Particle measurement apparatus

Abstract: Light receiving elements (8) detect the intensity of light scattered from a sample cuvette (3) containing particles irradiated by a beam from a light source (1). Signals from the light receiving elements are evaluated to determine the size and number of the particles for its time-series display. In measuring blood corpuscles, the clumps of aggregation can be determined in terms of size and number on a time-series base with high accuracy, thus providing useful means for clinically diagnosing various diseases including thrombosis and for determining the effectiveness of remedies.

Description: The present invention relates to a particle measurement apparatus, and more particularly to an apparatus for measuring the aggregation capability or aggregation rate of platelets and other blood corpuscles. Because of the precise picture it provides of the aggregation reaction, knowing the size and numbers of clumps (aggregates) of platelets and other such agglutinable blood corpuscles is essential for diagnosing various diseases. For this purpose, there are known blood platelet aggregability measurement apparatuses that measure such aggregates as particles. In a conventional apparatus for measuring platelet aggregability, a sample cuvette containing a platelet solution is irradiated by a visible ray, and light transmitted and scattered from a wide area that includes many aggregates is converted to electrical signals by a light receiving element, and the intensity thereof is used to determine platelet aggregation. US-A-4 623 252 discloses an apparatus for measuring particle size and number by means of light scattering. Detection means receive a scattered portion of the beam scattered by a particle and electronic means are coupled to the detection means for selecting a single maximum sample of the detection signal occurring during a selected portion of the time period required for the particle to more through the light beam. Measuring as it does the intensity of light transmitted and scattered from a wide area that includes large numbers of aggregates, a drawback of the prior art is that although the size and the number of aggregates are faithful indicators of quantitative changes in the aggregation reaction, both quantities cannot be measured on a time-course basis. Moreover, because in the early stages of the aggregation the intensity of scattered light from large numbers of non-aggregated blood platelets is much stronger than the intensity of scattered light from the small number of aggregates prevents changes in aggregation from being ascertained; in practice, with conventional measurement apparatuses such changes cannot be established even when there are aggregates of 30 to 40 percent of the platelets. An object of the present invention is to provide a particle measurement apparatus that is capable of time-series measurement of the size and number of platelet aggregates. An apparatus in accordance with the present invention is adapted to measure properties of particles by measuring the intensity of light scattered from a sample cuvette containing the particles and comprises a light source for producing a beam of light, means for collimating the beam from the light source to project it at the sample cuvette, a plurality of light receiving elements for receiving light scattered from the sample cuvette, characterized in that measuring means are provided wherein the measuring means comprise a plurality of comparison means that have upper and lower threshold values corresponding to particle diameter and discriminate particle diameters by comparing signals from the light receiving means with each threshold value, and counters that count signals from each of the comparison means, wherein the particle diameters and numbers discriminated into classes corresponding to the number of comparison means are determined on a time-series basis and further characterised in that a pinhole is disposed in front of each light receiving element such that each light receiving element receives scattered light from substantially one particle. With this arrangement the size and quantity of particles can be measured on a time-series basis, making it possible to determine multiple properties of the particles. The apparatus could also be arranged so that outputs from pairs of light receiving elements are subtracted to increase the effective signal ratio, thereby improving the S/N ratio during measurement. Preferably this particle measurement apparatus is an apparatus for measuring blood platelet aggregability. In such a case the particles would be clumps of agglutinable blood corpuscles such as platelets, and it would be the aggregability or aggregation rate of such corpuscles that would be measured. With the apparatus arranged thus to measure platelet aggregability, the size and numbers of aggregates of platelets or other corpuscles in the aggregation reaction can be measured in terms of a time-series, providing a more faithful observation of the aggregation reaction, and it also becomes possible to measure small aggregates in a weak aggregation reaction. An embodiment of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which:- Figure 1 illustrates the general arrangement of a particle measurement apparatus according to this invention; Figure 2 is a waveform of a scattered light intensity signal obtained from light receiving elements of the apparatus of Figure 1; Figure 3 is a schematic of the signal processing circuit; Figure 4A shows aggregation reaction data measured by the apparatus according to this invention, and Figure 4B shows data measured by a conventional apparatus; and Figures 5A and 5B show aggregation reaction data measured by the apparatus of this invention, and Figure 5C shows data measured by a conventional apparatus. Details of the present invention will now be described with reference to the embodiment illustrated in the drawings. In this embodiment the description relates to an example of the particle measurement apparatus configured to measure platelet aggregability. This type of platelet aggregation measurement apparatus is illustrated in Figure 1. With reference to Figure 1, for measuring the intensity of scattered light, a semiconductor laser light source 1 (40 mW) is driven by a drive circuit 9 to generate a beam of laser light. The laser beam collimated by converging lens 2 impinges on a glass sample cuvette 3 which contains a suspension of blood platelets or other such blood corpuscles. The suspension of blood corpuscles in the sample cuvette 3 is maintained at a constant temperature of 37°C and stirred at 1000 rpm by means of a stirring bar 4 and magnetic stirrer 5. Scattered light from the suspension of blood corpuscles passes via light receiving lens 6 to a plurality of photodiodes 8 (8a to 8d) and is thereby measured as an electrical signal. Disposed in front of each of the photodiodes is a (10-by-100 micrometer) pinhole 7 that receives scattered light from an observation region that statistically permits measurement of only one clump. The output of the photodiodes 8 undergoes current-voltage conversion and amplification by an amplifier 10, followed by analog-digital conversion by an A/D converter 11, and is then input to a computer 12. In the computer 12, the signal level is discriminated by a plurality of comparators corresponding to the clump particle diameter, and the signals output by the comparators are counted to thereby measure how many clumps there are of the prescribed particle diameter. An erroneous clump particle diameter count caused by part of a clump crossing an edge portion of a pinhole 7 can be corrected by personal computer measurement software, using statistical probability theory and standard particle measurements. Figure 2 shows changes in the intensity signal of light scattered during the aggregation of platelets, measured by one of the photodiodes 8a to 8d. The scattered light from the aggregate is measured as peak signals 13a to 13d that are correlated with aggregate size, and scattered light from individual, non-aggregated corpuscles is measured as background signals 14a to 14d. To eliminate the effect of these background signals, as shown in Figure 3, the outputs from two photodiodes 8a and 8b are each input to an operational amplifier 15 and subjected to subtraction. In this way, background signals produced by scattered light from non-aggregated corpuscles are canceled out, and only scattered light intensity values from clumps are measured, as indicated by 16. Signals from which background has thus been eliminated are then input to an absolute value circuit 17, which outputs background-free peak signals, as shown by 18. The signal output of the absolute value circuit 17 is input to window comparators 20_1, 20_2...20_n where the level thereof is discriminated. Each comparator compares the signal with a level corresponding to a clump particle diameter, so the output of each comparator is a signal corresponding to a clump particle diameter. These signals are counted by respective counters 21_1, 21_2.. .21_n to count the number of clumps of that particle diameter. This count data is then input to a calculating circuit 22, which computes the data representing the clump particle diameter and quantity, as described below. The functions of the comparators, counters and calculating circuit are implemented in the computer 12. While Figure 3 was used to describe the processing of the signals output by photodiodes 8a and 8b, the processing is the same for the other photodiodes 8c and 8d. Multiple sets of light receiving element pairs are used to raise the clump count probability. Figures 4 and 5 illustrate blood platelet aggregation, as measured by the apparatus of the present invention and by an apparatus for measuring blood platelet aggregability according to the prior art. With respect to measured results of blood platelet aggregation reactions induced using ADP (adenosine diphosphate) as the agglutinin, Figure 4A shows data obtained with a measurement apparatus according to this invention, and Figure 4B shows data obtained using a conventional apparatus for measuring blood platelet aggregability (a commercial aggregometer). As shown by Figure 4B, the conventional measurement apparatus does not measure aggregation reactions induced by an ADP concentration of 0.3 micromoles /liter or less. In contrast, as shown by Figure 4A, with the measurement apparatus according to this invention, with the comparators 20_1, 20_2...20_n particle diameters are discriminated in terms of aggregate particle size, and counts of these particle sizes are displayed along a time line as the number of aggregates. Also, the formation of many aggregates were observed when ADP in a concentration of 0.3 micromoles/liter was added. With this measurement apparatus, it is also possible to measure aggregation reactions produced by ADP at the low concentration of 0.03 micromoles/liter. This means that an apparatus embodying the present invention is capable of measuring aggregation reactions with 30 times the sensitivity of a conventional apparatus. Moreover, with the inventive apparatus it is possible to measure the size distribution and numbers of aggregates along a time baseline, and to observe how over time the aggregation reaction is accompanied by the formation of large aggregates from smaller aggregates. Figure 5 also illustrates blood platelet aggregation measurement by the apparatus of this invention and by a conventional apparatus for measuring blood platelet aggregability. With respect to measured results of blood platelet aggregation reactions induced using a collagen agglutinin, Figures 5A and 5B show data obtained with a measurement apparatus according to this invention, and Figure 5C shows data obtained using a conventional apparatus for measuring blood platelet aggregability (aggregometer). As shown by Figure 5C, an aggregation reaction induced by adding 0.7 micrograms/ml collagen could not be observed with the conventional measurement apparatus. As shown by Figure 5A, however, the formation of numerous aggregates resulting from the addition of 0.7 micrograms/ml collagen was observed with the measurement apparatus according to this invention. Moreover, as shown by Figure 5B, also observed was the clear suppression of aggregation induced by the addition of 0.7 micrograms/ml collagen in a calcium-ion-free solution containing EGTA (ethylenglycol tetraacetic acid) to suppress platelet aggregation.

Claims: An apparatus for measuring properties of particles by measuring the intensity of light scattered from a sample cuvette (3) containing the particles, comprising a light source (1) for producing a beam of light, means (2) for collimating the beam from the light source to project it at the sample cuvette, and a plurality of light receiving elements (8a to 8d) for receiving light scattered from the sample cuvette, characterized in that measuring means (12) are provided wherein the measuring means comprise a plurality of comparison means (20_1, 20_2,,20_n) that have upper and lower threshold values corresponding to particle diameter and discriminate particle diameters by comparing signals from the light receiving means with each threshold value, and counters (21_1, 21_2,, 21_n) that count signals from each of the comparison means, wherein the particle diameters and numbers discriminated into classes corresponding to the number of comparison means are determined on a time-series basis and further characterised in that a pinhole (7) is disposed in front of each light receiving element such that each light receiving element (8a to 8d) receives scattered light from substantially one particle. An apparatus according to claim 1, arranged such that outputs from pairs of light receiving elements are input to an operational amplifier and subjected to subtraction to increase the effective signal-to-noise ratio. An apparatus according to claim 1, in which the particles are clumps of agglutinable blood corpuscles such as blood platelets and the apparatus is arranged such that blood corpuscle aggregability or aggregation rate is measured.

Inventors: SHIRASAWA YOSHIAKI, YAMAMOTO TETSUYA, SHIRASAWA, YOSHIAKI, C/O KOWA CO. LTD., YAMAMOTO, TETSUYA, C/O KOWA CO. LTD.
Applicants: KOWA CO, KOWA COMPANY LTD.
Application year: 1993
Main classification: G01N15
IPC codes: G01N33, G01N21, G01N15