Synthetic-rubber mouldings of the human aorta and its branches.
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Aorta↗
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Results for “Models, Anatomic”
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Assessment of spatial resolution of pace mapping when using body surface potentials.
Using computer simulations and statistical methods, the resolution of pace mapping when used in combination with body surface potentials was systematically investigated. In an anatomical model of the human ventricular myocardium, pre-excitation sequences were initiated at 69 sites positioned along the atrioventricular (AV) ring and corresponding body surface potential maps (BSPMs) were calculated at 32 leads placed on the anterior torso. For each time after the onset of pre-excitation (every 4 ms to 40 ms) and each root-mean-square (RMS) noise level (5, 10, 20 and 50 microV), BSPMs were cros-correlated and the spatial resolution defined as the largest pacing site separation at which the differences in correlation coefficients were not statistically significant (level p > or = 0.05). The findings indicate that when random RMS noise of 5 microV was added to the simulated BSPMs, average spatial resolution over all 60 sites was at 20 ms after the onset of pre-excitation within 3.5 +/- 0.9 mm. The results provide theoretical evidence that statistical analysis of BSPMs obtained during pace mapping can offer improved means for subcentimetre identification of accessory pathways located along the AV ring.
Body Surface Potential Mapping↗
Three-dimensional teaching model for coronary angiography.
In order to improve the understanding and interpretation of cine coronary arteriograms obtained in various angled projections, a three-dimensional wire model was constructed. The main coronary arteries and most important muscular branches are simulated by a wire skeleton. The model can be rotated to simulate the standard right and left anterior oblique and left lateral projections. The degree of rotation is indicated on the base of the model. By tilting the model, cephalad and caudad tube angulation can be simulated. By placing the model in front of the cine projector, the shadows of the wires can be superimposed upon the projected cine coronary arteriogram. This simple, inexpensive model has greatly improved the three-dimensional understanding of the coronary arterial tree in various angled and nonangled views and in our practice had led to the development of additional useful projections.
Angiography↗
A simple technique for producing cast specimens of the cardiac ventricles.
In a convenient method, a methacrylate dental plastic, Kallocryl C, was used to make cast specimens of both ventricles of man. The casts are suitable for use in comparative measurements and highly accurate determinations of ventricular volumes.
Cardiac Volume↗
A dynamic model of the hand with application in functional neuromuscular stimulation.
Potential hand function in people with tetraplegia was evaluated using a three-dimensional dynamic mathematical model. The model was used to evaluate hand positioning, grasp force, and the outcome of surgeries such as tendon transfers and joint fusion, in situations typical of those encountered when using functional neuromuscular stimulation to restore function in people with tetraplegia. In the model, the hand is treated as a jointed multibody system. Each joint is subjected to muscle moments, passive joint moment, and moments due to grasp forces. Model simulations showed that function was highly dependent on both muscle strength and joint passive moments. The potential for tendon transfers, such as the Zancolli-lasso and intrinsicplasty, plasty, to improve hand function was demonstrated, but their value is subject-dependent. It was also shown that activation of multiple thumb muscles (adductor pollicis, abductor pollicis brevis, and flexor pollicis longus) without interphalangeal joint fusion can provide convenient lateral pinch posture with approximately 70% more grip force than a currently used method, which includes joint fusion but requires only one muscle. Finally, a grasp protocol was introduced and shown successful in palmar grasp and hold of movable cylindrical objects using only extrinsic muscles, provided the fingers could be extended sufficiently to enclose the object.
Algorithms↗
Impression method of the colon using sodium alginate--an experimental evaluation in dog.
An experimental study using adult dog was conducted on the impression of the colon whereby a screening test is done by making a mold of the intestine with sodium alginate. The mold of the intestine could be obtained easily and safely in a short time. Protrusions about 2 mm in diameter corresponding to lymphoid tissue of the rectum and sigmoid colon and shallow depressions on the surface of the protrusions were exactly imprinted on the surface of the mild. Compared with the barium study and endoscopy, this method requires neither special equipment nor high-grade technique, can be done easily in a short time and was not inferior in the diagnosis accuracy. Sodium alginate used in this method is a safe substance which is being used clinically as a plasma expander and laxative in addition to being used as an additive to various foods. When injected into the intestine, it exerted no injurious action whatsoever. from these findings, the possibility of this method being used clinically was considered high.
Alginates↗
Development of impression method of the colon using sodium alginate--experimental evaluation by the use of intestinal phantom.
We devised an impression method of the colon using sodium alginate as a screening method for diseases of the lower part of the colon and evaluated its usefulness by means of an intestinal phantom. Sodium alginate, when mixed with water, kept enough fluidity immediately after mixing and could easily be poured into the phantom. With this paste gelatinized sharply in the phantom about two minutes after, an impression of the intestinal phantom could easily be made. Sodium alginate is a safe substance which is already used clinically. This method is thus expected to become popular as a screening method for diseases of the lower part of the colon.
Alginates↗
Comparison study of different head model structures with homogeneous/inhomogeneous conductivity.
Most of the human head models used in dipole localisation research, which have been reported in the literature to date, assume a simplified cranial structure wherein the head is modelled as a set of distinct homogenous tissue compartments. The inherent inhomogeneity of the tissues has so far been ignored in these models due to the difficulties involved in obtaining the conductivity characteristics with sufficiently high enough spatial resolution throughout the head. A technique for developing an inhomogeneous head model based on the generation of pseudo-conductivity values from the existing but sparse conductivity values is proposed in this paper. Comparative studies are conducted on different model structures and different mechanisms for generating the pseudo conductivities. An evaluation of the results of these studies as reported in this paper, shows that contrary to current simplifying assumptions, tissue inhomogeneity has a major influence on the computation of electrical potential distributions in the head.
Brain↗
On the three-dimensional physiological position of the temporomandibular joint.
Despite intensive research regarding the position of the temporomandibular joint, only few evidence-based facts are known about a three-dimensional physiological condyle-fossa relationship. The aim of this systematic literature review was therefore to summarize the existing literature regarding the condyle position and to draw conclusions about a standardized three-dimensional condyle position. An extended search profile based on the search strategy of the Cochrane Oral Health Group and applied to twelve medical databases was used to identify existing studies. Articles which were not electronically accessible (mainly those published before 1960) were identified from reference lists and bibliographies. These publications were assessed independently by two clinicians with reference to points based on specified criteria. The interexaminer agreement was assessed on the basis of the kappa coefficient.1903 articles published in the period 1899-2001 and relating to condyle position were identified. These studies showed a pronounced variability in their methodological approaches, with only 49 of them meeting the inclusion criteria. The interexaminer agreement yielded a kappa-value of 0.92. Although numerous studies used three-dimensional data, no physiological three-dimensional condyle position was determined. The most frequent analytic method was two-dimensional projection of the temporomandibular joint onto a subjectively selected sagittal plane. This evaluation method revealed a noticeable shift over time in condyle position from posterior to anterior, suggesting a clear-cut publication bias. Publications with the highest evidence level favored no specific position (p > 0.05). Simplification of the three-dimensional structure of the temporomandibular joint to a two-dimensional projection is questionable for therapeutic positioning of the condyle in relation to the fossa.
Databases, Factual↗
Three-dimensional soft tissue prediction using finite elements. Part I: Implementation of a new procedure.
BACKGROUND AND AIM: The prediction of soft tissue esthetics is important for achieving an optimal esthetic outcome in orthodontic treatment planning. Applicable procedures have so far been restricted to two-dimensional profile predictions that have not proven to be very reliable. The goal of this investigation was therefore to develop a novel finite element-based procedure that allows a three-dimensional, easily visualized, quantitative analysis and prediction of soft tissue behavior for the clinician. The procedure to be developed should be easy to handle and not entail any additional radiation exposure for the patient. MATERIAL AND METHODS: Using a three-dimensional scanner, the facial surfaces of 20 probands were digitalized and individual FEM models were generated. RESULTS: After reduction of data redundancy via several conversion steps, a patient-specific simulation model was prepared consisting of 20,000 to 40,000 individual elements to which specific physical properties could be assigned. The average time required for generating a virtual model was 50 minutes. Problems occurring during model generation were rare (mainly shadowing phenomena and movement artifacts). CONCLUSION: The procedure outlined herein makes the reliable generation of patient-specific simulation models possible for facial soft tissue prediction in orthodontics.
Adult↗
Three-dimensional soft tissue prediction using finite elements. Part II: Clinical application.
BACKGROUND AND AIM: The goal of this study was to analyze the validity and prediction accuracy of a newly-developed procedure for three-dimensional soft tissue prediction based on Finite Element Method, and to compare the results with prediction produced using an existing two-dimensional prediction program (Dentofacial Planner Plus). PATIENTS AND METHODS: In twelve patients who underwent combined surgical-orthodontic treatment, profile prediction was generated using both procedures preoperatively and then compared at predefined measurement points with the patient's actual postoperative soft tissue status. RESULTS: The deviations observed depended on the facial region, whereby the prediction errors for both procedures were much greater in the lower facial third than in the midfacial third. Calculating in all the measurement points, the mean horizontal prediction error was 0.32 mm for the Finite Element Method and 0.75 mm for the Dentofacial Planner Plus. Overall, we were able to demonstrate the new procedure's superior validity and quality of visualization. In addition to profile prediction, the procedure allows a differentiated three-dimensional assessment of esthetically important regions such as the cheeks, nasolabial folds and the nasal wings. Additional X-radiation is not necessary in this risk-free and stress-free procedure. CONCLUSION: Three-dimensional soft tissue prediction employing finite element modeling is a useful aid for implementing esthetically-optimized treatment planning.
Adult↗
Proportional growth of craniofacial regions.
OBJECTIVE: The ratio of the cranium to the face has been traditionally reported in textbooks without any firm evidence base. The present study was undertaken to measure the increase in size with age of the cranium, face, upper and lower face components. METHOD: Bolton standard mean outlines for ages 1 to 18 years were analysed by the Autoceph computer program. We measured the area of each craniofacial component outline. RESULTS: The ratio of the size of the cranium to the face was less than previously reported at birth, 2 years, and 5 years of age, but more nearly correct in the adult. Growth of the cranium largely ceased by 9-years indicating precocious growth of the brain in relation to the face. The size of the face increased relative to the cranium by 69%. The lower face increased relative to the upper face by 22%. The average percentage increase in area was 78% lower face, 68.9% total face, 58.8% upper face, 26% cranium. The absolute growth rate of the face was greater than that of the cranium, and that of the lower face was greater than that of the upper face. The 95% confidence intervals for the growth rates did not overlap, indicating a statistically significant difference. The relative growth rate (cm2/cm2/yr) was 0.0444 lower face, 0.0391 total face, 0.0328 upper face, 0.0084 cranium. CONCLUSIONS: There was a differential gradient of change increasing from the cranium to the upper face to the lower face. This gradient was most clearly expressed by the relative growth rates and average percentage increases in area.
Adolescent↗
[Manipulator assisted endoscope guidance in functional endoscopic sinus surgery: proof of concept].
BACKGROUND: Functional endoscopic sinus surgery (FESS) is characterized by single-handed preparation and guidance of the endoscope by the nondominant hand. This results in an additional extension of operation time by up to 15% and ergonomic deficits. The aim of this study is the conception of an automated assistance system for FESS in view of the following questions: (1) Which degree of surgical automation is suitable for FESS? (2) Which design is suitable? (3) What are the properties of the technical system (planning, time, accuracy, precision) of the selected system? (4) Does the system offer potential for a clinical application? METHODS: In all 49 FESS were analyzed for surgical workflows. Measurement of the maximum forces within FESS was performed with 40 trials on an anatomical model. Three different mechanical systems were used in ten FESS and evaluated using the ICCAS Human-Machine Evaluation Scale. For realization of automated endoscope guidance an engine-driven and -braked manipulator (PA10-6c, Mitsubishi, Japan) was used. The technical parameters determined were expenditure of time for the preoperative planning of workspace, surgical accuracy and precision of the intraoperative endoscope positioning, maximal forces, and time. RESULTS: Concept-conditioned instrument changes amount to an average of 41.1 and 18.9% (5.21 min) time requirement for each FESS side. Maximum forces on the mucous membrane during a conventional FESS were measured at 9.8 N (5.9-9.8). Usability of the mechanical endoscope holder was estimated in 18 of 20 cases to be inferior to the standard procedure. The time needed for segmenting the intranasal workspace was 15.2 min (10.0-23.0). The maximum deviation of the automatically driven endoscope from a planned position amounted to 0.85 mm (manually 4.64 mm). The maximum force was measured with 1.1 N in the z direction (manually 9.8 N). Automated guidance of the endoscope to an intranasal position needed 7.25 s (6.4-7.9); manually 12.64 s (5.9-43.0). CONCLUSION: Guidance of the endoscope for FESS by an automated motor-driven system is possible. The conception which is based on workflow analysis favors a system with automatic definition of the workspace and a manual movement of the endoscope. The examined system offers a potential for clinical application. Definition of the automation level and development of a man-machine interface is more important than selection or reconstruction of a special manipulator for endoscope guidance in FESS from a surgical point of view.
Endoscopes↗
The endocannabinoid system in the physiology and pathophysiology of the gastrointestinal tract.
Numerous investigations have recently demonstrated the important roles of the endocannabinoid system in the gastrointestinal (GI) tract under physiological and pathophysiological conditions. In the GI tract, cannabinoid type 1 (CB1) receptors are present in neurons of the enteric nervous system and in sensory terminals of vagal and spinal neurons, while cannabinoid type 2 receptors are located in immune cells. Activation of CB1 receptors was shown to modulate several functions in the GI tract, including gastric secretion, gastric emptying and intestinal motility. Under pathophysiological conditions induced experimentally in rodents, the endocannabinoid system conveys protection to the GI tract (e.g. from inflammation and abnormally high gastric and enteric secretions). Such protective activities are largely in agreement with anecdotal reports from folk medicine on the use of Cannabis sativa extracts by subjects suffering from various GI disorders. Thus, the endocannabinoid system may serve as a potentially promising therapeutic target against different GI disorders, including frankly inflammatory bowel diseases (e.g. Crohn's disease), functional bowel diseases (e.g. irritable bowel syndrome) and secretion- and motility-related disorders. As stimulation of this modulatory system by CB1 receptor agonists can lead to unwanted psychotropic side effects, an alternative and promising avenue for therapeutic applications resides in the treatment with CB1 receptor agonists that are unable to cross the blood-brain barrier, or with compounds that inhibit the degradation of endogenous ligands (endocannabinoids) of CB1 receptors, hence prolonging the activity of the endocannabinoid system.
Animals↗
Bone tissue stiffness in the mandibular condyle is dependent on the direction and density of the cancellous structure.
Variation in the apparent stiffness of cancellous bone is generally ascribed to variation in cancellous structure and density, while the bone tissue stiffness is assumed to be constant. The purpose of the present study was to examine whether the bone tissue stiffness is dependent on the direction and density of the cancellous structure. Bone tissue stiffness was estimated by combining mechanical testing and micro-finite element (micro-FE) modeling on cylindrical bone specimens obtained from the human mandibular condyle. One set of specimens was tested in the vertical direction of the condyle (n = 39) and another set in the transverse direction (n = 30). The cancellous structure of the specimens was characterized by micro-CT. The apparent bone stiffnesses predicted by the FE model correlated strongly (r2 = 0.91) with the measured apparent bone stiffnesses. Apparent bone stiffness in the transverse direction was considerably smaller than that in the vertical direction. In contrast, the predicted bone tissue stiffness was significantly larger in the transverse direction (E = 13.70 GPa) than in the vertical direction (E = 11.87 GPa). In addition, bone tissue stiffness correlated negatively with the bone volume fraction and directional sensitivity of the bone tissue stiffness increased with a decrease of bone volume fraction. The results suggest that the transversely oriented trabeculae in the mandibular condyle are stiffer and more mineralized than the vertically oriented trabeculae and that bone loss is compensated by an increase in the degree of mineralization.
Aged↗
3D reconstruction of the diaphragm for virtual traumatology.
This study lies within the scope of passive road safety, and more particularly injury mechanisms of the abdominal area. The finite element modeling, which makes it possible to simulate a road accident and to observe the possible bone fractures or internal tissue injuries, allows large projections in the comprehension of injury mechanisms. However, the digital models already available and used in accidentology do not offer as one very simplified description of the diaphragm, as well for its geometry as for its bracing aspect and the modifications that this could induce in the behavior of abdominal organs and vessels at impact. In order to develop an accurate model of diaphragm for road safety research, a 3D reconstruction was performed, based on a sitting post-mortem Human subject sections. The resulting geometry was then turned into a segmented mechanical component (using the finite element method) and included in a full human model already available. The result is a valuable tool to improve the knowledge of injury mechanisms involved in car crashes at the abdominal level.
Computer Simulation↗
Kinematics of surface growth.
In this paper a general mathematical framework is developed to describe cases of fixed and moving growth surfaces. This formulation has the mathematical structure suggested by Skalak (1981), but is extended herein to include discussion of possible singularities, incompatibilities, residual stresses and moving growth surfaces. Further, the general theoretical equations necessary for the computation of the final form of a structure from the distribution of growth velocities on a growth surface are presented and applied in a number of examples. It is shown that although assuming growth is always in a direction normal to the current growth surface is generally sufficient, growth at an angle to the growth surface may represent the biological reality more fully in some respects. From a theoretical viewpoint, growth at an angle to a growth surface is necessary in some situations to avoid postulating singularities in the growth velocity field. Examples of growth on fixed and moving surfaces are developed to simulate the generation of horns, seashells, antlers, teeth and similar biological structures.
Animals↗
[Erbium:YAG laser vitrectomy: temperature measurements in different replacement materials].
BACKGROUND: The erbium:YAG laser has the potential of being used routinely for vitrectomy because of the excellent quality of liquefying vitreous structures and the low vacuum forces required. However, the use of silicone oil and perfluorocarbon may lead to unwanted temperature increases in the microsurgery probe. The aim of this work was to investigate this side effect. MATERIALS AND METHODS: Different replacement materials such as water, methocel, silicone oil and perfluorocarbon were used in a simple eye model. The temperature increase during laser application was measured by means of thermocouples. The maximum temperature increase and time decay were derived with and without aspiration from these time-resolved measurements. The average power at the distal end of the microsurgery probe was chosen to be 1 W. RESULTS: The temperature increase with aspiration in water was found to be significantly smaller than all other replacement materials. Interruption of aspiration leads to a critical temperature increase of approximately 14 K; however, this increase occurred very slowly (decay time 200 s). A comparable result could be observed for methocel, which was used to simulate condensed vitreous structures. In perfluorocarbon and silicone oil we measured a far higher increase in temperature of up to 130 K within a few seconds. Furthermore, small remnants of carbonized materials can be seen in the microsurgery probe after laser application. CONCLUSIONS: The temperature increase during erbium:YAG laser vitrectomy in water can be considered to be harmless for other intraocular structures. However, insufficient aspiration or increased vitreous condensation leads to increased temperature in the microsurgery probe. Our results demonstrate that the use of erbium:YAG laser vitrectomy in materials such as silicone oil or perfluorocarbons is contraindicated.
Contraindications↗