Application of a radiotherapy stimulator for imaging of body cross sections.
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Humans↗
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Results for “Models, Anatomic”
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Epoxy resin based tissue substitutes.
A series of epoxy resin based tissue substitutes, simulating adipose tissue, bone, breast, lung, muscle and skin is described. Details of the physical radiation characteristics of the formulated systems are given, together with the manufacturing procedures. The versatility of the range of substitutes is discussed in terms of both investigated and projected applications in experimental radiation studies.
Adipose Tissue↗
Finite element analysis of undermining of pressure ulcer with a simple cylinder model.
With pressure sores, surface damage indicates that subcutaneous fat tissue necrosis has occurred. We hypothesized that formation of necrosis under a pressure sore changes the stress distribution, which in turn affects further extension of the necrosis. In the present study, two-dimensional finite element models were used to perform analysis under different undermining size conditions. Greater stress concentration was observed in the larger undermining model. This may be the reason that, in clinical situations, a large area of undermining necrosis is sometimes observed under the skin of sores with a small area of damage.
Biomechanical Phenomena↗
Three-dimensional models for head and neck tumor treatment planning.
The authors have evaluated two types of practical maxillofacial model systems useful to the head and neck surgeon:1. plastic mandibular model generated by three-dimensional computerized tomography (CT) reconstruction, and 2. dental impression model of the maxilla. The first model is expensive and technology intensive; the second is simple but limited. Both three-dimensional models offer several advantages: 1. they provide segmental mandibular relationships that are not known because of oncologic restrictions or previous surgery; 2. they allow preoperative reconstructive planning including prosthesis fabrication and visualization of tumor extent not obvious by two dimensional imaging; and 3. they provide a permanent record for future needs or reconstructions. The disadvantages include cost, time, and possible inaccuracies secondary to image artifacts. We find both models to be of significant practical value in selected head and neck tumor patients.
Adenocarcinoma↗
Integrating simulation training into the nursing curriculum.
The use of simulation is gaining momentum in nurse education across the UK. The Nursing and Midwifery Council is currently investigating the use of simulation in pre-registration nursing. This article gives a brief history of simulation, discusses competence issues and why simulation is best placed to teach nurses in today's health service. An innovative approach to implementing simulation into the nursing curriculum is introduced.
Benchmarking↗
Correction of hammer toe with an extended release of the metatarsophalangeal joint.
Between March 1995 and January 2000 we reviewed retrospectively 84 patients with hammer-toe deformity (99 feet; 179 toes) who had undergone metatarsophalangeal soft-tissue release and proximal interphalangeal arthroplasty. The median follow-up was 28 months. Patients were assessed by the American Orthopaedic Foot and Ankle Society Scores (AOFAS) and reviewed by independent assessors. The median AOFAS score was 83, with 87% of patients having a score of more than 60 points; 83% were satisfied and 17% were dissatisfied with the procedure. Pain at the metatarsophalangeal joint was the commonest cause of dissatisfaction, with 14% having moderate or severe pain. Only 2.5% had instability and 9% had formation of callus. There was no statistical difference for the age and gender of the patients, the number of toes operated on, associated surgery for hallux valgus or length of follow-up. Our study was based on an anatomical model and shows good results with no recurrence of deformity.
Adult↗
Orientation of the acetabular component. A comparison of five navigation systems with conventional surgical technique.
We compared the orientation of the acetabular component obtained by a conventional manual technique with that using five different navigation systems. Three surgeons carried out five implantations of an acetabular component with each navigation system, as well as manually, using an anatomical model. The orientation of the acetabular component, including inclination and anteversion, and its position was determined using a co-ordinate measuring machine. The variation of the orientation of the acetabular component was higher in the conventional group compared with the navigated group. One experienced surgeon took significantly less time for the procedure. However, his placement of the component was no better than that of the less experienced surgeons. Significantly better inclination and anteversion (p < 0.001 for both) were obtained using navigation. These parameters were not significantly different between the surgeons when using the conventional technique (p = 0.966). The use of computer navigation helps a surgeon to orientate the acetabular component with less variation regarding inclination and anteversion.
Acetabulum↗
Bone adaptation to a mechanical loading program significantly increases skeletal fatigue resistance.
UNLABELLED: Using a mechanical loading program to induce bone adaptation, we found that small (<2-fold) changes in the structural properties of the rat ulna increased its fatigue resistance >100-fold. This indicates that a moderate exercise program may be an effective preventative strategy for stress fractures. INTRODUCTION: There are currently limited preventative strategies for stress fractures. Because stress fracture risk is directly influenced by skeletal properties, it has been hypothesized that modification of these properties using a mechanical loading program may positively influence risk. The aim of this study was to investigate whether the bone changes associated with a mechanical loading program can enhance skeletal fatigue resistance. MATERIALS AND METHODS: Site-specific mechanical loading was performed on one forearm of adult female Sprague-Dawley rats using the axial compression loading model. Loading was performed 3 days/week for 5 consecutive weeks to induce adaptation. The loaded and nonloaded ulnas in each animal were removed after the loading program, and their material and structural properties were determined. The ulna pairs were subsequently loaded until fatigue failure at the same constant peak axial load. RESULTS: Mechanical loading induced consistent and predictable changes in the structural properties of loaded ulnas, with the largest change being a nearly 2-fold increase in midshaft minimum second moment of area (I(MIN)). The mechanical-loading induced bone changes resulted in a >100-fold increase in fatigue resistance in loaded ulnas, with resistance being exponentially related to the structural properties of the ulna. CONCLUSIONS: This study found that by enhancing the structural properties of a bone through a mechanical loading program, its fatigue resistance could be significantly improved. This indicates that an exercise program aimed at modifying bone structure may be used as a possible prevention strategy for stress fractures.
Animals↗
Genetic variation in structure-function relationships for the inbred mouse lumbar vertebral body.
UNLABELLED: Structure-function relationships were determined for L(5) vertebral bodies from three inbred mouse strains. Genetic variability in whole bone mechanical properties could be explained by a combination of the traits specifying the amount, distribution, and quality of the cortical and trabecular bone tissue. INTRODUCTION: Although phenotypically correlated with fracture, BMD may be disadvantageous to use in genetic and biomechanical analyses because BMD does not distinguish the contributions of the underlying morphological and compositional bone traits. Developing functional relationships between the underlying bone traits and whole bone mechanical properties should further our understanding of the genetics of bone fragility. MATERIALS AND METHODS: Microarchitecture and composition of L(5) vertebral bodies (n = 10/strain) from A/J, C57BL/6J, and C3H/HeJ inbred mouse strains were determined using muCT with an isotropic voxel size of 16 mum(3). Failure load, stiffness, and total deformation as a measure of ductility were measured in compression using a noncontact strain extensometer imaging system. A correlation analysis related morphological and compositional bone traits to whole bone mechanical properties. A multivariate analysis identified structure-function relationships for each genotype. RESULTS: No single bone trait accurately explained the genetic variation in mechanical properties. However, a combination of traits describing the amount, distribution, and quality of cortical and trabecular bone tissue explained >70% of the variation in vertebral mechanical properties. Importantly, structure-function relationships were unique among genotypes. CONCLUSIONS: Different genetic backgrounds use different combinations of underlying bone traits to create mechanically functional structures. Using a single complex trait such as BMD or BV/TV as the sole phenotypic marker in genetic analyses may prove to be disadvantageous because of the complex relationship between mechanical properties and the underlying bone traits. Therefore, considering multiple bone traits and the interaction among these bone traits is necessary to understand the relationship between genetic background and complex whole bone mechanical properties.
Analysis of Variance↗
Near-infrared light propagation in an adult head model. I. Modeling of low-level scattering in the cerebrospinal fluid layer.
Adequate modeling of light propagation in a human head is important for quantitative near-infrared spectroscopy and optical imaging. The presence of a nonscattering cerebrospinal fluid (CSF) that surrounds the brain has been previously shown to have a strong effect on light propagation in the head. However, in reality, a small amount of scattering is caused by the arachnoid trabeculae in the CSF layer. In this study, light propagation in an adult head model with discrete scatterers distributed within the CSF layer has been predicted by Monte Carlo simulation to investigate the effect of the small amount of scattering caused by the arachnoid trabeculae in the CSF layer. This low scattering in the CSF layer is found to have little effect on the mean optical path length, a parameter that can be directly measured by a time-resolved experiment. However, the partial optical path length in brain tissue that relates the sensitivity of the detected signal to absorption changes in the brain is strongly affected by the presence of scattering within the CSF layer. The sensitivity of the near-infrared signal to hemoglobin changes induced by brain activation is improved by the effect of a low-scattering CSF layer.
Adult↗
Cone spacing and the visual resolution limit.
It is commonly assumed that the visual resolution limit must be equal to or less than the Nyquist frequency of the cone mosaic. However, under some conditions, observers can see fine patterns at the correct orientation when viewing interference fringes with spatial frequencies that are as much as about 1.5 times higher than the nominal Nyquist frequency of the underlying cone mosaic. The existence of this visual ability demands a closer scrutiny of the sampling effects of the cone mosaic and the information that is sufficient for an observer to resolve a sinusoidal grating. The Nyquist frequency specifies which images can be reconstructed without aliasing by an imaging system that samples discretely. However, it is not a theoretical upper bound for psychophysical measures of visual resolution because the observer's criteria for resolving sinusoidal gratings are less stringent than the criteria specified by the sampling theorem for perfect, alias-free image reconstruction.
Humans↗
Calculation of the influence of lateral chromatic aberration on image quality across the visual field.
The magnitude of lateral chromatic aberration and its effect on image contrast were computed for a modified, reduced-eye model of the human eye, using geometrical optics. The results indicate that lateral chromatic aberration is a major factor affecting image quality for obliquely incident rays of polychromatic light. Modulation transfer functions for white sinusoidal gratings decline monotonically with spatial frequency, with eccentricity of the stimulus in the peripheral visual field, with grating orientation relative to the visual meridian, and with decentering of the pupil. Image contrast is largely independent of the color temperature of white light over the range 2800 to 12,000 K, but it improves significantly for the polychromatic green light of the P-31 oscilloscope phosphor. Selective filtering by macular pigment increases image contrast by an amount that grows with spatial frequency to about a factor of 1.5 at the foveal resolution limit. Reduced contrast caused by lateral chromatic aberration accounts for most of the threefold loss of acuity that occurs for foveal viewing through a decentered pupil. The aberration probably has negligible effect on peripheral acuity but may act to limit aliasing of peripheral patterns.
Color Perception↗
A gain-field encoding of limb position and velocity in the internal model of arm dynamics.
Adaptability of reaching movements depends on a computation in the brain that transforms sensory cues, such as those that indicate the position and velocity of the arm, into motor commands. Theoretical consideration shows that the encoding properties of neural elements implementing this transformation dictate how errors should generalize from one limb position and velocity to another. To estimate how sensory cues are encoded by these neural elements, we designed experiments that quantified spatial generalization in environments where forces depended on both position and velocity of the limb. The patterns of error generalization suggest that the neural elements that compute the transformation encode limb position and velocity in intrinsic coordinates via a gain-field; i.e., the elements have directionally dependent tuning that is modulated monotonically with limb position. The gain-field encoding makes the counterintuitive prediction of hypergeneralization: there should be growing extrapolation beyond the trained workspace. Furthermore, nonmonotonic force patterns should be more difficult to learn than monotonic ones. We confirmed these predictions experimentally.
Adult↗
Embryonic origins of a motor system: motor dendrites form a myotopic map in Drosophila.
The organisational principles of locomotor networks are less well understood than those of many sensory systems, where in-growing axon terminals form a central map of peripheral characteristics. Using the neuromuscular system of the Drosophila embryo as a model and retrograde tracing and genetic methods, we have uncovered principles underlying the organisation of the motor system. We find that dendritic arbors of motor neurons, rather than their cell bodies, are partitioned into domains to form a myotopic map, which represents centrally the distribution of body wall muscles peripherally. While muscles are segmental, the myotopic map is parasegmental in organisation. It forms by an active process of dendritic growth independent of the presence of target muscles, proper differentiation of glial cells, or (in its initial partitioning) competitive interactions between adjacent dendritic domains. The arrangement of motor neuron dendrites into a myotopic map represents a first layer of organisation in the motor system. This is likely to be mirrored, at least in part, by endings of higher-order neurons from central pattern-generating circuits, which converge onto the motor neuron dendrites. These findings will greatly simplify the task of understanding how a locomotor system is assembled. Our results suggest that the cues that organise the myotopic map may be laid down early in development as the embryo subdivides into parasegmental units.
Animals↗
A teaching model for bronchoscopy.
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Bronchoscopy↗
Animal models of neuropathic pain.
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Anesthetics, Local↗
Cubozoan jellyfish: an Evo/Devo model for eyes and other sensory systems.
Cnidaria are the most basal phylum containing a well-developed visual system located on specialized sensory structures (rhopalia) with eyes and statocyts. We have been exploring the cubozoan jellyfish, Tripedalia cystophora. In addition to containing simple photoreceptive ocelli, each rhopalium in Tridedalia has a large and small complex, camera-type eye with a cellular lens containing three distinct families of crystallins which apparently serve non-lenticular functions. Thus, Tridpedalia recruited crystallins by a gene sharing strategy as have mollusks and vertebrates. Tripedalia has a single Pax gene, PaxB, which encodes a structural and functional Pax 2/5/8-like paired domain as well as an octapeptide and Pax6-like homeodomain. PaxB binds to and activates Tripedalia crystallin promoters (especially J3-crystallin) and the Drosophila rhodopsin rh6 gene in transfection tests and induces ectopic eyes in Drosophila. In situ hybridization showed that PaxB and crystallin genes are expressed in the lens, retina and statocysts. We suggest from these results that an ancestral PaxB gene was a primordial gene in eye evolution and that eyes and ears (mechanoreceptors) may have had a common evolutionary origin. Thus, the numerous structural and molecular features of Tridpalia rhopalia indicate that ancient cubozoan jellyfish are fascinating models for evo/devo insights into eyes and other sensory systems.
Animals↗
Retinal stem cells and regeneration.
The optic vesicle gives rise to several very different epithelial tissues, including the neural retina, the pigmented epithelium, the iris, the ciliary epithelium of the ciliary body and the optic stalk. Retinal regeneration can arise from several different cellular sources; in some species, the process involves interconversion, or transdifferentiation, among cells of the different tissue types. Therefore, prior to a discussion of retinal regeneration, we will briefly discuss current knowledge about the influence of signaling molecules in cell fate determination in ocular tissues. Next, we will detail the evidence for neurogenesis in the mature retina. Lastly, we will describe various types of regenerative phenomena that occur in the retina, from complete regeneration of functional retina in fish and amphibians, to the more limited neuronal production that occurs in avian and mammalian retinas.
Animals↗