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PubMed1992

Constrained least-squares restoration and renogram deconvolution: a comparison by simulation.

Before deconvolution can be used in renography, it is necessary to decide whether the renal function is sufficiently good to allow it. To see if this decision can be circumvented, an iterative constrained least-squares restoration (CLSR) method was implemented in which the point of termination of the iteration occurs when a residual vector has a value less than an estimate of the noise in the original renogram curve. The technique was compared with the matrix algorithm and with direct FFT division. The comparison was achieved by deconvolving simulated renogram data with differing transit time spectra and statistics. As expected, the FFT technique produced results of little value whereas the CLSR and matrix methods produced values of mean transit time (MTT) that differed slightly from the expected results. Analysis indicated that the matrix approach was superior when the percentage noise component was less than 6% and vice versa. No technique produced useful transit time spectra. As the CLSR technique produced better results than the matrix method in simulations with relatively long MTTs and high noise, it seems reasonable to suggest that it might be used for renogram deconvolution without the need for previous inspection of the curves.

Humans↗
PubMedDate not supplied

Deconvolution of chemical shift spectra in two- or three-dimensional [19F] MR imaging.

The chemical shift spectra of 19F in perfluorinated compounds (PFCs) present a nontrivial impulse response function for magnetic resonance (MR) imaging. The 19F images of organs containing PFCs can be degraded by blurring and ghost image artifacts. Two methods (noise masked deconvolution and maximum entropy deconvolution) are presented that allow the chemical shift spectra of 19F in PFCs to be used to extract high quality MR images free of chemical shift artifact. Both techniques rely on postprocessing of either the raw data or the original image to produce images that are not degraded by the chemical shift spectra of the compound being imaged and that exhibit a signal-to-noise ratio equal to or better than that observed in the original image. The techniques are general in that they can be used with many PFC spectra. Using MR imaging data obtained from phantoms filled with cis/transperfluorodecalin and perfluorotributylamine (FC-43), the methods are compared in terms of their (a) ability to eliminate the chemical shift artifact associated with the PFC spectrum; (b) signal-to-noise performance; and (c) ability to preserve information related to the density and the longitudinal relaxation rate of the resonant nuclei. The utility of these techniques is demonstrated by a series of three-dimensional Fourier transform in vivo images of FC-43 emulsion in a mouse liver.

Algorithms↗
PubMed1985

The individual kidney function. A comparison between frame summation and deconvolution.

A variety of methods have been developed to estimate the individual kidney function. Many methods use a scintillation camera the data from which are processed in a computer system. To compare two of these methods, the principles of which are completely different, such as the 'Oberhausen' method of frame summation and background subtraction and a method that uses deconvolution, the scintillation camera data of 121 patients have been collected. A computer program was written to calculate the individual kidney function by which both methods were used. It is often asserted that specific techniques of frame summation and background subtraction are not suitable to define the individual kidney function. To see if this assertion is true, two different methods have been compared using the contribution of the left kidney to the individual kidney function. An excellent correlation between the two methods was found (R = 0.9808, n = 121) which proves the ability of both the 'Oberhausen' method and the method that uses deconvolution. However, it is also seen that the 'Oberhausen' method may give false results, caused by an increasing background count outside the kidneys in patients with a large difference in function between the two kidneys.

Humans↗
PubMed1992

Mössbauer characterization of the tetraheme cytochrome c3 from Desulfovibrio baculatus (DSM 1743). Spectral deconvolution of the heme components.

Mössbauer spectroscopy was used to study the tetraheme cytochrome c3 from Desulfovibrio baculatus (DSM 1743). Samples with different degrees of reduction were prepared using a redoxtitration technique. In the reduced cytochrome c3, all four hemes are reduced and exhibit diamagnetic Mössbauer spectra typical for low-spin ferrous hemes (S = 0). In the oxidized protein, the hemes are low-spin ferric (S = 1/2) and exhibit overlapping magnetic Mössbauer spectra. A method of differential spectroscopy was applied to deconvolute the four overlapping heme spectra and a crystal-field model was used for data analysis. Characteristic Mössbauer spectral components for each heme group are obtained. Hyperfine and crystal-field parameters for all four hemes are determined from these deconvoluted spectra.

Cytochrome c Group↗
PubMed1990

Measurement of hepatocellular function with deconvolutional analysis: application in the differential diagnosis of acute jaundice.

A direct, noninvasive technique was developed to quantitate hepatocyte function with computer assessment of scintiscans obtained after administration of technetium-99m disofenin in 53 patients with acute jaundice: 32 patients with normal livers, 10 patients with acute biliary obstruction, and 11 patients with acute hepatocellular dysfunction. In all patients a final clinical diagnosis was obtained with follow-up for a minimum of 4 months and, in most patients with obstruction or dysfunction, with surgery, intraoperative cholangiography, ultrasound, and/or computed tomography. Heart (blood pool) and liver time-activity curves were generated for 32 minutes after intravenous injection of 5-15 mCi (185-555 MBq) of Tc-99m disofenin and were subjected to deconvolutional analysis to determine the first-pass hepatocyte extraction fraction (HEF) of the tracer. The difference in HEF between patients with obstruction and those with dysfunction was highly significant (P = 3.3 X 10(-19)). Deconvolutional analysis eliminates the effects of tracer recirculation, thus permitting direct measurement of hepatic disofenin extraction, and appears to provide functional information useful in evaluation of the patient with acute jaundice.

Acute Disease↗
PubMed1988

Thermal recovery after passage of the pulmonary circulation assessed by deconvolution.

For indicator-dilution studies, complete thermal recovery after passage of heat through the pulmonary circulation would be desirable. However, the results in the literature obtained by extrapolation techniques are inconsistent. To overcome problems of the extrapolation approach, transport functions of the pulmonary circulation (including the left heart) were computed by deconvolution of pulmonary arterial and aortic pairs of thermodilution curves after central venous indicator injection (10 ml of an ice-cold blood indocyanine green dye mixture). Thermal recovery was determined as the finite integral of the transport function. Thirteen mongrel dogs under piritramid-N2O anesthesia were examined under base-line conditions, in orthostasis to alter the distribution of pulmonary blood flow (9 dogs), and in oleic acid edema (8 dogs). Using the deconvolution approach, thermal recovery was 0.97 +/- 0.04 under base-line conditions, 0.96 +/- 0.03 in orthostasis, and 0.96 +/- 0.05 in pulmonary edema. Thermal recovery determined from extrapolated dilution curves was greater than 100% in all groups, a physically impossible finding. It is concluded that thermal recovery is incomplete but insensitive with respect to the distribution of blood flow and to the size of the extravascular compartment. Monoexponential extrapolation is unsuited for the determination of thermal recovery.

Animals↗
PubMed1987

The practical significance of two-dimensional deconvolution in echography.

This paper evaluates deconvolution (inverse filtering) as applied to ultrasonic imaging systems, and discusses the obstacles which are encountered employing the technique in practice. A minicomputer is used to generate artificial echo signals, simulating rf signals resulting from a set of point reflectors in a homogeneous medium, as recorded by an electronically focused group-steered linear array scanner. Two-dimensional deconvolution in combination with a Wiener noise reduction filter (i.e., a Wiener-Inverse filter) is applied to these simulated rf signals, which were contaminated with white noise. The efficacy of the Wiener-Inverse filter is defined in terms of its ability to resolve two point reflectors with a lateral spacing equal to the local -6 dB width of the ultrasonic beam. In favorable circumstances, the targets are resolved at signal-to-noise ratios (SNR) better than 20 dB, where SNR is defined as the maximum signal power divided by the average noise power level. Nonlinear effects due to quantization or signal clipping are investigated. In order to improve the resolution of an rf signal with a dynamic range of 40 dB, the input signal should be digitized at a minimum of 12 bits. The problem of signal clipping can be circumvented by oversampling. The two-dimensional Wiener-Inverse filter is defined in terms of both temporal and spatial properties of the insonification. Effects of wave diffraction give rise to a depth-dependent ultrasonic beam. As a result of a misfit of the Wiener-Inverse filter and the local properties of the ultrasonic beam, erroneous noisy texture arises in the image. Adaptation of the Wiener-Inverse filter with respect to the beam properties gives acceptable results, at the expense of a rather large computational effort.

Computer Simulation↗
PubMed1989

[Usefulness of radioisotope (RI) deconvolution analysis with Tc-99m-DTPA in transplanted kidney].

In 50 renal transplant recipients, we performed radioisotope (RI) deconvolution analysis, as reported by O'Reilly, in 179 renograms from dynamic renal scanning with Tc-99m-DTPA and obtained MTT (mean transit time) and H0 (initial height) values. We found characteristic features of various graft conditions using the combination of MTT and H0. The mean H0 value was greater in normally functioning grafted kidneys than in kidneys with other states. The mean MTT in the normal group was about 2 min. In the acute rejection group, the mean H0 value was lower and the mean MTT was more prolonged compared with the normal group. In ATN group, the mean MTT was similar to that in the acute rejection group, whereas the mean H0 value was lower. In the chronic rejection group, the mean MTT was similar to that in the normal group, but the mean H0 value showed a lower one. The hydronephrosis group had an extremely prolonged MTT. This study indicated that the combination of H0 and MTT obtained from RI deconvolution analysis is a valuable means of understanding the condition of renal grafts.

Graft Rejection↗
PubMed1988

[An experimental study of liver perfusion using non-diffusible radiotracers: differentiation of the arterial and portal venous components by deconvolution analysis of first-pass time-activity curves].

The transfer function of the liver perfusion is an idealized time-activity curve that could be registered over the liver if a non-diffusible tracer would be injected directly into the abdominal aorta and no tracer recirculation would occur. The reproducibility of the transfer function was experimentally investigated in foxhounds. Both the routes of tracer application and the modes of data evaluation were varied and the perfusion was investigated under physiological and pathological conditions. The transfer function was calculated by deconvolution analysis of first-pass time-activity curves using the matrix regularization method. The transfer function showed clearly distinguishable arterial and portal-venous components. Repeated peripheral venous and central aortic applications resulted in reproducible curves. In addition to the arterial and portal-venous components the subcomponents of the portal-venous component could also be identified in the transfer function after ligation of the appropriate vessels. The accuracy of the mathematical procedure was tested by computer simulations. The simulation studies demonstrated also that the matrix regularization technique is suitable for deconvolution analysis of time-activity curves even when they are significantly contaminated by statistical noise. Calculation of the transfer function of liver perfusion and of its quantitative parameters seems thus to be a reliable method for non-invasive investigation of liver hemodynamics under physiological and pathological conditions.

Animals↗
PubMed1988

Hepatocyte versus biliary disease: a distinction by deconvolutional analysis of technetium-99m IDA time-activity curves.

A combination of quantitative hepatobiliary imaging techniques was developed to study normal control subjects and patients with 3 categories of hepatobiliary disease: 1) alcoholic cirrhosis; 2) sclerosing cholangitis; and 3) isolated common bile duct obstruction. Scintigraphic images were supplemented by quantitative measurement of hepatic extraction fraction by deconvolutional analysis and liver excretion T 1/2 by a nonlinear least squares method. In diseases confined primarily to the biliary tract (isolated common bile duct obstruction and sclerosing cholangitis), the mean hepatic extraction fraction as measured by deconvolutional analysis was not different from that in normal controls. In severe alcoholic cirrhosis, considered primarily a hepatocyte disease, the hepatic extraction fraction was markedly reduced. The T 1/2 excretion, compared to normal subjects, was prolonged in all three liver disease categories. We conclude that these quantitative parameters were able to detect hepatobiliary disease and to separate severe hepatocyte disease from biliary tract disease.

Biliary Tract Diseases↗
PubMedDate not supplied

Drug absorption evaluation in the presence of changes in clearance: an algorithm and computer program for deconvolution with exact clearance correction.

Most commonly drug absorption is evaluated with a reference dosing given on separate occasions. The assumption that no change in drug disposition is taking place between the drug administrations is often violated resulting in errors in the calculations. A novel deconvolution method is presented which exactly compensates for a change in drug clearance. The method is based on a model independent disposition decomposition-recomposition technique. The distribution function is obtained from an i.v. administration by disposition decomposition. This distribution function is assembled together with the elimination kinetics containing the perturbed clearance to construct the perturbed disposition function in the subsequent disposition recomposition operation. The perturbed absorption response is finally deconvolved using the corresponding perturbed disposition function. It is shown that the perturbed clearance can be obtained from the log-linear terminal disposition phase once the distribution function has been obtained from an i.v. administration. The proposed method is implemented in an algorithm and computer program DCONB and demonstrated using human cimetidine drug level data from an i.v. and oral administration. The usage of DCONB is identical to DECONV previously published. It requires only regular sums of exponentials to be fitted to drug level data. Such fittings are routinely done in pharmacokinetics thereby enabling DCONB to be implemented very simply.

Algorithms↗
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↗
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↗
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↗
PubMed1988

Applications of a general method for deconvolution using compartmental analysis.

A method of deconvolution is illustrated using compartmental models. The approach can be used to determine an arbitrary unknown input function from a measured response and the impulse response of the system. Compartmental models are constructed to specify (a) the function fitting the response data and (b) the impulse response of the system. Simulation of these models is then used to construct the unknown input function.

Alanine↗
PubMed1988

Quantitation of collagen fragments and gelatin by deconvolution of polarimetry denaturation curves.

A method for quantitating nicked or shortened molecules (fragments) in pepsinized bovine type I collagen preparations using polarimetry thermal denaturation curves is described. The shortened molecules denature about 4 degrees C lower than intact collagen molecules. The analog output of a polarimeter was digitized and stored on a microcomputer disk. A BASIC program was written which retrieves the specific rotation data from the disk, smooths the data with a boxcar average, and plots the derivative of the denaturation curve. The derivative curve was deconvoluted by fitting three Gaussian curves to the derivative curve using published algorithms. The area of the Gaussian centered at 37 degrees C was proportional to the amount of collagen fragments. A good correlation between the amount of fragments determined by polarimetry and by a trypsin sensitivity assay was observed. The overall precision of the method was about 10% RSD, and the method was repeatable by multiple analysts. Application of the method to reconstituted fibrillar collagen samples showed that more fragments are generated when pepsin digestion time is lengthened. By fitting a fourth Gaussian component to the derivative curve, the method can also be used to determine relative amounts of denatured collagen (helix partially unwound but alpha chains not nicked). The detection limit for denatured collagen is about 20%.

Algorithms↗
PubMed1989

Evidence for radical anion formation during liquid secondary ion mass spectrometry analysis of oligonucleotides and synthetic oligomeric analogues: a deconvolution algorithm for molecular ion region clusters.

It is shown that one-electron reduction is a common process that occurs in negative ion liquid secondary ion mass spectrometry (LSIMS) of oligonucleotides and synthetic oligonucleosides and that this process is in competition with proton loss. Deconvolution of the molecular anion cluster reveals contributions from (M-2H).-, (M-H)-, M.-, and (M + H)-. A model based on these ionic species gives excellent agreement with the experimental data. A correlation between the concentration of species arising via one-electron reduction [M.- and (M + H)-] and the electron affinity of the matrix has been demonstrated. The relative intensity of M.- is mass-dependent; this is rationalized on the basis of base-stacking. Base sequence ion formation is theorized to arise from M.- radical anion among other possible pathways.

Algorithms↗