MAGNETIC RESONANCE IN MEDICINE zyxwvutsrq 18,28-38 zyxwvu ( 1991 ) A Reduced Power Selective Adiabatic Spin-Echo Pulse Sequence STEVEN CONOLLY, GARY GLOVER, * DWIGHT NISHIMURA, AND ALBERT MACOVSKI zyxw Department ofElectrica1 Engineering, Stanford University, Durand zyxw 120, Stanford, California 94305: and *GE Medical Systems Group Received December 19, 1989, revised April 6, 1990 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 selectiveadiabatic inversion pulses. The nonlinear phase across the slice is compensated perfectly by the second zyxwv T 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 zyx 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 rnag- nitude normally encountered in MR imaging. 0 1991 Academic Press, Inc. INTRODUCTION Selective adiabatic zyxwvu 7r pulses have been applied to inverting slices in MR imaging for several years ( 1 ) . Adiabatic fast passage ( AFP) pulses’ immunity to RF variations (2-4) makes the pulses attractive for selective spin-echo experiments in MR imaging and spectroscopy. Conventional AFP 7r pulses present two problems with respect to spin-echo generation for MR imaging: they deposit relatively high power in the patient, and they leave a nonlinear phase variation across the excited slice. Recent research has seen the development of compensated 7r pulses that mitigate these problems. Kunz zyxwvu (5) compensated the phase of the 7r pulse with the 7r/2 pulse. Although this solution is reasonable in terms of RF power, the phase compensation varies with any RF field variations because the 7r/2 pulse is not adiabatic. We con- structed a selective spin-echo pulse by prefacing an inversion pulse with a selective 27r pulse (6). However, this 37r pulse deposits four times the power of a conventional inversion pulse, which precludes clinical use. Ugurbil et al. introduced four AFP spin- echo pulses in ( 7), but none of these pulses is suitable for selective spin-echo generation in multislice MR imaging. In this paper, we introduce a spin-echo pulse sequence that addresses both the power and phase problems. The pulse sequence generates a selective spin-echo with full immunity to RF variations while depositing the same power as a conventional ir pulse. Furthermore, our pulse sequence is suitable for multislice magnetic resonance imaging. 0740-3194/9 I $3.00 28 Copynghl zyxwvutsrqpo 0 zyxwvu 1991 by Academic Press, Inc. All nghts of reproduction in any form reserved.