P-31 H-1 WALTZ-4 BROAD-BAND DECOUPLING AT 1.5 T - DIFFERENT VERSIONS OF THE COMPOSITE PULSE AND CONSEQUENCES WHEN USING A SURFACE COIL/

Two derivatives of the wideband alternating-phase low-power technique for zero residual splitting (WALTZ)-4 decoupling sequence for broadban d decoupling named WALTZ-4a and WALTZ-4b were compared for their proto n decoupling performance in P-31 nuclear magnetic resonance (NMR) spec troscopy using a Siemens Magnetom SP 1.5 T whole-body imager, Version WALTZ-4a originally implemented by the manufacturer doubles and triple s the transmitter amplitude of the 90 degrees pulse to achieve the 180 degrees and 270 degrees hip angle required for one composite pulse R in the WALTZ sequence, WALTZ-4b follows the sequence reported from Sha ka et al. and leaves the transmitter amplitude constant but increases the durations of the 180 degrees and 270 degrees pulses. The decouplin g performance of WALTZ-4b is superior because it requires less transmi tter power and, therefore, it is advantageous in all in vivo studies w here a low specific absorption rate is desired. When WALTZ-4 is used i n combination with a surface coil for transmission the theoretically r equired flip angles cannot be achieved in the entire sensitive volume of the coil. The decoupling performance was therefore investigated at lower and higher flip angles. Again, WALTZ-4b is advantageous and prov ides, in certain ranges that are off-resonant from the decoupling freq uency, a good decoupling quality even for hip angles that are only 60% of the theoretically required. (C) 1998 Elsevier Science Inc.