Patent GB-1211122-A (GB)
Title: Scintillation scanning of radioactive isotopes
IPC: G01T1/166
Filed: 1968-08-15
Abstract: 1,211,122. Television; coloured radiographs; transistor switching circuits. PICKER CORP. 15 Aug., 1968 [15 Aug., 1967], No. 39139/68. Headings H3T, H4F and H5R. In a device for scintillation scanning of a radio-active isotope, a multi-coloured photographic record is produced by detecting the intensity of radiation from the isotope and assigning a different colour to each of a number of ranges of the intensity. A scintillation probe 10, Fig. 1, scans the subject and provides a pulse output at a rate indicative of the radiation intensity. These pulses are amplified at 12 and passed to a multivibrator 16, a ratemeter 14, and a stylus which produces a graphic image on a sheet of paper in a known manner. Rate meter 14 provides an output whose amplitude varies according to the pulse rate from 12 which is passed to a normalizing amplifier 54 whose function is to provide an output within a predetermined amplitude range, whatever the input amplitude range. The output from amplifier 54 is passed to three level discriminators 58, 60 and 62, each of which pass a signal only when the input amplitude is within certain predetermined limits. A contrast enhancement control 56 is provided which alters the levels at which the dsicriminators 58, 60, 62 operate in order to alter the range of radiation intensity being studied. Signals from the discriminators are passed to AND gates 64, 66 and 68 which are switched by pulses from a derandomizer 70 (to be described later) which are in accordance with the pulses from probe 10. These signals activate light sources 74, 76 and 78, the light outputs of which are fed through colour filters 80, 82 and 84 and along light guides 86, 88 and 90 to a collimator 92 which is mechanically attached to probe 10. The light passes through an aperture 92a in the collimator and impinges on a sheet 94 of colour sensitive photographic film. The derandomizer 70 comprises logic to ensure that no overlapping of pulses from multivibrator 16 occurs. This would cause dark spots in the coloured image on film 94. Apparatus for producing a record on a black and white film 52 using a cathode ray tube 30 mechanically connected to probe 10 is also shown in Fig. 1. The output from rate meter 14 is passed to a variable gain amplifier 24 which has the same purpose as amplifier 54, and is then used to control a power supply 26 which has its output connected to the accelerating electrode 28 of tube 30. The control grid 40 of this tube is supplied by pulses from multivibrator 16. The apparatus for producing a black and white record is described in detail in U.S. Specification 3,159,744. Figs. 2 to 5 show circuit diagrams of the amplifier 54, the discriminators 58, 60, 62 and gates 64, 66, 68, and the derandomizer 70. In Fig. 2 units 58, 60 and 62 are amplitude level discriminator swhich switched on light the sources 74, 76 and 78 (Fig. 1) through gates 64, 66 and 68 when the signal input to the level discriminators is between certain predetermined limits. In the described embodiment discriminator 62 is operative from 0-17% and 67-100% of the input amplitude, discriminator 60 for 34-38% and discriminator 58 for 0- 50%. The gates also have pulse inputs at terminals 146, 220 and 298, said gates switching on the light sources only when the amplitude level is correct and when a pulse is received. Transistors 126, 196 and 274 conduct only if two conditions are satisfied: they have each received a signal from the appropriate level discriminator, and the transistors 128, 198, and 276 respectively are conducting. These latter transistors conduct only when they receive a pulse from terminals 146, 220 and 298. The light source 74, for example, is energized when transistors 126 and 128 conduct providing a path from a - 24 V supply to terminal 142 and through to a positive voltage + V at terminal 145. In Fig. 4, a variable gain direct-coupled amplifier is shown which has amplitude limiting to provide a predetermined output range at terminal 326 whatever the input range at terminal 300. Potentiometers 312 and 320 adjust the two limits while variable resistor 308 alters the amplifier gain. In Fig. 5, logic circuits are shown which operate to ensure that pulses (possibly overlapping) which arrive at terminal 350 are not overlapping at the output terminal 362. The NAND gate 352 is closed after a pulse has passed through it by a signal from a single-shot multivibrator 364. This gate remains closed until the signal from multivibrator 364 returns to zero potential. This will occur after a time determined by the setting of a speed control 72 (Fig. 3, not shown) which alters the width of the output pulses from the multivibrator to achieve the desired effect.