Abstract: In a CT scanner system electrical signals are provided for radiation paths in a fan-shaped distribution through a region of interest of the patient. The signals are processed and further signals derived therefrom are mapped onto elements of a matrix defined in the region by being summed in storage locations corresponding to the elements. The mapping includes weighting by a factor related to the angle of the respective beam in the fan, the factor being different for each matrix element. To achieve more efficient use of the circuits handling the signals it is proposed to stretch the signals onto a line parallel to lines of matrix elements applying an angular part of the weighting common to all of the rows and leaving a straightforward stepping through the signals to be followed as they are allocated to the storage locations.