Two-dimensional radial sodium heart MRI using variable-rate selective excitation and retrospective electrocardiogram gating with golden angle increments

摘要

Purpose Two-dimensional projection reconstruction methods provide advantages over three-dimensional techniques because of higher flexibility regarding the resolution and shorter scan time needed. To optimize a two-dimensional radial sequence with respect to signal-to-noise ratio, variable-rate selective excitation and retrospective electrocardiogram gating is investigated. Methods The minimal radiofrequency pulse duration is simulated in dependence of the flip angle and coil parameters using sinc waveforms with two different variable-rate selective excitation approaches and a Fermi pulse. Retrospectively electrocardiogram-gated imaging with Golden Angle incremented projections was implemented to allow for continuous data acquisition enabling the possibility of dynamic electrocardiogram-gated heart imaging. Results Especially for abdominal coils with high transmitter voltages required, variable-rate selective excitation strongly reduces the radiofrequency pulse duration and echo time resulting in a signal-to-noise ratio gain up to 15.5% (if the fast relaxation component of sodium is in the order of the radiofrequency pulse duration) compared with standard sinc-shaped radiofrequency pulses. Retrospective electrocardiogram gating shows higher flexibility with regard to the trigger delay enabling the trade-off between heart motion artifacts and signal-to-noise ratio. Conclusion A two-dimensional radial sequence is optimized for sodium heart imaging regarding signal-to-noise ratio. Different sodium contrasts of the human heart are shown, which can give additional information on heart diseases.