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Abstract

A multi-pulse radio frequency signal sequence includes a 90.degree. excitation pulse (50) and at least a first 180.degree. refocusing pulse (52) and a second 180.degree. refocusing pulse (54). The excitation pulse and first refocusing pulse are separated by a duration A and the first and second refocusing pulses are separated by A+B. A free induction decay (60) follows the excitation pulse, a first spin echo (62) occurs a duration A after the first refocusing pulse and a second spin echo (64) occurs the duration B after the second refocusing pulse. A first read gradient (90) is applied between the excitation and first refocusing pulses; a second read gradient (92) is applied between the first refocusing pulse and the first spin echo; a third read gradient (94) is applied between the first spin echo and the second refocusing pulse; and a fourth read gradient (96) is applied between the second refocusing pulse and the second spin echo. Because the 90.degree. and 180.degree. pulses are imperfect, parasitic echoes occur at durations 3A+B, 3A+2B, and 4A+2B after the 90.degree. excitation pulse. To avoid contamination of the spin echo data by the parasitic echoes, the durations A and B are selected such that the parasitic echoes are each displaced from the spin echoes. To shift the parasitic echoes into times which are non-coincident with the spin echoes, the amplitudes of the read gradients are similarly varied between the spin echoes to shift the parasitic echoes relative to the spin echoes.

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