Optimization of two-dimensional spatially selective NMR pulses by simulated annealing

Abstract Two-dimensional spatial localization can be achieved with a single NMR inverting or refocusing pulse, by applying the RF pulse in the presence of a net magnetic field gradient which reorients through two dimensions during the course of the pulse. Simple rotating (“ϱ”) pulses of this type, however, have the disadvantage of producing ringing outside the central selected volume of the 2D sensitivity profile. In order to eliminate this ringing, a simulated annealing technique has been used to simultaneously optimize the RF and gradient waveforms, producing pulses which leave the NMR signal localized to a well-defined cylinder. These pulses have been implemented on a whole-body NMR system to produce restricted field-of-view images of agarose disk phantoms and of the head. Applications of optimized ϱ pulses include localization in 31 P spectroscopy and elimination of aliasing artifacts in NMR imaging.