Patent US 4,189,775

An apparatus and method for tomographic analysis comprising a detecting system for detecting a number of radiation beams having penetrated a sectional area of a subject and producing projection data signals; a CPU and a memory for applying a filter function to the projection data signals by a convolution integration or by a computational technique included in a filtered-back projection, thereby calculating modified projection data signals, and conducting back projection operations only with respect to points in a partial region or subsection of the sectional portion area by means of the modified projection data, thereby calculating the radiation beam absorption coefficients at said points, the integral operation used in the calculation of the modified projection data signals being limited to an interval in which the quality of an image of said partial region or subsection to be displayed can exclusively be improved by the filter function; and a display unit for displaying the image of the partial region on the basis of said absorption coefficients.