| abstract |
The apparatus according to the invention comprises an x-ray image intensifier of the near plan type (18) for detecting a fan beam of x-rays (8) and for producing an intensified output of the x-ray. an image of light visible on a projection screen (26) of the output which is detected by a searchable linear array of integrated circuit diode detectors (38, 42). In a first embodiment, a pair of side-by-side networks (38, 42) are used to eliminate the effects of the center spot in the projection screen. One of the linear networks (38) looks towards the line signal (32) on the output screen (26) and the second linear network (42) looks towards a point on the output screen (26) which is adjacent and parallel to the line signal. A clear signal is derived by subtracting the signals from adjacent elements (Fig. 3) of the two parallel arrays (38, 42) such that the signal spot in the image intensifier tube is removed. In a second embodiment, the stain of the projection screen is removed by covering the vacuum side of the projection screen (26) with a metallic layer (90) having a thickness sufficient to dissipate one third of the thickness. kinetic energy of photoelectrons passing through it. |