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Title: A 4x500 mm{sup 2} cloverleaf detector system for in vivo bone lead measurement

Abstract

A 4x500 mm{sup 2} 'cloverleaf' low energy germanium detector array has been assembled for the purpose of in vivo bone lead measurement through x-ray fluorescence. Using {sup 109}Cd as an exciting source, results are reported from a leg phantom simulating measurement of lead in a human tibia. For high activity (4.0-4.4 GBq) and low activity (0.18-0.19 GBq) sources, measurement results are reported for both the cloverleaf system and a conventional single detector system of equivalent surface area (2000 mm{sup 2}). The mean uncertainty and reproducibility of measurement were both significantly improved for the cloverleaf system with a high activity {sup 109}Cd source. When using a source activity of 4.4 GBq, measurement of the phantom resulted in an average bone lead uncertainty of 0.79 {mu}g/g and a reproducibility of 0.84 {mu}g/g. These results represent the highest precision yet reported from a bone lead x-ray fluorescence system.

Authors:
;  [1]
  1. Department of Physics, Mount Allison University, 67 York Street, Sackville, New Brunswick, E4L 1E6 (Canada)
Publication Date:
OSTI Identifier:
20951107
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 3; Other Information: DOI: 10.1118/1.2436973; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; CADMIUM 109; FLUORESCENCE; GE SEMICONDUCTOR DETECTORS; IN VIVO; LEAD; PHANTOMS; SURFACE AREA; TIBIA; X-RAY FLUORESCENCE ANALYSIS

Citation Formats

Fleming, David E. B., and Mills, Caitlin E. A 4x500 mm{sup 2} cloverleaf detector system for in vivo bone lead measurement. United States: N. p., 2007. Web. doi:10.1118/1.2436973.
Fleming, David E. B., & Mills, Caitlin E. A 4x500 mm{sup 2} cloverleaf detector system for in vivo bone lead measurement. United States. doi:10.1118/1.2436973.
Fleming, David E. B., and Mills, Caitlin E. Thu . "A 4x500 mm{sup 2} cloverleaf detector system for in vivo bone lead measurement". United States. doi:10.1118/1.2436973.
@article{osti_20951107,
title = {A 4x500 mm{sup 2} cloverleaf detector system for in vivo bone lead measurement},
author = {Fleming, David E. B. and Mills, Caitlin E.},
abstractNote = {A 4x500 mm{sup 2} 'cloverleaf' low energy germanium detector array has been assembled for the purpose of in vivo bone lead measurement through x-ray fluorescence. Using {sup 109}Cd as an exciting source, results are reported from a leg phantom simulating measurement of lead in a human tibia. For high activity (4.0-4.4 GBq) and low activity (0.18-0.19 GBq) sources, measurement results are reported for both the cloverleaf system and a conventional single detector system of equivalent surface area (2000 mm{sup 2}). The mean uncertainty and reproducibility of measurement were both significantly improved for the cloverleaf system with a high activity {sup 109}Cd source. When using a source activity of 4.4 GBq, measurement of the phantom resulted in an average bone lead uncertainty of 0.79 {mu}g/g and a reproducibility of 0.84 {mu}g/g. These results represent the highest precision yet reported from a bone lead x-ray fluorescence system.},
doi = {10.1118/1.2436973},
journal = {Medical Physics},
number = 3,
volume = 34,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • Traditionally, clinical studies of lead`s effect on health have relied on blood lead levels to indicate lead exposure. However, this is unsatisfactory because blood lead levels have a half-life of approximately 5 weeks, and thus reflect recent exposure. Over 90% of the lead body burden is in bone, and it is thought to have a long residence time, thus implying that measurements of bone lead reflect cumulative exposure. So, measurements of bone lead are useful in understanding the long-term health effects of lead. Ahlgren reported the first noninvasive measurements of bone lead in humans, where {gamma}-rays from {sup 57}Co weremore » used to excite the K series x-rays of lead. The lead detection system at McMaster University uses a {sup 109}Cd source which is positioned at the center of the detector face (HPGe) and a near backscatter ({approx}160{degrees}) geometry. This arrangement allows great flexibility, since one can sample lead in a range of different bone sites due to a robust normalization technique which eliminates the need to correct for bone geometry, thickness of overlying tissue, and other related factors. The effective radiation dose to an adult during an x-ray fluorescence bone lead measurement is extremely low, being 35 nSv. This paper addresses the issue of how bone, whole blood, and serum lead concentrations can be related in order to understand a person`s lead exposure history.« less
  • An x-ray fluorescence system which utilizes polarized radiation to measure lead in vivo in human subjects is described. The minimum detection limit is approximately 6.4 ppm wet weight lead in the cortex of the tibia with 4 mm of overlying soft tissue. This appears to be adequate for assessing lead stores in lead-toxic preschool children. The measurement requires 16.5 min and is associated with an effective equivalent whole body dose to the subject of 2.5 /mu/Sv. The system, its calibration and its validation are described herein.
  • Initially, Wielopolski used x-rays from either a {sup 125}I or a {sup 109}Cd source to estimate lead (Pb) in tibial cortical bone in intact legs, postmortem, This system utilized the L{gamma} and L{Beta} x-rays of Ph with energies of 10.5 and 12.6 keV, respectively. The minimum detection limit (MDL) was considered to be comparable with existing K-line x-ray fluorescence (KXRF) instruments, namely, 20-30 ppm. The feasibility of partially polarized radiation was assessed from a {sup 125}I source on Pb (NO{sub 3}){sub 2}, (10,000 ppm) dissolved in water. Reduction of the detector total count rate was observed by a factor ofmore » two; and reduction in background by the same factor was appaent. This preliminary study suggested that, with proved design, the MDL might be lowered by a factor of five. A second post-mortem study was carried out using an {sup 125}I source. Tibial Pb concentration at the site of irradiation was subsequently measured by graphite furnace atomic absorption spectroscopy; the latter results ranged from 15 to 35 {mu}g Pb/g wet weight. The MDL for this instrument, calculated by multiplying the square root of background counts by a factor of 3, was estimated to be 22 ppm. The correlation coefficient between LXRF measurements and those carried out by atomic absorption was 0.90 (p < .03). In the same study, the use of a {sup 109}Cd source produced a higher degree of partial polarization with improvement in the sensitivity of the instrument. {sup 109}Cd was preferable, because its photoelectric cross section is higher than that of {sup 125}I.« less
  • Two X-ray fluorescence (XRF) methods have been developed and used for the in vivo measurement of lead in bone (primarily the tibia). The L XRF method was developed by Wielopolski and coworkers, and it consists of using a polarized X-ray tube source to excite the characteristic L lead X rays and detect them with a Si (Li) detector. It is quite sensitive and is capable of detecting lead to the parts-per-million level, but it suffers from errors due to the variation of covering skin thickness and the interference of other elements present in the bone. The inherent signal-to-noise (S/N) ratiomore » is low due primarily to the Compton scattering from the exciting source. This causes the minimum detectable concentration (MDC) of lead to be higher than desired.« less
  • Independent experiments have been performed at two centers, to evaluate the dosimetric properties of their respective {sup 109}Cd K X-ray fluorescence (XRF) bone lead measurement systems. Measurements were made of the dose to several points on the skin of the lower leg, at the surface of the tibia, in the red marrow tibia cavity, at the midcalf, and in the abdominal region occupied by the conceptus. Overall agreement between the two data sets was found. Similarities and differences are discussed. The effective dose values for an in vivo measurement of tibia lead concentration in 1-, 5-, and 10-year-old and adultmore » subjects were calculated from one data set to be 1,100, 420, 190, and 34/38 (male/female) nSv, respectively, for an in vivo median precision of 4.9 {mu}Pb (g bone mineral){sup {minus}1} for a 30-min adult measurement.« less