Abstract:
A device for automatic preparation of blood smears on plates comprises a spreading unit that spreads a drop of sample blood on individual plates in order to produce a regularly distributed blood smear on each plate. After the blood smear is dried, the plate is passed to a fixative bath filled with a fixative agent. Following submersion of the dried blood in the fixative agent, the plate is then removed from the fixative bath and delivered to a revolving stainer. The revolving stainer processes the plate and colors the blood smear on the plate. The revolving stainer is separate from the fixative bath and moves independent of the fixative bath. After the plate is processed in the stainer, the plate having a colored blood smear is unloaded from the device. A robotic pick and place is used to move the plate between the conveyor, fixative bath and revolving stainer.

Description:
BACKGROUND  
       [0001]     The invention relates to the field of hematological analyses, and more specifically to the preparation of blood smears on plates.  
         [0002]     In this particular field, it is known to deposit a drop of a blood sample on a plate (also referred to herein as a “slide”), such as a glass plate for analysis under a microscope, and to spread this drop on the plate in order to produce what is known as a blood smear. The latter is then dried, and then colored by at least one appropriate reagent, in order to permit subsequent analysis under the microscope. In fact, analysis of plates of this type makes it possible to determine the composition of the blood sample concerned, which is of great importance for the diagnosis of specific pathologies.  
         [0003]     Blood smears of this type can be prepared by automated devices, which, on the basis of a stock of new plates, carry out a multiplicity of operations of depositing and spreading of blood on plates and miscellaneous subsequent processing operations such as drying and coloring. The plates thus processed are then collected in appropriate containers, and sent to a laboratory for analysis.  
         [0004]     Many commercially available devices of this type include a coloring unit (also referred to herein as a “stainer”). After a blood smear is deposited on a plate and dried, the plate it is then delivered to the coloring unit where color is added to the blood smear. Many of these coloring units revolve such that each plate positioned on the coloring unit is processed from a starting position to an ending position. In between the starting position and the ending position, each plate is subjected to a plurality of processing stations operable to add color to the blood smear on the plate. In one embodiment, the revolving coloring unit is a rotatable carousel comprising a plurality of wells with each of the wells designed to hold one of the plates. An example of such a coloring unit is disclosed in U.S. Pat. No. 6,319,470, which is incorporated herein by reference in its entirety.  
         [0005]     Typically, a fixative bath is the first processing station encountered by a plate on such a revolving coloring unit. The fixative bath may be provided by filling the well holding the plate with a fixative agent, such as pure methanol. The fixative agent is provided to assure the blood cells on the plate are “fixed” and will remain free of water-induced defects during subsequent processing. In some situations, a stain may be included with the fixative agent in the first processing station.  
         [0006]     After the plate is subjected to the fixative bath, the carousel is rotated in an indexing fashion to another position where the fixative agent is removed, and a second fluid is placed in the well holding the plate. This process is repeated for various subsequent staining stages, as the well holding the plate is rotated through a complete revolution by the carousel. The later stages of the staining process typically involve water-based solutions. The final step of the process is to drain the well, remove the stained slide, and place a new unstained slide in the well to repeat the process.  
         [0007]     The foregoing process works well for a first set of plates that move through the process starting in completely dry wells. However, it has been noticed that a problem occurs when the wells are reused to move additional plates through the process before the wells are thoroughly dried. In particular, after a well moves a first plate through the process, a small amount of water remains in the well. If the well is reused before it dries to move a subsequent plate through the process, the small amount of water in the well adulterates the pure methanol fixative agent placed in the well. The result following processing is that red blood cells on the subsequent slide appear to have a halo or bright ring in their center when viewed under a microscope. This halo makes it difficult to observe the internal features of the cell and makes analysis of the sample difficult and possibly inaccurate.  
         [0008]     Accordingly, it would be desirable to provide a device for automatic preparation of blood smears on plates that includes a revolving stainer, but avoids the above-described problem.  
       SUMMARY  
       [0009]     A device for automatic preparation of blood smears on plates comprises a storage unit that stores new plates in a stack. An extractor unit is used to extract plates from the stack and place the plates on a conveyor one at a time. As the plates pass along the conveyor, a depositing unit deposits a drop of blood on each plate extracted from the stack. A spreading unit spreads the drop of blood on each plate in order to produce a regularly distributed blood smear on the plate. A drying unit dries the blood smear on the plate. After the blood smear is dried, the plate is passed to a fixative bath. The fixative bath is filled with a fixative agent, and the blood smear is submerged in the fixative agent when it is placed in the fixative bath. The plate is then removed from the fixative bath and delivered to a revolving stainer that colors the blood smear on the plate. The revolving stainer is separate from the fixative bath and moves independent of the fixative bath. After the plate is processed in the stainer, the plate having a colored blood smear is unloaded from the device. A robotic pick and place is used to move the plate between the conveyor, fixative bath and revolving stainer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic perspective view of a device according to the invention;  
         [0011]      FIG. 2  is a plan view of the device in  FIG. 1 ;  
         [0012]      FIG. 3  is a plan view of the storage unit and the extractor unit;  
         [0013]      FIG. 4  is an illustration of the method of action of the extractor unit;  
         [0014]      FIG. 5  shows a sensor which is part of the depositing unit, depositing a drop of blood on a plate which is supported by a carriage;  
         [0015]      FIG. 6  shows an optical transmission measuring unit, which is associated with the spreading unit;  
         [0016]      FIG. 7  shows a tool of the spreading unit;  
         [0017]      FIG. 8  shows a tilter of the drying and tilting unit;  
         [0018]      FIG. 9  is a view in vertical cross-section of the coloring unit;  
         [0019]      FIG. 10  shows schematically the various paths of the handling bracket;  
         [0020]      FIG. 11  is a schematic elevational view of the handling bracket; and  
         [0021]      FIG. 12  is a schematic plan view of the handling bracket and a moveable fixative bath.  
     
    
     DESCRIPTION  
       [0022]     Reference is made firstly to  FIGS. 1 and 2 , which represent a device  10  for preparation of blood smears according to the invention. In this example, this device is combined with a device  12 , which produces haemograms in parallel.  
         [0023]     The device  10  comprises a rectangular base plate  14 , which supports various units, and a unit  16  for storage of new plates  18 . These plates are rectangular glass plates, which are disposed horizontally, and are superimposed in a vertical stack, and are maintained between columns  20  ( FIG. 1 ). This arrangement permits re-supply during operation, since the operator simply has to place new plates on top of the stack.  
         [0024]     The device according to the invention additionally comprises an extractor unit  22  ( FIG. 3 ), which is provided in order to extract the plate which is disposed at the base of the stack, in order to bring it onto a carriage  23  (shown schematically in  FIG. 3 ), which then conveys the plate towards other units contained in the device according to the invention. The extractor unit  22  comprises a thruster  24 , which can be displaced in a direction of extraction DE, as shown by an arrow in  FIGS. 2, 3  and  4 . The thruster  24  is in the form of a horizontal blade, the thickness of which is smaller than that of the plate to be extracted. This blade comprises a longitudinal edge  26 , which is also known as a front edge, which can act on a longitudinal edge  28  of the plate  18 .  
         [0025]     The thruster  24  is guided in translation by rods  30  ( FIG. 3 ), and its displacement is advantageously obtained by an assembly  32 , shown schematically in  FIG. 3 , which comprises a step motor and a ballscrew.  
         [0026]     Once the plate has been placed on the carriage  23 , it is at the level of the following unit of the installation, i.e. the depositing unit  34  ( FIG. 2 ). At the unit  34 , there is provided a sensor  36  (see  FIG. 5 ) which, in the example, is part of the device  12 , but which, as a variant, can be part of the device  10  itself. This sensor is moved by displacement means (not shown), and is designed to collect blood from a sample tube (not shown), and then to deposit a drop of blood  38  ( FIGS. 2 and 5 ) on the new plate  18  which has just been deposited on the carriage  23 . On the carriage  23 , the plate  18  is maintained between a fixed stop  40  and a tilting gripper  42 , which is also known as a clip.  
         [0027]     The drop of blood is deposited by means of the sensor  36 , in a pre-determined position on the plate, which is kept secured, the carriage  23  being immobilized in translation. The volume of the drop of blood is pre-determined, and can be adjusted by the user.  
         [0028]     The carriage  23  can be displaced in horizontal translation, according to a direction of translation DT ( FIGS. 2 and 5 ) which is perpendicular to the direction of extraction DE. The displacement in translation of the carriage is carried out by a conveyor with appropriate drive means, for example by a belt  44  driven by rollers, which is shown schematically in  FIG. 5 .  
         [0029]     As can be seen in  FIG. 2 , the plate  18  has a reserved area  46  with a generally rectangular shape, which is provided at one end of the plate  18 , and the drop of blood  38  is deposited on the plate, in the vicinity of this reserved area.  
         [0030]     The conveyor then displace the carriage  23  towards a unit  48 , which is known as the spreading unit  48  ( FIG. 2, 6  and  7 ), and is provided in order to spread the drop of blood, and thus form a smear  50 . The spreading unit  48  is disposed on the path of the carriage  23  which provides transfer of the plate.  
         [0031]     The spreading unit  48  ( FIG. 6 ) comprises a measuring unit  49  which can measure the optical transmission of the drop of blood  38  deposited on the plate. This measuring unit comprises an electro-luminescent diode  52  and a photo-diode  54 , which are disposed on both sides of the plate  18 , in the position of the drop of blood  38 . In this case, the electro-luminescent diode  52  is disposed on the same side as the upper surface  56  of the plate, which receives the drop of blood. In the example, the electro-luminescent diode emits at 560 nm.  
         [0032]     There is then deduced a measured value of the optical transmission (TO), which depends on the thickness of the drop and its content. It has been shown by tests that this measurement is inversely proportional to the haematocrit reading of the blood concerned. On the basis of the measurement thus obtained, the spreading speed of the blood, and thus the thickness of the smear, is adjusted.  
         [0033]     Thus, a blood sample which contains many cells, and therefore has a high haematocrit reading, provides a lower TO measurement, thus generating a high spreading speed. Conversely, a sample which has a low hematocrit reading provides a high TO measurement, and a low spreading speed.  
         [0034]     On the basis of this measurement, it is thus possible to control the spreading speed accurately, and to obtain regular distribution of the cells on the plate, irrespective of the quantity of cells present in the blood sample.  
         [0035]     When this measurement has been carried out, the spreading is carried out at the spreading unit  48  by a tool  58 , which is represented in  FIG. 7 . The tool  58  comprises a fixed support  60 , which supports a counter-block  62 , which is designed to carry out the spreading by relative displacement between the counter-block  62  and the plate  18 , which is supported by the carriage  23 . In the example, it is the displacement of the plate  18  by the carriage  23 , in the direction of translation DT, which gives rise to the spreading. The counter-block  62  remains in a fixed position, except that the height of the support  60  can be regulated as shown by the arrow H. In addition, as can be seen, the counter-block  62  has a ridge  64  which is connected to an edge  66 , which forms an adjustable angle B with the upper surface  56  of the plate. This adjustable angle B can be modified as required, in order to adjust the thickness of the smear. In general, the angle B is approximately 30 degrees.  
         [0036]     As can be seen in  FIG. 7 , the counter-block  62  does not come directly into contact with the drop of blood. For this purpose, the invention comprises a flexible strip  68  made of plastics material, for example of polyethylene, which is stretched around the counter-block  62  such as to cover completely the ridge  64  and the edge  66  of the counter-block. The tool  60  comprises means for winding and unwinding the strip  68 . These means comprise a first bobbin  70  (unwinding bobbin), from which the new strip is unwound, and a second bobbin  72  (winding bobbin), onto which the strip which is soiled by the blood is wound. Between its passage around the counter-block and winding around the bobbin  72 , the strip passes around return rollers  74 ,  76  and  78 .  
         [0037]     The part of the strip which is in contact with the blood is displaced between two successive spreading operations, such as to provide a blank portion of strip for the following smear, and thus to prevent any risk of contamination.  
         [0038]     Advantageously, the bobbins  70  and  72  are contained in a case, which must be changed when the strip is completely used up.  
         [0039]     The plate  18  which supports the smear  50  is then transferred, again by the carriage  23 , to a marking unit  79  ( FIG. 2 ), which comprises a marking head, which for example can consist of a print head of the needle matrix type, with an ink ribbon. The plate is marked on the reserve area  46  previously described. This area must be ground or pre-painted, in order to allow the printing inks to adhere well. The marking can also be carried out in other manners, for example by means of a ribbon or other printing means disposed in the position of the spreading unit previously described.  
         [0040]     When the marking has been carried out, the carriage  23  transfers the plate  18  to a unit  80 , which is a drying and tilting unit ( FIGS. 1 and 8 ). The carriage deposits the plate at the unit  80 , and the latter is received by a tilter  82 , which allows the empty carriage to return to the depositing unit in order to receive a subsequent plate.  
         [0041]     The plate is supported by the tilter  82 , by means of rollers  84 , and which are made of polymer. The plate is then subjected to a flow of warm air, maintained at about 40° C., which is conveyed by a forced air heater  86 . The tilter  82  ( FIGS. 2 and 8 ) then tilts the plate by 90°, in order to bring it into a vertical position (shown in broken outline in  FIG. 8 ), in which the reserved area  46  of the plate is disposed at the top.  
         [0042]     The plate thus brought into a vertical position can then be collected by a handling bracket  88  ( FIG. 2 ), which is described in detail hereinafter with reference to  FIGS. 10 and 11 . The handling bracket may be a robotic pick-and-place device as is known in the art for moving structures from one location to another. In particular, this handling bracket makes it possible to transfer the plate  18  from a loading position  81  ( FIG. 2  and  8 ) to a fixative bath  200 , a coloring unit  90 , and/or an output unit  92 .  
         [0043]     As shown in  FIG. 11 , the fixative bath  200  generally comprises a dedicated fixative well  201  designed and dimensioned to receive at least one plate  18 . The fixative well  201  is typically deep enough such that the substantial part of a plate will rest in the well below the top rim of the well. The fixative well  201  is substantially filled with a fixative agent, such as pure methanol. The fixative agent is provided to assure the blood cells on the plate are “fixed” and will remain free of water-induced defects during subsequent processing. When a plate with a dried blood smear is placed in the fixative well, the dried blood smear is bathed in the fixative agent. After bathing in the fixative agent, the plate is ready for transfer to the coloring unit  90 .  
         [0044]     The coloring unit  90  ( FIG. 9 ) comprises a revolving turntable  94  (also referred to herein as a “carousel”). The revolving turntable is mounted to rotate around a shaft  96  with a vertical axis XX. This turntable supports a plurality of receptacles  98  known as “wells”, which are distributed circumferentially, and of which there are thirty two in the example shown. These wells are disposed vertically, and have dimensions which are adapted to those of the plates. The turntable  94  is connected to a drive means  100 , which are shown schematically in  FIG. 9 , and can rotate the turntable in successive increments, such as to bring the wells in sequence into different positions. Thus, the turntable can carry out angular rotation sequentially from well to well, for example every 30 seconds. Initially, an empty well is disposed at right-angles to the bracket  88 , in order to receive a plate.  
         [0045]     The plate then undergoes at least one operation in each sequential position of the turntable.  
         [0046]     For this purpose, the coloring unit additionally comprises filling and emptying means  102 , which comprise a support  104 , which can be displaced in vertical translation parallel to the axis of rotation of the turntable. In the example, the support  104  comprises a drum  106 , which can slide along the shaft  96 , as shown by the arrow F 1 . The support  104  supports two plunger needles, which are disposed vertically, i.e. an injection needle  108  and an emptying needle  110 . The support  104  can be displaced between a high position, in which the needles are extracted from the well  98  (as shown as a solid line in  FIG. 9 ), and a low position in which the needles are plunged into the well. The position of the needles determines the incubation time, such that the needles are displaced in accordance with the coloring conventions selected.  
         [0047]     As can be seen in  FIG. 9 , in the position in which the plate  18  is accommodated in the well  98 , the reserved area  46  of the plate, which bears the means of identification, is disposed at the top, such that it is outside the fluid which is contained in the well.  
         [0048]     The coloring unit additionally comprises a closed enclosure, comprising a base  112  and a cover  114 , which surrounds completely the turntable  94  and the wells  98  which it contains, such as to prevent migration of toxic vapors derived from the reagents or solvents which are injected into the well. The cover  114  contains holes  116 , in order to permit passage of the needles.  
         [0049]     The plates which are installed in the wells are immersed in succession in dyes and other treatment fluids, in order to carry out one of the coloring operations necessary in order to identify a plate, according to the known methods of MAY-GRUNWALD, GIEMSA, WRIGHT &amp; WRIGHT GIEMSA.  
         [0050]     The device  10  comprises a recess  118  ( FIG. 1 ) in order to accommodate bottles containing various fluids which can be injected into the wells, then emptied.  
         [0051]     In the example, a bottle  120  is provided in order to contain a solvent (in this case methanol), as well as two bottles  122  and  124  to contain respectively two different dyes.  
         [0052]     It should be noted that the device  12 , with which the device  10  according to the invention is combined, comprises recesses to accommodate other reagents  126 ,  128 ,  130  and  132  ( FIG. 2 ).  
         [0053]     After a complete rotation, the plate  18 , which has thus been processed, returns to its original position (i.e., the load/unload position of the stainer). In this position the plate  18  is ready to be transferred to the dry well of the output unit  92 .  
         [0054]     In one embodiment, the plate is transferred to a dry well  202  before it is transferred to the output unit. The dry well  202  may be attached to the fixative well in the fixative bath  200 . Like the fixative well  201 , the dry well  202  is typically deep enough such that the substantial part of a plate will rest in the well below the top rim of the well. The dry well  202  is separated from the fixative well  201  by a dividing wall  203 . The dry well includes no reagent and is generally used as a holding tank for plates removed from the coloring unit  90  and awaiting delivery to the output unit  92 . After a short period in the dry well  202 , the plate  18  is next transferred to the output unit  92 .  
         [0055]     The output unit  92  comprises a receptacle  134  ( FIGS. 1 and 2 ) which can accommodate empty stacked baskets  136 . These baskets are then displaced one by one in a passage  138  in the direction of the arrow F 2  ( FIGS. 1 and 2 ). In the example, each of the baskets contains twenty recesses, which can each accommodate a plate in a vertical position, which has been supplied by the handling bracket. A mechanical feed device (not shown) makes it possible to feed the baskets in successive increments, in order to position each recess of a basket in succession beneath the handling bracket, and on each occasion to receive a pre-treated plate. When the baskets have been filled, they are stored in a storage area  140 , before being retrieved by the operator.  
         [0056]     In addition, the device  10  comprises a receptacle  142  for storage of plates which are spread manually, and need to be colored. In fact, in some cases, it is necessary to color plates which are already provided with blood which has been smeared manually. This receptacle  142  is also disposed at right-angles relative to the bracket, which thus makes it possible to collect a plate from the receptacle  142 , in order to bring it directly to the coloring turntable. When the plate has been colored, it is displaced, and brought into a basket.  
         [0057]      FIG. 10  shows schematically various exemplary possibilities which are provided by the handling bracket, i.e.: path T 1 , in order to bring a plate which is provided with a smear to the fixative bath  201  and then to the coloring turntable  90 , or to a basket in the storage area, depending on whether or not a fixative agent and coloring is required for this plate. It also makes it possible to travel a path T 2 , in order, as previously described, to bring a plate which has been spread outside the receptacle  142 , to the fixative bath  201  and coloring platform  90 . It is also possible to travel a path T 3 , in order to displace a plate from the coloring platform  90 , to the dry well  202 , and then to a basket in the storage area.  
         [0058]     Reference is now made to  FIG. 11 , in order to describe the general structure of the bracket  88 . The latter comprises a fixed support  144 , which consists of two vertical columns which form guide means, a horizontal beam  146 , which can be displaced vertically relative to the fixed support, a slide  148 , which can be displaced in translation along the beam, and a controlled gripper  150 , which can grasp a plate and then release it, in order to displace it from one unit to another.  
         [0059]     Appropriate drive means (not shown) make it possible to displace the beam  146  and the slide  148 , such that the gripper  150  can occupy different positions in a vertical plane. The gripper  150  can be actuated by any appropriate means, for example by an electromagnet. It should be noted that the gripper acts on the reserved area  46  of the plate.  
         [0060]     With reference to  FIG. 12 , in one alternative embodiment the fixative bath  200  comprises both the fixative well  201  and the dry well  202 . In this embodiment, the fixative bath  200  is moveable along a first axis  211 , which is perpendicular to a second axis  212  along which the slide  148  moves when moving in a horizontal direction. Because the fixative bath  200  is moveable, the fixative well  201  may be placed under the path of the slide  148  and associated gripper  150  when a plate is being moved from the loading position  81  to the fixative well  201  of the fixative bath  200  and from the fixative well  201  to the revolving stainer  90 . Then, when plates are moved in the opposite direction, i.e., from the stainer  90  to the dry well  202  and from the dry well to the output unit  92 , the fixative bath is shifted along the first axis  211  such that the dry well  202  is positioned under the path of the slide. Because the fixative well  201  and dry well  202  may be moved in this fashion, the gripper  150  can easily pick up and drop off plates in their proper position.  
         [0061]     Thus, the above-described device is designed such that the fixative well never needs to be rinsed with water or an aqueous solution. When the fixative agent needs to be replaced, the old fixative agent is drained from the well and it is simply refilled with a new fixative agent. Accordingly, water never enters the fixative bath, and the problem of water contamination of the fixative agent is avoided.  
         [0062]     Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. For example, in one alternative embodiment, the pick-and-place device includes two grippers. A first gripper used to transport plates between the fixative bath and the conveyor and/or output unit. A second second gripper used to transport plates between the rotatable stainer and the fixative bath. In another alternative embodiment, two pick-and-place devices are utilized. The first pick-and-place device is used to transport plates between the unloading position, the fixative well, and the revolving stainer. The second pick-and-place device is used to transport plates between the revolving stainer, the dry well, and the output unit. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.