Studies in selected grid ratio of objective thickness on X-ray exposure
X-線은 被寫體를 透過할 때에 散亂線이 發生되고 이 散亂線은 寫眞의 fog를 增加시켜 선예도와 대조도에 영향을 미치게 한다. 즉, 散亂線을 除去시키는 것은 contrast를 向上시키고 X-線상의 畵質을 改善시키는데 있으며 그 方法으로서는 格子法과 Air Gap Techniq
ue法이 있다. 그 중에서 格子法은 그 效能이 좋고 다루기가 용이하므로 現在 많이 利用되고 있으며 ICRU와 JIS에 의해서도 좋은 方法으로 인정되어 권장 되여지고 있다.
저자는 患者대신 인체조직 등가물질인 acryl-phantom을 使用하여 散亂線을 除去할 目的으로 여러 종류의 格子를 使用하여 實驗하였다.
格子比에 따르는 X-線 透過度의 實驗結果는 다음과 같다.
1) 直接 X-線 透過率은 격자비가 증가할수록 減少되었고 管電壓과 phantom 두께에 따른 變化는 큰 差異가 없었다.
2) 散亂線 含有率은 被寫體 增加에 따라 增加되었고 격자 使用時 管電壓 上昇과 함께 약간 增加하나 格子가 없을 때는 별 영향이 없었다.
3) 一次線과 二次線 透過率의 比는 格子比 增加와 함께 增加하였으나 被寫體두께에 따라서는 減少하고 管電壓이 上昇하면 약간 減少되었다.
4) acryl-phantom 10-15㎝에 해당하는 곳의 X-線 撮影時는 5:1 格子를 使用하고 25㎝ acryl-phantom 두께에는 10:1 格子를 使用함이 適合하다.
When unattenuated X-ray radiation passes through the object it is transmitted and scattered from objects and impinging on the film, During this process certain radiation is absorbed within the object and others transmitted in reduced scattering.
The scattering radiation influence upon radiation image quality, confining X-ray beam which means scattering radiation produce increased fog on X-ray film image and as a consequence decrease contrast and less detail of the film there for the
elimination of fog and for absorbing scattered radiation, the girl has been used between the object and the film in order to rid of scattering rays.
Using grid is good method for the qualification of the better image as well as in using air gap technique. The grid is easy to manipulate and promote good efficiency which is defined by ICRU and JIS.
It is the purpose to study for elimination scattered radiation from the tissue equivalent acryl phantom using grid, we have studied and evaluated the grid permeability about the X-ray exposure, the selection of grid ratio according to phantom thickness, on X-ray exposure are performed as follows.
1) The penetrating ratio of primary X-ray is remarkably decreased by increasing of the grid ratio, but it is almost not influenced in KVP difference and phantom thickness.
2) The scattered radiation is proportionaly increased by thickness of the phantom, having nothing to do with grid ratios.
3) The relative between the penetrition rate of primary and secondary X-ray is improved by increasing grid ratio, and decreased by phantom thickness, and slightly decreased by high tube voltage.
4) The grid of 5:1 and 10:1 ratio are adequate to the phantom of 10 cm and 15 cm thickness, respectively.