Band‐selective spin echoes for in vivo localized 1H NMR spectroscopy

Abstract

This study describes a new single spin-echo spatial localization sequence, BASSALE or BAnd-Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achieves conformal volume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine-modulated sinc refocusing pulse to acquire localized ¹H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termed bandselective spin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin-spin interactions to permit localized editing and T₂ relaxometry of metabolites with J-coupled spins (e.g., lactate), is insensitive to homonuclear multiple-quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms and in situ in the rat brain.