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 concentration. Therefore, we wish to conduct this study to clarify if the routinely applied X-ray computed tomography examination may induce a higher concentration of ROS in the peripheral blood. Study subjects will be participants of health check program at our hospital. The only enrollment condition will be a scheduled X-ray computed tomography examination for either lung (20 cases) or heart (20 cases) of the study subject. Another 20 participants receiving health check program without X-ray computed tomography examination will be included as the control group. The formal consent will be delivered to the participants of health check program several days before their admission for health check and will be retrieved before the proceeding of health check.

Measurements and comparison of ROS concentration will be performed in the sampled peripheral blood before and after the performance of X-ray computed tomography examination during a regular health check program. Totally 120 blood samples will be collected from included 60 study subjects within 3 months. Reactive oxygen species（ROS）levels will be measured by a chemiluminescence (CL) analysing system (CLD-110, Tohoku Electronic Industrial, Sendai, Japan).