CHEMICAL-SHIFT-SELECTIVE ACQUISITION OF MULTIPLE-QUANTUM-FILTERED NA-23 SIGNAL

Equations describing the multiple-quantum (MQ) signal produced by an M Q pulse sequence are systematically derived in both absence and presen ce of refocusing RF pulses. When the RF pulses in an MQ pulse sequence satisfy certain conditions, these equations may be arranged in a fact orized form. The off-resonance effects on the MQ signal due to chemica l shift can then be analyzed separately during the preparation and evo lution times. Using the reformulated equations, the dependence of the amplitude of an MQ signal on the phase shift induced by the resonance offset during the preparation and evolution times is demonstrated. By use of the new equations, it is shown that the off-resonance effects, occurring during both the preparation and evolution times, may be desc ribed in terms of the same physical process, i.e., interference betwee n echo and antiecho. In applying the off-resonance effects for the eli mination of the MQ signal in the presence of chemical shift, it is pos sible to suppress the MQ signal over a wider off-resonance bandwidth b y use of the nonrefocused preparation and evolution times than by use of a single time, Furthermore, by taking an alternative approach in de riving the equations, the interference between echo and antiecho due t o the resonance offset is shown to be insensitive to the dip angle of the creation RF pulse (usually the second pi/2 RF pulse), The theoreti cal findings were experimentally verified by use of a phantom containi ng sodium in agarose. (C) 1996 Academic Press, Inc.