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At least 1,153 records · Page 64Linked to original sources
PubMed1999

Peroperative determination of safe superior transarticular screw trajectory through the lateral mass.

STUDY DESIGN: Computerized anatomic reconstruction of the dry axis vertebra was performed to determine radiologic guidelines for safe superior transarticular screw trajectory. OBJECTIVES: To reconstruct the transarticular screw trajectory, using computer-aided design techniques, and develop a technique that provides real-time intraoperative guidance during screw placement. SUMMARY OF BACKGROUND DATA: A recent osteometric study of 50 dry specimens of the axis noted significant vertebral artery groove anomalies in 22% of specimens. There are presently no anatomic or radiologic guidelines to help surgeons avoid an enlarged vertebral groove, despite the fact that a safe screw trajectory through the lateral mass is primarily dependent on the its depth and the internal height of the lateral mass. METHODS: Using computer-aided design techniques, we re-analyzed the vertebral grooves of 50 dry specimens and mapped minimum and corrected safe superior trajectories for any given depth of this groove. This knowledge was extrapolated to spiral computed tomographic scan data, which was used to develop the clinical method for safe superior trajectory. Real-time fluoroscopy was used to apply the method intraoperatively. RESULTS: Internal height less than 2.1 mm or values less than 0.85 for the ratio of the mean internal height over the mean vertebral groove depth would result in unacceptable risk to vertebral artery injury and improper screw purchase. With every 0.5-mm increase in groove depth, the angle of trajectory increases by 1 degree at a pedicle length of 30 mm. There is an inverse linear relation between the superior angle of trajectory and the pedicle length (2 degrees = 5 +/- 0.5 mm). Screw diameter-dependent trajectory correction is required (3.5 mm = 7 degrees). CONCLUSIONS: Before atlantoaxial transarticular surgery, vertebral groove depth should be evaluated and a safe screw trajectory angle should be plotted to determine anatomic suitability. This trajectory angle can be used with intraoperative real-time fluoroscopy to guide the surgeon during screw insertion.

Atlanto-Axial Joint↗
PubMed2005

Neural network screening of electromyographic signals as the first phase to design novel human-computer interaction.

The present aim was to describe the first phase attempts to recognise voluntarily produced changes in electromyographic signals measured from two facial muscles. Thirty subjects voluntarily activated two facial muscles, corrugator supercilii and zygomaticus major. We designed a neural network based recognition system that screened out muscle activations from the electromyographic signals. When several subjects were tested according to the same test protocol, the neural network system was able to correctly recognise more than 95 % of all muscle activations. This is a promising result and we shall next proceed to modify the system for real-time functioning and then design its utilisation for various multimodal human-computer interaction techniques. The subsequent phase in the future will be the interaction backwards: when a computer program first recognised the use of the facial muscles, it will then follow the instructions given by the user. For instance, by using the facial muscles the subject could select or activate objects on the computer screen. This would be one of the opportunities that we develop to help, e.g., disabled persons, who are unable to use their hands.

Electromyography↗
PubMed1995

Design methodology for a multifunctional hand prosthesis.

The first part of this paper reviews different approaches to define the motion of the fingers and the thumb in order to obtain prehension. The last part presents the design of a hand prosthesis based on a new plane of action for the thumb and on proposed design specifications and functional characteristics. The design methodology consists of two steps: the morphology design of the hand prosthesis and the 4-bar mechanism design for each finger. A 3-D computer-aided design (CAD) interactive program was used as a design tool to obtain the hand morphology. This CAD technique was also used to check the geometry, the relative motions of the fingers, and the possibility of interference for the proposed model with two prehension patterns (tridigital and lateral). It is noted that identical flexion angles of the finger joints were obtained for these two prehension patterns, the difference being in the inclination angle of the thumb's plane of flexion. This finding greatly simplified the design of the internal mechanisms of the fingers. CAD was a powerful tool in the design process of this hand prosthesis and will be more and more useful in the future.

Artificial Limbs↗
PubMed1992

Computer-specific spectacle lens design preference of presbyopic operators.

Twenty-nine presbyopic subjects who spent at least 20 hours a week at a video display terminal compared a progressive addition lens designed for this function, with another commonly prescribed task-specific lens. Each of the paired lens types was worn for 4 weeks and then compared directly for 1 week. A statistically significant (P < .05) portion of the subjects (76%) preferred the task-specific lenses overall. It also was preferred more frequently for each feature compared, although the difference was statistically significant (P < .05) only for utility of distance vision. Both of the task-specific designs contributed to symptomatic relief. The presence of a distance-clear zone and the absence of lens discontinuities most likely account for user preference for the task-specific lenses. That preference suggests improved performance for presbyopic computer users wearing task-specific progressive addition lenses.

Adult↗
PubMed2003

Design of a miniature implantable left ventricular assist device using CAD/CAM technology.

In this study, we developed a new miniature motor-driven pulsatile left ventricular assist device (LVAD) for implantation into a Japanese patient of average build by means of computer-aided design and manufacturing (CAD/CAM) technology. A specially designed miniature ball-screw and a high-performance brushless DC motor were used in an artificial heart actuator to allow miniaturization. A blood pump chamber (stroke volume 55 ml) and an inflow and outflow port were designed by computational fluid dynamics (CFD) analysis. The geometry of the blood pump was evaluated using the value of index of pump geometry (IPG) = (Reynolds shear stress) x (occupied volume) as a quantitative index for optimization. The calculated value of IPG varied from 20.6 Nm to 49.1 Nm, depending on small variations in pump geometry. We determined the optimum pump geometry based on the results of quantitative evaluation using IPG and qualitative evaluation using the flow velocity distribution with blood flow tracking. The geometry of the blood pump that gave lower shear stress had more optimum spiral flow around the diaphragm-housing (D-H) junction. The volume and weight of the new LVAD, made of epoxy resin, is 309 ml and 378 g, but further miniaturization will be possible by improving the geometry of both the blood pump and the back casing. Our results show that our new design method for an implantable LVAD using CAD/CAM promises to improve blood compatibility with greater miniaturization.

Computer-Aided Design↗
PubMed2004

Computer-aided tissue engineering: application to biomimetic modelling and design of tissue scaffolds.

Computer-aided tissue engineering (CATE) enables many novel approaches in modelling, design and fabrication of complex tissue substitutes with enhanced functionality and improved cell-matrix interactions. Central to CATE is its bio-tissue informatics model that represents tissue biological, biomechanical and biochemical information that serves as a central repository to interface design, simulation and tissue fabrication. The present paper discusses the application of a CATE approach to the biomimetic design of bone tissue scaffold. A general CATE-based process for biomimetic modelling, anatomic reconstruction, computer-assisted-design of tissue scaffold, quantitative-computed-tomography characterization, finite element analysis and freeform extruding deposition for fabrication of scaffold is presented.

Biocompatible Materials↗
PubMed1997

Accuracy of computer-assisted pedicle screw placement. An in vivo computed tomography analysis.

STUDY DESIGN: A computer-assisted planning and visualization system (the Orthopaedic Surgery Planning System) was tested for pedicle screw insertion in vivo. OBJECTIVES: To evaluate the system's applicability for regular intraoperative use and its accuracy for pedicle screw placement in vivo. SUMMARY OF BACKGROUND DATA: Pedicle screw placement poses considerable anatomic and biomechanical risks. The reported rates of screw misplacement with conventional insertion techniques are unacceptably high. It previously has been shown in vitro that computer assistance offers the potential to decrease the number of screws perforating the pedicular cortex. METHODS: The accuracy of 162 pedicle screws inserted with the Orthopaedic Surgery Planning System was assessed by means of postoperative computed tomography evaluation. Reconstructions of the horizontal, frontal, and sagittal planes were analyzed. Cortex perforations were graded in steps of 2 mm. RESULTS: The cortex was perforated in 2.7% of pedicles. Complete preoperative computed tomography scanning of the levels to be operated on is essential to allow for a precise image reconstruction. Initial difficulties in applying the system contribute to the malplacements. A learning curve for general handling of the Orthopaedic Surgery Planning System was observed. CONCLUSIONS: The system provides a safe and reproducible technique for pedicle screw insertion. Other applications in the field of spine surgery are under evaluation.

Bone Screws↗
PubMedDate not supplied

Initial experience with the development and numerical and in vitro studies of a novel low-pressure artificial right ventricle for pediatric Fontan patients.

The Fontan operation, an efficient palliative surgery, is performed for patients with single-ventricle pathologies. The total cavopulmonary connection is a preferred Fontan procedure in which the superior and inferior vena cava are connected to the left and right pulmonary artery. The overall goal of this work is to develop an artificial right ventricle that can be introduced into the inferior vena cava, which would act to reverse the deleterious hemodynamics in post-Fontan patients. We present the initial design and computational analysis of a micro-axial pump, designed with the particular hemodynamics of Fontan physiology in mind. Preliminary in vitro data on a prototype pump are also presented. Computational studies showed that the new design can deliver a variety of advantageous operating conditions, including decreased venous pressure through proximal suction, increased pressure rise across the pump, increased pulmonary flows, and minimal changes in superior vena cava pressures. In vitro studies on a scaled prototype showed trends similar to those seen computationally. We conclude that a micro-axial flow pump can be designed to operate efficiently within the low-pressure, low-flow environment of cavopulmonary flows. The results provide encouragement to pursue this design to for in vitro studies and animal studies.

Animals↗
PubMed1997

How fibers subserve computing capabilities: similarities between brains and machines.

Can the principles underlying the design of computers help to explain the cognitive capabilities of the human brain? This chapter shows that these principles can provide insight into the capabilities of the human cerebellum, the internal structure of which bears a remarkable resemblance to the design of a versatile computer. In computers, information processing is accomplished both by the hardware in the system (its circuitry) and by the software (the communication capabilities inherent in its circuitry), which is combination can produce a versatile information-processing system, capable of performing a wide variety of functions, including motor, sensory, cognitive, and linguistic ones. Such versatility of function is achieved by computer hardware in which many modules of similar circuits are organized into parallel processing networks; this structural organization is exemplified in the cerebellum by its longitudinal modules of similar circuits, which are arrayed in parallel zones throughout the structure. On the basis of this known cerebellar "hardware," it is possible to investigate the "software" capabilities inherent in the circuitry of the modules. Each module in the lateral cerebellum seems able to communicate with the cerebral cortex by sending out signals over a segregated bundle of nerve fibers, which is a powerful way of communicating information. We show why this bundling of fibers can enable the cerebellum to communicate with the cerebral cortex (including the prefrontal cortex) at a high level of discourse by using internal languages that are capable of conveying complex information about what to do and when to do it. We propose that such communication activity is reflected in the activation obtained on functional imaging of the cerebro-cerebellar system during the performance by humans of complex motor, sensory, cognitive, linguistic, and affective tasks. Further, we propose a new way of analyzing such cerebro-cerebellar activation, in order to ascertain whether the cerebellar circuitry can (like the circuitry in a versatile computer) perform a wide repertoire of computations on this wide range of information. It seems important to ascertain whether cerebellar circuitry is versatile in its computing capabilities because the demonstration of such versatile capabilities would enable theorists to resolve many of the current controversies about cognitive processing in the mammalian brain.

Animals↗
PubMedDate not supplied

An interactive computer simulation program for the design of statistical control procedures in clinical chemistry.

A computer simulation program has been developed to aid in the design of statistical quality control procedures in clinical chemistry. This 'QC simulator' permits the user to study the effects of parameters in the analytical procedure (method standard deviation, components of variance, rounding of data) and parameters in the control procedure (choice of statistics, control limits, decision criteria, number of control observations). The performance of the control procedures being studied are characterized by their probability for ejection, estimated at several different levels of random and systematic error, and presented by plots of statistical power vs the size of the analytical errors. The relative performance of different control procedures can be compared based on these performance characteristics. Another important application of the program is in the design of control procedures to assure that a specified level of analytical quality is achieved in routine laboratory analyses. The utility of this interactive simulation tool is illustrated in two typical sample runs.

Chemistry, Clinical↗
PubMed2001

Design and effectiveness of a computer-based continuing education program for orthodontists.

The design of computer-based continuing education for health professionals is an important consideration for Internet delivery because the size of graphic files greatly affects the speed with which information is delivered. Orthodontists who had indicated an interest in computer-based continuing education were shown via CD-ROM either a dynamic version of a computer continuing education program (with transitions and animations to liven up the content) or a plain version (identical content except that the transitions and animations were omitted). The program provided new information about superelastic arch wires for the initial stage of orthodontic treatment. For both versions, over 90% of the viewers thought the program was well done and provided useful information. Six of the orthodontists who received the dynamic version felt that the animations were distracting rather than helpful; only one who received the plain version felt that it was lifeless. A follow-up questionnaire showed that two-thirds of those who viewed the program had subsequently reviewed the performance data for the initial wire they were using and 20% had changed it, so the computer program was effective in changing clinical behavior. Those who saw the plain version also were more likely to have changed their clinical procedures. For Internet delivery of information to highly motivated professionals, it appears that transitions and animations are not necessary and may be more likely to decrease than increase the effectiveness of the teaching material.

Adult↗
PubMed2006

Optimal design and experimental investigation of surfactant encapsulated microbubbles.

The diagnostic capabilities of ultrasound imaging can be improved with contrast-specific nonlinear imaging modalities such as harmonic and subharmonic imaging. The nonlinear response of an encapsulated microbubble in an acoustic field is strongly influenced by the shell viscoelastic properties that are determined by the shell composition and thickness. In this paper, the subharmonic performance of a surfactant encapsulated microbubble was optimized by choosing the appropriate composition of shell material with the aid of theoretical model. To study the effects of viscoelastic properties of microbubble shell materials on the nonlinear scattered response of microbubbles, a theoretical model-modified Herring equation for the oscillation of encapsulated microbubbles in the ultrasound field was employed. Based on this model, a computer aided design system was developed to optimize and analyze the acoustic properties, particularly subharmonic responses, of microbubbles under different shell parameters. Furthermore, surfactant encapsulated microbubbles with different viscoelastic properties were prepared by changing the shell composition. Their shell viscoelastic behavior was measured indirectly as dilational modulus of monolayer film formed with surfactant molecular. Moreover, in vitro quantitative acoustic properties measurements of these microbubbles were carried out to evaluate their subharmonic performance. Both of the theoretical simulation and acoustic measurement showed that the surfactant encapsulated microbubbles with good subharmonic properties could be designed and prepared by adjusting the shell material composition with the guide of the computer aided design system.

Capsules↗
PubMed1994

Coronary arteries: new design for three-dimensional arterial phantoms.

Few three-dimensional (3D) anthropomorphic phantoms are available for testing 3D reconstruction and quantitation of vessels. The authors built a new realistic model of arteries with use of stereolithography, a computer-aided design and computer-aided manufacturing technique. Each phantom is composed of the physical object and its digital "twin." The entire coronary artery tree and complex stenoses were manufactured with a precision below 0.1 mm.

Arteries↗
PubMed2001

Hydroxyapatite implants with designed internal architecture.

Porous hydroxyapatite (HA) has been used as a bone graft material in the clinics for decades. Traditionally, the pores in these HAs are either obtained from the coralline exoskeletal patterns or from the embedded organic particles in the starting HA powder. Both processes offer very limited control on the pore structure. A new method for manufacturing porous HA with designed pore channels has been developed. This method is essentially a lost-mold technique with negative molds made with Stereolithography and a highly loaded curable HA suspension as the ceramic carrier. Implants with designed channels and connection patterns were first generated from a Computer-Aided-Design (CAD) software and Computer Tomography (CT) data. The negative images of the designs were used to build the molds on a stereolithography apparatus with epoxy resins. A 40 vol% HA suspension in propoxylated neopentyl glycol diacrylate (PNPGDA) and iso-bornyl acrylate (IBA) was formulated. HA suspension was cast into the epoxy molds and cured into solid at 85 degrees C. The molds and acrylate binders were removed by pyrolysis, followed by HA green body sintering. With this method, implants with six different channel designs were built successfully and the designed channels were reproduced in the sintered HA implants. The channels created in the sintered HA implants were between 366 microm and 968 microm in diameter with standard deviations of 50 microm or less. The porosity created by the channels were between 26% and 52%. The results show that HA implants with designed connection pattern and well controlled channel size can be built with the technique developed in this study.

Journal Article↗