Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Models, Anatomic”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,603 records · Page 89Linked to original sources
PubMed2004

Multiphysics simulation of left ventricular filling dynamics using fluid-structure interaction finite element method.

To relate the subcellular molecular events to organ level physiology in heart, we have developed a three-dimensional finite-element-based simulation program incorporating the cellular mechanisms of excitation-contraction coupling and its propagation, and simulated the fluid-structure interaction involved in the contraction and relaxation of the human left ventricle. The FitzHugh-Nagumo model and four-state model representing the cross-bridge kinetics were adopted for cellular model. Both ventricular wall and blood in the cavity were modeled by finite element mesh. An arbitrary Lagrangian Eulerian finite element method with automatic mesh updating has been formulated for large domain changes, and a strong coupling strategy has been taken. Using electrical analog of pulmonary circulation and left atrium as a preload and the windkessel model as an afterload, dynamics of ventricular filling as well as ejection was simulated. We successfully reproduced the biphasic filling flow consisting of early rapid filling and atrial contraction similar to that reported in clinical observation. Furthermore, fluid-structure analysis enabled us to analyze the wave propagation velocity of filling flow. This simulator can be a powerful tool for establishing a link between molecular abnormality and the clinical disorder at the macroscopic level.

Biophysical Phenomena↗
PubMed2005

MSP dynamics drives nematode sperm locomotion.

Most eukaryotic cells can crawl over surfaces. In general, this motility requires three sequential actions: polymerization at the leading edge, adhesion to the substrate, and retraction at the rear. Recent in vitro experiments with extracts from spermatozoa from the nematode Ascaris suum suggest that retraction forces are generated by depolymerization of the major sperm protein cytoskeleton. Combining polymer entropy with a simple kinetic model for disassembly we propose a model for disassembly-induced retraction that fits the in vitro experimental data. This model explains the mechanism by which disassembly of the cytoskeleton generates the force necessary to pull the cell body forward and suggests further experiments that can test the validity of the models.

Actins↗
PubMed2005

A model for diffusion in white matter in the brain.

Diffusion of molecules in brain and other tissues is important in a wide range of biological processes and measurements ranging from the delivery of drugs to diffusion-weighted magnetic resonance imaging. Diffusion tensor imaging is a powerful noninvasive method to characterize neuronal tissue in the human brain in vivo. As a first step toward understanding the relationship between the measured macroscopic apparent diffusion tensor and underlying microscopic compartmental geometry and physical properties, we treat a white matter fascicle as an array of identical thick-walled cylindrical tubes arranged periodically in a regular lattice and immersed in an outer medium. Both square and hexagonal arrays are considered. The diffusing molecules may have different diffusion coefficients and concentrations (or densities) in different domains, namely within the tubes' inner core, membrane, myelin sheath, and within the outer medium. Analytical results are used to explore the effects of a large range of microstructural and compositional parameters on the apparent diffusion tensor and the degree of diffusion anisotropy, allowing the characterization of diffusion in normal physiological conditions as well as changes occurring in development, disease, and aging. Implications for diffusion tensor imaging and for the possible in situ estimation of microstructural parameters from diffusion-weighted MR data are discussed in the context of this modeling framework.

Algorithms↗
PubMed2002

The evolution of multiplanar diagnostic imaging: predictable transfer of preoperative analysis to the surgical site.

Presurgical planning and communication between the prosthodontist and the surgeon is essential to achieve optimal placement of functional implants. Besides the basic clinical examination and the use of mounted study casts, radiographic imaging is an essential adjunctive aid in treatment planning. In the past decade, multiplanar reformatted computerized tomography (CT) has become the most comprehensive and accurate aid for implant treatment planning. Available software programs allow precise assessment of the 3-dimensional architecture and internal anatomy of the jaws. The programs enable accurate preoperative evaluation for planning implant placement with a maximum use of bone. However, the accurate transfer of the implant analysis from 2- and 3-dimensional computer reconstruction to the surgical site was not predictable until recently. As advancements occurred in technology with the advent of the helical CT scanner and rapid prototype 3-dimensional model production by stereolithography, a CAD-CAM program was developed to create an accurate transfer from the image to the surgical site. Detailed preoperative analyses of the quantity and quality of bone as well as the ideal positioning of implant fixtures may be established with the aid of a surgical guide that is placed directly on the bone for precise implant insertion.

Computer Simulation↗
PubMed2006

Dimensional accuracy of a binder jet model produced from computerized tomography data for dental implants.

A full-scale model produced by multislice helical computerized tomography (CT) was made by using the binder jet method and applied for presurgical diagnosis, surgical simulation, and the production of surgical templates for dental implant treatment. In this study, accuracy of the full-scale model with plaster powder was assessed by shifting the binary threshold values. A step phantom was made from bone-equivalent material. When it was placed in water, the CT imaging was performed with a multislice helical CT unit. Three-dimensional (3-D) images were reconstructed by 3-D visualization software. Using 4 different threshold values, full-scale models were produced by a binder jet method with plaster powder. All sides of the full-scale models were directly measured, and their values were compared with that of the step phantom. The mean difference was approximately 0.1 mm in the axial plane when the setting was 0.75 for the threshold. In total, the mean difference was approximately 0.2 mm when the setting was 0.50 for the threshold. It is suggested this full-scale model could be applied for presurgical diagnosis, surgical simulation, and the production of surgical templates in dental implant treatment.

Computer-Aided Design↗
PubMed2006

In vitro evaluation of a new autologous valve-stent for deep venous incompetence.

PURPOSE: To report the results of in vitro hydrostatic bench testing of a new vein-stent combination to correct deep venous incompetence. METHODS: Twelve valves were constructed from a modified Palmaz stent encased in a segment of great saphenous vein harvested from patients during routine varicose vein surgery. An in vitro flow circuit was set up to evaluate opening and closing pressures (in cm H(2)O), and the valve was subsequently subjected to repetitive cycles of increasing prograde flow and reflux pressures. Duplex scanning was used to evaluate valve closure time and detect any possible reflux. RESULTS: The valve mechanism required only 1 to 3 cm H(2)O for opening and 2 to 4 cm H(2)O for closing. Prograde flow of up to 1000 mL/min passed easily through this valve, which remained competent with reflux pressures up to 180 cm H(2)O. Mean valve closure time was 0.15+/-0.07 seconds. Unligated side branches or damage from dissection impaired the competence of 3 valves. CONCLUSION: This new vein-stent valve functions as a normal deep vein valve, requiring only minimal pressures for opening and closing. It allows high flow passage and still remains competent at high reflux pressures. This valve may provide a minimally invasive solution for the correction of deep venous incompetence using autologous material. Further in vivo evaluation will be mandatory.

Angioplasty, Balloon↗
PubMed2006

Should conventional angiography be the gold standard for carotid stenosis?

PURPOSE: To compare conventional angiography (CA) and rotational angiography (RA) to assess the degree of angiographically-measured stenosis versus cross-sectional area (CSA) stenosis in an in vitro carotid model. METHODS: Various grades of stenosis were created by adhering different amounts of silicone rubber sealant onto the inner wall of clear, radiolucent tubes. Following 2- and 3-projection CA and 20-projection RA, the tubes were transected at the actual maximum stenosis. The cross-sectional areas were digitally photographed, and CSA stenosis was calculated using ImageJ planimeter software. The differences among CA, RA, and CSA stenosis measurements were compared statistically. RESULTS: There was no significant difference between RA and CSA stenosis measurements (p=0.46). Conventional angiography with 2 or 3 projections between 0 degrees and 90 degrees underestimated the severity of disease in 19 (63%) of 30 samples. The maximum stenosis percentage was significantly lower in CA versus RA (p<0.0001 in 2-projection, p<0.0003 in 3-projection) and in CA versus CSA stenosis (p<0.0004 in 2-projection, p<0.001 in 3-projection). The maximum stenosis percentages measured by RA were less than CSA stenosis in 5 (71.4%) of 7 tubes (p=NS) containing 50% to 69% stenoses. Eight tubes had mountain-shaped lesions, which was significantly overestimated by RA (11.5%+/-9.7%, p<0.012). CONCLUSION: CA with 2 or 3 projections significantly underestimates the maximum stenosis in an in vitro model. RA may overestimate disease in patients with mountain-shaped plaques and may underestimate disease if the stenosis is <70%. Our data suggest that CA should not be the gold standard for the qualification of carotid endarterectomy in asymptomatic patients, nor for vascular laboratory quality assurance analysis.

Angiography↗
PubMed2005

Educational material of dental anatomy applied to study the morphology of permanent teeth.

The purpose of this report is to present educational material that would allow the dental student to learn to easily identify the morphologic characteristics of permanent teeth, and how they fit together (occlusion). In order to do this, macro models of permanent teeth with no attrition were carved in wax and later molded with alginate. These molds were filled with plaster, dental stone and/or cold-cured acrylic resin. The large individual dental stone tooth models were mounted on a wax base, thus obtaining maxillary and mandibular arches which were occluded. These dental arches were molded with plaster or dental stone. The authors suggest that these types of macro models allow an excellent visualization of the morphologic characteristics of permanent teeth and occlusion. Dental students are able to carve the permanent dentition in wax with great facility when they can observe macro models.

Acrylic Resins↗
PubMed1995

Landmark positioning on maxilla of cleft lip and palate infant--a reality?

In this study, we tested the precision of landmark positioning for a set of landmarks that can be used for the edentulous cleft lip and palate maxilla of the infant, by analyzing intraobserver and interobserver repositioning and measuring on a series of 121 (unilateral and bilateral) study casts. To date, no data on interobserver and only minimal data on intraobserver reproducibility are available. We found intraobserver reproducibility acceptable with total measurement errors ranging from 0.51 to 1.54 mm. Interobserver reproducibility was only slightly less with total measurement errors ranging from 0.63 to 1.57 mm. Total measurement errors were found to be relatively high for some variables. Both the intra- and interobserver analyses show insight into expected precision of landmark positioning during placement of these points on casts. A learning effect for precise positioning has been demonstrated in both analyses. The points with the highest precision overall are Q and Q', followed by the linear measurements PL and P'L'. Quality of regular study casts (impressions) is an important factor, with room for improvement. Reproducible landmark positioning on the cleft lip and palate infant's maxilla, can only be a reality if the quality of the cast is optimal and the investigator is experienced. Intraobserver and interobserver reproducibility are in the same range, which justifies the comparison of results from different studies and relieves future investigators of the need to have all measurements within a study conducted by the same investigator. Aspects of the biologic meaning of landmarks are also discussed.

Cephalometry↗
PubMed1997

Comparison of numeric techniques in the analysis of cleft palate dental arch form change.

OBJECTIVE: Quantitative descriptions of form (size and shape) changes are significant to the understanding of the development, treatment planning, and prognosis of patients born with cleft lip and palate. This study compared the results of traditional dental arch form change measurements, such as width, depth, perimeter, and area, with four numeric methods: finite element scaling analysis, macroelement method, Euclidean distance matrix analysis, and conventional least-squares and resistant-fit theta rho Procrustes analyses. DESIGN: Using tooth cusp landmarks on maxillary study casts, form change measurements of a male with complete bilateral cleft lip and palate at ages 2, 5, and 6 years were made comparing each age to the next older. RESULTS AND CONCLUSIONS: With the exception of the 2- to 5-year resistant-fit analysis, all numeric method: 1) provide comparable results, 2) provide more detailed descriptions than do traditional methods, and 3) provide results that correlate well with the reported effects of increased lip pressure due to lip closure surgery. The use of finite-element scaling analysis on study casts is somewhat limited since: 1) there is more than one solution at teeth shared by many finite elements, 2) gross averaging of form change occurs within triangular elements, and 3) solutions can vary with the choice of element location. The use of the macroelement method circumvented the above finite element limitations without compromising finite-element advantages. Procrustes results vary with the chosen superposition algorithm. The choice of the most appropriate Procrustes method required some a priori knowledge of form difference. The large number of results obtained by Euclidean distance matrix analysis and the nongraphic presentation of these results hamper quick interpretation but may be best suited for definitive statistical analysis. The graphic representation of both the magnitude and direction of: 1) landmark displacement in the Procrustes analyses (once size difference is eliminated), and 2) the rate of form change in the macroelement method provide an intuitive appreciation of how and where the casts differ.

Age Factors↗
PubMed1998

Three-dimensional analysis of cleft palate topology in newborn infants with reference to the cranial skeleton.

OBJECTIVE: To describe a method of determining the three-dimensional topology of the palatal crest relative to a reproducible anthropomorphic coordinate system in newborn infants with unilateral cleft palate. For this purpose, physical models of the maxilla and face were analyzed by computer morphometry. DESIGN: The study was limited to infants referred to the craniofacial center during the first 11 days after birth. SETTING: The study was performed at a craniofacial center servicing a large geographic area. PARTICIPANTS: The method was applied to 12 infants with unilateral cleft lip, alveolus, and palate (eight patients with left-side clefts and four with right-side clefts). MAIN OUTCOME MEASURES: The three-dimensional topology of the palatal crest referenced to an anthropometric coordinate system was the primary outcome measure. The anthropometric reference system is defined by the tragus points and the midpoint of a line connecting the endocanthia. RESULTS: The topology of the maxillary crests of the patients was characterized by considerable variability. The center of the premaxilla as defined by the attachment of the frenulum was frequently displaced by several millimeters from the midsagittal plane. The displacement was to the left in infants with right-side clefts and to the right in infants with left-side clefts. The premaxilla can be rotated by more than 30 degrees relative to the normal position. No significant retroposition of the minor segment as determined by the location of the tuber points was found. Several morphometric anomalies were found to be correlated linearly. CONCLUSIONS: We propose that the morphologic deviations are in part caused by the neuromotor activity of the tongue and of the interrupted M. orbicularis oris. The data can serve as the starting point for a longitudinal study of craniofacial development in children with cleft palate and for studies on the efficacy of different therapeutic approaches.

Alveolar Process↗
PubMed2000

Video-imaging assessment of nasal morphology in individuals with complete unilateral cleft lip and palate.

OBJECTIVE: The purpose of this study was to develop a video-imaging mathematical method to assess nostril morphology. DESIGN: This retrospective study involved two age-matched groups: 28 subjects with complete unilateral cleft lip and palate (CUCLP) and 19 noncleft controls. Nose casts were reproducibly oriented in a jig such that the casts could be rotated about the coronal axis. Video images of the nostrils were captured and then analyzed for area, perimeter, centroid, principal axis, moments about the major and minor axes (I11, I22), anisometry, bulkiness, lateral offset, internostril angle, and rotational angle. RESULTS: All parameters identified nostril asymmetry in both groups. The results of the analyses using anisometry, I11, and I22 showed that, in both groups, one nostril was rounder and one was more elliptical. This asymmetry, however, differed between the two groups, and the difference was primarily based on the degree of ellipticity of the nostrils. Maximum dimension, perimeter, lateral offset, I11, and I22 were more asymmetric in the cleft group. In the control group, the right nostril was more elliptical and had a greater perimeter, and the left-side nostril had a greater bulkiness (enfolding). CONCLUSIONS: The method developed was validated for assessment of nasal morphology in cleft and noncleft samples. Nostril morphology was asymmetric in both groups but more asymmetric in the cleft group than the control group. The dominant influence of the cleft resulted in more elliptical noncleft nostrils and greater nostril shape asymmetry in the cleft group. The validated video-imaging method can now be used to assess the efficacy of treatment on nasal morphology.

Adolescent↗
PubMed2001

Facial reconstruction on the abnormal skull model of a living patient.

OBJECTIVE: The concept of using a skull as the armature upon which to reconstruct a face has been understood for many years. The objective of this study was to blindly test this technique by using a skull that was reconstructed from the computed tomography (CT) scans of a living 48-year-old man. DESIGN: The patient had a bilateral cleft lip, alveolus, and palate. A model of the complete skull produced by a computer-controlled milling machine that used data from the CT scans was used for the reconstruction. Surgery was then performed, and new dental prostheses were also constructed. After surgery, a second model of the relevant part of the skull was made and the reconstruction modified accordingly. CONCLUSION: Despite having no information about the patient apart from that which could be gleaned from the model skull, the reconstructions demonstrate the approximate appearance of the face before and after surgery. Even without the extra information routinely available in forensic cases, a face broadly similar to that of the living patient could be achieved.

Anatomy, Artistic↗
PubMed1995

Finite element methods in spine biomechanics research.

The finite element method has been used in spine biomechanics research for nearly a quarter of a century. Recent developments have made it possible to simulate a variety of clinically relevant situations in an increasingly realistic manner, elevating the finite element method into a fully complementary partnership with experimental approaches for the investigation of clinical problems in the spine. These new developments are presented in a historical context to evaluate their potential impact on future spine biomechanics research.

Age Factors↗
PubMed1975

Pliable metacrylate casts of blood vessels: use in a scanning electron microscope study of the microcirculation in rat hypophysis.

Methyl methacrylate mixed with 30-50 percent hydroxy ethyl or hydroxy propyl methacrylate produces a pliable replica suited to manipulation. The advantages of this improved casting medium were discussed, demonstrating the scanning electron micrographs of the isolated and dissected blood vascular replica of the rat cerebral hypophysis. In the micrographs it was unequivocally indicated that the vascular bed of the anterior lobe is supplied by the capillary plexus of the median eminence and the neural stalk, and that the vascular meshwork of the intermediate lobe is formed by vessels extended from the posterior lobe and is drained into the anterior lobe. The subependymal network intercalated between the plexus of the median eminence and the meshwork of the hypothalamus is directly supplied by arterial branches. It was also demonstrated that the plexus of the median eminence is, at its periphery, in direct communication with the systemic venous twigs.

Animals↗
PubMed1992

Experimental tests of three-dimensional model of urinary concentrating mechanism.

Recently, a new model of the urinary concentrating process has been proposed that takes into account the three-dimensional architecture of the renal medulla. Under the assumptions of the model, computer simulations predicted significant axial osmolality gradients in the inner medulla without active transport by the inner medullary loop of Henle. Two of the model assumptions (which constitute hypotheses for this study) were: (1) the osmotic water permeability of the initial part of the inner medullary collecting duct (initial IMCD) is very low even in the presence of vasopressin; and (2) there is significant lateral separation of structures such that thin descending limbs are far from the collecting ducts at the same inner medullary level. The first hypothesis was addressed by perfusing rat initial IMCD segments in vitro and measuring osmotic water permeability. With the osmotic gradient oriented as predicted by the model (lumen greater than bath), vasopressin increased the osmotic water permeability from 286 to 852 microns/s. Three additional series of experiments confirmed the high water permeability in the presence of vasopressin. The second hypothesis was addressed by morphometric analysis of histologic cross-sections of the rat renal medulla. Mean distances of descending limbs to the nearest adjacent collecting duct were very small throughout the inner medulla (less than 6 microns) and substantially less than in the outer medulla (28 microns). It was concluded that the data are inconsistent with both hypotheses and therefore do not support the feasibility of the "three-dimensional" model of the renal inner medulla. The axial distributions of loops of Henle and collecting ducts in the rat renal medulla are also reported.

Animals↗
PubMed1997

Comparative in vitro effectiveness of closed root debridement with fine instruments on specific areas of mandibular first molar furcations. II. Furcation area.

The purpose of this study was to demonstrate the extent of deposits removed from within the furcation area of mandibular first molars following the use of curets with a modified blade and slim ultrasonic inserts in an in vitro model simulating a closed root debridement approach to furcation treatment. The furcation areas of 100 artificial mandibular first molars were uniformly coated with black model paint. The molars were fixed into a custom acrylic model, maintained in a firm position with modified occlusal splints, and the roots covered with a heavy rubber dam. The model was set in a mannequin and mounted on a dental chair recreating a clinical situation. Fifty molars (25 right, 25 left) were instrumented with the experimental curets and an equivalent number of molars with the ultrasonic inserts. An experienced dental hygienist completed all the instrumentation, spending 4 minutes on each molar. The molars were sectioned buccolingually from the crown apically to separate the roots, and areas in the internal surface of mesial and distal roots were analyzed to determine the percentage of deposits remaining using a computerized imaging routine system. A 2-factor analysis of variance was conducted to test for differences between both types of instruments. The curets produced furcation root surfaces with significantly less percentage of residual deposits than the ultrasonic inserts (P < 0.01). This study indicates the potential value of small bladed curets in debriding involved furcations during initial therapy and supportive periodontal therapy. The current findings should be corroborated in a clinical study.

Acrylic Resins↗
PubMed1997

Development of a new algorithm for heat transfer equation in the human body and its applications.

A computer program has been developed for the numerical analysis of thermal conditions within the human body. In this study, a cylindrical model, which consists of internal multi-layers, is adapted for the segment of the human body. For the present concentric cylindrical model we developed a new numerical solution method using a linear combination of the modified Bessel functions. By using the present computer program the internal tissue temperatures, heat fluxes and blood temperatures of the thigh, crus and foot segments are calculated. This paper describes a new algorithm solving heat transfer equation in the human body and the example of calculated results of the combination of thigh, crus and foot segments. The calculated results show the local characteristics of each segment in the human body.

Algorithms↗