Anaesthesia in neonates

We have a lot of groups looking at neurodevelopment and so far we've been able to use Isofluorane for all of the studies, but one group are planning on doing Ca2+ imaging and the Isoflurane is thought to affect the imaging so they would like to look at using an injectable protocol.  They have proposed Medetomidine, Midazolam (+/- fentanyl) or Urethane, but I have no experience using these agents in neonates and wondered if anyone has experience they could share. In this case it is neonatal rats aged P6-11.  The imaging would be terminal and last between 10-30 minutes and is non-invasive.  There is a surgical set up which we may try and carry out under the same anaesthetic if possible.