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Biomedical subjects

J G Hunt

Publications and source records attributed to J G Hunt.

13 recordsLinked to original sources
PubMed2005

Dose reconstruction of a Brazilian industrial gamma radiography partial-body overexposure case.

In May 2000, an operator of a (60)Co industrial gamma radiography apparatus, during a routine service, was involved in a partial-body radiological accident, which caused serious injuries to his left hand. Dose reconstruction was started aiming to assess the radiation doses, in order to assist the medical staff in the evaluation and prescription of suitable medical procedures for the patient's treatment and follow-up. This work presents the dose reconstruction used for assessment of the distribution of doses on the patient's left hand, which was made using two methods: physical and computational techniques. For the first technique a physical hand simulator was built. The computational method was performed using microcomputer software for external dose calculations, named 'Visual Monte-Carlo-VMC', together with a hand voxel simulator. The values obtained through both methods for the distribution of absorbed doses on the operator's left hand were compared. About half of them were similar within a range of uncertainty of 20%.

Adult↗
PubMed2005

Estimation of the dose to the nursing infant due to direct irradiation from activity present in maternal organs and tissues.

Radionuclides deposited internally in the mother will give rise to a radiation dose in the infant in two ways. The radionuclides may be transferred through milk and give rise to an internal dose in the infant, or the radionuclides may emit photons that are absorbed by the infant, giving rise to an external dose. In this paper, the external dose to the newborn infant caused by direct irradiation was estimated for monoenergetic photons. Voxel models (also called voxel phantoms) of the mother and infant were made in three geometries. These models, consisting of volume elements, or voxels, were designed so that the infant model was placed in the lap, at the breast and on the shoulder of the mother model. The Visual Monte Carlo (VMC) code was used to transport the photons through the voxel models. Source regions for the emitted photons, such as the whole body, the thyroid, the lung, the liver and the skeleton, were chosen. For the validation of the calculation procedure, VMC results were favourably compared with the results obtained by using other Monte Carlo programs and also with the previously published results for specific absorbed fractions. This paper provides estimates of the external dose per photon to the infant for photon energies between 0.05 and 2.5 MeV. The external dose per photon estimates were made for the three geometries and for the sources listed above. The results show that, for the geometry of the nursing infant model at the breast, the highest dose to the infant per photon comes from radionuclides deposited in the mother's liver. For the nursing infant model at the shoulder, the highest dose to the infant per photon comes from radionuclides deposited in the mother's thyroid, and for the nursing infant model in the lap, the highest dose to the infant per photon comes from radionuclides deposited uniformly in the whole body. The dose per photon results were then used to estimate the dose an infant might receive over the lactation period (6 months) due to the incorporation of 1 Bq of a radionuclide by the mother. This information may be used to provide external dose estimates to the infant in the case of a known or suspected radionuclide incorporation by the mother due to, for example, a nuclear medicine procedure.

Adult↗
PubMed2004

The validation of organ dose calculations using voxel phantoms and Monte Carlo methods applied to point and water immersion sources.

The Monte Carlo program 'Visual Monte Carlo-dose calculation' (VMC-dc) uses a voxel phantom to simulate the body organs and tissues, transports photons through this phantom and reports the absorbed dose received by each organ and tissue relevant to the calculation of effective dose as defined in ICRP Publication 60. This paper shows the validation of VMC-dc by comparison with EGSnrc and with a physical phantom containing TLDs. The validation of VMC-dc by comparison with EGSnrc was made for a collimated beam of 0.662 MeV photons irradiating a cube of water. For the validation by comparison with the physical phantom, the case considered was a whole body irradiation with a point 137Cs source placed at a distance of 1 m from the thorax of an Alderson-RANDO phantom. The validation results show good agreement for the doses obtained using VMC-dc and EGSnrc calculations, and from VMC-dc and TLD measurements. The program VMC-dc was then applied to the calculation of doses due to immersion in water containing gamma emitters. The dose conversion coefficients for water immersion are compared with their equivalents in the literature.

Humans↗
PubMed2003

Voxel phantoms and Monte Carlo methods applied to in vivo measurements for simultaneous 241Am contamination in four body regions.

A Monte Carlo program, Visual Monte Carlo (VMC) in vivo, was written to simulate photon transport through an anthropomorphic phantom and to detect radiation emitted from the phantom. VMC in vivo uses a voxel phantom provided by Yale University and may be used to calibrate in vivo systems. This paper shows the application of VMC in vivo to the measurement of 241Am deposited simultaneously in the thoracic region, the bones, the liver and in the rest of the body. The percentages of 241Am in the four body regions were calculated using the biokinetic models established by the ICRP, for a single intake via inhalation. The four regions of the voxel phantom were then 'contaminated' in accordance with the calculated percentages. The calibration factor of the in vivo system was then obtained. This procedure was repeated for the radionuclide distributions obtained 5, 30, 120, 240 and 360 days after intake. VMC in vivo was also used to calculate the calibration factor of the in vivo system in which the radionuclide was assumed to be deposited only in the lung, as is normally done. The activities calculated with the radionuclide distributed in the four body regions as a factor of time, and the activities calculated with the radionuclide deposited in the lung only are compared.

Americium↗
PubMed1996

Protamines of reptiles.

We have characterized for the first time the complete primary structure of the main protamine components of the sperm from four reptiles: Chrysemys picta (turtle), Elaphe obsoleta (snake), Anolis carolinensis (lizard), and Alligator mississipiensis (crocodilian). These species were chosen to represent one of each of the main phylogenetic branches of this taxonomic group. Comparison of these protamine sequences with those already available from other vertebrate groups allows us to define properly the chemical consensus composition of protamines and provides a unique insight into their molecular evolution and classification.

Alligators and Crocodiles↗
PubMed1991

Medical and related aspects of the Goiânia accident: an overview.

On 13 September 1987, a radiation accident occurred in the city of Goiânia in Central Brazil. Approximately 250 people were exposed to a 137Cs source from an abandoned radiotherapy unit. At least 14 patients showed some degree of bone marrow depression, and eight developed the classical signs and symptoms of acute radiation syndrome (ARS). Twenty-eight people presented local radiation injuries ranging from first to third degree, and 104 individuals showed evidence of internal contamination. This paper describes the circumstances of the event, the first-aid measures taken, the criteria adopted for triage of the exposed population, and the radiation protection procedures used during the clinical management of the irradiated individuals.

Accidents↗
PubMed1983

Detection and persistence of specific IgM antibody to Coxiella burnetii by enzyme-linked immunosorbent assay: a comparison with immunofluorescence and complement fixation tests.

An enzyme-linked immunosorbent assay (ELISA) for specific IgM antibody to Coxiella burnetii was compared with the indirect immunofluorescence (FA) test in studies of 130 serum samples from 38 patients with Q fever. The IgM fractions obtained after rate zonal-density gradient ultracentrifugation of 37 serum samples from 12 patients were also studied in a complement fixation test (CF-DG). Specific IgM antibody to C burnetii was detected by all three methods in sera collected two to eight weeks after the onset of symptoms. The longest period for which specific IgM was shown to persist was 17 weeks by ELISA and FA and 10 weeks by CF-DG. The ELISA is performed with a single dilution of convalescent-phase serum and offers advantages over the subjective FA and the technically tedious CF-DG methods. The estimation of C burnetii-specific IgM by ELISA or FA is useful for the confirmation of infection when a rising titer of complement-fixing antibody cannot be demonstrated because acute-phase blood samples are not available.

Antibodies, Bacterial↗
PubMed1983

Immunoglobulin responses to Coxiella burnetii (Q fever): single-serum diagnosis of acute infection, using an immunofluorescence technique.

Blood specimens were collected over various periods of time from 30 abattoir workers with a clinical diagnosis of Q fever. All specimens were tested for complement-fixing antibodies and for specific immunoglobulin M (IgM) globulins to phase 1 and 2 Coxiella burnetii organisms by an immunofluorescence technique. All 22 patients with increasing levels of complement-fixing antibodies were shown to have generated specific IgM globulins, as did 4 patients with high convalescent titers but from whom "acute" specimens were not collected. Four individuals who did not show increasing levels of complement-fixing antibodies did not produce measurable levels of specific IgM. All patients with Q fever gave positive specific IgM results by 2 weeks after the onset of symptoms. IgM to phase 1 antigen persisted for 27 weeks in one patient, but IgM to phase 2 antigen was not detectable beyond 17 weeks. The estimation of Q fever-specific IgM has proved useful in confirming infection when only a "convalescent" blood specimen is available.

Abattoirs↗
PubMed1981

Retrospective diagnosis of Q fever ina country abattoir by the use of specific IgM globulin estimations.

Twenty-two cases of pyrexial illness which occurred amongst workers in a country abattoir were investigated retrospectively for Q fever, brucellosis, and leptospirosis. In 18, the illness was shown to be Q fever. No diagnoses were established for the other four. The demonstration of circulating Q-fever-specific IgM globulin was instrumental in establishing the diagnosis in many of the cases.

Abattoirs↗