral blood will be sampled just before the performance of computed tomography.ROS level in the sampled peripheral blood, before and after the performance of abdominal X-ray computed tomography, will be measured, compared, and analyzed. Totally 120 blood samples, including 60 samples just before and 60 samples 2 hours after the performance of computed tomography, will be collected from 60 study subjects within 5 months (August 10 ~ December 30, 2008). Reactive oxygen species（ROS）levels will be measured by a chemiluminescence (CL) analysing system (CLD-110, Tohoku Electronic Industrial, Sendai, Japan).