Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Data Compression”

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 1,171 records · Page 65Linked to original sources
PubMed1997

Lumbar spinal canal stenosis examined electrophysiologically in a rat model of chronic cauda equina compression.

STUDY DESIGN: A model of chronic cauda equina compression with conductive stress was studied electrophysiologically. OBJECTIVE: To analyze the pathophysiology arising from chronic compression electrophysiologically. SUMMARY OF BACKGROUND DATA: This rat model of cauda equina compression that is chronic, not acute, has been reported elsewhere. METHODS: A stainless steel wire and plate were fastened to the spine at L5 of 8 rats 3 weeks old. One year later, the ascending and descending nerve action potentials were recorded and the conduction velocities (CVs) were measured. Electrophysiologic changes after high-frequency stimulation (HFS) were observed. RESULTS: The waveform of the ascending cauda equina action potential at the cauda equina had three peaks, and that at the conus medullaris had a peak followed by a broad wave. The waveform of the descending nerve action potential had two peaks. The mean ascending and descending CVs of the treated rats were slower (P < 0.001) than those of the control rats. In the control rats, the mean CV and mean amplitude after HFS decreased slightly and returned to normal within 30 seconds, and the waveform was unchanged. In treated rats, the mean CV decreased after HFS but returned to normal within 10 minutes. The mean amplitude decreased after HFS and did not return to normal within 10 minutes. The waveform was unchanged. CONCLUSIONS: Because the differences between treated and control rats in amplitude (and CVs) were greater before HFS than after HFS, we concluded that treated rats had disturbance of the blood flow in vessels around the nerves of the cauda equina with histologic damage. In human patients, such disturbance may be one cause of intermittent claudication.

Action Potentials↗
PubMed1985

Surgical treatment of spinal cord compression in patients with lung cancer.

We analyzed the clinical features, radiological findings, and results of surgical treatment in a series of 25 patients with lung cancer and invasion of the spine. In 12 of the 25 (40%) patients, involvement of the spine was present at the time of initial presentation of malignancy. Computed tomography revealed the presence of a large paravertebral soft tissue mass with destruction of adjacent ribs in the majority. The surgical approach consisted of an anterolateral exposure through a formal thoracotomy in 22 patients and a thoracoabdominal flank approach in the 3 patients with lumbar lesions. All gross tumor was resected from the involved paravertebral tissues, vertebral body, and epidural space. Immediate stabilization of the spine was then achieved with methyl methacrylate. Local brachytherapy (iridium-192 implants) was used in 19 patients. After treatment, 87% were ambulatory, and 67% maintained ambulation for more than 6 months. Our data suggest that compression of the spinal cord in many patients with lung cancer results from direct extension of tumor through the chest wall. Because the majority of such patients often have localized disease involving the spine, aggressive surgical treatment is indicated.

Adenocarcinoma↗
PubMed2001

Assessment of cardiovascular dynamics by pressure-area relations in pediatric patients with congenital heart disease.

OBJECTIVES: It is particularly useful to separately quantify the ventricular contractility and loading conditions for a better understanding of the cardiovascular dynamics in congenital heart disease, where abnormalities in chamber and loading properties may coexist. Furthermore, ventricular contractility and loading conditions may alter independently or simultaneously with disease progression and therapeutic intervention. The objectives of the present study were (1) to test whether ventricular pressure-area analysis can provide such quantitation among patients with various forms of congenital heart disease, (2) to reveal basal cardiovascular interaction in congenital heart disease by means of pressure-area analysis, and (3) to test the feasibility of this method in a simplified and less invasive form to further enhance its clinical value. METHODS: We constructed pressure-area loops during caval occlusion by using transthoracic echocardiographic automated border detection combined with ventricular pressure recordings in 59 pediatric patients with congenital heart disease and in 7 normal control subjects. RESULTS: Area measurements obtained by automated border detection were highly reproducible, and area changes reflected volume changes. The pressure-area data provided load-independent measures of contractility, which were consistently increased by use of dobutamine (P <.05). End-systolic and arterial elastance individually quantified simultaneous changes in ventricular contractility and loading with milrinone infusion and predicted net cardiac performance. The pressure-area analysis better characterized the ventricular contractile states under a variety of loading conditions in congenital heart disease, whereas predominant load dependence of conventional indices confounded them. Furthermore, pressure-area relations were reasonably estimated from a single beat and from aortic pressure data during abdominal compression. CONCLUSIONS: Pressure-area analysis should provide a useful modality with which to assess cardiovascular dynamics in pediatric patients with congenital heart disease in more detail and should thus help improve the management of patients with this disease.

Adolescent↗
PubMed1999

Mixtures of probabilistic principal component analyzers.

Principal component analysis (PCA) is one of the most popular techniques for processing, compressing, and visualizing data, although its effectiveness is limited by its global linearity. While nonlinear variants of PCA have been proposed, an alternative paradigm is to capture data complexity by a combination of local linear PCA projections. However, conventional PCA does not correspond to a probability density, and so there is no unique way to combine PCA models. Therefore, previous attempts to formulate mixture models for PCA have been ad hoc to some extent. In this article, PCA is formulated within a maximum likelihood framework, based on a specific form of gaussian latent variable model. This leads to a well-defined mixture model for probabilistic principal component analyzers, whose parameters can be determined using an expectation-maximization algorithm. We discuss the advantages of this model in the context of clustering, density modeling, and local dimensionality reduction, and we demonstrate its application to image compression and handwritten digit recognition.

Algorithms↗
PubMed2005

A space-efficient construction of the Burrows-Wheeler transform for genomic data.

Algorithms for exact string matching have substantial application in computational biology. Time-efficient data structures which support a variety of exact string matching queries, such as the suffix tree and the suffix array, have been applied to such problems. As sequence databases grow, more space-efficient approaches to exact matching are becoming more important. One such data structure, the compressed suffix array (CSA), based on the Burrows-Wheeler transform, has been shown to require memory which is nearly equal to the memory requirements of the original database, while supporting common sorts of query problems time efficiently. However, building a CSA from a sequence in efficient space and time is challenging. In 2002, the first space-efficient CSA construction algorithm was presented. That implementation used (1+2 log2 |summation|)(1+epsilon) bits per character (where epsilon is a small fraction). The construction algorithm ran in as much as twice that space, in O(| summation|n log(n)) time. We have created an implementation which can also achieve these asymptotic bounds, but for small alphabets, and only uses 1/2 (1+|summation|)(1+epsilon) bits per character, a factor of 2 less space for nucleotide alphabets. We present time and space results for the CSA construction and querying of our implementation on publicly available genome data which demonstrate the practicality of this approach.

Animals↗
PubMedDate not supplied

Hormone stimulation and chemotherapy in advanced prostate cancer: preliminary results of a prospective controlled clinical trial.

Preliminary evidence suggests that the sensitivity of endocrine-dependent neoplasms to chemotherapy may be enhanced by transient hormonal stimulation of tumor growth. To test this concept, we are conducting a prospective controlled trial in men with stage D2 prostate cancer who have relapsed following orchiectomy. All patients are continuously treated with aminoglutethimide and hydrocortisone to lower adrenal androgen secretion plus cyclic chemotherapy. Patients in the stimulation arm receive, in addition, the synthetic androgen fluoxymesterone for 3 days before and on the day of chemotherapy. Of 41 patients entered to date, 26 are evaluable. Twenty-one (81%) obtained either an objective remission or stabilization of disease with a mean duration of 9+ months and 10 patients still responding. Thus far, the response rate is similar in the control and stimulation groups. Androgen administration was associated with a rise in acid phosphatase and usually a modest flare of symptoms except for 2 patients who developed spinal cord compression. These preliminary data indicate that the combination of aminoglutethimide and chemotherapy has a potent antitumor effect on advanced prostate cancer refractory to orchiectomy. A large number of patients and a longer follow up are needed to assess whether transient androgen administration potentiates the effect of chemotherapy.

Acid Phosphatase↗
PubMed1996

A study of the advantages of elastic stockings for leg lymphedema.

To assess the efficacy of compression therapy alone, we report herein the long-term results of leg lymphedema using elastic stockings. Between January 1965 and March 1993, 41 primary lymphedema and 74 secondary lymphedema of the lower extremities have been treated at our hospital. Ten patients had recurrence of cancer, and 5 patients had surgical therapy. The remaining 100 patients were analyzed for the clinical results following treatment with elastic stockings. During the follow-up period of 5 +/- 0.2 years, 3 of 39 limbs (8% or 30 patients) with primary lymphedema wearing elastic stockings experienced enlargement of limb circumference and 36 limbs (92% or 27 patients) showed decrease or no change. Without elastic stockings, 1 out of 13 limbs (8% or 8 patients) with primary lymphedema showed worsening of their symptoms. In contrast, only 1 of 61 limbs (1.7%) in 46 patients with secondary lymphedema who wore elastic stockings showed deterioration of their symptoms. Although elastic stockings did not influence the incidence of the lymphangitis, their effect in maintaining limb circumference was apparent in all the patients with inflammation caused by secondary lymphedema. Among 20 patients with secondary lymphedema who had recurrent lymphangitis, only 1 out of 19 limbs (5%) in 16 patients experienced deterioration of the symptom with the use of elastic stockings while 1 out of 4 limbs (25%) in 4 patients showed improvement or no change without elastic stockings. Our data demonstrate that compression stockings are associated with long-term maintenance of reduced limb circumference, especially in secondary lymphedema regardless of the association with recurrent lymphangitis.

Adolescent↗
PubMed1994

Compressive stress-relaxation behavior of bovine growth plate may be described by the nonlinear biphasic theory.

The compressive behavior of the bovine distal femoral growth plate was studied in vitro. Strain-rate controlled, compression stress-relaxation experiments were performed on cylindrical bone-growth plate-bone specimens from the interior and periphery of the growth plate. The questions addressed in this study were (a) Can the nonlinear biphasic theory, one with strain-dependent permeability, be used to represent the compressive stress-relaxation behavior of bovine growth plate? (b) How do different assumptions concerning the permeabilities of the chondro-osseous interfaces influence the inferred material properties of the growth plate? and (c) Are there any differences in these properties between the periphery and the interior of the growth plate? Intrinsic biphasic material properties--aggregate modulus (HA), Poisson's ratio (v), and nonlinear strain-dependent permeability coefficients (ko and M)--were calculated from the compression stress-relaxation data with use of a finite element model and a least squares curve-fitting procedure. To verify this constitutive model for the growth plate, an independent set of finite element analyses was performed with use of the determined intrinsic biphasic properties, and comparisons were made between these finite element predictions and two additional sets of experimental data subsequently obtained for the same specimens with use of two slower rates of compression. Excellent agreement was achieved between these finite element predictions and the latter two sets of data. The aggregate modulus was found to be insensitive to the permeability of the chondro-osseous interface. The permeability coefficients were very sensitive to, and the Poisson's ratio was only slightly sensitive to the interface permeability condition. Therefore, the periphery of the growth plate is more compliant and permeable than the interior.

Animals↗
PubMed2006

Cost-effective handling of digital medical images in the telemedicine environment.

BACKGROUND: This paper concentrates on strategies for less costly handling of medical images. Aspects of digitization using conventional digital cameras, lossy compression with good diagnostic quality, and visualization through less costly monitors are discussed. METHOD: For digitization of film-based media, subjective evaluation of the suitability of digital cameras as an alternative to the digitizer was undertaken. To save on storage, bandwidth and transmission time, the acceptable degree of compression with diagnostically no loss of important data was studied through randomized double-blind tests of the subjective image quality when compression noise was kept lower than the inherent noise. A diagnostic experiment was undertaken to evaluate normal low cost computer monitors as viable viewing displays for clinicians. RESULTS: The results show that conventional digital camera images of X-ray images were diagnostically similar to the expensive digitizer. Lossy compression, when used moderately with the imaging noise to compression noise ratio (ICR) greater than four, can bring about image improvement with better diagnostic quality than the original image. Statistical analysis shows that there is no diagnostic difference between expensive high quality monitors and conventional computer monitors. CONCLUSION: The results presented show good potential in implementing the proposed strategies to promote widespread cost-effective telemedicine and digital medical environments.

Cost-Benefit Analysis↗
PubMed1998

Anatomic and mechanical properties of the lateral disc attachment of the temporomandibular joint.

PURPOSE: This study measured the strength to failure of the human temporomandibular joint (TMJ) lateral disc attachment (LDA) using a tension-compression machine. These data were correlated with the LDA location and its morphologic aspects, the age and sex of the subjects, and the amount of the lateral pterygoid muscle (LPM) inserted in the disc. METHODS: Forty-two TMJs without any obvious internal damage were carefully dissected to preserve the LDA. The width of insertion of the lateral pterygoid muscle fibers in the anterior band, as well as the width of the disc, were measured. The tension test was performed until the complete failure of the sample using a screw machine. RESULTS: Two types of LDA were recognized. In LDA 1, the anterior and posterior bands lateral disc junction were directly inserted on the lateral pole, whereas in LDA 2 this lateral junction was attached behind and below the pole through a sheet of fibrous tissue. The breaking points for LDA 1 (55.8 N) and LDA 2 (28.8 N) were significantly different (P = .03). No correlation was found between the amount of LPM discal fibers insertion, sex, age, or the LDA breaking strength point. CONCLUSION: The LDA 2 insertion strongly suggests that the lateral joint ligament together with the capsule may act as a substitute for the original disc attachment to the lateral pole of the condyle.

Age Factors↗
PubMedDate not supplied

Digital compression of echocardiograms: impact on quantitative interpretation of color Doppler velocity.

To test the impact of Joint Photographic Expert Group (JPEG) compression on the quantitative data encoded in color Doppler echocardiographic images, digital images from transesophageal echocardiography and an in vitro model of proximal flow convergence were analyzed before and after JPEG compression with compression ratios (CRs) as high as 65:1. Even at the highest CRs, greater than 95% of the pixels were categorized correctly as representing structure (gray scale) and greater than 98% were categorized correctly as representing velocity (color) data. Furthermore, the velocities and flows recovered from the compressed images agreed well (r = 0.998 [velocities] and r = 0.998 [flows] for CR = 7:1, falling to r = 0.881 [velocities] and r = 0.930 [flows] at CR = 65:1; p < 0.001 for the linear trend with CR). There was similarly little shift in the location of the red-blue aliasing contour, rising from an error of 0.05 +/- 0.19 (mean +/- SD) mm at CR = 7:1 to a maximum error of 0.11 +/- 0.36 mm at CR = 44:1. Thus JPEG compression has little impact on the quantitative velocity data encoded within color Doppler echocardiograms, which should allow widespread acceptance of digital transmission and storage.

Echocardiography, Doppler, Color↗
PubMed2003

Oral compression activity on a surrogate nipple in the newborn rat: nutritive and nonnutritive sucking.

Newborn rats, 3 hr after birth and before any experience in suckling, were exposed for 10 min to a surrogate nipple providing milk. One hour later, they were exposed to an empty nipple for another 10-min period. The basic characteristics of oral behavior (oral compression activity, OCA) were assessed by recording intranipple pressure during the pups' first attachment to a nipple. The peculiarities of milk-induced changes of OCA were examined with three modes of milk delivery (milk infusions, and intermittent and continuous milk deliveries). The pattern of OCA exerted by the newborn pups on a surrogate nipple consisted of rhythmic oscillations within a frequency range of 0.4 to 1.0 Hz superimposed on slow (frequency < 0.2 Hz), irregular intranipple pressure fluctuations. Oral behavior during the first minute after oral capture of the nipple differed significantly from that during any subsequent 1-min interval in terms of frequency content of OCA. The pattern of OCA changes induced by milk infusions or intermittent milk delivery included an abrupt rise in intranipple pressure, accompanied or followed by a burst of fast nipple compressions (bites). Our data suggest that newborn rats attached to a surrogate nipple demonstrate patterns of oral behavior that simulate, in terms of basic frequency characteristics, patterns of nutritive and nonnutritive suckling observed in more mature pups on the maternal nipple.

Animals↗
PubMed1996

Sarcomere length versus interfilament spacing as determinants of cardiac myofilament Ca2+ sensitivity and Ca2+ binding.

The Ca2+ sensitivity of skinned cardiac muscle can be increased by either an increase in sarcomere length or osmotic compression of the myofilament lattice. The length-dependent change in Ca2+ sensitivity is considered to be an important component of the steep force-length relation along the ascending limb of the force-length curve (Frank-Starling relation). Since an increase in sarcomere length is accompanied by a reduction in the spacing between myosin and actin filaments it is not clear whether length-dependent changes in Ca2+ sensitivity are related to changes in sarcomere length, interfilament spacing or some combination of both. To obtain quantitative information on the relative contributions of these two parameters to the determination of Ca2+ sensitivity skinned bovine cardiac muscle bundles of varying sarcomere lengths (1.7-2.3 microns) were exposed to varying concentrations (0-5%) of Dextran T-500. Measurements were made of changes in muscle width in response to Dextran T-500 addition and both force-pCa curves and bound Ca(2+)-pCa curves were obtained as a function of sarcomere length and lattice compression. From the data obtained it was possible to compare Ca2+ sensitivity and Ca(2+)-troponin C affinity at different sarcomere lengths under conditions of changing interfilament spacing and constant interfilament spacing. Both Ca2+ sensitivity and Ca2+ binding correlated more closely with change in interfilament spacing than with change in sarcomere length. These results suggest that length-dependent force generation in cardiac muscle is based primarily on length-dependent changes in the separation between myosin and actin filaments.

Actin Cytoskeleton↗
PubMed1992

Psycho-sensorimotor performance in divers exposed to six and seven atmospheres absolute of compressed air.

In the present study, we investigated the psycho-sensorimotor abilities of divers exposed to 6 ATA (50 m of sea water; corresponding to legal limit for occupational diving in North America, United Kingdom, and Northern Europe), or 7 ATA (60 m; the legal limit in France and Southern Europe) of compressed air (1 ATA = 100,000 Pa), using psychometric tests of manual dexterity, visual choice reaction time, and number ordination. The results of the present study showed that abilities in these tests were not significantly altered by pressure exposure to 6 ATA of compressed air. However, data obtained at 7 ATA showed slight but significant decreases in performance. Nevertheless, a few subjects presented large decreases in performance ranging from -20% to -25% of control. Finally, our results supported the ergonomic point of view that the laws limiting occupational diving to 6 ATA (50 m) are better adapted to reality and the requirements of underwater activity.

Adult↗
PubMed2000

Quantification of plaque volume, shear stress on the endothelium, and mechanical properties of the arterial wall with intravascular ultrasound imaging.

Present intravascular echographic imaging (IVUS) is based on either the mechanically rotated single element catheter or the multi-element phased array catheter principle. In both methods the ultrasonic beam is rotated through 360 degrees and the cross-sectional echo image of plaque and wall structures is visualised. A new development based on intravascular ultrasound is calculation of mechanical properties of the arterial wall. In this so-called elastographic approach, high frequency information obtained at identical positions in the arterial wall is compared under systolic and diastolic pressures. Minute shifts in the echo data indicate local compressibility. It thus becomes possible to indicate areas of high or low strain, which correspond to soft and hard material. Three-dimensional information can be obtained if the position of cross sectional slices is recorded with a pull-back device and slices are united into a 3D image. On the basis of such information it has become possible to view stents in 3D, and with interactive software, to calculate automatically plaque volume. With pull-back information only, the artery is reconstructed as a "straight pipe". Only when the biplane X-ray information is combined with the intravascular pull-back echo information can the true 3D reconstruction of the artery be constructed. Given the true geometric lumen information, it becomes possible, under certain assumptions, to derive the luminal fluid dynamics. From this, shear stress values close to the arterial wall can be calculated. Under the assumption that low values for local shear stress are areas prone to restenosis, predictions of endangered areas can be made.

Arteriosclerosis↗
PubMed2005

Anisotropic constitutive equations and experimental tensile behavior of brain tissue.

The present study deals with the experimental analysis and mechanical modeling of tensile behavior of brain soft tissue. A transversely isotropic hyperelastic model recently proposed by Meaney (2003) is adopted and mathematically studied under uniaxial loading conditions. Material parameter estimates are obtained through tensile tests on porcine brain materials accounting for regional and directional differences. Attention is focused on the short-term response. An extrapolation of tensile test data to the compression range is performed theoretically, to study the effect of the heterogeneity in the tensile/compressive response on the material parameters. Experimental and numerical results highlight the sensitivity of the adopted model to the test direction.

Animals↗
PubMed1977

Adaptive segmentation of EEG records: a new approach to automatic EEG analysis.

The first step in a procedure for automatic EEG analysis is to compress the incoming data into a manageable format while preserving the essential diagnostic information. In our approach we mimic the visual procedure of looking through the record for segments and events of particular interest. We assume that the EEG is composed of roughly stationary segments of variable length, possibly superposed by sharp transients. By using an autoregressive model we have developed a procedure to detect the segment boundaries and locate transients, and to represent the information in the segments in terms of a set of parameters specifying their power spectra. In this way, the time structure as well as the frequency content of the signal is preserved. Examples of segmentation and transient detection are shown for several EEG signals, and the quality of the representation is demonstrated by simulating the original signal from the parameters. Possible applications to practical EEG analysis are discussed.

Adult↗
PubMed1987

Representation of sleep stages by color density spectral array.

Multiple-channel color density spectral array (CDSA) was used to graphically represent sleep stages. This technique uses color coding of Fast Fourier Transforms to provide a compact display of frequency, power, and real time. Distinct CDSA patterns correlate to the awake, non-REM, and REM sleep states. The graphic compression of sleep data could considerably shorten the time required to stage overnight sleep recordings.

Color↗