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G H Kenner

Publications and source records attributed to G H Kenner.

At least 19 recordsLinked to original sources
PubMed2000

Preliminary report on the development of a virtually nondestructive additive dose technique for EPR dosimetry.

We propose a new approach to the additive dose method in EPR dosimetry studies for tooth enamel specimens. We outline a specialized routine whereby the sample may be left for the most part unirradiated, while only a small aliquot of the sample will be additively irradiated to relatively large doses. The routine is done in such a way so as not to significantly compromise either precision or accuracy of the dose reconstruction. It is also demonstrated that the overall throughput of the dose reconstruction is not appreciably compromised. With this potential ability, the utility of an international dose/sensitivity standard for EPR dosimetry of teeth is considered.

Dental Enamel↗
PubMed1999

An EPR dosimetry method for rapid scanning of children following a radiation accident using deciduous teeth.

Electron paramagnetic resonance dosimetry may be applied to whole deciduous teeth of children. This makes it feasible to make direct measurement of absorbed gamma ray dose in the days and weeks following a nuclear accident, particularly if used in conjunction with a public awareness program. The technique reported here requires little sample preparation and has resulted in precision of approximately 30 mGy (1 sigma) for a deciduous incisor. Under conditions for rapid screening procedures, the methodology is estimated to provide 0.5 Gy accuracy. The largest error in the process is the determination of an appropriate background native signal for subtraction from the whole tooth spectrum. The native signal is superimposed on the radiation-induced signal, and the subtraction requires knowledge of a sample's relative content of enamel and dentin along with their relative native signal intensities. Using a composite background standard, an equivalent absorbed dose of 70+/-38 mGy (1 sigma) was determined. The lower detection limit of the technique was achieved by the elimination of anisotropic effects through rotation of the sample during measurement, together with subtraction of the standard native background signal and empty tube background spectra from the sample spectra.

Child↗
PubMed1998

EPR properties of synthetic apatites, deorganified dentine, and enamel.

Electron paramagnetic resonance spectroscopy (EPR) was used to study synthetic hydroxyapatite and approximately 1, 2, and 6% synthetic carbonated apatites, deorganified dentine, and enamel. The carbonated apatites were synthesized by hydrolysis of dicalcium phosphate. Comparisons were made with spectra from enamel and deorganified dentine. Microwave power saturation and dose responses were determined for the synthetic materials. The Marquardt version of the Levenberg decomposition method was used to extract individual signals from the apatite data. Two samples of dentine were irradiated with 25 and 100 Gy, respectively, from a 60Co source. The first sample was then deorganified at 200 degreesC using the Soxhlet extraction technique. A third sample was irradiated with 100 Gy after deorganification. The resulting EPR spectra were then compared. It was determined that the dosimetric signal of 2% synthetic carbonated apatite was approximately the same as that of enamel. It was also verified that the dosimetric signal saturates at about 2% in synthetic carbonated apatites. The study established that the precenters responsible for the dosimetric signal (g perpendicular = 2.0018, g parallel = 1.9985) are preferentially concentrated in the surface-accessible region of the mineral component, as shown by the approximately 80% attenuation of the dosimetric signal in dentine following deorganification. The precenters responsible are not destroyed by the deorganification since the magnitude of the dosimetric signal from the dentine specimen irradiated following deorganification was approximately twice that of the comparable untreated, irradiated sample. Finally, the dose response of 2 and 6% synthetic carbonated apatites was determined.

Apatites↗
PubMed1997

Electron paramagnetic resonance techniques and space biodosimetry.

This paper was presented at a workshop addressing the potential of biodosimetry techniques for use in the interplanetary space program. Some of the concerns for adequate dosimetry in space include: (1) a dosimeter that provides a permanent record of the cumulative dose and can be read independently on return to Earth; (2) a dosimeter which cannot be lost, forgotten or inadvertently removed by an individual; and (3) appropriate assessments of radiation exposures that pose an acute health risk and could jeopardize the success of an interplanetary mission. Tooth enamel is a permanent, stable biological dosimeter showing great promise in retrospective dosimetry of radiation accidents. With a proper technique, the minimum detectable dose can be in the range of tens of milligrays in extracted, prepared teeth. In addition to transient accidental doses, the cumulative dose from chronic low-level exposures (which individually may be below reportable limits) is recorded in the enamel of teeth. While many teeth remain with an individual over all or most of a lifetime, one or more are often removed due to dental problems and provide an opportunity to make dosimeteric measurements. The collection and analysis of extracted teeth in later life allows measurement of cumulative lifetime dose using the high-sensitivity techniques described in this paper. The goal of a lightweight, high-sensitivity, in vivo EPR spectrometer has not yet been realized, but its benefit to all aspects of retrospective dosimetry, terrestrial or otherwise, would be great. This paper reviews the current status of EPR dosimetry of teeth as applied to retrospective measurements of accidental exposures and outlines future research directions which will further reduce the limits of detection.

Aerospace Medicine↗
PubMed1995

Electron paramagnetic resonance dosimetry of dentine following removal of organic material.

The feasibility of using dentine from surgically extracted human teeth as in vivo dosimeters was investigated. The organic fraction of human dentine was removed by Soxhlet extraction with diethylenetriamine. The specimens were then crushed and 75 to 250 microns granules were given doses of gamma radiation ranging from 50 mGy to 8 Gy. Following irradiation, electron paramagnetic resonance spectra were collected. Signals were detected with Lande factors of g = 2.0018, line width = 0.903 mT; and g = 1.9961, line width = 0.444 mT. These signals have both been reported for hydroxyapatite of bone and enamel. Several other signals were also seen but not characterized. It was concluded that doses of 500 mGy or less may be resolved with prior removal of the organic component of dentine.

Dentin↗
PubMed1994

Thermoluminescence measurements of gamma-ray doses attributable to fallout from the Nevada test site using building bricks as natural dosimeters.

During the 1950's, the U.S. Government conducted an intensive atmospheric nuclear testing program in Nevada. Fallout from these atmospheric tests was measured throughout the U.S. with some of the heaviest concentrations to populated areas falling east of the test site in Washington County, UT. External exposures from 6.5 x 10(-4) C kg-1 to 26 x 10(-4) C kg-1 (2.5-5.0 R) were reported for this region. This study provides an independent measurement of fallout radiation doses to selected communities in Utah using a thermoluminescence technique originally developed for the dating of ancient pottery. The application of the predose thermoluminescence technique to fallout dosimetry is described. A mean dose of 38 +/- 15 mGy (4.4 +/- 1.7 R), attributed to fallout radiation, was measured in quartz grains extracted from the outer centimeter of bricks removed from six communities in Washington and Kane Counties in Utah.

Construction Materials↗
PubMed1991

Corpus callosum: multiple parameter measurements in rodents and humans.

A magnified drawing of a human or a rodent corpus callosum is traced on a digitizing tablet. From this tracing the computer calculates callosal area, perimeter, length, and 99 widths, one for each percentile location along the longitudinal axis of the callosum. In addition, the human program encloses the callosum within a rectangle to obtain several other measures. The use of percentile widths allows one to generate a callosum profile to compare different clinical groups or different species. The human callosum program is compared to one recently reported by another research group.

Algorithms↗
PubMed1990

A computer-aided procedure for measuring swim rotation.

As a rat or mouse swims in a small cylinder, its movements are tracked by an observer using a joystick, and the information is sent to a Macintosh computer. The swimming circle is broken into quadrants. The sequence of quadrants entered and the time spent in each quadrant are recorded as the basic data. From the data set one can extract full or partial turns, clockwise or counterclockwise rotations, total activity, and speed of swimming clockwise and counterclockwise. Two laterality indices, one based on full turns and the other on partial turns, are calculated. Test-retest reliability for rats and mice for 3-minute and 5-minute observation intervals are reported.

Animals↗
PubMed1990

A computer-aided procedure for measuring Morris maze performance.

A common procedure for recording Morris maze performance is to trace the animal's path on a template of the maze. This procedure is used in a computer-based recording system. A maze template is placed on a digitizing tablet, an electronic cursor with pen attachment is used to trace the animal's path, and the data are sent to a computer where a program called Spatial Maze obtains the following measurements: total time in seconds, total distance traveled in inches, average speed, absolute and percent time in each quadrant, absolute and percent time in each annulus, the XY coordinate information needed to reconstruct the complete path of the animal, swimming angles, and the number of rears while on the platform. These measurements are then sent to Excel for statistical and graphic analyses.

Animals↗
PubMed1990

A computer-aided procedure for measuring discrimination learning.

A computer program is described for a two-choice black-white T-maze discrimination task involving 10 trials per day for 5 days. A Gellerman series of 44 semirandom L/R sequences is included within the program to specify the location of the reinforcing stimulus on each trial. A picture of the T-maze appears on the screen, and the experimenter tracks the animals's movements as it goes through the maze. At the end of the 10 trials, the following statistical information is obtained: number of initial choices into the left alley, number of correct choices, number of trials in which no choice was made, median time to make a choice, and a learning score based upon the path taken by the animal. These data are then sent to Excel for statistical processing.

Animals↗
PubMed1982

Intramedullary fixation of artificial hip joints with bone cement-precoated implants. I. Interfacial strengths.

In order to minimize the problems associated with implant fixation using acrylic bone cement, a new technique has been investigated. Canine hip prostheses were precoated with self-curing acrylic bone cement and implanted in random source dogs using the same cement for fixation, a precoated prosthesis on one side and an uncoated (control) on the other. After 1, 3, and 6 months, both femora were excised and sectioned for mechanical assessment of the interfaces among bone, cement, and implant. It was found that the precoated implants had much higher interfacial shear strengths than the uncoated ones (average 14.2 and 6.8 MPa for implant-cement interface; 2.0 and 1.2 MPa for the cement-bone interface for all implant periods). The precoated "old" cement and the "new" cement's interfacial shear strength was the strongest with an average of 15.1 MPa for all implant periods. The present results indicate that the precoated hemiarthroplastic implants provide a firmer intramedullary fixation than the traditional, uncoated implants.

Animals↗
PubMed1982

Intramedullary fixation of artificial hip joints with bone cement-precoated implants. II. Density and histological study.

Bilateral coxofemoral hemiarthroplasties were performed in dogs using experimental and control implants, which were fixed with bone cement. The stem of the experimental implant was precoated with bone cement, about 2 mm thick. After 1, 3, and 6 months the femora with implant specimens were harvested and sectioned for mechanical and histological evaluation. Histological observations on the implant-bone interface and density measurements of the bone cement are reported. The density of the precoated bone cement was higher than the same cement used for implant fixation at the time of implantation (1.202 vs. 1.188 g/mL). The precoating also resulted in milder histological reactions, including thinner fibrous tissue capsule and smaller gap between bone and cement. The present results and the previously reported mechanical findings strongly support our hypothesis that a better and longer lasting prosthesis fixation can be achieved using cement-precoated prosthesis combined with the customary cement fixation technique.

Animals↗
PubMed1981

Piezoelectric ceramic implants: in vivo results.

The suitability of barium titanate (BaTiO3) ceramic for direct substitution of hard tissues was evaluated using both electrically stimulated (piezoelectric) and inactive (nonpolarized) test implants. Textured cylindrical specimens, half of them made piezoelectric by polarization in a high electric field, were implanted into the cortex of the midshaft region of the femora of dogs for various periods of time. Interfacial healing and bio-compatibility of the implant material were studied using mechanical, microradiographical, and histological techniques. Our results indicate that barium titanate ceramic shows a very high degree of biocompatibility as evidenced by the absence of inflammatory or foreign body reactions at the implant-tissue interface. Furthermore, the material and its surface porosity allowed a high degree of bone ingrowth as evidenced by microradiography and a high degree of interfacial tensile strength. No difference was found between the piezoelectric and the electrically neutral implant-tissue interfaces. Possible reasons for this are discussed. The excellent mechanical properties of barium titanate, its superior biocompatibility, and the ability of bone to form a strong mechanical interfacial bond with it, makes this material a new candidate for further tests for hard tissue replacement.

Animals↗
PubMed1980

Piezoelectric ceramic implants: a feasibility study.

A piezoelectric ceramic has been investigated as a direct substitute for hard tissues. Barium titanate (BaTiOz) power was slipcast and fired at 1430 degrees C for 2 hr, then made piezoelectric by polarizing. After 16 and 86 days of implantation in the cortex of the femoral midshafts, the femora with test specimens were sectioned into about 4-cm lengths. Their voltage outputs were measured under cyclic load at 1 Hz. The present results show that the voltage gradient at the implant surface is 0.15 mV/mm for the 16-day implantation with a 445-N (100-lbs.) load. This in turn can give rise to about 0.01 microA current flow in the adjacent area of the 16-day implant. The 86-day implant showed an order of magnitude higher voltage output compared to the 16-day implant with the same magnitude of loads. This is probably due to the "load-transfer" efficiency through the implants, since the voltage output is directly proportional to the actual load transferred to the implant. The more bone implant interface matures, the better the load transfer occurs through the implant, resulting in higher voltage output.

Animals↗