노이즈 변화에 따른 전산화단층촬영장치의 팬텀성능 평가

Phantom performance evaluation of computed tomography from the noise change

Purpose The image quality relies on how it can clearly and correctly present the fine structure of human body into the image and the factors influencing on the quality of CT image are accuracy of CT number, noise, spatial resolution and contrast resolution, artifact, dosimetry and accuracy of device. Among these factors, this paper finds out the change of CT number, spatial resolution, contrast resolution, linearity of CT number, etc. followed by the noise change which is the standard deviation of CT number. Materials and Methods As for CT device, Light speed CT/I/pro of GE medical company was used for the CT device of this experiment. CT phantom used in this experiment is the Nuclear Associates CT for CT performance evaluation designed by the American Association of Physicists in Medicine (AAPM) and manufactured by Victoreen, and it is used for CT performance evaluation in Korea. For the method of experiment, the size of noise in CT Phantom was changed into 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18 and 20 and its change was compared and recorded by measuring CT number, high contrast spatial resolution, low contrast spatial solution, linearity of CT number, etc. for 4 times. The size of noise was changed with slice thickness, reformative algorithm, kVp, dosimetry, etc. Results 1. CT numb.er CT number in the change of noise changed from 0 to 0.9HU with the noise change from 1 to 10 and changed about -3HU with the noise change from 12 to 20. 2. High contrast resolution The high contrast resolution in the change of noise changed from 0.75 to 1mm with the noise change from 1 to 8 and decreased to 1.25mm with the noise change from 9 to 20. 3. Low contrast resolution The low contrast resolution in the change of noise changed from 3.2 to 6.4mm with the noise change from 1 to 4 and changed from 19. 5 to 25. 4mm with the noise change from 7 to 10. However, the low contrast resolution changed a lot above the scale of measuring Phantom with the noise change up to 12-20. 4. Linearity of CT number The linearity of CT number in the change of noise uniformly showed the change of CT number such as water, acrylic, nylon, polystyrene, polyethylene and lexan which are used for the linearity within the permitted limit with the noise change from 1 to 10, however, CT number rapidly fell down with the noise change from 12 to 20. Conclusion In the CT performance evaluation from the noise change, the result shows that CT. number, high contrast resolution and linearity of CT number maintained their performance recommended by Korean Institute for Accreditation of Medical Image within the permitted limit of noise but low contrast resolution ran off the permitted limit of noise in the noise with over 7. In the experiment, the result does not satisfy the current condition which has the accepTable standard easier than the company’s regulation. Therefore, it is necessary to suggest the performance evaluation list and criteria satisfying the condition used in the real examination for the patients.