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E Polig

Publications and source records attributed to E Polig.

At least 37 records · Page 2Linked to original sources
PubMed1990

A model of osteon closure in cortical bone.

A model of osteon closure is presented that incorporates some physiologic features of cortical bone remodeling, such as matrix synthesizing activity of osteoblasts, their burial as osteocytes, and elimination of cells. A simplified version of the model assumes a constant osteoblast activity throughout radial closure. An extended version allows for variable osteoblasts activity and is based on Lee's law of radial closure kinetics. The model calculations (extended model) show that both in humans and beagle dogs osteoblast activity steadily decreases during radial closure of the osteon. The potential of the model is also illustrated by calculating the dynamic change of the geometrical shape of the closing cone and the time dependence of the osteoid seam width, number of osteoblasts and bone formation rate in the closing cone.

Animals↗
PubMed1989

Radiation dose factors for alpha-emitters in osteons and some considerations on dose non-uniformity ratios and relative distribution factors.

Dose factors for locations within a tissue-filled cylindrical cavity bounded by an infinite medium of bone labelled with an alpha-emitter are calculated by means of a Monte Carlo procedure. The calculational approach is general and allows us to determine dose factors for specific distances or target volumes defined by concentric cylinders, as well as various source geometries including surface sources, buried surface sources, infinite and bounded volume sources, and also comprises plane (trabecular) surfaces as a limiting case. Values for the dose factors and the contribution of cross-fire traversals are calculated mainly for 239Pu and 226Ra and a typical Haversian canal diameter of 30 microns in beagles and 70 microns in humans. Also tables are given that allow dose factors to be derived for the relevant range of alpha-particle energies, diameters and target distances. The dose non-uniformity factors (local dose rate/average skeletal dose rate) for 239Pu are 27.2 in humans and 14.0 in beagles. The corresponding values for 226Ra are in the ranges 1.18-1.26 (humans) and 0.90-0.97 (beagles) for a 222Rn retention between 10-30%. The relative distribution factors 239Pu/226Ra are 21.5-23.0 for humans and 14.5-15.6 for dogs. General expressions for calculating non-uniformity factors and relative distribution factors are derived and implications are discussed in the light of some experimental findings.

Alpha Particles↗
PubMed1989

Kinetic model of the distribution of 239Pu in the beagle skeleton.

A model is presented to analyze the retention of Pu in the major deposition organs of the beagle dog and predict the dynamic behavior of skeletal labels. The kinetic part describing the gross organ distribution was represented by a compartment model. A fit to empirical retention equations of liver and skeleton yielded skeletal clearance corresponding to turnover rates of 93.8% y-1 and 3.8% y-1 in trabecular and cortical bone, respectively. Initially about 9% of skeletal Pu is deposited in cortical bone. The blood flow changes over a period of 3000 d from an initial 0.15% of the injected dose per day to 0.05% d-1 at the end of this period. More than 100% of the injected Pu is recirculated back to the skeleton during this interval. The calculation of the label dynamics showed that nearly complete volumization of Pu was only possible assuming a very high affinity ratio of forming vs. resting surfaces and high bone turnover rates. There was a steady increase in the fractional activity of surface and secondary diffuse labels in cortical bone whereas in trabecular bone these labels showed maximum activity at about 2 y after injection. The Pu concentration on pre-existing trabecular bone surfaces that were not remodeled within 3000 d post injection increased by a factor of 3.6. The model may be applied to single bones or the skeleton as a whole. The flow of Pu in the blood can be derived in human cases where urinary excretion rates are available. With the blood flow known, the model enables one to simulate the dynamic behavior of skeletal labels even for very general conditions of human contamination, including inhalation.

Animals↗
PubMed1989

Bone structural parameters, dosimetry, and relative radiation risk in the beagle skeleton.

A variety of morphometric and histomorphometric parameters such as the mass of bone and marrow, bone surface areas, percentage of bone volume, percentage of the surface that is trabecular, and percentage of surfaces that are forming and resting are calculated for all major parts of the beagle skeleton. The total bone surface of the beagle is estimated at 2.9 m2 with 53.7% of the surface area being associated with trabecular bone. There are about 4.5 x 10(9) bone-lining cells and about 1 x 10(9) osteoblasts. From the fractional retention in each part of the skeleton, the initial surface concentration of 239Pu after a single injection of 592 Bq/kg body wt (0.016 microCi/kg) on resting surfaces and at sites of bone formation is calculated for various values of the affinity ratios of trabecular/cortical and forming/resting surfaces. These estimated concentrations then yield dose rates as well as cumulative and collective doses to bone-lining cells and osteoblasts in the different parts of the skeleton. On the assumption that the relative risk of tumor induction is proportional to the collective dose to either bone-lining cells or osteoblasts, the frequency of tumor occurrence is calculated and compared to observed frequencies. Both hypotheses yield approximate agreement with experimental data for different ratios of trabecular/cortical radiation sensitivity, although the differences between some bones are statistically significant.

Animals↗
PubMed1988

Microdistribution and local dosimetry of 226Ra in trabecular bone of the beagle.

Sections of lumbar vertebral bodies of young adult beagle dogs have been analyzed autoradiographically to characterize and quantify the local distribution of 226Ra by means of a scanning microscope photometer. The animals received a single injection of 355 kBq/kg body weight and were serially sacrificed at 5 to 1381 days postinjection. Hotspot concentrations decreased from about 51 kBq/g bone at 5 days to 20 kBq/g at 1381 days postinjection. The diffuse concentration changed from 8.3 to 1.9 kBq/g. The mean 226Ra concentration in the trabecular areas scanned was initially higher and at the end of the observation period lower than the average calculated for the whole lumbar vertebral column. Density and area of, and fraction of bone activity in, hotspots virtually remained constant. With time hotspots tended to become translocated into bone volume. Mean dose rates to lining cells from both hotspots and diffuse labels decreased from about 210 mGy/d at early postinjection times to 105 mGy/d. This corresponds to 2.5 to 1.1 times the average skeletal dose rate. A discussion of the level of irradiation in terms of hit frequencies shows that osteoblasts in the initial phase of hotspot formation receive about 60 hits to their nucleus for the duration of bone formation. After about 6 months, however, the 226Ra concentration in new bone and the corresponding hit frequency appears to be low enough that interference with bone formation is unlikely. Morphometric measurements showed that abnormal bone accretion and thickening of trabeculae occurred. This was interpreted as an imbalance between bone formation and resorption. Both formation and resorption seem to be substantially lowered compared to control animals.

Animals↗
PubMed1987

Bone age and remodeling: a mathematical treatise.

Remodeling of an element of mineralized bone is described by specifying the probability per unit time of being replaced as a function of age of the element. The functional dependence of this probability is called the "law of remodeling." The properties of this stochastic law of remodeling are discussed in terms of random, selective, and redundant remodeling. A relationship between the law of remodeling and the mean bone tissue age is derived. It is shown how the probability density of bone age for individual elements of bone depends on the law of remodeling. The mathematical formalism is exemplified by assuming a specific parametric form of the law. A procedure for experimentally determining the law is suggested based on tracing the resorption of single fluorescent labels. Finally, the extension of the model to a real skeleton with regional differences in turnover rates is discussed.

Age Determination by Skeleton↗
PubMed1984

Microdistribution and localized dosimetry of 241Am in bones of beagle dogs.

The microdistribution of 241Am in selected bones of seven beagle dogs was analysed using a computer controlled microscope photometer. Four of the animals receiving between 102.5 and 165 kBq/kg were killed between 7 and 20 days after injection, and three animals receiving 32.9-34.0 kBq/kg were killed between 1300 and 1569 days. Using the photometric scanning technique, the concentrations of 241Am in several anatomical regions, as well as the specific surface activities and their variations, dose rates, accumulated radiation doses, burial depths and morphometric parameters, were derived. Dose rates to the 0-10 micron marrow band adjacent to surfaces were found to be between 8.6 and 15.7 times higher than the average skeletal dose. Accumulated radiation doses from initial deposits to lining cells were estimated to be between 87 and 252 Gy. The average burial depth in the animals killed at later times was around 8 micron. Morphometric parameters showed that radiation damage occurred in these animals, resulting in abnormal trabecular architecture. A positive correlation between specific surface activity and local turnover rates was established.

Americium↗
PubMed1984

Morphometry of bone cell nuclei and their location relative to bone surfaces.

The shapes and locations of lining cells, osteoblasts and osteoprogenitors in sections of rat bone have been quantified by means of a digitiser. The nuclei of all three types of cells can be characterised by oblate spheroids (ellipsoids of revolution). The axis dimensions, their relative variations and the correlation between these parameters have been determined by computer simulation. The nuclear volume of progenitors (288 microns) is more than twice the volume of osteblasts and lining cells (127 microns and 113 microns, respectively). The true mean perpendicular distances of nuclei are 3.1 microns, 5.7 microns and 7.7 microns for lining cells, osteoblasts and progenitors, respectively. The probability densities for true perpendicular distances have been calculated and analytical expressions are given that formally characterise these densities.

Animals↗
PubMed1983

Specific energy spectra at alpha-contaminated bone surfaces.

Spectra of specific energy f(z) in spherical and disc-shaped targets are determined for plane sources of alpha-particles. The radioactive plane is assumed to be coincident with bone surfaces or 'buried' within bone. Parameters determining energy straggling and the spectrum of delta-rays generated outside the target were determined from published parallel beam experiments with wall-less counters. An analytical procedure for calculating single and multiple event spectra for the sphere is demonstrated. For discs spectra are derived from Monte-Carlo calculations. In discs of 6.5 micrometers radius and 1 micrometer thickness adjacent to bone surfaces the mean specific energy per event is 2967 erg/g, while tht in a sphere of equal volume is 5247 erg/g. The relative variation of specific energy in the disc is about twice as large as in the sphere.

Bone and Bones↗
PubMed1983

Microdosimetry of alpha-emitting bone seekers.

Microdosimetric probability distributions of specific energy f(z) in cell nuclei at alpha-contaminated bone surfaces are determined. The calculations are based on autoradiographic measurements of specific endosteal surface activities of rats injected with 239-Pu. The effect of a variation of the surface activity and target density and a correlation of both is discussed. A mathematical description of trabecular bone remodeling is given and the dependence of specific energy deposition on remodeling processes is demonstrated. For non-age-dependent remodeling and relatively large numbers of hits (greater than 20) the main contribution to the variation of f(z) comes from the variation of residual lifetimes and specific surface activities. With small numbers of hits (less than 1) the variation is mainly determined by the Poisson hit statistics and the width of the single event spectrum.

Bone and Bones↗
PubMed1981

Hit probability for cellular targets by bone-surface-seeking alpha emitters.

Irradiation of cellular targets near bone surfaces with surface-seeking alpha-emitters is discussed in terms of hit probabilities to spheres. The geometrical factor describing the average number of hits as a function of distance from the surface is shown to be approximately proportional to the dose rate over most of the particle range. The hit probability is calculated for the case of a non-uniform distribution of cell nuclei at the bone surfaces of the thoracic vertebrae of beagles. The effect of a spatial variation of the specific surface activity and burial depth along bone surfaces is evaluated and a general expression derived, relating the hit probability to the dose rate distribution. From this expression numerical results are calculated using measured dose rate distributions in the lumbar vertebrae of rats. The validity of the underlying assumption and the consequences with respect to tumour models are discussed.

Alpha Particles↗
PubMed1976

The influence of 241-Am and DTPA on morphometric parameters of the rat femur.

Microradiographically detectable alterations of the bone structure in the femur of young rats induced by monomeric 241-Am(III) (i.v., 30 muCi/kg) were studied. The morphometric and dosimetric measurements were carried out by means of an electronic image analyzer. 8 weeks after injection of 241-Am a characteristic alteration of the frequency distribution of the chord lengths over the trabeculae in the epiphysis and over the metaphyseal marrow spaces was found. The structure of the spongiosa is irregular with both large, coarse and small fragmented trabeculae. The complexity of the bone architecture and the area of the endosteal surfaces is reduced. The surface/volume ratio in control animals varies between 36 mm-1 in the epiphysis and 64 mm-1 in the region of the epiphyseal cartilage plate. From the specific surface burden (pCi/mm2) the average dose rates were determined. There is no significant difference between the calcified tissue fraction in controls and animals with 241-Am, with the exception of the metaphyseal band where the locally high dose rates cause a devitalization of the tissue with inhibition of bone resorption as well as an abnormal trabeculation in the metaphysis. Treatment by Ca-DTPA reduces the 241-Am deposition nonuniformly and the pathological manifestations are markedly less pronounced. The mean trabecular width is about 100 mum in the epiphysis and has a minimum of 40 mum in the central part of the epiphyseal plate. The mean chord length over the marrow spaces varies between 90 and 210 mum.

Americium↗
PubMed1975

Microphotometry as a tool for automatic scanning of solid state nuclear track detectors.

By use of a scanning microphotometer the light transmission with both dark field and bright field illumination was determined as a function of the alpha-track density on cellulose nitrate detectors. The so obtained calibration curves allow a rapit measurement of the number of tracks per field and, thus, of the dose rate. To illustrate the application of the method, a scan of a detector exposed on a bone section of a rat injected with 241Am is presented.

Americium↗