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At least 973 records · Page 54Linked to original sources
PubMed1991

Evaluation of a sensitive immunoenzymometric assay for thyrotropin suitable for emergency and paediatric use.

This short communication compares a luminescent-labelled immunometric assay (BeriLux) with an enzyme-labelled immunometric assay (NovaPath) for thyrotropin determinations. The NovaPath assay lends itself to paediatric use, because it only uses 25 microliters sample, and to emergency use, because the main incubation can be reduced to 30 minutes. The correlation between both kits was acceptable (r = 0.825, n = 167 data pairs) although the NovaPath kit gave lower values than the BeriLux it (Median-BeriLux 1.00 mU/l, NovaPath 0.70 mU/l, p less than 0.001 = Wilcoxon Test). From 167 sera (range less than 0.01-44 mU/l) 3 gave discrepant values, being euthyroid in the BeriLux kit and hyperthyroid in the NovaPath kit. All 3 patients were undergoing thiamazole (Favistan) therapy at the time of sampling. The coefficients of variation were lower in the BeriLux kit (intraassay less than 4.5%, interassay less than 5.5% for the range 0.1-50 mU/l) than in the NovaPath kit (intraassay less than 7.5%, interassay less than 12.5%). This reflects the larger dynamic range (signal/noise ratio) of the BeriLux kit.

Child↗
PubMed1982

Rapid quantitation of serum immunoglobulins with a miniature centrifugal analyzer.

For these quantitative turbidimetric assays for immunoglobulins IgG, IgA, and IgM in serum, the reagents used are commercially available in kit form. The two-point assays are performed with a miniature centrifugal analyzer (GEMENI, Electro-Nucleonics, Inc.). The reading taken 5 s after mixing is used to correct for specimen turbidity. Run-to-run precision (CV) was typically 5% (range: 3.0-8.7%). Excellent correlation with radial immunodiffusion was observed for each test (r greater than 0.98 for each test). The dynamic range of each test extends above and below the reference-interval ranges.

Centrifugation↗
PubMed1981

[Air conduction or bone conduction hearing aids? Comments on hearing aids for sound conduction deafness (author's transl)].

Measuring curves and psycho-acoustical measurements are used for an investigation of the extent to which the bone-conduction hearing aid is equivalent to the air-conduction hearing aid. It can be shown that basically there is no objection against the use of a bone-conduction hearing aid (ear-level aid) for patients suffering only from sound-conduction hearing defects. The air-conduction hearing aid significantly superior in those cases where the requirements to be met by the hearing aid with respect to the frequency range (music) are higher. If the sound conduction disorder is accompanied by a sound paralgia, this means that the essentially reduced dynamic range of the bone-conduction hearing aid significantly restricts the possible applications of the bone-conduction hearing aid.

Bone Conduction↗
PubMed2000

A method for removing imaging artifact from continuous EEG recorded during functional MRI.

Combined EEG/fMRI recording has been used to localize the generators of EEG events and to identify subject state in cognitive studies and is of increasing interest. However, the large EEG artifacts induced during fMRI have precluded simultaneous EEG and fMRI recording, restricting study design. Removing this artifact is difficult, as it normally exceeds EEG significantly and contains components in the EEG frequency range. We have developed a recording system and an artifact reduction method that reduce this artifact effectively. The recording system has large dynamic range to capture both low-amplitude EEG and large imaging artifact without distortion (resolution 2 microV, range 33.3 mV), 5-kHz sampling, and low-pass filtering prior to the main gain stage. Imaging artifact is reduced by subtracting an averaged artifact waveform, followed by adaptive noise cancellation to reduce any residual artifact. This method was validated in recordings from five subjects using periodic and continuous fMRI sequences. Spectral analysis revealed differences of only 10 to 18% between EEG recorded in the scanner without fMRI and the corrected EEG. Ninety-nine percent of spike waves (median 74 microV) added to the recordings were identified in the corrected EEG compared to 12% in the uncorrected EEG. The median noise after artifact reduction was 8 microV. All these measures indicate that most of the artifact was removed, with minimal EEG distortion. Using this recording system and artifact reduction method, we have demonstrated that simultaneous EEG/fMRI studies are for the first time possible, extending the scope of EEG/fMRI studies considerably.

Adult↗
PubMed2005

Development of immunoaffinity solid phase microextraction probes for analysis of sub ng/mL concentrations of 7-aminoflunitrazepam in urine.

We report on the development of solid phase microextraction probes for drug analysis, prepared with antibodies specific for benzodiazepines covalently immobilized to the surface. In the technique, immobilized antibody probes are exposed to a sample containing the drug for 30 min. Extracted drugs are subsequently desorbed from the probes in 500 microL of methanolic desorption solution, which is dried, reconstituted in a small volume of injection solution and analysed by LC-MS/MS. The antibodies were characterized both before and after immobilization, to facilitate the rational selection of antibodies for such analyses. Polyclonal and monoclonal antibodies were compared as was the impact of affinity purification of the polyclonal antibody to isolate the drug-specific fraction. The probes were evaluated for utility in analyzing 7-aminoflunitrazepam at sub ng/mL concentrations in urine, which is expected to be found several days after a single oral dose of 2 mg of flunitrazepam. Such analyses are required in monitoring for abuse of this drug, both in terms of 'club drug' use and in cases of drug-facilitated sexual assault. In these cases drug concentrations in blood and urine are much lower than in chronic abuse cases and are difficult to analyse by conventional methods. The method developed has a limit of detection of 0.02 ng/mL, with accuracy ranging from 1% to 27% and precision (% R.S.D.) ranging from 2% to 10% between the lower and upper limits of quantitation for the analysis of 7-aminoflunitrazepam in urine. The dynamic range of the method is from 0.02 ng/mL, which is limited by the instrument sensitivity, to 0.5 ng/mL, which is approaching the capacity of the probes. This would allow for quantitative analysis of samples at concentrations below that measurable by many other methods for general benzodiazepines analysis from urine, and a highly selective screen for samples at higher concentrations. The method has similar limits of detection to the most sensitive literature methods specifically designed for such analysis but with the advantage of significantly simplified sample preparation. This simplification makes the technique more amenable for use by both professionals and non-professionals.

Algorithms↗
PubMed1996

Computed radiography X-ray exposure trends.

RATIONALE AND OBJECTIVES: Computed radiography provides correct optical density on film, independent of the incident radiation exposure, but it can result in under- or overexposure of the imaging plate. In the current study, we evaluated the radiation exposure trends of computed radiography over a 2-year period for portable chest examinations to determine and compare the radiographic techniques of the computed radiography system relative to conventional screen-film detectors. METHODS: A Fuji computed radiography system was interfaced to a digital workstation to track system usage and examination demographics, including examination type and sensitivity number. Hard-copy films were used for diagnosis. The sensitivity number, a value inversely related to incident exposure on the imaging plate, was used to determine whether the proper techniques were used by the technologists. RESULTS: The initial use of the computed radiography system revealed a broad distribution of exposures being used; complaints regarding noisy films (e.g., underexposure) resulted in subsequent overexposure for a significant number of films. A quality-control audit indicating excessive exposure resulted in educational feedback and a tighter distribution of exposures within the optimal range as determined by our radiologists. The average technique was approximately equivalent to a 200-speed system. CONCLUSION: Computed radiography provides excellent dynamic range and rescaling capabilities for proper film optical density, and thus fewer repeat examinations. However, underexposure results in suboptimal image quality that is related to excessive quantum mottle. Overexposure requires film audits to limit unnecessary radiation exposure. In general, the optimal exposures are achieved with approximately 1.5-2 times the incident detector exposure of a 400-speed rare-earth system. The ability of computed radiography to reduce radiation exposure is unlikely when compared with a typical rare-earth screen-film combination (400 speed) in terms of adequate image quality for the diagnosis of subtle, low-contrast findings. For certain diagnostic procedures (e.g., nasogastric tube placement verification), lower exposures can be tolerated.

Humans↗
PubMed2005

Compact FPGA-based beamformer using oversampled 1-bit A/D converters.

A compact medical ultrasound beamformer architecture that uses oversampled 1-bit analog-to-digital (A/D) converters is presented. Sparse sample processing is used, as the echo signal for the image lines is reconstructed in 512 equidistant focal points along the line through its in-phase and quadrature components. That information is sufficient for presenting a B-mode image and creating a color flow map. The high sampling rate provides the necessary delay resolution for the focusing. The low channel data width (1-bit) makes it possible to construct a compact beamformer logic. The signal reconstruction is done using finite impulse reponse (FIR) filters, applied on selected bit sequences of the delta-sigma modulator output stream. The approach allows for a multichannel beamformer to fit in a single field programmable gate array (FPGA) device. A 32-channel beamformer is estimated to occupy 50% of the available logic resources in a commercially available mid-range FPGA, and to be able to operate at 129 MHz. Simulation of the architecture at 140 MHz provides images with a dynamic range approaching 60 dB for an excitation frequency of 3 MHz.

Analog-Digital Conversion↗
PubMed2004

Variable ratio of hepatitis C virus RNA to viral core antigen in patient sera.

Quantification of hepatitis C virus (HCV) core antigen and RNA in serum samples leads to a highly variable ratio of both. It is not clear whether this is due to the inaccuracy of RNA quantification or whether both are independent parameters in a certain range. We established a real-time reverse transcription (RT)-PCR for HCV RNA that combines very high sensitivity with a large dynamic range and minimal standard deviations. The assay was calibrated with the first international standard, 96/790, and the international genotype panel for HCV from the National Institute of Biological Standardisation and Control. A linear readout was obtained between 200 and 5 x 10(7) IU/ml. The detection limit was 80 IU/ml, the reproducibility was <0.05 log, and the standard error within one run was <0.01. Comparison of the method with the Roche Monitor competitive RT-PCR revealed its high accuracy. The core protein concentration was determined within a range from 1.5 to 400 pg/ml by using the preliminary trak-C assay from Ortho Clinical Diagnostics. Correlating the HCV RNA levels with core antigen concentrations in 197 serum samples from 23 interferon-treated patients, a average ratio of 7,900 IU of HCV RNA per pg of core antigen was estimated, but the variability of this ratio exceeded largely the variability of the two assays, ranging from 50 to 20,000 IU/pg. Theoretically, HCV should contain ca. 43,000 IU of RNA/pg core. In conclusion, the core antigen assay seems to detect, in addition to complete virions, RNA-free core protein structures, which enhances its sensitivity (98% in this group). The variable ratio of RNA and core protein is not mainly due to standard deviations of quantification but could be an additional parameter for treatment follow-up and state of viral replication.

Antigens, Viral↗
PubMed1975

White noise analysis of Phycomyces light growth response system. I. Normal intensity range.

The Wiener-Lee-Schetzen method for the identification of a nonlinear system through white gaussian noise stimulation was applied to the transient light growth response of the sporangiophore of Phycomyces. In order to cover a moderate dynamic range of light intensity I, the imput variable was defined to be log I. The experiments were performed in the normal range of light intensity, centered about I0 = 10(-6) W/cm2. The kernels of the Wierner functionals were computed up to second order. Within the range of a few decades the system is reasonably linear with log I. The main nonlinear feature of the second-order kernel corresponds to the property of rectification. Power spectral analysis reveals that the slow dynamics of the system are of at least fifth order. The system can be represented approximately by a linear transfer function, including a first-order high-pass (adaptation) filter with a 4 min time constant and an underdamped fourth-order low-pass filter. Accordingly a linear electronic circuit was constructed to simulate the small scale response characteristics. In terms of the adaptation model of Delbrück and Reichardt (1956, in Cellular Mechanisms in Differentiation and Growth, Princeton University Press), kernels were deduced for the dynamic dependence of the growth velocity (output) on the "subjective intensity", a presumed internal variable. Finally the linear electronic simulator above was generalized to accommodate the large scale nonlinearity of the adaptation model and to serve as a tool for deeper test of the model.

Adaptation, Physiological↗
PubMed1989

Response characteristics of vibration-sensitive neurons in the midbrain of the grassfrog, Rana temporaria.

European grassfrogs (Rana temporaria) were stimulated with pulsed sinusoidal, vertical vibrations (10-300 Hz) and the responses of 46 single midbrain neurons were recorded in awake, immobilized animals. Most units (40) had simple V-shaped excitatory vibrational tuning curves. The distribution of best frequencies (BF's) was bimodal with peaks at 10 and 100 Hz and the thresholds ranged from 0.02 to 1.28 cm/s2 at the BF. Twenty-three neurons showed phasic-tonic and 11 neurons phasic responses. The dynamic range of seismic intensity for most neurons was 20-30 dB. In contrast to the sharp phase-locking in peripheral vibration-sensitive fibers, no phase-locking to the sinusoidal wave-form was seen in the midbrain neurons. The midbrain cells did not respond at low stimulus intensities (below 0.01-0.02 cm/s2) where a clear synchronization response occurs in saccular fibers. Six midbrain neurons had more complex response characteristics expressed by inhibition of their spontaneous activity by vibration or by bi- and trimodal sensory sensitivities. In conclusion, the vibration sensitive cells in the midbrain of the grassfrog can encode the frequency, intensity, onset and cessation of vibration stimuli. Seismic stimuli probably play a role in communication and detection of predators and the vibration-sensitive midbrain neurons may be involved in the central processing of such behaviorally significant stimuli.

Acoustic Stimulation↗
PubMed2006

Ca2+ indicators based on computationally redesigned calmodulin-peptide pairs.

The binding interface of calmodulin and a calmodulin binding peptide were reengineered by computationally designing complementary bumps and holes. This redesign led to the development of sensitive and specific pairs of mutant proteins used to sense Ca(2+) in a second generation of genetically encoded Ca(2+) indicators (cameleons). These cameleons are no longer perturbed by large excesses of native calmodulin, and they display Ca(2+) sensitivities tuned over a 100-fold range (0.6-160 microM). Incorporation of circularly permuted Venus in place of Citrine results in a 3- to 5-fold increase in the dynamic range. These redesigned cameleons show significant improvements over previous versions in the ability to monitor Ca(2+) in the cytoplasm as well as distinct subcellular localizations, such as the plasma membrane of neurons and the mitochondria.

Amino Acid Sequence↗
PubMed2005

Identification of dynamical correlations within the myosin motor domain by the normal mode analysis of an elastic network model.

In order to systematically analyze functionally relevant dynamical correlations within macromolecular complexes, we have developed computational methods based on the normal mode analysis of an elastic network model. First, we define two types of dynamical correlations (fluctuation-based and density-based), which are computed by summing up contributions from all low-frequency normal modes up to a given cutoff. Then we use them to select dynamically important "hinge residues" whose elastic distortion affects the fluctuations of a large number of residues. Second, in order to clarify long-range dynamical correlations, we decompose the dynamical correlations to individual normal modes to identify the most relevant modes. We have applied these methods to the analysis of the motor domain of Dictyostelium myosin and have obtained the following three interesting results that shed light on its mechanism of force generation: first, we find the hinge residues are distributed over several key inter-subdomain joints (including the nucleotide-binding pocket, the relay helix, the SH1 helix, the strut between the upper 50 kDa and the lower 50 kDa subdomains), which is consistent with their hypothesized roles in modulating functionally relevant inter-subdomain conformational changes; second, a single mode 7 (for structure 1VOM) is found to dominate the fluctuation-based correlations between the converter/strut and the nucleotide-binding pocket, revealing a surprising simplicity for their intriguing roles in the force generation mechanism; finally, we find a negative density-based correlation between the strut and the nucleotide-binding pocket, which is consistent with the hypothesized signaling pathway that links the actin-binding site's opening/closing with the nucleotide-binding pocket's closing/opening.

Animals↗
PubMed2002

Contribution of AMPA and NMDA receptors to excitatory responses in the inferior colliculus.

Brain slice studies of neurons in the central nucleus of the inferior colliculus (ICC) indicate that excitatory responses evoked by electrical stimulation of the lateral lemniscus consist of two components, an early, rapid response mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and a later, a slower one mediated by N-methyl-D-aspartate (NMDA) receptors. The early response can be selectively blocked by AMPA receptor antagonists (1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium [NBQX]; or 6-cyano-7-nitroquinoxaline-2,3-dione) [CNQX], and the later one by NMDA receptor antagonists ((+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid [CPP]; or (+/-)-2-amino-5-phosphonovaleric acid) [APV]. Both AMPA and NMDA receptor-mediated responses can be elicited at resting potential, although the NMDA response is voltage dependent and makes a greater contribution when the cell membrane is depolarized. In vivo studies indicate that both AMPA and NMDA receptors contribute to sound-evoked responses. Both AMPA and NMDA receptor antagonists reduce the firing rate of single neurons in the ICC to contralaterally presented tones. Both classes of antagonist lower evoked activity over a wide range of sound intensities from threshold to maximum sound pressure levels. Thus, both NMDA and AMPA receptors contribute to responses over the full dynamic range of auditory sensitivity. The AMPA receptor antagonist, NBQX, is more effective than the NMDA receptor antagonist, CPP, in blocking responses of onset cells. Furthermore, NBQX and CPP have preferential effects in blocking the early or late responses of neurons that exhibited sustain activity to a 100 ms tone. Excitatory responses to sinusoidally amplitude-modulated stimuli are also reduced by application of either AMPA or NMDA antagonists. However, the synchrony of firing of action potentials to the modulation period (vector strength) is largely unaffected. The data suggest that the synchrony of firing of neurons in the inferior colliculus is determined primarily by the pattern of activity at lower levels of the auditory pathway and/or the local intrinsic properties of the cells.

Acoustic Stimulation↗
PubMed2000

Evolutionary consequences of changes in species' geographical distributions driven by Milankovitch climate oscillations.

We suggest Milankovitch climate oscillations as a common cause for geographical patterns in species diversity, species' range sizes, polyploidy, and the degree of specialization and dispersability of organisms. Periodical changes in the orbit of the Earth cause climatic changes termed Milankovitch oscillations, leading to large changes in the size and location of species' geographical distributions. We name these recurrent changes "orbitally forced species' range dynamics" (ORD). The magnitude of ORD varies in space and time. ORD decreases gradual speciation (attained by gradual changes over many generations), increases range sizes and the proportions of species formed by polyploidy and other "abrupt" mechanisms, selects against specialization, and favor dispersability. Large ORD produces species prone neither to extinction nor gradual speciation. ORD increases with latitude. This produces latitudinal patterns, among them the gradient in species diversity and species' range sizes (Rapoport's rule). Differential ORD and its evolutionary consequences call for new conservation strategies on the regional to global scale.

Biological Evolution↗
PubMed2006

A longitudinal study of electrical stimulation levels and electrode impedance in children using the Clarion cochlear implant.

CONCLUSIONS: Electrical stimulation levels and electrode impedance values (EIVs) in children using the Clarion cochlear implant (CI) programmed with CIS strategy stabilized after 3 months of implant use. The data presented here may be useful as a general guideline for the programming of infants and young children and may further be of help for the identification of patients who fall outside the "average" range. OBJECTIVES: The purpose of the present study was to evaluate changes in electrical stimulation levels, i.e. threshold (T) levels, comfortable (M) levels, dynamic range (DR), and EIVs during the first 18 months of implant use, in children using the Clarion CI. MATERIALS AND METHODS: The maps of 18 pre-lingual children (mean age at implantation 4.2 years; range 1-8), using the Enhanced Bipolar 1.2 or Bipolar standard electrode with the S-Series speech processor programmed with CIS strategy, were examined at five time points: connection, and 3, 6, 12, and 18 months post-initial stimulation. T levels, M levels, DR and EIVs were analyzed according to four cochlear segments: apical, apical-medial, medial-basal, and basal. RESULTS: During the first 3 months of implant use T levels increased to some extent, whereas M levels and DR increased significantly. From 3 months and through the entire follow-up, T and M levels as well as DR were stable. EIVs of current carrying electrodes decreased significantly from connection to the 3-month visit; thereafter a stabilization of values was evident. Electrical stimulation levels and EIVs did not differ among the cochlear segments during the entire follow-up.

Adolescent↗
PubMedDate not supplied

Quantitative determination of sildenafil (Viagra) and its metabolite (UK-103,320) in fluid and tissue specimens obtained from six aviation fatalities.

During the investigation of aviation accidents, postmortem samples from victims are submitted to the Federal Aviation Administration's Civil Aerospace Medical Institute for toxicological analysis. This report presents a rapid and reliable method for the identification and quantitation of sildenafil (Viagra) and its active metabolite, UK-103,320. This procedure utilizes sildenafil-d(8) as an internal standard for more accurate and reliable quantitation. The quantitation of sildenafil and UK-103,320 in postmortem fluid and tissue specimens obtained from victims from six separate aviation fatalities is described. The method incorporates solid-phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS-MS) and MS-MS-MS utilizing an atmospheric pressure chemical ionization ion trap MS in the positive chemical ionization mode. Solid-phase extraction provided an efficient sample extraction yielding recoveries ranging from 79 to 88%. The limits of detection for sildenafil and UK-103,320 were 0.39 and 0.19 ng/mL, respectively. The linear dynamic range for both compounds was 0.78-800 ng/mL. The current method proved to be simple, accurate, and robust for the identification and quantitation of sildenafil and UK-103,320 in postmortem fluids and tissues.

Accidents, Aviation↗
PubMed2004

The long-term stability of amorphous silicon flat panel imaging devices for dosimetry purposes.

This study was carried out to determine the stability of the response of amorphous silicon (a-Si)-flat panel imagers for dosimetry applications. Measurements of the imager's response under reference conditions were performed on a regular basis for four detectors of the same manufacturer. We found that the ambient temperature influenced the dark-field, while the gain of the imager signal was unaffected. Therefore, temperature fluctuations were corrected for by applying a "dynamic" darkfield correction. This correction method also removed the influence of a small, irreversible increase of the dark-field current, which was equal to 0.5% of the dynamic range of the imager per year and was probably caused by mild radiation damage to the a-Si array. By applying a dynamic dark-field correction, excellent stability of the response over the entire panel of all imagers of 0.5% (1 SD) was obtained over an observation period up to 23 months. However, two imagers had to be replaced after several months. For one imager, an image segment stopped functioning, while the image quality of the other imager degraded significantly. We conclude that the tested a-Si EPIDs have a very stable response and are therefore well suited for dosimetry. We recommend, however, applying quality assurance tests dedicated to both imaging and dosimetry.

Calibration↗
PubMed2006

Quantitative determination of total methamphetamine and active metabolites in rat tissue by liquid chromatography with tandem mass spectrometric detection.

High-throughput liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) methodology for the determination of methamphetamine (METH), amphetamine (AMP), 4-hydroxymethamphetamine (4-OH-METH), and 4-hydroxyamphetamine (4-OH-AMP) was developed and validated using simple trichloroacetic acid sample treatment. The method was validated in rat serum, brain, and testis. Lower limits-of-quantitation (LOQ) for METH and AMP were 1 ng x mL(-1) using positive ion electrospray tandem mass spectrometry (MS/MS). The accuracy of the method was within 25% of the actual values over a wide range of analyte concentrations. The within-assay precision was better than 12% (coefficient of variation). The method was linear over a wide dynamic range (0.3-1000 ng x mL(-1)). Quantitation was possible in all 3 matrices using only serum standards because of minimal matrix-associated ion effects or the use of an internal standard. Finally, the LC-MS/MS method was used to determine serum, brain, and testis METH and AMP concentrations during a subcutaneous infusion (5.6 mg kg(-1) day(-1)) of METH in rats. Concentrations of 4-OH-AMP and 4-OH-METH were below the LOQ in experimental samples. The bias introduced by using serum calibrators for the determination of METH and AMP concentrations in testis and brain was less than 8% and insignificant relative to the interanimal variability.

Animals↗