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1.
Appl Radiat Isot ; 49(5-6): 533-5, 1998.
Article in English | MEDLINE | ID: mdl-9569536

ABSTRACT

Total body chlorine (TBCI), used to estimate the extracellular space, is measured by delayed-gamma neutron activation (DGNA) using the reaction 37Cl(n, gamma)38Cl, at Brookhaven National Laboratory. During the calibration process, we noticed that different values were obtained when different amounts of Cl were placed in the phantom. This non-linear relationship is due to the thermal neutron flux suppression by the thermal neutron capture reaction 35Cl(n, gamma)36Cl. Monte Carlo simulations confirm the results of phantom measurements showing an inverse relationship between the Cl content in the phantom and the gamma-ray yield per gram Cl. Thus, it is important to calibrate the DGNA system for TBCl using phantom standards containing an amount of Cl close to that expected in the individual undergoing measurement.


Subject(s)
Body Composition , Chlorine/analysis , Extracellular Space , Phantoms, Imaging , Calibration , Computer Simulation , Female , Gamma Rays , Humans , Male , Monte Carlo Method , Neutron Activation Analysis/methods , Radioisotopes , Reproducibility of Results , Skeleton
2.
Appl Radiat Isot ; 49(5-6): 531-2, 1998.
Article in English | MEDLINE | ID: mdl-9569535

ABSTRACT

Differences in body size and shape can cause large variances in the results of in vivo neutron activation analysis. Preliminary body-size correction data were obtained for the delayed-gamma neutron activation facility (DGNA) at Brookhaven National Laboratory (BNL), based on phantom standards of different sizes, used in combination with computer simulations on the effect of different body sizes.


Subject(s)
Body Composition , Body Constitution , Phantoms, Imaging , Body Mass Index , Calcium , Computer Simulation , Female , Gamma Rays , Humans , Male , Monte Carlo Method , Neutron Activation Analysis/methods , Regression Analysis
3.
Phys Med Biol ; 43(2): 339-49, 1998 Feb.
Article in English | MEDLINE | ID: mdl-9509530

ABSTRACT

The prompt-gamma neutron activation facility at Brookhaven National Laboratory was upgraded to improve both the precision and accuracy of its in vivo determinations of total body nitrogen. The upgrade, guided by Monte Carlo simulations, involved elongating and modifying the source collimator and its shielding, repositioning the system's two NaI(Tl) detectors, and improving the neutron and gamma shielding of these detectors. The new source collimator has a graphite reflector around the 238PuBe neutron source to enhance the low-energy region of the neutron spectrum incident on the patient. The gamma detectors have been relocated from positions close to the upward-emerging collimated neutron beam to positions close to and at the sides of the patient. These modifications substantially reduced spurious counts resulting from the capture of small-angle scattered neutrons in the NaI detectors. The pile-up background under the 10.8 MeV 14N(n, gamma)15N spectral peak has been reduced so that the nitrogen peak-to-background ratio has been increased by a factor of 2.8. The resulting reduction in the coefficient of variation of the total body nitrogen measurements from 3% to 2.2% has improved the statistical significance of the results possible for any given number of patient measurements. The new system also has a more uniform composite sensitivity.


Subject(s)
Gamma Rays , Neutron Activation Analysis/instrumentation , Neutrons , Nitrogen/analysis , Phantoms, Imaging , Humans , Models, Theoretical , Monte Carlo Method , Neutron Activation Analysis/methods , Nitrogen Isotopes , Nuclear Reactors , Radiation Protection , Reproducibility of Results , Sensitivity and Specificity
4.
Health Phys ; 72(3): 443-9, 1997 Mar.
Article in English | MEDLINE | ID: mdl-9030846

ABSTRACT

An artificial skeleton was designed and placed inside a bottle manikin absorber phantom to provide a new reference standard for measurements of total body calcium by in vivo neutron activation analysis at Brookhaven National Laboratory. The composition of the epoxy-based calcium and phosphorus mixture used to construct the skeleton, the dimensions and weight of each bone are given for two phantoms representing an adult male and female. Also, the dimensions, composition, and weights of overlays designed to simulate the influence of obesity on in vivo neutron activation analysis are given for each.


Subject(s)
Calcium/analysis , Neutron Activation Analysis/standards , Adult , Body Height , Body Weight , Bone and Bones/chemistry , Female , Humans , Male , Models, Structural , Organ Size
5.
Med Phys ; 23(2): 273-7, 1996 Feb.
Article in English | MEDLINE | ID: mdl-8668109

ABSTRACT

The delayed-gamma neutron activation facility at Brookhaven National Laboratory was originally calibrated using an anthropomorphic hollow phantom filled with solutions containing predetermined amounts of Ca. However, 99% of the total Ca in the human body is not homogeneously distributed but contained within the skeleton. Recently, an artificial skeleton was designed, constructed, and placed in a bottle phantom to better represent the Ca distribution in the human body. Neutron activation measurements of an anthropomorphic and a bottle (with no skeleton) phantom demonstrate that the difference in size and shape between the two phantoms changes the total body calcium results by less than 1%. To test the artificial skeleton, two small polyethylene jerry-can phantoms were made, one with a femur from a cadaver and one with an artificial bone in exactly the same geometry. The femur was ashed following the neutron activation measurements for chemical analysis of Ca. Results indicate that the artificial bone closely simulates the real bone in neutron activation analysis and provides accurate calibration for Ca measurements. Therefore, the calibration of the delayed-gamma neutron activation system is now based on the new bottle phantom containing an artificial skeleton. This change has improved the accuracy of measurement for total body calcium. Also, the simple geometry of this phantom and the artificial skeleton allows us to simulate the neutron activation process using a Monte Carlo code, which enables us to calibrate the system for human subjects larger and smaller than the phantoms used as standards.


Subject(s)
Body Composition , Bone and Bones/chemistry , Calcium/analysis , Models, Anatomic , Neutron Activation Analysis/instrumentation , Neutron Activation Analysis/methods , Phantoms, Imaging , Gamma Rays , Humans , Monte Carlo Method
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