A REDUCED POWER SELECTIVE ADIABATIC SPIN-ECHO PULSE SEQUENCE

We introduce a selective adiabatic pulse sequence suitable for generating selective spin‐echoes for both MR imaging and spectroscopy. The technique is simple; one uses the echo generated by any pair of identical selective adiabatic inversion pulses. The nonlinear phase across the slice is compensated perfectly by the second π pulse. This compensation is immune to RF inhomogeneity and nonlinearity. For imaging applications, we concentrate on a reduced‐power version of the pulse sequence in which time is traded off variably for RF amplitude in the presence of a time‐varying gradient. This technique, known as variable‐rate excitation, mildly degrades the off‐resonant slice profile when applied to amplitude‐modulated pulses. We present theoretical explanations and experimental results that show that the variable‐rate adiabatic pulses are immune to off‐resonant degradation of the magnitude normally encountered in MR imaging. © 1991 Academic Press. Inc. Copyright © 1991 Wiley‐Liss, Inc., A Wiley Company