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Biomedical subjects

M Eden

Publications and source records attributed to M Eden.

18 recordsLinked to original sources
PubMed1987

Optimal background estimation in EELS.

In quantitative electron energy loss spectrometry, it is desirable to estimate the background law below core edge energy in a way that provides the maximum signal-to-noise ratio. Assuming an inverse power background model and independently Poisson distributed measurements, it is shown how to achieve this goal by using a maximum likelihood (ML) estimation technique which provides unbiased and minimum mean square error estimates of all parameters of interest. An efficient and computationally stable implementation of this procedure is proposed. Standard logarithmic least squares estimations are then compared with the ML approach and the gain in performance due to optimal processing is quantified.

Electrons↗
PubMed1985

The relationship between mean channel selection and the calculated coefficient of variation.

Calculated coefficients of variation (CV) taken from the quotient of the standard deviation (S.D.) and the mean value of measured distributions are often used as an indicator of system performance in linear flow cytometry (FCM). The ability of the calculated CV to estimate the true CV of the underlying experiment before grouping (channelization) is dependent on the relationship between the width of the data channels and the magnitude of the S.D. of the measured distribution. When the channel width is equal to the S.D. of a distribution, the calculated CV is approximately 20% larger than the true CV of an experiment. By the time the S.D. is only one-half of a channel width, the calculated CV is unreliable. When the distribution S.D. is narrower than a channel's width, small changes in the distribution mean value will cause large variations in the calculated CV. As the true CV decreases, the calculation must be made with higher mean channel values. This dependence of calculated CV accuracy upon the relationship between S.D. and channel width places limitations upon mean channel selection that must be considered when using CV calculations for evaluating system performance, especially when looking for small improvements during optical alignment procedures. When an instrument is assumed to have a constant CV and the data are collected linearly, it is possible to improve the CV estimation accuracy by placing distributions in higher-numbered channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow Cytometry↗
PubMed1985

Weighted least squares estimation of background in EELS imaging.

In quantitative Electron Energy Loss Spectrometry, a weighted least squares estimation should theoretically be used to estimate the background law below core edge energy, since the variances of the data vary. However, it is found that proper weighting makes the above edge signal-to-noise ratio decrease rather than increase. This result is discussed, and the influence of the bias introduced by the logarithmic transformation of the data is quantified.

Spectrum Analysis↗
PubMed1984

Analysis of emission tomographic scan data: limitations imposed by resolution and background.

The proper analysis of positron emission tomographic scan data requires a careful knowledge of the limitations of the tomographic system used so that scan data can be collected and sampled in a manner consistent with those limitations. The present investigation was undertaken to clarify some of the limitations imposed by resolution. The usual imaging situation, e.g., 218FDG , C15O2, or 15O2 , involves imaging structures of limited size in all three dimensions which may appear either warm or cool in relation to some background level of activity. In emission tomography the importance of adequate data sampling within a given plane has been frequently emphasized. Little attention, however, has been given to proper z axis sampling for clinical scanning. The actual selection of regions of interest from scans can have a significant impact on the subsequent statistical analysis. Previous work on this subject has experimentally examined the relationship of object size to quantitative estimation in the hot spot-cold background situation for the one- and two-dimensional cases. Approximate three-dimensional recovery coefficients for the hot spot-cold background situation have been calculated. An examination of the factors discussed above, three-dimensional objects with varying contrast, z axis sampling, and selection of regions of interest, has not yet been addressed in the literature. The purpose of the present investigation is to examine these factors.

Background Radiation↗
PubMed1984

Optimized acquisition parameters and statistical detection limit in quantitative EELS.

Optimizing the acquisition parameters for EELS recording has to be accomplished simultaneously from the physical and the statistical points of view; the statistical aspect of the question is covered here. Approximate probability density functions of the variables of interest are derived, which provide a global measure of signal-to-noise ratio taking into account every step of the EELS edge area estimation process. Qualitative and quantitative advice is given regarding the critical choice of the estimation and integration energy regions. The notion of visual contrast is presented; it permits the introduction of the concept of statistical detection limit. It is found that for typical experimental conditions, when other factors are equal, the required analysis time for the sample varies approximately as the inverse square of the concentration.

Electron Probe Microanalysis↗
PubMed1979

An interactive computer system for the analysis of cell lineages.

We have developed an interactive computer system for analysing cell lineage data. It can be utilized in studies of cell motility, cell division, cell differentiation, and cell aging. It has enabled us to document the heterogeneity of human foreskin fibroblasts in culture and to propose that loss of proliferative potential may mean that cells enter a state of differentiation which makes them unable to respond to mitotic stimulation. Our method, which enables us to apply immunological and cytochemical probes after recording the history of a cell lineage, should allow us to define precisely features which uniquely distinguish cycling from noncycling cells on an individual cell basis.

Cell Cycle↗
PubMed1978

Loss of division potential in vitro: aging or differentiation?

We have examined the hypothesis that diploid cells grown in vitro age, and propose that only proliferative potential and not life-span is telescoped. We suggest that explanted or transplanted diploid cells are driven to divide by the process of subculturing in vitro or in vivo and, in response to this pressure, also complete their differentiation and become refractory to further mitotic stimulation. We conclude that differentiation rather than "mortality" distinguishes diploid from transformed cells and that the former may not age in vitro, but are lost because culture methods are selective for cycling cells.

Cell Cycle↗
PubMed1976

A technique for multiple-cell chromosome karyotyping.

A new approach to a system for chromosome karyotyping is presented. The system assembles the information about chromosomes from several cells at a time, thereby filtering out noise due to variations in the slide preparations. The system makes i possible to use metaphase spreads which are incomplete due to missing chromosomes, touching and overlapping chromosomes and stain particles. The system gives a precise description of the chromosome complement in terms of distribution function parameters, with the uncertainty of the parameters specificed. The system is adaptive with respect to the initial reference parameter set so that both recognition of normal chromosomes, in spite of the variation displayed among individuals, and identification of aberrant chromosomes are possible. The precise chromosome descriptors can be used to detect differences between the tested individual and various references, in order to find chromosomal abnormalities.

Autoanalysis↗
PubMed1973

Feasibility of computer screening of blood films for the detection of malaria parasites.

This paper considers the feasibility of automatic screening procedures for detecting malaria parasites in blood smears prepared in the field. A simple programme for pattern recognition by computer has been developed for thin blood films that identifies parasites as densely stained particles within an erythrocyte. The parasites are detected correctly, but platelets falling accidentally within the outline of an erythrocyte and perhaps reticulocytes may be wrongly classified as parasites. The results indicate that automated detection of parasites is technically feasible but that the technique needs to be refined to reduce the incidence of false positives. A substantial increase in processing speed is required if the automatic procedure is to be economically feasible in screening programmes. The complexity of the equipment and the need for well prepared blood smears point to a possible use of the technique in laboratory checks but not under usual field conditions.

Bacteriological Techniques↗