), was designed to have intrinsic eddy-current compensation. However, this sequence is less suitable for cardiac imaging due to a lack of velocity compensation resulting in a higher likelihood of intravoxel dephasing caused by myocardial motion during the diffusion pulses. Secondly, concomitant gradient fields are unbalanced in Doramapimod clinical trial the TRSE sequence (whereas they are cancelled out in the bipolar spin-echo sequence due to the symmetry). Lastly, the addition of an extra refocusing pulse makes the sequence
more susceptible to RF pulse imperfections. Although adjustments to the gradients and RF pulses can be made to reduce concomitant gradient fields and RF pulse imperfections, the lack of velocity compensation in the TRSE sequence leads to signal loss in the beta-catenin inhibitor presence of motion. Such signal loss cannot easily be corrected by retrospective methods, and thus, the TRSE sequence is left out of the comparison in this study. One aim of this study is to investigate the higher-order spatial effects of eddy currents and their time-varying nature , , ,  and  in the unipolar and bipolar sequences. Correction of higher-order effects have led to improved image quality in previous studies ,  and . However, the temporal dynamics and relative magnitudes of higher-order effects among different sequences have received less attention. The reason for measuring higher-order effects
is that unlike linear offsets, dynamic higher-order phase variations cannot be corrected for by standard pre-emphasis techniques ( and references therein). It is possible to characterize eddy-current induced phase offsets at very high temporal resolution using NMR field probes ,  and . A dynamic field camera with 16 NMR probes is capable of measuring Palmatine eddy-current phases up to 3rd spatial order. This technique has recently been used to monitor such phase contributions with first applications to diffusion imaging  and phase-contrast imaging . The purpose of the present study is to use a field-monitoring approach to measure, characterize and
correct for linear and higher-order eddy-current effects in the unipolar and bipolar sequences. Eddy currents are not patient-specific and the field-monitoring approach potentially allows calibration scans to be used for the correction of temporal and higher-order spatial effects during reconstruction for any organ imaged with a given sequence. As such, this study has been restricted to a phantom study to minimize the confounding effects of additional artifacts, including bulk motion, as found in in vivo studies. All scans were performed on a 3T Philips Achieva TX system (Philips Healthcare, Best, The Netherlands) operated in a gradient mode that provides 63 mT/m maximal strength and 100 mT/m/ms slew rate. Unipolar and bipolar diffusion sequence diagrams are shown in Fig. 1a and b.