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PubMed2002

Training and assessment of laparoscopic skills using a haptic simulator.

Surgical simulation is a promising technique for training of laparoscopic surgery. Computer based simulation provides not only a cost effective alternative to traditional training but also a way to assess the surgeons performance. In this paper, we present a haptic simulator that allows for training and assessment of basic laparoscopic skills. The skills trained are modeled around a cholecystectomy procedure and include bi-manual dissection, clips setting, catheter insertion and cutting. The system uses accurate anatomic models of the organs involved in the procedure. This combined with effective methods for soft tissue deformation and haptic feedback, giving the surgeon a precise feeling of the interaction between organs and surgical instruments, provides a realistic training environment. The system has been designed with procedural training in mind and by putting together the individual tasks it will be possible to train on performing a complete cholecystectomy procedure.

Anatomy, Cross-Sectional↗
PubMed2001

Dosimetry modeling of inhaled formaldehyde: the human respiratory tract.

Formaldehyde (HCHO), which has been shown to be a nasal carcinogen in rats and mice, is used widely and extensively in various manufacturing processes. Studies in rhesus monkeys suggest that the lower respiratory tract may be at risk and some epidemiologic studies have reported an increase in lung cancer associated with HCHO; other studies have not. Thus, an assessment of possible human risk to HCHO exposure based on dosimetry information throughout the respiratory tract (RT) is desirable. To obtain dosimetry estimates for a risk assessment, two types of models were used. The first model (which is the subject of another investigation) used computational fluid dynamics (CFD) to estimate local fluxes in a 3-dimensional model of the nasal region. The subject of the present investigation (the second model) applied a 1-dimensional equation of mass transport to each generation of an adult human symmetric, bifurcating Weibel-type RT anatomical model, augmented by an upper respiratory tract. The two types of modeling approaches were made consistent by requiring that the 1-dimensional version of the nasal passages have the same inspiratory air-flow rate and uptake during inspiration as the CFD simulations for 4 daily human activity levels. Results obtained include the following: (1) More than 95% of the inhaled HCHO is predicted to be retained by the RT. (2) The CFD predictions for inspiration, modified to account for the difference in inspiration and complete breath times, are a good approximation to uptake in the nasal airways during a single breath. (3) In the lower respiratory tract, flux is predicted to increase for several generations and then decrease rapidly. (4) Compared to first pulmonary region generation fluxes, the first few tracheobronchial generations fluxes are over 1000 times larger. Further, there is essentially no flux in the alveolar sacs. (5) Predicted fluxes based on the 1-dimensional model are presented that can be used in a biologically based dose-response model for human carcinogenesis. Use of these fluxes will reduce uncertainty in a risk assessment for formaldehyde carcinogenicity.

Animals↗
PubMed2006

Integrating VBM into the General Linear Model with voxelwise anatomical covariates.

A current limitation for imaging of brain function is the potential confound of anatomical differences or registration error, which may manifest via apparent functional "activation" for between-subject analyses. With respect to functional activations, underlying tissue mismatches can be regarded as a nuisance variable. We propose adding the probability of gray matter at a given voxel as a covariate (nuisance variable) in the analysis of voxelwise multisubject functional data using standard statistical techniques. A method is presented to assess the extent to which a functional activation can reliably be explained by underlying anatomical differences, and simultaneously, to assess the component of the functional activation which cannot be attributed to anatomical difference and thus is likely due to functional difference alone. Extension of the method to other intermodal imaging applications is discussed. Two exemplary data sets, one PET and one fMRI, are used to demonstrate the implementation and utility of this method, which apportions the relative contributions of anatomy and function for an apparent functional activation. The examples show two distinct types of results. First, a so-called functional activation may actually be caused by a systematic anatomical difference which, when modeled, diminishes the functional effect. In the second result type, including the anatomical differences in the model can account for a large component of otherwise unmodeled variance, yielding an increase in the functional effect cluster size and/or magnitude. In either case, ignoring the readily available structural information can lead to misinterpretation of functional results.

Brain↗
PubMedDate not supplied

Development of a human body model for numerical calculation of electrical fields.

Knowledge of the distribution of electrical fields in the human body is of importance for scientists, engineers and physicians. This paper shows one way to achieve this knowledge by numerical calculation based on macroscopic models of the human body. An anatomical model is created by preprocessing, segmentation and classification of the digital images within the Visible Man data set. Conductivity models are derived, which describe the distribution of electrical conductivity in the human body. A conductivity model is applied to solve an exemplary forward problem in electrophysiology, which consist of the calculation of the electrical field distribution arising from cardiac sources. The cardiac sources are obtained by a model of the excitation process within the heart. The calculation of electrical fields is carried out numerically by employing the finite difference method.

Anatomy, Cross-Sectional↗
PubMed1995

The prevention of mechanical birth trauma by means of computer aided simulation of delivery by means of nuclear magnetic resonance imaging and finite element analysis.

Anatomic disproportion gains an increasing interest in obstetrics. Imaging procedures (radiologic pelvimetry, computed or magnetic resonance imaging (MRI) fail to reflect the dynamics of delivery including deformations of the birth channel as well as of fetal structures. To validate findings of imaging procedures in this respect a method has been developed to perform a dynamic, biomechanical postprocessing of the static informations obtained from MRI. Using an especially developed software MRI pixel matrices of maternal pelvis and fetal head were color-codef1p4d--according to the principle of same density--line data were created. After sectional attribution of the resulting polygones a three-dimensional mesh of so called Finite elements (FE) was created, which then can be used for deformation analysis. Fetal head was then moved through the birth channel by means of computed simulation. This allows not only ongoing deformations to be visualized but also resulting forces to be calculated for at any time of the delivery process for any point of the anatomical model. Performing these simulations assuming various anatomic and physiologic conditions an obstetrical-biomechanical data basis could be obtained, that was implemented in a PC-based expert system. This allows interpretation of pelvimetric data with regard to birth dynamics.

Biomechanical Phenomena↗
PubMed1994

Putting the anatomical doll controversy in perspective: an examination of the major uses and criticisms of the dolls in child sexual abuse evaluations.

Through an extensive review of guidelines and protocols on the use of anatomical dolls in sexual abuse evaluations, seven functional uses of the dolls were identified: Comforter, Icebreaker, Anatomical Model, Demonstration Aid, Memory Stimulus, Diagnostic Screen, and Diagnostic Test. These functional uses are discussed in light of several criticisms that have been raised about the use of anatomical dolls in sexual abuse evaluations. The relevancy of these criticisms is shown to vary greatly by doll use. As a result, the authors argue that any critique of anatomical dolls must consider the specific function the dolls serve in the evaluation. Although there seem to be widespread perceptions in both lay and professional circles that young children's behavior with the dolls is commonly used to make definitive diagnoses of sexual abuse (Diagnostic Test Use), such a use of the dolls was not endorsed by any of the guidelines reviewed and is open to significant criticism. The most common criticisms of the dolls, that they are overly suggestive to young, sexually naive children, is not supported by available research. Finally, the continued, informed use of anatomical dolls in sexual abuse evaluations of young children is strongly supported.

Child↗
PubMed2006

A topologically faithful, tissue-guided, spatially varying meshing strategy for the computation of patient-specific head models for endoscopic pituitary surgery simulation.

This paper presents a method for tessellating tissue boundaries and their interiors, given as input a tissue map consisting of relevant classes of the head, in order to produce anatomical models for finite element-based simulation of endoscopic pituitary surgery. Our surface meshing method is based on the simplex model, which is initialized by duality from the topologically accurate results of the Marching Cubes algorithm, and which features explicit control over mesh scale, while using tissue information to adhere to relevant boundaries. Our mesh scale strategy is spatially varying, based on the distance to a central point or linearized surgical path. The tetrahedralization stage also features a spatially varying mesh scale, consistent with that of the surface mesh.

Algorithms↗
PubMed2004

Review and standardization of cell phone exposure calculations using the SAM phantom and anatomically correct head models.

We reviewed articles using computational RF dosimetry to compare the Specific Anthropomorphic Mannequin (SAM) to anatomically correct models of the human head. Published conclusions based on such comparisons have varied widely. We looked for reasons that might cause apparently similar comparisons to produce dissimilar results. We also looked at the information needed to adequately compare the results of computational RF dosimetry studies. We concluded studies were not comparable because of differences in definitions, models, and methodology. Therefore we propose a protocol, developed by an IEEE standards group, as an initial step in alleviating this problem. The protocol calls for a benchmark validation study comparing the SAM phantom to two anatomically correct models of the human head. It also establishes common definitions and reporting requirements that will increase the comparability of all computational RF dosimetry studies of the human head.

Artifacts↗
PubMed2004

The WEBD project: a research of new methodologies for a distant-learning 3D system prototype.

OBJECTIVES: To create and to spread a new interactive multimedia instrument, based upon virtual reality technologies, that allows both the running simulation of machines and equipment and the reproduction via Web of complex three-dimensional (3D) anatomical models such as the skull. METHODS: There were two main aspects of the project, one of design engineering and the other biomedical engineering, for the creation of "artificial" and anatomical objects. The former were made with 3D Studio Max R4 by Autodesk, San Rafael, CA, while the latter were created starting from real bones scanned with a CT system or a surface scanner and elaborated with different programs (3D Studio Max R4, Scenebuilder by Viewpoint, New York, NY and Spinfire by Actify, San Francisco, CA). The 3D models were to be integrated into web modules and had to respect file limits while preserving a sufficient definition. Two systems of evaluation were used, a questionnaire on a selected sample and an external evaluation by a different university. RESULTS: The Viewpoint format offers the best interactivity and size reduction (up to 96% from the original 3D model). The created modules included production of radiological images, rapid prototyping, and anatomy. The complete "3D Distant Learning Prototype" is available at www.webd.etsii.upm.es. CONCLUSIONS: The software currently available permits the construction of interactive modules. The verification on the selected sample and the evaluation by the University of Naples show that the structure is well organized and that the integration of the 3D models meets the requirements.

Computer Graphics↗
PubMed2004

Thoracic pedicle screw insertion using a transpedicular drill guide: a preliminary study.

Insertion of thoracic pedicle screws can lead to major complications. This study reports the use of a transpedicular drill guide (TDG) for safe pedicle screw insertion in the thoracic spine. The conventional anatomic technique and the TDG were both used to drill pilot holes into the pedicles of four anatomic models of the thoracic spine. Ninety-nine percent of the 96 pilot holes drilled with the TDG were within 2 mm from the pedicle wall compared with 79% for the anatomic technique (P < 0.001). The TDG reduced the proportion and the extent of medial perforations. The TDG was easy to use and was superior to the conventional anatomic technique. It could be combined with fluoroscopy and pedicle palpation in certain clinical applications, especially for training surgeons, but only after confirming its accuracy in a cadaveric study.

Bone Screws↗
PubMed2003

3D reconstruction of organ surfaces using model-based snakes.

In this article a new segmentation approach is described that is based on case-based reasoning and a combination of various established image processing concepts described in the current literature. Previously segmented data sets are used as anatomical models that represent the cases, called reference models. They describe the expected surface shape and representation of the organ in the data material. The segmentation task is solved by finding a reference model that is similar to the current data set and then by adapting the reference segmentation to the current data set. Image segmentation can be divided into the steps "determination of the image context", "selection and adjustment of the reference model", and "application of the model-based snake". The necessary interaction time was reduced by more than 60%, including postprocessing to correct for possible segmentation errors.

Computer Simulation↗
PubMed1991

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

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

Afferent Pathways↗
PubMed1997

Virtual reality publication of spiral ct-derived three-dimensional models: or, creation of spiral, CT-derived, three-dimensional VRML objects.

Three-dimensional models can be generated from slice images, such as those obtained from computed tomography (CT) and magnetic resonance imaging (MRI) using a variety of techniques. A popular method for rendering 3D anatomical models is the creation of polygonal mesh surfaces representing the boundary between tissues. Mesh surfaces can be rendered extremely quickly using conventional personal computers, without recourse to more expensive graphic workstations. The dissemination of three-dimensional (3D) models across the Internet has been made significantly easier by the definition of the Virtual Reality Markup Language (VRML) format. The VRML definition allows the parameters and relationships of 3D objects to be described in a text format. The text file can be transfered from a host computer to a remote client computer through the World Wide Web and viewed using readily available software (See Appendix). VRML is based on the definition of primitive 3D objects such as polygons and spheres. Consequently, the transition from a mesh surface derived from a clinical image data set to a VRML object is relatively simple, allowing for convenient and cost-effective dissemination of 3D clinical models across the internet.

Bronchi↗
PubMed2006

Bounds for damping that guarantee stability in mass-spring systems.

Mass-spring systems are often used to model anatomical structures in medical simulation. They can produce plausible deformations in soft tissue, and are computationally efficient. Determining damping values for a stable mass-spring system can be difficult. Previously stable models can become unstable with topology changes, such as during cutting. In this paper, we derive bounds for the damping coefficient in a mass-spring system. Our formulation can be used to evaluate the stability for user specified damping values, or to compute values that are unconditionally stable.

Algorithms↗
PubMed1987

A flow-limited simulation model of isotopic water dilution.

A model of the kinetics of water metabolism is not synonymous with an anatomic model of body water pools. Quantitating the anatomic relations of pools of body water that are separable on a kinetic basis is very difficult, and these relations are influenced by the physiological state of the animal. A fifteen-pool, flow-limited simulation model of body water distribution and mixing was constructed based on literature values to study the relationship between anatomical and kinetic pools of body water. The blood dilution curve predicted by the model agrees well with dilution curves in the literature. Altering rumen water volume in the model does not alter the blood dilution curve. Segmenting anatomical pools of water on the basis of blood deuterium oxide (D2O) dilution curves is not a realistic goal. Total body water, independent of the physiological state of the animal, can be measured by D2O dilution after isotopic equilibration has been established if corrections are made for the amount of D2O that is lost prior to attaining equilibrium. The model can be used to search for dosing and sampling schemes that have the potential for fractionating anatomical pools of body water. Although the model is not predictive of any particular situation, it does provide a good base for researching kinetics of body water distribution and body composition.

Animals↗
PubMed2006

A discrete soft tissue model for complex anatomical environment simulations.

Among the current challenges in human soft tissue modeling for medical purposes, the ability to model complex anatomical structures, their interactions and to accurately simulate them with physical realism are in the forefront of research. This paper describes a discrete soft tissue model which is geared toward solving these challenges. In this model, objects can be described as volumetric or surfacic sets of nodes depending on the level of precision required. Nodes have their own physical properties and a definition of their neighborhood. All these objects are submitted both to internal cohesive forces and to external attractive or interaction forces with other objects. Volume preservation is insured by a constraint. The model is applied to the simulation of the prostate and its surrounding organs.

Computer Simulation↗
PubMed1992

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

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

Animals↗
PubMed1995

[Zonal anatomy of the prostate using endorectal MRI].

The development of an endorectal surface coil now permits a partial study of the anatomical model developed by McNeal. Axial and coronal views, which were used to establish the model can be obtained in a short period of time with fast spin echo sequences. Axial views are performed along the proximal urethra and coronal views are performed along the axis of the distal urethra and the ejaculatory ducts. Anatomical boundaries of the transitional zone are well delineated on axial views, illustrating the concept of "inner gland". The prostatic capsule and the neuro-vascular bundles, pathways of extension of the cancer out of the prostate are also well delineated. Coronal sections allow a very good anatomical study of the caudal junction of the vas deferens and the seminal vesicles (the so called weak space), pathway of tumor extension to the seminal vesicles. Differences in signal of the prostatic zones make the outer gland cancers very conspicuous as well as some transitional cancers which can show, in some cases, an homogeneous hyposignal.

Humans↗