Single‐shot magnetic resonance spectroscopic imaging with partial parallel imaging

A magnetic resonance spectroscopic imaging (MRSI) pulse sequence based on proton–echo‐planar‐spectroscopic‐imaging (PEPSI) is introduced that measures two‐dimensional metabolite maps in a single excitation. Echo‐planar spatial–spectral encoding was combined with interleaved phase encoding and parallel imaging using SENSE to reconstruct absorption mode spectra. The symmetrical k‐space trajectory compensates phase errors due to convolution of spatial and spectral encoding. Single‐shot MRSI at short TE was evaluated in phantoms and in vivo on a 3‐T whole‐body scanner equipped with a 12‐channel array coil. Four‐step interleaved phase encoding and fourfold SENSE acceleration were used to encode a 16 × 16 spatial matrix with a 390‐Hz spectral width. Comparison with conventional PEPSI and PEPSI with fourfold SENSE acceleration demonstrated comparable sensitivity per unit time when taking into account g‐factor–related noise increases and differences in sampling efficiency. LCModel fitting enabled quantification of inositol, choline, creatine, and N‐acetyl‐aspartate (NAA) in vivo with concentration values in the ranges measured with conventional PEPSI and SENSE‐accelerated PEPSI. Cramer–Rao lower bounds were comparable to those obtained with conventional SENSE‐accelerated PEPSI at the same voxel size and measurement time. This single‐shot MRSI method is therefore suitable for applications that require high temporal resolution to monitor temporal dynamics or to reduce sensitivity to tissue movement. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.