Soft Tissue Substitution Research Articles

Tissue-equivalent materials for construction of tomographic dosimetry phantoms in pediatric radiology.

Tissue equivalent materials have a variety of uses, including routine quality assurance and quality control in both diagnostic and therapeutic physics. They are frequently used in a research capacity to measure doses delivered to patients undergoing various therapeutic procedures. However, very few tissue equivalent materials have been developed for research use at the low photon energies encountered in diagnostic radiology. In this paper, we present a series of tissue-equivalent (TE) materials designed to radiographically mimic human tissue at diagnostic photon energies. These tissue equivalent materials include STES-NB (newborn soft tissue substitute), BTES-NB (newborn bone tissue substitute), LTES (newborn as well as a child/adult lung tissue substitute), STES (child/adult soft tissue substitute), and BTES (child/adult bone tissue substitute). In all cases, targeted reference elemental compositions are taken from those specified in the ORNL stylized computational model series. For each material, reference values of mass density, mass attenuation coefficients (10-150 keV), and mass energy-absorption coefficients (10-150 keV) were matched as closely as permitted by material selection and manufacturing constraints. Values of mu/rho and mu(en)/rho for the newborn TE materials are noted to have maximum deviations from their ORNL reference values of from 0 to -3% and from +2% to -3%, respectively, over the diagnostic energy range 10-150 keV. For the child/adult TE materials, these same maximal deviations of mu/rho and mu(en)/rho are from +1.5% to -3% and from +3% to -3%, respectively. Simple calculations of x-ray fluence attenuation under narrow-beam geometry using a 66 kVp spectrum typical of newborn CR radiographs indicate that the tissue-equivalent materials presented here yield estimates of absorbed dose at depth to within 3.6% for STES-NB, 3.2% for BTES-NB, and 1.2% for LTES of the doses assigned to reference newborn soft, bone, and lung tissue, respectively.

Synthesis and Characterization of a Soft-tissue Substitute for Neutron Dosimetry

To develop a physical phantom for neutron dosimetry, a solid soft-tissue substitute was synthesized. The synthesized tissue substitute, NAN-JAERI, is improved in both hydrogen and oxygen elemental composition in comparison with existing tissue substitutes. To examine the radiation characteristics of the new soft-tissue substitute, absorbed dose distributions in NAN-JAERI were measured using a 252 Cf neutron source. The measured absorbed dose distributions of neutrons and photons agree with those calculated by a Monte Carlo simulation code MCNP. The agreement between the experiment and the simulation verifies this method of evaluating the soft-tissue equivalence of NAN-JAERI for 252 Cf neutrons. Similar simulations for some mono-energetic neutron sources showed that the newly developed tissue substitute has soft-tissue equivalent characteristics in the neutron energy range from 1 MeV up to 14 MeV, in terms of the absorbed dose distributions in a slab phantom. Neutron dosimetry has become more important for radi- ation protection than it has been in the past, since neutron sources, obtained from nuclear reactors or accelerators, have been widely used in solid state physics, material science, nuclear physics and neutron therapy. Experimental tech- niques of neutron diffraction or neutron scattering are so useful that they are applicable to other research fields men- tioned above. To perform experiments safely using the neu- tron sources, neutron dosimetry of high precision is required. Under the present circumstances, however, neutron dosimetry in radiation protection depends highly on numerical methods. Dose conversion coefficients relating neutron fluence to or- gan doses or to the effective dose have been used for dose assessments of workers and the public. The dose conversion coefficients have been calculated using mathematical anthro- pomorphic human models and radiation transport simulation techniques. Although it is almost impossible to construct re- alistic human models, experimental verification of the dose assessment technique is needed. To perform accurate neutron dose assessments based on ex- periments, elements such as appropriate neutron sources, de- tectors and phantoms are indispensable. Among these three elements, the appropriate phantom is one of the most impor- tant elements for dose assessments and for the calibration of detectors as an alternative to the human body. For photon dosimetry, various phantoms have been developed. The tis- sue substitutes of phantoms for photons are made of materi- als whose electron densities are close to those of the body tis- sues, because the photon deposits its energy through interac- tions with atomic electrons. In the case of neutrons, it is ideal that phantoms are made of materials with elemental compo- sitions that are identical to those of the body tissues, because the neutron interacts with the atomic nuclei. In ICRU Report

New reconstructive technologies in skull base surgery: role of titanium mesh and porous polyethylene.

To report on 8 years of experience with 156 titanium mesh and porous polyethylene implants used for craniofacial reconstruction after skull base surgery in 100 patients. Cohort study with a mean follow-up of 5 years. Population based. A consecutive sample of 100 patients treated for skull base tumors or craniofacial trauma who underwent reconstruction with 156 3-dimensional titanium mesh and/or porous polyethylene implants. A retrospective review of the Skull Base Program database, along with photographic and imaging documentation, was undertaken. Rate of complications as well as the degree of functional and esthetic reconstruction. The reconstructive technique focused primarily on the substitution of removed craniofacial skeleton for oncologic reasons or soft tissue defects. After completion of follow-up (mean, 5 years), all 100 patients remained healed except for 7 patients (7%) with 8 implants (5%). Overall, excellent craniofacial symmetry and stability were achieved with both types of implants. Immediate craniofacial skeletal reconstruction and soft tissue augmentation is feasible with 3-dimensional titanium mesh and porous polyethylene implants. The reviewed 8-year evolution in the use of these technologies (156 implants in 100 patients) highlights the excellent tolerance of these implants (5% implant complication rate) in 100 patients (7% complication rate). The few encountered complications were judged to be primarily related to the quality of the overlying soft tissue and not to the implants themselves. The advantages of using these implants for immediate 3-dimensional skeletal and soft tissue substitution, including availability, easy contouring, stability, primary healing, and tolerance of adjuvant therapy, translate to an improved function and esthetic appearance, with a better quality of life for patients.

Complications and toxicities of implantable biomaterials used in facial reconstructive and aesthetic surgery: a comprehensive review of the literature.

The use of implantable biomaterials has become an integral part of aesthetic and reconstructive surgery of the face. Metals are used for fracture fixation devices, whereas polymers are used primarily for bone or soft-tissue substitution. This review of the scientific literature examines the risks and complications of these materials. First, we present an overview of commonly used materials. Second, we address general considerations of toxicity relevant to all biomaterials. Third, we present data from a large number of clinical series on the incidence of complications for individual materials used in specific applications.

Disposition of intraperitoneally injected calcium-45 in suckling rats.

The time course of the concentration of radiocalcium was studied in the serum, skeleton, pelt, muscles, and pooled internal organs of 10-day-old rats. Within 10 hours of injection, the specific activity of the tissue groups exceeded the specific activity of the serum and remained above it during the period studied (120 hours). Chemical and autoradiographic analyses showed how rapidly most of the injected Ca(45) found its way into the skeleton. A model was constructed with the assumption that the skeleton constitutes an essentially irreversible reservoir for the tracer in a multicompartment system in which the blood is the central or feeding compartment. The rate of transfer of the tracer from the soft tissue compartments to the serum was calculated from the equation See PDF for Equation in which C = concentration in serum (expressed as a series of exponential terms) C' = concentration in a given soft tissue Substitution in the integrated form of this equation yielded equations which had the major properties of the empirical equations fitted to the experimental points. The relative order of transfer constants (k'(-1)) was: organs >/= pelt > muscle.