PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Models, Anatomic”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1991

A simple height-specific and rate-specific step test for children.

Recently an anatomic model was reported for adults that standardized the platform height for step tests using an individual's stature and a specified hip angle. In order to determine if the model could be used to predict the platform height for children, platform heights were calculated and hip angles were measured in 146 boys and 140 girls ages 6 to 18 years who were divided into four age groups (6 to 8, 9 to 11, 12 to 15, and 16 to 18 years old). There were no statistical differences between measured and calculated hip angles in any of the age groups. In order to determine the validity for predicting maximal oxygen consumption from stepping using a calculated platform height, three step tests were employed using one platform height and stepping frequencies of 22, 26, or 30 ascents/min. Each of the tests was administered to 93 6- to 18-year-olds. Correlation coefficients between the 15-second recovery heart rate after stepping and maximal oxygen consumption measured on a treadmill were .80 at 30 ascents/min, .79 at 26 ascents/min, and .81 at 22 ascents/min. Each of the correlation coefficients was significant at the P less than .01 level. It can be concluded that the model is valid for standardizing the platform height for children for use with a single stage step test for estimating maximal oxygen consumption.

Adolescent↗
PubMedDate not supplied

[Possible applications of a method for 3D reconstruction of CT image data. OP-planning, finishing of individual alloplastic implants for replacement of cranial and maxillofacial bone structures].

A method for the three-dimensional reconstruction of CT-image data permits manufacturing of natural size anatomical models thus enabling preoperative measurements of relevant parameters (length, areas, and volumes). The methods described allow for new perspectives in preoperative planning of dental implants, particularly for the maxillary problem area. The use of 3D image data for manufacturing individual alloplastic implants simplifies the exact reconstruction of symmetrical bone structures, which up to now was impossible to achieve with conventional methods. Applications in the fields of orthodontic surgery and in neurological surgery are suggested. Refinement of available techniques is possible by means of additional segmentation of soft tissues, and by implementation of more sophisticated software for better visualisation and smoothly shaped surfaces. Future applications may even include aesthetic surgery.

Adult↗
PubMed1977

External rotational injury of tha ankle joint with displacement of the talus.

The mechanism of second-degree external rotational injury of the ankle, with fracture of the lower end of the fibula, is discussed with reference to experiments on an anatomical model. It is concluded that with this type of injury there is lateral displacement of the talus because the deltoid ligament is ruptured, but there is no diastasis of the inferior tibiofibular syndesmosis. The results of conservative treatment of 10 patients with second-degree external rotational injury of tha ankle are reviewed.

Adolescent↗
PubMed1979

[Pathological-anatomical teaching models in moulages. Manufacturing technic and history].

Wax moulages were used as pathological-anatomical teaching objects in medicine well into this century. On the occasion of the restauration of the moulage collection of the Department of Dermatology, University of Munich, the history of Munich wax artists is reviewed. The historical development of reproductions in wax in previous centuries is described. Several moulages showing various dermatological diseases are pictured. The technical details of moulage manufacture are mentioned.

Germany, West↗
PubMed1991

Computer simulations of activation in an anatomically based model of the human ventricular conduction system.

Simulations of the electrical activity during excitation were performed in an anatomically based model of the human ventricular conduction system. Each of the 33,000 elements of this model represented a unit bundle of Purkinje or atrioventricular nodal tissue. The Ebihara-Johnson model for sodium defined the active membrane characteristics. Using a combination of new and existing modeling techniques, simulations of excitation were completed in approximately 5 min CPU time on an IBM 3090 at the Cornell National Supercomputer Facility. Activation times at sites in the model were compared to experimental measurements for the excitation of the ventricular myocardium on the endocardial surface. These "literature-based" times were estimated from a number of reported human heart mapping studies. Initially, the times fit poorly. The major factor for the discrepancy was the conduction velocities of the elements, which were a result of the physical and electrical parameters derived from a review of histologic and electrical properties studies. In addition, there was a latency between activation of the system in the left ventricle of the model and that in the right ventricle when compared to the experimental work. When the times were scaled to adjust for the conduction velocity and ventricular latency effects, the match between the simulation and literature-based times was much improved. Quantitative comparison between normalized times resulted in correlation coefficients CCF = 0.76 for the right ventricle and CCF = 0.64 for the left ventricle.

Atrial Function↗
PubMed1991

Knowledge-based system for the three-dimensional reconstruction of blood vessels from two angiographic projections.

A knowledge-based system for the three-dimensional reconstruction of blood vessels from wide-angle coronary and stereoscopic cerebral angiographic projections is developed. For the reconstruction of the coronary vessels, the left coronary artery (LCA) is automatically labelled on standard RAO and LAO projections, using anatomical models of the LCA. The labelling system succeeds in giving the most important coronary arteries a correct anatomical label. These labelling results enable us to find corresponding segments in both images. In the case of the reconstruction of the cerebral vessels however, such an anatomical model is clearly unavailable. To find corresponding segments, small-angle projections must be relied on, resulting in very similar images. Owing to the small angular separation between both projections, the three-dimensional reconstruction will be less accurate. Once the corresponding segments in both projections are obtained, the three-dimensional artery trajectory is reconstructed with dynamic programming techniques. The three-dimensional reconstructed coronary vessels are also used for an automatic quantification of stenotic lesions.

Blood Vessels↗
PubMed1992

The computer synthesis of expressive faces.

This paper presents a methodology for the computer synthesis of realistic faces capable of expressive articulations. A sophisticated three-dimensional model of the human face is developed that incorporates a physical model of facial tissue with an anatomical model of facial muscles. The tissue and muscle models are generic, in that their structures are independent of specific facial geometries. To synthesize specific faces, these models are automatically mapped onto geometrically accurate polygonal facial representations constructed by photogrammetry of stereo facial images or by non-uniform meshing of detailed facial topographies acquired by using range sensors. The methodology offers superior realism by utilizing physical modelling to emulate complex tissue deformations in response to coordinated facial muscle activity. To provide realistic muscle actions to the face model, a performance driven animation technique is developed which estimates the dynamic contractions of a performer's facial muscles from video imagery.

Computer Graphics↗
PubMed1991

A veterinary digital anatomical database.

This paper describes the Veterinary Digital Anatomical Database Project. The purpose of the project is to investigate the construction and use of digitally stored anatomical models. We will be discussing the overall project goals and the results to date. Digital anatomical models are 3 dimensional, solid model representations of normal anatomy. The digital representations are electronically stored and can be manipulated and displayed on a computer graphics workstation. A digital database of anatomical structures can be used in conjunction with gross dissection in teaching normal anatomy to first year students in the professional curriculum. The computer model gives students the opportunity to "discover" relationships between anatomical structures that may have been destroyed or may not be obvious in the gross dissection. By using a digital database, the student will have the ability to view and manipulate anatomical structures in ways that are not available through interactive video disk (IVD). IVD constrains the student to preselected views and sections stored on the disk.

Anatomy, Veterinary↗
PubMed1990

Pulsed and color Doppler analysis of normal carotid bifurcation flow dynamics using an in-vitro model.

An anatomically accurate model of the human carotid bifurcation was studied by using color Doppler flow mapping and pulsed Doppler signal analysis. In concordance with dye injection studies, a zone of flow separation was clearly demonstrated at the origin of the internal carotid artery opposite the flow divider. This zone of flow reversal was detected when the ratio of external to common carotid flow rates was greater than 0.27 and became progressively larger as the ratio increased, finally evolving into a zone of heterogenous flow at a ratio greater than 0.5. The authors conclude that the zone of flow reversal seen in the human carotid artery is a geometric property of the bifurcation and that its size depends on the relative flow between both branches. Doppler color imaging can be used to noninvasively map out its extent.

Blood Flow Velocity↗
PubMed1990

The construction of an anatomically based model of the human ventricular conduction system.

The ventricular conduction system is a complicated network of specialized muscle cells responsible for the transmission of electrical activity between the atria and the ventricles of the human heart. It has been the focus of numerous electrical and anatomical studies at both the microscopic and macroscopic levels. An understanding of its behavior at both levels is considered important, because it is primarily responsible for the spread of excitation in the ventricles. Previous computer models have been very simple ones that have been primarily adjuncts to models of the ventricles. This paper describes a strategy for the construction of conduction system models which is based on real microscopic and macroscopic features, although the model still is much simpler than reality. The model contains almost 35,000 individual cylindrical elements, each of whose physical dimensions approximate unit bundles of Purkinje and atrioventricular nodal cells. The model, whose physical appearance closely resembles that of the conduction system, was generated from limited anatomical data in less than 2 min CPU time on an IBM 3090 at the Cornell National Supercomputer Facility.

Atrioventricular Node↗
PubMed1991

Generalized Stein's model for anatomically complex neurons.

A neuron with a large dendritic structure is considered. The number of synapses located on the dendrites is substantially higher than on the soma. The synaptic input effect on the neuronal excitability decreases with distance between a synapse ending and the trigger zone. Two areas are distinguished in accordance with the effect of synaptic input--dendritic and somatic. The dendritic area, when compared to the soma, is characterized by much higher intensity of its activation but the amplitudes of synaptically evoked changes of the membrane potential at the trigger zone are in general small. This situation is suitable for a diffusion approximation. However, on the soma, especially in the proximity of the trigger zone, the membrane potential changes are a large fraction of the threshold depolarization. The membrane potential at the trigger zone is modelled by a one-dimensional stochastic process. The diffusion Ornstein-Uhlenbeck process serves as a basis of the model; however, at the moments of somatic synapses activation its voltage changes in jumps. Their sizes represent the amplitudes of the evoked postsynaptic potentials. The unimodal histograms of interspike intervals can be explained by the model. The values of the coefficient of variation greater than one are connected with substantial inhibition.

Animals↗
PubMedDate not supplied

Knowledge-based multi-modality three-dimensional image analysis of the brain.

With the recent advances in medical imaging, three-dimensional anatomical and metabolic images of the brain are now available through MR/CT and PET/SPECT imaging modalities. Computerized multi-modality three-dimensional brain image registration and analysis can provide important correlated information for improving diagnosis and studying the pathology of disease. Such analysis may also provide help in planning brain surgery. Further, an anatomical model based quantification and analysis of internal structure can be used to develop a computerized anatomical atlas. Conventional anatomical atlases provide rigid spatial distribution of internal structures extracted from a single subject. The proposed computerized anatomical atlas provides probabilistic spatial distributions which can be easily updated to incorporate the variability of brain structures of subjects selected from pre-defined groups. This paper first presents a review of the current trends in knowledge-based segmentation, labeling, and analysis of MR brain images and then describes the Principal Axes Transformation based registration of three-dimensional MR brain images to develop composite models of selected internal brain structures. The composite models can be used as a computerized anatomical atlas in model-based segmentation and labeling of MR brain images. Three-dimensional labeled MR images of the brain can also be registered and correlated with PET images for analyzing the metabolic activity in the anatomically selected volume of interest. On the other hand, a volume of interest can be selected using the metabolic information and then analyzed for correlated anatomical information using the registered MR-PET images.

Algorithms↗
PubMed1992

Specific absorption rates and induced current distributions in an anatomically based human model for plane-wave exposures.

We have previously reported local, layer-averaged, and whole-body-averaged specific absorption rates and induced currents for a 5,628-cell anatomically based model of a human for plane-wave exposures 20-100 MHz (Chen and Gandhi 1989). Using a higher resolution, 45,024-cell model of the human body, calculations have now been extended to 915 MHz using the finite-difference time-domain method. Because of the higher resolution of the model, it has been possible to calculate specific absorption rates for various organs (brain, eyes, heart, lungs, liver, kidneys, and intestines) and for various parts of the body (head, neck, torso, legs, and arms) as a function of frequency in the band 100-915 MHz. Consistent with some of the experimental data in the literature, the highest part-body-averaged specific absorption rate for the head and neck region (as well as for the eyes and brain) occurs at 200 MHz for the isolated condition and at 150 MHz for the grounded condition of the model. Also observed is an increasing specific absorption rate for the eyes for frequencies above 350 MHz due to the superficial nature of power deposition at increasing frequencies.

Algorithms↗
PubMed1991

A computational model of the vertical anatomical organization of primary visual cortex.

A method for modeling anatomical connectivity for a vertically organized slab of cortical tissue in mammalian primary visual cortex has been developed. The modeled slab covers 500 x 500 microns of cortical surface and extends vertically throughout the full depth of the cortex. The model slab was divided into 6 laminae and neuronal somata were distributed in three dimensions through the slab in accordance with experimentally derived cell densities. Axonal and dendritic arborizations were modeled as line segments. A total of 17 morphological types of neurons were included. Connectivity was established based on proximity between axonal and dendritic arbors. There is good general agreement between the vertical distribution of connections generated by the model and the vertical distribution of synapses observed for cat area 17. In all layers, fewer connections were generated in the model than synapses in cat area 17. This is due, at least in part, to the exclusion of long range intracortical projections and sources of afferent input other than the dorsal lateral geniculate nucleus from the model. The connection scheme described here will be used in conjunction with a physiology model to model vertical signal flow, and will be expanded further to model receptive fields of cortical neurons.

Afferent Pathways↗
PubMed1992

Intracardiac therapy following emergency thoracotomy in the accident and emergency department: an experimental model.

For a select group of patients with penetrating chest trauma, immediate thoracotomy in the accident and emergency department offers the only chance of survival. Foley catheters have been used to achieve haemostasis in cardiac wounds but are not widely used for intracardiac fluid and drug administration during resuscitation. In an anatomical model designed to assess this procedure an average flow rate of 275 ml min-1 was achieved. The equipment required is readily available and easily assembled.

Animals↗
PubMed1990

The foot as a shock absorber.

A mathematical analysis of the deformation of the foot is developed to determine the role that stretch of ligaments and tendons plays in absorbing shock following impact. Our analysis is based on an anatomical biomechanical model that includes each of the bones of the foot. We calculate the time course of the deflection of the joints and the elongation of the ligaments and tendons and determine the ground reaction force acting on the heel. Quasi-linear viscoelastic theory is used for soft tissue constitutive relationships. With biomechanical data selected from the literature, we obtain a vertical force impact peak of 8000 N, occurring at 16 ms following heel strike. This is of higher magnitude and shorter duration than is found experimentally, as is to be expected, since we did not include the heel pad in our model and we assumed that the impact surface was ideally rigid.

Biomechanical Phenomena↗
PubMedDate not supplied

Mapping between MR brain images and a voxel model.

This paper describes an approach to establish the correspondence between a magnetic resonance (MR) image of the brain and a slice through a 3D anatomical model. The model is of voxel structure that symbolically labels primary tissue types such as grey matter, white matter, CSF, etc. In this approach a slice is first searched for in the model to achieve the best general match with the brain MR image in question. The operation involves a minimization of parameters such as position, rotation, slant, tilt and enlargement. Having thus found a globally good registration between the image and the model, local matches that link every pixel in the image through to the model slice are then searched for. This pixel-by-pixel match is expressed within a pair of maps, one for the vertical deformation and the other for the horizontal one. The matching algorithm consists of a series of octave separated blurring convolutions combined with exhaustive grey-valued correlation. Because every pixel in the model slice is labelled in terms of its tissue type, and because every pixel in the image has been matched directly to the model, every pixel in the image is now classified. This classification is used directly to perform segmentation which serves as a basis for the computation of medically relevant indices.

Algorithms↗