X-ray examination apparatus having a stray radiation grid with anti-vignetting effect

Claim 1

In an X-ray examination apparatus of the type comprising: X-ray source means which produce a divergent beam of X-rays which are directed through an object to be examined wherein the intensity of the X-ray beam which has passed through the object decreases as a function of distance from a centerline of the beam as a result of vignetting; X-ray detecting means disposed in the beam of radiation which has passed through the object which produce an image therefrom; a stray radiation grid disposed in the radiation beam between the object and the detecting means to reduce the intensity of secondary radiation incident upon the detector means, said grid comprising a plurality of absorbing regions which substantially absorb primary radiation in the radiation beam and a plurality of transmitting regions which transmit primary radiation in the radiation beam without substantial absorption; wherein, as an improvement the local ratio of the area of said transmitting regions to the area of said absorbing regions on the stray radiation grid increases as a function of distance from a nominal center of the beam to the edges of the grid in proportion to the intensity decrease resulting from vignetting, whereby the effects of vignetting are mitigated.

Claim 6

The apparatus of claims 1, 2, 3 or 4 wherein the detecting means comprise an X-ray image intensifier tube having a curved input window and wherein the grid is curved in conformance with the window and is mounted against the window.