NAA-weighted imaging of the human brain using a conventional readout gradient.

An imaging sequence incorporating two complementary forms of water suppression was used in conjunction with conventional readout and phase-encoding gradients to acquire images of N-acetylaspartate (NAA) in human brain. The sequence consisted of CHESS water suppression pulses followed by dual echo sequence to select the imaging volume and frequency-selective refocusing pulses with asymmetric crushers to further reduce the water signal. Spectra and conventional spectroscopic images acquired with the sequence demonstrated robust suppression of water and other resonances down field from the 2.0-ppm NAA resonance with 98% of the brain signal resulting from the 3.0-ppm to 2.0-ppm region. The technique was found to provide NAA maps with a large (256 x 128) imaging matrix and to allow a flexible tradeoff between signal to noise ratio (SNR), matrix size, data acquisition window length, and imaging time. Since spectral information is not directly obtained, the length of the data acquisition window is not determined by the spectral resolution needed to resolve the components of the brain spectrum, allowing a significantly shorter readout period. The shorter acquisition window could potentially facilitate the acquisition of multi-echo or multi-slice brain NAA maps.