Fast proton spectroscopic imaging using steady-state free precession methods

Various pulse sequences for fast proton spectroscopic imaging (SI) using the steady-state free precession (SSFP) condition are proposed. The sequences use either only the FID-like signal S-1, only the echo-like signal S-2, or both signals in separate but adjacent acquisition windows. As in SSFP imaging, S-1 and S-2 are separated by spoiler gradients. RF excitation is performed by slice-selective or chemical shift-selective pulses. The signals are detected in absence of a B-0 gradient. Spatial localization is achieved by phase-encoding gradients which are applied prior to and rewound after each signal acquisition. Measurements with 2D or 3D spatial resolution were performed at 4.7 T on phantoms and healthy rat brain in vivo allowing the detection of uncoupled and J-coupled spins. The main advantages of SSFP based SI are the short minimum total measurement time (T-min) and the high signal-to-noise ratio per unit measurement time (SNRt). The methods are of particular interest at higher magnetic field strength B-0, as TR can be reduced with increasing B-0 leading to a reduced T-min and an increased SNRt. Drawbacks consist of the limited spectral resolution, particularly at lower B-0(,) and the dependence of the signal intensities on T-1 and T-2. Further improvements are discussed including optimized data processing and signal detection under oscillating B-0 gradients leading to a further reduction in T-min. (C) 2003 Wiley-Liss, Inc.