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 , SkeletonABSTRACT
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 AnalysisABSTRACT
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.
