MRI Motion Compensation by Ultrasound Navigators

Introduction: There is a long history of motion compensation in MRI using navigator echoes, now a mature technique [1]. MR navigators work well, but their applications have been limited by several factors: the need to slow down imaging in order to make time for the navigator, interference with the steady state of the base sequence, and substantial engineering needed to implement and validate new navigated sequences. For this investigation, we have built a simple prototype ultrasound navigation system, analogous to MR navigation but using an ultrasound echo for position measurement. Previous efforts in this area have employed entire ultrasound imaging arrays, resulting in dramatically slower tracking and requiring considerably more expensive equipment [2].