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 1,693 records · Page 94Linked to original sources
PubMed2006

Light field compression using disparity-compensated lifting and shape adaptation.

We propose disparity-compensated lifting for wavelet compression of light fields. With this approach, we obtain the benefits of wavelet coding, such as scalability in all dimensions, as well as superior compression performance. Additionally, the proposed approach solves the irreversibility limitations of previous light field wavelet coding approaches, using the lifting structure. Our scheme incorporates disparity compensation into the lifting structure for the transform across the views in the light field data set. Another transform is performed to exploit the coherence among neighboring pixels, followed by a modified SPIHT coder and rate-distortion optimized bitstream assembly. A view-sequencing algorithm is developed to organize the views for encoding. For light fields of an object, we propose to use shape adaptation to improve the compression efficiency and visual quality of the images. The necessary shape information is efficiently coded based on prediction from the existing geometry model. Experimental results show that the proposed scheme exhibits superior compression performance over existing light field compression techniques.

Algorithms↗
PubMed1989

Compressed spectral arrays for the analysis of 24-hr heart rate variability signal: enhancement of parameters and data reduction.

Heart rate variability signal in the form of an R-R interval tachogram is detected in Holter type 24-hr ECG recordings. Spectral analysis is carried out over consecutive nonoverlapping records, and the information is displayed in the form of a compressed spectral array through parametric techniques. The trends of spectral parameters such as low-frequency (LF) and high-frequency (HF) powers and central frequencies are also plotted, together with the classical mean R-R value and variance relative to each single spectrum. These parameters quantify the effect of sympatho-vagal balance on heart rate control during the 24-hr period and provide important elements for the diagnostic evaluation of various pathologies, like hypertension. A spectral compression algorithm which checks the position of the poles relative to LF and HF bands inside the unitary circle in the complex zeta-plane is also developed. Applications of this procedure are foreseen in the clinical evaluation of ambulant patients as well as in the study of physical and psychological stress.

Algorithms↗
PubMed2001

Evaluation of the role of ligaments, facets and disc nucleus in lower cervical spine under compression and sagittal moments using finite element method.

Cervical spinal instability due to ligamentous injury, degenerated disc and facetectomy is a subject of great controversy. There is no analytical investigation reported on the biomechanical response of cervical spine in these respects. Parametric study on the roles of ligaments, facets, and disc nucleus of human lower cervical spine (C4-C6) was conducted for the very first time using noninvasive finite element method.A three-dimensional (3D) finite element (FE) model of the human lower cervical spine, consisted of 11,187 nodes and 7730 elements modeling the bony vertebrae, articulating facets, intervertebral disc, and associated ligaments, was developed and validated against the published data under three load configurations: axial compression; flexion; and extension. The FE model was further modified accordingly to investigate the role of disc, facets and ligaments in preserving cervical spine motion segment stability in these load configurations. The passive FE model predicted the nonlinear force displacement response of the human cervical spine, with increasing stiffness at higher loads. It also predicted that ligaments, facets or disc nucleus are crucial to maintain the cervical spine stability, in terms of sagittal rotational movement or redistribution of load. FE method of analysis is an invaluable application that can supplement experimental research in understanding the clinical biomechanics of the human cervical spine.

Aged↗
PubMedDate not supplied

Behavioral toxicity associated with antiepileptic drugs: concepts and methods of assessment.

The BTB designed for the VA Epilepsy Cooperative Study is a conceptually organized and practical set of test procedures that can be utilized to assess change in the areas of motor integration, visual perception, speech and language, and mood that might be attributable to AED therapy. If the data warrant, these categories can be compressed into motor, attention-concentration, and mood. The unique methodological advantages of the VA Epilepsy Cooperative Study provide an opportunity to determine empirically the occurrence of behavioral toxicity for specific AED. The advantage of the BTB is the capacity to measure change from an objective baseline over an extended period during chronic AED treatment. The disadvantages are the requirements for apparatus, trained technicians, and additional time for the patient, which now limit its use to research. If BTB data confirm its sensitivity to behavioral toxicity often unappreciated during a neurological exam, the BTB will become a useful clinical tool. Additionally, a common vocabulary for communicating behavioral toxicity may emerge. This optimistic picture is presented with the simultaneous acknowledgment that a clear solution to the problem lies in accumulation of data in future studies which will have had the opportunity to examine the forthcoming results of this multicenter study.

Anticonvulsants↗
PubMed1994

Evaluation of muscle force prediction models of the lumbar trunk using surface electromyography.

Optimization-based models for prediction of muscle forces in the lumbar region of the torso are used to estimate the forces acting on spinal motion segments, especially for asymmetric tasks. The objectives of this study were to determine (a) which of four torso model formulations best predicted the electromyographic data, (b) the difference in muscular contribution to spinal compression force for the four models, and (c) the effect of using the lowest possible muscle stress bound in the model formulation. An approach for the investigation of competing optimization model formulations was developed and was illustrated with electromyographic data from static asymmetric loading conditions. This method is based on (a) the choice of experimental conditions in which models predict decidedly different muscle forces, and (b) the ability to ensure that the experimental conditions are such that the minimum number of assumptions about the force-electromyogram relationship must be made in order to choose between competing model predictions. Of the four models analyzed, only the formulation with an objective function that was the sum of cubed muscle stresses predicted the electromyographic data acceptably. The muscular contribution to spinal compression force predicted by these models differed by as much as 160% for some experimental conditions. The use of the lowest possible muscle stress bound does not appear to predict muscle forces that are in agreement with electromyographic data.

Adult↗
PubMed1981

The diagnosis of osteoporosis.

A rational approach to the diagnosis of osteoporosis by the primary care physician is outline, with emphasis on the patient who presents with chronic back pain and a vertebral compression fracture. The basic information includes data from the patient's history and physical examination, laboratory, x-ray and bone biopsy studies, and determination of bone mineral content (BMC) by photon absorptiometry. Characteristic radiologic features associated with bone loss, BMC changes, and bone biopsy findings are illustrated. This diagnostic approach, summarized in a flow diagram, poses a series of questions; the answer to each question leads either ot a diagnostic conclusion or to further questions which must be answered. This permits decision as to whether a compression fracture is due to trauma, local osteoporosis, osteomalacia, secondary osteoporosis or primary osteoporosis. In te study population (150 subjects), 80 percent of patients presenting with vertebral compression fractures had primary osteoporosis.

Adult↗
PubMed2005

The results of compression forces applied to the isolated human calvaria.

Data for the force necessary to fracture the isolated calvaria (skull cap) are not available in the extant literature. Twenty dry adult calvaria were tested to failure quasistatically at the vertex using a 15-kN load cell. The forces necessary to fracture or cause diastasis of calvarial sutures were then documented and gross examination of the specimens made. Failure forces had a mean measurement of 2772 N. Initial fractures did not cross suture lines. Prior to complete destruction of the calvaria there were 7 specimens in which all sutures of the calvaria became diastatic, 6 specimens in which the calvaria became diastatic along only the coronal sutures, 2 specimens in which the calvaria became diastatic along only the sagittal suture and 5 specimens in which there were diagonal linear parietal bone fractures. Our hopes are that these data may contribute to the structural design of more safer protective devices for use in our society, assist in predicting injury and aid in the construction of treatment paradigms.

Adult↗
PubMed2004

Content-based retrieval of historical Ottoman documents stored as textual images.

There is an accelerating demand to access the visual content of documents stored in historical and cultural archives. Availability of electronic imaging tools and effective image processing techniques makes it feasible to process the multimedia data in large databases. In this paper, a framework for content-based retrieval of historical documents in the Ottoman Empire archives is presented. The documents are stored as textual images, which are compressed by constructing a library of symbols occurring in a document, and the symbols in the original image are then replaced with pointers into the codebook to obtain a compressed representation of the image. The features in wavelet and spatial domain based on angular and distance span of shapes are used to extract the symbols. In order to make content-based retrieval in historical archives, a query is specified as a rectangular region in an input image and the same symbol-extraction process is applied to the query region. The queries are processed on the codebook of documents and the query images are identified in the resulting documents using the pointers in textual images. The querying process does not require decompression of images. The new content-based retrieval framework is also applicable to many other document archives using different scripts.

Abstracting and Indexing↗
PubMed2006

Surgical simulation of instrumented posterior occipitocervical fusion in a child with congenital skeletal anomaly: case report.

STUDY DESIGN: Case report of a child with a congenital skeletal anomaly who underwent instrumented surgery at the craniovertebral junction (CVJ). OBJECTIVES: To describe the utility of surgical simulation using three-dimensional full-scale models for preoperative planning. SUMMARY OF BACKGROUND DATA: Instrumented fusion of cervical spine with pedicle screws has several advantages compared with conventional sublaminar wiring, such as stronger fixation and reduction of malalignment. However, studies have reported a risk of injury to the vertebral artery (VA) from the insertion of screws. Especially in pediatric patients, the safety of pedicle screw insertion has not been fully established. METHODS: A 7-year-old girl with a congenital skeletal anomaly presented with gait disturbance and clumsiness of her right hand. Radiographs showed dysplasia of the C1 posterior arch, leading to compression of the spinal cord posteriorly. Data from three-dimensional computed tomography (CT) angiography showed that the right VA was dominant and was shifted medially at the C2 pedicle. A surgical procedure was scheduled to resect the C1 posterior arch and perform an instrumented occiput-C2 fusion with a system of rod and screws. To evaluate the adaptation of the system to the small and deformed anatomic structure of her CVJ, we produced a three-dimensional full-scale model from CT data and performed a simulation of the scheduled surgery. RESULTS: Simulation of the surgery on the model showed acceptable adaptation of the system. However, the right C2 pedicle screw penetrated the medial wall of the VA foramen. In response to these results, we altered the surgical procedure and performed occiput-C3 fixation with a system of contoured loop and wiring. Although the patient had to use a halo-vest for 2 months, no complication occurred during surgery, and she experienced relief of her myelopathy after surgery. CONCLUSIONS: The three-dimensional full-scale model was useful for determining the safety of instrumented posterior occipitocervical fusion for a pediatric patient with a skeletal anomaly.

Atlanto-Occipital Joint↗
PubMed2001

Thromboembolic disease in total knee arthroplasty.

Good data exist to support the use of low molecular weight heparins, warfarin, or intermittent pneumatic compression to prevent thromboembolic disease in TKA patients. Emerging data suggest that low molecular weight heparins may be more efficacious than warfarin, but are probably associated with slightly higher bleeding complications. There is little data to support the efficacy of aspirin alone as a prophylactic agent in TKA patients. Routine screening in asymptomatic low risk patients is probably not cost-effective. Prophylactic inferior vena caval filters are recommended in high-risk patients in whom other forms of anticoagulation are not feasible.

Adult↗
PubMed2003

[Medullary compression in men with prostatic cancer. A retrospective study of medical records].

INTRODUCTION: The aim of the study was to describe symptomatology and prognosis in patients with spinal cord compression and prostate cancer. MATERIAL AND METHODS: The material was retrospective and included patients from 1.1.1996 to 31.12.2000 with compression of the medulla, dura or intraspinal roots. Data collection was concluded on 30.6.2001. RESULTS: Seven patients had the cancer diagnosis at the time of the intraspinal compression. The most frequent debut-symptom was acceleration of pain, two thirds had neuropathic pain, and three patients were free of pain. Paresis was present in 23 patients and 18 had sensory symptoms. External irradiation was given to 29 patients, three had a neurosurgical procedure and irradiation and two patients had just endocrine manipulation. The treatment result was good or moderately good on pain in three fourths of the patients, and on the neurological symptoms in two thirds. Eight patients had recurrence. Median survival was three months for patients with hormone resistant progression and two years for those patients, who got their cancer diagnosis in connection with the intraspinal compression. CONCLUSION: Rapid acceleration of pain is an early symptom of intraspinal compression. Morphine-resistant pain or neuropathic pain and neurologic symptoms are typical findings, but none of the symptoms are obligatory. Early acute treatment may give good recovery and the survival is comparable with the survival of patients whose illnesses are in the same stadium but who do not suffer from intraspinal compression.

Aged↗
PubMed2007

Factors affecting sagittal malalignment due to cage subsidence in standalone cage assisted anterior cervical fusion.

Fusion of cervical spine in kyphotic alignment has been proven to produce an acceleration of degenerative changes at adjacent levels. Stand-alone cages are reported to have a relatively high incidence of implant subsidence with secondary kyphotic deformity. This malalignment may theoretically lead to adjacent segment disease in the long term. The prospective study analysed possible risk factors leading to cage subsidence with resulting sagittal malalignment of cervical spine. Radiographic data of 100 consecutive patients with compressive radiculo-/myelopathy due to degenerative disc prolapse or osteophyte formation were prospectively collected in those who were treated by anterior cervical discectomy and implantation of single type interbody fusion cage. One hundred and forty four implants were inserted altogether at one or two levels as stand-alone cervical spacers without any bone graft or graft substitute. All patients underwent standard anterior cervical discectomy and the interbody implants were placed under fluoroscopy guidance. Plain radiographs were obtained on postoperative days one and three to verify position of the implant. Clinical and radiographic follow-up data were obtained at 6 weeks, 3 and 6 months and than annually in outpatient clinic. Radiographs were evaluated with respect to existing subsidence of implants. Subsidence was defined as more than 2 mm reduction in segmental height due to implant migration into the adjacent end-plates. Groups of subsided and non-subsided implants were statistically compared with respect to spacer distance to the anterior rim of vertebral body, spacer versus end-plate surface ratio, amount of bone removed from adjacent vertebral bodies during decompression and pre- versus immediate postoperative intervertebral space height ratio. There were 18 (18%) patients with 19 (13.2%) subsided cages in total. No patients experienced any symptoms. At 2 years, there was no radiographic evidence of accelerated adjacent segment degeneration. All cases of subsidence occurred at the anterior portion of the implant: 17 cases into the inferior vertebra, 1 into the superior and 1 into both vertebral bodies. In most cases, the process of implant settling started during the perioperative period and its progression did not exceed three postoperative months. There was an 8.7 degrees average loss of segmental lordosis (measured by Cobb angle). Average distance of subsided intervertebral implants from anterior vertebral rim was found to be 2.59 mm, while that of non-subsided was only 0.82 mm (P < 0.001). Spacer versus end-plate surface ratio was significantly smaller in subsided implants (P < 0.001). Ratio of pre- and immediate postoperative height of the intervertebral space did not show significant difference between the two groups (i.e. subsided cages were not in overdistracted segments). Similarly, comparison of pre- and postoperative amount of bone mass in both adjacent vertebral bodies did not show a significant difference. Appropriate implant selection and placement appear to be the key factors influencing cage subsidence and secondary kyphotisation of box-shaped, stand-alone cages in anterior cervical discectomy and fusion. Mechanical support of the implant by cortical bone of the anterior osteophyte and maximal cage to end-plate surface ratio seem to be crucial in the prevention of postoperative loss of lordosis. Our results were not able to reflect the importance of end-plate integrity maintenance; the authors would, however, caution against mechanical end-plate damage. Intraoperative overdistraction was not shown to be a significant risk factor in this study. The significance of implant subsidence in acceleration of degenerative changes in adjacent segments remains to be evaluated during a longer follow-up.

Adult↗
PubMed2000

Practicability and quality of outpatient management of acute deep venous thrombosis.

PURPOSE: The purpose of this study was to review the practicability and quality of a standardized management approach of deep venous thrombosis (DVT) provided by private practices. METHODS: There were 152 consecutive patients and 156 episodes. We determined the patients' diagnoses with estimation of clinical probability, D-dimers, duplex ultrasound scan, and venography. Patients were treated on an outpatient basis on principle, with dalteparin, phenprocoumon, different modalities of external leg compression, and deliberate ambulation. We followed up at 4 weeks. RESULTS: Proximal DVT was diagnosed in 101 episodes (65%). Results of the D-dimer test were false-negative in 6%, and venography was indicated in 15%. Calf vein thrombosis was found in 55 patients. Results of the D-dimer test were false-negative in 30%, and venography was required in 37%. Eleven patients were hospitalized (9 for thrombectomy or thrombolysis), and 145 episodes (93%) were treated according to our standardized approach (provided by the referring physicians alone in 43%). For 5 days, dalteparin was injected by the patients themselves or their relatives, in 78% of the cases. The international normalized ratio values were more than 2 in 88% of the cases, with no difference between providers. In all but two cases, external leg compression was applied immediately: a modified Unna's boot in 28% and compressing stockings in 72% (Sigvaris 503 in 91%; calf length in 100% of distal DVT, and 83% of proximal DVT). During follow-up, there was no clinical evidence of recurrence or progression, 1 possible pulmonary embolism, 1 injection site hematoma, and 1 hospitalization unrelated to the DVT. CONCLUSION: Diagnosis of proximal DVT is straightforward, but calf DVT often requires venographic confirmation because of discrepancies among clinical probability, D-dimer estimation, and ultrasound scan. Outpatient treatment can be offered to patients who can comply with the regimen. The quality of anticoagulation is in accordance with published data, and compliance with external leg compression is almost perfect.

Acute Disease↗
PubMed2003

Pathomechanisms of nerve root injury caused by disc herniation: an experimental study of mechanical compression and chemical irritation.

STUDY DESIGN: An electrophysiologic and histologic study on nerve roots after mechanical compression and/or local application of nucleus pulposus (NP) was performed. OBJECTIVE: To assess the effects of mechanical compression and/or chemical irritation caused by NP. SUMMARY OF BACKGROUND DATA: It has been shown that application of NP to nerve roots without compression induces histologic and functional changes in nerve roots and the dorsal root ganglia. In clinical situations, however, mechanical compression has also been considered an important factor in disc herniation. METHODS: Eighteen dogs (9-15 kg) were used in this study. Four groups were used to assess the effect of each factor: 1) sham group (n = 3); 2) NP group (NP applied under the S1 lamina) (n = 5); 3) comp group (a plastic balloon placed under the S1 lamina) (n = 5); and 4) comp+NP group (a balloon and NP placed under the S1 lamina) (n = 5). Ascending cauda equina action potentials (CEAPs) and cauda equina-sensory nerve conduction velocity (SCV) were recorded before, immediately after, and 1 week after treatment. Histologic changes were also assessed by light microscopy. RESULTS: There were no significant differences in CEAP and SCV among the four groups immediately after the treatment. However, 1 week after treatment, the amplitudes in the NP group, comp group, and comp+NP group were statistically significantly lower compared with those in the sham group. The comp+NP group showed significantly lower amplitude than did the NP group and comp group. Immediately after treatment, SCV in the NP group and comp group did not show significant differences compared with that in the sham group. However, 1 week after treatment, SCV in the comp+NP group was significantly lower compared with that in the sham group. Histologic changes such as intraneural edema, Schwann cell edema, and nerve fiber injury seemed to be more pronounced in the comp+NP group than in the other groups. CONCLUSIONS: It was shown that each of the assessed factors induces nerve dysfunction. However, the combination of mechanical compression (mass effect of herniated NP) and chemical irritation (inflammation around nerve root) may induce more nerve root injury than each factor per se.

Animals↗
PubMed2002

Effect of belt pressure and breath held on trunk electromyography.

STUDY DESIGN: This study examined the effect of a belt on ventilation and trunk muscle activities during repetitive lifting tasks with a control of breathing type and belt pressure. OBJECTIVES: To evaluate the effect of the lifting belt on the trunk muscle electromyography (EMG) and to parse out potential interaction between ventilatory changes and lifting belts. SUMMARY OF BACKGROUND DATA: Although both tensed thorax and compressed abdomen are considered to assist transferring the force from torso to pelvis in lifting, there has not been any consideration of the interaction between the two chambers in most published analyses. METHODS: Eleven male study participants participated in the study. They performed five minutes of paced repetitive squat lifts at frequencies of one or three lifts per minute, with loads of 10 or 25 kg. Belt pressure was set at 0 (no belt), 10, and 20 mm Hg. Study participants lifted with inspire-hold and expire-hold for a period of 5 minutes. Lift ventilation data and trunk muscle normalized electromyography (NEMG) (including rectus abdominis, external oblique, latissimus dorsi, and erector spinae) for the final lift were collected for analysis. RESULTS: The results indicate that the ventilation demand for lifting was not different with or without use of a belt. The prelifting erector spinae NEMG was 8-11% maximum voluntary contraction (MVC) lower and the latissimus dorsi NEMG was 15-21% MVC lower than that without belt. This is also the case in the lifting phase. The rectus abdominis NEMG was increased by 4% MVC and the external oblique NEMG was increased by 3-5% MVC while lifting with a belt. CONCLUSIONS: These data do not lead to a statistical effect of lifting belt pressure on ventilatory behavior. It appears that the use of a belt in lifting significantly decreased the back muscular activation yet increased the abdominal muscular activation. Thus, claims of benefits derived from the use of a belt in lifting remain controversial. The simultaneous controls of the air volume held and pressure of the belt during the moment-controlled lifting tasks allowed this presentation of belt effects on trunk muscle NEMG unique from that in most of the literature.

Abdomen↗
PubMed1994

Cervical spondylotic stenosis and myelopathy: evaluation with computed tomographic myelography.

OBJECTIVE: To determine which components of cervical spondylosis are most frequently present in patients with myelopathy. DESIGN: We reviewed the findings in 93 patients who underwent surgical decompression for cervical spondylotic myelopathy between January 1986 and December 1989 at Mayo Clinic Rochester. MATERIAL AND METHODS: All 93 patients (72 men and 21 women) underwent computed tomographic (CT) myelography. In addition, magnetic resonance imaging scans were available in 25 patients, and plain CT scans were obtained in 2. RESULTS: A review of CT myelograms revealed that all neurocompressive intraspinal spondylotic changes were reflected in the shape of the spinal cord. Among the 93 patients with myelopathy, the configuration of the spinal cord could be categorized into primarily three dominant types: A (severe encroachment that compressed the cord into the shape of a banana; N = 40), B (moderate encroachment that produced less prominent compression; N = 23), and C (moderate bilateral uncovertebral spurs; N = 12). As a comparison group, 30 patients with similar spinal cord deformities but without progressive myelopathy were analyzed. Correlation of the two groups showed that myelopathy was present in up to 98% of patients with type A spinal cord, in 75% with type B, and in 71% with type C. The findings on magnetic resonance imaging were similar to those on CT myelography, but the bony spondylotic components were less readily seen. CONCLUSION: The precise pathophysiologic mechanism of myelopathy in spondylosis remains an enigma. Although the bulk of the data on our patients supports direct compression, we believe that the cause is multifactorial.

Adult↗
PubMed1986

Intracranial microvascular decompression for "cryptogenic" hemifacial spasm, trigeminal and glossopharyngeal neuralgia, paroxysmal vertigo and tinnitus: I. Surgical technique and results.

Intracranial microvascular decompression was performed in 21 out of 24 patients with hyperactive dysfunction of cranial nerves: 8 cases of hemifacial spasm, 12 of trigeminal neuralgia, 3 of glossopharyngeal neuralgia and 1 case of paroxysmal vertigo and tinnitus. In 21 cases an abnormal vascular loop was found to impinge on the root entry zone of the nerve in the brainstem. Dissection of this loop with decompression of the nerve resulted in long-lasting relief of symptoms in all but two patients who presented early recurrence; in one of these a second procedure was eventually successful. In two patients with trigeminal neuralgia a benign tumor of the cerebellopontine angle that had escaped preoperative diagnosis was present. Finally, in one case no compressive lesions were found. From the data of the literature and from our present experience microvascular decompression can be considered a safe as well as an effective procedure, affording a high success rate in conditions often or usually resistant to medical treatment and erroneously considered "idiopathic".

Adult↗
PubMed1997

Confirmation of ethanol compressed gas standard concentrations by an NIST-traceable, absolute chemical method and comparison with wet breath alcohol simulators.

This study compares compressed-gas Ethanol Breath Standards (EBS) with wet simulators as calibration standards for breath alcohol analyzers. After reviewing the technical basis and traceability for the two calibration sources, new analytical data verifying the ethanol content of EBS gas are presented. Based on collection of ethanol in an impinger and titration using a modified California Department of Health method, the data confirm the alcohol content of EBS compressed gas standards by an absolute, wet chemical method. These results establish the concentration accuracy and the NIST traceability of the EBS gas by two independent methods, gas chromatographic analysis traceable to NIST standards and the new wet chemical method. Effluent gas from a wet simulator standard is then analyzed by the wet method to show its equivalence with EBS gas.

Breath Tests↗