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 1,189 records · Page 66Linked to original sources
PubMed2004

15-year experience with the management of extrinsic ureteral obstruction with indwelling ureteral stents.

PURPOSE: We assessed the success of retrograde placement of indwelling ureteral stents in the management of ureteral obstruction due to extrinsic compression. MATERIALS AND METHODS: Between July 1987 and December 2002 adequate followup was available for 101 patients who underwent primary retrograde ureteral stenting for extrinsic ureteral obstruction. Mean age at presentation was 61.4 years (range 33 to 90). Chart review was performed on all patients for primary diagnosis, symptomatology, degree of hydronephrosis, creatinine levels (baseline, treatment and posttreatment), location of compression, size and number of stents used, progression to percutaneous nephrostomy tube (PNT), stent failure, days to stent failure, post-stent therapy and status at last followup. RESULTS: Mean length of followup was 11 months (range 1 to 127). In 101 patients 138 ureteral units (UU) were stented. Total stent failure occurred in 41 (40.6%) patients and 58 (42.0%) UU. A total of 40 (29.0%) UU required PNTs at a mean of 40.3 days (range 0 to 330) with 18 PNTs placed in less than 1 week. Cases of stent failure that did not undergo PNT placement included 18 (13.0%) UU at a mean of 52.4 days (range 3 to 128). A total of 90 (89.1%) patients had metastatic cancer at stenting with 32.2% dead at 5.8 months (range 1 to 32). Univariate and multivariate analyses identified cancer diagnosis, baseline creatinine greater than 1.3 mg/dl and post-stent systemic treatment as predictors of stent failure. Proximal location of compression and treatment creatinine greater than 3.11 mg/dl were marginal predictors of failure on univariate analysis, while proximal location of obstruction was also marginally significant on multivariate analysis. No predictors were identified for early stent failure (less than 1 week). CONCLUSIONS: At almost 1 year followup stent failure due to extrinsic compression occurred in nearly half of treated patients. Analysis of data revealed a diagnosis of cancer, baseline mild renal insufficiency and metastatic disease requiring chemotherapy or radiation as predictors of stent failure. Managing extrinsic compression by retrograde stenting continues to be a practical but guarded decision and should be tailored to each patient.

Adult↗
PubMed2000

Lossless compression of emission tomography images.

An adaptive lossless compression method using predictive coding with the Rice codes is proposed for low resolution three-dimensional biomedical images. The method is evaluated with the brain positron emission tomography (PET) images. The results are considerably better than with static arithmetic coding.

Algorithms↗
PubMed2003

The compressed feature matrix--a fast method for feature based substructure search.

The compressed feature matrix (CFM) is a feature based molecular descriptor for the fast processing of pharmacochemical applications such as adaptive similarity search, pharmacophore development and substructure search. Depending on the particular purpose, the descriptor may be generated upon either topological or Euclidean molecular data. To assure a variable utilizability, the assignment of the structural patterns to feature types is arbitrarily determined by the user. This step is based on a graph algorithm for substructure search, which resembles the common substructure descriptors. While these merely allow a screening for the predefined patterns, the CFM permits a real substructure/subgraph search, presuming that all desired elements of the query substructure are described by the selected feature set. In this work, the CFM based substructure search is evaluated with regard to both the different outputs resulting from varying feature sets and the search speed. As a benchmark we use the programmable atom typer (PATTY) graph algorithm. When comparing the two methods, the CFM based matrix algorithm is up to several hundred times faster than PATTY and when using the CFM as a basis for substructure screening, the search speed is accelerated by three orders of magnitude. Thus, the CFM based substructure search complies with the requirements for interactive usage, even for the evaluation of several hundred thousand compounds. The concept of the CFM is implemented in the software COFEA. FIGURE CFM based substructure search using the compounds dopamine and benzene-1,2-diol

Algorithms↗
PubMed2005

Location-dependent analysis of porosity and pore direction in tablets.

PURPOSE: Several phenomena in tablets indicate that an inhomogeneous pore distribution is formed during the compaction process. Examples are lamination and the capping of corners. In order to gain an understanding of the relation between structure and compact properties, analyzing the structure in a location dependent manner would be extremely useful. Our aim was to visualize and to quantitatively analyze the pore distribution in compacts. METHODS: This was done by embedding a cubic (sodium chloride) compact with polymer, allowing the compact to be cut without disrupting the structure. By doing so, it was possible to make scanning electron microscopic images from different angles at different locations in the compact. These images were made binary with a two-means cluster algorithm (Isodata) after which the porosity could be calculated. Counting the number of transitions from the pixels in the pores to the pixels in the sodium chloride particles in two perpendicular directions allows us to construct a measure for the anisotropic connectivity of the particles. RESULTS: The results show an increase in porosity toward the bottom of the compact and showed a preferred orientation of the pores in the direction of compression. CONCLUSIONS: The proposed method is suitable for analyzing the pore distribution quantitatively and for evaluating anisotropy.

Anisotropy↗
PubMed2002

Ultrasonic imaging in air using fan-beam tomography and electrostatic transducers.

Air-coupled ultrasonic capacitance transducers operating at frequencies of up to 1 MHz have been employed in a fan-beam configuration for the cross-sectional tomographic imaging of temperature fields and flow fields in air, and the location of solid objects. Separate transmitter and receiver transducers were manufactured using thin polymer dielectric membranes and polished metal backplates, and used to acquire through-transmission data. The fan-beam reconstruction was developed in LabVIEW using a re-bin routine combined with a filtered backprojection algorithm and a difference technique to generate the cross-sectional images. The system was first used to reconstruct images showing the locations of solid objects positioned within the scanned region through interpretation of the arrival time of the transmitted ultrasound. The technique was then extended to image the temperature fields produced in air above a small heat source and the flow field produced by a nozzle connected to a regulated compressed air source. Reconstructed temperatures were within 4% of the measured background air temperature and 9% of the air temperature measured above the heat source. Reconstructed images of the flow field above a small nozzle were also presented, showing that the horizontal component of the flow velocity could be resolved using this method.

Journal Article↗
PubMed2003

Optimization of technique factors for a silicon diode array full-field digital mammography system and comparison to screen-film mammography with matched average glandular dose.

Contrast-detail experiments were performed to optimize technique factors for the detection of low-contrast lesions using a silicon diode array full-field digital mammography (FFDM) system under the conditions of a matched average glandular dose (AGD) for different techniques. Optimization was performed for compressed breast thickness from 2 to 8 cm. FFDM results were compared to screen-film mammography (SFM) at each breast thickness. Four contrast-detail (CD) images were acquired on a SFM unit with optimal techniques at 2, 4, 6, and 8 cm breast thicknesses. The AGD for each breast thickness was calculated based on half-value layer (HVL) and entrance exposure measurements on the SFM unit. A computer algorithm was developed and used to determine FFDM beam current (mAs) that matched AGD between FFDM and SFM at each thickness, while varying target, filter, and peak kilovoltage (kVp) across the full range available for the FFDM unit. CD images were then acquired on FFDM for kVp values from 23-35 for a molybdenum-molybdenum (Mo-Mo), 23-40 for a molybdenum-rhodium (Mo-Rh), and 25-49 for a rhodium-rhodium (Rh-Rh) target-filter under the constraint of matching the AGD from screen-film for each breast thickness (2, 4, 6, and 8 cm). CD images were scored independently for SFM and each FFDM technique by six readers. CD scores were analyzed to assess trends as a function of target-filter and kVp and were compared to SFM at each breast thickness. For 2 cm thick breasts, optimal FFDM CD scores occurred at the lowest possible kVp setting for each target-filter, with significant decreases in FFDM CD scores as kVp was increased under the constraint of matched AGD. For 2 cm breasts, optimal FFDM CD scores were not significantly different from SFM CD scores. For 4-8 cm breasts, optimum FFDM CD scores were superior to SFM CD scores. For 4 cm breasts, FFDM CD scores decreased as kVp increased for each target-filter combination. For 6 cm breasts, CD scores decreased slightly as kVp increased for Mo-Mo, but did not change significantly as a function of kVp for either Mo-Rh or Rh-Rh. For 8 cm breasts, Rh/Rh FFDM CD scores were superior to other target-filter combinations and increased significantly as kVp increased. These results indicate that low-contrast lesion detection was optimized for FFDM by using a softer x-ray beam for thin breasts and a harder x-ray beam for thick breasts, when AGD was kept constant for a given breast thickness. Under this constraint, optimum low-contrast lesion detection with FFDM was superior to that for SFM for all but the thinnest breasts.

Equipment Failure Analysis↗
PubMed2006

Quality of cardiopulmonary resuscitation among highly trained staff in an emergency department setting.

BACKGROUND: Recent reports have highlighted the poor standard of cardiopulmonary resuscitation (CPR) achieved by health care professionals in diverse situations. We explored what can be achieved in an emergency department by highly trained permanent staff. METHODS: In a prospective observational study conducted from June 1, 2002, to August 31, 2005, 80 of 213 patients requiring CPR and admitted to the emergency department of a tertiary care hospital were eligible for study participation. Owing to several logistic problems with CPR, 133 patients could not be studied. The CPR team consisted of emergency- and critical care-trained physicians with more than 10 years of acute care experience, most of whom were instructors of European Resuscitation Council courses in basic and advanced life support. A specially designed defibrillator was used to assess the quality of CPR. RESULTS: For 80 patients, 95 data sets were available for analysis, yielding a total of 1065 minutes of cardiac arrest time. Chest compressions were performed at a rate of 114 (95% confidence interval [CI], 112-116) per minute, resulting in a mean of 96 (95% CI, 93-99) delivered chest compressions per minute. We further observed a mean hands-off ratio of 12.7% (95% CI, 12.3%-13.1%), and the hands-off ratio was linearly associated with the duration of CPR (R(2) = 0.95; mean, 4.3% increments per 5-10 minutes; P<.001). Patients were hyperventilated with a median of 18 (interquartile range, 14-24) ventilations per minute. CONCLUSIONS: Highly trained professionals in an emergency department can achieve appropriate chest compression rates during CPR with a low hands-off ratio. Increased attention must be paid in all situations to the avoidance of hyperventilation.

Aged↗
PubMedDate not supplied

A chemometrics method for separation of size dependent and size independent attributes of microspheres for medical ultrasound imaging.

The size dependent and size independent contributions to the mechanical properties of poly(ethyleneglycol) microspheres with encapsulated air, made for medical ultrasound imaging, have been studied. A relation between the size of microspheres in a reference group and their acoustic attenuation efficacy was derived by partial least square regression. The developed model was used to estimate acoustic attenuation as a function of the measured size distribution for various preparations made during formulation and process studies. The ratio between the measured attenuation and model estimated attenuation was then used to evaluate variations in the mechanical properties of the polymer shell and the contribution of such variations to the acoustical properties of the substance. The statistical parameter was compared with results for the mechanical compressibility derived from a theoretical approach and the results from the two methods mutually confirmed each other. The statistical procedure outlined has been found applicable for studies of other particulate products with size dependent in vitro or in vivo properties.

Acoustics↗
PubMed2002

Language trees and zipping.

In this Letter we present a very general method for extracting information from a generic string of characters, e.g., a text, a DNA sequence, or a time series. Based on data-compression techniques, its key point is the computation of a suitable measure of the remoteness of two bodies of knowledge. We present the implementation of the method to linguistic motivated problems, featuring highly accurate results for language recognition, authorship attribution, and language classification.

Algorithms↗
PubMed2004

KASER: Knowledge Amplification by Structured Expert Randomization.

In this paper and attached video, we present a third-generation expert system named Knowledge Amplification by Structured Expert Randomization (KASER) for which a patent has been filed by the U.S. Navy's SPAWAR Systems Center, San Diego, CA (SSC SD). KASER is a creative expert system. It is capable of deductive, inductive, and mixed derivations. Its qualitative creativity is realized by using a tree-search mechanism. The system achieves creative reasoning by using a declarative representation of knowledge consisting of object trees and inheritance. KASER computes with words and phrases. It possesses a capability for metaphor-based explanations. This capability is useful in explaining its creative suggestions and serves to augment the capabilities provided by the explanation subsystems of conventional expert systems. KASER also exhibits an accelerated capability to learn. However, this capability depends on the particulars of the selected application domain. For example, application domains such as the game of chess exhibit a high degree of geometric symmetry. Conversely, application domains such as the game of craps played with two dice exhibit no predictable pattern, unless the dice are loaded. More generally, we say that domains whose informative content can be compressed to a significant degree without loss (or with relatively little loss) are symmetric. Incompressible domains are said to be asymmetric or random. The measure of symmetry plus the measure of randomness must always sum to unity.

Algorithms↗
PubMed2001

Assessing portal design skills in the radiation oncology interactive case management examination.

The American Board of Radiology is developing a computerized interactive case management examination to be used to evaluate the clinical skills of radiation oncologists. In the past, these skills have been evaluated by a pencil and paper written examination and an oral examination. With the increasing capabilities of computers, these skills can be easily, and perhaps even better, evaluated digitally. The aim is to develop an examination, which will be based on actual clinical cases, and be interactive so that it better mimics the clinical practice of a radiation oncologist than a written examination. It will also be less labor-intensive and less expensive than an oral examination. One of the most important skills of a radiation oncologist is the ability to design treatment portals that will encompass the entire cancer and yet minimize the irradiation of critical tissues and normal organs. Important parameters for radiation oncologists include the direction of the treatment beam, the size and shape of the portals, and the location of the margins of the field relative to patient anatomy and tumor location. In order to evaluate a physician's ability to design treatment portals, the computer-based examination has the capability to interactively construct field lines. The computer interface allows the candidate to draw field lines on a digitized x-ray image in a manner similar to practice. After the candidate illustrates the field lines, the evaluation of the response must be performed quickly to avoid interrupting the flow of the examination. The answer key is stored as a lossless compressed image. The key contains three regions consisting of (1) the must include region, which contains the tumor; (2) the must-exclude region, which contains tissues that if damaged would affect patient vitality and quality of life; and (3) the envelope of acceptable curves. Each region is assigned a unique byte code. The candidate's response is assigned a fourth byte code. Using basic logic operations, the response is swiftly evaluated. The scoring algorithm scores a candidate's action as correct if his/her drawn area encompasses all of the "must-include region" and is within the "envelope of acceptable curves." It scores a candidate's action as incorrect if his/her drawn area overlaps any part of the "exclude region" and/or exceeds at any point the "envelope of acceptable curves."

Algorithms↗
PubMed2004

Feasibility of shock advice analysis during CPR through removal of CPR artefacts from the human ECG.

Mechanical activity from chest compressions and ventilations during cardiopulmonary resuscitation (CPR) introduces artefact components into the electrocardiogram (ECG). CPR must therefore be discontinued for reliable shock advice analysis in automated external defibrillators. Reducing or eliminating this detrimental "hands-off" time by removing the CPR artefacts, should significantly improve the defibrillation success rate. The feasibility of this was tested by removing the CPR artefacts using a multichannel adaptive filter, the multichannel recursive adaptive matching pursuit (MC-RAMP) algorithm. Human ECG and reference channel data from episodes with both shockable and non-shockable underlying heart rhythms were recorded from 105 patients with out-of-hospital cardiac arrest. The performance of a shock advice algorithm was evaluated before and after artefact removal using the MC-RAMP algorithm. From a test set consisting of 92 shockable and 174 non-shockable episodes a sensitivity of 96.7% and specificity of 79.9% was achieved, an increase of approximately 15 and 13%, respectively, compared to no filtering. Good sensitivity was achieved, enabling ECG analysis during CPR that would reduce the hands-off time on patients with shockable rhythms. However, CPR artefact removal on non-shockable rhythms proved a more difficult problem. We need a better understanding of the physiological mixing of artefacts and the underlying heart rhythm and suggest clinical trials to investigate the nature of CPR artefacts further.

Algorithms↗
PubMed2004

Spinal muscle forces, internal loads and stability in standing under various postures and loads--application of kinematics-based algorithm.

This work aimed to evaluate trunk muscle forces, internal loads and stability margin under some simulated standing postures, with and without external loads, using a nonlinear finite element model of the T1-S1 spine with realistic nonlinear load-displacement properties. A novel kinematics-based algorithm was applied that exploited a set of spinal sagittal rotations, initially calculated to minimize balancing moments, to solve the redundant active-passive system. The loads consisted of upper body gravity distributed along the spine with or without 200 N held in the hands, either in the front of the body or on the sides. Nonlinear and linear stability/perturbation analyses at deformed, stressed configurations with a linear stiffness-force relationship for muscles identified the system stability and critical muscle stiffness coefficient. Predictions were in good agreement with reported measurements of posture, muscle EMG and intradiscal pressure. Minimal changes in posture (posterior pelvic tilt and lumbar flattening) substantially influenced muscle forces, internal loads and stability margin. Addition of 200 N load in front of the body markedly increased the system stability, global muscle forces, and internal loads, which reached anterior shear and compression forces of approximately 500 N and approximately 1,200 N, respectively, at lower lumbar levels. Co-activation in abdominal muscles (up to 3% maximum force) substantially increased extensor muscle forces, internal loads and stability margin, allowing a smaller critical muscle coefficient. A tradeoff existed between lower internal loads in passive tissues and higher stability margins, as both increased with greater muscle activation. The strength of the proposed model is in accounting for the synergy by simultaneous consideration of passive structure and muscle forces under applied postures and loads.

Algorithms↗
PubMed2000

An interspike interval method for computing phase locking from neural firing.

Inner hair cells (IHCs) transform the mechanical movements of the basilar membrane into electrical impulses. The impulse coding of the IHCs is the main information carrier in the auditory process and is the basis for improvements of cochlea implants as well as for low rate, high-quality speech processing and compression. This paper shows how to compute the speech signal from the neural firing based on the analysis of the interspike interval histogram. This new approach solves problems that other standard analysis methods do not solve sufficiently well.

Action Potentials↗
PubMed2005

An amplitude-bandwidth expansion method for hearing-aid adjustment.

The basic concept for a technique that facilitates the adjustment of a hearing aid by a person of normal hearing is proposed. The technique involves processing using an amplitude-bandwidth expansion method to expand the hearing-aid output to fit to the user's hearing requirements and loudness recruitment. The expansion is a reversal of the cochlear compression model. As the expansion method introduces distortion of the waveform and a reduction of the expansion rate, the support technique presented here includes solutions to these problems. The difference between the original speech signal and the expanded output generated from the compressed output of the original signal is virtually inaudible. This technique, which effectively simulates a patient's hearing characteristics in order to allow an audiologist to set up a patient's hearing aid, is worth further investigation.

Acoustic Stimulation↗
PubMed2006

Segmentation of elastographic images using a coarse-to-fine active contour model.

Delineation of radiofrequency-ablation-induced coagulation (thermal lesion) boundaries is an important clinical problem that is not well addressed by conventional imaging modalities. Elastography, which produces images of the local strain after small, externally applied compressions, can be used for visualization of thermal coagulations. This paper presents an automated segmentation approach for thermal coagulations on 3-D elastographic data to obtain both area and volume information rapidly. The approach consists of a coarse-to-fine method for active contour initialization and a gradient vector flow, active contour model for deformable contour optimization with the help of prior knowledge of the geometry of general thermal coagulations. The performance of the algorithm has been shown to be comparable to manual delineation of coagulations on elastograms by medical physicists (r = 0.99 for volumes of 36 radiofrequency-induced coagulations). Furthermore, the automatic algorithm applied to elastograms yielded results that agreed with manual delineation of coagulations on pathology images (r = 0.96 for the same 36 lesions). This algorithm has also been successfully applied on in vivo elastograms.

Algorithms↗
PubMed2005

Evaluation of different fast melting disintegrants by means of a central composite design.

Fast-disintegration technologies have encountered increased interest from industries in the past decades. In order to orientate the formulators to the choice of the best disintegrating agent, the most common disintegrants were selected and their ability to quickly disintegrate direct compressed tablets was evaluated. For this study, a central composite design was used. The main factors included were the concentration of disintegrant (X1) and the compression force (X2). These factors were studied for tablets containing either Zeparox or Pearlitol 200 as soluble diluents and six different disintegrants: L-HPC LH11 and LH31, Lycatab PGS, Vivasol, Kollidon CL, and Explotab. Their micromeritics properties were previously determined. The response variables were disintegration time (Y1), tensile strength (Y2), and porosity (Y3). Whatever the diluent, the longest disintegration time is obtained with Vivasol as the disintegrant, while Kollidon CL leads to the shortest disintegration times. Exception for Lycatab PGS and L-HPC LH11, formulations with Pearlitol 200 disintegrate faster. Almost the same results are obtained with porosity: no relevant effect of disintegrant concentration is observed, since porosity is mainly correlated to the compression force. In particular, highest values are obtained with Zeparox as the diluent when compared to Pearlitol 200 and, as the type of disintegrant is concerned, no difference is observed. Tensile strength models have been all statistically validated and are all highly dependent on the compression force. Lycatab PGS concentration does not affect disintegration time, mainly increased by the increase of compression pressure. When Pearlitol 200 is used with Vivasol, disintegration time is more influenced by the disintegrant concentration than by the compression pressure, an increase in concentration leading to a significant and relevant increase of the disintegration time. With Zeparox, the interaction between the two controlled variables is more complex: there is no effect of compression force on the disintegration time for a small amount of disintegrant, but a significant increase for higher concentrations. With Kollidon CL, the main factor influencing the disintegration time is the compression force, rather than the disintegrant concentration. Increasing both the compression force and the disintegrant concentration leads to an increase of the disintegration time. For lower Kollidon CL percentages, the compression pressure increases dramatically the tablet disintegration. With the Explotab, whatever the increase of compression force, the disintegrant concentration leads to an increase of the disintegration time. According to Student's t-test, only the compression force significantly and strongly influences the disintegration time when Pearlitol 200 is used. A slight interaction and some trends nevertheless appear: above 150 MPa, increasing the disintegrant concentration leads to a shortened disintegration time, below this limit the opposite effect is observed.

Algorithms↗
PubMed2004

Wavelet analysis in a canine model of gastric electrical uncoupling.

Abnormal gastric motility function could be related to gastric electrical uncoupling, the lack of electrical, and respectively mechanical, synchronization in different regions of the stomach. Therefore, non-invasive detection of the onset of gastric electrical uncoupling can be important for diagnosing associated gastric motility disorders. The aim of this study is to provide a wavelet-based analysis of electrogastrograms (EGG, the cutaneous recordings of gastric electric activity), to detect gastric electric uncoupling. Eight-channel EGG recordings were acquired from 16 dogs in basal state and after each of two circular gastric myotomies. These myotomies simulated mild and severe gastric electrical uncoupling, while keeping the separated gastric sections electrophysiologically active by preserving their blood supply. After visual inspection, manually selected 10 min EGG segments were submitted to wavelet analysis. Quantitative methodology to choose an optimal wavelet was derived. This 'matching' wavelet was determined using the Pollen parametrization for 6-tap wavelet filters and error minimization criteria. After a wavelet-based compression, the distortion of the approximated EGG signals was computed. Statistical analysis on the distortion values allowed us to significantly (p < 0.05) distinguish basal state from mild and severe gastric electrical uncoupling groups in particular EGG channels.

Algorithms↗