A method is disclosed in which projection images of a certain cross-section of an object are produced through irradiation from various directions to the cross-section, and a three-dimensional image of the cross-section is reconstructed from the projection images. A convolution integral operation is performed on the projection images by means of a weighting function obtained from a function whose second differentiation is positive in at least a predetermined range of a spacial frequency domain and which has a positive first-differential coefficient at a point where the spacial frequency is equal to zero.

Computerized axial tomographic apparatus provides sets of "edge readings" which relate to the absorption suffered by penetrative radiation on traversing respective paths through a part of interest in a body, the various paths being coplanar. These edge readings are processed to permit the evaluation of the absorption coefficients at a plurality of locations distributed over the part of the body in the irradiated plane. In accordance with the invention the necessity for such processing to involve large scale multiplication is overcome by employing a processing technique which utilizes Walsh functions.

In a computed tomography system using radiation, a large number of radiation beams are projected into a selected slice-like sectional portion of a subject to be reconstructed, in various directions. A profile of measured projection data is obtained from the radiation beams penetrated in parallel at each given angular interval. The profile of measured projection data thus obtained is subjected to a filtering operation to produce profiles of first modified projection data. The profile of modified projection data is recasted at properly selected intervals to produce second modified projection data. This results in a remarkable reduction of the amount of weight coefficients required in an interpolation to calculate the modified projection data for a large number of picture elements defined in matrix fashion on the sectional portion.

The data derived from a computerized axial tomographic apparatus in respect of a number of slices through a body are processed to produce a representation of the variation of absorption of X-rays over each slice. The representations are operated upon individually to identify areas which are of reduced interest and/or which are obscuring regions of especial interest. This having been done, the representations for all the slices are correlated to produce a pseudo three-dimensional display of part of the body with the identified areas being displayed with reduced or zero intensity as compared with other areas. Alternatively, the identified and other areas can be represented in different colors.

A method and apparatus for examining relative movement of two masses of different radiation attenuation characteristics, separated by a boundary and moving relative to one another over a repetitive motion cycle. The masses are examined from a plurality of successive angles about a common center of rotation. The object is scanned over each motion cycle from each of these angles to derive a plurality of attenuation coefficients encompassing the entire motion cycle. A plurality of differential points is calculated between adjacent scans of a single motion cycle, and a single composite image of all of these differential points is reconstructed for each individual time period of each motion cycle for display.