Slice selection with gradient-modulated adiabatic excitation despite the presence of large B1 inhomogeneities

Single‐shot, variable flip‐angle slice‐selective excitation with four gradient‐modulated adiabatic half‐passage segments

“…However, Fig. 2 shows this not to be the case for gradient-modulated waveforms (i.e., when the second dimension g is added to the optimization), consistent with observations reported in previous studies (4,5 ) . Although in the present study no appreciable difference was observed in the simulation and experimental results obtained using sin/cos or tanh/sech as NOM input functions, these findings do not preclude the existence of a better choice of input function, especially for different ranges of optimization parameters u and g.…”

“…Recently, two gradient-modulated slice-selection techniques, namely GMAX (4) and BISS-8 (5), have been introduced. GMAX relies on the cancellation of the out-of-slice signal be-tween excitations in opposite directions of nutation, hence requiring a minimum of two excitations (i.e., averaging in multiples of 2).…”

Adiabatic pulses

“…(18) demands that F 3 (t) is not proportional to F 2 (t). The theoretical development for the case in which these functions are proportional to each other, as in GMAX 43,56 and BISS-8, 16 will be addressed in forthcoming work.…”

The Return of the Frequency Sweep: Designing Adiabatic Pulses for Contemporary NMR

“…A procedure known as the numerically optimized modulation (NOM) method offers the possibility to obtain driving functions which yield optimal adiabaticity across a specified range of ω max 1 and/or values (7,64,67). By this latter approach, the time-dependence of the AM and FM functions is distorted to ensure that the level of adiabaticity (across the desired range of ω max 1 and values) does not fall below a certain threshold level at any time during the pulse.…”