Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Compression Algorithms”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1995

An EMG-assisted model of trunk loading during free-dynamic lifting.

One of the continuing challenges in biomechanics has been to assess loading of the spine during dynamic lifting exertions. A model was developed to accurately simulate multi-dimensional spinal loads and trunk moments from measured muscle coactivity and external forces during free-dynamic lifting exertions. Model validity was demonstrated by comparing measured and predicted trunk extension moments. Its purpose was to examine realistic representations of lifting kinetics, kinematics, and dynamic trunk mechanics that may influence spinal loading, and to demonstrate that EMG-assisted modeling techniques can be applied to the analysis of free-dynamic exertions. Spinal loads and trunk moments were predicted from the muscle force vectors and external loads. Muscle tensile forces were determined from the product of normalized EMG data modulated to account for contractile dynamics, muscle cross sectional area, and muscle force per unit cross-sectional area. Model output was physiologically valid, i.e. average predicted muscle force per unit cross-sectional area of 50-65 N cm-2, and accurately predicted measured, dynamic, lifting moments, with an average R2 = 0.81 in the sagittal plane and R2 = 0.76 in the lateral plane. Results indicated that compressive and shear loading increased significantly with exertion load, lifting velocity, and trunk asymmetry.

Abdominal Muscles↗
PubMed1997

Lossless ECG encoding.

We have studied the lossless encoding of ECG signals. With suitable code we aim to reduce the storage space needed by ECG signals. Several methods designed for ECG compression use lossy, i.e. irreversible techniques, in which the original signal is lost, but the restored approximation is almost equal to the original. We aimed, however, to use reversible methods which are able to restore the original signal exactly. We have examined various methods and developed a new approach based on structural recognition and extraction of ECG complexes. Comparative conclusions are drawn from the compression efficiency of lossless and lossy methods. In this study, the effect of sampling frequency, resolution and filtering is also examined.

Algorithms↗
PubMed2003

Atomically resolved field emission patterns of single-walled carbon nanotubes.

The electron emission and structural properties of single-walled carbon nanotubes (SWCNTs) were investigated by using field emission microscopy (FEM). The transmission electron microscopy micrograph confirmed the existence of an SWCNT bundle on the W tip. Under appropriate experimental conditions, an FEM image with an elliptic ring-like structure composed of separated bright dots was obtained, a reasonable interpretation of it is that it was produced from the open end for a zigzag (16,0) SWCNT protruding from the SWCNT bundle, each bright dot corresponding to a single atom at the open end. And, if true, this means that the FEM demonstrated 0.2nm resolution, which was theoretically possible for the assumed geometry. The calculated value of the magnification of the pattern was also consistent with the measured value if the value of the compression factor beta was set at 1.76.

Algorithms↗
PubMed2001

[Meconium in the amniotic fluid: prevention of meconium aspiration and elective tracheal suction].

For many years early systematic intubation and tracheal suction have been advocated for meconium-stained infants. Recent data show that they do not reduce the frequency of pulmonary meconium aspiration and underline the importance of a preventive attitude (i.e., intrapartum oropharyngeal suction before shoulder clearing and thoracic compression before first breathing) together with a selective tracheal suction only in the newborns with obvious oropharyngeal meconial staining.

Algorithms↗
PubMed2001

ECG data compression using truncated singular value decomposition.

The method of truncated singular value decomposition (SVD) is proposed for electrocardiogram (ECG) data compression. The signal decomposition capability of SVD is exploited to extract the significant feature components of the ECG by decomposing the ECG into a set of basic patterns with associated scaling factors. The signal informations are mostly concentrated within a certain number of singular values with related singular vectors due to the strong interbeat correlation among ECG cycles. Therefore, only the relevant parts of the singular triplets need to be retained as the compressed data for retrieving the original signals. The insignificant overhead can be truncated to eliminate the redundancy of ECG data compression. The Massachusetts Institute of Technology-Beth Israel Hospital arrhythmia database was applied to evaluate the compression performance and recoverability in the retrieved ECG signals. The approximate achievement was presented with an average data rate of 143.2 b/s with a relatively low reconstructed error. These results showed that truncated SVD method can provide an efficient coding with high-compression ratios. The computational efficiency of the SVD method in comparing with other techniques demonstrated the method as an effective technique for ECG data storage or signals transmission. Index Terms-Data compression, electrocardiogram, feature extraction, quasi-periodic signal, singular value decomposition.

Algorithms↗
PubMed2004

Beamlet dose distribution compression and reconstruction using wavelets for intensity modulated treatment planning.

Intensity modulated radiation therapy (IMRT) treatment planning is often formulated as the optimization of weights of fixed-geometry subfields (beamlets). Efficient optimization techniques can be based on direct storage of the influence matrix relating beamlet weights to dose values. However, direct storage of beamlet dose distributions for IMRT treatment planning can easily exceed several gigabytes, and is therefore often not feasible. We present a method for rapidly calculating full three-dimensional IMRT dose distributions, based on a vector of beamlet weights. The method is based on compressed beamlet dose distributions using fast digital wavelet transforms and so-called hard thresholding. We studied the method with a rectangular beamlet of 0.5 cm x 0.5 cm cross section from a monoenergetic 6 MeV photon point source simulated in homogeneous (water) and heterogeneous (CT-data) phantoms. Dose was calculated using the accurate VMC+ + Monte Carlo engine. The beamlet dose distributions were wavelet transformed and compressed by dropping wavelet coefficients below a given threshold value. Dose is then computed using the remaining wavelets. Selection of the wavelet basis function, decomposition level, and threshold values, for different slice orientations (transverse or parallel to the beam) and varying angles of beamlet incidence are studied. A typical in-slice compression ratio for a plane containing a beamlet was 32:1 using the sym2 wavelet and a threshold of 0.01, with a typical root-mean-square error, for voxels above 50% of the maximum dose, of about 0.04%. The overall compression performance, which includes many planes with little information content, is on the order of 100:1 or greater compared to full matrix storage. Although other methods are available to make the use of stored influence matrix values more feasible in IMRT treatment planning (such as using coarse grids or restricting values to defined volumes of interest) we conclude that wavelet compression facilitates the storage and use of full pencil dose deposition (influence matrix) data in IMRT treatment planning.

Algorithms↗
PubMed1988

Towards a digital model for an electron-microscope image.

An image model is defined based on the boundaries between image regions with different textures and series of descriptions of those textures. Six models of texture are studied under the categories of pixel-based and region-based models. Several techniques for the determination of the unit-cell of textures are presented. The model is applied to the consideration of (a) image correction, (b) the classification of image texture, (c) image enhancement including averaging of detail in periodic specimens, and (d) image data compression. A floating point format, which provides a significant simplification for the Huffman code, is also introduced.

Algorithms↗
PubMed1993

Toward a theory of optimal hearing aid processing.

An ideal hearing aid for a peripheral hearing loss would process the incoming signal in order to give a perfect match between the cochlear outputs of the impaired ear and a reference normal ear. As a first step toward this objective, a model of the normal and impaired peripheral auditory system was used to derive the optimal hearing-aid processing filter based on a minimum mean-squared error criterion. The auditory model includes the compression and suppression effects of the cochlear mechanics and the sensitivity of the neural transduction process. Simplifying assumptions were then incorporated into the processing to yield a practical frequency-dependent adaptive gain system. Processing examples of several individual speech sounds are presented for a flat hearing loss, and the results indicate that a three-channel compression system with adjustable gains and band edges will be close to the optimal solution for this case.

Adaptation, Physiological↗
PubMed1997

Anterior hip pain in the adult: an algorithmic approach to diagnosis.

The adult patient who complains of anterior hip pain is a dilemma frequently encountered by the primary care physician. Detailed history taking, physical examination, and plain x-ray films are indicated for the initial evaluation. Anterior hip pain is often diagnosed as musculoskeletal strain/sprain and treated with a conservative regimen represented by the acronym NICER (nonsteroidal anti-inflammatory drugs, ice, compression, elevation, and rest) with or without physical therapy. On occasion, this therapy fails to eradicate the symptoms. When these symptoms are refractory to diagnosis by conventional means, a more comprehensive evaluation of the etiology is warranted. Refractory pain is defined in the authors' practice as pain that persists after 4 weeks of initial conservative management. This subsequent evaluation includes the use of such laboratory tests as complete blood cell count with differential count, Chem 20 health profile, erythrocyte sedimentation rate, and an arthritic panel (assessment of rheumatoid factor, antinuclear antibody, C-reactive protein). Ancillary radiologic tests warranted include a nuclear bone scan, a magnetic resonance imaging scan, a computed tomography arthrogram with hip aspiration, and/or a scan of white blood cells labeled with indium 111. The test chosen depends on the etiology most suspected. A useful diagnostic algorithm for the investigation of anterior hip pain in the adult is provided. An illustrative case presentation of carcinoma of an unknown primary site presenting as anterior hip pain demonstrates the algorithm as it applies in the authors' practice.

Adenocarcinoma↗
PubMed2001

Hematologic and oncologic emergencies. Doing the most good in the least time.

Broad categories of emergency hematologic and oncologic situations are metabolic crises, compressions and obstructions, and symptomatic cytopenias. In each instance, a decision to intervene should be made on the basis of findings on diagnostic assessment in combination with prognostic information. Management should be directly proportional to the possibility for cure, significant remission, or improved quality of life. Numerous diseases, including potentially curable cancer, can be modified and patients' quality of life substantially improved with appropriate emergency intervention. Fortunately, the modern therapeutic arsenal provides many specific measures to manage these challenging clinical situations.

Algorithms↗
PubMed1995

Comparison of residual stability in thoracolumbar spine fractures using neutral zone measurements.

Because treatment algorithms for spinal injuries depend largely on the clinical assessment of stability after injury, this study both quantified and compared the mechanical stability after three different patterns of injury in the thoracolumbar spine. We created compression fractures, burst fractures, and flexion-distraction injuries in 26 thoracolumbar specimens from human cadavers in order to compare residual stability as a function of type of injury. Spinal stability was evaluated using measurements of the boundaries of the neutral zone, which provide a measure of spinal laxity in various directions of motion. An increase after injury was indicative of greater spinal laxity and hence reduced residual stability. Geometric characteristics (or parameters) of the neutral zone boundaries were used for statistical comparison between the types of injury. Of the three groups, burst fractures retained the least residual stability and compression fractures, the greatest. The angular ranges of motion in the neutral zone for burst fractures demonstrated increases (compared with average values for intact specimens) of 154% in flexion-extension, 134% in lateral bending, and 108% in torsion after injury. The results for flexion-distraction injuries were similar to those for burst fractures in flexion-extension (126%) and torsion (62%); however, more residual stability was retained in lateral bending than was seen for burst fractures (48%). Compression fractures retained the most residual stability, with increases in motion of 40% in flexion-extension, 56% in lateral bending, and 3% in torsion. These findings may be useful in determining the necessity for surgical stabilization of the spine and selection of the appropriate system of fixation.

Biomechanical Phenomena↗
PubMed2000

A model for pulse jet fabric filters.

A new model for pulse jet fabric filtration is proposed. In contrast to the earlier model of Ravin and Humphries, which was formulated on the steady state assumption, the present study is aimed at developing a predictive capability for both transient and steady state operations, taking into account the compression effect of filter cakes. The model's relative simplicity allows frequent updating of the model parameter values, thus improving the accuracy of predictions. As a result, the model is particularly useful in developing control algorithms and designing controllers of pulse jet fabric filtration systems.

Air Pollution↗
PubMed1991

Signals in DNA sequences and their potential properties.

DNA and RNA molecules contain signals which are recognized by regulatory proteins or enzymes either directly, through their nucleotide sequences or indirectly, through induced structural changes on their neighboring sequences. To date, most signal searches have been focused on specific recurrences of nucleotide sequences. Much less attention has been directed towards the structure, flexibility and hydrogen-bonding patterns that recognition elements may possess. Here we review the various methods involved in such searches. In particular, however, we also address the searches for potential properties. In this regard it is of interest to inspect the asymmetry in the distributions of complementary oligomers near biological features. Upstream of transcription initiation the frequencies of G-rich oligomers are particularly high (Nussinov, 1987a; 1990). The frequencies of C-rich oligomers are lower. A-tracts are also very frequent in these regions. This may correlate with the recent finding that guanine, but not cytosine, tracts enhance A-tract directed bends (Milton et al., 1990). Presumably A-tracts near G-tracts on the same strand may induce a structural change in the G-tracts which may enhance the bend. G-tracts may have the potential for participating in a DNA bend due to their compression of the major groove. Thus, proteins may not always be necessary to induce DNA conformational changes. This example illustrates the importance of studies of the properties of DNA oligomers in regulatory regions, and of algorithms for their detection.

Algorithms↗
PubMed2000

Acute tolerance to continuously infused alfentanil: the role of cholecystokinin and N-methyl-D-aspartate-nitric oxide systems.

UNLABELLED: To test the role of cholecystokinin (CCK) and N-methyl-D-aspartate-nitric oxide (NMDA-NO) systems in the development of acute tolerance to analgesia during alfentanil IV infusion, we conducted experiments in rats with the use of an infusion algorithm designed to maintain a constant plasma level of the opioid for 4 h. The degree of acute tolerance was determined on the basis of decline in the level of analgesia measured with a tail compression test. CCK(B) receptor antagonists (proglumide, CI-988, and L-365,260) and NMDA-NO cascade inhibitors (dizocilpine and NO synthase inhibitor) were administered before the start of alfentanil infusion. Use of 30 mg/kg proglumide, 10 mg/kg CI-988, and 1 mg/kg L-365,260 attenuated acute tolerance at 1 h of alfentanil infusion by approximately 60%, 55%, and 70%, respectively, and by the end of 4-h infusion by 50%, 50%, and 25%, respectively. Use of 0.1 mg/kg dizocilpine and 10 mg/kg N(G)-nitro-L-arginine methyl ester attenuated acute tolerance at 1 h of alfentanil infusion by approximately 65% and 65% and by the end of 4-h infusion by 30% and 0%, respectively. Comparison of the results with CCK(B) receptor antagonists and inhibitors of NMDA-NO cascade demonstrates that both groups of drugs provide more or less similar degrees of attenuation of acute tolerance to the antinociceptive effect of alfentanil, and none of these drugs completely prevents tolerance development. IMPLICATIONS: The mechanism of acute tolerance to the analgesic effect of alfentanil depends on participation of multiple systems of adaptation that include cholecystokinin(B) receptors and N-methyl-D-aspartic acid-nitric oxide cascade. Drugs that inhibit function of these systems attenuate tolerance development.

Alfentanil↗
PubMed2000

The effect of ketamine on opioid-induced acute tolerance: can it explain reduction of opioid consumption with ketamine-opioid analgesic combinations?

UNLABELLED: Ketamine administered intraoperatively in very small doses reduces postoperative opioid consumption. We suggest that this effect is the result of attenuation of acute tolerance to the analgesic effect of opioids. We sought to demonstrate that acute tolerance induced by alfentanil infusion can be attenuated by a dose of ketamine that is too small to produce a direct antinociceptive effect. The experiments were conducted in rats with the use of an infusion algorithm designed to maintain a constant plasma level of the opioid for 4 h. The degree of acute tolerance was determined on the basis of decline in the level of analgesia measured with a tail compression test. Ketamine (10 mg/kg) did not change the baseline pain threshold and did not increase the peak of alfentanil-induced analgesia. At the same time, it attenuated the development of acute tolerance to analgesia during alfentanil infusion and suppressed rebound hyperalgesia observed the day after the infusion. These effects were similar to those observed with dizocilpine (0.1 mg/kg). The development of acute tolerance to analgesia induced by the infusion of an opioid can be attenuated by ketamine administered in doses that are not large enough to provide a direct antinociceptive effect. Therefore, ketamine has the potential to reduce opioid consumption even in subanalgesic doses. IMPLICATIONS: Ketamine attenuated the development of acute tolerance to analgesia during alfentanil infusion and suppressed rebound hyperalgesia observed the day after the infusion.

Alfentanil↗
PubMedDate not supplied

Comparison of a neural net-based QSAR algorithm (PCANN) with Hologram- and multiple linear regression-based QSAR approaches: application to 1,4-dihydropyridine-based calcium channel antagonists.

A QSAR algorithm (PCANN) has been developed and applied to a set of calcium channel blockers which are of special interest because of their role in cardiac disease and also because many of them interact with P-glycoprotein, a membrane protein associated with multidrug resistance to anticancer agents. A database of 46 1,4-dihydropyridines with known Ca2+ channel binding affinities was employed for the present analysis. The QSAR algorithm can be summarized as follows: (1) a set of 90 graph theoretic and information theoretic descriptors representing various structural and topological characteristics was calculated for each of the 1,4-dihydropyridines and (2) principal component analysis (PCA) was used to compress these 90 into the eight best orthogonal composite descriptors for the database. These eight sufficed to explain 96% of the variance in the original descriptor set. (3) Two important empirical descriptors, the Leo-Hansch lipophilic constant and the Hammet electronic parameter, were added to the list of eight. (4) The 10 resulting descriptors were used as inputs to a back-propagation neural network whose output was the predicted binding affinity. (5) The predictive ability of the network was assessed by cross-validation. A comparison of the present approach with two other QSAR approaches (multiple linear regression using the same variables and a Hologram QSAR model) is made and shows that the PCANN approach can yield better predictions, once the right network configuration is identified. The present approach (PCANN) may prove useful for rapid assessment of the potential for biological activity when dealing with large chemical libraries.

Algorithms↗
PubMed1996

Non-linear algorithms for processing biological signals.

This paper illustrates different approaches to the analysis of biological signals based on non-linear methods. The performance of such approaches, despite the greater methodological and computational complexity is, in many instances, more successful compared to linear approaches, in enhancing important parameters for both physiological studies and clinical protocols. The methods introduced employ median filters for pattern recognition, adaptive segmentation, data compression, prediction and data modelling as well as multivariate estimators in data clustering through median learning vector quantizers. Another approach described uses Wiener-Volterra kernel technique to obtain a satisfactory estimation and causality test among EEG recordings. Finally, methods for the assessment of non-linear dynamic behaviour are discussed and applied to the analysis of heart rate variability signal. In this way invariant parameters are studied which describe non-linear phenomena in the modelling of the physiological systems under investigation.

Algorithms↗
PubMed2005

[The diagnosis of pulmonary embolism: the best strategies according to the results of a large Dutch multicentre study].

The Dutch national guidelines for the diagnosis of patients with clinically suspected pulmonary embolism (from 1992 en 1998) are poorly followed in clinical practice, due especially to practical objections. A large multicentre trial to investigate the diagnostic accuracy of the available modalities and of recently developed techniques such as D-dimer determination, (99m)Tc-gas-scintigraphy and spiral CT scanning was started in I997. In the first phase, the diagnostic value was assessed of: spiral CT (sensitivity 69%, specificity 84%; sensitivity for segmental and larger pulmonary embolisms (PE) 86% and for subsegmental PE 21%), (99m)Tc-gas-ventilation scintigraphy (no improvement compared to conventional ventilation scintigraphy), D-dimer determination (sensitivity for segmental PE 93% and for subsegmental PE 53%, specificity 63%), clinical decision rules (in combination with D-dimer determination; sensitivity 100%, specificity 11%) and echography of the deep venous system (sensitivity 26% for segmental PE and 7% for subsegmental PE, specificity 97%). In the second phase, the feasibility of two new potentially cost-effective diagnostic algorithms was evaluated on the basis of the results obtained in the first phase and data in the literature. In 631 patients, a clinical risk estimate was made and D-dimer determination was done, followed by a ventilation-perfusion scan and serial compression echography of the leg veins. An apparent recurrence of PE occurred in 6 of 466 patients in whom no PE had been found originally (1.3%; 95% CI: 0.5-2.8). The average costs were 812 Euro,--per patient. In 510 patients, a spiral CT followed by compression echography was performed. Recurrent PE occurred in 3 of 378 patients with initial normal tests (0.8%; 95% CI: 0.2-2.3). The average costs were 883 Euro,--per patient. A combination of both strategies can be cost-effective with a cost 674 Euro,--per patient (recurrence rate: 1.9%). Both the strategy starting with a clinical-risk estimate and a D-dimer determination as well as the strategy consisting of spiral CT and serial echography were safe and cost-effective. According to the results of a survey of hospital directors, internists and pulmonologists, both are well accepted in clinical practice.

Algorithms↗