[en] This patent describes a calibration phantom for a quantitative computerized tomography (QCT) system of bone mineral measurement in which a series of graduated reference samples having x-ray attenuation characteristics closely proximate to human tissue are retained within cavities integral with the material forming the phantom base and wherein the cavities are located closely proximate the upper and lower surfaces of the phantom so as to reduce the size and mass of the phantom and thus reduce x-ray base hardening, scatter and image artifacts. It comprises: a base formed of a material having x-ray attenuation properties with a CT number closely approximate to human tissue; elongated cavities formed in the base, so that the upper and lower surfaces of the base are closely proximate the cavities with a thickness of less than one cm of base material between the upper surface and lower surface of the base and the cavities; a series of graduated concentrations of reference samples having x-ray attenuation characteristics corresponding to human bone retained within the cavities such that the samples are indirect contact with the base material; and a closure which seals the cavity to encapsulate the samples within the cavity