AUTOMATION IN CERVICAL-CANCER SCREENING .2. FLOW SYSTEMS AND OTHER TECHNIQUES

The basic features of a simple flow system for cytological analysis are described. The biological significance and measuring techniques are then discussed for each of the various cell parameters which have been successfully measured in flow systems: cell volume, optical absorption, cell fluorescence and light scattering. Two types of cell sorter are described, whereby ″normal″ cells are separated from ″suspect″ cells according to results of the analysis; one type sorts cells electrostatically, the other uses fluidic logic. The earliest flow system to be investigated for automated cancer screening, the Coulter counter, is described, and the clinical experiences of various workers with it are reported. Other flow system techniques and the associated clinical experiences are reviewed. It is concluded that successful automation in screening for cervical cancer has not yet been achieved. There are perhaps three major reasons for this failure. Firstly, the cervical cytology specimen is highly variable, composed as it is of a mixture of cells from different origins, admixed with mucus, serous exudate, micro-organisms and often blood. Secondly, the criteria for ″abnormality″ are poorly definable, again because of the polyglot cell composition and the often obscuring substrate. Thirdly, the relatively simple analysis techniques which have been used so far in automated cytology systems have been unable to cope with these problems at the required accuracy, speed and cost. Problem areas needing further work are defined.