Metabolic imaging (CSI) consists in recording the spectroscopic data for a group of voxels, in slice(s) (2D) or by volume (3D). It is based on a repetition of STEAM or PRESS type sequences to which is added spatial phase encoding. The number and direction of phase encodings depend on the number of dimensions explored (1D, 2D or 3D), adding on to acquisition time. The duration of the sequence is equal to TR ∙ Nph1D ∙ Nph2D ∙ Nph3D ∙ NSA (NphxD number of phase encoding steps in direction x).
To reduce acquisition time, variants of the basic sequence have been proposed:
Signal processing calls on Fourier transforms (1 for each phase-encoded dimension phase + 1 for spectral analysis) and requires data correction (correction of the baseline, phase, smoothing truncation artifacts…).
The results appear in the form of parametric images («metabolic maps ») or a matrix of the spectra of the regions to be studied.