Standard spectroscopic imaging techniques are time-intensive due to the need for phase-encoding in two or three spatial dimensions in addition to spectral encoding. Scan times are further lengthened by the long data acquisition period required for high spectral resolution. As a consequence, a compromise must be made among imaging volume, total scan time, signal to noise ratio, and spatial and spectral resolutions. The typical bargain is of lengthy duration and still restricts the measurements to a few slices of the brain with poor spatial resolution.

The method presented here is based on an earlier technique [2] that selectively excites NAA while suppressing the signals from water and other metabolites. The original technique employed a point-resolved spectroscopy (PRESS) excitation method paired with a conventional readout gradient. This and additional imaging sequences, including echo-planar imaging (EPI) and other fast-acquisition methods, were evaluated for their efficiency and signal-to-noise ratios for a given spatial resolution and imaging time. Other considerations in designing the optimal pulse sequence included the specific absorption rate (SAR) of radio frequency power and sensitivity to magnetic-field inhomogeneities.

[1] Tsai, G and Coyle, JT Prog Neurobio 46:531-540(1995)
[2] Wald, LL et al. Magn Reson Med. 1999 Jan;41(1):187-92.