Surface to volume ratios of bone determined by computer analysis of microradiographs

Bone Mass Determination from Microradiographs by Computer-Assisted Videodensitometry

The mass of hard-tissue specimens is assessed by optimised microradiography followed by computer-assisted videodensitometry. Radiographs are produced with 27 kV roentgen radiation, filtered through 0.5 to 1 mm of aluminium, on high-resolution glass plates. Aluminium step wedges are used for density calibration, the result being expressed as ‘aluminium equivalent mass’. The plates are subjected to digital image analysis by an operator in interaction with a computer-based image processor, a television camera being used for image input. The program stored in the computer provides calibration of geometry and—via the stepwedge images—of densitometry, background adjustment, etc. Measurement takes place by integration over the specimen-image area. No assumptions being needed concerning a specific attenuation model, the errors stemming from the common presumption of exponential attenuation are eliminated. Density profiles or maps of mass distribution are readily obtained from the computer. From measurements of aluminium phantom samples, the total random error (coefficient of variation) was determined at 1.8 per cent, the microradiographic and videodensitometric procedures contributing 1.6 per cent and 0.9 per cent, respectively, whereas the systematic error was negligible. Since specimens need not be sectioned, this method does not interfere with subsequent histologic preparation.

A quantitative analysis of the structure of human sternum

An extensive study of the human sternum has been carried out to obtain estimates of the omnidirectional path-length distributions and structural parameters for trabeculation and marrow spaces. Data for sternum samples have been collected, using an object plane scanning microscope. These data have been used to produce the omnidirectional path-length distributions and values of structural parameters for the whole sternum. For a typical adult man the mean trabecular and marrow space path lengths are 224 and 1364 μm, respectively. The percentage bone volume is 13.8 and the surface to volume ratio is 190 cm. Data on the structural variations within the whole sternum are presented. They show a percentage difference in bone volume between the manubrium and the body of sternum of about 36%.

Beta-particle dosimetry of the trabecular skeleton using Monte Carlo transport within 3D digital images

Presently, skeletal dosimetry models utilized in clinical medicine simulate electron path lengths through skeletal regions based upon distributions of linear chords measured across bone trabeculae and marrow cavities. In this work, a human thoracic vertebra has been imaged via nuclear magnetic resonance (NMR) spectroscopy yielding a three-dimensional voxelized representation of this skeletal site. The image was then coupled to the radiation transport code EGS4 allowing for 3D tracing of electron paths within its true 3D structure. The macroscopic boundaries of the trabecular regions, as well as the cortex of cortical bone surrounding the bone site, were explicitly considered in the voxelized transport model. For the case of a thoracic vertebra, energy escape to the cortical bone became significant at source energies exceeding approximately 2 MeV. Chord-length distributions were acquired from the same NMR image, and subsequently used as input for a chord-based dosimetry model. Differences were observed in the absorbed fractions given by the chord-based model and the voxel transport model, suggesting that some of the input chord distributions for the chord-based models may not be accurate. Finally, this work shows that skeletal mass estimates can be made from the same NMR image in which particle transport is performed. This feature allows one to determine a skeletal S-value using absorbed fraction and mass data taken from the same anatomical tissue sample. The techniques developed in this work may be applied to a variety of skeletal sites, thus allowing for the development of skeletal dosimetry models at all skeletal sites for both males and females and as a function of subject age.

Evaluation and modification of a physiologically based model of lead kinetics using data from a sequential isotope study in cynomolgus monkeys

Endogenous (predominantly bone) and exogenous lead were differentially labeled in two 11-year-old female cynomolgus monkeys (Macaca fascicularis) to establish the contributions of the two sources to blood lead. The monkeys had been administered a common lead isotope "mix" at the rate of about 1300 micrograms Pb/kg body wt/day from age 10 months until the start of the study. On day 0, common lead was replaced in sequence by mixes artificially enriched in 204Pb, 206Pb, and 207Pb, given for periods of from 50 to 281 days. Total lead ingestion rate was held constant except during administration of the 207Pb-enriched mix to one of the monkeys, when it was reduced to 650 micrograms/kg/day. Blood and bone were sampled at intervals and analyzed for their content of each of the isotope mixes. A physiologically based model of human lead kinetics was scaled to the cynomolgus monkey and fit to the data to test the correctness of the model structure and to assist with interpretation of study results. Fractional absorption was varied to achieve the best visual fits of the scaled model to blood and bone concentration data for each monkey. The model failed to reproduce the sharp drop in isotope concentrations in blood observed after each exchange of isotope mix. Consequently, it was revised to include a rapid-turnover trabecular bone compartment and a slow-turnover cortical bone compartment, using estimates of trabecular and cortical bone turnover rates from histomorphometric studies in adult cynomolgus monkeys. The revised model fit most of the sets of bone and blood concentrations well. About 17% of the blood lead originated from bone after 11 years of exposure, at blood lead concentrations in excess of 50 micrograms/dl. The rate of return of common lead from bone, as estimated from the model, was 28 micrograms/day just before termination of controlled common lead exposure on day 0. Based on the success of the scaled human model in fitting these data and on the absolute and relative values of bone and blood lead concentrations, the metabolism of lead in the cynomolgus monkey appears to be similar to human lead metabolism.

"Physiological osteoporosis" and "osteoblast insufficiency" in old age. Comparative radiological-morphometric and statistical studies on the spongy bone of lumbar and cervical vertebral bodies

To investigate the expectation of general insufficiency of osteoblasts with increasing age, we studied autotopsy material from 105 deceased persons of both sexes who had died between 16 and 91 years and in whom clinically manifest diseases of the bone had been excluded. Quantitative morphometric examination of the structure of the spongy bone of the 3rd-5th lumbar vertebral bodies (LVBs) and of the 5th-7th cervical vertebral bodies (CVBs) was carried out in frontal and sagittal planes, the parameters analysed being volumetric density (Vv), surface density (Sv) and specific surface area (S/V), and the results were subjected to statistical evaluation. The results showed that in the three LVBs, Vv, Sv and S/V behave in a similar manner, Vv and Sv decreasing after the age of 50 years by more than one-third while S/V remains constant throughout life. The three lower CVBs had higher values than the LVBs for all three structural parameters. In the 7th CVB somewhat lower Vv and Sv values and higher S/V values were found than in the 5th and 6th. The age-related changes, by contrast, were very small. This differing behavior of the spongy bone in the two regions of the spinal column is an expression of the different characteristic loading forces in each regions: LVB loading is predominantly static, CVB loading mainly dynamic. Thus, from the functional point of view, what is known as "physiological osteoporosis due to ageing" is nothing more than adaptation by an ageing bone to physical activity, reflecting--like the bone of the young adult--the current loading of the cancellous bone by the actions of the musculoskeletal system. Since such physical activity is often age-related, the performance of the osteoblasts does not depend upon age per se, but merely on the remaining functional adaptive capacities of the ageing organism as whole.

Regional measurement of bone calcium accretion rate and exchangeable pool with a whole-body counter: method and studies in subjects without bone disease

A whole-body counter was used to measure the retention and distribution of radioactivity along the longitudinal axis of the body during 10 days after the intravenous injection of 50 microCi of 47Ca. These data and the simultaneous measurements of the serum specific activity allowed us to calculate, by the Bauer-Carlsson-Lindquist (BCL) formulas generalized by Marshall, the calcium accretion rate and exchangeable pool in 7 areas: skull, thorax, pelvis, thighs, knees, legs, and ankles and feet. For the whole body, the accretion rate was 336 +/- 115 mg/24 h, and the exchangeable pool 5668 +/- 1221 mg, in 26 subjects without bone disease. Both parameters were significantly correlated with body height; the exchangeable pool was significantly higher in men than in women. The accretion rate and exchangeable pool expressed on a basis of bone content varied widely from one area to another, reflecting the ratio of spongy to compact bone: the thorax, pelvis, and arms, which contain 49% of the skeletal mass, accounted for 57% of the total accretion rate and 53% of the exchangeable pool; the skull, 18% of the skeletal mass, accounted for 14% of the accretion and 11% of the pool.

Effects of therapeutic radiation on microstructure of the human mandible

Mandibular bone from eight patients who had received therapeutic radiation (6,000-7,200 rads) for intra-oral cancer was obtained at surgery (1 month to 9 years after radiation) and compared histologically with non-irradiated mandibular bone from five subjects. Measurements made on the internal remodeling process of cortical bone included the extent of internal surface and the fraction indicating resorption, and the proportions of osteones which were incomplete (less than 3/4 filled with matrix), complete, and plugged. Appreciable differences were observed in all parameters except plugged osteones. The findings suggested early cessation of osteogenesis, and somewhat later cessation of resopriton, without subsequent resumption of either process. The histologic appearance of the osteoblasts, osteoclasts, and osteones was in accord. Microfractures found in the irradiated bone were not seen to have healed. Radiation damage to the osteoprogenitor cells is postulated.

Measurements of trabecular bone structure in man

A quantitative analysis of trabecular bone structure is presented, based on omnidirectional distributions of paths across (a) trabeculation and (b) marrow cavities. The omnidirectional distributions, which take into account structural anisotropy, are generated from measured distributions of paths. Representative examples are given, together with values of two commonly quoted structural parameters, the ratio of endosteal surface to bone volume and percentage bone volume. Data on the biological and age variations in the third lumbar vertebra are also presented and an index of trabecular anisotropy suggested. Finally, the results are compared with those of other workers and estimates of useful skeletal parameters given.