Finding and synthesizing a lost projection

A basic problem in diagnostic radiology is to decide from X-ray pictures if anatomic changes have occurred in the patient. When comparing the present pictures with similar pictures from a previous X-ray examination difficulties arise because even without any anatomic changes there may be differences in projection. The directions of projection are not likely to be identical for the two pictures. The authors have designed a method to overcome this problem. This method is based on matching a predetermined set of projections f_n(x₀, y₀) n=1,2,. . ., k, taken at a later occasion, against f₀(x₀, y₀), a picture taken at a previous occasion. All matching is done in the Fourier domain. When the matching is done one synthesizes the picture f _r(x₀, y₀), which is identical in projection with f₀(x₀, y₀)