Reassessment of tritium dose coefficients for the general public

Concerns of increased risk from tritium intake by humans have been claimed in the past. The arguments concerning the radiobiological effectiveness of tritium, its longer retention in the human body and the presence of tritium in the DNA hydration shell are analysed in this paper. A biokinetic model for tritiated water and organically bound tritium retention in the human body is used, based on a common approach for mammals using energy and hydrogen metabolism and tested separately with animal experiments. Extension to this model to humans considers the increased role of the brain, food quality and unique growth patterns of humans. Various ages and genders for Caucasians are considered. For an intake of tritium in organic forms in the diet, the retention for the female is of about a factor 2 compared with ICRP recommendations. Effective dose coefficients are estimated to be about a factor of 2 to 3 higher than those of the ICRP.     

MCNPX alpha particle dose estimate to the skin tissue from a low-enriched uranium fuel fragment

Three alpha volume sources (low-enriched uranium-U(3)Si) were analysed using Monte Carlo modelling in order to calculate the dose delivered to the dermis from a small embedded fuel fragment (sliver). Three shapes were analysed using MCNPX 2.6.0 code: sphere, cylinder and parallelepiped. Essentially, two kinds of runs were performed: count rate run and dosimetry run. The two results were combined to estimate dose coefficients that can be used for alpha dose assessments in the field. The two results were obtained for the 1 and 0 cm counting geometries. These results are very stable and show that the actual dose delivered to the skin per unit count rate for the recovered particle is independent of the shape of the volume alpha source.     

A dose index as a tool to estimate paediatric patient doses in digital projection radiography

Radiation exposure during childhood is estimated to have a lifetime risk up to seven times greater than exposures at adult age. Therefore, paediatric patient dose monitoring is a major concern in radiology. The aim of this study is to evaluate the validity of a dose index, displayed at the digital imaging and communication in medicine (DICOM) header of the images, as a dosimetric quantity to estimate the entrance surface dose (ESD) for each procedure. It was carried out over a sample of 156 paediatric patients who underwent a chest examination. National Radiation Protection Board Report 318 model was used to categorise patients by age and to estimate their thickness. Corrected dose index values were compared with calculated ESD, estimated from tube output and radiographic technique. The deviation between both values remained within 2% for every age group, except for patients up to 1 y. Therefore, the index could be used to estimate ESD, allowing to manage greater patient dose databases.     

Evaluation of methods to estimate the patient dose in interventional radiology

Dosimetric methods used for interventional and diagnostic radiology are reviewed and evaluated, including terms, quantities, equipment, calibration and measurements. Measurement of local skin dose and estimation of maximum local skin dose are emphasised. Aspects related to dosimetry in computed tomography and to methods of determining organ and tissue doses are not considered.     

A small scale Z-pinch device as an intense soft X-ray source

A small scale (400 J) device to study the application of radiation emitted by a plasma Z-pinch to microscopy and microlithography has been built. As a pulsed emitter of soft X-rays the Z-pinch is an inexpensive source for high resolution flash microscopy of thin films, and live and unstained biological specimens. In the repetitive mode, radiation from the device was used to expose resists for microlithography. Windows of different plastics shielded the resists from debris and allowed exposure of resists in air. The use of different pinching gases allowed tunability of radiation.     

Monte Carlo simulation of trabecular bone remodelling and absorbed dose coefficients for tritium and 14C

A Monte Carlo simulation of multiple trabecular bone cavities in adult bone was developed and the absorbed radiation dose factors evaluated for 3H and 14C. The model was developed to assess the dose from radionuclide uptake in quiescent bone, but also the effects of temporal changes in bone turnover by incorporating bone-modelling units (BMU). Absorbed dose fractions were calculated for target regions that include the endosteal layer where radiation-sensitive stem cells in bone marrow are considered to reside preferentially. There were large differences in the absorbed fractions for two types of bone surface, quiescent and forming. Tritium in quiescent bone results in a dose to the endosteum about 20 times that for the same activity in forming bone surface irradiating osteoblasts. When the quiescent bone surface source was extended from an infinitely thin layer to a more realistic 1 microm thick, the tritium absorbed fractions for endosteum and red marrow targets fell by more than 2-fold.     

Mechano-biology as an optimization principle for biological tissue engineering

Rapid prototyping and direct fabrication has provided researchers and scientist with a wealth of opportunities to fabricate synthetic tissue replacements, so called scaffolds. The goal is to fill critical size defects with such materials and allow the body to slowly degrade them and build de-novo biological tissue on its place. However, for this process to take place the structural organization levels of these synthetic tissue replacements need to follow design criteria that promote cell attachment, cell proliferation, and maintain the cell's differentiated function. The scaffold's architecture defines the ultimate shape of the newly grown tissue. Furthermore, since most scaffolds are needed for tissue repair in load-bearing applications, the mechano-biological component affects tissue growth long after biochemical factors (e.g., growth hormones) or pre-seeded cells are lasting. This article describes current efforts in identifying mechano-biological principle that are believed to guide tissue formation based on biomechanical loading.     

Modification of the soft tissue response to implanted materials through the use of an anti-inflammatory drug

The soft tissue response of adult rats to a drug-loaded copolymer hydrogel was studied histologically by using monoclonal antibodies specific for certain inflammatory cell types. A hydrogel was loaded with Diclofenac sodium, a non-steroidal anti-inflammatory drug, and designed to release the drug at a constant rate after implantation into muscle tissue. The sites of antibody binding were analysed automatically, by using an image analysis system, providing information on the number of inflammatory cells and their distribution relative to the hydrogel implant. The ability to measure these and other parameters is considered to be of major importance in the assessment of biocompatibility. The experiments demonstrate that Diclofenac sodium (25–30 µg ml^–1) reduced the number of macrophages and neutrophils found at the implant site compared with a PBS control. Diclofenac sodium did not have any effect on the T cell response.     

Heating of bone and soft tissue by ultrasound

Abstract

The absorption of ultrasound in human tissue always causes some local increase in temperature. In the case of ultrasound imaging, the power is usually much less than that used therapeutically and is unlikely to produce any significant physiological effect. However, a reliable means of calculating the maximum temperature rise to be expected in any given case will assist in both the development and the safe use of new ultrasound devices. To validate earlier work on ultrasonic tissue heating, including both experiment and finite element modelling (FEM), an analytical method is described for calculating the steady-state temperature rise along the axis of an axially symmetrical beam of ultrasound incident through water on a two-layer phantom consisting of agar gel and a bone mimic, the practical beam profile being modelled by a pair of coaxial Gaussian functions. It is shown that, in the absence of perfusion, the steady-state temperature distribution for the extended heat source generated by the ultrasound absorption can be obtained by integrating the point-source solution to the Bioheat transfer equation (BHTE). The boundary conditions associated with the difference in thermal properties of the mimic materials are satisfied by introducing images of the extended heat source in the gel/bone–mimic interface.     

A re-evaluation of the occupancy factors for effective dose estimate in tropical environment

In the estimation of the effective dose to the public, outdoor and indoor occupancy factors have been an important parameter. These factors vary, depending on the prevailing environmental condition in a particular location. The factors have been estimated for the rural and urban areas in Nigeria. An outdoor factor of 0.3 and 0.22 have been estimated for rural and urban dwellers, respectively. The rural outdoor factor is 50% above the value recommended as the world average by the UNSCEAR. The urban outdoor factor is 10% higher than this value. The total outdoor gamma dose rate in the air due to (40)K, (238)U and (232)Th in the soil for some rural population in the southern part of Nigeria is 29.50 +/- 3.80 nGy h(-1) and the average outdoor effective dose has been estimated to be 54.28 +/- 6.95 microSv y(-1) using the present occupancy factor.     

Dimethyl sulfoxide as an anticalcification agent for glutaraldehyde-fixed biological tissue

Dimethylsulfoxide has been found to mitigate the calcification of glutaraldehyde-fixed biological tissue in the rat subdermal model. This effect is achieved with neat dimethylsulfoxide either prior to or after glutaraldehyde fixation of the biological tissue. The calcium levels for the 21 days post-implant for both methods are over 20 times less than the controls. However, fixation of the tissue with glutaraldehyde before dimethylsulfoxide treatment appears to better control calcification over the longer term. Histological examination of samples after exposure before or after implantation show no deleterious effects to the tissue due to dimethylsulfoxide.     

Structural properties of polysaccharide-based microcapsules for soft tissue regeneration

Autologous and eterologous cell encapsulation has been extensively studied for clinical application in functional organs substitution, recombinant cell transplantation in gene therapy or in muscle and cartilage regeneration to treat degenerative pathologies. In this work, calcium alginate, calcium alginate/chitosan, calcium alginate/gelatin and pectin/chitosan microcapsules were prepared to be used as innovative injectable scaffolds for soft tissue regeneration by a simple extrusion method from aqueous solutions. Prepared microcapsules had spherical morphology, whereas their size was deeply influenced by the polymeric composition. When incubated in a physiological-like environment up to 30 days, they underwent an initial swelling, followed by weight loss at different rates, depending on the microcapsules formulation. The encapsulation of mouse myoblast cells (C2C12 cell line) was obtained in calcium alginate, calcium alginate/chitosan, calcium alginate/gelatin microcapsules. Cells were alive throughout the encapsulation procedure, and were recovered by a mechanical rupture of the microcapsules. After 7 days, fractured microcapsules led cells to migrate gradually out.     

Development of lung and soft tissue substitutes for photons

The use of solid tissue substitutes is a well-accepted and common practice in dosimetric studies and in the production of counting standards for radiological protection. However, only a few solid tissue substitutes simulating a particular body tissue with respect to a set of physical characteristics are commercially available. Hence, we have developed polyurethane-based tissue substitutes simulating soft tissue, muscle, muscle-adipose mixture tissue (90% muscle + 10% adipose), brain, cartilage, larynx, thyroid, trachea, liver, kidney, skin and lungs. Tissue substitutes for photons were formulated using the basic data method together with an equation for calculating the optimum relative mass of corrective additives. The tissue substitutes were formulated to be phantom materials in the photon energy range of at least 8 keV-10 MeV. In particular, they were designed to match the body tissues with linear attenuation coefficients for low photon energy (13.6, 17.2 and 20.2 keV from 239Pu) and to have the same mass densities as the tissues. The tissue substitutes developed in the present study were examined for the photon transmissions using 16.6 keV KX rays from 93Nb(m). The experimental transmission curves of the tissue substitutes were found to be consistent with those derived from data on the body tissues in ICRP Publication 23. It was found that the developed tissue substitutes are suitable to the corresponding body tissues defined by ICRP.     

The effect of titanium debris on soft tissue response

The tissue response to titanium fracture plates after 18 months implantation has been analysed quantitatively, and the distribution of different cell types compared to the distribution of tissue discolouration. A tissue response including macrophages, fibroblasts and T lymphocytes, many of which were activated (CD25), helper/inducer (CD4), or cytotoxic/suppressor (CD8). These cells were indicative of a chronic granulomatous reaction. There was no correlation between the presence of such cells and their distribution around the plates with and without the presence and distribution of black debris in the tissue.     

Computer simulation of forward wave propagation in soft tissue

A method for simulating forward wavefront propagation in heterogeneous tissue is discussed. The intended application of this method is for the study of aberration produced when performing ultrasound imaging through a layer of soft tissue. A one-way wave equation that permits smooth variation in all acoustically important variables is derived. This equation also describes tissue exhibiting nonlinear elasticity and arbitrary frequency-dependent relaxation. A numerical solution to this equation is found by means of operator splitting and propagation along the spatial depth coordinate. The numerical solution is accurate when compared to analytical solutions for special cases, and when compared to numerical solutions of the full wave equation by other methods. The presented implementation provides a fast numerical method for studying the impact of aberration in medical ultrasound imaging through soft tissue--both on the transmitted beam and the nonlinearly generated harmonic beam.     

DEM simulations of stiff and soft materials with crushable particles: an application of expanded perlite as a soft granular material

The mechanical behavior of granular materials is largely affected by particle breakage. Physical and mechanical properties of granular materials, such as grain size distribution, deviatoric and volumetric behavior, compressibility and mobilized friction angle are affected by particle crushing. This paper focuses on the evolution of the above mentioned characteristics using the Discrete Element Method (DEM). Behaviors of stiff and soft materials are studied using well established crushing criteria. Results from simulations indicate that stiff materials, have a typical fractal distribution of particle size, which is dominant when confining pressure increases. The fractal characteristic parameter of grain size effect is discussed. Evolution of shear stresses and volumetric strains during shearing are also predicted and analyzed. Expanded perlite, selected as a soft material, is investigated in terms of shear and volumetric behavior. For perlite, triaxial compression tests and corresponding DEM simulations are also performed. Results show good agreement between experiments and simulations and support the fact that the DEM can be considered as a useful tool to predict the behavior of crushable granular materials.     

Optically stimulated luminescence of some thermoluminescent detectors as an indicator of absorbed radiation dose

Stimulation spectra of several TLD materials in the short-wave spectral region are measured using the optically stimulated afterglow (OSA) method for determination of absorbed dose. Optical stimulation spectra are studied in the region of wavelengths lower than those of emission spectra. The effective optical stimulation hands have been found for examined materials in the regions of wavelengths which overlap with fluorescence excitation bands. Application of short-wave OSA bands for determination of absorbed dose is analysed.     

Analysis of the uncertainty in internal dose estimate resulting from biological stochastic variability of excretion

A method for investigating the uncertainty in internal dose estimate resulting from biological stochastic variability of excretion is proposed in the paper. The method is based on analysing generated cases of individual monitoring data using Monte Carlo simulation technique. In case of a single intake and assumption of stochastic variability of excretion is a single source of uncertainty it was shown that the intake (dose) uncertainty depends exclusively on the uncertainty of the bioassay data and the number of daily urine (faeces) measurements. Assuming a log-normal distribution for describing the variability of excretion a simple expression for calculating the uncertainty was proposed. In case of routine monitoring data it was shown that the uncertainty of annual intake (dose) estimate would depend on biological stochastic variability of excretion, type of excretion function and the number of monitoring intervals in a year. By the example of Pu and U aerosols it was shown that the effects of decreasing uncertainty in the dose estimate resulting from increasing the number of monitoring intervals in a year and from decreasing the uncertainty of bioassay data (performing a number of successive daily measurements, once in a year) should be estimated to optimise the routine monitoring program.     

Atomic tritium as a surface nanoprobe in a structural investigation of molecular assemblies

Possibilities of atomic tritium application as surface nanoprobe for structural investigations of adsorption layers on the liquid–air interface have been demonstrated. Frozen aqueous solutions of a series of amino acids and their mixtures and one well-known surface-active substance (cetyltrimethylammonium bromide, CTAB) were exposed to bombardment by tritium atoms generated on hot tungsten wire in a special vacuum device. This procedure resulted in substitution of hydrogen atoms by radioactive tritium in the thin surface layer of investigated samples. Curves of radioactivity changes depending on bombardment time and solution concentration for applied compounds were obtained and analyzed.