A Z-Gradient Array for Simultaneous multi-slice excitation with a single band RF pulse

UMRAM researchers has recently published an article titled as “A z-gradient array for simultaneous multi-slice excitation with a single band RF pulse”. It is shown that multiple slices can be excited with a single band RF pulse using a custom designed z-gradient array. In recent years, imaging multiple slices at the same time, multi-slice MRI, has become popular due to reduced imaging time or increased SNR. In the conventional techniques, excitation of multiple slices cause increase in the peak voltage, peak power, specific absorption rate (SAR). Therefore, design of multi-slice RF pulses are limited by RF power amplifier limitations or safety limits related to SAR. In this study, a z-gradient array is used to create spatially oscillating magnetic fields such that multiple locations can be excited with a conventional single band RF pulse; therefore, increase in the peak power, peak voltage, SAR or RF pulse durations can be avoided. Novel z-gradient hardware including 9 channel z-gradient array, Tx/Rx RF coils, 9 power amplifiers and control circuits are introduced. Design techniques and performance evaluations for various target specifications are also analyzed. At last, MR experiments has been conducted to validate the proposed technique and multiple slices are successfully excited with a single band RF pulse using the z-gradient array coil.