Computer-aided sperm analysis (CASA): image digitization and processing

The active undulations of a sperm flagellum are a basic expression of cell vitality. They reflect a number of intracellular processes, and also reveal the interaction between the sperm and its environment. The pattern of sperm-head motion during locomotion is a hydrodynamic consequence of the behavior of the flagellum. Hence, studies of sperm-head motion should provide insights into cellular function and membrane integrity. Because of its importance in fertility, considerable attention is devoted to the analysis of sperm-head motion at both a clinical and basic biological level. Historically, such work has been done by hand. Recently, new, computer-aided sperm analysis (CASA) systems have become available to automate this process. These new systems promise to advance the study of cell behavior because they facilitate the objective collection of large amounts of data at relatively low cost. At present, however, few workers understand the relative strengths and limitations of such systems. There is a tendency to uncritically accept CASA results because they are computer generated. In this article, we describe how CASA systems work, and discuss several technological and methodological problems which can produce spurious results. We argue for the development of optical, machine, and specimen preparation standards which will facilitate inter-laboratory comparisons of CASA data.