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D P Hickman

Publications and source records attributed to D P Hickman.

5 recordsLinked to original sources
PubMed1995

Development of a method for calibrating in vivo measurement systems using magnetic resonance imaging and Monte Carlo computations.

Research efforts towards developing a new method for calibrating in vivo measurement systems using magnetic resonance imaging (MRI) and Monte Carlo computations are discussed. The method employs the enhanced three-point Dixon technique for producing pure fat and pure water MR images of the human body. The MR images are used to define the geometry and composition of the scattering media for transport calculations using the general-purpose Monte Carlo code MCNP, Version 4. A sample case for developing the new method utilizing an adipose/muscle matrix is compared with laboratory measurements. Verification of the integrated MRI-MCNP method has been done for a specially designed phantom composed of fat, water, air, and a bone-substitute material. Implementation of the MRI-MCNP method is demonstrated for a low-energy, lung counting in vivo measurement system. Limitations and solutions regarding the presented method are discussed.

Adipose Tissue↗
PubMed1994

Calibration of a 241Am wound-monitoring system using Monte Carlo techniques.

Monte Carlo techniques have been used to establish calibration factors and to predict gamma spectra for well-defined measurements. These techniques are routinely used to predict shielding requirements and critical specifications. The Lawrence Livermore National Laboratory is researching the feasibility of using Monte Carlo techniques to establish calibration factors for in vivo measurement systems. A pilot study was conducted to demonstrate the use of the Monte Carlo technique to calibrate in vivo measurement systems, to predict the efficiency of a wound measurement system and compare the predicted efficiency with the measured efficiency, and to investigate the effects of the source geometry and the detector size on the measured efficiency. Results of this study demonstrate good agreement between the Monte-Carlo-predicted efficiency and the measured efficiency for a wound calibration phantom. The effects of the source geometry and the detector size tend to conform to the physical processes that govern the measurement process. These results demonstrate that the Monte Carlo technique accurately predicts the in vivo measurement efficiency if the characteristics of the attenuating material and the Monte Carlo source geometry are properly established.

Americium↗
PubMed1992

Long-term retention of 210Pb in man: a unique case of internal contamination.

Knowledge of the long-term effective half-life of 210Pb in man is essential for estimating the cumulative exposure to inhaled short-lived radon daughters from measured values of the 210Pb skeletal burden. For this purpose, the effective half-life has been obtained from sequential measurements of 210Pb made in vivo during a 10-y period and by bioassay of 210Pb excreted in the urine of an individual with a 43-y-old body burden. The long-term effective half-lives obtained by these two methods were 18.1 +/- 4.8 y and 15.8 +/- 0.8 y, respectively. These values are not very different from the estimate of 12.3 y previously adopted by the ICRP.

Accidents, Occupational↗
PubMed1988

Reconstruction of a human skull calibration phantom using bone sections from an 241Am exposure case.

New York University Medical Center's Institute of Environmental Medicine (NYUMC/IEM) was called upon by representatives of the United States Transuranic Registry to reconstruct a human skull phantom for the purpose of producing a calibration structure to be used for determining 241Am skeletal content from in vivo measurements. The human skull represented a deposition pattern of 241Am in the bone matrix which had accumulated into the bone via natural metabolic processes after an accidental intake. Soon after death, the skull was sagittally divided and the left lateral side was analyzed radiochemically. Assuming symmetry of deposition, and based on measurements of the right lateral side of the skull performed at NYUMC/IEM as well as results of radiochemical analysis of sections of the left side, the activity content of the right side was estimated to be 307 +/- 4 Bq (8.3 +/- 0.1 nCi). The right side was subsequently paired with a blank left lateral of a control skull and embedded into tissue-equivalent material. The reconstructed skull phantom was then evaluated to determine its applicability as a calibration phantom which could be used to estimate skeletal burdens of 241Am.

Americium↗