X-ray computer tomography apparatus, determines the attenuation correction function appropriate to patient, from measurements on filter and reference materials

摘要

Evaluation unit (22) stores a correction function k(z). For each total attenuation (g), the component patient (14) attenuation (p) is calculated from a function having terms for filter (16) attenuation in respective projection region, location terms and constants. k(z) is determined by combining filter material and reference material to get reference total attenuations at various thicknesses, accounting for beam hardening. From these results an attenuation error function is determined, in terms of error attributable to filter and reference material thickness, and theoretical, individual linear attenuations for these materials. A further intermediate function and its constants are evaluated to determine an attenuation error along a reference curve in the attenuation error characteristic diagram, finally evaluating the correction function k(z).