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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↗
PubMed1995

Deconvolution of detector size effect for small field measurement.

Parametrization of the small fields employed in stereotactic applications is a painstaking process involving extensive film dosimetry to achieve acceptable beam edge definition. Use of cylindrical or spherical detectors for profile measurements would simplify data acquisition but add a volume averaging artifact to beam edge definition. We demonstrate a simple approach to unfolding the chamber size artifact from measured small beam profiles using typical cylindrical chambers. In comparison with film measurements we have found good agreement when the detector response function is deconvoluted from the measured profiles, although the amount of correction needed is fairly minimal for the detectors studied.

Film Dosimetry↗
PubMed1998

Inverse radiosurgery treatment planning through deconvolution and constrained optimization.

An inverse radiosurgery treatment planning approach is presented which calculates conformal dose distributions for small, irregularly shaped targets. Two general approaches have been suggested for solution of the inverse radiotherapy problem: explicit and implicit. Explicit methods are typically fast, but generally require geometric and/or dosimetric simplifications. Implicit methods have also been used, but are computationally expensive because they require iterative manipulation of each beam's individual elements. The method presented here incorporates an integrated approach in order to efficiently solve the inverse problem without requiring simplifications which may affect the accuracy of the final result. A deconvolution algorithm (explicit approach) is utilized to determine the intensity modulation function for multiple user-selected beam's eye views of the desired dose distribution. A simulated annealing algorithm (implicit approach) then optimizes each beam's macroscopic weight. Additionally, this method is fully three-dimensional and accurately models phantom scatter by incorporating Monte Carlo generated energy deposition kernels into the dosimetry process. Several small target structure examples are presented and applicability of this methodology to larger targets for general radiotherapy cases is addressed.

Algorithms↗
PubMed2003

Synthetic aperture imaging using sources with finite aperture: deconvolution of the spatial impulse response.

A method for ultrasonic synthetic aperture imaging using finite-sized transducers is introduced that is based on a compact, linear, discrete model of the ultrasonic measurement system developed using matrix formalism. Using this model a time-domain algorithm for deconvolution of the transducer's spatial impulse responses (SIRs) is developed that is based on a minimum mean square error (MMSE) criterion. The algorithm takes the form of a spatiotemporal filter that compensates for the SIRs associated with a finite-sized transducer at every point of the processed image. A major advantage of the proposed method is that it can be used for any transducer, provided that its associated SIRs are known. This is in contrast to the synthetic aperture focusing technique (SAFT), which treats the transducer as a point source. The performance of the method is evaluated with simulations and experiments, performed in water using a linear phased array. The results obtained using the proposed method are compared to those obtained with a classical time-domain SAFT algorithm. For a finite aperture source, it is clearly shown that the resolution obtained using the proposed method is superior to that obtained using the SAFT algorithm.

Journal Article↗
PubMed2004

Deconvolution of evoked responses obtained at high stimulus rates.

Continuous loop averaging deconvolution (CLAD) is a new general mathematical theory and method developed to deconvolve overlapping auditory evoked responses obtained at high stimulation rates. Using CLAD, arbitrary stimulus sequences are generated and averaged responses deconvolved. Until now, only a few special stimulus series such as maximum length sequences (MLS) and Legendre sequences (LGS) were capable of performing this task. A CLAD computer algorithm is developed and implemented in an evoked potential averaging system. Computer simulations are used to verify the theory and methodology. Auditory brainstem responses (ABR) and middle latency responses (MLR) are acquired from subjects with normal hearing at high stimulation rates to validate and show the feasibility of the CLAD technique.

Acoustic Stimulation↗
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↗
PubMed2000

Performance of some sparseness criterion blind deconvolution methods in the presence of noise

A comparison of the spareseness (simplicity) norm criterion blind deconvolution methods of Cabrelli and Wiggins is made in order to ascertain relative performance for underwater acoustic transient source signal estimation, especially in the presence of noise. Both methods perform well at high signal-to-noise ratios, producing source estimates that are significant improvements over the original received signal for classification purposes. At moderate and lower SNRs, the Cabrelli method tends to generate results that are superior to the Wiggins method. This is especially true for a damped sinusoid transient source, for which the Wiggins method fails completely at lower SNRs, while the Cabrelli method can still produce good source estimates.

Journal Article↗
PubMed2000

Maximum a posteriori deconvolution of ultrasonic signals using multiple transducers

A new method for deconvolution of ultrasonic pulse-echo measurements employing multiple-transducer setup is proposed in the paper. An optimal way of estimating the material reflection sequence for a linear signal generation model using maximum a posteriori estimation is proposed. The method combines the measurements from a number of transducers covering different frequency bands yielding an optimal estimate of the reflection sequence. The main idea of this approach is to complement the information unavailable from one transducer in some frequency bands with the information from the other transducers. The method is based on the assumption that the measurements are performed using transducers with identical apertures and apodization, which are located exactly at the same position relative to the test object during the measurement. An error analysis presented in the paper proves that when the above assumptions are fulfilled, the proposed method, by utilizing more data for estimation, consistently yields more accurate reflection sequence estimates than the classical Wiener filter. Experimental evidence is presented using both simulated and real ultrasonic data as a verification of the correctness of the multiple-transducer model and the estimation scheme. An illustration of the advantages of the method is also given using real ultrasonic data.

Journal Article↗
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↗
PubMed2000

Deconvolution of event-related fMRI responses in fast-rate experimental designs: tracking amplitude variations.

Recent developments towards event-related functional magnetic resonance imaging has greatly extended the range of experimental designs. If the events occur in rapid succession, the corresponding time-locked responses overlap significantly and need to be deconvolved in order to separate the contributions of different events. Here we present a deconvolution approach, which is especially aimed at the analysis of fMRI data where sequence- or context-related responses are expected. For this purpose, we make the assumption of a hemodynamic response function (HDR) with constant yet not predefined shape but with possibly variable amplitudes. This approach reduces the number of variables to be estimated but still keeps the solutions flexible with respect to the shape. Consequently, statistical efficiency is improved. Temporal variations of the HDR strength are directly indicated by the amplitudes derived by the algorithm. Both the estimation efficiency and statistical inference are further supported by an improved estimation of the noise covariance. Using synthesized data sets, both differently shaped HDRs and varying amplitude factors were correctly identified. The gain in statistical sensitivity led to improved ratios of false- and true-positive detection rates for synthetic activations in these data. In an event-related fMRI experiment with a human subject, different HDR amplitudes could be derived corresponding to stimulation at different visual stimulus contrasts. Finally, in a visual spatial attention experiment we obtained different fMRI response amplitudes depending on the sequences of attention conditions.

Algorithms↗
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↗