RF gradient BIRD/TANGO sequence to eliminate uncoupled magnetization

A modification of the BIRD and TANGO sequences is presented which employs radiofrequency field gradients to eliminate the net magnetization from uncoupled spins, while completely preserving coupled magnetization. The standard BIRD and TANGO sequences cause selective nutation of protons directly bound to a coupling partner, while returning uncoupled magnetization to +z. These sequences lend themselves naturally to modification using RF gradients, which require no increase in pulse-sequence complexity while providing substantial suppression of uncoupled resonances and elimination of typical antiphase and multiple-quantum error terms that arise from improperly set pulse lengths or delays. In the RF-gradient BIRD/TANGO sequence, the uncoupled magnetization is dephased in a plane orthogonal to the RF axis, while the desired signal components are refocused, effectively in a rotary echo. The sequence has applications to solvent suppression and selective isotopomer excitation. It is demonstrated for selective excitation of the satellites in a sample of chloroform, yielding suppression of the uncoupled magnetization by factor of approximately 800.