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Results for “data independence acquisition”

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At least 163 records · Page 9Linked to original sources
PubMed1988

Image analysis of Scheimpflug negatives. Comparative quantitative assessment of the film blackening by area planimetry and height measurements of linear densitograms.

Evaluation of various long-term studies on changes of different lens opacities, as had been rendered possible by microdensitometric image analysis of the film blackening of Scheimpflug photographs, showed that only in a few special cases an extension of the opacification to adjacent lens layers is to be expected within the observation period of 2-3 years. This means that one of the reasons for evaluating the densitometer curve by area planimetry is no longer valid and may be neglected. A further advantage of the measurement of film blackening by height evaluation (height of densitometer deflection above baseline, i.e., noise level) is the fact that it is highly independent of subjective factors and, therefore, ensures a far better reproducibility with respect to data acquisition. The results of both evaluation procedures, obtained by evaluating the identical film material (2 photoexaminations) of 14 volunteers, are presented, and the advantage of height measurement as opposed to planimetry is demonstrated.

Cataract↗
PubMed2003

Optical measurements of presynaptic release in mutant zebrafish lacking postsynaptic receptors.

Differentiation of presynaptic nerve terminals is mediated, in part, through contact with the appropriate postsynaptic target cell. In particular, studies using dissociated nerve and muscle derived from Xenopus embryos have indicated that the properties of transmitter release from motor neurons are altered after contact with skeletal muscle. This maturation of presynaptic function has further been linked to retrograde signaling from muscle that involves activation of postsynaptic ACh receptors. Using FM1-43 optical determinants of exocytosis, we now compare calcium-mediated exocytosis at neuromuscular junctions of wild-type zebrafish to mutant fish lacking postsynaptic ACh receptors. In response to either high-potassium depolarization or direct electrical stimulation, we observed no differences in the rate or extent of FM1-43 destaining. These data indicate that the acquisition of stimulus-evoked exocytosis at early developmental stages occurs independent of both postsynaptic receptor and synaptic responses in zebrafish.

Animals↗
PubMed2004

Reaction-time measurement and real-time data acquisition for neuroscientific experiments in virtual environments.

This paper describes an approach to neuroscientific reaction-time experiments and resulting methods for data processing under real-time constraints in virtual environments (VE). Immersive VEs produce huge amounts of data, which has to be processed in real-time to meet the interactivity requirement of VE. Furthermore, data is needed often with a timing resolution and even more crucial with an accuracy in the range of milliseconds. Unfortunately recent operating systems do not in general guarantee timing precision in this range. For these purposes we have researched possibilities for reaction-time measurement and real-time data acquisition. Our system enables neuroscientists to perform reaction-time experiments in platform-independent virtual environments.

Neurosciences↗
PubMed2006

Adult age differences in the effects of goals on self-regulated sentence processing.

The authors examined age differences in adults' allocation of effort when reading text for either high levels of recall accuracy or high levels of efficiency. Participants read a series of sentences, making judgments of learning before recall. Older adults showed less sensitivity than the young to the accuracy goal in both reading time allocation and memory performance. Memory accuracy and differential allocation of effort to unlearned items were age equivalent, so age differences in goal adherence were not attributable to metacognitive factors. However, comparison with data from a control reading task without monitoring showed that learning gains among older adults across trial were reduced relative to those of the young by memory monitoring, suggesting that monitoring may be resource consuming for older learners. Age differences in the responsiveness to (information-acquisition) goals could be accounted for, in part, by independent contributions from working memory and memory self-efficacy. Our data suggest that both processing capacity ("what you have") and beliefs ("knowing you can do it") can contribute to individual differences in engaging resources ("what you do") to effectively learn novel content from text.

Adult↗
PubMedDate not supplied

Assessing whether the plane of section on CT affects accuracy in demonstrating facial fractures in 3-D reconstruction when using a dried skull.

CT slice thickness and threshold value are well-known determinants of accuracy in three-dimensional (3-D) CT image reconstruction. The purpose of this study was to assess whether the plane selected for primary CT data acquisition, axial vs coronal, might also contribute to the accuracy and ease of identification of abnormalities in 3-D image reconstruction independent of the 3-D processing system used. Two sets of 10 observers evaluated fractures created in a dried skull and corresponding 3-D image data. A General Electric 9800 scanner was used to acquire the two-dimensional CT data. The 3D98 Quick software and ISG Camra Allegra workstation were used for two sets of 3-D reconstructions. The expected result was that fractures oriented perpendicularly to the initial plane of CT section would be better reconstructed on 3-D than when the initial plane of CT imaging paralleled the fracture. Our results indicate that Le Fort fractures (types I and III) are better displayed with coronal CT data and that zygomatic tripod fractures may be better displayed in 3-D with axial CT image data.

Cadaver↗
PubMed2006

Neural correlates of response reversal: considering acquisition.

Previous work on response reversal has typically used a single pair of stimuli that serially reverse. This conflation of acquisition and reversal processes has prevented an examination of the functional role of neural systems implicated in response reversal during acquisition despite the relevance of such data in evaluating accounts of response reversal. In the current study, participants encountered 16 independent reversing stimulus pairs in the context of a probabilistic response reversal paradigm. Functional regions of interest identified as involved in response reversal through a contrast used in the previous literature (punished errors made in the reversal phase versus rewarded correct responses), were interrogated across conditions. Consistent with suggestions that middle frontal cortex codes reward, this region showed significantly greater responses to rewarded rather than punished trials irrespective of accuracy or learning phase (acquisition or reversal). Consistent with the suggestion that this coding of the expectation of reinforcement is acquired via input from the amygdala, we observed significant positive connectivity between activity within the amygdala and a region of rostral anterior cingulate cortex highly proximal to this region of middle frontal/mesial prefrontal cortex. In contrast, inferior frontal cortex, anterior cingulate cortex and caudate showed greater responses to punished errors than to the rewarded correct responses. These three regions also showed significant activation to rewarded errors during acquisition, in contrast to positions suggesting that inferior frontal cortex represents punishment or suppresses previously rewarded responses. Moreover, a connectivity analysis with an anterior cingulate cortex seed revealed highly significant positive connectivity among them. The implications of these data for recent accounts of response reversal and of response reversal impairments in specific neuropsychiatric populations are discussed.

Adult↗
PubMed1990

Herpes simplex virus type 2 and other genital ulcerative infections as a risk factor for HIV-1 acquisition.

We studied the role of genital ulcerative infections for acquisition of human immunodeficiency virus type 1 (HIV-1) infection in a cohort of 989 homosexual men in Amsterdam between October 1984 and December 1988. Among 53 HIV-1 seroconverters serological and anamnestic data were gathered regarding herpes simplex virus type 2 (HSV-2) and syphilis in the 6 months before seroconversion. For statistical analysis a control who remained seronegative during the same interval was selected at random for each HIV-1 seroconverter. A significant difference between the prevalence of HSV-2 antibodies among HIV-1 seroconverters and controls was found (72% vs 38%). HSV-2 seroconversions among men initially seronegative for HSV-2 were found among three of 18 HIV-1 seroconverters and among three of 36 controls. (O.R. = 2.2, 95% C.I. 0.4-12.1). Self-reported cases of anogenital herpes were found more frequently among HIV-1 seroconverters (8) than among controls (4). One case of syphilis was diagnosed among HIV-1 seroconverters, and one among controls. Summing up these cases we assessed the total number of genital ulcerative infections: 12 among HIV-1 seroconverters and eight among controls (23 vs 15%, O.R. 1.7, C.I. 0.6-4.62). These data suggest little evidence for genital ulcerative infections being an important independent risk factor for HIV-1 acquisition among homosexual men in Amsterdam during the time period studied.

Acquired Immunodeficiency Syndrome↗
PubMed2006

An independent component analysis-based approach on ballistocardiogram artifact removing.

Interest about simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data acquisition has rapidly increased during the last years because of the possibility that the combined method offers to join temporal and spatial resolution, providing in this way a powerful tool to investigate spontaneous and evoked brain activities. However, several intrinsic features of MRI scanning become sources of artifacts on EEG data. Noise sources of a highly predictable nature such as those related to the pulse MRI sequence and those determined by magnetic gradient switching during scanning do not represent a major problem and can be easily removed. On the contrary, the ballistocardiogram (BCG) artifact, a large signal visible on all EEG traces and related to cardiac activity inside the magnetic field, is determined by sources that are not fully stereotyped and causing important limitations in the use of artifact-removing strategies. Recently, it has been proposed to use independent component analysis (ICA) to remove BCG artifact from EEG signals. ICA is a statistical algorithm that allows blind separation of statistically independent sources when the only available information is represented by their linear combination. An important drawback with most ICA algorithms is that they exhibit a stochastic behavior: each run yields slightly different results such that the reliability of the estimated sources is difficult to assess. In this preliminary report, we present a method based on running the FastICA algorithm many times with slightly different initial conditions. Clustering structure in the signal space of the obtained components provides us with a new way to assess the reliability of the estimated sources.

Adult↗
PubMed1999

Fast acquisition of quantitative T2 maps.

A rapid new technique called T2 fast acquisition relaxation mapping (T2 FARM) was developed to allow T2 maps to be reconstructed directly from k-space data acquired in 3 sec. A single acquisition measured two sets of k-space data, the first with T1 and T2 weighting independent of phase encode position, and the second with T2 weighting varying with phase encode position. These data were processed using an iterative least squares algorithm to produce a quantitative T2 map from the k-space data. T2 values of phantoms and an egg were determined from T2 FARM maps and spectroscopic Carr-Purcell-Meiboom-Gill (CPMG) measurements, demonstrating the validity of the new technique.

Algorithms↗
PubMedDate not supplied

Reduction of artifacts from breathing and peristalsis in phase-contrast MRA of the chest and abdomen.

Strategies for the acquisition of temporally resolved phase-contrast angiography are described and demonstrated. Projections are acquired through the entire thickness of the subject permitting excitation geometries to be independent of image orientation. Minimal delays are used between the acquisition of oppositely flow-encoded data resulting in fewer artifacts from movement of nominally stationary tissue. A protocol that suppresses artifacts from both peristalsis and breathing is presented for the aortic arch and iliac arteries.

Abdomen↗
PubMed2003

Time-dependent interactions of oxidant-sensitive fluoroprobes with inhibitors of cellular metabolism.

SUMMARY: We tested three oxidant sensitive fluoroprobes (dihydrorhodamine [DHR], 2',7'-dichlorodihydrofluorescein [H(2)DCF], and dihydroethidium [DHE]) for interactions with three inhibitors of mitochondrial electron transport. DHR, H(2)DCF, and DHE produced large time-dependent increases in fluorescence in a cell-free medium that contained either of the site III inhibitors antimycin (A) and 2-heptyl-4-hydroxy-quinoline-N-oxide but minimal increases in medium that contained another site III inhibitor, myxothiazol (Mx). The interactions between A and each of the fluoroprobes occurred at concentrations of agent/probe that are frequently used in experiments designed to investigate cellular oxidant production. To define more effectively the nature of these agent/probe interactions, we determined the oxygen dependence of the interactions between A and each probe. The A/H(2)DCF and A/DHR interactions either were highly oxygen-dependent or exhibited a small degree of oxygen dependence, respectively, whereas the A/DHE interaction was oxygen-independent. Finally, we determined multiple ways to reduce the impact of the agent/probe interaction on data acquisition. The addition of either fetal bovine serum (10%) or albumin (5%) to the media abolished the A/DHR and A/H(2)DCF interactions. Shifting the excitation wavelength of DHE (from 470 to 530 nm) reduced measurement of the A/DHE interaction while preserving measurement of the intracellular signal. Collectively, these results emphasize the importance of testing for interactions between agents and probes, because these interactions can interfere with the accurate interpretation of experimental results. In addition, the methods presented for circumventing these interactions may be applicable to other experiments in which agent/probe interactions are an obstacle to accurate interpretation of the experimental results.

Antimycin A↗
PubMed1975

Quantification of ventricular performance: a computer-based system for the analysis of angiographic data.

A computer-based quantitative angiography system for the acquisition and analysis of ventriculographic data has been developed. In addition to the apparatus normally required for angiography and left ventricular pressure recording, a digitizing tablet, PDP 11/20 mini computer, and TV monitor with a hard-copy device is employed. Four modes of operation are currently in use: data acquisition, analysis, mini cine, and data tape editor. Data acquisition facilitates forming a magnetic tape record of the digitized pressure, timing, and event identification, together with anywhere from 4 to 100 digitilized LV contours. A number of error checks and feedbacks are incorporated to provide some measure of quality control. In the event an error is written onto the magnetic tape record, the data tape editor can be used to review the record and correct most errors. Analysis of the generated data tape consists of several options which include: pump function, muscle function, pressure derived indices of contractility and systolic time intervals, and contour pattern recognition which is still under development. If the complete analysis option is chosen, a summary of the analysis, referred to as the quick-sight list, is also presented. The so called mini cine option employs a separate and independent acquisition-analysis program. This requires only the end-diastolic (with a segment of wall) and end-systolic contours (without pressure data) to extract the most essential parameters (EDV, EF, CI, HR, and wall mass). As a result of the relative straightforward processing and inherent simplicity, the mini cine option is most frequently used. This system has done much to reduce the time required for analysis of angiographic data, while at the same time maintaining and even improving the quality of the results. Other less tangible benefits include: the possibility to build a readily accessible library of patient data files facilitating a posteriori studies, precise and uniform definition of the rules to input and analyze data, and finally providing a useful step towards fully automatic ventriculographic processing.

Angiocardiography↗
PubMed2005

Multitensor approach for analysis and tracking of complex fiber configurations.

A multidiffusion-tensor model (MDT) is presented containing two anisotropic and one isotropic diffusion tensors. This approach has the ability to detect areas of fiber crossings and resolve the direction of crossing fibers. The mean diffusivity and the ratio of the tensor compartments were merged to one independent parameter by fitting MDT to the diffusion-weighted intensities of a two-point data acquisition scheme. By an F-test between the errors of the standard single diffusion tensor and the more complex MDT, fiber crossings were detected and the more accurate model was chosen voxel by voxel. The performance of crossing detection was compared with the spherical harmonics approach in simulations as well as in vivo. Similar results were found in both methods. The MDT model, however, did not only detect crossings but also yielded the single fiber directions. The FACT algorithm and a probabilistic connectivity algorithm were extended to support the MDT model. For example, a mean angular error smaller than 10 degrees was found for the MDT model in a simulated fiber crossing with an SNR of 80. By tracking the corticospinal tract the MDT-based tracks reached a significantly greater area of the gyrus precentralis.

Algorithms↗
PubMed1997

Class I mGlu receptor antagonist 1-aminoindan-1,5-dicarboxylic acid blocks contextual but not cue conditioning in rats.

It is widely believed that metabotropic glutamate (mGlu) receptors play a potential role in memory formation. However, the particular function of different classes of mGluRs, or even subtypes, remains elusive. We show here that intraperitoneal injection of the class I selective antagonist 1-aminoindan-1,5-dicarboxylic acid (AIDA) in concentrations of 0.18 or 1.8 mg/kg 25 min prior to acquisition training blocks hippocampus-dependent contextual, but not hippocampus-independent cue, conditioning in rats. These data provide the first evidence for a specific role of mGlu receptors, class I in particular, in hippocampus-dependent learning tasks.

Acoustic Stimulation↗
PubMed2003

Principles and features of single-scan two-dimensional NMR spectroscopy.

Two-dimensional nuclear magnetic resonance (2D NMR) provides one of the foremost contemporary tools available for the elucidation of molecular structure, function, and dynamics. Execution of a 2D NMR experiment generally involves scanning a series of time-domain signals S(t(2)), as a function of a t(1) time variable which undergoes parametric incrementation throughout independent experiments. Very recently, we proposed and demonstrated a general approach whereby this serial mode of data acquisition is parallelized, enabling the acquisition of complete bidimensional NMR data sets via the recording of a single transient. The present paper discusses in more detail various conceptual and experimental aspects of this novel 2D NMR methodology. The basic principles of the approach are reviewed, various homo- and heteronuclear NMR applications are illustrated, and the main features and artifacts affecting the method are derived. Extensions to higher-dimensional experiments are also briefly noted.

Magnetic Resonance Spectroscopy↗
PubMed2005

Multilocus sequence typing of methicillin-resistant Staphylococcus aureus from an area of low endemicity by real-time PCR.

A protocol for multilocus sequence typing (MLST) of methicillin-resistant Staphylococcus aureus (MRSA) was adapted to real-time LightCycler System PCR for efficient and rapid amplification of seven housekeeping genes in the same PCR run and real-time detection of the products. The method was evaluated on a representative and well-characterized collection of clinical MRSA isolates (n = 57) obtained from an area of low endemicity. Twenty sequence types (STs) and nine clonal complexes were identified. Combining STs and the staphylococcal cassette chromosome mec (SCCmec) type identified 27 different genotypes, and type IV SCCmec was present in 11 different STs. The presence of the Panton Valentine leukocidin (PVL) genes was found in isolates of four different STs. Eleven different STs were found among the community-acquired as well as among the hospital-acquired MRSA. The genetic heterogeneity was also denoted by pulsed-field gel electrophoresis analysis that showed 24 different pulsotypes among the 57 MRSA isolates. The presence of more than one different type of SCCmec in the same ST indicates that the MRSA clones have arisen at several occasions in the same genetic background by independent acquisition of SCCmec into methicillin-sensitive strains. This circumstance shows the importance of combining MLST data with SCCmec-typing results when investigating the origins of MRSA.

Bacterial Proteins↗
PubMed1994

Rates of acquisition and loss of Wuchereria bancrofti infection in Culex quinquefasciatus.

Rates of acquisition and loss of parasitic infection in the vector host of Wuchereria bancrofti were estimated using a new method. The age of parasitic infections was estimated from the abdominal condition, determined on the basis of Sella's stages of blood digestion and ovary development, and parity of the vector host and larval stages of the parasite. A negative exponential relationship between age and number of W. bancrofti infections provided estimated daily losses of 25.3% and 33.2% of the initial infection from the resting and biting populations, respectively, of the mosquito Culex quinquefasciatus. The rates per day of acquisition of infection estimated from resting and biting female Cx. quinquefasciatus were found to be 9.6% and 8.6%, respectively. The mean minimum developmental time for W. bancrofti infective larvae estimated from the natural resting and biting populations were 8.9 +/- 1.41 (+/- SEM) and 8.33 +/- 0.85 days, respectively, which was somewhat less than the duration observed under laboratory conditions. Comparisons of the estimates (mean age, rates of acquisition, and loss of infections) based on the resting and biting data suggest that the rates are independent of the method of collecting mosquitoes.

Animals↗
PubMed1975

NUMEDICS: a system for on-line data processing in nuclear medicine.

A multiterminal system --NUMEDICS--has been developed to study the problems of on-line acquisition, processing, and display of scintigraphic data. The hardware-software configuration of NUMEDICS permits simultaneous and independent operation of terminals in the Division of Nuclear Medicine, the Physics Research Laboratory, and the Cyclotron Laboratory of the Massachusetts General Hospital. This paper describes the hardware and software developments in NUMEDICS which have been proven to be of value in clinical and research applications. These features are illustrated by applications to the evaluation of left ventricular performance, three-dimensional imaging, and functional imaging of rCBF.

Nuclear Medicine↗