A method detection limit for potential in vivo arsenic measurements with a 50 W x-ray tube.

Using a 50 W x-ray tube as the fluorescing source, an x-ray fluorescence system was designed to measure arsenic in superficial layers of tissue-simulating phantoms. The detection limit for arsenic in the phantoms at a setting of 35 kV and with 200 microm of a Mo filter was 0.40 +/- 0.06 microg As g(-1). This measurement results in an effective dose of 0.6 microSv.

Monte Carlo simulations of in vivo K-shell X-ray fluorescence bone lead measurement and implications for radiation dosimetry.

In order to improve measurement precision and decrease minimum detectable limit, recent applications of K-shell X-ray fluorescence (KXRF) bone lead measurement have used shorter source-to-sample (S-S) distances (approximately 0.5 cm) than the traditionally standard values ranging between 2.0 and 3.0 cm. This alteration will have an effect on subject radiation dose. This paper reports a comprehensive Monte Carlo study performed to investigate the radiation energy deposition values delivered to the leg of model human subjects of various ages. The simulations were run for models approximating 1-year, 5-year, and adult subjects, assuming lead concentrations of 10 microg/g in bone and tracing 500 million photons in each simulation. Trials were performed over a range of S-S distances, from 0.5 to 6.0 cm. The energy deposition due to photoelectric and Compton processes occurring in bone and soft tissue are presented. For each subject age, the Monte Carlo analysis demonstrates that the amount of energy deposited in the bone is increased as the sample is moved closer to the source (from 3.0 to 0.5 cm). The amount of energy deposited in the bone was found to increase by approximately 91% (1-year old), 66% (5-year old), and 41% (adult). The amount of energy deposited to the leg sample as a whole increased by approximately 43% (1-year old), 32% (5-year old), and 21% (adult). Results are used to estimate the changes in the amount of dose received by subjects of different ages.

The study of age influence on human bone lead metabolism by using a simplified model and X-ray fluorescence data.

Long term lead metabolism in the human body has never been fully understood due to the lack of human data in this area. The technological improvement of bone lead measurement systems has made bone lead data of substantial populations available. In this study, a set of X-ray fluorescence bone lead data was used to test Leggett's lead metabolism model (R. W. Leggett, Environ. Health Perspect., 1993a, 101, 598-616), especially the model of metabolism in bone. The data set includes the bone lead concentration of 539 occupationally exposed workers, of whom 327 were measured twice in five years. The bone lead concentrations of both cortical bone (tibia) and trabecular bone (calcaneus) were obtained by Cd-109 gamma-ray induced XRF measurement. The histories of blood lead concentration for these workers were used to regulate the input file of the model. The results show that the bone lead concentrations predicted by Leggett's model greatly underestimate the measured values, especially for older workers. This data set was then organized into five age groups. A new simplified model was applied to estimate the lead transfer rates between blood and lead compartments for these age groups. The original transfer rates and the new transfer rates are compared, and the differences are discussed. When the transfer rates derived from measured bone lead data were put into the input file of the model to replace the existing parameters, the predicted values were much closer to the measured values for both cortical bone and trabecular bone.

Detection of silver protein complex injections in the bovine udder using X-ray fluorescence: a preliminary investigation.

To determine the feasibility of using x-ray fluorescence (XRF) to detect the presence of silver in the mammary gland of dairy cows injected with mild silver protein suspension. The XRF spectroscopy was conducted on cadaver udders with and without mild silver protein injected. Spectral analysis was performed in order to determine the amplitude of the silver K-alpha peak that was detected. By comparing the amplitude of the K-alpha peak to the background, a minimum time of collection was determined, as a measure of the time required to observe a silver signal that is significantly non-zero. The minimum detection time required for evidence of injected silver suspension was calculated to be 2.8 +/- 0.2 s. Even with an additional requirement that the net signal exceed 50 counts, the clear indication of the presence of silver will be observed within 4 min of interrogation. X-ray fluorescence spectroscopy was shown to be a viable method for the detection of injected silver protein in cadaver mammary glands of dairy cows. While these findings are promising, further studies must be conducted to investigate the time dependence of the silver signal when diffusion, absorption, and redistribution are involved, under conditions that better mimic those encountered at an exhibition. This technique, used in conjunction with screening ultrasound examinations, has the potential to confirm sites of injection of silver compounds.

Estimation of a method detection limit for an in vivo XRF arsenic detection system.

An x-ray fluorescence measurement system has been developed with an 125I source to detect arsenic in superficial layers of phantoms and tissue. Based on in vivo measurements, in conjunction with Monte Carlo simulations, the detection limit for arsenic in skin ranges between 2.6+/-0.5 and 5.7+/-1.1 microg g(-1), depending on skin thickness and assuming that arsenic is uniformly distributed in the skin. The effect of skin arsenic distribution was also examined.

An investigation of the 109Cd gamma-ray induced K-x-ray fluorescence (XRF) bone-lead measurement calibration procedure.

Two sets of phantoms have been used to calibrate a 109Cd y-ray induced K-XRF bone-lead measurement system. Both sets of phantoms are made of plaster of Paris, but the calibration lines are significantly different. This results in a significant difference for the derived concentrations of bone lead for the same person using these two sets of phantoms. This study shows that the different calibration lines are due to the different compositions of the phantoms, which can then be accounted for by adjusting the parameters related to the phantom composition in spectral analysis. Bone-lead concentrations for ten lead-exposed smelter workers were computed before and after analysis modification, and the results show that the bone-lead concentrations for the same person calculated from two sets of phantoms are not significantly different, only after the modifications are incorporated. Through these investigations, it was discovered that a common practice of setting the ratio of the calcium edge amplitude to the coherent scatter amplitude as a constant is only valid when all spectra are acquired at the same system resolution. When there is a change in the resolution between spectra, it has been determined that the ratio of the calcium edge amplitude to the coherent area should instead be used as the constant factor in the analysis program.

Monte Carlo investigations of distance-dependent effects on energy deposition in K-shell x-ray fluorescence bone lead measurement.

Radiation energy deposition results are presented from a Monte Carlo code simulating the lower part of a leg during an in vivo 109Cd K-shell x-ray fluorescence (KXRF) bone lead measurement. The simulations were run for a leg phantom model representing an adult subject, assuming concentrations of 10 microg Pb per gram bone mineral and tracing 500 million photons in each simulation. Trials were performed over a range (0.5-6.0 cm) of source-to-sample (S-S) distances. Energies deposited due to Compton and photoelectric processes occurring in the bone and the soft tissue were obtained. The data show an increase in the amount of energy deposited in the bone as the sample is moved closer to the source (from 2.0 cm to 0.5 cm). However, there is a decrease in the amount of energy deposited in the soft tissue as the sample is moved closer to the source over the same distance interval. In decreasing the S-S distance from 2.0 cm to 0.5 cm, the amount of energy deposited in the sample as a whole was found to increase by 11%. By calculating the energy deposition in the bone and in the soft tissue as a fraction of the total energy deposited in the sample, the corresponding changes are quantified as a function of S-S distance. Similarly, the proportions of energy deposited via the photoelectric effect and Compton scattering are presented as a function of S-S distance.