The gVERSE RF Pulse: An Optimal Approach to MRI Pulse Design

A Variable Rate Selective Excitation (VERSE) is a type of Radio Frequency (RF) pulse that reduces the Specific Absorption Rate (SAR) of molecules in a specimen. As high levels of SAR lead to increased patient temperatures during Magnetic Resonance Imaging (MRI) procedures, we develop a selective VERSE pulse that is designed to minimize SAR while preserving its duration and slice profile; called the generalized VERSE (gVERSE). After the formulation of a rigorous mathematical model, the nonlinear gVERSE optimization problem is solved via an optimal control approach. Using the state of the art Sparse Optimal Control Software (SOCS), two separate variations of SAR reducing gVERSE pulses were generated. The Magnetic Resonance (MR) signals produced by numerical simulations were then tested and analyzed by an MRI simulator. Computational experiments involved with the gVERSE model provided constant RF pulse levels and had encouraging results with respect to MR signals. The testing results produced by the gVERSE pulse illustrate the potential advanced optimization techniques have in designing RF sequences.