CT 검사 시 촬영조건에 따른 Image Quality와 Dose에 관한 연구

A Research on Image Quality and Dose according to Optimal Exposure factor in CT Examination

Purpose To provide an advice on the patient dosimetry quantities without obstructing the medical purposes through the decrease in kVp and the use of Dose modulation program, Care dose 4D for tube current with patient screening by weight in CT examination. Materials and Methods Each weight group(51kg~60kg, 61kg~70kg, 71kg~80kg, 81kg~90kg) consists of 5 patients from total 20 patients with follow-up abdomen CT examination. CT values and noise according to the tube ctuTent were measured, and exposure dose and image quality were compared. Somatom Sensation 16 equipment was used for measurement. Dose modulation program, Care dose 4D was used for tube current, and tube voltage was measured using 100kVp at Pre Enhancement phase on the abdomen. Examination range was compared and analyzed by applying same FOV with the recently examined tube potential of 120kVp. Results In case of 120 kVp and 100 kVp by using Dose modulation program, Care dose 4D, CT values were decreased on the whole. However, the tendency of CT values of adjacent abdominal organs were measured similarly. 1his means that the contrast resolution is not greatly influenced by the lowered tube voltage of 100 kVp. When we measured the noise of the liver, the spleen, and the descending aorta according to the weight of the patient in the image quality measurement, as the weight of the patient decreases the noise ratio was also reduced as follows : from 0.76:1 to 0.88:1 for the liver, from 0.75:1 to 0.87:1 for the descending aorta, and from 0.73:1 to 0.85:1 for the spleen. Therefore, we can conclude that high quality image can be obtained using 100 kVp in the patient having a weight of 60 kg and the height of at least 165~175 cm. If the tube voltage was reduced from 120 kVp to 100 kVp, no tube current change was observed, and the CTDIvol value was decreased over 30%. Conclusion It would be very helpful in reducing radiation exposure to perform CT examination using optimal shooting condition according to the patient’s weight and physical constitution presented by the clinical trial results. Once the standard protocol is presented at the conference or public agency, We think that the radiation exposure of a patient can be greatly decreased by using optimal shooting condition for each hospital based on the protocol.