Vertebrobasilar stroke is currently realized to be a more frequent problem than diagnosed in the past. THe nature and characteristic of obstructive vs vasculitic lesions also seems poorly understood. The higher Teslas systems jhad many artifact problems but experience seems to have improved. So would you now prefer MRA Time of Flight studies to study evolving insufficiency with a 1.5T or 3.2T system and can the two present confusing artifact when used interchangeably to monitor evolution in a single patient?