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At least 145 records · Page 8Linked to original sources
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↗
PubMed1984

Range resolution improvement by a fast deconvolution method.

Range resolution improvement in ultrasonic echography is considered as an estimation problem which is solved using a new fast minimum variance deconvolution algorithm specially designed for a microprocessor-based on-line processing. This method is used to accurately study the lenses and fundus of the eye and to follow variations of an arterial wall thickness during the cardiac cycle.

Animals↗
PubMed1990

Temporal structure of in vivo adrenal secretory activity estimated by deconvolution analysis.

Circadian and ultradian rhythms of plasma cortisol concentrations have been documented under physiological conditions in diverse animal species. Using a novel, biophysical convolution model to remove subject-specific metabolic clearance rates, we have now estimated spontaneous adrenal secretory events in vivo. The latter were characterized by prominent ultradian rhythms of discrete secretory bursts with periodicities averaging 32, 46, 76, and 130 min. These ultradian cortisol secretory rhythms represented a 17- to 240-fold larger fraction of circadian secretory variations than did cortisol concentration rhythms. We conclude that deconvolution analysis can unmask underlying ultradian rhythms in adrenal secretory activity in vivo.

Activity Cycles↗
PubMed1984

Cytokinetics of subpopulations in mixed heteroploid tumors by television imaging. I. Deconvolution of the S-phase DNA ploidy composition. II. Analysis of the S-phase emptying profile of ploidy subpopulations.

A scheme has been developed for deciphering the cell cycle time parameters of cell subpopulations that differ in their DNA ploidy level and that coexist in mixed heteroploid tumors. The S-phase analysis is presented. The approach is coupled to an automated imaging methodology for simultaneous determination of the Feulgen-stained DNA content and grain count of 3H-thymidine-labeled cells in autoradiographs (Sklarew RJ: J Histochem Cytochem 30:35, 30:49, 1982). The experimental designs involve 3H- and 14C-thymidine double labeling and Colcemid incubation. The deconvolution of the S-phase ploidy composition is illustrated in rat sarcoma cultures comprising four major ploidy subpopulations; with G-2 and mitotic DNA contents of approximately 4C, 8C, 16C, and 32C. The components were identified by their DNA ploidy level, and their S frequencies and labeling indices were obtained. A scheme is also developed and validated for obtaining the S-phase emptying profile of component ploidy subpopulations, and their cell flux at the S/G-2 and G-2/mitosis phase boundaries. In the sarcoma cultures S mobility was found to decrease with increasing DNA ploidy level over the entire ploidy range.

Animals↗
PubMed1992

Elevated growth hormone secretory rate in premature infants: deconvolution analysis of pulsatile growth hormone secretion in the neonate.

Premature infants have higher circulating concentrations of growth hormone (GH) than term infants. Previous investigations of these differences have used sampling frequencies of every 30 min with subsequent application of pulse detection algorithms, such as the CLUSTER program, to assess serum GH pulse parameters. To determine differences in GH secretory rates or GH t1/2 values between premature and term infants, we have sampled 11 neonates at 15-min intervals. We performed deconvolution analysis of the resultant plasma GH values to estimate GH secretory and clearance parameters. Five premature infants (gestational age range 24-34 wk) and six term infants (gestational age range 38-42 wk) were sampled every 15 min for 6 h. All subjects had indwelling arterial catheters. GH was measured (in duplicate) by RIA using 10 microL of plasma. Premature infants had higher secretory burst amplitudes (2.2 +/- 0.13 micrograms/L/min versus 1.4 +/- 0.27 micrograms/L/min, p = 0.02), higher production rates (product of the total number of bursts and the mean mass of GH secreted per burst, 811 +/- 173 micrograms/L/6 h versus 283 +/- 77 micrograms/L/6 h, p = 0.03), and a higher mass of GH per secretory burst (106 +/- 25 micrograms/L versus 38 +/- 11 micrograms/L, p = 0.049) than term infants. The integrated plasma GH concentration exhibited a strong trend toward a higher value in the premature infants (18,100 +/- 800 micrograms/L versus 10,200 +/- 2,700 micrograms/L, p = 0.067).(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1995

Deconvolution analysis of spontaneous nocturnal growth hormone secretion in prepubertal children with preterminal chronic renal failure and with end-stage renal disease.

We sought to determine whether elevated circulating growth hormone (GH) concentrations in uremic prepubertal children are due to an increase in GH secretory activity by the pituitary gland or a decrease in the metabolic clearance of GH consequent to reduced GFR. Deconvolution analysis was applied to the nighttime plasma GH profiles of 1) 11 children with preterminal chronic renal failure, 2) 12 children with end-stage renal disease (ESRD), and 3) a control group of matched children with idiopathic short stature (n = 12). Mean (+/- SEM) half-life of endogenous GH in children with ESRD (27.5 +/- 2.7 min) and preterminal chronic renal failure (23.1 +/- 2.1 min) was significantly higher than in controls (14.8 +/- 1.6 min; p < 0.001). GH half-life correlated inversely with GFR (r = -0.65, p < 0.001). The number of GH secretory bursts/10 h in ESRD (8.1 +/- 0.4) was amplified compared with preterminal chronic renal failure (6.4 +/- 0.5) and with controls (5.9 +/- 0.4; p < 0.005). GH production rate varied over a broad range in the three groups: It was highest in ESRD (202 +/- 56.6 microgm/L/10 h; range 36-683), mainly as a result of an increased number of GH secretory bursts, and not statistically different in preterminal chronic renal failure (66.2 +/- 11.4 microgm/L/10 h; range 25-168) and in controls (129 +/- 27.7 microgm/L/10 h; range 39-392). Increased GH half-life, in concert with an increased GH production in some individuals with ESRD, leads to a 2.5-fold increase in the mean plasma GH concentration in ESRD compared with the two other groups (p < 0.005) [corrected].(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Endogenous growth hormone secretion and clearance rates in normal boys, as determined by deconvolution analysis: relationship to age, pubertal status, and body mass.

Mean plasma GH concentrations increase in normal boys during mid- to late-puberty. To investigate the nature of the pituitary secretory events and/or altered metabolic clearance responsible for these serum GH concentration changes, we performed multiple-parameter deconvolution analysis of 46 24-h serum GH concentration-time series obtained from normal boys at various stages of puberty and young adulthood. The subjects ranged in chronological age from 7-27 yr. The height and weight of each subject were between the 5th and 95th percentile for age. The calculated daily mass of GH secreted was greatest (P less than 0.001) in late pubertal boys (mean +/- SE, 1810 +/- 250 micrograms/24 h) and was triple the value in prepubertal boys (610 +/- 65 micrograms/24 h). When the values were normalized and expressed as mass of GH secreted per unit (m2) body surface area or per L distribution volume, GH secretion in late pubertal boys was still significantly greater than that in any other group (P less than 0.05). These values for late pubertal boys were nearly double the corresponding values for prepubertal boys (1160 +/- 160 vs. 600 +/- 58 micrograms GH/m2.24 h and 440 +/- 63 vs. 270 +/- 25 micrograms GH/L vol.24 h, respectively). When the effect of clearance mechanics on serum GH concentrations was removed mathematically, the primary change in predicted GH secretory burst parameters during pubertal development was an increase in GH mass released per burst resulting from an increase in the maximal rate of GH secretion attained within the bursts. These changes in the amplitude of GH release events were specific, in that they were largely independent of any accompanying alterations in duration or frequency of the GH secretory bursts or in serum GH half-life. Correlation analysis revealed that the 24-h GH secretion rate varied inversely with the subjects' body mass index SD score (r = -0.65; P less than 0.01), suggesting that differences in body mass, even within the normal range, contribute to the wide variability in daily GH secretion rates among normally growing children. The plasma insulin-like growth factor-I concentrations of all subjects correlated positively with the calculated 24-h GH secretion rate (r = 0.51; P less than 0.001). In summary, the primary neuroendocrine alteration responsible for the augmented serum GH concentrations characterizing mid- to late-puberty in boys is an increased mass of GH released per pituitary secretory episode resulting from an increased maximal rate of GH secretion within each burst.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1992

Determination of the arterial flow fraction in normal and diseased livers using constrained deconvolution.

There is some evidence that the ratio of the blood flow to the liver through the hepatic artery to the total flow to the liver through the hepatic artery and portal vein (the hepatic arterial flow fraction, AFF) is altered in the presence of cirrhosis. Several methods have been published that seek to provide an index of this ratio. These indices are dependent on factors other than the AFF and cannot provide a true measure of it. The impulse retention function of the liver has two components and these may be derived using a model-driven deconvolution of the arterial tracer concentration curve and the curve of tracer concentration in the liver. The AFF may then be obtained from the relative heights of these two components. Simulation studies show that the AFF calculated using this method is reasonably accurate and a small clinical series shows that it is capable of appropriate clinical classification of patients into cirrhotic and non-cirrhotic groups.

Colloids↗
PubMed1975

Deconvolution analysis of the scintillation camera renogram.

A scintillation camera with digital data store has been used to assess renal function. Analysis of the renogram by deconvolution, using an on-line digital computer, shows promise as a means of expressing renal function in terms of tubular transit times for 123I-Hippuran.

Computers↗