Estimation of mineral concentration in bone samples by backscattering of beta-rays

The method of using backscattered β-rays for the determination of density is used for the first time to measure the mineral concentration in specimens of bone and its usefulness as an aid in the diagnosis of osteopathies is investigated. The reliability of the technique is studied on the basis of methodical examinations employing model substances that are similar in composition to bone. For the geometry chosen for the measureing set-up, a calibration is carried out both for the determination of the effective atomic number and for the mineral concentration of measuring samples. The axial-symmetrical arrangement chose, permits the determination of the concentration to an accuracy of max. +-1% standard deviation. In agreement with computed deviations experiments confirm that with this set-up there is no dependence of the backscatter on sample density. After appropriate calibration, both mineral concentration and density can be measured in two suitable fixed positions of the beta source, sample and detector. The figure for mineral concentration calculated from the backscattering rates are compared with corresponding figure obtained with analytical chemical determinations. It can be seen that two methods have a high degree of agreement. The backscatter method seems to have the advantage of simplicity of the set-up that provides accurate results in thin specimens having a diameter of only 10 mm. With repect to measurements in bone, however, the method is limited to biopsy specimens obtained from compact bone. In such samples, however, both the absolute figure for mineral concentration can be determined and also its local variation in large parts of the skeleton examined. From the mineral concentration and density, the mineral content of the bone substance is computed; this provides differential diagnostic information on osteopathic conditions. (orig.)