The application of dual energy subtraction technique to sialography

(1)图像处理系统的升级图像处理计算机增加了随机存储器和磁性光盘单元。提高了图像文件存储的处理速度和容量。该软件系统采用双能量减法对骨骼图像进行抑制。包括x光片输入扫描在内的所有减法程序在10分钟内完成。(2)优化模拟通过计算机模拟对x射线滤光材料、管电位和强化筛的最佳选择进行了探索，发现钆或钨复合材料用于重铬化x射线滤光片，Gd_2O_2S和CaWO_4复合材料用于筛光片，铜或锡复合材料用于盒式滤光片，10ookvcp复合材料用于管电位具有较高的性能。(3)幻影实验用不同直径的聚乙烯管填充造影剂和骨幻影楔和水浴制成幻影。在该方法生成的这些幻影图像中，识别出了厚度大于0.5mm的造影剂代码。然而，观察到造影剂对比度的显著降低和噪声的增加。(4)讨论从理论上证明，碘造影剂的降低是由于骨与碘之间衰减系数的能量依赖性相似。噪声的增加是由膜屏系统粒度的统计加性引起的。特别是高速筛分产生的高能量图像中的噪声，在铜/锡滤波器后面放大了4或5倍。因此，目前的双能量减法技术不适合提高唾液造影的图像质量。

(1) Grade up of the image processing systemRandom access memories and a magnetic optical disk unit were added to the image processing computer. The processing speed and capacity of image file storage were advanced. The soft ware system for the dual energy subtraction to suppress the bone image. It took within 10 minutes to process all the procedure for subtraction including input scan of x-ray film.(2) Simulation for optimizationThe optimum selection of x-ray filter materials, tube potential and intensifying screen was searched for by means of computer simulation, and found that the combination of gadrinium or tungsten for dichromizing x-ray filter, Gd_2O_2S and CaWO_4 for the screen and copper or tin for in-cassette-filter and 1OOkVcp for tube potential were expected to have high performance.(3) Phantom experimentPhantoms were made of polyethyrene tube of various diameter filled with contrast agents and bone phantom wedge and a water bath. In the images of these phantoms produced by this method, codes of contrast media thicker than 0.5mm were recognized. The remarkable reduction of contrast of the contrast media and increment of the noise were, however, observed.(4) DiscussionIt was theoretically proved that reduction of the iodine contrast was due to the similarity of the energy dependency of attenuation coefficient among the bone and the iodine. The increment of the noise was caused by the statistically additive nature of the granuality of the film-screen systems. Especially, the noise in the high edergy image, which was produced by high speed screen place behind the copper/tin filter, magnified by factor 4 or 5. It was concluded, therefore, that the present dual energy subtraction technique was not suitable for improvement of image quality of the sialography.