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At least 1,153 records · Page 64Linked to original sources
PubMed2003

Single-detector helical computed tomography as the primary diagnostic test in suspected pulmonary embolism: a multicenter clinical management study of 510 patients.

BACKGROUND: Helical computed tomography (CT) is a readily available tool for diagnosing pulmonary embolism (PE); however, its role in the management of patients with clinically suspected PE has not been fully established. OBJECTIVE: To determine the effectiveness and safety of using helical CT of the pulmonary arteries as the primary diagnostic test in patients with suspected PE. DESIGN: Multicenter, prospective clinical outcome study. SETTING: Two academic hospitals and one large teaching hospital in the Netherlands. PATIENTS: 510 consecutive inpatients and outpatients with clinically suspected PE followed for 3 months. INTERVENTIONS: Patients underwent helical CT of the pulmonary arteries within 24 hours after presenting with signs and symptoms of PE. If CT results were normal or inconclusive, compression ultrasonography was performed on the same day as CT and repeated on days 4 and 7 if findings on the first compression ultrasonography were normal. When CT or compression ultrasonography results were positive for thromboembolism, anticoagulation was started. Anticoagulation was not started when results of CT were negative for PE or indicated an alternative diagnosis that explained the clinical signs and symptoms, or when results on serial compression ultrasonography were normal. MEASUREMENTS: Patients received instructions to report any symptoms or signs of PE or deep venous thrombosis (DVT) during the 3-month follow-up period. The authors performed compression ultrasonography or phlebography for suspected DVT and pulmonary angiography for suspected PE. RESULTS: Computed tomography identified PE in 124 of 510 patients (24.3%) and an alternative diagnosis in 130 patients (25.5%); CT scans were normal in 248 patients (48.6%). The CT scan could not be interpreted in 8 patients (1.6%) and was not obtained in 2. Compression ultrasonography revealed DVT in 2 patients at the first examination; findings on repeated compression ultrasonography at days 4 and 7 were normal. Mortality in the patients with normal helical CT scans was 4.1% (10 of 246 patients). No patients in this group died of fatal PE, 1 patient developed nonfatal PE, and venous thromboembolism occurred in 0.4% of these patients (95% CI, 0% to 2.2%). In the patients with alternative diagnoses, 1 patient had DVT on objective testing during follow-up. Mortality in this group was 21.5% (28 of 130 patients); in 1 of these patients, PE could not be confidently ruled out as a contributing cause of death. Venous thromboembolism occurred in 1.5% of these patients (CI, 0.2% to 5.6%). CONCLUSIONS: In patients with suspected PE, helical CT can be used safely as the primary diagnostic test to rule out PE. Serial compression ultrasonography has limited additional value.

Algorithms↗
PubMed2004

Knee loads in the standard and recumbent cycling positions.

The recumbent cycling position (RCP) has become increasingly popular in recent years as a mode of exercise and rehabilitation. However, subtle, but important, differences are expected to exist between the RCP and the standard, upright cycling position (SCP). The differences are due primarily to the altered orientation of the rider's lower extremities relative to gravity. In order to determine if one cycling position may be preferential to another for certain types of rehabilitation, knee loads from a planar, inverse-dynamics model were examined. Nineteen recreational cyclists (24.6 +/- 4.2 yrs) were acclimated to recumbent cycling prior to measuring kinetics and kinematics in both a RCP and SCP (90 rpm; 250 W; max hip-to-pedal distance = 105% leg length). Significance was set at p [symbol: see text] 0.01. Lower-extremity kinematics were not different between the two positions, suggesting that muscle, ligament, and supporting structures travel through the same ranges of motion in both forms of cycling. However, the anterior/posterior forces were altered in such a way that the magnitude of the forces tending to displace the tibia anterior relative to the femur were significantly reduced in the RCP, suggesting that less load may be placed on the anterior cruciate ligament (ACL) while recumbent cycling. No changes in the tension/compression forces were observed at the knee, suggesting no differences in knee stability resulting from compressive forces between the tibia and femur. These findings indicate that the RCP may be beneficial when attempting to minimize ACL loads while utilizing cycling as an exercise and rehabilitative modality.

Adult↗
PubMed2000

Effect of compression on the global optimization of atomic clusters

Recently, Locatelli and Schoen proposed a transformation of the potential energy that aids the global optimization of Lennard-Jones clusters with nonicosahedral global minima. These cases are particularly difficult to optimize because the potential energy surface has a double funnel topography with the global minimum at the bottom of the narrower funnel. Here we analyze the effect of this type of transformation on the topography of the potential energy surface. The transformation, which physically corresponds to a compression of the cluster, first reduces the number of stationary points on the potential energy surface. Secondly, we show that for a 38-atom cluster with a face-centered-cubic global minimum the transformation causes the potential energy surface to become increasingly dominated by the funnel associated with the global minimum. The transformation has been incorporated in the basin-hopping algorithm using a two-phase approach.

Journal Article↗
PubMed1996

Near-infrared spectroscopic characterization of pharmaceutical powder blends.

Near-infrared (near-IR) spectroscopy was used to qualitatively assess the homogeneity of a typical direct compression pharmaceutical powder blend consisting of hydrochlorothiazide, fast-flo lactose, croscarmellose sodium, and magnesium stearate. Near-IR diffuse reflectance spectra were collected from thieved powder samples using a grating-based spectrometer. A second-derivative calculation and principal component analysis were performed on the spectra prior to qualitative evaluation. Blend homogeneity was determined using single- and multiple-sample bootstrap algorithms and traditional chi-square analysis. The results suggested that bootstrap techniques provided greater sensitivity for assessing blend homogeneity than chi-square calculations and that near-IR has great potential as an analytical tool in powder blend analysis.

Carboxymethylcellulose Sodium↗
PubMed2002

Calculating the bulk modulus for a lipid bilayer with nonequilibrium molecular dynamics simulation.

Nonequilibrium molecular dynamics (NEMD) computer simulations are used to calculated the bulk modulus for a dimyristoylphosphatidylcholine bilayer. A methodology is developed whereby NEMD can be effectively used to calculate material properties for complex systems that undergo long time-scale conformational changes. It is found that the bulk modulus upon expansion from a zero stress state agrees well with experimental estimates. However, it is also found that the modulus upon contraction from a zero stress state is larger. From a molecular perspective, it is possible to explain this phenomena by examining the molecular origins of the pressure response. The finding that the two moduli are not equal upon compression and expansion is in apparent contradiction to osmotic stress experiments where the area modulus was found to be the same upon expansion and contraction. This issue is addressed.

Algorithms↗
PubMed1999

Modelling of location- and time-dependent deformation of chondrocytes during cartilage loading.

Experimental evidence suggests that the biosynthetic activity of chondrocytes is regulated primarily by the mechanical environment. In order to study the mechanisms underlying remodeling, adaptation, and degeneration of articular cartilage in a joint subjected to changing loads, it is important to know the time-dependent fluid pressure and stress-strain state in chondrocytes. The purpose of the present study was to develop a theoretical model to simulate the mechanical behaviour of articular cartilage and to describe the time-dependent stress-strain state and fluid pressure distribution in chondrocytes during cartilage deformation. It was assumed that the volume occupied by the chondrocytes is small and that cartilage can be treated as a macroscopically homogenized material with effective material properties which depend on the material properties of the cells and matrix and the volumetric fraction of the cells. Model predictions on the time-dependent distribution of fluid pressure and stress and on the time-dependent cell deformation during confined and unconfined compression tests agree with previous theoretical predictions and experimental observations. The proposed model supplies the tools to study the mechanisms of degeneration, adaptation and remodelling of cartilage associated with cell loading and deformation.

Adaptation, Physiological↗
PubMedDate not supplied

[The clinical and epidemiological characteristics of acute brain injury in children of the Republic of Kabardino-Balkaria].

The paper provides the data of an epidemiological survey for acute brain injury in the pediatric population in Nalchik (Republic of Kabardino-Balkaria) during 3 years (1991-1993). The incidence of acute brain injury was 4.32 +/- 0.30, 5.13 +/- 0.34, and 5.44 +/- 0.36 per 1000 children in 2001, 2002, and 2003, respectively, i.e. there is a statistically significant trend for the figures to increase (t = 2.39; p < 0.01). The death of victims was caused by their severe condition and mortality rates were 0.91; those due to brain contusion and compression were 2.68. The paper also presents the structure of victims by the severity of injury and by the differentiation of these parameters by age, and the relationship of craniocerebral traumatism to a number of social factors. Particular emphasis is laid on the quality of specialized aid. The minimum required diagnostic equipment is determined for the correct evaluation of the severity of injury. Algorithms of delivering care to children depending to their age are given, which make the work of an admission department physician easier, reduce the number of diagnostic and therapeutic errors, and promote a reduction in economic costs. The findings enable one to gain an idea of the level of craniocerebral traumatism and to define measures to improve health care.

Adolescent↗
PubMed2006

Development of a content-validated venous ulcer guideline.

Evidence-based practice for venous ulcers may improve healing and reduce costs of care. The Association for the Advancement of Wound Care Government and Regulatory Task Force developed a content-validated venous ulcer guideline based on best available evidence supporting each aspect of venous ulcer care. After compiling all-inclusive lists of elements in venous ulcer algorithms published before August 2002, the Task Force objectively rated and summarized up to five best references from MEDLINE, CINAHL, and EMBASE literature searches covering each aspect of care. Sixteen multidisciplinary wound care professionals and educators used judgment quantification to content validate all steps. A 2004 email survey of AAWC members (N = 1,514) clarified effects of under-reimbursement on evidence-based venous practice. The Venous Ulcer Guideline containing all elements with A-level evidence plus those with a Content Validity Index >0.75 now resides on the AAWC and the Agency for Healthcare Research and Quality National Guideline Clearinghouse websites. However, a review of US healthcare environment components, including reimbursement policies, and the results of the survey identified many barriers to implementation of A-level evidence supported steps (sustained graduated high compression, autolytic debridement, and moist wound environments) in practice. Sufficient evidence supports improved venous ulcer care in the US but inadequate and/or inconsistent reimbursement policies impede quality evidence-based venous ulcer practice, delaying healing and increasing the burden of venous ulcers on society.

Algorithms↗
PubMed2006

Analytical calculation of volumes-of-intersection for iterative, fully 3-D PET reconstruction.

Use of iterative algorithms to reconstruct three-dimensional (3-D) positron emission tomography (PET) data requires the computation of the system probability matrix. The pure geometrical contribution can easily be approximated by the length-of-intersection (LOI) between lines-of-response (LOR) and individual voxels. However, more accurate geometrical projectors are desirable. Therefore, we have developed a fast method for the analytical calculation of the 3-D shape and volume of volumes-of-intersection (VOI). This method provides an alternative robust projector with a uniformly continuous sampling of the image space. The enhanced calculation effort is facilitated by using several speedup techniques. Exploiting intrinsic symmetry relations and the sparseness of the system matrix allows to create an efficiently compressed matrix which can be precomputed and completely stored in memory. In addition, a new voxel addressing scheme has been implemented. This scheme avoids time-consuming symmetry transformations of voxel addresses by using an octant-wise symmetrically ordered field of voxels. The above methods have been applied for a fully 3-D, iterative reconstruction of 3-D sinograms recorded with a Siemens/CTI ECAT HR+ PET scanner. A comparison of the performance of the reconstruction using LOI weighting and VOI weighting is presented.

Algorithms↗
PubMed2005

The Twente Photoacoustic Mammoscope: system overview and performance.

We present PAM, the Photoacoustic Mammoscope developed at the University of Twente, intended for initial retrospective clinical studies on subjects with breast tumours. A parallel plate geometry has been adopted and the breast will be gently compressed between a glass plate and a flat ultrasound detector matrix. Pulsed light (5 ns) from an Nd:YAG laser will impinge the breast through the glass plate in regions of interest; an appropriate number of the 590 elements of the detector matrix will be activated in succession to record photoacoustic signals. Three-dimensional image reconstruction employs a delay-and-sum beamforming algorithm. We discuss various instrumental aspects and the proposed imaging protocol. Performance studies of the ultrasound detector are presented in terms of sensitivity, frequency response and resolution. Details of the patient-instrument interface are provided. Finally some imaging results on well-characterized breast tissue phantoms with embedded tumour simulating inserts are shown.

Acoustics↗
PubMed1996

Cervical Radiculopathy: Diagnosis and Nonoperative Management.

Cervical radiculopathy presents as pain in a dermatomal distribution. This frequently represents compression of an exiting cervical nerve root by either a herniated disk or a degenerative cervical spondylotic change. Most patients will improve with nonoperative treatment, and a small percentage will require further diagnostic evaluation and ultimately surgical intervention. An understanding of the normal anatomy and the pathologic changes in cervical radiculopathy will improve the understanding of diagnosis and decision making regarding nonoperative interventions. An algorithmic approach for decision making and a review of nonoperative management are presented.

Journal Article↗
PubMed1970

Mechanization of library procedures in the medium-sized medical library. X. Uniqueness of compression codes for bibliographic retrieval.

Two-word compression techniques, the University of Chicago experimental search code and a phonetic code similar to the SOUNDEX coding system, were tested as search codes on a data base of 7,464 bibliographic records. These codes were automatically generated and tested for uniqueness. A modified version of the University of Chicago search code produced the best results with a uniqueness factor of 98.83 percent. The algorithms for generating these codes are explained, and implication of the findings for medium-sized libraries are discussed.

Bibliographies as Topic↗
PubMed2004

[Imaging of neuro-ophthalmological emergencies].

MRI often is mandatory in the diagnostic work-up of visual loss, visual field alterations and oculomotor problems. It is performed emergently in patients with painful diplopia associated to mydriasis, to exclude aneurysm, or in patients with painful Horner syndrome to exclude dissection of the internal carotid artery. CT scan in emergency remains useful in case of acute lateral hemianopsia or acute post traumatic visual loss. Progressive neuro-ophthalmological symptoms may require imaging examination in a short delay to define the therapeutic strategy: monocular transient blindness (dissection or carotid stenosis), progressive visual loss (optic nerve compression), bitemporal hemianopsia (optic chiasm lesion), painful visual loss (optic neuritis). A very precise clinical indication is helpful for the choice of imaging protocol and to improve its diagnosis value.

Acute Disease↗
PubMed2005

The effect of logarithmic compression on estimation of the Nakagami parameter for ultrasonic tissue characterization: a simulation study.

Previous studies have demonstrated that the Nakagami parameter estimated using the envelopes of backscattered ultrasound is useful in detecting variations in the concentration of scatterers in tissues. The signal processing in those studies was linear, whereas nonlinear logarithmic compression is routinely employed in existing ultrasonic scanners. We therefore explored the effect of the logarithmic compression on the estimation of the Nakagami parameter in this study. Computer simulations were used to produce backscattered signals of various scatterer concentrations for the estimation of the Nakagami parameters before and after applying the logarithmic compression on the backscattered envelopes. The simulated results showed that the logarithmic compression would move the statistics of the backscattered envelopes towards post-Rayleigh distributions for most scatterer concentrations. Moreover, the Nakagami parameter calculated using compressed backscattered envelopes is more sensitive than that calculated using uncompressed envelopes in differentiating variations in the scatterer concentration, making the former better at quantifying the scatterer concentration in biological tissues.

Algorithms↗
PubMed2006

Spatiotemporal salient points for visual recognition of human actions.

This paper addresses the problem of human-action recognition by introducing a sparse representation of image sequences as a collection of spatiotemporal events that are localized at points that are salient both in space and time. The spatiotemporal salient points are detected by measuring the variations in the information content of pixel neighborhoods not only in space but also in time. An appropriate distance metric between two collections of spatiotemporal salient points is introduced, which is based on the chamfer distance and an iterative linear time-warping technique that deals with time expansion or time-compression issues. A classification scheme that is based on relevance vector machines and on the proposed distance measure is proposed. Results on real image sequences from a small database depicting people performing 19 aerobic exercises are presented.

Algorithms↗
PubMed1993

Non-diagnostic fine needle aspiration biopsy: a dilemma in management of nodular thyroid disease.

The implications of a persistent "non-diagnostic" fine needle aspiration biopsy (FNAB) has yet to be defined in patients with a solitary thyroid nodule. Four hundred and eleven patients from 1986 to 1990 with a solitary cold thyroid nodule underwent thyroidectomy, including 92 with a "non-diagnostic" FNAB, despite a minimum of two repeat samples. Pathology revealed cancer in eight (9%)--six papillary, one lymphoma, and one squamous cell--follicular adenoma in 38 (41%), Hurthle cell adenoma in two (2%), colloid nodule in 41 (45%), epithelial cyst in two (2%), and thyroiditis in one patient (1%). The operation was uncomplicated by hypoparathyroidism or nerve dysfunction. Age, sex, nodule size, and a history of neck irradiation were examined as possible predictors of cancer risk. Male sex, previous neck irradiation and larger nodules were more common among thyroid cancer patients, but only male sex was statistically significant (P < 0.05). Persistent "nondiagnostic" cytology is a significant limitation of FNAB associated with a 52% neoplasia rate and a 9% incidence of malignancy. "Non-diagnostic" FNAB should be repeated and, if necessary, performed under ultrasound guidance. In order to avoid a missed carcinoma, surgical treatment of persistent "non-diagnostic" FNAB in a dominant hypofunctioning nodule is indicated for the male patient, radiation-associated nodular thyroid disease, recurrent cysts, compression symptoms, and failure of a 6-month trial of thyroid suppression. Lack of needle biopsy and operative morbidity justifies the aggressive exclusion of cancer.

Adolescent↗
PubMed2003

Noncontacting lateral transportation using gas squeeze film generated by flexural traveling waves--numerical analysis.

This paper presents the theory describing the dynamical behavior of a noncontacting lateral transportation of planer objects by means of a gas squeeze film created by traveling flexural waves of a driving surface. An oscillating motion in the normal direction between two surfaces can generate a gas film with an average pressure higher than the surrounding. This load-carrying phenomenon arises from the fact that a viscous flow cannot be instantaneously squeezed; therefore, fast vibrations give rise to a cushioning effect. Equilibrium is established through a balance between viscous flow forces and compressibility forces. When the oscillatory motion between two surfaces creates traveling waves, lateral viscous forces are generated in addition to the normal levitation forces. These forces are produced as a result of nonuniform pressure gradients in the lateral direction between the surfaces. The combination of normal and lateral forces could be used for transporting objects without any direct contact with the driving surface. The numerical algorithm in this work couples the squeeze film phenomenon, which is represented by means of finite difference equations, to model a variant of the Reynolds equation, together with the equations describing the dynamics of the floating object. Numerical simulations are presented and investigated to highlight noteworthy topics.

Journal Article↗
PubMed1994

Nonuniform sampling of urodynamic signals: a comparison of different methods.

Several different techniques for urodynamic signal compression have been proposed in the last few years. Using these techniques it is possible to reduce the requirements for digital storage or transmission. There are a number of applications where it is essential to use such techniques in diagnostic and ambulatory urodynamics. The purpose of this study is to compare different techniques of urodynamic data compression. The so-called FAN, voltage triggered, two point projection and second difference methods. The comparison between the methods is based on 65 pressure, 46 uroflow and 18 surface electromyogram signals. The reduction ratio achieved for different allowable errors between the original and compressed signals is calculated and compared for the different techniques. Results show that it is possible to store urodynamic signals accurately at a low sampling rate, where FAN and voltage triggered methods seem to be superior to the rest.

Algorithms↗