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At least 127 records · Page 7Linked to original sources
PubMed1991

Perfect-mixer retention function by analytical deconvolution of tracer histograms: application to evaluation of left-ventricular contractility and competence.

The analytical solution for the perfect-mixer retention function, r(t), was developed from tracer histograms sampled at the system input, i(t), and its output, y(t), linked by the convolution integral y = i * r. Theories were developed for both continuous-output mixer and pulsatile, discrete mixer. The latter method was applied in first-pass radioangiography (FPRA) to calculate the forward ejection fraction of the left ventricle (LVFEF). Curves generated over the lungs and the ventricle provided system input and output respectively. LVFEF correlated strongly with the reference values obtained with simultaneously acquired gated FPRA(LVGEF) in 32 non-regurgitant patients: LVGEF = 0.90LVFEF + 5.93, r = 0.96, SEE = 3.98, p less than 0.001. In 14 patients with left-side valvular incompetence LVFEF values (0.41 +/- 0.13) were consistently lower than the corresponding LVGEF values (0.63 +/- 0.11). The method is free from instability inherent in numerical deconvolution. Applied in FPRA it yielded accurate estimates of LV contractility and competence. The continuous-mixer theory may apply to arbitrary compartmental models studied via tracer kinetics.

Adolescent↗
PubMed1989

Scatter compensation in digital chest radiography using Fourier deconvolution.

The authors present a numerical deconvolution technique to compensate for image degrading effects caused by scattered photons in radiographic chest images. Fourier transform techniques are used to deconvolve a shift invariant model of the two dimensional point spread response functions of the scattered radiation. This approach uses a digitized radiograph acquired with a standard chest imaging protocol, so no specialized imaging equipment is required. While the shift variant shape of the scatter model is optimized for the lung field, effective compensation is provided when this model shape is applied to other chest regions. Preliminary evaluation suggests that this technique can provide improved image contrast over the entire chest region.

Computer Simulation↗
PubMed1984

99Tcm-TDG renography with deconvolution analysis: a comparative study with 99Tcm-DTPA and 123I-hippuran.

TDG has been compared with hippuran and DTPA in normal subjects and the derived gamma camera renograms of both the whole kidney and parenchymal regions subjected to deconvolution analysis using the matrix algorithm. The transit time of TDG was found to be longer than both hippuran and DTPA. The parenchymal mean transit time of TDG was 3.0 +/- 0.6 min (mean +/- S.D.). That of hippuran was 2.2 +/- 0.7 min and DTPA, 2.6 +/- 0.5 min. It is thought that a small fraction of the TDG is bound to the renal parenchyma thus prolonging both the mean and maximum transit times.

Adult↗
PubMed1985

The reduction of renogram deconvolution to a direct method of transit time determination.

It is known that the intrarenal mean transit time (MTT) can be determined using renography by first deconvoluing the kidney retention function from the obtained time-activity curve and then integrating the retention function. A direct and approximate calculational method, based on an integral mathematical model, has also been employed to estimate the MTT. In this work it is shown that the direct approximate method is equivalent to the standard deconvolution method applied with the assumption of a time independent retention function. Potential errors incurred using the direct method are thus quantified and assessed over a range of representative decay parameters.

Humans↗
PubMed1990

[Delimiting the molecular envelope of a protein by deconvolution of the Patterson function for native proteins].

A process, based on the superposition method, is described to delimit the molecular envelope of a protein by deconvolution of the Patterson function. The object is to obtain a preliminary set of phases from native structure-factor amplitudes with only native intensity data. The method has been tested with data from two immunoglobulin Fab fragments, Fab NEW and Fab R19.9. Several zones of resolution were explored.

Immunoglobulin Fragments↗
PubMed1991

Deconvolution of tracer and dilution data using the Wiener filter.

In the study of living systems it is often necessary to inject or infuse a substance into the peripheral circulation and monitor its subsequent concentration in the plasma with time. Examples abound in the pharmacokinetic study of drugs and in the use of the indicator dilution technique for measuring blood flow. Furthermore, it is often necessary to deconvolve one such measured, and hence noisy, data set with another. One of the standard methods for deconvolving noisy signals is the Wiener filter, which is generally derived as a real window in the frequency domain such that the mean squared error between the estimated deconvolved function and the truth, on average, is minimized. Application of the Wiener filter requires some (often crude) model of the noise-to-signal power ratio as a function of frequency. In the pharmacokinetic and indicator dilution situations, however, one invariably has a good model of the actual function to be deconvolved in the form of a sum of decaying exponential functions. Such a model may be employed to calculate the signal-to-noise power ratio for use in the Wiener filter, or alternatively may be directly deconvolved itself. It is shown that better results are achieved with the Wiener filter if the model of the signal is not particularly accurate, whereas with a very accurate model it is better to deconvolve the model itself. The point at which the two deconvolution approaches perform comparably occurs when the error in the model is of a similar magnitude to the noise.

Mathematical Computing↗
PubMed1995

Deconvolution of infrequently sampled data for the estimation of growth hormone secretion.

In this paper, the deconvolution of infrequently and nonuniformly sampled data is addressed. A nonparametric technique is worked out that provides a smooth estimate of the unknown input signal and takes into account nonnegativity constraints. In spite of the size of the problem, efficient algorithms for solving the constrained optimization problem and computing confidence intervals are proposed. The new technique is used to estimate growth hormone (GH) secretion after repeated GH-releasing hormone (GHRH) administration from samples of blood concentration.

Adult↗
PubMed1991

A deconvolution technique for improved estimation of rapid changes in ion concentration recorded with ion-selective microelectrodes.

In biological preparations, measurements of rapid, stimulus-evoked changes in ion concentration by ion-selective microelectrodes can be distorted by the limited bandwidth of these sensors. Techniques were developed to reconstruct the actual change in ion concentration using deconvolution of the electrode's output signal and the electrode's transfer function. In the vertebrate retina, a knowledge of the actual time course of a light-evoked increase in extracellular K+ concentration was used to provide a rigorous test of a hypothesis regarding the electrical origin of a clinically important component of the electroretinogram.

Animals↗
PubMed1990

The application of deconvolution analysis to elucidate the pulsatile nature of growth hormone secretion using a variable half-life of growth hormone.

A deconvolution analysis model to calculate pituitary growth hormone (GH) secretion rate from measured serum GH concentration has been developed. This uses an iterative method of 'curve-stripping' based on an estimate of the half-life. The model has been applied to serum GH profiles and demonstrates that GH secretion occurs in discrete bursts with quiescent periods between secretory episodes, an 'on-off' phenomenon. The model can clearly dissect complicated concentration profiles such as the serum GH concentration response to growth hormone releasing hormone. The estimate was derived from calculating the half-life of serum GH in 10 subjects following an intravenous bolus injection of 50 mU of biosynthetic human growth hormone (b-hGH) and following infusions of the exogenous hormone (3 mU/kg/h) for 15, 30, 60 and 180 min. Endogenous GH secretion was suppressed by a continuous infusion of somatostatin (1-14). An asymptotic relationship between the duration of GH infusion and the GH half-life was established. A half-life of 15.3 min was achieved after exposure to GH for 60 min and a maximum half-life of 15.7 min after 180 min exposure.

Adolescent↗
PubMed1989

Determination of microscopic dissociation constants of 3-hydroxy-alpha-(methylamino)methyl-benzenemethanol by a spectral deconvolution method.

Microscopic dissociation constants of 3-hydroxy-alpha-(methylamino)methyl-benzenemethanol have been calculated from the titration spectrophotomeric data (c = 3.8 x 10(-4) M. Ionic strength = 0.16; buffer system: H3BO3/KOH) by application of a spectral deconvolution method. The results found (pKa = 9.48; pKb = 9.71; pKc = 10.12 and pKd = 9.88) are in good concordance with those obtained from the conventional regression linear method (pKa = 9.45; pKb = 9.77; pKc = 10.14 and pKd = 9.81).

Chemical Phenomena↗
PubMedDate not supplied

Removal of image intensifier veiling glare by mathematical deconvolution techniques.

X-ray images acquired with an image intensifier detector system suffer from veiling glare, a low-frequency degradation described by a point spread function (PSF). The PSF has two experimentally determined parameters unique to a given image intensifier. This information is utilized to deconvolve the degradation from digitally acquired images. Results demonstrate a significant increase in contrast ratio of high-contrast objects after deconvolution and image restoration.

Animals↗
PubMedDate not supplied

Deconvolution techniques for removing the effects of chemical shift in 19F nuclear magnetic resonance imaging of perfluorocarbon compounds.

Nuclear magnetic resonance (NMR) imaging of perfluorocarbon (PFC) emulsions and neat liquids has shown potential for in vivo oxygen imaging in blood and organ tissue. PFC compounds exhibit complicated NMR spectra caused by chemical shifts and spin-spin couplings which can lead to artifacts and degraded spatial resolution of resulting NMR images. To correct for the chemical shift artifacts, the technique of spectral deconvolution has been applied to NMR imaging of PFC compounds. The temporal filter for this process can be directly applied to raw free induction decay data in projection reconstruction or to spin-echo data in two-dimensional Fourier transform imaging techniques. The effect of chemical shift artifacts was demonstrated through the NMR imaging of two PFC compounds (F-tributylamine and F-decalin) in phantoms. Methods are presented and demonstrated which allow the chemical shift artifacts to be removed and true images of the spatial distribution of the PFC's to be recovered.

Blood Substitutes↗
PubMedDate not supplied

X-ray scatter removal by deconvolution.

The distribution of scattered x rays detected in a two-dimensional projection radiograph at diagnostic x-ray energies is measured as a function of field size and object thickness at a fixed x-ray potential and air gap. An image intensifier-TV based imaging system is used for image acquisition, manipulation, and analysis. A scatter point spread function (PSF) with an assumed linear, spatially invariant response is modeled as a modified Gaussian distribution, and is characterized by two parameters describing the width of the distribution and the fraction of scattered events detected. The PSF parameters are determined from analysis of images obtained with radio-opaque lead disks centrally placed on the source side of a homogeneous phantom. Analytical methods are used to convert the PSF into the frequency domain. Numerical inversion provides an inverse filter that operates on frequency transformed, scatter degraded images. Resultant inverse transformed images demonstrate the nonarbitrary removal of scatter, increased radiographic contrast, and improved quantitative accuracy. The use of the deconvolution method appears to be clinically applicable to a variety of digital projection images.

Computer Simulation↗
PubMed1984

An improvement in the range resolution of ultrasonic pulse echo systems by deconvolution.

Ultrasonic pulse echo systems are often limited in range resolution by the bandwidth of the piezoelectric transducer. Significant improvements in the range resolution of such systems can be obtained by minimizing the effects of the transducer's dynamic response on the overall pulse echo process. An approach to minimize the effects of the transducer is developed from linear system and impulse response techniques. In essence, the pulse echo voltage of interest is deconvolved with a pulse echo reference voltage which is obtained from an air/water interface in the nearfield of the transducer . A computer study of the pulse echo process and the deconvolution process is presented to illustrate the nature of the improvement in range resolution for several cases of interest. Finally, experimental results are presented to illustrate the improvement using commercially available transducers.

Transducers↗
PubMed1989

Growth hormone secretory rates in children as estimated by deconvolution analysis of 24-h plasma concentration profiles.

The kinetics of growth-hormone (GH) distribution and elimination was estimated in five GH-deficient children who received 11 intravenous single injections of GH. The plasma disappearance data were analyzed in terms of a two-compartment model. The kinetic parameters obtained were then used in calculating the GH-secretory rate by a numerical deconvolution technique. A simple formula was derived for calculation of the cumulated secretion from the area under the concentration curve of 145 healthy children of various ages, heights, and stages of puberty. The estimated 24-h GH secretion increased with age, corresponding to a two- to fourfold increase during the adolescence period. The highest secretions were found in pubertal stages 3-4. In prepubertal children the heights correlated markedly with the secretion of GH (r = 0.83). Thus an indication of the range of the GH secretion in normal growing children is found, which is important to estimate substitution doses for treatment of GH-deficient children.

Activity Cycles↗
PubMed1994

Estimation of growth hormone secretory patterns in children with use of a numerical deconvolution technique: experimental design with use of computer simulation.

Growth hormone (GH) secretion rates were estimated from 24-hour plasma GH concentration profiles using a model-based numerical deconvolution method. The basic kinetic parameters describing GH distribution and elimination were obtained from studies using single intravenous injections in GH-deficient children. Computer simulation techniques were used to produce 24-hour GH secretion profiles, which could serve as reference curves for analysis of the impact of certain practical aspects of the estimation of GH secretion, such as the method of blood sampling (discrete or integrated), sampling frequency and analytical errors. The results show that sampling intervals of 20 min are acceptable even in the presence of analytical errors, and that with this sampling interval, discrete blood sampling does not seem to be preferable to continuous withdrawal of blood.

Blood Specimen Collection↗
PubMed1995

An information-maximization approach to blind separation and blind deconvolution.

We derive a new self-organizing learning algorithm that maximizes the information transferred in a network of nonlinear units. The algorithm does not assume any knowledge of the input distributions, and is defined here for the zero-noise limit. Under these conditions, information maximization has extra properties not found in the linear case (Linsker 1989). The nonlinearities in the transfer function are able to pick up higher-order moments of the input distributions and perform something akin to true redundancy reduction between units in the output representation. This enables the network to separate statistically independent components in the inputs: a higher-order generalization of principal components analysis. We apply the network to the source separation (or cocktail party) problem, successfully separating unknown mixtures of up to 10 speakers. We also show that a variant on the network architecture is able to perform blind deconvolution (cancellation of unknown echoes and reverberation in a speech signal). Finally, we derive dependencies of information transfer on time delays. We suggest that information maximization provides a unifying framework for problems in "blind" signal processing.

Algorithms↗
PubMed1984

Lateral deconvolution of ultrasonic beams.

A number of papers have appeared recently describing methods of lateral resolution improvement in ultrasonic images by deconvolution of the amplitude detected cross-beam characteristic. It is the intention of this paper to demonstrate that such methods of resolution improvement are appropriate only for a limited class of targets. In general, the effect of interference between the r.f. signals from multiple targets at differing distances is such that the amplitude beam width obtained for these targets cannot be considered as the linear combination of shifted replicas of the amplitude beam width for an individual target. This is a consequence of the non-linear character of the detection process. In these cases the method of deconvolving the detected responses, although capable of giving reduced spot sizes, makes errors in the position of the images and is susceptible to false images and sidelobes . The phenomenon is demonstrated with computer and experimental data on point targets.

Computers↗