In vivo free induction decay based 3D multivoxel longitudinal hadamard spectroscopic imaging in the human brain at 3 T

We propose and demonstrate a full 3D longitudinal Hadamard spectroscopic imaging scheme for obtaining chemical shift maps, using adiabatic inversion pulses to encode the spins' positions. The approach offers several advantages over conventional Fourier-based encoding methods, including a localized point spread function; no aliasing, allowing for volumes of interest smaller than the object being imaged; an option for acquiring noncontiguous voxels; and inherent outer volume rejection. The latter allows for doing away with conventional outer volume suppression schemes, such as point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM), and acquiring non-spin-echo spectra with short acquisition delay times, limited only by the excitation pulse's duration. This, in turn, minimizes T₂ decay, maximizes the signal-to-noise ratio, and reduces J-coupling induced signal decay. Results are presented for both a phantom and an in vivo healthy volunteer at 3 T.