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At least 253 records · Page 14Linked to original sources
PubMed2004

[Development of method to estimate delay time for arterial imput function with [15O]CO2-PET study using sinogram data and attenuation map].

The difference in tracer arrival times between the external radiation detector and the brain following administration of radioactivity (delay time) must be estimated correctly in order to quantitatively measure regional cerebral blood flow (rCBF) with positron emission tomography and [15O]H2O by autoradiographic method. Instead of intervenous injection of [15O]H2O, bolus inhalation of [15O]CO2 gas is sometimes used to simplify the measurement of rCBF. In the case of [15O]CO2, radioactive gas in mask and nasal cavity contributes large artifact on the sinogram data and it is difficult to estimate delay time from the sinogram data. In this paper, we proposed a new method to estimate the delay time using the sinogram data and the attenuation map (attenuation weighted sinogram method). In the present method, the attenuation map was used to eliminate the effect of the gas outside the brain region from the sinogram data. For the validation of the present method, PET data with [15O]CO2 (n = 10) were analyzed. Three methods, namely the image method, the sinogram method and the attenuation weighted sinogram method were used to estimate the delay time. The estimated delay times and calculated rCBF images by three methods were compared. Due to the radioactivity outside of the brain, the sinogram method significantly overestimated the delay time and thus underestimated the rCBF value compared with the image base method. On the other hand, there were good agreements between the delay times estimated by the attenuation weighted sinogram method and the image method. The present method can eliminate the effect of the radioactivity outside of the brain on the sinogram data and estimate the delay time accurately and fast enough for clinical use.

Autoradiography↗
PubMed1991

Applications of multiple imputation to the analysis of censored regression data.

The first part of the article reviews the Data Augmentation algorithm and presents two approximations to the Data Augmentation algorithm for the analysis of missing-data problems: the Poor Man's Data Augmentation algorithm and the Asymptotic Data Augmentation algorithm. These two algorithms are then implemented in the context of censored regression data to obtain semiparametric methodology. The performances of the censored regression algorithms are examined in a simulation study. It is found, up to the precision of the study, that the bias of both the Poor Man's and Asymptotic Data Augmentation estimators, as well as the Buckley-James estimator, does not appear to differ from zero. However, with regard to mean squared error, over a wide range of settings examined in this simulation study, the two Data Augmentation estimators have a smaller mean squared error than does the Buckley-James estimator. In addition, associated with the two Data Augmentation estimators is a natural device for estimating the standard error of the estimated regression parameters. It is shown how this device can be used to estimate the standard error of either Data Augmentation estimate of any parameter (e.g., the correlation coefficient) associated with the model. In the simulation study, the estimated standard error of the Asymptotic Data Augmentation estimate of the regression parameter is found to be congruent with the Monte Carlo standard deviation of the corresponding parameter estimate. The algorithms are illustrated using the updated Stanford heart transplant data set.

Algorithms↗
PubMedDate not supplied

[Criteria of imputation of acute hepatitis to a drug. Results of consensus meetings].

The use of an official drug adverse reaction assessment procedure became compulsory in France in 1984. The method proposes various qualifications for chronologic and semiologic criteria but does not define them. Consensus meetings have been organized in order to define, in the main pathologic fields, the adverse reactions themselves and the various qualifications of the criteria. This paper reports the results of meetings attended by hepatologists from university hospitals, members of the National Network of pharmacovigilance and representatives of Roussel Uclaf Drug Monitoring Department for drug-induced acute hepatitis. Participants studied (a) the limits of the time interval between the appearance of the adverse reaction and the beginning or the end of the treatment with the suspected drug; (b) the interpretation of the course of disease with or without cessation of treatment; (c) the interpretation of a possible rechallenge; (d) the signs evoking a drug-induced origin and the risk factors, as well as the investigations to be performed in order to eliminate other possible causes.

Acute Disease↗