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PubMedDate not supplied

Construction of the geometrical-conductivity human chest model in simulation of the cardiac electrical field.

In this article the problem of the construction of the geometrical-conductivity model of a human chest in a computer simulation of the cardiac electrical field, applying image diagnostic data (CT, conventional radiography and 2D projections of a torso) is presented. On the basis of these data parameters are defined which allow the determination of locations and sizes of significant chest organs. Calculations and comparison of the values of these parameters for CT and radiographic data of the example patient, using image processing methods, have been carried out. A numerical experiment has been performed to determine the epicardial maps, applying two geometrical-conductivity models of the individual patient based on CT (accurate) and radiographic (approximate) image data, respectively. The credibility of the results obtained is discussed.

Action Potentials↗
PubMedDate not supplied

Determination of material constants and hydraulic strengthening of trabecular bone through an orthotropic structural model.

A statistical mathematical model is used to describe the viscoelastic behavior of trabecular bone from the description of its microstructure. Trabecular bone is regarded as an orthotropic composite material consisting of two phases: The trabeculae, modelled as a non-linear elastic material, and the marrow, modelled as a Maxwell element. The macroscopic constitutive equation contains, as parameters, the constants of the material phases' constitutive equations, the respective volume fractions and parameters descriptive of the geometry of trabecular bone. With this model, the contribution of the marrow to the mechanical behavior of trabecular bone is determined and it is calculated that, under a step load and at strain rate, 10 min-1, the marrow can bear about 25% of the applied load. The constants of the material phases are also calculated from a series of stress-relaxation curves on trabecular bone specimens. It is concluded that the trabeculae display non-linear elastic behavior.

Aged↗
PubMed1998

Hemodynamic effects of the geometric dimensions of graft vessels in coronary artery bypass graft models.

The objectives of this investigation are to evaluate the rheologic properties in atherosclerotic disease treated with the various coronary artery bypass graft (CABG) models by numerical analysis, we used four different CABG models for the assessment of spatial fluctuation in wall shear stress, pressure variation and mass flow rate with Carreau model and Navier-Stokes equation. Wall shear stress was higher in a naturally tapered model (model 1) and a constant (non-tapered) diameter of the graft vessel the same as the distal LAD (model 4) than in others. Pressure variation along the native coronary artery and graft vessels was higher in a model 4, model 1 than in a reverse tapering model (model 2) and a constant diameter of the graft vessel the same as the proximal LAD (model 3). The mass flow rate of the distal part (kg/sec,.m(o)) was the highest in model 3. This study suggests that in vitro spatial simulation following CABG revealed that small caliber or tapered graft vessels have adverse hemodynamic effects on the native and graft vessels. By this technique it is possible to simulate the optimal distribution of local hemodynamic variables in patients treated with CABG, also to minimize the degeneration of graft vessel.

Computer Simulation↗
PubMed2006

An unusual cause of hematemesis: Goiter.

Downhill varices are located in the upper part of the esophagus and are usually related to superior vena cava obstruction. Bleeding from these varices is extremely rare. We describe a 77-year-old patient with hematemesis due to downhill varices as a result of recurrent goiter. A right lobe thyroidectomy was carried out with disappearance of the varices.

Aged↗
PubMed2004

[Training simulators in digestive endoscopy].

Advanced techniques, optimal patient care, and quality management are currently important topics in clinical medicine. The increasing numbers of minimally invasive procedures being carried out in gastroenterology and surgery, and the effects of the learning curve on complication rates with various procedures, have given rise a recently debate on training standards. Public awareness and increasing legal pressure to show and document competence have further contributed to the importance of training in interventional medicine. Although evidence-based medicine is rapidly becoming the gold standard for treatment modalities, responsibility for education-including the theoretical background, as well as acquiring and refining manual skills in gastrointestinal endoscopy--is still a matter for the individual physician. Practical skills are routinely acquired by practicing on patients, initially under the supervision of a senior endoscopist. The development of new endoscopy simulators has brought out the debate whether training in basic manual skills is better obtained outside the patient. This paper presents an overview of the training simulators currently available and issues associated with them.

Animals↗
PubMed1996

Advanced telepresence surgery system development.

SRI International is currently developing a prototype remote telepresence surgery system, for the Advanced Research Projects Agency (ARPA), that will bring life-saving surgical care to wounded soldiers in the zone of combat. Remote surgery also has potentially important applications in civilian medicine. In addition, telepresence will find wide medical use in local surgery, in endoscopic, laparoscopic, and microsurgery applications. Key elements of the telepresence technology now being developed for ARPA, including the telepresence surgeon's workstation (TSW) and associated servo control systems, will have direct application to these areas of minimally invasive surgery. The TSW technology will also find use in surgical training, where it will provide an immersive visual and haptic interface for interaction with computer-based anatomical models. In this paper, we discuss our ongoing development of the MEDFAST telesurgery system, focusing on the TSW man-machine interface and its associated servo control electronics.

Computer Systems↗
PubMed1994

Virtual reality in surgery and medicine.

This report documents the state of development of enhanced and virtual reality-based systems in medicine. Virtual reality systems seek to simulate a surgical procedure in a computer-generated world in order to improve training. Enhanced reality systems seek to augment or enhance reality by providing improved imaging alternatives for specific patient data. Virtual reality represents a paradigm shift in the way we teach and evaluate the skills of medical personnel. Driving the development of virtual reality-based simulators is laparoscopic abdominal surgery, where there is a perceived need for better training techniques; within a year, systems will be fielded for second-year residency students. Further refinements over perhaps the next five years should allow surgeons to evaluate and practice new techniques in a simulator before using them on patients. Technical developments are rapidly improving the realism of these machines to an amazing degree, as well as bringing the price down to affordable levels. In the next five years, many new anatomical models, procedures, and skills are likely to become available on simulators. Enhanced reality systems are generally being developed to improve visualization of specific patient data. Three-dimensional (3-D) stereovision systems for endoscopic applications, head-mounted displays, and stereotactic image navigation systems are being fielded now, with neurosurgery and laparoscopic surgery being major driving influences. Over perhaps the next five years, enhanced and virtual reality systems are likely to merge. This will permit patient-specific images to be used on virtual reality simulators or computer-generated landscapes to be input into surgical visualization instruments. Percolating all around these activities are developments in robotics and telesurgery. An advanced information infrastructure eventually will permit remote physicians to share video, audio, medical records, and imaging data with local physicians in real time. Surgical robots are likely to be deployed for specific tasks in the operating room (OR) and to support telesurgery applications. Technical developments in robotics and motion control are key components of many virtual reality systems. Since almost all of the virtual reality and enhanced reality systems will be digitally based, they are also capable of being put "on-line" for tele-training, consulting, and even surgery. Advancements in virtual and enhanced reality systems will be driven in part by consumer applications of this technology. Many of the companies that will supply systems for medical applications are also working on commercial products. A big consumer hit can benefit the entire industry by increasing volumes and bringing down costs.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer Simulation↗
PubMed1998

Simulator for virtual surgery using deformable organ models and force feedback system.

This paper describes a real-time surgery planning system using virtual reality techniques. This system allows us to simulate incision of skin and organs which respond as elastic objects with surgical tools in virtual space. Inner structures such as blood vessels and lesions can be seen and manipulated in the simulation. In addition to these functions we attempted to add a feedback function that responds to the operator's hands. We developed a force feedback device to manipulate the elastic organ model based on pressure from the operator's fingers.

Abdomen↗
PubMed1999

Extradural temporal lobe retraction in the middle fossa approach to the internal auditory canal: biomechanical analysis.

HYPOTHESIS: The middle fossa (MF) approach is undergoing a marked resurgence in vestibular schwannoma surgery as a hearing conservation technique. It is widely recognized that the extradural temporal lobe retractors used in this procedure, despite their cleverness of design, could be improved. METHODS: To identify the characteristics of an ideal MF retractor, a systematic analysis of the safety and functionality of four commonly used retractors (House-Urban, Fisch, Garcia-Ibanez, and UCSF) in a human anatomical model was conducted. Intensity of temporal lobe compression, width of exposure, angle of visualization, obstruction to instrument access, ergonomic convenience of use, and adaptability to other subtemporal procedures (e.g. lesions of Meckel's cave and cavernous sinus) were quantified. RESULTS: Because the intracranial portions of the retractors are similar, the force transmitted to the brain differed little among the four retractors. Numerous differences were noted in the ergonomics of use and versatility of the various designs. CONCLUSIONS: The optimal MF retractor would incorporate the best features of each of the existing systems: the integral suction of the Garcia-Ibanez, the bone contour-following design of the Fisch retractor base, the unobtrusiveness and adaptability of the UCSF, and the three-plane adjustability of the vintage House-Urban. Evolution of an "ideal" MF retractor requires further technical refinements and the development of an experimental model of extradural brain retraction to assess the optimal strategy for obtaining exposure while minimizing the risk for temporal lobe injury.

Craniotomy↗
PubMed1999

Real-time rotation vectors.

Rotation vectors are a useful way of describing eye position without reference to arbitrary axes of rotation since any eye position can be reached from the reference position by rotation about a single axis. A real-time display of rotation vectors would not only help to acquire more reliable data, but would also widen the range of possible eye movement experiments. We describe a novel PC based data acquisition and analysis system which calculates and displays rotation vectors, velocity vectors and Listing's plane in real-time using voltages obtained from a two field coil system. The system was implemented using LabVIEW and optimised using Code Interface Nodes. Off-line processing can be sped up by varying parameters that indicate the amount of available RAM. During processing Listing's plane data can be rotated horizontally, vertically and torsionally. A computer controlled laser target changes position randomly every half second and so the targets are evenly spread, producing an appropriate range of eye positions which are used to calculate Listing's plane.

Algorithms↗
PubMed1999

DOSE3D: EGS4 Monte Carlo code-based software for internal radionuclide dosimetry.

UNLABELLED: MIRDOSE3 software is currently the main tool available in clinical practice to evaluate absorbed dose in nuclear medicine. Because MIRDOSE3 provides dosimetric parameters for specific anatomic models that cannot be modified by the user, it cannot be used to obtain information concerning metastases or to consider patients whose anatomy differs significantly from that of the standard models. METHODS: To address some of these inconveniences, we developed an original program based on the EGS4 Monte Carlo code, DOSE3D, which calculates dosimetric parameters for anthropomorphic phantoms defined with combinatorial geometry. DOSE3D allows the user to add spheres within the phantom for simulating tumors, to change the shape of one or more organs and, for organs defined by pair, to calculate individual dosimetric parameters for each organ. The program was validated for 131I and 99mTc by calculating S values for the Medical Internal Radiation Dose (MIRD) adult male phantom and comparing these results with data provided by MIRDOSE3. Moreover, two studies were performed to illustrate DOSE3D features. The first one concerned the evaluation of the individual influence of two bone metastases (located in the pelvis and in the lower spine and containing 131I) on testes in terms of S values compared with the influence on testes of other source organs (kidneys, liver, lungs, spleen, thyroid gland and urinary bladder contents). The second study determined the differences of S values between right and left lungs and right and left kidneys when 131I is contained in the liver. RESULTS: The DOSE3D S values were on average within 20% of the MIRDOSE3 results for both radionuclides. Regarding the bone metastases study, S(testes<--metastases) and S(testes<--any source organs) were of the same order of magnitude. In the second study, the S values ratio between right and left organs was 7.7 for the lungs and 5.2 for the kidneys. CONCLUSION: The agreement between DOSE3D and MIRDOSE3 results for most organs shows the validity of DOSE3D. The presented examples of calculation show that DOSE3D could provide additional data to dosimetric parameters given by MIRDOSE3 for a more patient-specific dosimetric approach.

Adult↗