Adiabatic RF pulses play an important role in spin inversion where G is the adiabatic parameter due to their robust behavior in presence of inhomogeneous RF fields. These pulses are characterized by the trajectory swept by the tip of the B eff vector and the rate of motion upon it. In this
paper, a method is described for optimizing adiabatic inversion pulses to achieve a frequency-selective magnetization inversion over a given bandwidth in a shorter time and to improve slice and tan u Γ
Dv/v 1 . Inversion is obtained when the effective profile. An efficient adiabatic pulse is used as an initial condition. field moves the longitudinal magnetization M z from the /z This pulse allows for flexibility in choosing its parameters; in parto the 0z axis over a wide band of Larmor frequencies. ticular, the transition sharpness may be traded off against the In the frame of reference of the slice center, i.e., for v 0 inverted bandwidth. The considerations for selecting the parame-Γ
v c , we may plot the route traced by the tip of the v eff ters of the pulse according to the requirements of the design are vector. This graph of v 1 (t) vs Dv(v c , t) is called the trajecdiscussed. The optimization process then improves the slice profile tory of the adiabatic pulse. An adiabatic pulse is characterby optimizing the rate of motion along the trajectory of the pulse while preserving the trajectory itself. The adiabatic behavior of ized by its trajectory and the rate of motion of v eff upon the optimized pulses is fully preserved over a twofold range of it. Three classic examples (expressed here as amplitude/ variation in the RF amplitude which is sufficient for imaging applifrequency modulation functions) include the sech/tanh (4), cations in commercial high-field MRI machines. Design examples sin/cos (5), and const/tan (3). Several methods have been demonstrate the superiority of the optimized pulses over the conproposed for the optimization of the modulation functions ventional sech/tanh pulse.