Application of XRF to Measure Strontium in Human Bone In Vivo

Strontium appears in the earth's crust at a concentration of about 400 ppm and in sea water about 8,1 ppm. Consequently, all living forms have evolved in the presence of this alkaline earth and have incorporated it in their tissues. The exact role of Sr in the human body remains ambiguous (1), even though Sr has been extensively studied with reference to the radiation hazard from 90Sr (2).

Metabolic behavior of Sr, in some aspects, is similar to that of Ca (3), but substantial dissimilarities between these two are also well recognized (1,4). It has been suggested that Sr stimulates the formation of bone matrix. At higher concentrations, however, it interferes with calcification mechanism of the bone matrix (5).

Absorption of strontium from the gastrointestinal tract into plasma in healthy human adults

The radioactive isotopes of strontium have always been a major concern in radiation protection. Currently, radiostrontium is of interest for evaluation of the health effects of the Chernobyl accident and for epidemiological studies in populations exposed to releases from the Mayak nuclear facilities in Russia. Ingestion is one of the most important exposure pathways involving radioactive strontium. The main sources of published data on the fraction of the ingested strontium that is transferred to plasma (f1) are summarized. For some of these studies, the original data had to be reanalyzed and a new iterative method to account for the elimination in feces of strontium of endogenous origin (i.e., that was absorbed to blood and has already been returned into feces) was employed. Data indicate no significant dependence of the absorbed fraction on sex or age at exposure within the adult group, but absorption of strontium is reduced if the intake of stable calcium is very high and is enhanced if the intake of calcium is very low. The probability distribution function of f1 values is well represented by a lognormal curve with a geometric mean of 22.3% and a geometric standard deviation of 1.44 (95% confidence interval 10.9% to 45.6%, or about a factor of 2 around the geometric mean). This distribution can be considered representative for the variability of the f1 values in a population of healthy adults.

Simultaneous measurements of twenty-four-hour whole-body retention of 47Ca-chloride and 99mTc-MDP: early differentiation of metabolic bone diseases in rat models

The 24-h whole-body retention (24-h WBR) of 47Ca-chloride and 99mTc-MDP was measured in four rat models over a 6-week period at 2 week intervals. Fine detail bone radiographs of the femurs and histologic bone specimens were also obtained simultaneously. In the osteomalacic (M) and steroid-induced osteoporotic (S) groups the 24-h WBR values of 47Ca were significantly lower, and in the osteoporotic (P) group were higher than in the control (C) group from the second week. The 24-h WBR values of 99mTc-MDP were significantly higher in the M group and were lower in the S group from the second week. Simultaneous measurements of 24-h WBR of these two radiopharmaceuticals facilitated the early differentiation of metabolic bone diseases in the animal models prior to the detection of radiologic bone changes.

Invasion of bone into porous fiber metal implants in cats

Bone ingrowth in porous Ti-6Al-4V implants in feline femurs was assessed for the amount and composition 4, 12 and 26 weeks after implantation. During the first 12 weeks there was a rapid ingrowth that levelled out during the ensuing weeks. Bone had penetrated the implants to an average depth of 0.5 mm over their entire surface at 26 weeks. The ingrown bone was deficiently mineralized at 4 and 12 weeks, but reached full mineralization at 26 weeks. A low calcium to phosphorus ratio persisted at all observation times. The ingrown tissue was compared to bone filling drill holes that had been made in the trochanters contralaterally to the implants. By means of radioactive strontium, the mineral deposits in the holes and implants could be compared. The overall results indicate that bone ingrowth in a porous implant and bone healing are similar processes both qualitatively and quantitatively.

Interferences in in vivo neutron activation analysis

Significant errors can occur in the measurement of the total amounts of N, P, Cl, Na, Ca and K in the human body by in vivo neutron activation analysis because of the presence of interfering activity in the gamma-ray energy spectrum. The interfering activity may be present for two reasons: firstly, patients may have received an administered radioisotope in an unrelated investigation; secondly, activation of elements not normally present in the body in large quantities may have occurred. The size and duration of these errors have been examined for two administered radioisotopes, 67Ga and 47Ca. The interferences due to activated iron and chromium from stainless steel prostheses have been examined, as well as those due to activated iodine and barium in radiographic contrast media. A description of the method by which we correct for those interferences is given. The effects of the shape of the standard spectra used in least squares analysis of the results have been examined.

A model-independent comparison of the rates of uptake and short term retention of 47Ca and 85Sr by the skeleton

1. A method has been devised for comparing the impulse response functions of the skeleton for two or more boneseeking tracers, and for estimating the contribution made by measurement errors to the differences between any pair of impulse response functions. 2. Comparisons were made between the calculated impulse response functions for 47Ca and 85Sr obtained in simultaneous double tracer studies in sixteen subjects. Collectively the differences between the 47Ca and 85Sr functions could be accounted for entirely by measurement errors. 3. Because the calculation of an impulse response function requires fewer a priori assumptions than other forms of mathematical analysis, and automatically corrects for differences induced by recycling of tracer and non-identical rates of excretory plasma clearance of tracer, it is concluded that differences shown in previous in vivo studies between the fluxes of Ca and Sr into bone can be fully accounted for by undetermined oversimplifications in the various mathematical models used to analyse the results of those studies. 85Sr is therefore an adequate tracer for bone calcium in most in vivo studies.

A new method for calculating the accretion rate of bone calcium and some observations on the suitability of strontium-85 as a tracer for bone calcium

1. A new method for calculating the accretion rate (A) of bone calcium is proposed, based on an impulse analysis of 47Ca data. The method is free of most of the assumptions inherent in previous methods of analysis and appears to give more accurate estimates. 2. In fourteen normal subjects and twelve patients with metabolic bone disease, measurements of A by the new method gave very similar results to the mineralization rate calculated by the method of Burkinshaw et al. (1969). Analysis of twelve studies performed by Neer et al. (1967) gave good agreement with their five compartment model. A close relation between A and Marshall's (1964) A5 was observed, but the latter gave systematically higher results. 3. In sixteen studies both 47Ca and 85Sr were injected simultaneously. Although there were no systematic differences between the values of A for the two tracers, the differences between individual values were greater than the known experimental errors.