Changes in the Linear Attenuation Coefficient of Canine Appendicular Bone Following Intravenous Infusion of Strontium Lactate, Measured Using Gamma-Ray Computed Tomography

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (γ-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3–4.7 g of Sr over a period of 110–160 minutes into 20-kg dogs resulted, within 6–8 hours, in an increase of 0.019–0.045 cm ^-1 (P<0.002) in the LAC. Calibration of the γ-CT system showed that 0.44 mg/cm ³ of Sr produced a change of 0.01 cm ^-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using γ-CT.