GB1497396A - Radiography - Google Patents

Abstract

1497396 Radiography EMI Ltd 14 March 1975 [23 March 1974 20 April 1974 26 July 1974] 13018/74 17402/74 33033/74 Heading H4F [Also in Division H1] Apparatus for examining a slice of a body by X- or γ-radiation which is of the type described in Specification 1,283,915 in which the body is irradiated with a fan shaped spread 23 of radiation which is detected by a plurality of detectors 10, the radiation source Bu and detectors 10 being orbited around the body so that it is irradiated along a plurality of angular positions and the resulting data from the detectors being processed to derive a reconstruction of the distribution of absorption of radiation within the scanned body slice, wherein the effect of differences between the sensitivities of the different detectors is reduced by displacing the source (from Bu to Bd) relative to the detectors and utilizing the signals derived from a first detector while the source and detectors occupy the two relative positions to predict the value of the output signal which should have been obtained from an adjacent detector, this predicted value being then compared with the value of the output signal actually provided by the adjacent detector and any difference therebetween used to correct said latter output signal. This prediction and comparison is effected along the line of detectors in a progressive manner using the corrected output signals for each detector to predict the output signal from the next adjacent detector. The fan shaped beam 23 may be kept in position Bu for one half of the period over which the detector output signals have previously been integrated (e.g. corresponding to a 1 degree rotation of the fan beam relative to the body) and then moved to position Bd for the remaining half of the period. (Alternatively it is possible to oscillate the position of the source of the fan beam more rapidly so that each position is occupied several times during the increment of angular motion.) Timing pulses separated by a time equivalent to rotation of the source and detectors through ¢ degree are generated photoelectrically by radial lines on a disc 70, and these pulses are used to control the displacement of the source and the passing of the output signals corresponding to each position thereof to respective stores. The corrected values are calculated from these stored signals and the resulting corrected outputs processed in accordance with a convolution technique according for example to that described in Specification 1,471,531. An X-ray tube arrangement in which the exciting electron beam is deflected to thereby provide the alternation of relative positions of the source and detectors is described (see Division H1).