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At least 163 records · Page 9Linked to original sources

PubMed1993

Use of running fractal dimension for the analysis of changing patterns in electroencephalograms.

Running fractal dimensions were measured on four channels of an electroencephalogram (EEG) recorded from a normal volunteer. The changes in the background activity due to eye closure were clearly differentiated by the fractal method. The compressed spectral array (CSA) and the running fractal dimensions of the EEG showed corresponding changes with respect to change in the background activity. The fractal method was also successful in detecting low amplitude spikes and the changes in the patterns in the EEG. The effects of different window lengths and shifts on the running fractal dimension have also been studied. The utility of fractal method for EEG data compression is highlighted.

Alpha Rhythm↗

PubMedDate not supplied

Radiological image compression using full-frame cosine transform with adaptive bit-allocation.

We report a new bit-allocation scheme based on the full-frame cosine transform for radiological image compression. The new technique differs from a previously reported method in its use of a two-dimensional bit-allocation table to encode the compression data. This allows for an improved treatment of high frequency components in the transform domain. Consequently, it has the capability of faithfully reproducing limited numbers of high-contrast sharp edges in the image. Previously reported artifacts, induced in the reconstructed image by sharp edges in the original, have been eliminated. Experiments with 10 radiological chest images show almost no perceivable degradation in the reconstructed image at compression ratios below 10:1. Image quality at a fixed compression ratio is, in every case, comparable or superior to results using the old method. Furthermore, the new algorithm lends itself to hardware implementations that are both simple and fast.

Algorithms↗

PubMed1986

Toward computerized morphometric facilities: a review of 58 software packages for computer-aided three-dimensional reconstruction, quantification, and picture generation from parallel serial sections.

This review gives an inventory of 58 computer-aided three-dimensional reconstruction applications in the domain of biomedical research. It is devoted to the formulation of a set of recommendations thought to be necessary for improved performance of software packages in this field. These recommendations can be used to select packages and to guide future developments of existing reconstruction systems. The survey is restricted to three-dimensional reconstructions based upon a series of parallel sections of an object. Subjects treated are programming languages, resolution and sampling, input preparation, realignment, local deformation of slices, numerical quantifications, topological complexity, internal representation, display complexity (hidden surfaces, shading, smoothing), structure extraction, descriptive elements, database, data compression, time efficiency of systems and algorithms, hardware configuration, input devices, input media, interactive aids, display devices, and output devices. Information for this survey comes from articles that appeared between 1965 and 1985.

Computers↗

PubMedDate not supplied

Selective archiving of radiologic images.

The increasing number of radiographic images is a problem in most radiology departments. The problem will be emphasized with the introduction of digital acquisition and storage of radiographs. Changes in image management strategies will therefore become necessary. Such strategies will have great technologic and financial impact and will probably determine the applicability and success of digital radiography. Based on the experience that not all radiographs are equally important and on the assumption that not every image in a radiology archive can be maintained on-line, we investigated the effect of storing only selected, clinically informative radiographs; i.e., clinical data compression. In 165 routine examinations (77 barium enemas, 16 barium meals and 72 urographies) 2433 films were used (14.7 films per examination). We archived only the 461 films (19%) which were considered to be of future informative value. During a one-year follow-up period none of the 1972 removed films was requested. This indicates that a considerable number of films and a considerable amount of image data can be removed from the archive without affecting the clinical work.

Humans↗

PubMed1993

Discovering simple DNA sequences by the algorithmic significance method.

A new method, 'algorithmic significance', is proposed as a tool for discovery of patterns in DNA sequences. The main idea is that patterns can be discovered by finding ways to encode the observed data concisely. In this sense, the method can be viewed as a formal version of the Occam's Razor principle. In this paper the method is applied to discover significantly simple DNA sequences. We define DNA sequences to be simple if they contain repeated occurrences of certain 'words' and thus can be encoded in a small number of bits. Such definition includes minisatellites and microsatellites. A standard dynamic programming algorithm for data compression is applied to compute the minimal encoding lengths of sequences in linear time. An electronic mail server for identification of simple sequences based on the proposed method has been installed at the Internet address pythia/anl.gov.

Algorithms↗

PubMed1987

Data collection and analysis from a respiratory inductance plethysmograph.

A respiratory inductance plethysmograph, Respitrace, was used to assess the respiratory effects of narcotic analgesia for the first 24 hours after surgery. Data were collected on-line from the plethysmograph with an Apple][+ microcomputer and stored on disc for later analysis of respiratory rates and tidal volumes, and also periods of central or obstructive apnoea using the difference in phase angle between the abdominal and respiratory components. This involved the measurement of, on average, more than 20,000 breaths per patient and techniques of data compression were required to store this amount of information on a single floppy disc. Frequent nursing interventions reduced the accuracy of tidal volume and phase angle measurements, but respiratory rates were obtained accurately breath by breath.

Calibration↗

PubMedDate not supplied

Endoscopic surgery teleconferencing.

Modern telecommunication allowing the transmission of digitalized voice and images through telephone lines has expanded to medicine. The Integrated Digital Network System (ISDN) can be used to transmit 128 kbit/sec (ISDN-2) to 2 Mbit/sec (ISDN-30). Together with smart compression techniques a teleconferencing system can be implemented to transmit images of an endoscopic operation. In this paper 2 such experiments are described. In the first experiment a laparoscopic cholecystectomy performed in the Netherlands is followed at the same time by surgeons in Hawaii through ISDN-2 lines. In the second experiment a laparoscopic hernia repair was followed in Orlando during a congress using ISDN-6 lines. The images sent over the ISDN-2 lines are rather blurry with rapid movement. The images over the ISDN-6 lines were more acceptable. Data compression and decompression results in a time delay of approximately 1 second, which seems not disturbing during the connection. The cost of communication is comparable to telephone communication, which makes this form of telecommunication feasible in surgical practice.

Algorithms↗

PubMed1988

An interactive multivariate analysis of FCM data.

The procedure and results of the interactive multivariate analysis of FCM data are described. Using principal-components analysis, cluster analysis, and interactive maneuvers, this procedure facilitates an effective data compression from a four-dimensional space into two-dimensional space, then allows cluster separation. The procedure is especially effective for separating clusters, which are degenerated in the usual scattergrams. Programs were mostly written in C language on MS-DOS and were tested on four-dimensional analysis of the blood cells, which resulted in a successful separation of the degenerated clusters.

Cell Separation↗

PubMedDate not supplied

A cryptologic based trust center for medical images.

OBJECTIVE: To investigate practical solutions that can integrate cryptographic techniques and picture archiving and communication systems (PACS) to improve the security of medical images. DESIGN: The PACS at the University of California San Francisco Medical Center consolidate images and associated data from various scanners into a centralized data archive and transmit them to remote display stations for review and consultation purposes. The purpose of this study is to investigate the model of a digital trust center that integrates cryptographic algorithms and protocols seamlessly into such a digital radiology environment to improve the security of medical images. MEASUREMENTS: The timing performance of encryption, decryption, and transmission of the cryptographic protocols over 81 volumetric PACS datasets has been measured. Lossless data compression is also applied before the encryption. The transmission performance is measured against three types of networks of different bandwidths: narrow-band Integrated Services Digital Network, Ethernet, and OC-3c Asynchronous Transfer Mode. RESULTS: The proposed digital trust center provides a cryptosystem solution to protect the confidentiality and to determine the authenticity of digital images in hospitals. The results of this study indicate that diagnostic images such as x-rays and magnetic resonance images could be routinely encrypted in PACS. However, applying encryption in teleradiology and PACS is a tradeoff between communications performance and security measures. CONCLUSION: Many people are uncertain about how to integrate cryptographic algorithms coherently into existing operations of the clinical enterprise. This paper describes a centralized cryptosystem architecture to ensure image data authenticity in a digital radiology department. The system performance has been evaluated in a hospital-integrated PACS environment.

Algorithms↗

PubMed1991

Circular harmonic averaging of rotary-shadowed and negatively stained creatine kinase macromolecules.

The structure of mitochondrial creatine kinase is investigated by high-resolution shadowing at very low temperature and conventional negative staining. The electron microscopic images are analyzed with circular harmonic averaging, a method suited for the processing of single molecules. The rotational alignment and averaging is performed with the circular harmonic components, which allows data compression and several steps of noise reduction to be carried out within the averaging procedure. In addition, the symmetry can be deduced. For the mitochondrial creatine kinase, a fourfold symmetry is found that is compatible with the biochemical and biophysical characterization of the molecule.

Creatine Kinase↗

PubMedDate not supplied

Structure of Lumbricus terrestris hemoglobin at 30 A resolution determined using angular reconstitution.

The three-dimensional (3D) structure of the giant hemoglobin of the common earthworm Lumbricus terrestris was determined from cryomicroscopical images of a vitrified molecular solution. From about 5000 molecular images, the best-fit 3D structure was calculated using recently developed analysis techniques. Multivariate statistical analysis data compression and automatic classification were used to find the characteristic projection images of the oligomer. The angular reconstitution approach was then applied to find the Euler angle orientations of these characteristic views. The Lumbricus hemoglobin molecule has an overall D6 (622) point-group symmetry and is found to have a local threefold symmetry axis within the 1/12th subunit. This additional symmetry appears to predict the presence of 36 abcd globin tetramers in the Lumbricus hemoglobin or a total of 144 heme chains for the whole oligomer. A distinct doughnut-shaped structure is elucidated in the center of the molecule. This central subunit, representing around 10% of the protein volume, may consist of non-heme-containing linker chains found generally in giant annelid hemoglobins.

Animals↗

PubMed1991

Flexibility of globular proteins in water as revealed by compressibility.

In order to elucidate the flexibility-structure-function relationships of proteins, the adiabatic compressibility of about 30 globular proteins, including food proteins, was determined by means of sound velocity and density measurements in aqueous solutions. Most proteins studied showed positive compressibility, indicating the large internal flexibility of the molecules. The volume fluctuation was in the range of 30-200 ml/mol, which corresponded to about 0.3% of the total protein volume. From the statistical analyses of the compressibility data, it was found that the flexibility of proteins is closely related to structural factors such as hydrophobicity, helix element, and amino acid composition, and to functional properties such as digestibility and foaming capacity. These results indicate that the dynamics of protein structure should be taken into account in predicting precisely the functions and properties of a protein from its primary or tertiary structure.

Amino Acids↗

PubMed1988

Auto-association by multilayer perceptrons and singular value decomposition.

The multilayer perceptron, when working in auto-association mode, is sometimes considered as an interesting candidate to perform data compression or dimensionality reduction of the feature space in information processing applications. The present paper shows that, for auto-association, the nonlinearities of the hidden units are useless and that the optimal parameter values can be derived directly by purely linear techniques relying on singular value decomposition and low rank matrix approximation, similar in spirit to the well-known Karhunen-Loève transform. This approach appears thus as an efficient alternative to the general error back-propagation algorithm commonly used for training multilayer perceptrons. Moreover, it also gives a clear interpretation of the rôle of the different parameters.

Mathematics↗

PubMed1991

The application of delta modulation to EEG waveforms for database reduction and real-time signal processing.

The large volume of digital data and the demanding processing task involved in electroencephalogram (EEG) analysis place stringent requirements on computer resources in terms of data transfer, computation speed, and temporary or permanent storage. The reduction of the database to a manageable size is therefore necessary for economical use of transmission channels and the storage media. The two criteria, waveform reproducibility and processing applications, must be analyzed and optimized in terms of signal-to-noise ratio (SNR) using the various factors affecting the coding. This analysis and optimization can become cumbersome, and a specialized workstation has been developed specifically for analysis of digital coding. Our interest in data compression stems from the study of the feasibility of predicting pilots' acceleration (Gz) tolerance during flight by processing both their uncoded and coded EEG.

Aerospace Medicine↗

PubMed1991

Management and clinical utilization of computed tomography, magnetic resonance imaging, and angiography in Hokkaido University Hospital picture archiving and communication system.

We made a preliminary assessment of the Hokkaido University picture archiving and communication system (HU-PACS). Data access time from either imaging machines or data base to workstations was 1.5 minutes, which is great benefit for data communication in routine examinations. Image quality of the work station was estimated in terms of brain computed tomography (CT) and digitized cerebral angiograms. Cerebral infarction was definitely observed on the cathode-ray tube (CRT) monitor of the work station. Although the picture quality of CRT was acceptable, we had to manipulate window level and width for CRT diagnosis of cerebral angiography. Data compression was routinely used without significant degradation of those image quality. Nevertheless, further improvement of maneuverability of the workstation should be considered.

Angiography, Digital Subtraction↗

PubMed1997

Neural networks in higher levels of abstraction.

Existing artificial neural network models are not very successful in understanding or generating natural language texts. Therefore it is proposed to design novel neural network structures in higher levels of abstraction. This concept leads to a hierarchy of network layers which extract and store local details in every layer and transfer the remaining nonlocal context information to higher levels. At the same time data compression is provided from layer to layer. The use of the same network elements (meta-words) in higher levels for different word series in the basis level is introduced and discussed for grammatical identity or similarity. Thus text can be compressed to forms which are almost free of redundancy. Possible applications are storage, transmission, understanding, generating and translation of texts.

Cybernetics↗

PubMed1986

High pressure volumetric measurements in dipalmitoylphosphatidylcholine bilayers.

The one previously reported high pressure volumetric experiment on a phospholipid bilayer investigated a region of pressure between 0 and 25 MPa and obtained isothermal compressibility values for the liquid crystal and intermediate phases which differed by more than a factor of ten. We report new volumetric measurements around the main transition in dipalmitoylphosphatidylcholine (DPPC) from 0 to 100 MPa. The isothermal compressibility data for the two phases are of the same order of magnitude, and the experimentally determined coexistence curve, specific volume dependence, and volume discontinuity values are compared with the predictions of the phenomenological theory according to Sugar and Tarjan ((1982) Sov. Phys. Crystallogr. 27, 4-5). Significant discrepancies between this theory and experiment are found. Finally, the data indicate that steric interactions play a more dominant role in the main transition of phospholipid bilayers than in transitions in most thermotropic liquid crystals.

Atmospheric Pressure↗

PubMed1979

A computer feedback system for clinical research.

This paper presents a computerized data base management and information retrieval system for a heroin addiction research clinic, which has potential application for any type of clinical research. It describes data input checking programs, file structures, and output programs. The system contains several interesting features: built-in feedback error detection and correction; patient month matrix formatting and data compression; and a virtual blocking system to reduce the size of the files.

Computers↗