[Separate measurements of compact and spongy bone density using a transverse rotation scanner. Determination of mineral content of the radius using a least squares algorithm].

The absorption profile of the distal forearm, which depends on bone mineralisation, was measured using a high resolution microcomputer-controlled transverse rotational scanner with a tightly collimated I-125 photon source and a scintillation counter. Reconstruction of the anatomical structures within the measured area occurred in two stages. Subsequently the linear attenuation coefficient for soft tissues, compacta and spongiosa was obtained by a "least-square" algorithm. The absorption coefficient of the compacta and spongiosa provided a measure of bone mineralisation. Correlation between the reconstructed images and the calculated results and measurements was tested by calculation. Ten measurements of a model and of in vivo bones resulted in a coefficient of variation of 1.8% and 3.3% for the compacta and 2.5% and 3.8% for the spongiosa. Relative deviation from the standard varied from +1.3% to -1.0%, depending on mineral content. This new, technically simple procedure for the separate determination of the compacta and spongiosa in the distal radius is useful for the early recognition of changes in bone mineralisation which are usually apparent first in the spongiosa.