The factors affecting the accuracy and minimum detectable concentration of in vivo tibia lead measurement are discussed, and it is demonstrated that the use of a 109Cd source in a backscatter geometry and using the 88 keV coherently scattered photon for normalisation optimizes both criteria. The measurement is shown to be independent of variations in source-sample distance, thickness of overlying tissue and tibia size and shape. Applying the same technique in vitro to samples of human tibia and metatarsals, it is shown that the results are not significantly different (p approximately equal to 0.9) from atomic absorption spectrometry results from another laboratory. The results of Monte Carlo dose distribution calculations are presented and compared with measurements using thermoluminescent dosemeters: the mean absorbed dose to a 20 cm leg section is less than 0.1 mGy (10 mrad) and the maximum absorbed skin dose is 0.45 mGy (45 mrad). For this dose the minimum detectable lead concentration is 10 micrograms g-1. Finally, the technique has been applied to groups of normals and occupationally exposed workers, and the means have been shown to be significantly different, namely 10 and 31 micrograms g-1 respectively. In the normal subjects tibia lead correlated strongly with age (r = 0.63, p less than 0.001).

In-vivo measurements of lead concentrations in calcaneus (mainly trabecular bone) and tibia (mainly cortical bone) were performed by x-ray fluorescence (XRF) in 70 active and 30 retired lead smelter workers who had long-term exposure to lead. Comparison was made with 31 active and 10 retired truck assembly workers who had no known occupational exposure to lead. After physical examination, all participants provided blood and urine samples and answered a computerized questionnaire. Since 1950, blood lead has been determined repeatedly in lead workers at the smelter, which made it possible to calculate a time-integrated blood lead index for each worker. Lead concentrations in blood, urine, calcaneus, and tibia in active and retired lead workers were significantly higher than in the corresponding control groups (p < .001). The highest bone lead concentrations were found among retired lead workers (p < .001), which was the result of considerably higher lead exposure during 1940 to 1960. Lead concentrations in calcaneus in active lead workers were significantly higher than in tibia when expressed in ug of lead per gram of bone mineral, which suggests a quicker absorption over time in this mainly trabecular bone. The estimated biological half-times were 16 y in calcaneus (95% confidence interval [95% CI] = 11-29 y) and 27 y in tibia (95% CI = 16-98 y). A strong positive correlation was found between lead concentrations in calcaneus and tibia for all lead workers (r = 0.54; p < .001). A strong positive correlation was also found between the bone lead concentrations and the cumulative blood lead index. Blood lead, at the time of study, correlated well with bone lead concentrations in retired--but not in active--workers, reflecting the importance of the endogenous (skeletal) lead exposure. The findings in this study indicate that bone lead measurements by XRF can give a good index of long-term lead exposure. Tibia measurements offer a higher precision than calcaneus measurements. The method is of particular interest in epidemiologic studies of adverse health effects caused by long-term lead exposure.

In vivo tibia lead measurements of 20 non-occupationally exposed and 190 occupationally exposed people drawn from three factories were made using a non-invasive x ray fluorescence technique in which characteristic x rays from lead are excited by gamma rays from a cadmium-109 source. The maximum skin dose to a small region of the shin was 0-45 mSv. The relation between tibia lead and blood lead was weak in workers from one factory (r = 0 11, p > 0.6) and among the non-occupationally exposed subjects (r = 0 07, p > 0 7); however, a stronger relation was observed in the other two factories (r = 0 45, p < 0 0001 and r = 0 53, p < 0-0001). Correlation coefficients between tibia lead and duration of employment were consistently higher at all three factories respectively (r = 0-86, p < 0-0001; r = 0-61, p < 0-0001; r = 0 80, p < 0 0001). A strong relation was observed between tibia lead and a simple, time integrated, blood lead index among workers from the two factories from which blood lead histories were available. The regression equation from two groups of workers (n = 88, 79) did not significantly differ despite different exposure conditions. The correlation coefficient for the combined data set (n = 167) was 0-84 (p < 0-0001). This shows clearly that tibia lead, measured in vivo by x ray fluorescence, provides a good indicator of long term exposure to lead as assessed by a cumulative blood lead index.As a consequence of the well established toxicity of lead, workers occupationally exposed to it in the United Kingdom and other industrialised countries are subjected to regular monitoring of blood lead concentrations. In In vivo tibia lead measurements as an index ofcumulative exposure in occupationally exposed subjects is relatively stable, as with the tibia, it is feasible to normalise per mass of wet bone. The relation between wet bone mass and bone mineral in trabecular bone, however, is less well defined and changes with, among other things, age, particularly in women. Because our technique normalises to the gamma rays coherently scattered from both calcium and phosphorus, the most logical normalisation is therefore to the bone mineral mass. This is equivalent to quoting the lead content per mass of bone ash, a unit that is widely used for in vitro analysis. A possible alternative, particularly for those making biopsy measurements using atomic absorption spectrometry, is to normalise to the calcium content: however, the relation between the two procedures is readily established assuming bone mineral to consist of calcium hydroxyapatite (Ca10(P04)6(OH)2). As our measurement programme is being extended to include trabecular bone we have therefore chosen to normalise to bone mineral mass throughout.x Ray fluorescence, which involves stimulation of characteristic x ray emission from the element of interest using a beam of photons, has been used by several groups to measure bone lead. The first to do so were Ahlgren and co-workers,45 who measured the lead K. x ray emission (at 75 0 and 72-8 keV for K., and...

BackgroundSeveral epidemiologic studies have suggested an association between Parkinson’s disease (PD) and exposure to heavy metals using subjective exposure measurements.ObjectivesWe investigated the association between objective chronic occupational lead exposure and the risk of PD.MethodsWe enrolled 121 PD patients and 414 age-, sex-, and race-, frequency-matched controls in a case–control study. As an indicator of chronic Pb exposure, we measured concentrations of tibial and calcaneal bone Pb stores using 109Cadmium excited K-series X-ray fluorescence. As an indicator of recent exposure, we measured blood Pb concentration. We collected occupational data on participants from 18 years of age until the age at enrollment, and an industrial hygienist determined the duration and intensity of environmental Pb exposure. We employed physiologically based pharmacokinetic modeling to combine these data, and we estimated whole-body lifetime Pb exposures for each individual. Logistic regression analysis produced estimates of PD risk by quartile of lifetime Pb exposure.ResultsRisk of PD was elevated by > 2-fold [odds ratio = 2.27 (95% confidence interval, 1.13–4.55); p = 0.021] for individuals in the highest quartile for lifetime lead exposure relative to the lowest quartile, adjusting for age, sex, race, smoking history, and coffee and alcohol consumption. The associated risk of PD for the second and third quartiles were elevated but not statistically significant at the α = 0.05 level.ConclusionsThese results provide an objective measure of chronic Pb exposure and confirm our earlier findings that occupational exposure to Pb is a risk factor for PD.

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The need for in vivo bone strontium assessment arises because strontium may exert a number of effects on bone, which may be either beneficial or toxic. Measurements discussed here are noninvasive, no sample is taken, nor is there discomfort to patients. The developed source excited x-ray fluorescence system employs a 109Cd source to excite the strontium K x rays, with the source and detector in approximately 90 degree geometry relative to the sample position. The factors affecting the accuracy and minimal detectable limit for bone strontium in vivo measurements are discussed. A system calibration revealed a minimum detectible limit of approximately 0.25 mg Sr/g Ca, which is sufficient for the monitoring of strontium levels in healthy subjects and patients with elevated bone strontium concentrations. Preliminary in vivo measurements in ten healthy subjects at two bone sites (phalanx and tibia) indicated that this system can be applied for cumulative bone strontium estimation while delivering a low effective dose of 80 nSv during the measurement time. Future work will involve attempts to enhance system precision with alternative fluorescing sources and further optimization of the detection system.

In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women.

An x-ray fluorescence (XRF) system using 125I as the source was developed to measure strontium in bone in vivo. As part of an in vivo pilot study, 22 people were measured at two bone sites, namely the index finger and the tibial ankle joint. Ultrasound measurements were used to obtain the soft tissue thickness at each site, which was necessary to correct the signal for tissue attenuation. For all 22 people, the strontium peak was clearly distinguishable from the background, proving that the system is able to measure Sr in vivo in people having normal bone Sr levels. Monte Carlo simulations were carried out to test the feasibility and the limitations of using the coherently scattered peak at 35.5 keV as a means to normalize the signal to correct for the bone size and shape. These showed that the accuracy of the normalized Sr signal when comparing different people is about 12%. An interesting result arising from the study is that, in the measured population, significantly higher measurements of bone Sr concentration were observed in continental Asian people, suggesting the possibility of a dietary or race dependence of the bone Sr concentration or a different bone biology between races.