Resolving trabecular metaphyseal bone profiles downstream of the growth plate adds value to bone histomorphometry in mouse models.

Introduction: Histomorphometry of rodent metaphyseal trabecular bone, by histology or microCT, is generally restricted to the mature secondary spongiosa, excluding the primary spongiosa nearest the growth plate by imposing an 'offset'. This analyses the bulk static properties of a defined segment of secondary spongiosa, usually regardless of proximity to the growth plate. Here we assess the value of trabecular morphometry that is spatially resolved according to the distance 'downstream' of-and thus time since formation at-the growth plate. Pursuant to this, we also investigate the validity of including mixed primary-secondary spongiosal trabecular bone, extending the analysed volume 'upstream' by reducing the offset. Both the addition of spatiotemporal resolution and the extension of the analysed volume have potential to enhance the sensitivity of detection of trabecular changes and to resolve changes occurring at different times and locations. Method: Two experimental mouse studies of trabecular bone are used as examples of different factors influencing metaphyseal trabecular bone: (1) ovariectomy (OVX) and pharmacological prevention of osteopenia and (2) limb disuse induced by sciatic neurectomy (SN). In a third study into offset rescaling, we also examine the relationship between age, tibia length, and primary spongiosal thickness. Results: Bone changes induced by either OVX or SN that were early or weak and marginal were more pronounced in the mixed primary-secondary upstream spongiosal region than in the downstream secondary spongiosa. A spatially resolved evaluation of the entire trabecular region found that significant differences between experimental and control bones remained undiminished either right up to or to within 100 µm from the growth plate. Intriguingly, our data revealed a remarkably linear downstream profile for fractal dimension in trabecular bone, arguing for an underlying homogeneity of the (re)modelling process throughout the entire metaphysis and against strict anatomical categorization into primary and secondary spongiosal regions. Finally, we find that a correlation between tibia length and primary spongiosal depth is well conserved except in very early and late life. Conclusions: These data indicate that the spatially resolved analysis of metaphyseal trabecular bone at different distances from the growth plate and/or times since formation adds a valuable dimension to histomorphometric analysis. They also question any rationale for rejecting primary spongiosal bone, in principle, from metaphyseal trabecular morphometry.

A post-scan method for correcting artefacts of slow geometry changes during micro-tomographic scans.

Micro-CT imaging of objects at very high magnification runs into the problem of small geometric movements of the x-ray emission spot relative to the object, thermally induced or otherwise, causing magnified shifts in the projection images during scanning. This produces movement artefacts in the reconstructed images. Here a technique is described to correct such movements by adding a short reference scan at the end of a high magnification scan, with a very large rotation step. Where geometry changes during a scan are slow, such movements can be considered minimal during this very short "post-scan". Registration of the post-scan images with corresponding images in the main scan allow X/Y pixel shifts in the projection images associated with the geometry movement to be calculated, and corrected during reconstruction. This post-scan correction method was applied here to scans of three small objects, all with a voxel size less than one micron, in a desktop micro-CT and a nano-CT scanner. The method substantially reduced movement artefacts from the reconstructed images, improving image quality and resolution. Where the geometry movement results largely from thermal movement of the x-ray micro-focus emission spot, the post-scan method allows the reconstruction of the spatio-temporal trajectory of this spot movement.

Alpha-particle doses to cells of the bone remodeling cycle from alpha-particle-emitting bone-seekers: indications of an antiresorptive effect of actinides.

There are indications that alpha-particle-emitting bone-seekers such as plutonium or americium could enhance bone mass by suppressing bone resorption. To assess this possibility, this study calculates doses from alpha-particle emitters to the cells involved in trabecular bone turnover. Alpha-particle energy deposition in tissue from a bone surface source was calculated by Monte Carlo modeling. This was combined with bone surface cellular geometry to yield dose rates to cells during the remodeling cycle. Bone-resorbing osteoclasts receive on average 50 times the dose rate that bone-forming osteoblasts receive. Newly formed bone shields osteoblasts from alpha particles emitted by the buried deposit of alpha-particle emitters. However, at alpha-particle bone-seeking radionuclide intakes known to cause changes in remodeling (about 3700 Bq/kg body weight), the alpha-particle dose to osteoclasts corresponds to an extremely low rate of cell traversals (0.07% per cycle). It is therefore unlikely that perturbation of bone remodeling by alpha-particle bone-seeking radionuclides is directly caused by alpha-particle traversals of remodeling cells; some other indirect mechanism might be involved.

Age and microdistribution of 210Pb at caribou bone surfaces measured by repeated alpha spectroscopy of 210Po.

PURPOSE: To measure microdistibution and age of 210Pb in Canadian caribou bone, and assess the accuracy of ICRP biokinetic and dosimetric models for 210Pb-supported 210Po at bone surfaces. MATERIALS AND METHODS: The previously described use of alpha spectroscopy to study 210Pb microdistribution at bone surfaces was expanded in a study of femora from 23 caribou. A new technique for measuring the age in vivo of Pb in bone, on the basis of the ratio of 210Po/210Pb activity, was carried out on eight caribou femora. RESULTS: The measured thickness p of the layer containing elevated concentration of 210Pb at femoral endosteal surfaces was 0.79 +/- 0.52 microm (SD). This thickness increased linearly with age in caribou aged 2-11 years. The surface/volume concentration ratio of 210Pb (As/Av) varied from 1 to 18, geometric mean 3.8. No trend in As/Av with caribou age was observed. In the upper 1 microm/210Pb was 17 +/- 22 days old, and at depths of 1-22 microm the age was 146 +/- 17 days. Thus Pb at the bone surface was about nine times younger than in underlying bone. CONCLUSIONS: Modifications to the ICRP 67 biokinetic model for Pb are proposed. The alpha dose to tissue above endosteal surfaces is reduced three times due to the low ingrowth ratio of 210Po.

Monte Carlo/numerical treatment of alpha-particle spectra from sources buried in bone and resultant doses to surface cells.

PURPOSE: To calculate the depth distribution of radioactive decays in bone by fitting a calculated alpha-particle energy spectrum to a measured spectrum. The dose to bone surface cells is then calculated from the depth distribution. MATERIALS AND METHODS: The spectra are calculated using Monte Carlo methods and a numerical depth distribution obtained by trial and error. RESULTS: Alpha spectra for 210Po and 226Ra (plus decay products) in bone were calculated and fitted to experimental spectra. The dose to bone surface cells was calculated using the numerical technique and compared to previously published data. CONCLUSIONS: Alpha-particle spectra can be successful fitted using this method, which gives a more realistic distribution of decays with depth than simple surface and volume models.

Distribution of 210Pb at endosteal surfaces of bone from Canadian Arctic caribou.

Alpha particle energy spectra were measured at femoral endosteal surfaces of Canadian Arctic caribou (Rangifer tarandus) to assess the profile of concentration with depth of 210Po supported by 210Pb. Femur samples from five caribou all showed a pronounced superficial concentration of 210Po, in a layer 1.9 - 6.4 microns thick. Within this layer 210Po was concentrated 1.5 - 10 times with respect to diffuse volume-distributed 210Po. This result is consistent with an earlier study of 210Po at human cranial bone surfaces, which showed 210Po to be concentrated about four times in a surface layer <3 microns thick. However, the present results have higher precision than the human bone data due to the much greater concentration of 210Pb and 210Po in caribou bone. The validity of using 210Po as a marker of 210Pb, and the in vivo 210Po/210Pb ratio are discussed. As a result of the measured endosteal superficial concentration of 210Po in caribou, the alpha particle dose was calculated to be enhanced by a factor of 1.06 - 1.96 (mean 1.48) for bone lining cells, and of 1.08 - 2.39 (mean 1.69) for soft tissue above the bone surface, assuming equilibrium between 210Pb and 210Po. It is suggested that an additional longer-lived compartment for bone surface lead could be incorporated into bio-kinetic models for lead.

TASTRAK spectroscopy of polonium-210 alpha-particle activity at bone surfaces: evidence for a concentrated surface deposit less than 3 microns deep.

The technique of alpha-particle spectroscopy by CR-39 type TASTRAK plastic has been used to study the depth distribution of natural alpha-particle emitters at the surface of human bone. The predominant component of this alpha-particle activity was 210Po supported by 210Pb, although a smaller activity of 226Ra was also detected. Autopsy samples of human femur and cranium were obtained from subjects age 63 to 86. Both cortical and trabecular surfaces were analyzed. The results indicate that 210Pb-supported 210Po is concentrated at the surfaces of human bone from elderly subjects, in a narrow band 3 microns deep or less, by a factor of about four. As a result, the alpha-particle dose to the nuclei of cells lining bone surfaces is around 1.8 times greater than that calculated for a uniform volume distribution. Polonium-210 activity indicates the distribution of 210Pb, and of stable lead, received by continuous intake throughout life at a very low level. A persistent bone surface concentration of lead and other osteotropic metals may be associated with the hypermineralized layer about 1 micron thick which occurs at the surface of resting bone mineral.

Viewing the client's world through drawings.

This article discusses the therapeutic use of drawings, outlines a specific drawing technique, and describes two case illustrations. Emphasis is placed on the healing quality of the drawing experience, a creative process in and of itself. These case illustrations were derived from an interpretive study in which life history and drawing methods were used to gather a holistic description about the experiences of women living with HIV disease. By making drawings depicting their illness, the ten women were offered another way to express and communicate their experiences, revealing rich descriptions that may not have been obtained by interviews alone. The drawings allowed the women to explore feelings that are often difficult to verbalize, offering additional insights about their worldview. For the practitioner, the use of drawings can therefore be a valuable tool to further understand a client, assess needs, and formulate a more inclusive approach to care.