Quantitative characterization of bone: a computer analysis of microradiography

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.

Blood flow measurements with [(15)O]H2O and [18F]fluoride ion PET in porcine vertebrae

A dual positron emission tomography (PET) tracer study with [18F]fluoride and the freely diffusible tracer [(15)O]H2O was performed to measure the capillary transport of [18F]fluoride and to evaluate the potential of [18F]fluoride ion PET to quantitate bone blood flow. Under the condition of a high predictable single-pass extraction fraction (E(F)) for [18F]fluoride, the [18F]fluoride ion influx transport constant (K1F), derived from kinetic [18F]fluoride ion PET measurements, can be used to estimate bone blood flow. Bone blood flow was measured in vertebral bodies by dynamic [(15)O]H2O PET during continuous ventilation with N2O, O2, and Isoflurane (FiO2 = 0.3) in seven adult mini pigs, followed by dynamic [18F]fluoride ion PET. The mean blood flow measured by [(15)O]H2O (FlowH2O) was 0.145 +/- 0.047 ml x minute(-1) x ml(-1) and the mean K1F was 0.118 +/- 0.031 ml x minute(-1) x ml(-1), respectively (mean +/- SD). Regional analysis showed excellent agreement between FlowH2O and K1F at low flow and a significant underestimation of flow by K1F relative to FlowH2O in regions of normal and elevated flow. The observed relationship between parameters followed the Renkin-Crone distribution. The permeability-surface product was determined as 0.25 minute(-1) for vertebral bodies consisting of a mixture of trabecular and cortical bone. We conclude that [18F]fluoride ion PET can be used to estimate bone blood flow in low and normal flow regions, as long as the flow dependency of the E(F) is taken into consideration. Above blood flow values of 0.2 to 0.35 ml x minute(-1) x ml(-1), the magnitude of K1F is increasingly independent on blood flow because diffusion limits tracer transport.

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.

Effect of dose, sex and age on the drug disposition of incadronate, a new bisphosphonate, in rat bone

We investigated the effects of dose, sex and age on the uptake and elimination of incadronate, a new biosphosphonate, in rat bone after intravenous administration. Following administration of 0.03-3 mg/kg to young male rats (age 7 weeks),intact drug concentration in humerus at 24 hr after administration (C24 hr) increased in a dose-dependent manner, indicating the linear uptake of the drug into bone. The estimated bone uptake clearance of 0.13 ml/min./g bone is comparable to the estimated plasma flow rate in bone, suggesting that uptake into bone is plasma flow-limited. Concentration from 24 hr after administration had declined bi-exponentially. Although t1/2 beta (350-444 days) was little altered among doses, t1/2 alpha was prolonged with increasing dose from 13.4 to 16.2 days. This effect seemed to be due to inhibition of bone resorption at higher doses resulting in the suppression of drug release from bone. No sex difference was seen on C24 hr in young rats, while the value in senescent (age 12 months) rats was 24% greater in females than in males. When comparing between ages it is seen that C24 hr values in senescent rats decreased to 50-66% of those in young rats. As for elimination from bone, t1/2 beta values in senescent rats were shortened to 76-79% of those in young rats. In contrast, little difference in t1/2 alpha was observed between ages or in either t1/2 alpha and t1/2 beta between sexes.

Comparison of the radiographic vertebral trabecular pattern with the vertebral fracture prevalence and spinal bone density

Spinal bone densitometry allows accurate and precise measurement of the severity of bone loss. Where densitometry is not yet available medical practitioners have to continue to rely on clinical radiography. Since the grey levels of the radiographic image are highly inaccurate we studied the radiographic vertebral trabecular pattern for its suitability as a semiquantitative assessment of vertebral bone loss. We defined four vertebral trabecular pattern indices (VTPI 4 = normal, VTPI 1 = severe bone loss) and tested these for correlations with the prevalence of vertebral fractures, and with spinal and hip bone mineral density measured by dual-energy X-ray absorptiometry (DXA). We found negative correlations between VTPI and the percentage of patients with vertebral fractures (p = 0.0001), between VTPI and the number of vertebral fractures per patient (r = 0.606, p = 0.001) and between VTPI and the severity of vertebral fractures, and a positive correlation between VTPI and spinal (r2 = 0.556, p = 0.0001) and hip DXA values (r2 = 0.315, p = 0.0001). We conclude that the vertebral trabecular pattern index can be used to assess the severity of spinal bone loss when a bone densitometer is not available.

Effect of controlled local release of sodium fluoride on trabecular bone

Systemic sodium fluoride has been used in the treatment of osteoporosis. Recent studies have shown that it has a positive risk/benefit ratio for use in increasing spinal trabecular bone density. However, thinning of the cortices of the long bones with a resulting increase in fracture incidence has been observed. This study was designed to determine the response of bone to sodium fluoride released from a biodegradable polymer matrix, a technique which could potentially deliver it locally to a site of need in the skeleton which has a positive response to fluoride. In one group of mature New Zealand white rabbits, cylindrical poly(D,L-lactic acid) (PLA) implants, with or without impregnated sodium fluoride, were implanted into the contralateral femoral trochanters and tibial metaphyses. In a second group, similar implants were placed in adjacent vertebrae. Four weeks postimplantation, the femora, tibiae, and vertebrae were removed, sectioned, cleaned of all but mineralized tissue, and the surfaces of the sections stained. The stained surfaces were imaged and analyzed for morphometric properties of the trabeculae. Comparing contralateral vertebrae, those exposed to sodium fluoride had significantly thickened trabeculae, with decreased spacing between them and a greater bone fraction. A similar increase in trabecular width was found in the subchondral bone of the proximal tibiae exposed to local release fluoride. Femoral sections showed no difference, possibly due to the lack of extensive trabecular bone in the region chosen for study.

Cortical and cancellous bone: age-related changes in morphologic features, fluid spaces, and calcium homeostasis in dogs

The changes in cortical and cancellous bone that occur with aging were studied by measuring morphologic and physiologic variables for both types of bone in dogs. The percentage area of cortical and cancellous bone, rate of bone formation, vascular volume, bone water, and volume of distribution of calcium tracer all showed statistically significant changes at the time of bone maturity. Canine cortical bone cell volume progressively decreased with advancing age, and cancellous bone cell volume significantly decreased between adult and old dogs. The volume of distribution technique can be used to determine the relative contributions of cortical and cancellous bone to the total body exchangeable calcium ion pool.

Lead in vertebral bone biopsies from active and retired lead workers

Samples of vertebral bone were obtained by skeletal biopsy and lead concentrations were determined by atomic absorption spectroscopy. The median level of lead in bone in 27 active lead workers was 29 micrograms/g wet weight (range 2-155), corresponding to 370 micrograms/g calcium (range 30-1,120). In 9 retired workers, the corresponding levels were 19 micrograms/g (5-76) and 250 micrograms/g calcium (60-700); in 14 reference subjects without occupational exposure, 1.3 micrograms/g (1-4) and 13 micrograms/g calcium (8-40). The bone lead content rose with time of exposure. Comparison of levels in vertebra with those in fingerbone, as measured by in vivo x-ray fluorescence in the same subjects, strongly suggested the presence of lead pools with different kinetics. The accumulation pattern, as well as the relation between levels in vertebra and fingerbone, suggests a much shorter half-time of lead in the mainly trabecular vertebral bone as compared to the mainly cortical fingerbone. Further, there was an association between vertebral and blood lead levels in the retired workers, which shows a considerable endogenous lead exposure from the skeletal pool.

The dosimetry of 224Ra in mouse bone

Calculations are described, based on experimental findings, which show the variation of absorbed dose from 224Ra in bone marrow of CBA/H mice. These calculations indicate that, following an injection of a leukaemogenic amount of 16 kBq 224Ra into these mice, most marrow cells in the cancellous bone of femur ends are killed but most marrow cells in the femur shaft survive. The calculations also suggest that the mean leukaemogenic absorbed dose of about 1.5 Gy is received by a population of marrow cells about 30 microns from bone surface in the femur shaft.

Automatic quantification of vertebral cancellous bone remodeling during aging

Anatomical transformation changes in vertebral spongy bone were quantified by automatic image analysis of microradiographs of 1 mm-thick sagittal slices from autopsied normal lumbar vertebrae (24 men and 28 women, age 35 to 96). Over a period of four decades, aging bone loss is 60% in women and 45% in men in the center of the vertebral body. With age, there is a new distribution of trabeculae: weight-bearing ones are twice (in young people) to six times (in old people) more numerous than transverse ones (measured on a sagittal slice). In the elderly, intertrabecular spaces enlarge while the proportion of the thinnest trabeculae increases.

The uptake and turnover of 90Sr in the human skeleton

In the United Kingdom, measurements have been made of the concentration of 90Sr in human bone from 1955 to 1970, and in human diet since 1958. A correlation of these two series of observations has enabled estimates to be made of (i) the fraction of the dietary intake of 90Sr that reaches the skeleton, (ii) the rate of turnover of 90Sr in the skeleton, and (iii) the way in which both these parameters vary with age. The results may be used to predict future levels of 90Sr in human bone from measurements of the radionuclide in diet, and also to calculate the radiation doses received by tissues in bone from intakes of 90Sr and 89Sr.

Dose delivered to various bone and marrow sites of radium 226 injected mice related to the observed heterogeneity in damage to haemopoietic marrow cells

A method of determining local radiation doses from 226Ra to selected bone marrow sites of 226Ra-injected mice is presented. The 226Ra burden in selected cortical and trabecular bone sites of BALB/c mice and the morphometric characteristics of these bone sites and of their marrow cavities in BALB/c mice are measured. These data, along with information on dosimetry from the literature, are used to calculate the cumulative dose in the selected bone and marrow cavity sites. The amount of 226Ra picked up by a bone is shown to be linearly related to the area of bone surface. The energy absorption in various bone and bone marrow sites is not homogeneous. The relationship between local marrow doses and the observed non-uniformity in damage to haemopoietic marrow cells of different marrow sites 300 days after 226Ra injection is discussed. The degree of marrow damage does not simply reflect the calculated marrow dose. This dose-effect study gives some indications for (1) a modification of the approach used in local 226Ra dosimetry and (2) additional damage to the stem cells due to irradiation of their regulating system.

Morphometric studies on mouse bone using a computer-based image-analysis system

The morphological structure of the ilium, femur, third lumbar vertebra and a central caudal vertebra of the female CBA mouse has been studied using 5 micrometer thick, plastic embedded, transverse and longitudinal sections. The sections were analysed on a Quantimet 720, system 30, image analyser connected on-line to a PDP11 computer. Separate endosteal and periosteal surface to volume ratios were calculated for each position of sampling in each bone. For this calculation the anisotrophy of the bone was estimated from measurements of mean chord lengths in longitudinal sections of the bone using a new analytical technique. Chord length distributions in transverse sections of bone were also measured and the relevance of such measurements to the study of morphological changes in the bone and its included marrow are briefly discussed.

Skeletal blood flow in Paget's disease of bone

Using a modified plasma clearance technique, with 18F as a tracer, it is possible to measure blood flow to bone in man. In the normal adult skeleton, blood flow amounts to about 300 ml/min. In untreated Paget's disease of bone there is a striking increase, which is proportional to the biochemical severity of the disease : total blood flow to the skeleton is approximately doubled at an alkaline phosphatase of 50 KAu/dl (i.e. about four times the normal upper limit). Treatment with calcitonin brings a rapid return to normal, possibly before there is a detectable biochemical response. This may explain the rapid pain relief often reported on starting treatment with calcitonin.

Applicability of macro- and microradiography in diagnosis of malignant neoplasms infiltrating the jaw bones

The subject of this paper is the evaluation of the applicability of structural jaw and mandible radiograms in diagnosing malignant neoplastic processes infiltrating the osseous tissue. The material studied comprised 20 patients treated surgically due to neoplasms of the faciocranium. The group investigated consisted of 17 males, aged 35--65 years and three females 45--60 years old. The most numerous group of neoplasms was composed of cancers: 18 patients; the remaining two were fibrosarcomas. For structural radiographs fine grained films and folialess cassettes were used, with soft X-rays being applied for irradiating the preparations. The radiograms were prepared by means of X-ray apparatus with a small focal lamp with a diameter of 0.3 mm, and with the point-focal apparatus. On the basis of analyses covering 24 macroradiograms and 71 microradiograms, criteria for estimating the malignant infiltration of the bone were established. The possibility of practical applicability of these investigations during intraoperative evaluation of the clinically suspicious bone segments has been emphasized.

Use of tracer microspheres to measure bone blood flow in conscious dogs

Blood flow was measured in mature and immature dogs by means of tracer microspheres. Microspheres of 15 micron were found to be the most suitable size in the dog. Total body nonentrapment in the awake, standing dog is likely to be less than 10%. Cortical bone flood flow, devoid of periosteum and marrow, is 2.5 ml/100 g/min in mature dogs and 7.0 ml/100 g/min in immature dogs, P < 0.005. Blood flow in cancellous bone is greater than that in cortical bone in mature (P < 0.001) and immature (P < 0.02) dogs. Flow is different in different regions of a long bone because of different proportions of cortical and cancellous bone, probably because of interrelationships of function (surfaces undergoing remodeling) and, therefore, of energy metabolism and blood flow.

Lymphoid tumours and leukaemia induced in mice by bone-seeking radionucleides

Single intraperitoneal doses of soluble 90Sr and monomeric 239Pu induced generalized lymphomatosis in laboratory mice. Leukaemogenesis due to soluble 226Ra was more uncertain. Clinical expression was variable, but as a generalization the disease was a lymphosarcoma with haematogenous (leukaemic) spread. Only rarely, unlike the commonly recorded forms of natural and X-ray-induced lymphosarcomas, was the thymus apparently the site of onset. The cell-type was lymphoblastic of undifferentiated null form (not T, not B). The average doses of alpha or beta radiation accumulated in the bone-marrow, the presumed site of induction, were at the time of diagnosis usually more than 2500 rad, but, if the cases occurring after radium or low activities of plutonium are accepted as induced, 300-1500 rad of alpha radiation. Mice converted to chimaeras only rarely exhibited any lymphoma, general or local. Abdominal lymphomas were not numerically increased by these radionucleides (perhaps due to shortening of life-span) though some may have been prematurely induced.

Density and composition of trabecular and cortical bone in perinatally irradiated beagles with chronic renal failure

Bone density and composition were studied in trabecular and cortical bone from control 2 and 4 year old beagles and those which had various degrees of renal failure as a result of perinatal irradiation. Changes in the two types of bone were qualitatively similar but consistently greater in trabecular bone. In a group identified as markedly uremic, the decrease (P less than 0.025) from control levels in specific gravity was about 4 times greater in trabecular than in cortical samples. The decrease (P less than 0.025) in grams of ash/ml was 9% in trabecular bone and 2% in cortical bone. These changes were associated with an increase (P less than 0.001) in water content and, on a percent by volume basis, approximately equal decreases in ash (P less than 0.025) and combustible matter (P less than 0.025). In a mildly uremic group there were similar trends in mean values but the only significant difference was an increase (P less than 0.001) in trabecular bone water.

The measurement of blood flow in mouse femur and its correlation with 239Pu deposition

The concentration of 18F was measured in three parts of the femur and in the blood of 36 mice killed at intervals of from 1 min to 2 h after intravenous injection. Blood supply to the bone sections, calculated by dividing the increase in 18F concentration in bone by the integral of 18F concentration in blood between selected time intervals, was shown to be unaffected by the return of 18F from bone to blood at times earlier than 90 min following injection. The supply of blood per unit mass of bone was greatest in distal end of the femur, less in proximal end and least in shaft. In whole femur average blood flow was 230 mm3 per gram fresh bone per min. The deposition of 239Pu in three parts of the mouse femur was shown to be linearly related to blood flow and the nature of the relationship is discussed.

Aspects of the dosimetry of alpha-emitting radionuclides in bone with particular emphasis on 226Ra and 239Pu

The dosimetry of alpha-emitting radionuclides in bone is discussed. Results are presented for average dose rates to tissues close to endosteal surfaces and to haematopoietic bone marrow from thin plane sources of radionuclides buried to different depths in bone and emitting alpha-particles with energies in the range 3-8 MeV. These results are used to demonstrate that on an activity basis 239Pu is unlikely to be more than fifteen times as toxic as 226Ra with respect to osteosarcoma and leukaemia induction in man.

Errors in area measurement in thick sections, with special reference to trabecular bone

A formula is derived for the errors caused by section thickness in the measurement of the mean cross-sectional areas of opaque material embedded in a transparent medium. There are some simplifying assumptions which can only be justified by limiting the maximum thickness of the section, but no restriction whatever is placed upon the shape of the opaque material. For isotropic materials a very simple formula is found, relating the relative error in cross-sectional area to measurements of area and boundary profile length on the section surface. The effect of anisotropy in the material may be very large. To illustrate this, numerical calculations are made for two particular classes of simple anisotropic material, those which might be made from isotropic materials by linear distortions.

The actions of parathyroid hormone on bone: relation to bone remodeling and turnover, calcium homeostasis, and metabolic bone disease. Part I of IV parts: mechanisms of calcium transfer between blood and bone and their cellular basis: morphological and kinetic approaches to bone turnover

The supracellular organization of living bone enables the study of isolated cellular and subcellular systems to be related to the study of the whole organism. Bone is formed by osteoblasts in successive stages, separated in both time and space, of matrix formation and primary mineralization. Osteoblasts are joined by tight junctions and largely cover the osteoid seam which separates them from mineralized bone. Secondary mineralization is not completed for several months and is not regulated by the osteoblast. Bone is resorbed by osteoclasts which simultaneously accomplish mineral dissolution and matrix digestion. Active osteoblasts occupy about 5% of the free bone surface, osteoid seams with less active osteoblasts about 10%, active osteoclasts about 0.5%, and Howship's lacunae at which bone remodeling is either quiescent or arrested about 5%. The remaining 80% of the free bone surface is covered by a leaky envelope of thin flattened cells, termed surface osteocytes. Some osteoblasts become permanently buried in the bone as deep osteocytes, around which a specialized and metabolically active perilacunar bone is formed. This bone is less highly mineralized and can temporarily lose or gain calcium in accordance with homeostatic needs. Deep osteocytes maintain contact with each other and with the surface osteocytes, their cell processes within canaliculi being joined by gap junctions. Remodeling of cortical bone proceeds with the excavation by osteoclasts of a longitudinal tunnel which is refilled by osteoblasts to form a new osteon. The anatomically discrete longitudinally oriented structure consisting of a cutting cone of osteoclasts in front and a closing cone of osteoblasts behind is termed a cortical remodeling unit. The events of centrifugal resorption and centripetal formation which occur in a single cross section is termed a cortical remodeling cycle. Normally each new cycle is slightly out of phase with its predecessor. The quantities which characterize cortical remodeling are the birth rate of new remodeling cycles or activation frequency (mu), and the durations of the resorptive period (sigma r), the quiescent interval (sigma q) and the formation period (sigma f). The average distances traveled by the osteoclast and osteoblast are indicated respectively by the mean cement line diameter and mean wall thickness of completed osteons. These quantities show little interindividual variation. Because of this constancy the magnitude of bone turnover (the bone formation rate) is almost entirely a function of mu, the activation frequency of new remodeling cycles. Variations in the velocity of advance of osteoclasts (the linear resorption rate) or of osteoblasts (the appositional rate) alter inversely both the extent of surface engaged in resorption or formation and the time taken to replace a particular moiety of bone, but in a steady state do not influence the rate of turnover of the skeleton as a whole...

Scanning electron micrographs of cancellous bone from the human sternum

Thick sections from the manubrium and the first and second sternabrae were polished and the marrow removed. Low magnification scanning electron micrographs show that the cancellous bone near the medial plane is lightly constructed, is not markedly anisotropic and does not vary greatly from place to place. In the lateral parts of the sternabrae the trabeculae are somewhat thicker and the spaces between them are larger. Measurements on the polished surface lead to numerical values of a number of parameters characteristic of the surface patterns, such as the relative surface occupied by bone, the mean widths of the trabecular sections, the mean path lengths through the bone or marrow, and a number representing the departure from isotropy of the pattern. Parameters characteristic of the three-dimensional trabecular structure can be deduced, viz., the relative volume of bone, the area of the interface between bone and marrow and the mean thickness of the trabeculae. The sternum is compared with other bones which have been investigated by the same methods. There is little resemblance to the rib or to the proximal femur. The cancellous bone in the sternum and in the lumbar vertebral body are similar in appearance but the former has slighter trabeculae and larger marrow spaces.