Evaluation and Development of an In-vivo Bone Densitometer

Archer-Hall et al, 1973, have described an in-vivo bone densitometer (scanning machine) which employs a conventional X-ray set and has many merits. The scanning machine was designed to give a scan of the ulna. The work described in this thesis is a continuation of this work. Various improvements have been made on the machine to make it more accurate and reproducible in clinical use. An artificial bone reference material has been made which is homogeneous, machinable and has attenuation coefficients similar to a real compact bone. It serves to calibrate the output signals in scanning measurements. An optical transform system has been designed to give a linear area representation of the quantity of bone mineral shown non— linearly on the trace. The total mineral in a scanned bone section can be determined by the use of a planimeter on this area transform. In a series of an in-vitro measurements on post mortem ulnar sections, good correlations were found between the scan areas and the following weights: total bone, dry fat-free bone and ash. The scan areas were also correlated to calcium content of the bone as found by neutron activation. The effect of arm repositioning errors on scans were also studied. Measurements have been made using the scanning machine in-vivo, on volunteers and in several cases involving metabolic bone diseases.