Electrical pulse counters – pulse dividers – or shift registers: c – Applications – Counting animate or inanimate entities
Patent
1998-01-15
1999-11-02
Wambach, Margaret R.
Electrical pulse counters, pulse dividers, or shift registers: c
Applications
Counting animate or inanimate entities
377 12, 364555, G06M 1102
Patent
active
059784350
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to counting particles or cells in liquid samples and in particular in connection with flow cytometry, which is a widely used technique for determining e.g. the number of somatic cells in milk samples.
BACKGROUND ART
In typical flow cytometers, the determination procedure is a simple counting procedure where a part of a milk sample is mixed with dye and the number of cells therein is counted using e.g. a fluorescence measurement.
The uncertainty of a measurement can be expressed by the standard deviation (cf. D. A. Skoog `Principles of instrumental analysis`, Saunders College Publishing, Philadelphia, U.S.) e.g. the relative standard deviation, also called the coefficient of variation, "CV". The `CV` of a value determined by a counting procedure will depend on the number counted. For a typical Poisson distribution the `CV` is inversely proportional to the square of the number counted, Thus, the uncertainty of a large number of particles or cells, e.g. somatic cells in milk will be smaller than the uncertainty of a small number of cells.
In typical, known flow cytometers, this is not taken into account. In these instruments, the number of cells is determined in a pre-determined volume of a milk/dye mixture. However, in some instruments, this is taken into account by performing an alternative measurement by detecting a pre-selected number of cells and by determining the volume in which this number of cells are present. Cell counting is also performed using techniques other than flow cytometry. Manual cell counting is often performed on human blood. In this technique, the cells in a pre-selected volume of the blood are counted. Alternatively a volume of blood containing a predetermined number of cells may be measured.
The above two methods have the disadvantages that they in a sense are static. Either the uncertainty is the same for all measurements or it is allowed to drift for all measurements. Therefore, there is a risk of obtaining results having a large uncertainty. The solution to this is to either increase the volume examined in order to count more particles or cells or to use the alternative method using a predetermined number of cells and therefore a pre-selected uncertainty. By this method, however, the measurement procedure may for some samples take an unacceptably long period of time.
SUMMARY OF THE INVENTION
The present invention provides a solution to this problem by providing a measurement where the uncertainty is "dynamic" (i.e. variable). The uncertainty may be selected dependently or independently of the results of the measurement.
In fact, in a first aspect, the present invention relates to a method of determining the number of particles or cells in a liquid sample, the method comprising: liquid sample, particles in said first volume, determining the number of particles or cells in a further volume of the liquid sample, determined in step d), sample, until the uncertainty determined in step e) is lower than said pre-determined value or until a predetermined total volume of the liquid sample in which the number of cells or particles has been determined exceeds a pre-determined volume being larger than said first volume.
In this way, the volume examined and the uncertainty of the measurement may be selected so that a suitable compromise between the uncertainty and the time required to perform the measurement can be obtained.
Naturally, there are different ways of expressing a statistical uncertainty depending also on the determination in question. Thus, if the uncertainty is expressed as the relative standard deviation (CV), this uncertainty is proportional to the inverse of the square of the counted number.
In the present invention, the uncertainty is evaluated a number of times during the determination, in order to not unnecessarily continue the determination after the point in time at which a suitable uncertainty has been reached. In this way, the determination is performed substantially as fast as possible and still with an uncertainty a
REFERENCES:
patent: 4021117 (1977-05-01), Gohde et al.
patent: 4667335 (1987-05-01), Deindoerfer
Skoog, D. A., "Principles of Instrumental Analysis," Saunders Golden Sunburst Series, Edition 3 (1984) pp. 1-25.
English language Abstract for Japanese Patent Publication 1-105136 A dated Mar. 20, 1987.
Asmussen Tove
Born Christian
Christensen Steen Kold
Larsen Mogens Bering
Foss Electric A/S
Wambach Margaret R.
LandOfFree
Method and an apparatus for determining the number of particles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and an apparatus for determining the number of particles , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and an apparatus for determining the number of particles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2145955