Effect of pulse angle imperfection and resonance offset in the phase-modulated rotating-frame spectroscopic imaging experiment

Abstract

Phase-modulated rotating-frame imaging, a technique which has been used for localized 31P spectroscopy in vivo, has been modeled using rotation matrices to predict the response of an isolated spin- 1 2 system to the two-pulse experiment under conditions of off resonance and nonideal phase-encoding pulse. Two experiments are carried out in order to remove the phase twist inherent in the phase-modulated experiment; the incremental pulse (θ) is applied with phase φ σ = 0 and φ σ = π with respect to the phase-encoding pulse (λ) phase of φ λ = π/2 The peak shape resulting from the 2D FT is described in terms of a combination of absorption- and dispersion-mode peaks in the chemical-shift and spatial dimensions. Using this model, it is possible to set out guidelines for the implementation of the phase-modulated rotating-frame imaging method. The effective sweep width in ( B 0) and ( B 1) over which the experiment can be usefully performed and the nature of the two-dimensional peak shape at a point can be readily derived from the model.