Measuring and Characterizing Short-Term High Order Eddy Currents with a Phantom

Eddy currents (EC) on an MR scanner in general include higher spatial order terms, in addition to the linear and constant terms which are typically well compensated with preemphasis. Long term (e.g., time constants ranging from several ms to several hundred ms) high order EC (HOEC) can be measured with phantom based system calibration and corrected to reduce image distortions in diffusion weighted echo planar imaging (EPI) [1]. However, the method in [1] cannot accurately measure short term (e.g., time constants below 5 ms) HOEC because of its relatively long echo time. One could extend the method in [2] to characterize short term HOEC. However, this would require repositioning the local pickup coil fixture multiple times in order to obtain enough samples for high order terms, which can be a tedious and error prone task. In this paper, we propose to extend the phantom based method in [3] to 3D to measure and characterize short term HOEC, which can be useful input to applications such as correction of phase errors in phase contrast imaging where short term HOEC is believed to be one of the main contributors of the errors [4].