CT Mammography검사 시 자세변화에 따른 영상평가 및 적정선량에 관한 연구

Study of image quality and optimum dose with change of position in CT Mammography

Purpose The subject of this study is female breast cancer patient who had. CT mammography before and after surgery. The study covers effects on exposure dose and image quality by change of exposure condition are observed, and makes comparative, analytic study of difference between a breast image taken with supine position and the other one with prone position. Materials & Methods Qualities of supine position image were compared with those of prone position image and difference between two of the images were analyzed with change of kVp and mAs by 3grades(Equivalent, Acceptable, Unacceptable). A special equipment was used for prone position image so as to breast of the subjects don’t be squeezed. CTDIvol was recorded scanning by 120kVp/100mAs during usual scanning and 100kVp/70mAs for this study. 20 female breast cancer patients were subjects, and Somatom Sensation16(Siemens, Erlagen, Germany) was used by 2 observers in this study. Two studies were conducted on phantom. First, ion chambers were put into holes around and center of a phantom, and exposure dose on reader was recorded after scanning the phantom with change of kVp and mAs. Second, CTDIvol that was changing by exposed area differ by position of the breast phantom was measured with change of kVp and mAs, Results According to the 20 scanned images based on change of position and image quality, It gives 1 case on Equivalent, 19 cases on Acceptable and 0 case on Unacceptable. CTDIvol is measured as 7.8mGy at 120kVp/100mAs and 3.5mGy at 100kVp/70mAs. but there was no relation with position. Surface dose decreased by mean 59% and deep dose decreased by 63% at 100kVp/70mAs compared at 120kVp/100mAs in phantom study while dose is measured as 1.11mGy at 100kVp/70mAs with straighten up position for maximum exposed area which is reduced by 10% compared with a lateral position in the same condition. Conclusion It’s impossible for exposure dose to be less than a certain value in order to satisfy a proper condition, 100kVpn/70mAs, at which the image quality is not effected. In this study, it results that prone position makes fine image especially for diagnosing patients before surgery rather than supine position does. consequently, this study shows that prone position have decisive role for the accurate examination of breast cancer