Patent GB-1263948-A (GB)
Title: Photographic colour scanning apparatus
IPC: G01T1/166
Filed: 1969-04-30
Abstract: 1,263,948. Local viewing. CEDARS OF LEBANON-MT. SINAI HOSPITALS OF THE LOS ANGELES JEWISH MEDICAL CENTER. 30 April, 1969 [21 May, 1968], No. 21995/69. Heading H4F. To produce a chart showing the distribution of radio-active isotopes e.g. in human organs, in a colour code, consecutive Z-pulses of an amplitude corresponding to the radiation intensity and, e.g., of 600 Ás duration and spaced 10,000 Ás apart, are derived from scanning scintillation counters and corresponding light spots of constant intensity and duration, e.g. 600 Ás, are displayed on a cathode-ray tube 18 to be recorded on a colour film in a pack 36 through a wheel 38 which contains one or more contiguous bands of spectrally graded filters, the wheel 38 rotating at a constant speed, e.g. 9400 r.p.m., for two band patterns, such that the band pattern repeats at a greater rate than the incoming Z pulses, and the light spots being produced on the tube 18 at an interval after the start of a band pattern of wheel 38 determined by the amplitude of the Z pulses. In the preferred embodiment, which employs a linear array of ten spaced counters to simultaneously scan ten contiguous zones, each counter supplying one of each set of ten Z-pulses, Graph A, Fig. 3, each pulse is fed via a diode D, to be stored in a capacitor C 1  and also sets a Schmidt trigger 50 via a high-impedance circuit 54. The rate at which the capacitor C 1  discharges through a potentiometer R 1  and a transistor Q 1  determines the time when trigger 50 reverts to its initial state and produces an output pulse which is shaped and applied to the grid 24 of tube 18. To ensure that a linear part of the capacitor C 1  discharge curve is used, and thus that the delay produced at trigger 50 is proportional to the charge on C 1 , the transistor collector is held at a high negative potential. The potentiometer R 1  enables the range of delay produced to be matched with the time taken for one filter band to pass between the tube 18 and pack 36. A further diode D 3  clamps the capacitor C 1  to earth potential in time for the next Z-pulse. To ensure that the whole pulse is held by capacitor C 1  before discharge commences, and to phase the trigger 50 with rotation of the wheel 38, a bi-stable multivibrator 60, Fig. 4 (not shown), requires pulses to be supplied to inputs T 3  and T 4  in that order before it will enable transistor Q 1  to form part of the capacitor discharge path. Thus incoming Z-pulses actuate a monostable multivibrator 66 of pulse length adjustable so as to be greater than the length of a Z-pulse, e.g. 700 Ás. A pulse produced from the trailing edge of this pulse is applied to input T 3 . The wheel 38 includes two holes 73 through which a light source 70 shines intermittently to fall on a photo-cell 72 and produce a pulsed output having a predetermined phase relationship with the filter pattern which is applied to terminal T 4 . The output of circuit 60 is supplied as a pulse, of a length short enough to avoid interference between successive Z pulses, e.g. 6000 Ás, on the base of transistor Q, causing it to conduct. Position synchronism between a filter band and the gating signal from trigger 50 is achieved using the trailing edge of a pulse of adjustable length from a monostable multivibrator 76, while a further adjustable monostable multivibrator 80 acts as an exposure control.