GB1184304A - Tomographic Radioactivity Scanner with Simultaneous Readout of Several Planes - Google Patents

Abstract

1,184,304. Detecting position of radiation sources; tomographic apparatus. H.O. ANGER. 6 June, 1968 [15 June, 1967], No. 26947/68. Headings H4D and H5R. The Specification describes a tomographic scanner, whereby an object 13, Fig. 1, containing radiating sources 66, 67, 68, Fig. 3, is scanned to determine the positions of said sources in predetermined depth planes A, B, C, D, E. The image probe 43 fixed to frame 28 is moved in a raster scan by means of line scan motors 32 and 33 controlling the movement of platform 28 on wheels 29 (Fig. 2, not shown) and frame scan motor 24, Fig. 2, controlling the movement of platform 17. The image probe 43 comprises, Fig. 3, a scintillation crystal 61 and plurality of photo-tubes 65, the outputs from which indicate the area of the crystal in which a scintillation occurs. A collimator arrangement 63 is provided comprising a plurality of coaxial cones defining a plurality of conical passages, whereby radiation from source 66, at the " focus " 64 of the collimator, passes to all parts of the crystal, whilst that from a source 67 causes a scintillation at the left-hand edge of the crystal, which, for movement of the probe from right to left, moves to the light-hand edge of the crystal at a speed inversely proportional to the distance of plane A from " focus " plane C. Radiation from source 68 on the other hand will similarly cause a scintillation which moves from the right to the left-hand edge of the crystal, i.e. in the opposite direction. The outputs of the photo-tubes are fed to a cathode-ray tube 46, whereby a spot appears on its screen representing the position of the scintillation in the crystal 61. The variation of the cathode ray tube display as the probe scans across 66, 67 and 68, is shown in Fig. 5. The display is focused on areas 73a, 73b, 73d and 73e of a sheet of photographic paper 73, Fig. 4, by means of respective lens 89, 91, 96 and 98 and light from said display falls directly on area 73c through aperture 93. The final images on the five areas 73a, 73b, 73c, 73d, 73e will represent the position of the sources within the five respective planes A. B, C, D, E. Paper 73 is mounted on a platform, which by means of a servo control system describes a scanning motion synchronous with that of the probe 43. The focal length of lens 89 and the scanning speed of the paper is such that the left to right motion 72 of image 67c, Fig. 6, on the cathode-ray tube screen 71, when reversed by the lens to a right to left motion is matched by the right to left motion of the paper, and a concentrated " focused " spot image appears on the paper. The whole screen image 101 of source 66 is only momentary and does not affect the paper, whilst the motion of image 68c when projected on to the paper is against the paper motion and so produces a dispersed "unfocused " image. By means of inverter 97, Iens 98 produces " focused " image of image 68c and an " unfocused " image of image 67c. The whole screen image 101 causes a " focused " image on area 73c through aperture 93. Fig. 7 shows the developed appearance of the five areas of the paper. The output of the phototubes may be fed to a computer and storage device 111, whereby position data of the sources may be derived, or a read-out display on a pen recorder may be provided.