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PubMed1982

Neural networks and physical systems with emergent collective computational abilities.

Computational properties of use of biological organisms or to the construction of computers can emerge as collective properties of systems having a large number of simple equivalent components (or neurons). The physical meaning of content-addressable memory is described by an appropriate phase space flow of the state of a system. A model of such a system is given, based on aspects of neurobiology but readily adapted to integrated circuits. The collective properties of this model produce a content-addressable memory which correctly yields an entire memory from any subpart of sufficient size. The algorithm for the time evolution of the state of the system is based on asynchronous parallel processing. Additional emergent collective properties include some capacity for generalization, familiarity recognition, categorization, error correction, and time sequence retention. The collective properties are only weakly sensitive to details of the modeling or the failure of individual devices.

Animals↗
PubMed1997

Dynamic three-dimensional echocardiography: a new era in ultrasound technology.

The use of noninvasive methods to visualise the heart has had an extraordinary development over the last decade, with echocardiography demonstrating a particularly fast growth. Despite its unquestionable role in the diagnosis of heart disease and in the management of cardiac patients, it does have some limitations, both in the morphological visualisation, as well as in the functional assessment of the heart, such as blood flow, quantification of intracardiac volumes, etc. The recent development of dynamic three-dimensional (3D) echocardiography from two dimensional images has opened new perspectives in the study of cardiac pathophysiology. There are basically two methods of displaying three dimensional data sets: (1) a two-dimensional display from individual selected cut planes (any-plane echocardiography) or from parallel short axis cuts; (2) a volume rendered technique: from any defined cut plane, different algorithms are applied to represent the information in space. There are several potential clinical applications of 3D such as the measurement and serial follow-up of left ventricular volumes; in valvular heart disease (the abnormalities can be delineated more precisely and in greater detail than conventional imaging, including a detailed definition of mitral apparatus in mitral stenosis), in mitral valve prolapse both leaflets can be seen from the left atrial view and in endocarditis it can aid in deciding when and how to intervene; in complex congenital heart disease, such as reconstruction of double outlet right ventricle, left-sided obstructive and regurgitant lesions and subaortic obstructive cases, in atrial and ventricular septal defects, displaying size, geometry and relationships to other structures; another expression of cardiac disorders are blood flow disturbances (visualisation of flows in 3D could allow a better qualitative and quantitative assessment of their size and severity; the pictures so far generated allow a good perception of the size and shape of mitral, aortic and tricuspid regurgitation jets, by examining them from a new perspective, it also has the potential to display the flow convergence zone and quantify the regurgitant volume). Recent studies have clearly demonstrated the feasibility of performing three-dimensional imaging in a variety of cardiac diseases, but continued development of ultrasound technology must be made to improve better image resolution. The prolonged acquisition time is the most important limiting factor that currently restricts the routine use of 3D echocardiography. The development of faster computers will shorten the time needed for image acquisition, postprocessing, and data analysis, contributing to the goal of easy access and wide use. With improvements in computer technology and production of interactive software, 3D echocardiography will provide a dynamic view of the surgical anatomy of the heart. Thus, the three-dimensional reconstruction concept has the potential to and diagnostic assessment of cardiac pathology in every facet.

Cardiovascular Diseases↗
PubMed1994

A comparison of three electron planning algorithms for a 16 MeV electron beam.

PURPOSE: We report results of a comparison of three electron planning algorithms, an Age-Diffusion Pencil beam algorithm and two (2-D) and three dimensional (3-D) Hogstrom pencil beam algorithms, using simple 2 x 2 cm air and hard bone inhomogeneities and a complex anthropomorphic head and neck phantom. METHODS AND MATERIALS: The simple inhomogeneities have variable dimensions outside the plane of calculation to test the effects of out of plane scattering on 2-D algorithms, compared with dose measured by film below the inhomogeneity in the dose fall-off range. Comparisons are also made of a parotid treatment field for 16 MeV electrons, and the dose measured by high sensitivity thermoluminescent dosimeters in the head and neck phantom. RESULTS: Behind the simple inhomogeneities, the electron algorithms are found to underestimate the dose behind the air cavity by up to 40% and overestimated the dose behind bone by up to 30%. In the head phantom, the presence of inhomogeneities also presents problems for the algorithms, with overestimations of dose of up to 20% found behind bone-tissue interfaces, apparently due to shielding by high density bone. Overestimations of up to 17% are also found beside interfaces parallel to the beam. Underestimations of dose of up to 10% are found on the beam-side of interfaces, due to under-prediction of backscattered electrons. All three investigated algorithms underestimate the dose by up to 20% behind extreme surface curvature. One algorithm is found to underestimate the dose in the falloff region while another overestimates the dose around the 90% isodose. CONCLUSION: Clinicians should be aware of the limitations of their planning systems.

Algorithms↗
PubMed1985

Design and fitting of neural network transfer functions.

An algorithm is presented which (a) allows construction of mathematical models involving arbitrary combinations of linear cascades, parallel pathways, and feedback loops, (b) computes a total transfer function of the system, (c) performs a least-squares optimization of model parameters to best fit the model to experimental data, and (d) provides a measure of goodness-of-fit to the data. The technique has been employed to construct and test models of neural networks which mimic a class of responses observed in the cat vestibular nuclei in response to tilt, namely responses which show both a gain increase and progressive phase lag as the stimulation frequency goes from 0.01 to 2 Hz. A network consisting of a simple gain element in parallel with an inhibitory high-pass filtered version of the input provided a satisfactory fit to these data.

Animals↗
PubMed1984

Evoked potential techniques in the evaluation of visual function.

Visual evoked potentials (VEPs) can be used in a multitude of ways to assess the various levels of visual processing. The human visual system consists of multiple, parallel channels which process different information, and each channel constitutes a set of sequential processes. An algorithm of sequential steps that can be used to assess visual function is reviewed. The pathophysiology of retinal, anterior visual pathways and retrochiasmal pathways can be objectively evaluated by VEPs.

Adolescent↗
PubMed1996

Parallel hardware for sequence comparison and alignment.

Sequence comparison, a vital research tool in computational biology, is based on a simple O(n2) algorithm that easily maps to a linear array of processors. This paper reviews and compares high-performance sequence analysis on general-purpose supercomputers and single-purpose reconfigurable, and programmable co-processors. The difficulty of comparing hardware from published performance figures is also noted.

Algorithms↗
PubMed1997

Comparison of non parallel immunoassay curves resulting from mixtures of competing antigens.

Relative potency is a measure that has been used for many years to summarize the comparison of dose-response curves in parallel line bioassays. When response curves for two preparations are not parallel the traditional definition of relative potency no longer applies. We review the concept of relative potency and show that, in some situations, it can be given meaning for non-parallel curves as the ratio of biological activity in full strength assay preparations. Under an assumption that non-parallel curves result from the competition of mixtures of antigens for receptor binding sites, estimation of relative potency for non-parallel curves can be accomplished. We show that estimation of models for both parallel curve and response attenuation situations may be accomplished within the framework of generalized linear models. This estimation depends on the ability to deal with non-linear parameters appearing in the link function, and an iterative algorithm depending on direct parameter updates is outlined. The topics discussed are illustrated with the analysis of data from two immunoassays conducted with veterinary vaccines. The models developed here depend in an essential way on the assumption of response attenuation by competing antigens. Our methods may not be appropriate for non-parallel curves caused by other phenomena.

Algorithms↗
PubMed1991

Sample size estimation for comparing two or more treatment groups in clinical trials.

Methods for estimating required sample size for comparing two population means have been published. Most involve the use of complicated formulae and tables. These methods are limited to comparing two groups. Although techniques exist to determine sample sizes for comparing more than two groups, they are intrinsically far more complicated. A simple linear nomogram is proposed as a solution to these problems, and its use is illustrated with examples of parallel group, ordered parallel group and factorial designs.

Algorithms↗
PubMed1991

Asymmetric Boltzmann machines.

We study asymmetric stochastic networks from two points of view: combinatorial optimization and learning algorithms based on relative entropy minimization. We show that there are non trivial classes of asymmetric networks which admit a Lyapunov function L under deterministic parallel evolution and prove that the stochastic augmentation of such networks amounts to a stochastic search for global minima of L. The problem of minimizing L for a totally antisymmetric parallel network is shown to be associated to an NP-complete decision problem. The study of entropic learning for general asymmetric networks, performed in the non equilibrium, time dependent formalism, leads to a Hebbian rule based on time averages over the past history of the system. The general algorithm for asymmetric networks is tested on a feed-forward architecture.

Algorithms↗
PubMed1989

A two-dimensional pencil-beam algorithm for calculation of arc electron dose distributions.

A two-dimensional pencil-beam algorithm is presented for the calculation of arc electron dose distributions in any plane that is perpendicular to the axis of rotation. The dose distributions are calculated by modelling the arced beam as a single broad beam defined by the irradiated surface of the patient. The algorithm is two-dimensional in that the anatomical cross section of the patient and the skin collimators are assumed identical in parallel planes outside the plane of calculation. The broad beam is modelled as a collection of strip beams, each strip beam being characterised by its planar fluence, mean projected angular direction and a root-mean-square spread about the mean direction. Using these parameters, the dose distribution is calculated using pencil-beam theory. Examples of strip-beam parameters and resulting dose distributions for patient geometries are presented. Features of the algorithm, which include (1) incorporation of pencil-beam theory for the calculation of dose in heterogeneous tissue, (2) run times of only about twice that of comparable-sized fixed electron fields and (3) the input requirement of only a single depth dose and four off-axis dose profiles of measured data, make the algorithm practical for clinical use.

Algorithms↗
PubMed1994

Graded changes in the response of individual human basophils to stimulation: distributional behavior of early activation events.

These studies examine the distribution of single-cell responses in basophil preparations in the context of four events that may be associated with early activation by anti-immunoglobulin E (IgE) antibody and the bacterial peptide fMet-Leu-Phe (fMLP). In general, we measured the single-cell response distributions after challenge with a concentration of stimulus that resulted in an optimal response and compared this with the distribution that occurred after challenge with suboptimal concentrations of the same stimulus. The elevation in cytosolic calcium, as detected in Fura-2-labeled basophils, after challenge with anti-IgE or fMLP showed graded characteristics in that the distributions were unimodal under conditions of optimal or suboptimal challenge with little skewing from a normal distribution. Similarly, the up-regulation of the cell surface adhesion molecule CD11b, as determined by flow cytometry, showed graded unimodal increases after challenge with anti-IgE antibody at optimal and suboptimal concentrations. In addition, stimulation of basophils led to increased F-actin polymerization. After challenge with an optimal concentration of anti-IgE antibody, the F-actin content of basophils increased to a maximum between 10 and 15 min and returned to near prechallenge levels by 60 min. There was a close correlation between the maximum increase in F-actin content and histamine release regardless of the stimulus; anti-IgE antibody, fMLP, and phorbol ester (PMA) responses lay on the same regression line. The single-cell F-actin polymerization distributions were also unimodal and graded according to the magnitude of the histamine release response. During measurements of the calcium response under the microscope we noted that basophils underwent significant changes in morphology after challenge with any stimulus. These changes were related to both degranulation and nondegranulation events and could be quantitated by a series of image-processing algorithms, which are presented. The kinetics of the morphological change, measured as a change in cell perimeter, paralleled degranulation. Single-cell distributions of the morphologic changes were also unimodal under conditions of both optimal and suboptimal stimulation. Therefore, no evidence of all-or-nothing responses could be observed in the context of these four early activation events. In general, the response distributions resembled normal distributions at both optimal and suboptimal levels of stimulation, which indicated that single basophils responded in a graded manner.

Basophils↗
PubMed1996

Infrared spectroscopy of dystrophic mdx mouse muscle tissue distinguishes among treatment groups.

Four groups of mdx mice (deflazacort, high dose of 1.5 mg/kg and low dose of 0.75 mg/kg; prednisone, 1.0 mg/kg; and a placebo) were examined in a double-blind protocol. The experiments tested the hypothesis that infrared spectroscopy can distinguish among gastrocnemius muscle tissues derived from dystrophic animals (n = 22) from different treatment groups and from control muscle tissue (n = 23). Results showed that muscle, inflamed muscle, and tendon can be distinguished on the basis of their infrared absorption patterns. Distinctions among the spectra of the four treatment groups were sought with automated pattern-recognition methods. These classification methods, based either on spectral regions (900-1,500 cm-1) or on principal-component analysis, were in close agreement, assigning 15 or 16, respectively, of 22 mdx spectra to the correct treatment group. Both trials cleanly separated the high-dose deflazacort from the placebo group of muscles, whereas the prednisone and low-dose deflazacort groups were persistently confused in these classifications. Changes in the histology of muscle inflammation paralleled the spectral-classification results. Thus the proposed method, combining infrared spectroscopy with pattern-recognition algorithms, can distinguish treatment effects on muscle tissue. Specific spectral features characteristic of tissue type, disease progression, and treatment effects are not yet elucidated.

Algorithms↗
PubMed1987

High-resolution CT of the wrist: initial experience with scaphoid disorders and surgical fusions.

We performed high-resolution CT scans on 30 wrists in 27 patients with either previous surgical intercarpal fusion or known or suspected scaphoid abnormalities. Most examinations used the same protocol: contiguous 1.5-mm axial sections parallel to the long axis of the body of the scaphoid, small reconstruction circle, and bone reconstruction algorithm. Fifteen patients were evaluated for union of previous surgical carpal fusions; eight patients were evaluated for healing of scaphoid fractures; and the other four patients had miscellaneous disorders, including a midcarpal dislocation with a scaphoid fracture. High-resolution CT clearly showed whether the carpal fusions were united. In addition, metallic fixation devices were easy to locate and did not significantly degrade image quality. Osseous union of healing scaphoid fractures was reliably assessed. We conclude that high-resolution CT of the wrist is a useful method for evaluating surgical carpal fusions and various disorders of the scaphoid.

Arthrodesis↗
PubMed1995

Multimedic system for telepathology and interdisciplinary councils between doctors and various hospitals.

At present, the exchange of information between clinicians and pathologists are limited to mail, telefax and telephone. The bi-directional video communication using at least two digitized phone lines (ISDN) is an additional medium for video-conference and for image exchange. The MECOM system (Medical Communication) has been set up in the department of pathology of Aixla-Chapelle Hospital (Germany) and has routinely used for two years between 4 local hospitals. Now it is mainly used for staff discussions between pathologists and practitioners involved in different oncological fields. Mecom can transmit any kind of high resolution images (x rays films, scanner images, histologic slides...) which are useful or necessary during medical staff discussions. This system requires only two phone lines to be operative. However it can turn on up to twelve parallel ISDN lines which allow to transmit 768 kbytes/sec. It manages the SG3, HVQ and H320 compression algorithms and allows the transmission of still images at a resolution varying from 256/240 to 512/480 pixels. Mecom is a modulable system which adapts to the needs. It has the following advantages. Emergency inter-disciplinary conferences. Real time images, discussion between a pathologist and an expert to confirm histo-pathological diagnosis. Abolition of distances. That is specially useful or necessary in countries with low medical population and poor transportation network.

Computer Communication Networks↗
PubMed1992

Deblurring of 3-dimensional patterns of evoked rat cerebellar cortical activity: a study using voltage-sensitive dyes and optical sectioning.

One of the benefits of imaging neuronal activity is the capability of resolving spatial patterns in the x-y plane. With optical sectioning microscopy, the 3-dimensional (3-D) structure may also be studied without physical deformation by serially moving the focal plane of the microscope through the volume of interest along the focal axis. However, each image is blurred by contributions from neighboring planes. This degradation is most severe for low numerical aperture lenses and large amounts of defocus. In this study, an image restoration method using the optical properties of an aberration-free, defocused optical system has been developed for improving optical signals from voltage-sensitive dyes. Deblurring based on the optical transfer function (OTF) of the system was applied on two test sets of serially sectioned images: (1) fluorescent beads and (2) in vivo rat cerebellar cortex stained with the voltage-sensitive dye RH795. This method was shown to reduce significantly the out-of-focus contribution to the images, improving the spatial resolution not only in the x-y plane, but also the z axis. The algorithms were then applied to optical signals obtained by stimulation of the cerebellar surface. Optical signals having a distinct beam-like pattern were evoked and recorded over depths ranging from 0 to 300 microns prior to deblurring. Application of the deblurring algorithm reduced the depth of cerebellar cortex over which the optical signals were observed. In agreement, field potential recordings of the evoked parallel fiber volley and post-synaptic components were restricted to a narrow range of depths similar to the deblurred optical images. Removal of out-of-focus information is an essential step in the serial sectioning of central nervous system structures for neuronal imaging and 3-D reconstruction.

Algorithms↗
PubMed1994

Protein design by optimization of a sequence-structure quality function.

An automated procedure for protein design by optimization of a sequence-structure quality has been developed. The method selects a statistically optimal sequence for a particular structure, on the assumption that such a protein will adopt the desired structure. We present two optimization algorithms: one provides an exact optimization while the other uses a combinatorial technique for comparatively rapid results. Both are suitable for massively parallel computers. A prototype system was used to design sequences which should adopt the four-helix bundle conformation of myohemerythrin. These appear satisfactory to secondary structure and profile analysis. Detailed inspection reveals that the sequences are generally plausible but, as expected, lack some specific structural features. The design parameters provide some insight into the general determinants of protein structure.

Algorithms↗