Using 24 steps aluminum ladder mimiced the small mammary gland and radiography was taken with various parameters and different imaging plate ( IP) shading ways, then processed and printed, after that it was measured by density instrument. 用24阶铝梯模拟小乳腺,用不同的投照参数以及不同方法遮挡成像板(IP)直接曝光区进行投照,再用CR系统处理并直接打印出胶片,然后用密度仪分别测量。