관전압에 따른 적정 격자비에 관한 실험

Abstract

The physical properties of the grid, including the CNR and SNR of the image, were measuredin order to properly select the grid ratio, which affects the contrast and quality of an imageand greatly affects the exposure dose of the patient. The following are the conclusions arrived ataccording to the results of the study. The contrast improvement factor (K) increased as the gridratio increased, and the increased amount was highest at 8 : 1. The tube voltage increased up to 80kVp which resulted in maximum contrast improvement factor. Further increase of tube voltagetended to decrease the contrast improvement factor. The selectivity (Σ) increased as the grid ratioincreased, but such tendency slowed down when the ratio was 12 : 1. The selectivity increased asthe tube voltage increased, with the largest volume recorded at 80 kVp, whereas selectivity ratherdecreased when the tube voltage increased further. Bucky factor (B) continued to increase as thegrid ratio increased; however, such increase tendency slowed down from 80 kVp. The exposurefactor decreased as the tube voltage increased. SNR decreased as the grid ratio increased, and itbecame largest at the 6 : 1 grid. It was shown that SNR decreased as the tube voltage increased. CNR increased up to 10 : 1 grid as the grid ratio increased, but it decreased at 12 : 1 grid. It wasshown that there was no effect to the CNR as the tube voltage increased. According to the result ofthe physical evaluation on the conventional theory that the selection of grid depends on tube voltage,the grid ratio was suitable for 8 : 1 or 10 : 1 at all tube voltages. However, it is necessary to carefullydetermine the patients’ exposure dose. For SNR, 6 : 1 is good for all tube voltages but for CNR,10 : 1 is considered good for all tube voltages. Therefore, it is recommended to select a grid in considerationof the tube voltage used and exposure dose of the patients.