| 摘要 |
1509528 Radiographic apparatus EMI Ltd 23 May 1975 [7 June 1974] 25361/74 Heading H4F Radiological apparatus comprises a source 19 (of X or gamma rays) for irradiating a body 3 along a plurality of coplanar paths, detector means 25 for detecting the amount of radiation emergence along each path and emitting a signal indicative thereof, attenuator means 11, 12 which substantially equalize the absorption of radiation along different paths, the material of the attenuators being such (e.g. Al, B, Cu) as to shift the radiation spectrum by an amount dependent on the thickness of attenuator in each path, and means to operate on the output signals to compensate for variations in the amount of detected radiation due to the change in the spectrum. As described, body 3 is surrounded by a water sack 10 and held in frame 8 1 , 8 2 . The source 19, which produces a pencil beam or a fan-shaped swath, is mounted on belt 16 driven by motor 15 and is coupled through arm 24 to drive detector 25 in synchronism. After each run of the source along the track, disc 1 (on which everything but the clamped body is mounted) is rotated by motor 5 and drive wheel 6 through an angle corresponding to the angle of the swath 20, i.e. 10 degrees until the body has been scanned through over 180 degrees. Counterweight 22 is provided on belt 16 to counteract the effect of the mass of source 19. The output from the detector is operated on by the circuit of Fig. 3 wherein stores 36r, 40r, contain path variation a r and differential hardness b r weighting factors respectively-the latter compensating for the change in spectrum due to the material of the attenuators. These factors may respectively be determined empirically by scanning firstly with hole 2 filled with water and secondly by replacing body 3 with a bar of known size of the attenuating material. Alternatively the absorption factors may be determined mathematically assuming a knowledge of the absorption factors of the materials involved, including the nature of body 3.
|
