In vivo bone mineral measurement by microbeam x-ray and its clinical application

The evaluation of bone mineral content has qualitatively been made by use of skeletal radiography. Even when the film density has been calibrated by an aluminium step, the estimated bone mineral content has hardly been treated as fully quantitative. The purpose of this study is to establish and evaluate the technique of determining quantitatively bone mineral content of diseased bones, with the use of the unique X-ray scanner system specifically designed and developed for this purpose in Chiba University Hospital. The System generates pinhole-collimated microbeam X-rays which traverse the patient's body either in a single-pass mode or in multipass scanning mode. A large sodium iodide crystal sequentially detects microbeams and produces digitalized signals which are accumulated in a computer. The data on tissue absorption of X-ray beams is processed later, and single-pass absorption curves or multipass scanning images are displayed on CRT. Bone mineral content of the selected portion of patient's body is calculated by the same computer. The system resolution in terms of the value of bone mineral content was 0.05 g/cm2. The method reduced radiation dose to patients by order of hundredth compared with conventional X-ray film method and proved efficient enough for measuring bone mineral content not only in the generalized bone diseases but also in the localized ones. (author)