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 739 records · Page 41Linked to original sources
PubMed2006

Pseudo-organ boundary conditions applied to a computational fluid dynamics model of the human aorta.

In three-dimensional numerical studies of the aorta, it is difficult to apply proper boundary conditions at the end of each major aortic branch because of interactions between blood and organs. Organs and body parts were assumed to be likened to cylindrically shaped porous media, so-called pseudo-organs, and treated in the computational domain as forms of hemodynamic resistance. Permeability functions were determined from two-dimensional axisymmetric computations of each aortic branch and these functions were then used in an unsteady three-dimensional simulation of the complete aorta. Substantially accurate cardiac output (5.91 L/min) and blood distributions to the major branches were predicted.

Aorta↗
PubMed2007

3D heart model for computer simulations in cardiac surgery.

For a satisfactory computer simulation, a model, which imitates a natural situation, is needed. The Human heart is an irregular 3D object and thus difficult to reproduce. Basic data was taken from Visible Human Dataset (VHD), National Library of Medicine. The heart area was cut out of the original cross-sections and different tissues segmented. All the slices also had to be aligned to assure precise overlapping of the structures. A 3D computer heart model with the resolution of 1mm was designed. The heart model was dedicated to simulations of heat transfer during heart surgery however, it is applicable also to other medical simulations.

Cardiac Surgical Procedures↗
PubMed2004

Insight into the physiological functions of PDGF through genetic studies in mice.

Genetic analyses in mice have contributed significantly to the understanding of the physiological functions of platelet-derived growth factors (PDGFs) and their receptors. Phenotypic analyses of gene knockouts of PDGF-A, PDGF-B, PDGF alpha-receptors (PDGFRalpha) and beta-receptors (PDGFRbeta) have shown that these ligands and receptors play major roles during embryonic development. Conditional and subtle mutations in the same genes and analysis of chimeric mice have provided additional information about the roles of these genes in postnatal development. Transgenic over-expression studies have also demonstrated that PDGF ligands are capable of inducing pathological cell proliferation in a number of different organs. The present review summarizes these findings and discusses their implications for mammalian development and disease.

Animals↗
PubMed2006

Efficient 3D finite element analysis of dental restorative procedures using micro-CT data.

OBJECTIVES: This investigation describes a rapid method for the generation of finite element models of dental structures and restorations. METHODS: An intact mandibular molar was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different cavity preparations (MO/MOD preparations, endodontic access) and restorations (feldspathic porcelain and composite resin inlays). The different tooth parts were then imported in a finite element software package to create 3D solid models. The potential use of the model was demonstrated using nonlinear contact analysis to simulate occlusal loading. Cuspal deformation was measured at different restorative steps and correlated with existing experimental data for model validation and optimization. RESULTS: Five different models were validated by existing experimental data. Cuspal widening (between mesial cusps) at 100 N load ranged from 0.4 microm for the unrestored tooth, 9-12 microm for MO, MOD cavities, to 12-21 microm for endodontic access cavities. Placement of an MOD adhesive restoration in porcelain resulted in 100% cuspal stiffness recovery (0.4 microm of cuspal widening at 100 N) while the composite resin inlay allowed for a partial recuperation of cusp stabilization (1.3 microm of cuspal widening at 100 N). SIGNIFICANCE: The described method can generate detailed and valid three dimensional finite element models of a molar tooth with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications.

Bite Force↗
PubMed2006

Geometric models of the aortic and pulmonary roots: suggestions for the Ross procedure.

OBJECTIVE: To discuss geometric factors, which may influence long-term results relating to homograft competence following the Ross procedure, we describe the 3D morphology of the pulmonary and aortic roots. MATERIALS: Measurements were made on 25 human aortic and pulmonary roots. Inter-commissural distances and the heights of the sinuses were measured. For geometrical reconstruction the three commissures and their vertical projections at the root base were used as reference points. RESULTS: In the pulmonary root, the three inter-commissural distances were of similar dimensions (17.9+/-1.6mm, 17.5+/-1.4mm and 18.6+/-1.5mm). In the aortic root, the right inter-commissural distance was greatest (18.8+/-1.9mm), followed by the non-coronary (17.4+/-2.0mm) and left coronary sinus commissures (15.2+/-1.9mm). The mean height of the left pulmonary sinus was greatest (20+/-1.7mm) followed by the anterior (17.5+/-1.4mm) and right pulmonary sinus (18+/-1.66mm). In the aortic root, the height of the right coronary sinus was the greatest (19.4+/-1.9mm) followed by the heights of the non-coronary (17.7+/-1.8mm) and left coronary sinus (17.4+/-1.4mm). Measured differences between parameters determine the tilt angle and direction of the root vector. The tilt angle in the pulmonary root averaged 16.26 degrees , respectively; for the aortic roots, it was 5.47 degrees . CONCLUSIONS: Herein we suggest that the left pulmonary sinus is best implanted in the position of the right coronary sinus, the anterior pulmonary in the position of the non-coronary sinus and the right pulmonary sinus in the position of the left coronary sinus. In this way, the direction of the pulmonary root vector will be parallel to that of the aortic root vector.

Adult↗
PubMed2005

A novel method for the assessment of the accuracy of computing laminar flow stroke volumes using a real-time 3D ultrasound system: In vitro studies.

AIMS: Laminar flow stroke volume (SV) quantification in the ascending aorta or pulmonary artery can provide a measure for determining cardiac output (CO). Comparing flows across different valves can also compute shunt volumes and regurgitant fractions. Quantification methods for 3D color Doppler laminar flow volumes have been developed using reconstructive 3D, but these are cumbersome and time-consuming both in acquisition and measurement. Our study evaluated newly developed color Doppler mapping with real-time live 3D echo to test velocity, spatial and temporal resolution for computing SV. METHODS AND RESULTS: Five rubber tubes (diameters=3.0, 2.25, 2.0, 1.9, 1.7 cm), a freshly dissected porcine aorta (Ao) and a pulmonary artery (PA) (both 2-3 cm diameter) were connected to a pulsatile pump in a water bath. Different SV, from 10 to 80 ml/beat, were studied at pump rates of 40-60 bpm in this phantom model with flow quantified by timed collection. The Nyquist limit was set between 43 and 100 cm/s and frame rate ranged from 14 to 23/s. ECG triggered 3D color Doppler volumes were acquired with a 2-4 MHz probe. The digital scan line data from the 3D volumes, with retained velocity assignments, was exported and analyzed offline by MatLab custom software. Close correlations were found between 3D calculated SV and reference data for all tubes (r=0.98, y=1.14x-1.69, SEE=2.82 ml/beat, p<0.0001). Both Ao and PA flows were also highly correlated with the reference measurements (PA: r=0.98, SEE=3.17 ml/beat; Ao: r=0.99, SEE=3.20 ml/beat). CONCLUSIONS: Real-time 3D color Doppler method could provide an efficient, accurate and reliable method for clinical evaluation and quantification of flow volumes in patients.

Animals↗
PubMed2006

Simulator training in endoscopic hemostasis.

Simulation of upper gastrointestinal (GI) hemorrhage provides the opportunity to practice endoscopic hemostasis without the risk of patient harm and time limitations. Various models have been developed to simulate an acute bleeding source in the upper GI tract to evaluate the feasibility of new endoscopic devices or to practice interventional techniques in a calm and controlled environment. Increasingly available ex vivo models provide this opportunity without the ethical concerns involved with live-animal courses. Validation studies have proven acceptance of ex vivo models and improved clinical performance by repetitive training using these models.

Animals↗
PubMed2006

Endoscopic retrograde cholangiopancreatography simulation.

Endoscopic retrograde cholangiopancreatography (ERCP) has evolved from a mainly diagnostic to a mainly therapeutic endoscopic technique. Training in ERCP is labor-intensive and time-consuming. Computer- and animal-model-based simulations have been developed in the hope of standardizing and accelerating training. They also may be useful for evaluating trainees. Early efforts to develop computer simulations of endoscopic procedures were hampered by lack of processing power and memory and the cost of software development. Biologic systems seem to offer more realism at lower cost. Hybrid computer-biologic systems seem likely to be the next generation of ERCP simulators.

Animals↗
PubMed2006

Simulator training for endoscopic ultrasound.

Endoscopic ultrasound (EUS) is one of the most challenging endoscopic procedures to learn and requires integration of both cognitive and endoscopic skills. EUS also is an important technology with a growing number of therapeutic applications. Despite its increasing role in managing gastrointestinal diseases, EUS technology remains largely limited to the confines in academic medical centers and tertiary referral centers because of issues concerning cost, equipment availability, efficiency of implementation, reimbursement, and most importantly, training. This article reviews the factors that are considered important for EUS training and discusses the use of various simulators and the potential role of these simulators in the future.

Animals↗
PubMed2006

Simulators in training: defining the optimal role for various simulation models in the training environment.

Clearly, the potential applications for simulation training in endoscopy are vast. Endoscopy models may serve as a platform to introduce new skills, to maintain proficiency, or even to assess competency. As these applications are explored fully, the strengths and weaknesses of specific devices will dictate their roles. Educators must ensure that these roles are founded on reliable research but remain mindful that simulators are only tools to augment clinical training, with the goal of benefiting both student and patient, and are not a replacement for patient-based experience.

Animals↗
PubMed2006

Logistical considerations for endoscopy simulators.

A variety of endoscopy simulators have been produced during the last several decades. Multiple factors have influenced the types of simulators that have been developed and the ongoing evolution of existing models. Realistic simulation is only one issue in providing simulation-based training in GI endoscopy. Details such as cost, technologic limitations, management and availability of training facilities, personnel, animal welfare and the procurement, handling, and disposal of animal parts are all major factors when considering the options available among existing endoscopy simulators. Table 1 summarizes the logistical factors for the different types of endoscopy simulator. These considerations clearly are of major importance in simulator design and development and in the conceptualization and organization of simulator-based curricula and courses.

Animals↗
PubMed2004

Right ventricular volume measurement with single-plane Simpson's method based on a new half-circle model.

BACKGROUND: The complexity of right ventricular (RV) shape makes it more difficult for measuring its volume. However, the short-axis view of the right ventricle usually is crescent and might be assumed as half of a circle. This hypothesis can be applied to calculate RV volume by using the single-plane Simpson's method, but the final RV volume should be about half of the original calculated value. The aim of this study was to test the accuracy of RV volume measurement based on this new assumption in human RV casts. METHODS: Fifteen human RV casts were scanned with multislice helical CT and RV sagittal image that corresponds to right anterior oblique view were reconstructed. Single-plane Simpson's method was used to calculate RV volumes. The calculated RV volume was defined as the original calculated value divided by 2. The true RV cast volume was determined by water displacement. RESULTS: The true RV volume was 64.23+/-24.51 ml; the calculated volume was 53.18+/-26.22 ml. The calculated RV correlated closely with true volume with a regression equation of RV actual volume=21.04 0.406 x RV calculated volume (r=0.869, P<0.001), but significantly underestimated the actual volume by 11.05+/-13.09 ml (P<0.006). CONCLUSION: Right ventricular volume could be calculated with single-plane Simpson's method based on the new proposed half-circle model.

Body Weights and Measures↗
PubMed2004

Skilled birth attendant competence: an initial assessment in four countries, and implications for the Safe Motherhood movement.

OBJECTIVES: Percentage of deliveries assisted by a skilled birth attendant (SBA) has become a proxy indicator for reducing maternal mortality in developing countries, but there is little data on SBA competence. Our objective was to evaluate the competence of health professionals who typically attend hospital and clinic-based births in Benin, Ecuador, Jamaica, and Rwanda. METHODS: We measured competence against World Health Organization's (WHO) Integrated Management of Pregnancy and Childbirth guidelines. To evaluate knowledge, we used a 49-question multiple-choice test covering seven clinical areas. To evaluate skill, we had participants perform five different procedures on anatomical models. The 166 participants came from facilities at all levels of care in their respective countries. RESULTS: On average, providers answered 55.8% of the knowledge questions correctly and performed 48.2% of the skills steps correctly. Scores differed somewhat by country, provider type, and subtopic. CONCLUSION: A wide gap exists between current evidence-based standards and current levels of provider competence.

Benin↗
PubMed2004

Numerical investigation of the non-Newtonian blood flow in a bifurcation model with a non-planar branch.

The non-Newtonian fluid flow in a bifurcation model with a non-planar daughter branch is investigated by using finite element method to solve the three-dimensional Navier-Stokes equations coupled with a non-Newtonian constitutive model, in which the shear thinning behavior of the blood fluid is incorporated by the Carreau-Yasuda model. The objective of this study is to investigate the influence of the non-Newtonian property of fluid as well as of curvature and out-of-plane geometry in the non-planar daughter vessel on wall shear stress (WSS) and flow phenomena. In the non-planar daughter vessel, the flows are typified by the skewing of the velocity profile towards the outer wall, creating a relatively low WSS at the inner wall. In the downstream of the bifurcation, the velocity profiles are shifted towards the flow divider. The low WSS is found at the inner walls of the curvature and the lateral walls of the bifurcation. Secondary flow patterns that swirl fluid from the inner wall of curvature to the outer wall in the middle of the vessel are also well documented for the curved and bifurcating vessels. The numerical results for the non-Newtonian fluid and the Newtonian fluid with original Reynolds number and the corresponding rescaled Reynolds number are presented. Significant difference between the non-Newtonian flow and the Newtonian flow is revealed; however, reasonable agreement between the non-Newtonian flow and the rescaled Newtonian flow is found. Results of this study support the view that the non-planarity of blood vessels and the non-Newtonian properties of blood are an important factor in hemodynamics and may play a significant role in vascular biology and pathophysiology.

Arteries↗
PubMed2004

Evolutionary optimization for robust hierarchical computation of the rotation centres of kinematic chains from reduced ranges of motion the lower spine case.

A novel technique based on evolutionary optimization is proposed here to compute the average rotation centres (RCs) of ball joints linked into kinematic chains using 3D trajectories of the markers attached to the external surface of the corresponding articulated structures. The chain is hierarchically solved by iteratively minimizing the variance of the marker distances from the actual RC through an evolutional strategy method (ESM) from proximal to distal joints. In particular, the technique is compared to the non-rigid sphere-fitting method, recently proposed in literature and implemented through a closed-form solution (CFS), in conditions of random and systematic noise superimposed to the marker coordinates. Results from simulated motions showed that, in case of small range of motion (5 degrees , 10 degrees ) the performance of CFS is really unreliable whereas ESM provided satisfactory accuracy. Error propagation along the kinematic chain was found to be negligible. Also in the case of systematic errors, ESM provides an accuracy that is sensibly better than that of the CFS. As a case study, ESM was applied to the in vivo computation of the RCs of the vertebrae in the lower spine region using a specific marker protocol. A set of spine movements by a normal adult male, recorded by an optoelectronic motion capture system, were processed with the developed method. The variability of the estimated average RCs was small (few millimeters) in agreement with the literature data from cadaveric studies and X-ray imaging.

Algorithms↗
PubMed2004

A numerical and experimental study of compliance and collapsibility of preterm lamb tracheae.

Knowledge of the mechanical behaviour of immature tracheae is crucial in order to understand the effects exerted on central airways by ventilatory treatments, particularly of Total Liquid Ventilation. In this study, a combined experimental and computational approach was adopted to investigate the compliance and particularly collapsibility of preterm lamb tracheae in the range of pressure likely applied during Total Liquid Ventilation (-30 to 30 cmH2O). Tracheal samples of preterm lambs (n = 5; gestational age 120-130 days) were tested by altering transmural pressure from -30 to 30 cmH2O. Inflation (Si) and collapsing (Sc) compliance values were calculated in the ranges 0 to 10 cmH2O and -10 to 0 cmH2O, respectively. During the tests, an asymmetric behaviour of the DeltaV/V0 vs. P curves at positive and negative pressure was observed, with mean Si = 0.013 cmH2O(-1) and Sc = 0.053 cmH2O(-1). A different deformed configuration of the sample regions was observed, depending on the posterior shape of cartilaginous ring. A three-dimensional finite-element structural model of a single tracheal ring, based on histology measurements of the tested samples was developed. The model was parameterised in order to represent rings belonging to three different tracheal regions (craniad, median, caudal) and numerical analyses replicating the collapse test conditions were performed to evaluate the ring collapsibility at pressures between 0 and -30 cmH2O. Simulation results were compared to experimental data to verify the model's reliability. The best model predictions occurred at pressures -30 to -10 cmH2O. In this range, a model composed of median rings best interpreted the experimental data, with a maximum error of 2.7%; a model composed of an equal combination of all rings yielded an error of 12.6%.

Animals↗
PubMed2004

Analysis of the human and ape foot during bipedal standing with implications for the evolution of the foot.

The ratio of the power arm (the distance from the heel to the talocrural joint) to the load arm (that from the talocrural joint to the distal head of the metatarsals), or RPL, differs markedly between the human and ape foot. The arches are relatively higher in the human foot in comparison with those in apes. This study evaluates the effect of these two differences on biomechanical effectiveness during bipedal standing, estimating the forces acting across the talocrural and tarsometatarsal joints, and attempts to identify which type of foot is optimal for bipedal standing. A simple model of the foot musculoskeletal system was built to represent the geometric and force relationships in the foot during bipedal standing, and measurements for a variety of human and ape feet applied. The results show that: (1) an RPL of around 40% (as is the case in the human foot) minimizes required muscle force at the talocrural joint; (2) the presence of an high arch in the human foot reduces forces in the plantar musculature and aponeurosis; and (3) the human foot has a lower total of force in joints and muscles than do the ape feet. These results indicate that the proportions of the human foot, and the height of the medial arch are indeed better optimized for bipedal standing than those of apes, further suggesting that their current state is to some extent the product of positive selection for enhanced bipedal standing during the evolution of the foot.

Animals↗