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 filter assembly for separating and collecting a layer of particulate matter from a liquid containing the particulate matter, the filter assembly comprising:
 a holder having a base and a surrounding sidewall projecting from the base, the base and the sidewall defining an open cavity extending from the base to the rim of the sidewall at the distal end thereof;   an inner fluid pervious medium in the cavity having opposed inner and outer faces, the inner face facing the base;   a flow opening in the holder in fluid communication with the inner face of the inner fluid pervious medium; and   an outer fluid pervious medium overlying the outer face of the inner fluid pervious medium and attached to the sidewall, the exposed face of the outer fluid pervious medium adapted to collect a layer of the particulate matter, the inner fluid pervious medium being of low fluidic impedance relative to the outer fluid pervious medium so that the pressure drop across the inner fluid pervious medium is less than the pressure drop across the outer fluid pervious medium when liquid flows therethrough.   
     
     
         2 . A filter assembly according to  claim 1 , wherein the outer edge of the sidewall rim is chamfered, and the outer fluid pervious medium is attached to the chamfer. 
     
     
         3 . A filter assembly according to  claim 2 , wherein the outer face of the inner fluid pervious medium extends beyond the sidewall rim, and the outer fluid pervious medium is a membrane filter. 
     
     
         4 . A filter assembly according to  claim 3 , wherein the membrane filter is fused to the chamfer. 
     
     
         5 . A filter assembly according to  claim 1 , further comprising a seat in the cavity that supports the inner fluid pervious medium in spaced relation to the base so as to form a chamber that is bounded by the base, the inner face of the inner fluid pervious medium and the sidewall, and is in fluid communication with the flow opening. 
     
     
         6 . A filter assembly according to  claim 5 , wherein the seat comprises an annular shoulder. 
     
     
         7 . A filter assembly according to  claim 6 , further comprising a central support on the base in the chamber having a distal end that engages the inner face of the inner fluid pervious medium and supports the central portion of the inner fluid pervious medium. 
     
     
         8 . A filter assembly according to  claim 7 , wherein the distal end of the central support extends beyond the annular shoulder so that the central portions of the inner and outer fluid pervious media are bowed outwardly. 
     
     
         9 . A filter assembly according to  claim 8 , wherein the outer edge of the rim of the sidewall is chamfered, and the outer fluid pervious medium is attached to the chamfer. 
     
     
         10 . A filter assembly according to  claim 9 , wherein the outer face of the inner fluid pervious medium extends beyond the sidewall rim, and the outer fluid pervious medium is a membrane filter. 
     
     
         11 . A filter assembly according to  claim 10 , wherein the membrane filter is fused to the chamfer. 
     
     
         12 . A filter assembly according to  claim 8 , wherein the central support is hollow, the flow opening is in the base in alignment with the central support and communicates with the interior thereof, and the central support has at least one opening that provides fluid communication between the chamber and the flow opening through the interior of the central support. 
     
     
         13 . A filter assembly according to  claim 12 , wherein said at least one opening comprises a plurality of side openings in the central support. 
     
     
         14 . A filter assembly according to  claim 12 , wherein the outer edge of the sidewall rim is chamfered, and the outer fluid pervious medium is attached to the chamfer. 
     
     
         15 . A filter assembly according to  claim 14 , wherein the outer face of the inner fluid pervious medium extends beyond the sidewall rim, and the outer fluid pervious medium is a membrane filter. 
     
     
         16 . A filter assembly according to  claim 15 , wherein the membrane filter is fused to the chamfer. 
     
     
         17 . A filter assembly according to  claim 16 , wherein the inner fluid pervious medium is cylindrical, and the sidewall is annular and closely surrounds the inner fluid pervious medium. 
     
     
         18 . A filter assembly according to  claim 17 , wherein the holder and the membrane filter are made of polycarbonate.