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At least 343 records · Page 19Linked to original sources
PubMed2003

Band composition analysis: a new procedure for deconvolution of the mass spectra of organometallic compounds.

A new chemometric procedure called band composition analysis (BCA) designed for the deconvolution of mass spectra of organometallics is proposed. BCA generates theoretical bands T(i), then combines them to obtain a model band M, which is finally compared with the experimental band E. All of these steps are realized with computer assistance. This modeling yields four parameters characterizing the experimental band: theoretical and model variances s(2) (theor) and s(2) (model), a fit factor alpha and a contribution x(i) from the theoretical band. If s(2) (theor) > 20 the band is deemed complex and needs modeling. The values alpha > 90 indicate that there is good agreement between the experimental and model bands. BCA is particularly effective for the modeling of complex isotopic bands often present in organometallics. Two illustrations of BCA for tetrabutyltin, C(16)H(36)Sn, and 1,1',2,2',3,3'-hexachloroferrocene, C(10)H(4)Cl(6)Fe, are shown.

Ferrous Compounds↗
PubMed2003

In vitro-in vivo correlation in man of a topically applied local anesthetic agent using numerical convolution and deconvolution.

The aim of this study was to evaluate the relevance of the in vitro permeation method used at our laboratory in predicting in vivo dermal and transdermal absorption. Two different emulsions, a submicron oil-in-water (o/w) emulsion and a semisolid water-in-oil (w/o) emulsion, containing a model compound were investigated. The in vitro permeation rate of the compound from these emulsions was measured using static diffusion cells with human skin as membrane. The emulsions were allowed to remain in contact with the skin in the donor chamber for 15, 60, and 240 min. The study was monitored for 240 min and the steady state flux was calculated. The systemic concentration of the compound was measured in vivo as a function of time after dermal application to healthy volunteers with 15 and 60 min of application. A short-lasting i.v. infusion study in healthy volunteers was used to simulate the i.v. bolus dose. Numerical convolution was used to predict the in vivo plasma concentration of the compound while the in vivo absorption rate of the compound was estimated using numerical deconvolution. To establish correlation, the predicted in vivo flux was compared with the corresponding observed in vitro parameter after adjusting for the lag time. No major differences were seen in the systemic plasma levels between the two emulsions, which is in close agreement with the steady state flux measured in vitro. A linear correlation representing a point-to-point relationship was established for each of the investigated formulations and application times. The longer application time was predicted more accurately for both emulsions.

Administration, Cutaneous↗
PubMed1991

A computer program for the deconvolution of mass spectral peak abundance data from experiments using stable isotopes.

A computer program is described for deconvoluting the overlap which is often found in mass spectral peak abundance data from stable isotope experiments. Peak intensity data from calibration standards are corrected using parameters calculated from the analysis of separate external standard solutions of analytes and internal standard. If the calibration data are satisfactory, the same parameters and the slope and intercept values from the least squares analysis of the calibration data are used to correct and quantitate the mass spectral peak intensity data from the quality assurance and experimental samples. Reports and graphs appropriate to the process are produced. Applications are given for the analysis of plasma samples from stable isotope experiments with carprofen, cifenline, and midazolam.

Carbazoles↗
PubMed2002

Is quantification of bolus tracking MRI reliable without deconvolution?

Bolus tracking data obtained with paramagnetic intravascular tracers are commonly analyzed and quantified by the direct measurement of properties of the tissue concentration-time curve (e.g., time to peak (TTP)). The measurement of these "summary parameters" is used as an accessible alternative approach to the complex deconvolution procedure, and provides indirect measures of perfusion. However, summary parameters do not take into account differences in arterial input functions (AIFs) or residue functions (R(t)) between patients or studies. Simulations were performed to assess the variability of summary parameters over a realistic range of AIFs and for differing R(t), to establish whether they can be used as reliable measures of tissue perfusion status. Results showed that the value of each summary parameter investigated is highly dependent upon both the AIF and R(t). The referencing of summary parameters to their corresponding value in the AIF or in normal tissue is a method commonly used to normalize results, but this approach did not lead to any measures that were independent of both the AIF and R(t) in this study. The results presented here show that the use of summary parameters requires considerable caution, since tissue or patient types can easily be incorrectly classified due to the effect of variations in patient AIF and R(t).

Adult↗
PubMed2002

Mapping myocardial perfusion with an intravascular MR contrast agent: robustness of deconvolution methods at various blood flows.

Evaluation of quantitative parameters such as regional myocardial blood flow (rMBF), blood volume (rMBV), and mean transit time (rMTT) by MRI is gaining acceptance for clinical applications, but still lacks robust postprocessing methods for map generation. Moreover, robustness should be preserved over the full range of myocardial flows and volumes. Using experimental data from an isolated pig heart preparation, synthetic MR kinetics were generated and four deconvolution approaches were evaluated. These methods were then applied to the first-pass T(1) images of the isolated pig heart using an intravascular contrast agent and rMBF, rMBV and rMTT maps were generated. In both synthetic and experimental data, the fit between calculated and original data reached equally good results with the four techniques. rMBV was the only parameter estimated correctly in numerical experiments. Moreover, using the algebraic method ARMA, abnormal regions were well delineated on rMBV maps. At high flows, rMBF was underestimated at the experimental noise level. Finally, rMTT maps appeared noisy and highly unreliable, especially at high flows. In conclusion, over the myocardial flow range, i.e., 0-400 ml/min/100g, rMBF identification was biased in presence of noise, whereas rMBV was correctly identified. Thus, rMBV mapping could be a fast and robust way to detect abnormal myocardial regions.

Animals↗
PubMed2003

Tracer arrival timing-insensitive technique for estimating flow in MR perfusion-weighted imaging using singular value decomposition with a block-circulant deconvolution matrix.

Relative cerebral blood flow (CBF) and tissue mean transit time (MTT) estimates from bolus-tracking MR perfusion-weighted imaging (PWI) have been shown to be sensitive to delay and dispersion when using singular value decomposition (SVD) with a single measured arterial input function. This study proposes a technique that is made time-shift insensitive by the use of a block-circulant matrix for deconvolution with (oSVD) and without (cSVD) minimization of oscillation of the derived residue function. The performances of these methods are compared with standard SVD (sSVD) in both numerical simulations and in clinically acquired data. An additional index of disturbed hemodynamics (oDelay) is proposed that represents the tracer arrival time difference between the AIF and tissue signal. Results show that PWI estimates from sSVD are weighted by tracer arrival time differences, while those from oSVD and cSVD are not. oSVD also provides estimates that are less sensitive to blood volume compared to cSVD. Using PWI data that can be routinely collected clinically, oSVD shows promise in providing tracer arrival timing-insensitive flow estimates and hence a more specific indicator of ischemic injury. Shift maps can continue to provide a sensitive reflection of disturbed hemodynamics.

Aged↗
PubMed1989

Baseline deconvolution, phase correction, and signal quantification in Fourier localized spectroscopic imaging.

Lineshapes of spectra obtained through chemical-shift imaging are often distorted due to the delay in sampling necessary for application of phase-encoding gradients. We have developed an automated fitting procedure which simultaneously performs signal quantification, phase correction, and baseline deconvolution of such spectra. The fit is based on the maximum likelihood method and can be implemented in either the time or the frequency domain.

Fourier Analysis↗
PubMed2004

Deconvolution of dynamic contrast-enhanced MRI data by linear inversion: choice of the regularization parameter.

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast-enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel-by-pixel basis--generalized cross validation (GCV) and the L-curve criterion (LCC)--were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1-2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster.

Aged↗
PubMed2006

Improved deconvolution of perfusion MRI data in the presence of bolus delay and dispersion.

Cerebral blood flow (CBF) is commonly estimated from the maximum of the residue function deconvolved from bolus-tracking data. The bolus may become delayed and/or dispersed in the vessels feeding the tissue, resulting in the calculation of an effective residue function, Reff(t), whose shape reflects the distortion of the bolus as well as the hemodynamic tissue status. Consequently the CBF is often underestimated. Since regularizing the deconvolution introduces additional distortions to Reff(t), it is impossible to distinguish a true decrease in the CBF from bias introduced by abnormal vasculature. This may result in misidentification of tissue regions at risk of infarction, which could have serious clinical consequences. We propose a modified maximum-likelihood expectation-maximization (mML-EM) method, which is shown by way of simulations to improve the characterization of Reff(t) across a wide range of shapes. A pointwise termination approach for the iteration minimizes the effects of noise, and appropriate integral approximations minimize discretization errors. mML-EM was applied to data from a patient with left internal carotid artery (ICA) occlusion. The shape of each calculated Reff(t) was used to create a map indicating voxels affected by bolus delay and/or dispersion, where CBF estimates are inherently unreliable. Such maps would be a useful adjunct for interpreting bolus-tracking data.

Computer Simulation↗
PubMed1994

Maximum entropy deconvolution of heterogeneity in protein modification: protein adducts of 4-hydroxy-2-nonenal.

To explore the chemistry of the reactions of the cytotoxic aldehyde trans-4-hydroxy-2-nonenal (HNE) with proteins, we incubated this aldehyde in vitro with beta-lactoglobulin B, a model protein of molecular weight 18,277 Da. Direct characterization of reaction products using electrospray ionization mass spectrometry yielded spectra whose complexity suggested extensive product heterogeneity. Spectra were transformed to a true mass scale using both a conventional transform algorithm and a maximum entropy algorithm. Both transformations demonstrated the formation of aldehyde-protein adducts containing from three to nine aldehyde molecules per molecule of protein. Maximum entropy deconvolution resolved Schiff base adducts and/or dehydration products, differing from the Michael addition adducts by 18 Da. The dominant reaction pathway, however, was Michael addition of the aldehyde to nucleophilic functional groups on the protein. The large number of Michael adducts relative to the one available cysteine requires that other amino acids, such as histidine and lysine, also be modified. The data suggest that methods for analysis of HNE that involve displacement of Schiff base groups from proteins will only recover a small fraction of HNE.

Aldehydes↗
PubMed2006

Determination of ion and neutral loss compositions and deconvolution of product ion mass spectra using an orthogonal acceleration time-of-flight mass spectrometer and an ion correlation program.

Exact masses of monoisotopic ions, and the relative isotopic abundances (RIAs) of ions greater in mass by 1 and 2 Da than the monoisotopic ion, are independent and complementary physical properties useful for distinguishing among elemental compositions of ions possible for a given nominal mass. Using these properties to determine elemental compositions of product ions and neutral losses increases the masses of precursor ions for which unique compositions can be determined. Compositions of the precursor ion, product ion, and neutral loss aid mass spectral interpretation and guide modest chemical literature searches for candidate standards to be obtained for confirmation of tentative compound identifications. This approach is essential for compound characterization or identification due to the absence of commercial libraries of electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) product ion spectra. For a series of 34 exact mass measurements, an orthogonal acceleration time-of-flight mass spectrometer provided 34 and 29 values accurate to within 2 and 1 mDa, respectively, for ions from eight simulated unknowns with [M+H](+) ion masses between 166 and 319 Da. Of 36 RIA measurements for +1 Da or +2 Da ions, 35 were accurate to within 20% of their predicted values (or to within 0.4 RIA % when the RIA value was less than 1%) in the absence of obvious interferences, in cases where the monoisotopic ion peak areas were at least 1.7 x 10(5) counts and the ion masses exceeded 141 Da. An ion correlation program (ICP) provided the unique and correct compositions for all but three of the 34 ions studied. Manual inspection of the data eliminated the incorrect compositions. To test the utility of the ICP for deconvoluting composite product ion spectra, all 34 ions were tested for correlation. Six of eight precursor ions were identified as such, while two were compositional subsets of others and were not properly identified. The six precursor ion compositions were still found by the ICP even though ions with masses less than 158 Da were not considered since they could no longer be correlated with a single precursor ion. Finally, two unidentified analytes were characterized, based on data published by others and using the ICP together with mass spectral interpretation.

Acceleration↗
PubMed2006

Deconvolution filters to enhance resolution of dense time-of-flight survey spectra in the time-lag optimization range.

By applying time-domain filters to time-of-flight (TOF) mass spectrometry signals, we have simultaneously smoothed and narrowed spectra resulting in improved resolution and increased signal-to-noise ratios. This filtering procedure has an advantage over detailed curve fitting of spectra in the case of large dense spectra, when neither the location nor the number of mass peaks is known a priori. This time series method is directly applicable in the time lag optimization range, where point density per peak is constant. We present a systematic methodology to optimize the filters according to any desired figure of merit, illustrating the procedure by optimizing the signal-to-noise per unit bandwidth of matrix-assisted laser desorption/ionization (MALDI) data. We also introduce a nonlinear filter that reduces the spurious structure that often accompanies deconvolution filters. The net result of the application of these filters is that we can identify new structures in dense MALDI-TOF data, clearly showing small adducts to heavy biomolecules.

Algorithms↗
PubMed1995

Deconvolution of gel filtration chromatographs of human plasma lipoproteins.

Gel filtration chromatographs of lipoproteins represent a superposition, or convolution, of the intrinsic polydispersity of the solute and the dispersion due to transport phenomena. We describe a deconvolution technique for improving the resolution of gel filtration chromatographs applicable to lipoproteins and other polydisperse solutes. A matrix of spreading functions, characterizing the dispersive properties of the column, was determined by fitting chromatographic data from a series of monodisperse standards with the solution to the transport equations and interpolating between the fit parameters. A successive approximation scheme was used in which a test distribution was incrementally corrected by an amount proportional to the error between the measured chromatograph and that derived from the test distribution. A nonlinear relaxing function was used to constrain the correction term such that the solution remained physically realizable (i.e., nonnegative absorbance) as it evolved. Deconvolved chromatographs of lipoproteins provided resolution of peaks that were obscured by spreading in the original data. The distribution of particle sizes within each fraction was calculated and verified experimentally by further separating the contents of fractions by gradient gel electrophoresis. Our technique, however, provided comparable resolution of the peaks without the additional experimental procedure.

Algorithms↗
PubMed1998

Reference deconvolution, phase correction, and line listing of NMR spectra by the 1D filter diagonalization method.

We describe a new way to attack the problem of identifying and quantifying the number of NMR transitions in a given NMR spectrum. The goal is to reduce the spectrum to a tabular line list of peak positions, widths, amplitudes, and phases, and to have this line list be of high fidelity. In this context "high fidelity" means that each true NMR transition is represented by a single entry, with no spurious entries and no missed peaks. A high fidelity line list allows the measurement of chemical shifts and coupling constants with good accuracy and precision and is the ultimate in data compression. There are two parts to the problem. The first is to overcome common imperfections: the non-Lorentzian lineshapes that can arise whenever the magnetic field inhomogeneity is less than perfect, and nonzero time delays that cause frequency-dependent phase errors. The second is to fit the spectral features to a model of Lorentzian lines. We use the recently developed filter diagonalization method (FDM) to accomplish the reference deconvolution, the phase correction, and the fitting, and show good progress toward the goal of obtaining a high fidelity line list.

Fourier Analysis↗
PubMedDate not supplied

Maximum-entropy three-dimensional reconstruction with deconvolution of the contrast transfer function: a test application with adenovirus.

We have developed an objective, quantitative, and general algorithm to improve the fidelity of three-dimensional reconstructions made from electron micrographs while at the same time filtering much of the noise present in the recorded data. The new technique is called constrained maximum entropy tomography (COMET). The essence of the method is that it will produce the most featureless reconstruction that fits the projection data within their observational accuracy. In particular, the COMET procedure will minimise the detrimental effects of errors in the measured data and deconvolute the effects of the contrast transfer function. An objective test has been performed using COMET on a conventional image reconstruction obtained from cryo-electron micrographs of adenovirus. The density for hexon, the major coat protein of the virus, which is known to high resolution from X-ray crystallography, provided a known high-resolution control. The COMET reconstruction is in considerably better agreement with the crystallographic electron density than the original reconstruction, throughout the entire resolution range.

Adenoviridae↗
PubMed1994

Practical guidance for testing the accuracy of deconvolution results from quantal analysis.

A Monte Carlo study was carried out to test the reliability of the Maximum Likelihood Estimator (MLE) approach for quantal analysis. This widely used statistical method was applied to extract a finite mixture of Gaussian distributions from simulated data. The data were generated by convolving a distribution of discrete amplitude steps (multiples of a unitary step Q) with Gaussian noise of various standard deviations (sigma n). Our results offer practical guidance on when to use the MLE, taking into account the determining parameters: signal to noise ratio (Q/sigma n, the most important parameter), number of samples collected and the number of components (k). For a given set of parameters the algorithm always converged to the "true" values, never converged to the "true" values or converged in only a fraction of cases to the "true" values. The behavior of the fitting routine in the parameter space is displayed in contour plots. These contour plots can be used as a guide to test the accuracy of deconvolution results.

Computer Simulation↗
PubMed1986

Estimation of drug absorption rates using a deconvolution method with nonequal sampling times.

A method affording direct estimation of the drug absorption rate from blood level data using arbitrary time intervals has been derived based on the staircase input principle. In the derivation, the drug was assumed to follow linear kinetics where the plasma concentration of the drug after an impulse input is expressed by a multiexponential function. Drug absorption was assumed to occur at a constant rate during each subsequent sampling interval. The absorption rate profiles obtained by the method using several numerical examples were expressed as a set of rectangular pulses. Divergence in the profiles reflected blood sampling measurement errors rather than errors due to the deconvolution. Smoothing of the rate profiles by calculating the mean of the absorption rates between adjacent time intervals gave realistic results. Absorption rate profiles for theophylline obtained by the method using published data gave information on the initiation and termination of the absorption as well as the extent of absorption from the dosage form.

Humans↗