Multi-stage simulated annealing optimization of self-refocused radio frequency pulses with short T2
We investigate the design of self-refocused pulses using simulated annealing global optimization techniques with constraints specifying the amplitude of all magnetization components. The magnetization response is calculated by numerically solving the Bloch equations by including T2 terms. The profile of B1 is varied until an error function attains its minimum. The search for minimum is forcefully reset from beginning with smaller search step size. It is hoped that the initial coarse search avoids local minima while the repeated finer search locates the global minimum. We design a self-refocused RF pulse for exciting a rectangular slice with short T2 conditions by restricting T2 to be equal to the pulse length (Trf). The optimized B1 profiles using multi-stage optimization produces transverse magnetization response gain with reduced energy deposition.