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PubMed1998

Distributed parallel processing for multidimensional maximum entropy reconstruction.

We have developed a two-dimensional maximum entropy spectrum reconstruction program designed to run in parallel on workstation clusters. Test reconstructions of planes extracted from a three-dimensional NMR data set indicate that the parallel speedup is nearly equal to the number of processors provided that the individual processors have comparable performance and that there are at least as many planes as processors. The program also works well in a typical laboratory setting consisting of heterogeneous workstations.

Algorithms↗
PubMedDate not supplied

MR volumetry for monitoring intramuscular bromocriptine treatment in macroprolactinomas.

OBJECTIVE: To assess volumetric changes of pituitary prolactinomas, we applied a threshold-based segmentation algorithm in two patients during intramuscular bromocriptine treatment. MATERIALS AND METHODS: Tumor volumes were calculated from contiguous slices of a 3D GE sequence and from conventional SE images. RESULTS: After a single 50 mg i.m. bromocriptine administration, the prolactinoma volumes decreased by 25 and 35% within 7 and 11 days, respectively. Volume calculations from 3D GE images were more accurate than calculations from 3 mm 2D SE images, especially for smaller tumors. A decrease of prolactinoma size was paralleled by a decrease of serum prolactin levels and correlated with an improvement of visual field and endocrine function in both patients. The end of the bromocriptine effect was indicated by a reincreasing tumor volume, which was observed after 30 days in the first patients and after 43 days in the second patient. CONCLUSION: Our results suggest that MR volumetry represents a useful tool to monitor changes of prolactinoma volume during bromocriptine treatment and may improve the clinical management of these patients.

Adult↗
PubMed1999

Single- and multifrequency models for bioelectrical impedance analysis of body water compartments.

The 1994 National Institutes of Health Technology Conference on bioelectrical impedance analysis (BIA) did not support the use of BIA under conditions that alter the normal relationship between the extracellular (ECW) and intracellular water (ICW) compartments. To extend applications of BIA to these populations, we investigated the accuracy and precision of seven previously published BIA models for the measurement of change in body water compartmentalization among individuals infused with lactated Ringer solution or administered a diuretic agent. Results were compared with dilution by using deuterium oxide and bromide combined with short-term changes of body weight. BIA, with use of proximal, tetrapolar electrodes, was measured from 5 to 500 kHz, including 50 kHz. Single-frequency, 50-kHz models did not accurately predict change in total body water, but the 50-kHz parallel model did accurately measure changes in ICW. The only model that accurately predicted change in ECW, ICW, and total body water was the 0/infinity-kHz parallel (Cole-Cole) multifrequency model. Use of the Hanai correction for mixing was less accurate. We conclude that the multifrequency Cole-Cole model is superior under conditions in which body water compartmentalization is altered from the normal state.

Adult↗
PubMed1986

Apparent response incompatibility effects on P3 latency depend on the task.

Ten young women were tested with an ERP paradigm that used the words 'left,' 'right,' 'LEFT,' 'RIGHT' as stimuli. The stimulus sequence was presented as several separate runs with varying response instructions. Subjects were instructed to respond according to the meaning of the stimulus in the (WORD task), to the case in which the stimulus was written (CASE task), or to both the case and meaning of the stimulus (CASE/WORD) task. In each task, half the trials called for a response that was incompatible with the stimulus. For the WORD task, compatible and incompatible trials were presented as separate blocks of trials. For all 3 tasks an additional stimulus sequence was presented in which the words were degraded with superimposed visual random noise. Reaction time (RT) in the CASE/WORD task was more than 100 msec later than in the other tasks. In the WORD and CASE/WORD tasks, RT was delayed more than 100 msec when the response was incompatible with the stimulus. Degrading the stimulus additionally delayed RT by about 100 msec. In the WORD and CASE tasks, error RTs were earlier than correct RTs. P3 latency was measured with a single-trial latency adjustment algorithm. P3 latency was delayed in the CASE/WORD task compared to the other 2 tasks. P3 was delayed by degrading the stimuli. Contrary to some previous reports, P3 was delayed by about 70 msec when incompatible responses were required, but only in the WORD task. Taken together with error and RT data, these P3 latency data are consistent with the notion that the task causes subjects to adopt different strategies and hence different types of processing (i.e., serial vs. parallel). Depending on the type of processing, P3 may appear to be affected by response incompatibility.

Adult↗
PubMed1981

Seven-pinhole tomography--a technical description.

A single-photon emission tomography system was developed and studied. Based upon a seven-pinhile-collimated Anger camera, interfaced to a digital minicomputer, this imaging configuration yielded seven independent, nonoverlapping projection images of the radioactivity in a commonly viewed volume. The computer was used to implement an iterative algorithm that processed these projections to yield a three-dimensional reconstruction of the soruce distribution. The algorithm provudes a nonlinear first approximation to the reconstruction, then use a single iteration technique to reduce errors resulting from that approximation. Point spread functions (PSF) at various distances from the collimator face, and point-source sensitivity (PSS) at a location in the middle of the reconstruction volume were determined. The system was used for thallium-201 imaging, where it was shown to reduce imaging time and increase sensitivity without loss in specificity when compared with standard parallel-hole-collimated imaging. Seven-pinhole tomography is a practical three-dimensional imaging system that has been demonstrated to be useful in the emission cardiology setting.

Heart↗
PubMed1998

Measurement-based evaluation of optical pathlength distributions reconstructed from simulated differential interference contrast images.

Recently a method was presented for reconstructing optical pathlength distributions (OPDs) from images of weak phase objects obtained by a conventional differential interference contrast (DIC) microscope. A potential application of this technique is the determination of the mass of biological objects: by integrating the optical pathlength over the projected surface of the image of an object, a measure of the dry mass, i.e. the total mass of all solid constituents present in the object, is obtained. To assess the possibilities of DIC microscopy for this application, simulations were performed on computer-generated DIC images of objects of various sizes, shapes and orientation angles. After reconstructing the OPDs from these images, the integrated optical pathlength of each of the test objects was determined, and compared with the expected results. The parameter settings used in the reconstruction algorithm were found to be very important in obtaining a reliable measurement. Using optimal parameter settings, errors in the integrated OPD could be limited to a few per cent for circular objects within the investigated size range. For non-circular objects, however, the orientation angle of the object relative to the lateral shift was found to influence the measured values. Ellipses with their long axes perpendicular to the shift direction had a significantly higher integrated OPD than ellipses orientated parallel to the shift. By adjusting the reconstruction parameters the effect could be limited, but complete elimination of the artefact was not possible within the parameter range investigated.

Journal Article↗
PubMed1996

Analysis of domain structural class using an automated class assignment protocol.

The extent to which the contemporary dataset of protein structures can be segregated into four structural "classes" as originally defined by Levitt & Chothia in 1976 is examined and a simple method presented for the assignment of protein domains into these classes. Assignments are based on known three-dimensional structures, and for successful assignment it was found that helix/sheet content, contacts between secondary structures and their sequential order had to be used. The procedure attempts to maximise the automatic separation into classes for a dataset of 197 manually classified, non-homologous domains. It was found that approximately 90% of the structures were classified automatically; the remainder were borderline and were left for manual inspection. The method was then applied to a test set of 43 protein domains with similar results. The data support the concept of distinct classes of protein structure, although a few intermediate structures are found, demonstrating that it is possible to define relatively simple parameters complying with commonly accepted nomenclature that automatically define 90% of protein domains with essentially 100% accuracy. However, re-examination of the data also suggested that the previously separate alpha/beta and alpha + beta classes show considerable overlap and are more naturally represented as a single alpha beta class. This large alpha beta class can then be most easily subdivided by consideration of whether the sheets are mainly parallel, antiparallel or mixed. The correlation between structural class and function is discussed, together with the conservation of class within a sequence superfamily. This represents the first step in an automated phenetic description of protein structure complementing the usual phylogenetic approach to protein structure classification.

Algorithms↗
PubMed1984

Control of complex motor gestures: orofacial muscle responses to load perturbations of lip during speech.

The contribution of ascending afferents to the control of speech movement was evaluated by applying unanticipated loads to the lower lip during the generation of combined upper lip-lower lip speech gestures. To eliminate potential contamination due to anticipation or adaptation, loads were applied randomly on only 10-15% of the trials. Physical characteristics of the perturbations were within the normal range of forces and movements involved in natural lip actions for speech. Compensatory responses in multiple facial muscles and lip movements were observed the first time a load was introduced, and achievement of the multimovement speech goals was never disrupted by these perturbations. Muscle responses were seen in the lower lip muscles, implicating corrective, feedback processes. Additionally, compensatory responses to these lower lip loads were also observed in the independently controlled muscles of the upper lip, reflecting the parallel operation of open-loop, sensorimotor mechanisms. Compensatory responses from both the upper and lower lip muscles were observed with small (1 mm) as well as large (15 mm) perturbations. The latencies of these compensatory responses were not discernible by conventional ensemble averaging. Moreover, responses at latencies of lower brain stem-mediated reflexes (i.e., 10-18 ms) were not apparent with inspection of individual records. Response latencies were determined on individual loaded trials through the use of a computer algorithm that took into account the variability of electromyograms (EMG) among the control trials. These latency measures confirmed the absence of brain stem-mediated responses and yielded response latencies that ranged from 22 to 75 ms. Response latencies appeared to be influenced by the time relation between load onset and the initiation of muscle activation. Examination of muscle activity changes for individual loaded trials revealed complementary variations in the magnitude of responses among multiple muscles contributing to a movement compensation. These observations may have implications for limb movement control if multimovement speech gestures are considered analogous to a limb action requiring coordinated movements around multiple joints. In this context, these speech motor control data might be interpreted to suggest that for complex movements, both corrective feedback and open-loop predictive processes are operating, with the latter involved in the control of coordination among multiple movement subcomponents.

Electromyography↗
PubMed1995

Pruning of rat cortical taste neurons by an artificial neural network model.

1. Taste qualities are believed to be coded in the activity of ensembles of taste neurons. However, it is not clear whether all neurons are equally responsible for coding. To clarify the point, the relative contribution of each taste neuron to coding needs to be assessed. 2. We constructed simple three-layer neural networks with input units representing cortical taste neurons of the rat. The networks were trained by the back-propagation learning algorithm to classify the neural response patterns to the basic taste stimuli (sucrose, HCl, quinine hydrochloride, and NaCl). The networks had four output units representing the basic taste qualities, the values of which provide a measure for similarity of test stimuli (salts, tartaric acid, and umami substances) to the basic taste stimuli. 3. Trained networks discriminated the response patterns to the test stimuli in a plausible manner in light of previous physiological and psychological experiments. Profiles of output values of the networks paralleled those of across-neuron correlations with respect to the highest or second-highest values in the profiles. 4. We evaluated relative contributions of input units to the taste discrimination of the network by examining their significance Sj, which is defined as the sum of the absolute values of the connection weights from the jth input unit to the hidden layer. When the input units with weaker connection weights (e.g., 15 of 39 input units) were "pruned" from the trained network, the ability of the network to discriminate the basic taste qualities as well as other test stimuli was not greatly affected. On the other hand, the taste discrimination of the network progressively deteriorated much more rapidly with pruning of input units with stronger connection weights. 5. These results suggest that cortical taste neurons differentially contribute to the coding of taste qualities. The pruning technique may enable the evaluation of a given taste neuron in terms of its relative contribution to the coding, with Sj providing a quantitative measure for such evaluation.

Animals↗
PubMed1990

On the control of automatic processes: a parallel distributed processing account of the Stroop effect.

Traditional views of automaticity are in need of revision. For example, automaticity often has been treated as an all-or-none phenomenon, and traditional theories have held that automatic processes are independent of attention. Yet recent empirical data suggest that automatic processes are continuous, and furthermore are subject to attentional control. A model of attention is presented to address these issues. Within a parallel distributed processing framework, it is proposed that the attributes of automaticity depend on the strength of a processing pathway and that strength increases with training. With the Stroop effect as an example, automatic processes are shown to be continuous and to emerge gradually with practice. Specifically, a computational model of the Stroop task simulates the time course of processing as well as the effects of learning. This was accomplished by combining the cascade mechanism described by McClelland (1979) with the backpropagation learning algorithm (Rumelhart, Hinton, & Williams, 1986). The model can simulate performance in the standard Stroop task, as well as aspects of performance in variants of this task that manipulate stimulus-onset asynchrony, response set, and degree of practice. The model presented is contrasted against other models, and its relation to many of the central issues in the literature on attention, automaticity, and interference is discussed.

Attention↗
PubMed1987

Deformation analyses in cell and developmental biology. Part II--Mechanical experiments on cells.

This study employs the finite element approach developed in Part I to analyze mechanical experiments on cells. It views cells as axisymmetric membrane structures containing a body of incompressible material, and models the mechanical contact between a cell and the loading apparatus by a contact algorithm. Since the method is valid for analyzing axisymmetric shell-like bodies with arbitrary shapes, it treates various mechanical experiments on cells in a unified manner. For demonstration purposes, three commonly used mechanical experiments on cells are considered; the compression experiment; the suction (micropipette aspiration) experiment; and the magnetic particle experiment. Based on an estimate of the mechanical property data for unfertilized sea urchin eggs, this analysis method predicts the responses for all three experiments using the same assumptions and approximations. This parallel treatment gives a broad basis for data correlation with experiments. The method also provides insights into mechanical experiments not offered by other approximate methods. For example, it gives the distributions of tensions and stretches on the cell cortex, and suggests the role of friction in the suction experiment.

Animals↗
PubMed1994

Operations research survey and computer simulation of waiting times in two medical outpatient clinic structures.

Outpatient services are increasingly recognised as an important component of health care provision and may be improved through the application of modern management techniques. We have performed a time and role audit of consultation and waiting times in two medical clinics using different queuing systems: namely, a serial processing clinic where patients wait in a single queue and a quasi-parallel processing clinic where patients are directed to the shortest queue to maintain clinic flow. Data collected were used to construct a computer simulation of patient flows in clinic. Assessment of patient satisfaction in the clinic process was determined using a self-administered questionnaire. Mean waiting time was shorter in the quasi-parallel processing clinic: 26 (SD 17) minutes compared with 36(24) minutes in the serial processing clinic. In the serial processing clinic 61% of patients waited more than 30 minutes compared with 41% in the quasi-parallel processing clinic. In the serial processing clinic 8% of 142 patients surveyed complained of the time spent waiting. The computer simulation we produced was able to determine waiting times with different clinic structures. The simulation showed that reductions in waiting time up to 30% might be achieved by changing our serial processing clinic to a quasi-parallel processing one. Performance of medical outpatient clinics can be improved by examining and changing clinic management. Computer simulation of outpatient clinics offers a means of assessing the impact of such changes on waiting time in clinic and on waiting lists.

Algorithms↗
PubMed1989

Frequency domain analysis of contrast echocardiographic images.

Sequences of echocontrastographic images of the dog's myocardium are analysed in the frequency domain for the identification of underperfused areas. Owing to the fact that echo images are contaminated by noise and artifacts, we have applied filtering techniques based on Fourier's methods in sequences of raw frames recorded during perfusion with a contrast agent. Thus we have been able to assess correctly the spatial and temporal distribution of the contrast, i.e. the agent kinetics which parallel the distribution of coronary blood flow, in terms of the time necessary for the flow gradient to reach its maximum value, and to describe such a distribution by a functional image obtained by means of an original procedure.

Algorithms↗
PubMedDate not supplied

Concept for an intelligent anaesthesia EEG monitor.

Considering the fundamental difficulties to define the term 'depth of anaesthesia', a more feasible concept for assessment of 'adequacy of anaesthesia' will be explained. The basic requirements for a monitoring index are definite response, gradual scaling and independence from the anaesthetic technique used. Additionally the index should be predictive for appearance of clinical signs of an inadequate anaesthesia. Different signal-processing methods will be discussed to extract the relevant information from both the spontaneous and the evoked brain electrical activity. In this context well established methods like spectral analysis are investigated in combination with new and more sophisticated methods like bispectral analysis or wavelet decomposition. Since no single-parameter index has been defined for monitoring depth of anaesthesia, a set of EEG parameters may be more useful to take into account intra- and interindividual variability. In parallel to the description of the monitor concept, the investigation of neural nets and fuzzy techniques, in addition to or in substitution of conventional statistical methods, will be introduced. Examples are given for data quality assessment, parameter extraction and re-classification.

Algorithms↗
PubMed1999

Reliability of measurement of muscle fiber conduction velocity using surface EMG.

Cross-correlating two surface EMG signals detected at two different locations along the path of flow of action potential enables the measurement of the muscle fiber average conduction velocity in those active motor units monitored by the electrodes. The position of the peak of the cross-correlation function is the time delay between the two signals and hence the velocity may be deduced. The estimated velocity using this technique has been observed previously to depend on the location of the electrodes on the muscle surface. Different locations produced different estimates. In this paper we present a measurement system, analyze its inherent inaccuracies and use it for the purpose of investigating the reliability of measurement of conduction velocity from surface EMG. This system utilizes EMG signals detected at a number of locations on the biceps brachii, when under light tension, to look for any pattern of variations of velocity as a function of location and time. It consists of a multi-electrode unit and a set of eight parallel on-line correlators. The electrode unit and the parallel correlators ensure that these measurements are carried out under the same physical and physiological conditions of the muscle. Further, the same detected signals are used in different measurement configurations to try to understand the reasons behind the observed variations in the estimated velocity. The results obtained seem to suggest that there will always be an unpredictable random component superimposed on the estimated velocity, giving rise to differences between estimates at different locations and differences in estimates with time at the same location. Many factors contribute to this random component, such as the non-homogeneous medium between the muscle fibers and the electrodes, the non-parallel geometry and non-uniform conduction velocity of the fibers, and the physical and physiological conditions of the muscle. While it is not possible to remove this random component completely from the measurement, the user must be aware of its presence and how to reduce its effects.

Action Potentials↗
PubMed1992

Bacterial monitoring in vials using a spectrophotometric assimilation method.

Aseptic-filling processes are often used with fragile parenteral products that might be destroyed by terminal autoclaving. However, aseptic filling is not as effective as autoclaving in reducing contamination. As a result, time-consuming microbiological methods and turbidimetry are employed currently as product inspection techniques, but these processes can destroy the product and might not detect low levels of contamination. Thus, near-infrared (IR) light scattering was evaluated in this study as a new method for determining low levels of contamination noninvasively and nondestructively. A new parallel mathematical technique was used in conjunction with near-IR spectrophotometry to detect successfully contamination by several species of bacteria through intact glass vials. Using the near-IR method, products can be evaluated without introducing contamination, preserving the sample vial for dispensing or evaluation by another method.

Algorithms↗
PubMed1995

Laser profiling: a technique for the study of prosthetic heart valve leaflet motion.

A detailed understanding of the stresses and strains developed in functioning flexible-leaflet valves is necessary if a durable, non-thrombogenic heart valve replacement is to be realized. A new experimental tool, laser profiling, is presented for the study of flexible-leaflet heart valve dynamics. Profiles of moving leaflet surfaces are obtained by projecting parallel sheets of laser light onto valve leaflets as the valves open and close in a mock circulatory loop. Two versions of laser profiling have been developed. In two-dimensional mode multiple profiles are generated on a fixed plane in space but at discrete intervals in time, whereas in three-dimensional mode multiple profiles are generated across the leaflet surface at (effectively) a single instant in time. Highlighted leaflet profiles are captured by camera and transferred to an image processing system for analysis. A simple algorithm permits digitized profiles to be reconstructed within a computer-aided design software package, providing detailed visualization and quantification of valve motion. Extensive validation studies have been performed using the Medtronic-Hall mechanical prosthetic heart valve. Laser profiling enables computer reconstruction of the rigid occluder to an accuracy of +/- 200 microns from a 0.7 ms exposure taken during the period at which the occluder moves with greatest velocity. The technique has been applied to investigate the leaflet dynamics of a bovine pericardial heart valve prosthesis.

Acoustic Stimulation↗
PubMed1992

Combining logistic regression and neural networks to create predictive models.

Neural networks are being used widely in medicine and other areas to create predictive models from data. The statistical method that most closely parallels neural networks is logistic regression. This paper outlines some ways in which neural networks and logistic regression are similar, shows how a small modification of logistic regression can be used in the training of neural network models, and illustrates the use of this modification for variable selection and predictive model building with neural networks.

Algorithms↗