In Mortal Kombat (aka Mortal Kombat 9, 2011 version) for the PS3 and Xbox 360, you can perform combo breakers to break your opponents combo string and stun them for a moment. It comes at a cost though, since it takes two of your x-ray meter bars.
To perform at combo breaker, you need to hold forward and press block immediately as the second combo hit lands.
Combo breakers can only break regular combos, not the special x-ray attacks.