Phase-modulated rotating-frame spectroscopic localization using an adiabatic plane-rotation pulse and a single surface coil

Spectroscopic spatial localization based on B₁ gradients is generally performed as an amplitude-modulated experiment using a single surface coil, with a consequent loss in signal-to-noise ( S N) ratio. The phase-modulated implementation of such experiments with a single surface coil requires the ability to apply both B₁-dependent rotations and B₁-independent 90° plane rotations using the same surface coil. It is demonstrated that this is now possible using adiabatic plane-rotation pulses. These pulses can execute a plane rotation of any angle despite the presence of large B₁ inhomogeneities; therefore, they can be used to perform a 90° plane rotation throughout the sensitive volume of a surface coil. A new phase-modulated, spatial-localization experiment based on B₀ and B₁ gradients (RAPP-ISIS) is introduced. It is shown, using phantom and in vivo, intact animal studies, that the technique provides excellent spectroscopic localization and the expected gain in S N compared to its amplitude-modulated analogue.