GB1481785A - Radiography - Google Patents

Abstract

1481785 Radiography EMI Ltd 5 Sept 1974 [9 June 1973] 27569/73 Heading H4F A data processing arrangement for providing quickly a visual representation of a planar section through a body from absorption signals generated by X- or γ-ray scanning apparatus 1 of the type described in Specification 1,283,915, wherein the sets of absorption value signals f(r,#), each set corresponding to a different value of # (Fig. 1, not shown), are passed to a store 2 where they are held until required by a fast Fourier transform computer 3 which effects a one dimensional Fourier transform thereon with respect to the variable r (in any one set the values of r are selected so that the beam positions of the set are equally spaced). The resulting transform signals which are functionally related to two variables (# and #, Fig. 3, not shown) are then applied to modulate a faster scan of a photochromic tube 4 of the type disclosed in Specification 1,382,993, the cathodo-chromic crystal target of which is uniformly exposed to coherent radiation from a laser 5 and the resulting modulated radiation is incident via a lens 7 on a television type camera tube 8, the lens 7 having equal focal distances f and being a distance f from both tubes 4 and 8. Thus the pattern of radiation intensity incident upon the target of camera tube 8 is the two-dimensional Fourier transform of the pattern of radiation intensity emergent from the photochromic target of tube 4. The resulting video output of camera tube 8 may be displayed, stored on magnetic tape, or fed to a print-out machine. If desired camera tube 8 may be replaced by a photographic plate or a viewing screen for direct image viewing. The fast Fourier transform computer 3 may be replaced by optical apparatus serving the same end and following the principles of transformation performed by lens 7 although in this case transforming with respect to a single variable of transformation only and not two. A second embodiment based on the so-called layergram procedure is described with reference to Fig. 4 in which for each small region (element) of the body a signal is derived 20 which is related to the average of the absorptions signals of all the beams passing therethrough. These layergram signals are generated in synchronism with the sanning of a photochromic tube 21 which is illuminated by laser 22, the resulting Fourier transform of the pattern of light emergent from tube 21 being televised 25. The resulting signal is multiplied 24 by a factor K (see Specification) and applied to a second photochromic tube 25<SP>1</SP> illuminated by a laser 26, a signal representative of the absorption function being produced by a camera tube 28. An optical filter may be associated with the second photochromic tube instead of using multiplier 24.