| 摘要 |
PROBLEM TO BE SOLVED: To prevent or reduce the unnecessary exposure of a subject to X rays in the transition period for the energy shift in a bone density measuring apparatus for measuring the bone density by applying high-energy X rays and low-energy X rays alternately to the subject. SOLUTION: The period t1 in a gate signal (A) is the measuring time and the period t2 is the non-measuring time. The application voltage of an X-ray generator varies in the period t2 as indicated in (B). In the method of this embodiment as indicated in (D), a shield member is inserted on an X-ray beam path in the period t2, by which the exposure of the subject can be reduced. Accordingly, a rotating filter plate or a rotating filter drum can be used as a filter unit. COPYRIGHT: (C)2007,JPO&INPIT
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