Abstract:
A flow chamber which is particularly useful in slit-scan photometry and which has a predetermined configuration for orienting generally flat oval particles such as squamous cells in the direction of fluid flow such that the maximum cross-sectional area of each particle is substantially normal to a light path traversing the flow of particles at an observing station situated along the flow path of the particles.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for orienting particles in a fluid suspension and more particularly to an apparatus for orienting generally flat particles in a proper position for scanning the particles as they pass a monitor in a slit-scan photometry instrument. 
     BACKGROUND OF THE INVENTION 
     Optical particle sensors operate on the principle of measuring the amount of light scattered or intercepted when an intensive illuminating beam is projected through a flow steam containing suspended particles. Flow cells for containing this liquid flow have been developed for accurately containing the sample liquid within the center of a circularly laminar flow of a sheath fluid. These flow cells were designed for forming a nonturbulent, laminar flowing fluid that was then caused to surround a sample-containing fluid. These flow cells allowed the exact axial positioning of the flow of sample fluid such that it passed a scanning or observing device. The above-mentioned flow cells were utilized in a slit-scan photometry device described by Wheeless, Jr. et al, in U.S. Pat. No. 3,657,537 entitled, &#34;COMPUTERIZED SLIT-SCAN CYTOFLUOROMETER FOR AUTOMATIC CELL RECOGNITION.&#34; 
     In the Wheeless patent, a cytofluorometer was used to give graphic fluorescent contours of a fluorochromed cell. The technique described by Wheeless allowed nuclear fluorescence to be distinguished from nonspecific cytoplasmic fluorescence that was often observed in particles such as squamous cells. The shape of the pulse was an indication of the ratio of the areas of the nucleus and cytoplasm, which is an informative index. These squamous cells are generally flat and of so-called &#34;fried-egg shape.&#34; 
     The term &#34;fried-egg shape&#34; is used to describe squamous cells because such cells are generally circular in plan view and have a somewhat elevated nucleus which may or may not be centered. This general configuration resembles the shape of a fried egg. 
     The optical scanning device used in the above-described system responded to the maximum cross-sectional area of the particle perpendicular to the direction of the light beam of the scanning device. Due to the irregular shape and unpredictable orientation of the squamous cell, the cross-sectional area presented to the scanning device was found to vary widely, thereby precluding proper measuring results. 
     SUMMARY OF THE INVENTION 
     According to the invention, a flow chamber is used for orienting sample particles suspended in a sample fluid for observation by slit-scan photometry such that the particles are oriented with the maximum cross-sectional area of each particle transverse to the light beam used. The flow chamber has an entrance end and an exit end and is dimensioned so that, in the direction of fluid flow through the flow chamber, the ratio of a dimension in a first direction of the flow chamber to a dimension in a second direction of the flow chamber is constantly increasing; the first direction being transverse to the second direction and the cross-sectional area generally normal to the direction of fluid flow is decreasing gradually and monotonically so as to accelerate fluid flow monotonically in the direction of its flow through the chamber. A slit is provided along the longitudinal axis of the flow chamber located to establish a zone of least pressure, thereby more precisely arranging the sample particles for observation by slit-scan photometry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary medial sectional view of apparatus constructed in accordance with the invention; 
     FIG. 2 is a top view of the apparatus shown in FIG. 1; 
     FIGS. 3 and 4 are vectorial representations of the fluid velocity at different points in the apparatus of FIG. 1; 
     FIG. 5 is a sectional view taken along the line 5--5 of FIG. 1 and in the general direction indicated; 
     FIG. 6 is a vectorial representation of the fluid velocity along the longitudinal axis of the apparatus of FIG. 1; and 
     FIG. 7 is an enlarged fragmentary detail illustrating a portion of the apparatus shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the flow cell means embodying the invention is designated generally by the reference number 10. Sample cells, such as squamous cells 12 carried in suspension are introduced from a source of flowing sample particles, such as sample tube 14 into a flow chamber 16. The supply of the sample particles in sample tube 14 can be accomplished by any suitable means well known in the art. 
     The flow chamber 16 is defined by walls 17, as seen in FIG. 2, and walls 18, seen in FIG. 1. Walls 17 are parallel and straight whereas walls 18 preferably follow exponentially narrowing curves. The walls 18 converge to an outlet 20 for fluid discharge. 
     The cells 12 are scanned by a light source 22 shown as providing a light at a point in the flow chamber that is essentially transverse to the direction of flow of the sample particles 12. A photoresponsive means, such as a photocell 24, is positioned opposite the light source 22 to measure the amount of light passing through the flow chamber 16. The photocell 24, which can be a photomultiplier tube, provides a reading on the amount of light transmitted. This measurement can be used to count the number of cells traversing the light beam and also can be used to measure other physical properties of the cells such as opacity and color. The photocell can also be used to measure the cross-sectional area of the sample cells. By varying the source of light or staining the sample cells, electroluminescence of the cells can be measured also to assist in identifying on the type of cell present. 
     Referring again to FIG. 1, a conduit 26 is connected to the flow chamber 16 for conducting fluid flow into the flow chamber. A laminar sheath flow designated by the arrows 28 is provided by sheath flow means 30 located in the bore of conduit 26. Sheath flow means 30 may comprise a plurality of tubes 32 extending through the center of conduit 26 in the direction of fluid flow, as indicated, and surrounding the sample tube 14. The tubes 32 may function to prevent turbulent flow such that the fluid entering the flow chamber 16 is &#34;collimated&#34; and is nonturbulent. As the sheath fluid enters flow chamber 16, the fluid takes the form of a laminar sheath fluid flow. A more detailed discussion relevant to laminar flow will be made with reference to FIG. 3. 
     Referring to FIGS. 1 and 2, cells 12 are shown being introduced to flow chamber 16 from tube 14 in a random manner. As they enter the observing plane formed by light source 22 and photocell 24, the cells are shown lying in a plane that is transverse to a beam of light 33 from the light source 22. As can be seen in FIG. 2, which would be the view as seen by the light source 22, each cell is oriented such that its flat side is facing the light beam, i.e., the maximum cross-sectional area of each particle is transverse to the light beam. 
     Digressing now to FIG. 3, there is illustrated a vectorial representation of a fluid that exhibits laminar sheath flow as discussed previously. Such a laminar flow would be exhibited by fluid flow 28 as it enters the flow chamber 16. The horizontal arrows represent the vector velocites at the different locations across the conduit 26 comprising sheath flow in a parallel wall conduit, with the arrows being parallel, a typical one of which is designated 34. The locus of these vectors is a parabola as shown, the distance of any vector from a wall being typically as indicated at 35, this being the distance of the vector 34 from the wall. Once the laminar flow enters the flow chamber 16, vector flow as represented in FIG. 4 would result. The fluid closest to walls 18 of flow chamber 16 have their velocities changed by the monotonically changing width of walls 18. The velocity of the fluid within the flow chamber 16 now has a Y component of velocity imputed to it by the walls 18; the Y component of velocity decreasing in the fluid as the distance from the walls 18 increase until the velocity of the fluid in the center of fluid flow has approximately no Y component of velocity. In accordance with Bernoulli&#39;s principle, the fluid in the center of fluid flow in FIG. 4 will have the greatest velocity and the pressure at the center of fluid flow will be the least. Those cells located out of the center of fluid flow will have a Y component of fluid pressure acting on it to orient it towards the center of fluid flow. 
     When sample fluid is introduced isokinetically into the center of a laminar flow, similar to that shown in FIG. 3, the center flow will remain in the center not crossing any planes of laminar flow. It should be understood that laminar flow can be approximated without the use of tubes 32 if a slow velocity fluid is introduced into a substantially infinitely long conduit prior to entering the flow chamber 16 of cell 10. The converging configuration of walls 18 of flow chamber 16 is such as to cause a constant acceleration of the flow of fluid toward outlet 20. The substantially infinite width of the cross section of the flow chamber near the sensing zone as compared to its height causes the flow of fluid to be not only laminar, but planar-laminar. The substantially infinite width is provided by a slit 36 centered on a longitudinal axis of least pressure and operates further to decrease the effect of a longitudinal wall on the fluid flow. 
     Referring to FIG. 5, slit 36 can be seen extending along the full width of the flow chamber 16 and along the full width of the flow chamber, as shown in FIG. 2. The slit 36 extends in a direction which is approximately perpendicular to the plane of the light beam emanating from light source 22. This slit provides an enhanced axial plane of increased velocity which, by Bernoulli&#39;s principle, forms a plane of least pressure, thereby providing optimized particle orientation such that the particle assumes a position in which the flat side of the particle is transverse to the beam 33 from light source 22 of FIG. 1. The axial region of least pressure that is formed by the slit 36 in the walls 17 of flow chamber 16 effectively provides a zero pressure gradient in a direction perpendicular from the axial center of fluid flow towards the walls 17. The walls formed by slit 36 are farthest from the axial center of fluid flow and have negligible effect upon the fluid flow. 
     FIG. 6 is a vectorial representation of the velocities in the flow chamber 16 of FIG. 5 centered along the flow chamber&#39;s longitudinal axis and parallel to slit 36 of FIG. 5. As can be seen, the velocity along this region is approximately constant along the length of slit 36 thereby representing a region of least pressure change, as described above. 
     It is believed that when a particle is in the flow chamber 16, the fluid in contact with the forward or leading edge of the particle will be moving faster than the fluid in contact with the back or trailing edge of the particle. This is believed to apply a tension on the particle which tends to align the particle in the direction of flow. In addition, any particle which is tilted to the direction of the fluid flow is turned by the component of fluid velocity perpendicular to the direction of flow at the center of the flow chamber since, it is believed, due to the decreasing spacing of the chamber walls 18, the inwardly directed velocity component of fluid flow which is greater downstream than upstream is produced perpendicular in the direction of fluid flow off axis. These perpendicular velocity components are zero in the center of the flow chamber. The particles will then orient themselves along this axis of least pressure as described above wherein the plane formed by the maximum cross-sectional area of the flat-shaped particles will lie in a plane parallel to the axial plane of least pressure and orthogonal to beam 33 from light source 22. 
     The sectional view of FIG. 5 shows the entrance to the flow chamber 16. The entrance to the flow chamber is constructed to form an elongated oblong configuration similar to that of the sample squamous cells that are to be scanned. The sample tube 14 is shown positioned in the center of the flow chamber and having the elongated oblong configuration of the flow chamber 16 and axially centered within the chamber. 
     Sample squamous cells that are ejected from tube 14 into the flow chamber 16 will be on the center of the flow chamber as described above; the walls farthest away from the center providing a longitudinal axial region of least pressure. As stated above, it is believed that the fluid pressure increases as the distance from the axial center of flow increases thereby pushing cells that are tilted or not in the plane of symmetry towards the plane of symmetry due to the increase of pressure on points of the cells farthest from the plane of symmetry. Measurements are then made on the cells by projecting a cylindrical lens focused light beam 33 transverse to the direction of flow as shown in FIG. 7. This also is described in the previously mentioned Wheeless et al. patent. The light beam 33 intercepts the cells 12 at a point at which walls 18 are still tapering to orifice 20. When they reach the light beam, the &#34;fried-egg&#34; shape squamous cells are oriented in the center of the flow stream in a longitudinal direction extending towards the axis of least pressure at approximately a right angle to beam 33. As a result, the maximum cross-sectional area of each cell is presented to beam 33. This provides the desired efficient results in measurements by slit-scan photometry heretofore not realized. 
     After emerging from exit port 20, the discharged stream may be deposited on a sheet for further individual particle investigation or routed through appropriate plumbing to waste or recycling means.