双丝像质计（双线型像质计/ 双线型IQI），根据ISO19232-5/EN462-5/ASTM  E2002标准生产，ISO19232-5/  EN462-5/ASTM  E2002  双丝像质计（双线型像质计，双线型IQI）是由放置于刚性半透明塑料盒中的13个线对组成，双丝像质计丝的直径与丝与丝之间的距离相等，每个线对包含两条圆形截面的线。1D至3D线对是金属钨，其它线对是金属铂。双丝像质计（双线型像质计，双线型IQI）用于确定射线照相和实时射线透照系统的几何不清晰度。

          双丝像质计（双线型像质计，双线型IQI）应与线型或孔型像质计一用。双丝像质计应置于被检物体的源侧，并且应尽可能地靠近射线束轴线与轴线垂直。应借助4倍放大镜观察双丝像质计影像。zui大线对，其影像正好是两双线间距可以识别极限下的两独立线过渡到单线的影像，此时被认为是可辨别的极限值。图像不清晰度U可由2d表示，其中d是线的宽度和线的间隔距离（见下表）。
丝的代号          几何不清晰度U（mm）          丝的直径d（mm）
      13D                          0.10                                      0.050
      12D                          0.13                                      0.063
      11D                          0.16                                      0.080
      10D                          0.20                                      0.100
        9D                          0.26                                      0.130
        8D                          0.32                                      0.160
        7D                          0.40                                      0.200
        6D                          0.50                                      0.250
        5D                          0.64                                      0.320
        4D                          0.80                                      0.400
        3D                          1.00                                      0.500
        2D                          1.26                                      0.630
        1D                          1.60                                      0.800