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PubMed1994

Anatomical models for space radiation applications: an overview.

Extremely detailed computerized anatomical male (CAM) and female (CAF) models that have been developed for use in space radiation analyses are discussed and reviewed. Recognizing that the level of detail may currently be inadequate for certain radiological applications, one of the purposes of this paper is to elicit specific model improvements or requirements from the scientific user-community. Methods and rationale are presented which describe the approach used in the Space Shuttle program to extrapolate dosimetry measurements (skin doses) to realistic astronaut body organ doses. Several mission scenarios are presented which demonstrate the utility of the anatomical models for obtaining specific body organ exposure estimates and can be used for establishing cancer morbidity and mortality risk assessments. These exposure estimates are based on the trapped Van Allen belt and galactic cosmic radiation environment models and data from the major historical solar particle events.

Computer Simulation↗
PubMed2001

Currents induced in anatomic models of the human for uniform and nonuniform power frequency magnetic fields.

We have used the quasi-static impedance method to calculate the currents induced in the nominal 2 x 2 x 3 and 6 mm resolution anatomically based models of the human body for exposure to magnetic fields at 60 Hz. Uniform magnetic fields of various orientations and magnitudes 1 or 0.417 mT suggested in the ACGIH and ICNIRP safety guidelines are used to calculate induced electric fields or current densities for the various glands and organs of the body including the pineal gland. The maximum 1 cm(2) area-averaged induced current densities for the central nervous system tissues, such as the brain and the spinal cord, were within the reference level of 10 mA/m(2) as suggested in the ICNIRP guidelines for magnetic fields (0.417 mT at 60 Hz). Tissue conductivities were found to play an important role and higher assumed tissue conductivities gave higher induced current densities. We have also determined the induced current density distributions for nonuniform magnetic fields associated with two commonly used electrical appliances, namely a hair dryer and a hair clipper. Because of considerably higher magnetic fields for the latter device, higher induced electric fields and current densities were calculated.

Biophysical Phenomena↗
PubMed2001

Gross anatomy in the surgical curriculum in Switzerland: improved cadaver preservation, anatomical models, and course development.

The invention of new techniques for surgery and interventional radiology demand improved training for ongoing specialists. The Anatomical Institutes in Switzerland support these requirements by establishing hands-on practical training courses by using new procedures for cadaver embalming and model construction. Improvements allow courses to provide students with more realistic simulations of both established and experimental surgical methods. Through these changes, the value of in-depth gross anatomy is enhanced as a topic of fundamental importance for the postgraduate medical and surgical curriculum. The web site http://www.unifr.ch/sgahe/snga.html contains information on courses using the Thiel embalming solution. Details about training courses in Switzerland using anatomical models are available at http://www.heartlab.org, http://www.vascular-international.org, and http://www.elastrat.com.

Anatomy↗
PubMed2004

An anatomical model of the gastric system for producing bioelectric and biomagnetic fields.

Between 60 and 70 million people in the United States are affected by gastrointestinal disorders. Many of these conditions are difficult to assess without surgical intervention and accurate noninvasive techniques to aid in clinical assessment are needed. Through the use of a superconducting quantum interference device (SQUID) gradiometer, the weak magnetic field generated as a result of muscular activity in the digestive system can be measured. However, the interpretation of these magnetic recordings remains a significant challenge. We have created an anatomically realistic biophysically based mathematical model of the human digestive system and using this model normal gastric electrical control activity (ECA) has been simulated. The external magnetic fields associated with this gastric ECA have also been computed and are shown to be in qualitative agreement with recordings taken from normal individuals. The model framework thus provides a rational basis from which to begin interpreting magnetic recordings from normal and diseased individuals.

Digestive System Physiological Phenomena↗
PubMed1997

Onset of the neuromuscular block simulated in an anatomical model.

AIMS: The aim of this study was to develop a pharmacodynamic model for nondepolarizing muscle relaxants (neuromuscular blocking agents, NMBAs) based on anatomical, physiological, and pharmacological considerations and analyse whether the time to onset of the submaximal neuromuscular block (NMB) depends on the affinities of the NMBAs for the postsynaptic receptors or on the pharmacokinetic properties of the NMBAs. METHODS: A quantitative description of the development of neuromuscular block was achieved by formulating a pharmacodynamic model based on anatomical, physiological and pharmacological considerations. The principal characteristics of the model are: (1) Diffusion of the NMBAs out of the capillaries into the interstitial space of muscle and from there into the synaptic space of the motor end plates (2) Receptor concentration in the synaptic space of 300 microM and the total amount of receptors in 100 g muscle of between 1.43 x (10(-11) to 10(-10) mol. (3) Interaction of NMBAs with the receptors defined by the association (k(assoc) = 4 x 10(8) min-1 x M-1) and dissociation (k(dissoc) one of 4, 40, or 400 min-1) rate constants. RESULTS: The simulations demonstrated that different affinities of the NMBAs for the postsynaptic receptors (defined by k(assoc)/k(dissoc)) do not influence the onset of the submaximal NMB. On the other hand, the time to the peak submaximal NMB is dependent on the pharmacokinetic properties of the drugs: Those NMBAs that leave plasma rapidly produce the block faster but the fraction of the dose that contributes to the block is small. This fraction is larger for those NMBAs that produce NMB later and, hence, these NMBAs require smaller equieffective doses. CONCLUSIONS: We conclude that those muscle relaxants that produce neuromuscular block rapidly require larger equieffective doses due to their more rapid initial disappearance from plasma.

Dose-Response Relationship, Drug↗
PubMed2002

[A study of rebuild of a three-dimensional anatomic model of mandibles].

OBJECTIVE: The aim of this study was to rebuild the anatomic structures of the mandibular bone and the canal, and to testify the reliability of the rebuilt model. METHODS: 15 mandibular bones with teeth are chosen, and a three-dimensional model was built with the method of CT. The slices vertical to the compensating curve were made in every dental position. Then the authors collected the data of alveoli and mandibular canal in every slice. The same work was done to the bone specimen, and then comparative analysis was done. RESULTS: The wideness of the alveoli and 10 mm bellow increased from mesial to distal position. It was the same of the alveoli from the top to the bottom. The mandibular canal lied in the inner and inferior side of the mandibular body. There was no significant difference in data collected with these two methods. CONCLUSION: Different types of dental implants should be chosen according to the anatomic characteristic of the mandibular bone in every dental position before the operation to avoid complications. And a reliable, accurate and direct method of planning an implant operation is to rebuild a three-dimensional model.

Adult↗
PubMed1983

Radiofrequency-induced hyperthermia: computer simulation of specific absorption rate distributions using realistic anatomical models.

A description is given of a computer simulation technique which predicts the specific absorption rate (SAR) distribution within the human body resulting from the application of radiofrequency electromagnetic energy. The method uses an extension to the principle of over-relaxation of electric potentials and the basis of the simulation is a realistic three-dimensional model derived from both dielectric and anatomical data. Two of the principal means of applying radiofrequency hyperthermia, namely the use of capacitive electrodes and inductive coils, have been provided for. The accuracy of the simulation has been favourably tested using an agar split-phantom and an infrared thermograph camera. The simulations can be used to assist the design and clinical use of radiofrequency applicators, and examples are given of the application of both an inductive coil and switched capacitive electrodes to heat the thorax.

Computers↗
PubMed2006

Generation of variable anatomical models for surgical training simulators.

The generation of variable surgical scenes is a key element for effective training with surgery simulators. Our current research aims at a high fidelity hysteroscopy simulator which challenges the trainee with a new surgical scene in every training session. We previously reported on methods able to generate a broad range of pathologies within an existing healthy organ model. This paper presents the methods necessary to produce variable models of the healthy organ. In order to build a database of uteri, a volunteer study was conducted. The segmentation was carried out interactively, also covering the establishment of an anatomically meaningful correspondence between the individual organs. The variability of the shape parameters has been characterized by principal component analysis. A new method has been developed and tested, allowing the derivation of realistic new instances based on the stochastic model and complying with non-linear shape constraints which are defined and interactively controlled by medical experts.

Computer Graphics↗
PubMed1996

A revised anatomical model of the abdominal musculature for torso flexion efforts.

Models of the abdominal musculature, which used single slice MRI or CT scans to reconstruct the anatomy, were unable to explain magnitudes of abdominal flexion moment which exceed 100 Nm in living subjects. For example, the muscle areas and corresponding flexor moment arms measured from a transverse scan at L4-L5 predict maximum moments less than 50 Nm. The architecture of rectus abdominis, external and internal obliques, and transverse abdominis was examined from cadaveric specimens, from which the geometric details were incorporated into a revised model. Scaling of the muscles to obtain physiological cross-sectional areas were obtained using two methods: serial MRI slices; and from several locations of ultrasound measurement. The two major anatomically justified improvements that had dramatic effects on flexor moment production were: the increase in flexor moment arms of muscles (approximately 30%) measured in a standing posture when compared to the supine posture for MRI examination; reinterpretation of the line of action of the obliques which transmit their flexor forces through the linea semilunaris (increasing their effective flexor moment arm) to eventual skeletal attachment at the pelvis.

Abdomen↗
PubMed1999

Anatomic model of hippocampal encoding of spatial information.

Place cells were recorded simultaneously from identified locations along the longitudinal axis of the CA3 and CA1 subregions of hippocampus with a sixteen site electrode array while rats performed a simple pellet chasing task (Deadwyler et al., J Neurosci 1996;16:354-372; Hampson et al., Hippocampus 1996;6:281-293). Cells in CA3 or CA1, separated by 100-300 microm (two electrode locations), exhibited high cross-correlations with respect to place field firing in a given location in the chamber. This pattern of co-activity changed abruptly to low cross-correlations when the longitudinal distance between recording sites increased to 400-1,000 microm. Surprisingly, cells located 1,200-1,400 microm apart again exhibited similar place fields, suggesting a repeating pattern of place field representation within hippocampus. These features were used to construct a model of hippocampal place cell activation using known anatomic connections and projections between CA3 as well as CA1 pyramidal cells. The model provides a topographic representation in hippocampus of the animals' movements around the chamber as different place cells become activated. The model utilizes key landmarks (i.e., corners and walls) to define the animals' movement trajectories through successive place fields and to construct corresponding patterns of place cell firing in hippocampus. This is accomplished via a topological transformation of the chamber's key landmarks projected onto the anatomy of the CA3 and CA1 subregions. The primary feature of the model is that it can, within limited capacity, accurately encode where the animal has been, rather than where it is going. The model, therefore, appears to be more appropriate for memory required to return to particular locations than for initial guidance into those locations.

Animals↗
PubMed2002

Developing an anatomical model of the human laryngeal cartilages from magnetic resonance imaging.

The purpose of this work was to construct a three-dimensional anatomical framework of the cartilages of the human larynx. The framework included representative surface models of the four laryngeal cartilages and estimated attachment points for the intrinsic laryngeal muscles. High-resolution magnetic resonance imaging (MRI) was used to scan one female and four male human cadaveric larynges. The cartilages were segmented manually from the MRI volume for analysis. Two of these larynges were subsequently dissected and the landmark distances on the cartilages measured for comparison with the MRI measures and previous studies. The MRI measures were 8% smaller than the anatomical measures and 12% smaller than data reported in the literature. A laryngeal coordinate system was defined using the plane of symmetry of the cricoid cartilage. Measures of cricoid cartilage symmetry had less than 3% difference between the two sides for a series of measures. An algorithm for registering larynges that minimized the root-mean-square distance between the surface of a reference cricoid cartilage and the surfaces of nonisotropically scaled candidate cricoid cartilages was evaluated. This study provided an anatomical framework for registering different larynges to the same coordinate space.

Aged↗
PubMed2000

Modeling anatomical spatial relations with description logics.

Although spatial relations are essential for the anatomy domain, spatial reasoning is only weakly supported by medical knowledge representation systems. To remedy this shortcoming we express spatial relations that can intuitively be applied to anatomical objects (such as 'disconnected', 'externally connected', 'partial overlap' and 'proper part') within the formal framework of description logics. A special encoding of concept descriptions (in terms of SEP triplets) allows us to emulate spatial reasoning by classification-based reasoning.

Anatomy↗
PubMed2002

Electrical remodeling of the atrium in an anatomic model of atrial flutter: relationship between substrate and triggers for conversion to atrial fibrillation.

BACKGROUND: Atrial flutter (AFL) and atrial fibrillation (AF) frequently coexist, yet the specific relationship between these arrhythmias, and particularly whether sustained AFL leads to AF, is unknown. METHODS AND RESULTS: We investigated the electrophysiological consequences of chronic AFL using an ovine anatomic right atrial Y-lesion model. AFL was induced in 7 animals, and 4 remained in sinus rhythm (controls). Sheep were monitored for spontaneous conversion of AFL to AF. Six of 7 sheep sustained AFL for 28 days. In 1 of 7 sheep, spontaneous conversion of AFL to AF occurred on day 5. AFL produced a highly significant fall in right and left atrial refractoriness (AERP, P<0.001), with 74+/-10% of the reduction occurring by day 3. Right atrial conduction velocity also fell significantly (baseline 89+/-9 cm/s versus day 28 64+/-14 cm/s, P<0.001) but over a slower time course. AERP and conduction velocity changes coincided with a characteristic biphasic decrease and increase in the AFL cycle length. The excitable gap (percent of AFL cycle length) increased from 13+/-3% at baseline to 46+/-8% by day 28 (P<0.001). Sustained AF (>30 seconds) was not inducible at baseline but after 28 days of AFL could be induced in 6 of 6 sheep by critically timed single or multiple extrastimuli delivered either in sinus rhythm or AFL. There was no significant change in any parameter in control sheep. CONCLUSIONS: In this model, AFL produced electrical remodeling and the substrate for sustained AF. However, spontaneous conversion to AF was uncommon, and the development of AF was dependent on specific triggers.

Animals↗
PubMed1998

The pig kidney as an endourologic model: anatomic contribution.

We present detailed anatomic findings on collecting system anatomy and renal morphometry in the pig and compare these findings with previous findings in humans. We studied three-dimensional polyester resin corrosion endocasts of the pelviocaliceal system obtained from 100 kidneys (50 pigs). Eighty kidneys were evaluated morphometrically, considering length, cranial pole width, caudal pole width, thickness, and weight. The pig collecting system was classified into two major groups (A and B). Group A (40%) was composed of kidneys in which the mid-zone is drained by calices dependent on the cranial or the caudal caliceal group or both. Group B (60%) kidneys have the mid-zone drained by calices independent of the polar groups. Group B includes two subtypes (B-I and B-II). The pig collecting system showed only angles smaller than 90 degrees between the caudal (lower) infundibulum and the renal pelvis. Renal morphometric measurements revealed the following means: length 11.8 cm, cranial pole width 5.64 cm, caudal pole width 5.35 cm, thickness 2.76 cm, and weight 98 g. As in human kidneys, one may group the pig collecting system into two groups. Nevertheless, in pigs, we did not find a subdivision of Group A. The incidence of collecting systems in Groups A and B and the subtypes of Group B in pigs are different from those in humans. Also different from humans, in pigs, we found only angles smaller than 90 degrees between the caudal (lower) infundibulum and the renal pelvis. Except for the length, the means of the other morphometric measurements of the pig kidney are smaller than those of humans. From an anatomic standpoint, despite the differences pointed out, we conclude that the pig kidney is a good animal model for endourologic research and training.

Animals↗
PubMed2000

Considerations upon the anatomical model of reward-based learning in the basal ganglia.

The nigrostriatal pathway appears to be very important in the reward-based learning. The dopaminergic neurons in the substantia nigra pars compacta (SNC) fire in relation to primary rewards and reward-conditioned stimuli, but not to rewards that are expected. It has been hypothesized that the anatomical framework for the selective response of these neurons is organized in the projections from some paralimbic areas in the frontal lobe to the striosomes of the caudate nucleus, which are also directly connected with the dopaminergic neurons of the SNC. Here, we present two additional pathways that may be related with this neurophysiological finding. We hypothesize that the connections of the paralimbic cortices with the ventral system of the basal ganglia and then with the thalamus and the hypothalamus, and the circuit ventral striatum-substantia nigra pars reticulata-thalamus-striatum could be also involved in the reward-based learning.

Basal Ganglia↗
PubMed1991

The use of CT-based 3-D anatomical modeling in the design of customized perineal templates for interstitial gynecologic implants.

A system for preplanning interstitial treatment of gynecologic malignancies with a CT-based 3-dimensional planning system is presented. The preplan produces a custom template design that optimizes catheter placement. The procedure begins with a CT scan with a vaginal cylinder and blank template in place. Contours of the anatomic structures of interest, cylinder, and template are entered into the system, and 3-D surfaces are generated. The first view evaluated is oriented in a "cylinder's-eye view," which shows the path of the catheters placed parallel to the cylinder. In most cases this path to the tumor is obstructed by the pubic bones and bladder. By rotating the view posteriorly, the catheters can travel under the symphysis and bladder to the tumor. Once the optimum angle for visualization of the tumor has been determined, an array of catheters is designed to optimize the dose to the tumor. This array includes the special distribution in the oblique plane as well as the depth of insertion for each catheter. The design is then used in drilling the appropriate guide holes in the template. Orthogonal film dosimetry as well as CT verification of source placement will be compared to the preplan distribution.

Brachytherapy↗
PubMed1995

The N-methyl-D-aspartate antagonists phencyclidine, ketamine and dizocilpine as both behavioral and anatomical models of the dementias.

Phencyclidine (PCP) and ketamine can induce a model psychosis in drug addicts and exacerbate the symptoms of chronic schizophrenics. The model psychoses these drugs induce mimic a variety of schizophrenic symptoms, including flattened affect, dissociative thought disorder, depersonalization and catatonic states. These symptoms can persist for prolonged periods and chronic PCP and ketamine addicts have persisting memory deficits. Dizocilpine (MK-801) is a simpler drug than PCP or ketamine in its actions, but it shares with both the property of blocking in a non-competitive manner the N-methyl-D-aspartate (NMDA) ion-channel. Behavioral observations and drug-discrimination studies in animals indicate that PCP and dizocilpine are similar in their effects and they both have a neurotoxic effect on neurons in posterior cingulate cortex. Recent studies have indicated that both of these drugs, when given continuously for several days, further induce neuronal degeneration in other limbic structures. These include brain regions of rats related to olfaction, associated limbic structures such as piriform cortex and posterior regions of entorhinal cortex and in it's projections, through the perforant pathway, to dentate gyrus and other cells in ventral hippocampus. These degenerative consequences may be excitatory neurotoxic effects, for these compounds also induce an elevation in glucose metabolism maximal in just those structures where degeneration is observed and the degeneration involves entire cells, with all of their processes. It has been suggested these non-competitive NMDA antagonists induce an increase in firing rate in a limbic circuit which includes the perforant pathway. At least some competitive NMDA antagonists induce the same pattern of degeneration and altered glucose utilization. There is anatomical and functional evidence that alterations in these same limbic structures are present in the dementia syndrome manifested by some schizophrenics and most Alzheimer's patients. This suggests that these non-competitive NMDA antagonists may provide a more complete model of psychoses and memory disturbances than previously recognized, in that they can mimic both persisting symptomatology and neuroanatomical abnormalities. While the neurochemical underpinnings of this effect remain elusive, it appears to be both age and sex dependent. Further studies of the mechanisms by which NMDA antagonists induce increased glucose utilization and neurotoxicity in these limbic structures may clarify these alterations in this simplified Papez-like circuit.

Animals↗