A new method far fast proton spectroscopic imaging: Spectroscopic GRASE

A new fast spectroscopic imaging method is presented which allows both a ve ry short minimum total measurement time and effective homonuclear decouplin g. After each excitation, all data points from N-GE k(x)-k(y)-slices at dif ferent k(omega)-values are acquired by using a gradient and spin echo (GRAS E) imaging sequence. The delay between consecutive gradient echoes, which a re measured with uniform phase encoding between consecutive refocusing alph a -pulses, is the inverse of the spectral width (SW). A refocusing 180 degr ees pulse, which is applied within a constant delay between excitation and the GRASE sequence, is shifted in a series of measurements by an increment N-GE/(2 . SW) to cover the whole k(omega)-k(x)-k(y)-space. Spectroscopic GR ASE was implemented on a 4.7 T imaging system and tested on phantoms and no rmal rat brain in vivo. Measurements were performed with a nominal voxel si ze of 1.5 x 1.5 x 3 mm(3) and a spatial 64 x 64 matrix. The total measureme nt time was 2 or 4 min using a repetition time of 1.9 sec, 96 chemical shif t encoding steps, SW = 800 Hz, N-GE = 3, and 2 or 4 accumulations. (C) 2000 Wiley-Liss, Inc.