| 摘要 |
A pair of separated semi-radio opaque sheets having a similar target pattern removed therefrom are placed in parallel alignment with the targets in perpendicular alignment. When exposed to an X-ray beam of a diagnostic X-ray machine, the targets produce a pattern in the radiograph in which the two targets are superimposed in slight misalignment except where the X-ray beam is perpendicular, thereby locating the perpendicular X-ray beam position with respect to the collimator jaws and visual target of the machine.
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