By generating a progressive series of holograms, scientists can watch sperm move and look for structural anomalies that make them less viable.
The new technique can help doctors sort the good sperm cells from the less viable ones, using a tracking system, that takes 3-D movies of living sperm.
In addition to showing the sperm's movement and behaviour in real time, the novel method simultaneously provides detailed 3-D imaging of the sperm's form and structure to detect potential infertility-causing anomalies, such as the "bent tail" that prevents the cells from swimming straight.
The researchers say this is the first technique for collecting data on sperm cell motility - a key predictor of In vitro fertilisation (IVF) success - in three dimensions and over time.
Currently, sperm concentration and mobility in semen are assessed either by subjective visual evaluation or a process known as computer-assisted sperm analysis (CASA).
While the latter provides more detail and fewer errors than the former, CASA still only allows tracking and imaging in two dimensions.
Researchers combined microscopy and holography - the creation of 3-D images - to visualise live sperm in not only two dimensions (the x and y positions) but according to their depth (z position) as well.
"By acquiring a video of the moving sperm in 3-D, we add a fourth dimension time," said lead author Giuseppe Di Caprio from the National Research Council (NRC) in Italy, and Harvard University in Cambridge.
The researchers first separated laser light into two beams. They transmitted one beam through a dish containing live, swimming sperm cells and then recombined it, after magnification through a microscope, with the second beam.
"The superimposed beams generate an interference pattern that we can record on camera," Di Caprio said.
"The resulting image is a hologram containing information relative to the morphologies of the sperm and their positioning in three-dimensional space.
"Viewing a progressive series of these holograms in a real-time video, we can observe how the sperm move and determine if that movement is affected by any abnormalities in their shape and structure," said Di Caprio.
Di Caprio said that the 3-D imaging technique, known as digital holographic microscopy (DHM), yields morphology and motility data on sperm consistent with that found in previous studies, but with the unprecedented bonus of seeing cause and effect relationships between the two.
The findings appear in The Optical Society (OSA)'s journal Biomedical Optics Express.