Filtration system and method for obtaining a cytology layer

Abstract

A filter assembly for separating and collecting a layer of particulate matter (e.g., cells) from a liquid containing the particulate matter (e.g., a biological fluid specimen). The filter assembly has a holder and contiguous inner and outer fluid pervious media. The outer fluid pervious medium is attached to the sidewall of the holder. The inner fluid pervious medium is of low fluidic impedance relative to the outer fluid pervious medium. The filter assembly is designed for use in a separation housing that defines two flow paths between inlet and outlet, one directly through the filter and the other around the periphery of the filter. The inlet portion of the housing has a central inlet in a radially sloped surface that faces the filter collection site. A movable suction head is adapted to cooperate with the housing and the filter assembly.

1 . A method for collecting cells from individual specimens of biological fluid in specimen containers, each container having therein a processing assembly comprising an open-top separation chamber, adapted to receive a filter assembly having a downwardly facing collection site, and a depending aspiration tube that extends into the specimen and communicates with the separation chamber through the bottom wall thereof, the method comprising, for each container, the steps of:
 placing a filter assembly in the separation chamber;   coupling a movable suction head to the processing assembly and the filter assembly;   applying a vacuum to the filter assembly to aspirate specimen fluid from the container through the tube, into the separation chamber and through the filter until a layer of cells is collected on the filter collection site;   uncoupling the suction head from the processing assembly; and   elevating the suction head to remove the still-coupled filter assembly from the separation chamber.   
     
     
         2 . A method according to  claim 1 , wherein the suction head is coupled to the filter assembly by vacuum. 
     
     
         3 . A method according to  claim 1 , wherein the vacuum applied to couple the suction head to the filter assembly is on the order of 20″ Hg. 
     
     
         4 . A method according to  claim 2  or  claim 3 , wherein the vacuum applied to aspirate specimen fluid from the container is in the range of about 3″ Hg to about 7″ Hg. 
     
     
         5 . A method according to  claim 1 , further comprising positioning the suction head with the still-coupled filter assembly over a slide, and moving the suction head downwardly to press the filter assembly against the slide to transfer cells from the filter assembly to the slide. 
     
     
         6 . A method according to  claim 5 , further comprising uncoupling the filter assembly from the suction head and disposing of the filter assembly. 
     
     
         7 . An apparatus for collecting cells for cytology from individual specimens of biological fluid in specimen containers, each container having therein a processing assembly comprising an open-top separation chamber, defined by a bottom wall and an upstanding annular wall and adapted to receive a filter assembly, and a depending aspiration tube that extends into the specimen fluid and communicates with the separation chamber through the bottom wall, the filter assembly having a holder with a flow opening in its upper face and a filter arrangement in the holder having a downwardly facing collection site, the apparatus comprising:
 a suction head adapted to be positioned above a container and mounted for vertical movement relative to the container, the suction head comprising coaxial inner and outer portions, the outer portion having an annular skirt adapted to surround and sealingly engage the annular wall of the separation chamber, the inner portion having a lower face with an aspiration suction port and a retention suction port, the inner portion being mounted for axial movement relative to the outer portion and adapted to sealingly engage the upper face of the holder so that the aspiration suction port is in fluid communication with the flow opening and the retention suction port is in fluid communication with a sealed annular area on the upper face of the holder,   a head actuator for moving the suction head vertically; and   an inner portion actuator for separately moving the inner portion vertically.   
     
     
         8 . An apparatus according to  claim 7 , wherein the suction head is journaled for rotation about the coaxial axis to mix the specimen in the container, further comprising a mixing actuator for rotating the suction head. 
     
     
         9 . An apparatus according to  claim 7  or  claim 8 , wherein the suction head is mounted for lateral movement away from and toward the container, further comprising at least one lateral actuator for laterally moving the suction head. 
     
     
         10 . An apparatus according to  claim 9 , wherein the lateral movement of the suction head comprises pivotal movement about an axis parallel to the coaxial axis. 
     
     
         11 . An apparatus according to  claim 10 , wherein the lateral movement of the suction head comprises horizontal translating movement. 
     
     
         12 . An apparatus according to  claim 7 , wherein the annular skirt has an internal an O-ring that seals against the outer surface of the annular wall of the separation chamber, and the inner portion has two concentric O-rings on its lower face, the inner of the concentric O-rings surrounding the aspiration suction port, the retention suction port lying between the concentric O-rings, and the concentric O-rings forming the sealed annular area on the upper face of the holder when in contact therewith.