Radiography

Claim 1

Radiographic apparatus including means for projecting radiation through a slice of a body along a plurality of sets of beam paths, each set of paths being oriented at a respective angle or mean angle in the slice, detector means for detecting the radiation emergent from the body along each path and processing means for processing output signals derived from said detector means and indicative of the absorption suffered by the radiation on traversing each of said paths to evaluate the absorption coefficient, with respect to said radiation, at each of a plurality of locations distributed over a predetermined region of said slice, the apparatus being adapted so that some of said sets, hereinafter termed "extended sets", include more paths than others of said sets; the extended sets being regularly interspersed in angle, or mean angle, with the said other sets and the extra paths in said extended sets traversing a zone of said slice which surrounds said region; the processing means being adapted to utilize the output signals indicative of the absorption suffered by the radiation on traversing said extra paths not only in association with the respective ones of said extended sets in which the extra paths are included but also in association with those of said other sets disposed at less than a given angle, or mean angle to said extended sets to compensate said evaluation for errors introduced by the passage of said radiation through said zone along paths which also traverse said region.