The authors of a recent article on thrombolytic therapy  advocate revising the definition of transient ischemic attack (TIA) based on recent advances in brain imaging. There have been several serious attempts to do this since the original description by Miller Fisher in 1958 , including that by a distinguished US neurological group in 2002  but none have withstood the ordeal of the test of time. The task is made all the more difficult by continuing advances in imaging over the years, so the definition would need to change from year to year.
Stroke and TIA were purely clinical definitions made decades before imaging was available, and so will never change in the foreseeable future. Progress in brain imaging will need to adapt accordingly and not the other way round.