Droege R T, Bjärngard B E
Med Phys. 1979 Nov-Dec;6(6):487-93. doi: 10.1118/1.594610.
The radiographic contrast of metal screen-film detectors was investigated in order to determine the contrast capabilities of these detectors applied to megavoltage x-ray imaging. The film contrast gamma was found to be independent of the metal screen composition. Measurement of the scatter-to-primary film dose ratio in contact geometry demonstrated that a thick front screen of either 1.5 g/cm2 copper of 2.5 g/cm2 lead provides optimum contrast for the photon energies studied (60Co and 4- and 8-MV x rays). The same thickness were also found to be suitable in an air gap geometry which significantly improved the contrast compared to the contact geometry. Rear lead screens were found to provide no contrast improvement.
为了确定应用于兆伏级X射线成像的金属增感屏-胶片探测器的对比度能力，对其射线照相对比度进行了研究。发现胶片对比度γ与金属增感屏的成分无关。在接触几何条件下对散射与一次胶片剂量比的测量表明，对于所研究的光子能量（60Co以及4兆伏和8兆伏的X射线），1.5克/平方厘米的铜或2.5克/平方厘米的铅制成的厚前屏能提供最佳对比度。还发现相同的厚度在气隙几何条件下也适用，与接触几何条件相比，气隙几何条件显著提高了对比度。发现后置铅屏并不能提高对比度。
