Study of a New Source for Dual Proton Absorptiometry of the Lumbar Spine

Abstract

Bone disease and metabolic bone disorders are characterized by decrease in bone mineral content (BMC) and the vertebrae are primarily affected in osteoporosis. Thus it is essential to monitor changes in BMC due to disease, growth or therapy. Dual photon absorptiometry (DPA) is as yet the most efficient method for BMC determination in the lumbar vertebrae; most previous investigators have used ¹⁵³Gd which is generally accepted as possessing the ideal dual photon energy combination. Davis and Webber (1978) developed a method for routine production of ¹⁵³Sm which emits photons of nearly the same energy as ¹⁵³Gd and suggested its use in DPA. In the present study using ¹⁵³Sm, measurements with aluminum standards immersed in water resulted in errors of 4% and 4.5% in accuracy and precision respectively for mass of Al in the range 0.4-1.8 g.cm⁻². These results were obtained using different volumes of water, verifying that bone mineral mass determined by this method is independent of soft tissue content. Experiments with bone mineral phantoms gave values which correlated highly (r=0.97) with results obtained on a commercially available clinical densitometer using ¹²⁵I. Considering that these results are comparable with those obtained earlier using ¹⁵³Gd, that ¹⁵³Gd is scarcely available and several hundred times the cost, ¹⁵³Sm promises to be the potential source for routine clinical measurement of osteopenia in the lumbar spine by DPA. However, further invitro and invivo studies are necessary before it can be used regularly in nuclear medicine departments.