Search PubMed⌕ Search

Biomedical subjects

G H Kramer

Publications and source records attributed to G H Kramer.

At least 37 records · Page 2Linked to original sources
PubMed1997

Chest wall thickness measurements: the alternative approach extended for 241Am.

The Human Monitoring Laboratory has extended the technique of determining the chest wall thickness of an individual using information from the spectrum produced by internally deposited radionuclides. The technique has been investigated both theoretically and practically using germanium detectors and the Lawrence Livermore Torso Phantom. The phantom was used with a lung set containing homogeneously distributed 241Am. Chest wall thicknesses were varied by using a series of muscle equivalent overlay plates that gave a range of 1.6 cm to 3.9 cm thickness. It was found that a 3-cm chest wall thickness can be estimated to within 18%. Using a spectral addition technique 1 kBq was estimated to be the "practical" lower limit of activity for this method.

Americium↗
PubMed1997

Radiocesium body burdens in residents of northern Canada from 1963-1990.

Measurements of 137Cs body burdens in over 1,100 people from five northern Canadian communities were carried out with a portable whole body counting system during the winters of 1989 and 1990. These results are compared with over 3,000 similar measurements carried out during 1967-1969. Community mean body burdens and body concentrations had decreased by approximately a factor of 30 between the two survey periods. The dependence of body concentrations on the sex and age of the subjects has also changed significantly. This can be related to changes in the patterns of caribou consumption in the northern communities. Measurements of 137Cs in urine are also available for an earlier period (1963-1966) when world-wide fallout was at its highest level. A normalization procedure was developed to calculate the average radiocesium body concentration in each community from the concentrations in urine. From data spanning a period of nearly 30 y (1963-1990), lifetime radiation doses have been estimated for most communities in the Yukon and Northwest Territories. These cumulative doses vary from 0.3 to nearly 40 mSv, with an Arctic-wide average of about 12 mSv. No health effects would be expected at these levels.

Adolescent↗
PubMed1997

Examination of the effect of counting geometry on 125I monitoring using MCNP.

This paper theoretically investigates how the counting efficiencies of three selected detector (NaI) sizes are affected by neck-detector distance, detector misplacement, thickness of overlaying tissue, and size of the thyroid gland. The detector sizes were small, 2.54 cm diameter and 0.2 cm crystal thickness; medium, 7.62 cm diameter and 0.2 cm crystal thickness; large 30.48 cm diameter and 0.2 cm crystal thickness. The evaluations were determined using a Monte Carlo technique. The simulations show that the large detector minimizes the uncertainties for all problems except the thickness of overlaying tissue.

Humans↗
PubMed1997

Considerations in assigning dose based on uncertainties from in vivo counting.

Lung counting is highly geometry dependent, especially at low photon energies. Monte Carlo simulations have been used to determine the magnitude of the errors obtained if it is assumed that the deposition is homogeneous, when in fact it is not. Simulation for a germanium lung counting system consisting of four, 70 mm x 30 mm diameter thick detectors have been performed for 70 deposition patterns. The detector efficiencies for 20, 40, 60, 120, 240, 660, and 1000 kiloelectron volts were calculated for a homogeneous deposition and these efficiencies were used to estimate the bias when the deposition was heterogeneous. A bias of 800% was not unusual. Whole-body counting is prone to errors that can arise from the activity distribution and/or size of the subject. The latter are geometry dependent and, for example, a bias result of 200% can be obtained when measuring children in a chair geometry using a calibration factor based on reference man. Thyroid counting is the least prone to error. If the measurement is done correctly, biases can usually be kept below 20%. However, if the measurement is made with a collimator or if the detector is in contact with the subject's neck, biases exceeding 200% can be obtained.

Humans↗
PubMed1996

Dosimetry of an incident involving 14C.

High level contamination was observed on two workers during a routine hand check of personnel leaving a laboratory where barium carbonate labeled with 14C was handled. A third worker was found to have been exposed to airborne 14C (carbonate) aerosol during the investigation. Urinary excretion analysis and in vivo monitoring were carried out. This paper presents the results of more than one year of lung counting using phoswich detectors and gives some indication about the metabolism of the 14C over that period. Doses were difficult to estimate due to lack of information in the literature. Estimates were based on default parameters and information gathered in this study using ICRP 30 and the new ICRP lung models. These ranged from 0.3 mSv to 3 mSv depending on the assumptions and models.

Barium↗
PubMed1996

Comparison of the ANSI, RSD, KKH, and BRMD thyroid-neck phantoms for 125I thyroid monitoring.

The Human Monitoring Laboratory, which acts as the Canadian National Calibration Reference Centre for In Vivo Monitoring, has determined the performance characteristics of four thyroid phantoms for 125I thyroid monitoring. The phantoms were a phantom built to the specifications of the American National Standards Institute Standard N44.3; the phantom available from Radiology Support Devices; the phantom available from Kyoto Kagaku Hyohon; the phantom manufactured by the Human Monitoring Laboratory and known as the BRMD phantom. The counting efficiencies of the phantoms for 125I were measured at different phantom-to-detector distances. The anthropomorphic characteristics of the phantoms have been compared with the average man parameters. It was concluded that the BRMD, American National Standards Institute, and Radiology Support Devices phantoms have the same performance characteristics when the neck-to-detector distances are greater than 12 cm and all phantoms are essentially equivalent at 30 cm or more. The Kyoto Kagaku Hyohon phantom showed lower counting efficiencies at phantom-to-detector distances less than 30 cm. This was attributed to the design of the phantom. This study has also shown that the phantom need not be highly anthropomorphic provided the calibration is not performed at short neck-detector distances. Indeed, it might be possible to use t simple point source of 125I placed behind a 1.5 cm block of lucite at neck detector distances of 12 cm or more.

Adolescent↗
PubMed1996

The BRMD thyroid-neck phantom: design and construction.

The Human Monitoring Laboratory, which acts as the Canadian National Calibration Reference Center for In Vivo monitoring, has constructed a robust neck-thyroid phantom for use in the Canadian Thyroid Intercomparison Program. The phantom is rugged and capable of being distributed through the mail with no expectation of a leak of radioactive materials; it is anthropomorphic; the thyroid inserts simulate 125I and 131I; the phantom can be used to mimic different layers of adipose tissue over the thyroid insert; and it is cost effective. This paper describes the design criteria and the manufacturing process; the performance characteristics have been described in an earlier publication.

Canada↗
PubMed1995

Radiocesium body burdens in immigrants to Israel from areas of the Ukraine, Belarus and Russia near Chernobyl.

Of the 500,000 immigrants from the former Soviet Union who came to Israel during 1990-1993, about 100,000 are estimated to have come from radiocontaminated areas near Chernobyl. These people were subject to chronic uptake of environmental radiocesium over protracted periods. During October-November 1991, a joint Israeli-Canadian investigation measured radiocesium body burdens in immigrants to Israel from the Ukraine, Belarus, and the southern Russian republic in order to provide factual information on radiocesium levels to concerned immigrants and to relate the body burdens to the geographic area of residence before coming to Israel. Assessments were made of 137Cs body burdens in 1,228 volunteer men, women, and children. These measurements were accompanied by medical assessments based on clinical histories and examinations. Radiocesium levels were strongly dependent on the duration of residence in Israel, with the highest levels being found in the most recent immigrants. The maximum level, extrapolated back to the time of leaving the former Soviet Union, was estimated to be about 0.83 kBq (10.3 Bq kg-1). Of the most recent immigrants from the Kiev region (< 101 days in Israel), only 15% had back extrapolated body burdens > 50 Bq, whereas 53% of those coming from Gomel and other towns in the contaminated zones (> 3.7 x 10(10) Bq km-2 of radiocesium) had detectable levels > 50 Bq. People coming from the latter region had significantly higher body burdens as compared to those from the former, in accordance with the higher degree of ground radiocesium contamination reported for the latter region. Women and children showed considerably lower total radiocesium content in comparison to men. All radiocesium body burdens at the time of measurement were too low to be of health concern.

Adolescent↗
PubMed1995

The Canadian whole body counting intercomparison program: a summary report for 1989-1993.

The Human Monitoring Laboratory, which is the Canadian National Calibration Reference Centre for In-Vivo Measurements, has been conducting an annual intercomparison program for whole body counting facilities since 1989. Each year a number of phantoms are prepared for participants to measure the accuracy, precision, size dependency, and identification capabilities of their whole body counters. Other tests are designed to measure the sensitivity of the whole body counter to geometry factors. Some phantoms are prepared with the same radionuclide from year to year so that time dependent data can be acquired, whereas other phantoms are prepared as unknowns. This article describes the tests that were performed, gives the results for Canadian participants, and compares the results to interim performance criteria. Measurement results from a human volunteer who ingested 137Cs contaminated caribou meat and was counted at a number of facilities in 1990 are also presented.

Canada↗
PubMed1994

Measurement of the natural uranium content of fabricated, tissue substitute lung sets by dual photon absorptiometry.

The assessment of tissue substitute materials by dual photon absorptiometry has been extended to detect the presence of high atomic weight materials. Commercial dual photon systems dedicated to the measurement of bone mineral mass can be used to detect other elements in fabricated tissue phantoms. The technique is sufficiently sensitive to quantitate the mass of natural uranium that had been distributed throughout the lungs of a thorax phantom.

Absorptiometry, Photon↗
PubMed1994

Radiocesium in children from Belarus.

The body burdens of 137Cs were measured in 74 children from Belarus who had been exposed to fallout from the Chernobyl accident. The children were between the ages of 8 and 12 y old and were visiting the Ottawa area during the summers of 1991 and 1992. The body burdens varied from 0.04-2.25 kBq, which are less than or comparable to the amount of natural 40K in the children's bodies. There was no apparent dependence on age or sex. The body burdens were related, to some extent, with recorded fallout levels in the region of origin but did not appear to change significantly from 1991 to 1992. During their stay in Canada, radiocesium was being cleared from the children's bodies with a mean half-time of 33 d (range = 12-77 d). The highest intake rate of 137Cs was estimated to be 18 Bq d-1 and the highest dose rate was 0.13 mSv y-1.

Accidents↗
PubMed1994

Chest wall thickness measurements for enriched uranium: an alternative approach.

The Human Monitoring Laboratory has developed a technique to determine the chest wall thickness of an individual using information from the spectrum produced by internally deposited radionuclides. The technique has been investigated both theoretically and practically using phoswich detectors and the Lawrence Livermore Torso Phantom. The phantom was used with lung sets containing homogeneously distributed 93% enriched uranium, 20% enriched uranium, natural uranium, and 241Am. It was found that a 3-cm chest wall thickness can be estimated to within 9% when measuring 93% enriched uranium. The technique does not work for the latter two radionuclides because of an insufficient separation in the photon energies and poor resolution of the phoswich detectors. The technique is only of value for activity levels well above the detection limit.

Biometry↗
PubMed1994

The Canadian National Calibration Reference Center for Bioassay and in-vivo Monitoring: a program summary.

The Canadian National Calibration Reference Center for Bioassay and in-vivo Monitoring is part of the Radiation Protection Bureau, Department of Health. The Reference Center operates a variety of different intercomparison programs that are designed to confirm that workplace monitoring results are accurate and provide the necessary external verification required by the Canadian regulators. The programs administered by the Reference Center currently include urinalysis intercomparisons for tritium, natural uranium, and 14C, and in-vivo programs for whole-body, thorax, and thyroid monitoring. The benefits of the intercomparison programs to the participants are discussed by example. Future programs that are planned include dual spiked urine sample which contain both tritium and 14C and the in-vivo measurement of 99mTc.

Biological Assay↗
PubMed1994

The Canadian National Calibration Reference Centre for In-Vivo Monitoring: thyroid monitoring. Part III: A basic calibration procedure for thyroid monitoring.

This article is the third of a five-part series covering various aspects of occupational thyroid monitoring. This article introduces the basic concepts required to understand the procedure for determining the counting efficiency of a thyroid detector. The B.R.M.D. thyroid-neck phantom is used as the calibration source. A procedure for personnel monitoring is also discussed and the concept of Minimum Detectable Activity (MDA) is introduced. The last two articles in this series discuss energy calibration, counting system optimization based on a single-channel analyzer and placement error minimization.

Calibration↗
PubMed1994

The Canadian National Calibration Reference Centre for In-Vivo Monitoring: thyroid monitoring. Part IV: Optimizing a counting system that uses a single-channel analyzer.

This article is the fourth of a five-part series covering various aspects of occupational thyroid monitoring. This article describes the energy calibration of the monitoring system with particular emphasis on techniques for optimizing a system that is based on a single-channel analyzer, or any system that does not have a multi-channel analyzer. These systems cannot directly show the operator the photopeak of the calibration source. The article also briefly discusses quality control and problem solving.

Calibration↗