The IMSI is the selection of sperm through a high magnification (8000 magnifications instead of 400 for the classical ICSI) that allows us to observe the structures that had so far remained unnoticed.
Recent studies has shown that the morphological selection of the sperm has an impact on the success rates of the sperm microinjection techniques. The selection of a sperm with a head without vacuoles and morphologically correct increases the rates of fertilization, the number of good quality embryos and as a result, the rates of implantation.
http://www.youtube.com/watch?v=1FJJ4OksHog&feature=related