Although computer-aided sperm analysis (CASA) has become an important tool in male infertility research, some researchers believe that it is proving to be no more accurate than manual measurement techniques. Human sperm motion is extremely complex: they don’t swim in straight lines; they move their tails as well as their heads; and they change direction. Since the pattern and vigour of a sperm cell’s motion is an indicator of its health, it is important to analyse and model this motion accurately.
Sperm motion has to be simplified somewhat in order to be modelled, but it is difficult to know what to simplify. Current instruments compute an average sperm path by smoothing a sperm’s curvilinear trajectory with a fixed-length running average, and the measurements are taken only from the sperm head. According to researchers Russel Davis, Paul Niswander, and David Katz from the University of California Department of Obstetrics and Gynaecology, this method of measurement causes a great deal of information to be lost, so that inaccurate conclusions may be drawn about the viability of a sperm sample. Dr. Davis and colleagues felt that a new kind of analysis was required to bring out the hidden patterns in sperm paths.
They now use DADiSP to help them implement an alternative approach to sperm motion analysis. They believe that their new method gives a more accurate characterisation of sperm motion than traditional methods.
Applying the fixed-length running average (FLRA) analysis method to sperm has the effect of overly smoothing some trajectories and insufficiently smoothing others. These errors are compounded further when scientists try to produce average values for an entire cell population. The new method for analysis pioneered by Dr. Davis and colleagues adapts the width of the running average of a sperm cell’s path to the changing wavelengths of the major spatial oscillations of each curvilinear trajectory. This new method of measurement may provide more accurate modelling of sperm paths so that more accurate judgments can be made about the healthiness of the sperm.
A high-speed video camera and recorder running at 200 frames per second make a first observation of sperm swimming in seminal plasma at 37 degrees C. The trajectories are recorded and digitised, then analysed for kinematic parameters for one second (200 data points). The trajectory data are then imported into PathTool, a program written in the lab, which computes their average lengths and two vectors which are exported to DADiSP for harmonic analysis. These new measurements, which reveal the frequencies and amplitudes that occur in highly irregular motion, are based on fast Fourier transforms (FFTs). They include the fundamental harmonic of motion (HAR), the magnitude of HAR (MAG), and the power bandwidth of HAR (PWB), which are basic window calculations in a DADiSP worksheet.
Dr. Russel Davis states that he considers DADiSP’s ease of use “one of its most important features.” He says he likes being able to use it to design a number of signal processing pathways to use with different signals: “For exploratory data analysis it is very useful.” DADiSP allows Dr. Davis and colleagues to discover patterns and periodicities in sperm motion that until now have been obscured.
As a result of their findings, Davis and colleagues have recommended vigorous empirical testing of their methods, and have made suggestions for new CASA instruments. Ultimately these research efforts will result in greater refinement of the methods used to investigate infertility, and DADiSP will have been a part of the success.
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