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At least 397 records · Page 22Linked to original sources
PubMed1998

A simple method for visualization of influential landmarks when using euclidean distance matrix analysis.

Euclidean distance matrix analysis (EDMA) differs from most other morphometric methods for the analysis of landmark coordinate data in that it is coordinate-system invariant. However, strict adherence to coordinate-system invariance (for both biological and statistical reasons) introduces some difficulty in using graphic aids for the analysis and interpretation of EDMA results. We present a simple and effective graphic method to help localize important differences in form, growth, or shape by identifying "influential" landmarks. Examples are presented using simulated data and real data involving both children with craniofacial dysmorphologies and sexual dimorphism in adult Macaca fascicularis.

Acrocephalosyndactylia↗
PubMed1997

Modelling the assessment of port wine stain parameters from skin surface temperature following a diagnostic laser pulse.

BACKGROUND AND OBJECTIVE: Laser treatment of port wine stains (PWS) has become an established clinical modality over the past decade. However, in some cases full clearance of the PWS cannot be achieved. To improve the clinical results, it is necessary to match the laser treatment parameters to the PWS anatomy on an individual patient basis. Therefore, knowledge of the PWS structure is of great importance. The objective of this study is to describe a diagnostic method to assess the PWS blood vessels depth and diameter from the skin surface temperature-time course following a diagnostic laser pulse. STUDY DESIGN/MATERIALS AND METHODS: The Monte Carlo (MC) method was used to calculate the deposited laser energy into a port wine stain skin model following irradiation by a diagnostic laser pulse at 577 nm. The heat equation was solved numerically, using the deposited energy profile as the source term, yielding the temperature-time course at the skin surface. Subtraction of "bloodless" skin signal from that of the skin containing blood vessels gives us the net contribution of a heated dermal blood vessel to the skin surface temperature-time behaviour. RESULTS: The net blood vessel signal shows heat-diffusion behaviour and was found to be sensitive to the dermal blood vessel depth and diameter. The time delay for the peak signal temperature to occur depends quadratically on the blood vessel depth. The peak temperature relates linearly to the blood vessel diameter. The degree of epidermal melanin content can also be determined from the immediate temperature rise of the signal. CONCLUSION: The proposed method easily enables assessment of the blood vessel depth and diameter as well as the epidermal melanin content in a skin model. The method can be applied to a real PWS when using the adjacent normal skin as a reference.

Blood Vessels↗
PubMed1999

Dosimetry and growth hormone deficiency following cranial irradiation of childhood brain tumors.

BACKGROUND: Dosimetry of the hypothalamus-pituitary (HP) region could allow prediction of the risk of growth hormone deficiency (GHD) following cranial irradiation. PROCEDURE: Nineteen children (15 boys) with a median age of 6.3 years (range 1.7-16.5) at the time of irradiation of a brain tumor not involving the HP axis were followed for 1.2-6.3 years (median 3.4) from radiotherapy (RT). The dose to a standardized anatomical model including the HP region was calculated from dose-volume histograms of 10% to 100% in steps of 10% of the HP model based on data from a computer-based treatment planning system. If GHD was suspected from insulin-like growth factor-I, serum insulin-like growth factor binding protein-3, and/or height velocity measurements, an arginine stimulation test was performed. GHD was defined by a peak GH <15mU/liter. RESULTS: Ten patients developed GHD 10-26 months from irradiation. Cox regression analysis identified the 90% dose-volume of the HP box as the strongest predictor of development of GHD (P = 0.03). The median dose to the 90% dose-volume of the HP region was 37.5 Gy (range 2. 3-55.3). The cumulated risk of GHD 2.5 years after radiotherapy for children receiving more than and less than 37.5 Gy to the HP region was 87% and 33%, respectively (P = 0.036). CONCLUSIONS: Dosimetry of a defined HP volume provides the opportunity to 1) calculate the exact dose delivered to this region, 2) predict the risk of GHD and, 3) in the future revise the treatment planning and thus reduce the risk of endocrine adverse effects.

Adolescent↗
PubMed1999

Predictive medicine: computational techniques in therapeutic decision-making.

The current paradigm for surgery planning for the treatment of cardiovascular disease relies exclusively on diagnostic imaging data to define the present state of the patient, empirical data to evaluate the efficacy of prior treatments for similar patients, and the judgement of the surgeon to decide on a preferred treatment. The individual variability and inherent complexity of human biological systems is such that diagnostic imaging and empirical data alone are insufficient to predict the outcome of a given treatment for an individual patient. We propose a new paradigm of predictive medicine in which the physician utilizes computational tools to construct and evaluate a combined anatomic/physiologic model to predict the outcome of alternative treatment plans for an individual patient. The predictive medicine paradigm is implemented in a software system developed for Simulation-Based Medical Planning. This system provides an integrated set of tools to test hypotheses regarding the effect of alternate treatment plans on blood flow in the cardiovascular system of an individual patient. It combines an Internet-based user interface developed using Java and VRML, image segmentation, geometric solid modeling, automatic finite element mesh generation, computational fluid dynamics, and scientific visualization techniques. This system is applied to the evaluation of alternate, patient-specific treatments for a case of lower extremity occlusive cardiovascular disease.

Arterial Occlusive Diseases↗
PubMed1998

Influence of skull anisotropy for the forward and inverse problem in EEG: simulation studies using FEM on realistic head models.

For the sake of realism in the description of conduction from primary neural currents to scalp potentials, we investigated the influence of skull anisotropy on the forward and inverse problems in brain functional imaging with EEG. At present, all methods available for cortical imaging assume a spherical geometry, or when using realistic head shapes do not consider the anisotropy of head tissues. However, to our knowledge, no study relates the implication of this simplifying hypothesis on the spatial resolution of EEG for source imaging. In this paper, a method using finite elements in a realistic head geometry is implemented and validated. The influence of erroneous conductivity values for the head tissues is presented, and results show that the conductivities of the brain and the skull in the radial orientation are the most critical ones. In the inverse problem, this influence has been evaluated with simulations using a distributed source model with a comparison of two regularization techniques, with the isotropic model working on data sets produced by a nonisotropic model. Regularization with minimum norm priors produces source images with spurious activity, meaning that the errors in the head model totally annihilate any localization ability. But nonlinear regularization allows the accurate recovery of simultaneous spots of activity, while the restoration of very close active regions is profoundly disabled by errors in the head model. We conclude that for robust cortical source imaging with EEG, a realistic head model taking anisotropy of tissues into account should be used.

Anisotropy↗
PubMed1999

High-resolution intersubject averaging and a coordinate system for the cortical surface.

The neurons of the human cerebral cortex are arranged in a highly folded sheet, with the majority of the cortical surface area buried in folds. Cortical maps are typically arranged with a topography oriented parallel to the cortical surface. Despite this unambiguous sheetlike geometry, the most commonly used coordinate systems for localizing cortical features are based on 3-D stereotaxic coordinates rather than on position relative to the 2-D cortical sheet. In order to address the need for a more natural surface-based coordinate system for the cortex, we have developed a means for generating an average folding pattern across a large number of individual subjects as a function on the unit sphere and of nonrigidly aligning each individual with the average. This establishes a spherical surface-based coordinate system that is adapted to the folding pattern of each individual subject, allowing for much higher localization accuracy of structural and functional features of the human brain.

Brain Mapping↗
PubMed1997

Introduction to histology through the use of familiar objects: innovative teaching module.

To introduce first-year medical students to fundamental concepts in histology and facilitate interpretation of two-dimensional images in the context of the three-dimensional nature of the object, a simple teaching module consisting of active exercises plus group discussions, using familiar objects from everyday use, was planned. In the process of mentally reconstructing sections through familiar objects, and representing in diagrams the appearance of these sections, students learned the use of common histology terms; the value of studying sections in series and at different planes; and spatial relationships of a) a nucleus within a cell, and b) tissue components within solid and hollow organs. Their understanding of these concepts was found to be good when evaluated by a multiple-choice-questions test, suggesting that this is an effective method for introducing beginners to fundamentals of histology.

Education, Medical, Undergraduate↗
PubMed2000

Inter-laboratory comparison of numerical dosimetry for human exposure to 60 Hz electric and magnetic fields.

In recent years, with the availability of high resolution models of the human body, numerical computations of induced electric fields and currents have been made in more than one laboratory for various exposure conditions. Despite the verification of computational methods, questions are often asked about the reliability of these data. In this paper, computational results from two laboratories that presented data in compatible formats are compared, supplemented with additional data from the third laboratory. Two exposures to uniform fields at 60 Hz are evaluated. The human body models used in the computations are different and so are the computation al methods and codes. There are some differences in the conductivity values used for some of the tissues, as well. The results of the comparison confirm that these data are reliable, as the overall agreement is reasonably good and the differences can be rationally explained. This comparison also underscores the importance of accurate data on the dielectric properties of tissues.

Computer Simulation↗
PubMed2000

Online head motion tracking applied to the patient registration problem.

Image-guided systems for surgical procedures in the region of the head require a method to correlate the diagnostic image data with the corresponding site of pathology in the patient. Considering that patient movement can occur, detection and correction of such movement errors during the acquisition of images is a basic prerequisite for accurate treatment. For this reason, we developed a new registration method based upon on-line tracking of the patient's head to solve the problem of registration in the presence of head motion. The method provides non-invasive active patient registration for correction of movements during imaging and continuous update of the patient's head position during surgery. The patient motion correction applies the rigid body model to register the images using feature correspondence. The new registration method is described, and results of experiments that were performed to evaluate its accuracy and reliability in a plastic skull model and in patients are presented. The error analysis resulted in a final target registration error of 0.90 mm +/- 0.16 mm using experimental model data and 1.58 mm +/- 0.26 mm using clinical patient data. In addition, the residual registration error is modeled as a function of the measured and predicted head motion in order to determine the error that is introduced by motion tracking during image data acquisition. Furthermore, the clinical application of the method is demonstrated for oto-, rhino-, and neurosurgical procedures in the region of the head.

Algorithms↗
PubMed2000

A simulator for maxillofacial surgery integrating 3D cephalometry and orthodontia.

OBJECTIVES: This paper presents a new simulator for maxillofacial surgery that gathers the dental and maxillofacial analyses together into a single computer-assisted procedure. The idea is to first propose a repositioning of the maxilla via the introduction of 3D cephalometry applied to a 3D virtual model of the patient's skull. Orthodontic data are then integrated into this model, using optical measurements of plaster casts of the teeth. MATERIALS AND METHODS: The feasibility of the maxillofacial demonstrator was first evaluated on a dry skull. To simulate malformations (and thus simulate a "real" patient), the skull was modified and manually cut by the surgeon to generate a given maxillofacial malformation (with asymmetries in the sagittal, frontal, and axial planes). RESULTS: The validation of our simulator consisted of evaluating its ability to propose a bone repositioning diagnosis that would restore the skull to its original configuration. An initial qualitative validation is provided in this paper, with a 1.5-mm error in the repositioning diagnosis. CONCLUSIONS: These results mainly validate the concept of a maxillofacial numerical simulator that integrates 3D cephalometry and guarantees a correct dental occlusion.

Cephalometry↗
PubMed1980

An elementary introduction to stereology (quantitative microscopy).

Stereology is a branch of applied mathematics used for the three-dimensional analysis of organs and materials from two-dimensional measurements. Stereologic methods are versatile, easily understood, and simply applied. This paper provides anatomists with a practical guide to stereologic techniques and concepts and to ancillary morphometric methods. These methods allow investigators to calculate volume, surface, and numerical densities; make shape determinations; and calculate size distributions for spheres and rotatory ellipsoids. Other topics covered in this article include sampling methods, correction factors for shrinkage and section thickness, index of folding, automated and semiautomated image analysis, and three-dimensional reconstruction from serial sections.

Biometry↗
PubMed1995

Mechanics of cardiac looping.

During the early stages of embryonic development, the heart is a smooth-walled, muscle-wrapped tube that bends and rotates in a vital, but poorly understood, morphogenetic process called looping. Since looping involves biomechanical forces, this paper examines two mechanically based hypotheses for the bending component of cardiac looping. The first hypothesis is that an initial tension in or near the dorsal mesocardium (DM), a longitudinal structure along the outside of the ventricle, drives the deformation. To relieve the bending stresses in the tube, the myocytes change shape passively, and then they deform actively to continue the process to completion of a full loop. In the second hypothesis, contraction of circumferentially arranged actin macrofilaments produces circumferential compression and longitudinal expansion (due to incompressibility) of the myocytes. The DM locally constrains the longitudinal deformation, forcing the tube to bend. The feasibility of these hypotheses was evaluated using theoretical models and published experimental results. The models, which consist of beams composed of two layers representing the DM and the ventricular myocardium, show that the hypotheses are consistent with most of the known data, but further studies are necessary. In this regard, the models provide a conceptual framework for designing experiments to investigate the mechanics of looping.

Animals↗
PubMed2002

The promise of geometric morphometrics.

Nontraditional or geometric morphometric methods have found wide application in the biological sciences, especially in anthropology, a field with a strong history of measurement of biological form. Controversy has arisen over which method is the "best" for quantifying the morphological difference between forms and for making proper statistical statements about the detected differences. This paper explains that many of these arguments are superfluous to the real issues that need to be understood by those wishing to apply morphometric methods to biological data. Validity, the ability of a method to find the correct answer, is rarely discussed and often ignored. We explain why demonstration of validity is a necessary step in the evaluation of methods used in morphometrics. Focusing specifically on landmark data, we discuss the concepts of size and shape, and reiterate that since no unique definition of size exists, shape can only be recognized with reference to a chosen surrogate for size. We explain why only a limited class of information related to the morphology of an object can be known when landmark data are used. This observation has genuine consequences, as certain morphometric methods are based on models that require specific assumptions, some of which exceed what can be known from landmark data. We show that orientation of an object with reference to other objects in a sample can never be known, because this information is not included in landmark data. Consequently, a descriptor of form difference that contains information on orientation is flawed because that information does not arise from evidence within the data, but instead is a product of a chosen orientation scheme. To illustrate these points, we apply superimposition, deformation, and linear distance-based morphometric methods to the analysis of a simulated data set for which the true differences are known. This analysis demonstrates the relative efficacy of various methods to reveal the true difference between forms. Our discussion is intended to be fair, but it will be obvious to the reader that we favor a particular approach. Our bias comes from the realization that morphometric methods should operate with a definition of form and form difference consistent with the limited class of information that can be known from landmark data. Answers based on information that can be known from the data are of more use to biological inquiry than those based on unjustifiable assumptions.

Animals↗
PubMed1981

A model of the inguinal canal.

Medical students often find it difficult ot conceptualize and learn the anatomy of the inguinal region and canal. A model of the inguinal canal, appropriate for lecture and laboratory presentations, has been used for many years by one of the authors (J.J.J.), and based on student and staff feedback, is judged a successful visual learning aid. This paper outlines a step-by-step procedure for constructing the model out of plexiglass and colored, felt-tipped marking pens.

Humans↗