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PubMed1987

Predictive models for deposition of inhaled diesel exhaust particles in humans and laboratory species.

Mathematical and computer models of the respiratory tracts of human beings and of laboratory animals (rats, hamsters, guinea pigs) were used to estimate the deposition patterns of inhaled diesel exhaust particles from automobile emissions. The accuracy of these models was tested by comparing the calculated depositions in laboratory animals with actual laboratory data. Our goal was to be able to predict the relation between exposure to diesel exhaust particles and the deposition of these particles in the lungs of humans of various ages. Diesel exhaust particles are aggregates with a mass median aerodynamic diameter of approximately 0.2 micron. Their actual size depends on the conditions under which they are generated. Using an appropriate particle model, we derived mathematical expressions that describe the effects of diffusion, sedimentation, impaction, and interception on the deposition of these particles. Because of their small size, we found that most diesel exhaust particles deposited through diffusion, and that the role of the other mechanisms was minor. Anatomical models of the human lung from birth to adulthood, as well as models of the lungs of laboratory species were formulated mathematically using available morphometric data. We used these lung models, together with the corresponding ventilation conditions of each species, to calculate deposition of diesel exhaust particles in the lungs. Under normal breathing conditions, we calculated that 7 to 13 percent (depending on particle size) of inhaled diesel exhaust particles deposit in the alveolar region of the adult human lung. Although the breathing mode (nose or mouth breathing) did not appear to affect alveolar deposition, increasing the minute ventilation (the number of breaths per minute multiplied by the tidal volume) increased alveolar deposition significantly. The calculated deposition patterns for diesel exhaust particles in younger humans (under age 25) were similar. However, with the exception of alveolar deposition in very young children (under age two), predicted deposition was greater in the lungs of younger humans than in the lungs of humans age 25 or older. For an equal exposure, the surface minute dose (particle mass deposited per minute per unit surface area) of unciliated airways appeared to change profoundly with age. Predicted dose was maximal in the lung models of two-year-old children. At this age, the calculated dose was approximately twice as high as in the mature adult lung. Deposition predictions for laboratory species compared favorably with existing data. Distribution of deposition was found to be similar among all species studied, although surface minute dose decreased with body weight.

Adolescent↗

PubMed2005

The effect of muscle loading on the simulation of bone remodelling in the proximal femur.

A large number of finite element analyses of the proximal femur rely on a simplified set of muscle and joint contact loads to represent the boundary conditions of the model. In the context of bone remodelling analysis around hip implants, muscle loading affects directly the spatial distribution of the remodelling signal. In the present study we performed a sensitivity analysis on the effect of different muscle loading configurations on the outcome of the bone remodelling simulation. An anatomical model of the femur with the implanted stem in place was constructed using the CT data of the Visible Human Project dataset of the National Institute of Health. The model was loaded with three muscle force configurations with increasing level of complexity. A strain adaptive remodelling rule was employed to simulate the post-operative bone changes around the implant stem and the results of the simulation were assessed quantitatively in terms of the bone mineral content changes in 18 periprosthetic regions of interest. The results showed considerable differences in the amount of bone loss predicted between the three cases. The simplified models generally predicted more pronounced bone loss. Although the overall remodelling patterns observed were similar, the bone conserving effect of additional muscle forces in the vicinity of their areas of attachment was clear. The results of this study suggest that the loading configuration of the FE model does play an important role in the outcome of the remodelling simulation.

Adaptation, Physiological↗

PubMed2003

An EMG-driven musculoskeletal model to estimate muscle forces and knee joint moments in vivo.

This paper examined if an electromyography (EMG) driven musculoskeletal model of the human knee could be used to predict knee moments, calculated using inverse dynamics, across a varied range of dynamic contractile conditions. Muscle-tendon lengths and moment arms of 13 muscles crossing the knee joint were determined from joint kinematics using a three-dimensional anatomical model of the lower limb. Muscle activation was determined using a second-order discrete non-linear model using rectified and low-pass filtered EMG as input. A modified Hill-type muscle model was used to calculate individual muscle forces using activation and muscle tendon lengths as inputs. The model was calibrated to six individuals by altering a set of physiologically based parameters using mathematical optimisation to match the net flexion/extension (FE) muscle moment with those measured by inverse dynamics. The model was calibrated for each subject using 5 different tasks, including passive and active FE in an isokinetic dynamometer, running, and cutting manoeuvres recorded using three-dimensional motion analysis. Once calibrated, the model was used to predict the FE moments, estimated via inverse dynamics, from over 200 isokinetic dynamometer, running and sidestepping tasks. The inverse dynamics joint moments were predicted with an average R(2) of 0.91 and mean residual error of approximately 12 Nm. A re-calibration of only the EMG-to-activation parameters revealed FE moments prediction across weeks of similar accuracy. Changing the muscle model to one that is more physiologically correct produced better predictions. The modelling method presented represents a good way to estimate in vivo muscle forces during movement tasks.

Adult↗

PubMed2006

Patient-specific computational modeling of cerebral aneurysms with multiple avenues of flow from 3D rotational angiography images.

RATIONALE AND OBJECTIVES: Previous studies of aneurysm flow dynamics based on three-dimensional (3D) rotational angiography (RA) images were limited to aneurysms with a single route of blood inflow. However, aneurysms of the circle of Willis frequently involve locations with more than one source of inflow, such as aneurysms of the anterior communicating artery. The highest resolution images of cerebral vessels are from RA images, but this technique is limited to visualizing only one route of inflow at a time, leaving a significant limitation in the application of 3DRA image sets for clinical studies of patient-specific computational fluid dynamics (CFD) simulations. In this report, subject-specific models of cerebral aneurysms with multiple avenues of flow are constructed from RA images by using a novel combination of image co-registration and surface merging techniques. MATERIALS AND METHODS: RA images are obtained by means of contrast injection in each vessel that provides inflow to the aneurysm. Anatomic models are constructed independently of each of these vascular trees and fused together into a single model. The model is used to construct a finite element grid for CFD simulations of hemodynamics. RESULTS: Three examples of patient-specific models are presented: an anterior communicating artery aneurysm, a basilar tip aneurysm, and a model of an entire circle of Willis with five coincident aneurysms. The method is evaluated with a numeric phantom of an aneurysm in the anterior communicating artery. CONCLUSION: These examples show that this new technique can be used to create merged network numeric models for CFD modeling. Furthermore, intra-aneurysmal flow patterns are influenced strongly by merging of the two inflow streams. This effect decreases as distance from the merging streams increases.

Adult↗

PubMed2004

A study of age-related architectural changes that are most damaging to bones.

Osteoporosis-related bone damage causes major socioeconomic problems. For efficient use of therapeutic agents, it is necessary to be able to reliably identify patients with high propensity for nontraumatic fracture. Age-related bone loss imposes several architectural changes in bone; one of the few ways to estimate damage due to individual changes, and hence determine the most serious types of damage, is via the analysis of suitable mathematical models. Anatomical sites such as the vertebral body, proximal femur, and distal radius are locations where most age-related fractures occur. The inner porous (or trabecular) bone from these sites, which resemble disordered cubic networks, play a significant role in load transmission at these sites. Analysis of a mathematical model of porous bone is used to show that perforation of elements of the network is the most damaging architectural change to a bone. We also show that an expression for bone strength, derived on this basis, can capture changes in strength caused by the inclusion of other features like thinning of trabecular bone and the anisotropy of the network. We finally argue that bone density, which is currently the most routinely used diagnostic, cannot be a reliable surrogate for bone strength.

Aging↗

PubMed2004

[Virtual simulation of dental surgery using a three-dimensional computer model with a force feedback system].

BACKGROUND: Selective reduction of bone without injuring inner structures is an essential part of surgical techniques, especially during dental surgery. Virtual drilling is possible using a new simulator. The following illustrates simulation of an apicectomy. MATERIAL AND METHODS: Using the VOXEL-MAN system, a virtual three-dimensional model of a skull was created based on CT data. Both inferior alveolar nerves and apical inflammations of teeth 23, 25, 36, and 35 were virtually simulated. To achieve a realistic drilling effect with the force feedback system, special tools were integrated into VOXEL-MAN to obtain a high resolution of collision recognition. Adding drilling noises further improved the simulation. Spatial 3D perception was possible with the help of shutter glasses. RESULTS: The presented computer model enabled the visual and haptic observation of complex volume-based models and virtual interaction with them. The haptic feeling proved to be convincing because of collision recognition, consideration of drilling parameters, and addition of drilling noises. Via postoperative reconstructions, polydimensional verification of performed drilling routes is possible. CONCLUSION: Using apicectomies as examples, realistic simulation of dental surgical procedures, even in complex anatomical models, is possible. Generally, it is possible to add virtual pathologies in data sets and/or to use anonymous patient data sets to extend the range of simulated surgical procedures.

Apicoectomy↗

PubMed1999

Three-dimensional computer-simulated prostate models: lateral prostate biopsies increase the detection rate of prostate cancer.

OBJECTIVES: Urologists routinely use the systematic sextant needle biopsy technique to detect prostate cancer. However, recent evidence suggests that this technique has a significant sampling error. We developed a novel three-dimensional (3D) computer-assisted prostate biopsy simulator based on whole-mounted step-sectioned radical prostatectomy specimens to compare the diagnostic accuracy of various prostate needle biopsy protocols. METHODS: We obtained digital images of 201 step-sectioned whole-mounted radical prostatectomy specimens. 3D computer simulation software was developed to accurately depict the anatomy of the prostate and all individual tumor foci. Additional peripheral devices were incorporated into the system to perform interactive prostate biopsies. We obtained 18 biopsies of each prostate model to determine the detection rates of various biopsy protocols. RESULTS: The 10- and 12-pattern biopsy protocols had a 99.0% detection rate; the traditional sextant biopsy protocol rate was only 72.6%. The 5-region biopsy protocol had a 90.5% detection rate and the 14-pattern, which includes all the biopsies used in the patterns above, only added 1 additional positive case (99.5%). Transitional zone and seminal vesicle biopsies did not result in a significantly increased detection rate when added to the patterns above. Only one positive model was obtained when the transitional zone biopsies were added. The lateral sextant pattern had a detection rate of 95.5%, and the 4-pattern lateral biopsy protocol had a 93.5% detection rate. CONCLUSIONS: Our results suggest that all the biopsy protocols that use laterally placed biopsies based on the 5-region anatomic model are superior to the routinely used sextant prostate biopsy pattern. Lateral biopsies in the mid and apical zones of the gland are the most important.

Biopsy, Needle↗

PubMed2003

The hemodynamic effects of compliance, bulging, and curvature in a saphenous vein coronary artery bypass graft model.

The development of Intimal Hyperplasia (IH) in saphenous vein coronary artery bypass grafts (SV-CABG) is responsible for the short-term patency of these grafts. Previous studies of SV-CABG models were performed on rigid anastomotic vessels. However, the effects of compliance, bulging and curvature at the anastomosis on the general hemodynamic field, due to compliance and geometric mismatch between the vein and the artery have not been evaluated. We studied axial and transverse velocities by Laser Doppler Velocimetry on a compliant, in vitro, anatomical model of an end-to-side saphenous vein graft (SVG) to left anterior descending (LAD). The model incorporated a bulge at the sinus and curvature at the graft-host junction. Physiologic pressure and flow conditions pertaining to SV-CABG were applied. The presence of the bulge and curvature showed differences in the velocity profiles in comparison with previous rigid model studies. Dynamic separation zones were temporally augmented at the flow divider. The moving stagnation point at the floor of the host vessel was observed to move past the toe of the model during the accelerating portion of the cycle. These findings suggest that the presence of the bulge curvature and compliance may further favor conditions for the development of intimal hyperplasia (IH) at the floor of a CABG.

Coronary Artery Bypass↗

PubMed1984

Estimation of guinea pig tracheobronchial transport rates using a compartmental model.

Mucociliary clearance in the tracheobronchial tree of guinea pigs was examined using monodisperse 7.9 micrometers MMAD polystyrene particles. Animals were exposed for approximately 1 h by inhalation via an intratracheal tube to aerosols tagged with gold-198 and fluorescent dyes. Following exposure, animals were radioactively monitored and sacrificed at predetermined times. The lungs were removed, freeze-dried, sectioned completely, and examined with a fluorescent microscope. Measurements were made of airway diameters where particles were found. An anatomic model for guinea pig lung morphology was used to assign ranges of airway diameters to five zones, which were incorporated into a compartmental model for lung clearance. Kinetic analysis of particle distributions in the zones led to development of first-order equations describing the compartmental clearance. Rate constants obtained from the kinetic analysis were used to estimate mucociliary transport rates in specific bronchial generations, which ranged from approximately 0.001 mm/min in the distal bronchioles to approximately 8 mm/min in the trachea, and resulted in a calculated 24-h clearance time for tracheobronchial clearance in the guinea pig. No evidence for either bronchial penetration by particles or relatively prolonged bronchial retention of particles was found in this study.

Aerosols↗

PubMed2006

Preclinical testing of a new clot-retrieving wire device using polyvinyl alcohol hydrogel vascular models.

INTRODUCTION: Cerebral embolism is the principal cause of cerebral infarction. Recently, mechanical embolectomy has been proposed as an effective method. We performed a preclinical evaluation of a new mechanical clot-retrieving wire. METHODS: This clot-retrieving wire consisted of three nitinol loops at the tip of a microguidewire. These three loops could be collapsed into a 0.018-inch wire compatible microcatheter. Each loop was 8 mm long and 3.5 mm wide. For simulation, polyvinyl alcohol (PVA) vascular anatomical models of the human carotid (eight models) and vertebrobasilar (three models) circulation were constructed. A pulsatile flow circulation system was used. Embolic clots were produced using pig blood plasma. The microcatheter and the microguidewire were advanced beyond the clot. The wire was then exchanged for the retrieving wire. The microcatheter was then pulled slightly back to open the loops. The clot was then caught by withdrawal of the system. Once caught, the clot was retrieved to the guiding catheter tip. We investigated the following points: ease of device deployment, clot capture ability, clot removal against blood flow and removal of the clot out of the introducer system. RESULTS: A total of 104 procedures were performed in 11 PVA models and evaluated. The drop rate was 19%. We succeeded in partial and total recanalization in 51.0% of the procedures (53/104) within 30 minutes. CONCLUSION: This new clot-retrieving wire could be useful for mechanical clot extraction in stroke.

Embolectomy↗

PubMed2002

Progressive failure analysis of laminated composite femoral prostheses for total hip arthroplasty.

In this research program, a numerical method was developed to predict the progressive failure of a thick laminated composite femoral component for total hip arthroplasty. A 3-D global/local technique was used to capture the overall structural response of this system while also enabling the 3-D ply level stress state to be determined efficiently and accurately. Different failure criteria and different material degradation models were incorporated as individual subroutines in the numerical method, giving it the flexibility to model a wide range of materials and structures. Numerical modeling was also conducted to design experimental test methods for component fatigue testing that closely simulate in vivo loading conditions. Parametric studies were then conducted with the numerical model of the experimental system and the results were compared to the actual experimentally determined damage behavior of fabricated laminated composite femoral component to assess which parameter set most accurately predicted the actual damage development behavior. The best fitting parameter set was then applied to the failure problem of the composite hip prosthesis implanted in an anatomically modeled femur to predict in vivo performance. This work provides a ply level understanding of the damage behavior of laminated composite femoral components and a numerical tool which can serve as a guide for the design of fatigue resistant implants made from composite material for this and other implant applications.

Arthroplasty, Replacement, Hip↗

PubMed1997

The neuroanatomy of 5-HT dysregulation and panic disorder.

The advent of highly effective antipanic medications with specific serotonin reuptake inhibition as a mechanism of action has prompted the need for new pathophysiological models of panic disorder. The authors attempt an integration of the emerging basic science literature regarding the neuro-anatomy and physiology of the mammalian central serotonin nervous system, its influence on neural substrates that underlie fear and defense responses, and the clinical literature pertaining to serotonin-related abnormalities in panic disorder. A neuro-anatomical model for the potential sites of action of the specific serotonin reuptake inhibitors in panic disorder is proposed.

Afferent Pathways↗

PubMed2000

Diffusion-convection equation solved in parallel regions of the lung.

The single path model of airway gas transport was incorporated into each of Cruz (Cruz, J. C. Respir. Physiol. 86:1-14, 1991). Thus, the effect of time on the predicted gas fractions in and out of the lung could be evaluated. Two experimental maneuvers were simulated: (1) fast inhalation of an argon-oxygen mixture from a functional residual capacity and fast exhalation to residual volume, including inspiratory breath holdings of 5-20 s, and (2) the standard single-breath nitrogen washout test. Expired argon and nitrogen are predicted within a +3% error of the experimental data with no breath holding. Breath holding predictions were at variance with experimental results because the solution of the diffusion-convection equation produced even mixing in the alveoli at the end of inspiration. The minimum square of the difference between the experimental data (standard single-breath nitrogen washout test) and those provided by the model was 0.0016. This model is capable of generating a nitrogen expirogram with four phases when a vital capacity of oxygen is inhaled. However, the model failed to produce a sharp distinction between phase 3 and phase 4. Thus, we conclude that uneven emptying of parallel regions generates any expirogram (a fast or slow expiratory maneuver). The alveolar gas stratification that is created during inspiration disappears at the end of the inspiratory maneuver. As a result, breath holding maneuvers cannot be predicted in the anatomical model used.

Biomedical Engineering↗

PubMed1995

Comparison by computerized numeric modeling of energy losses in different Fontan connections.

BACKGROUND: Different surgical techniques for creating a Fontan circulation can be used. The option of including an atrium in the circuit, or the technique used for connecting the caval veins to the pulmonary artery in a total cavopulmonary connection, frequently is empirical and is based on personal experience and preference. The hemodynamic and energetic differences between the different circuits are small, and short-term results are comparable. However, small, energetic differences may have significant implications for the long-term follow-up. The finite element method allows a computer-based modeling of the flow dynamics and pressure losses. It permits comparison of different Fontan connections in a single patient with identical geometry and functional conditions. METHODS AND RESULTS: We compared the atriopulmonary connection with different types of cavopulmonary connections, which differed in the degree of symmetry of implantation of both caval veins into the right pulmonary artery. Based on anatomic models and physiological flow dynamics, three-dimensional geometries and finite element meshes were created with PATRAN; flows were calculated with POLYFLOW (B), and results were visualized with DATA VISUALIZER. CONCLUSIONS: The atriopulmonary connection produces higher energy losses than the cavopulmonary connection (+/- 1 mm Hg at rest). The cavopulmonary connection is more efficient when the connection of the caval veins to the pulmonary artery is asymmetrical.

Blood Flow Velocity↗

PubMed1992

Prediction of bone adaptation in the ulnar-osteotomized sheep's forelimb using an anatomical finite element model.

A method for the prediction of the time-course of bone adaptation based on an alternative hypothesis of strength optimization has been previously investigated and developed by Prendergast and Taylor. This paper extends our work in the study of the effectiveness of this bone adaptation model in predicting similar bone remodelling to that observed in animal experiments. In particular the experimental work which has been modelled is that of Lanyon, Goodship, Pye and McFie. An anatomical finite element model of the sheep's forelimb has been generated for this purpose and is used to estimate stresses in the bone structure for the normal and osteotomized condition. The propensity for remodelling of the altered bone structure is predicted using the proposed remodelling law for the new stress field in the bone structure. The preliminary results indicate an initial bone adaptation pattern similar to that observed experimentally without the necessity to use arbitrarily different constants for the endosteal and periosteal surfaces. We therefore suggest that the remodelling law based on damage and repair gives a better predictive model of bone adaptation than previous models.

Adaptation, Physiological↗

PubMed1993

Verification of a free vascularized nerve graft model in the rat with application to the peripheral nerve allograft.

We report a vascularized sciatic nerve graft in the rat, based upon the femoral popliteal superior muscular artery pedicle. The pedicle may be raised from the common femoral artery via the popliteal artery, with accompanying venous drainage to the femoral vein. We have characterized two vessels: the middle tibial artery to the posterior tibial nerve and the arteria comitas nervus peroneus to the peroneal nerve. Plastic monomer and Evans blue labeled albumin injections established the anatomic model. The graft was reliably perfused at the time of isolation and 24 hours post-transplantation. The model was used to evaluate regeneration across allogeneic (ACI to Lewis, n = 12) versus syngeneic (Lewis to Lewis, n = 6) nerve grafts. Electrophysiologic and histomorphometric assessments demonstrated that the vascularized immunosuppressed allograft was similar to the vascularized syngeneic graft. Both were superior to the vascularized allograft without immunosuppression.

Action Potentials↗

PubMed2006

Photorealistic virtual anatomy based on Chinese Visible Human data.

Virtual reality based learning of human anatomy is feasible when a database of 3D organ models is available for the learner to explore, visualize, and dissect in virtual space interactively. In this article, we present our latest work on photorealistic virtual anatomy applications based on the Chinese Visible Human (CVH) data. We have focused on the development of state-of-the-art virtual environments that feature interactive photo-realistic visualization and dissection of virtual anatomical models constructed from ultra-high resolution CVH datasets. We also outline our latest progress in applying these highly accurate virtual and functional organ models to generate realistic look and feel to advanced surgical simulators.

Adult↗

PubMed2003

Atrial noninvasive activation mapping of paced rhythm data.

INTRODUCTION: Atrial arrhythmias have emerged as a topic of great interest for clinical electrophysiologists. Noninvasive imaging of electrical function in humans may be useful for computer-aided diagnosis and treatment of cardiac arrhythmias, which can be accomplished by the fusion of data from ECG mapping and magnetic resonance imaging (MRI). METHODS AND RESULTS: In this study, a bidomain-theory-based surface heart model activation time (AT) imaging approach was applied to paced rhythm data from four patients. Pacing sites were the right superior pulmonary vein, left inferior pulmonary vein, left superior pulmonary vein, coronary sinus, posterior wall of right atrium, and high right atrium. For coronary sinus pacing, the AT pattern of the right atrium was compared with a CARTO map. The root mean square error between CARTO geometry (85 nodal points) and the surface model of the right atrium was 8.6 mm. The correlation coefficient of the noninvasively obtained AT map of the right atrium and the CARTO map was 0.76. All pulmonary vein pacing sites were identified. The reconstructed pacing site of right posterior atrial pacing correlates with the invasively determined pacing catheter position with a localization distance of 4 mm. CONCLUSION: The individual anatomic model of the atria of each patient enables accurate noninvasive AT imaging within the atria, resulting in a localization error for the pacing sites within 10 mm. Our findings may have implications for imaging of atrial activity in patients with focal arrhythmias or focal triggers.

Adult↗